Source file src/net/http/server.go

     1  // Copyright 2009 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  // HTTP server. See RFC 7230 through 7235.
     6  
     7  package http
     8  
     9  import (
    10  	"bufio"
    11  	"bytes"
    12  	"context"
    13  	"crypto/tls"
    14  	"errors"
    15  	"fmt"
    16  	"internal/godebug"
    17  	"io"
    18  	"log"
    19  	"maps"
    20  	"math/rand/v2"
    21  	"net"
    22  	"net/http/internal"
    23  	"net/textproto"
    24  	"net/url"
    25  	urlpkg "net/url"
    26  	"os"
    27  	"path"
    28  	"runtime"
    29  	"slices"
    30  	"strconv"
    31  	"strings"
    32  	"sync"
    33  	"sync/atomic"
    34  	"time"
    35  	_ "unsafe" // for linkname
    36  
    37  	"golang.org/x/net/http/httpguts"
    38  )
    39  
    40  // Errors used by the HTTP server.
    41  var (
    42  	// ErrBodyNotAllowed is returned by ResponseWriter.Write calls
    43  	// when the HTTP method or response code does not permit a
    44  	// body.
    45  	ErrBodyNotAllowed = internal.ErrBodyNotAllowed
    46  
    47  	// ErrHijacked is returned by ResponseWriter.Write calls when
    48  	// the underlying connection has been hijacked using the
    49  	// Hijacker interface. A zero-byte write on a hijacked
    50  	// connection will return ErrHijacked without any other side
    51  	// effects.
    52  	ErrHijacked = errors.New("http: connection has been hijacked")
    53  
    54  	// ErrContentLength is returned by ResponseWriter.Write calls
    55  	// when a Handler set a Content-Length response header with a
    56  	// declared size and then attempted to write more bytes than
    57  	// declared.
    58  	ErrContentLength = errors.New("http: wrote more than the declared Content-Length")
    59  
    60  	// Deprecated: ErrWriteAfterFlush is no longer returned by
    61  	// anything in the net/http package. Callers should not
    62  	// compare errors against this variable.
    63  	ErrWriteAfterFlush = errors.New("unused")
    64  )
    65  
    66  // A Handler responds to an HTTP request.
    67  //
    68  // [Handler.ServeHTTP] should write reply headers and data to the [ResponseWriter]
    69  // and then return. Returning signals that the request is finished; it
    70  // is not valid to use the [ResponseWriter] or read from the
    71  // [Request.Body] after or concurrently with the completion of the
    72  // ServeHTTP call.
    73  //
    74  // Depending on the HTTP client software, HTTP protocol version, and
    75  // any intermediaries between the client and the Go server, it may not
    76  // be possible to read from the [Request.Body] after writing to the
    77  // [ResponseWriter]. Cautious handlers should read the [Request.Body]
    78  // first, and then reply.
    79  //
    80  // Except for reading the body, handlers should not modify the
    81  // provided Request.
    82  //
    83  // If ServeHTTP panics, the server (the caller of ServeHTTP) assumes
    84  // that the effect of the panic was isolated to the active request.
    85  // It recovers the panic, logs a stack trace to the server error log,
    86  // and either closes the network connection or sends an HTTP/2
    87  // RST_STREAM, depending on the HTTP protocol. To abort a handler so
    88  // the client sees an interrupted response but the server doesn't log
    89  // an error, panic with the value [ErrAbortHandler].
    90  type Handler interface {
    91  	ServeHTTP(ResponseWriter, *Request)
    92  }
    93  
    94  // A ResponseWriter interface is used by an HTTP handler to
    95  // construct an HTTP response.
    96  //
    97  // A ResponseWriter may not be used after [Handler.ServeHTTP] has returned.
    98  type ResponseWriter interface {
    99  	// Header returns the header map that will be sent by
   100  	// [ResponseWriter.WriteHeader]. The [Header] map also is the mechanism with which
   101  	// [Handler] implementations can set HTTP trailers.
   102  	//
   103  	// Changing the header map after a call to [ResponseWriter.WriteHeader] (or
   104  	// [ResponseWriter.Write]) has no effect unless the HTTP status code was of the
   105  	// 1xx class or the modified headers are trailers.
   106  	//
   107  	// There are two ways to set Trailers. The preferred way is to
   108  	// predeclare in the headers which trailers you will later
   109  	// send by setting the "Trailer" header to the names of the
   110  	// trailer keys which will come later. In this case, those
   111  	// keys of the Header map are treated as if they were
   112  	// trailers. See the example. The second way, for trailer
   113  	// keys not known to the [Handler] until after the first [ResponseWriter.Write],
   114  	// is to prefix the [Header] map keys with the [TrailerPrefix]
   115  	// constant value.
   116  	//
   117  	// To suppress automatic response headers (such as "Date"), set
   118  	// their value to nil.
   119  	Header() Header
   120  
   121  	// Write writes the data to the connection as part of an HTTP reply.
   122  	//
   123  	// If [ResponseWriter.WriteHeader] has not yet been called, Write calls
   124  	// WriteHeader(http.StatusOK) before writing the data. If the Header
   125  	// does not contain a Content-Type line, Write adds a Content-Type set
   126  	// to the result of passing the initial 512 bytes of written data to
   127  	// [DetectContentType]. Additionally, if the total size of all written
   128  	// data is under a few KB and there are no Flush calls, the
   129  	// Content-Length header is added automatically.
   130  	//
   131  	// Depending on the HTTP protocol version and the client, calling
   132  	// Write or WriteHeader may prevent future reads on the
   133  	// Request.Body. For HTTP/1.x requests, handlers should read any
   134  	// needed request body data before writing the response. Once the
   135  	// headers have been flushed (due to either an explicit Flusher.Flush
   136  	// call or writing enough data to trigger a flush), the request body
   137  	// may be unavailable. For HTTP/2 requests, the Go HTTP server permits
   138  	// handlers to continue to read the request body while concurrently
   139  	// writing the response. However, such behavior may not be supported
   140  	// by all HTTP/2 clients. Handlers should read before writing if
   141  	// possible to maximize compatibility.
   142  	Write([]byte) (int, error)
   143  
   144  	// WriteHeader sends an HTTP response header with the provided
   145  	// status code.
   146  	//
   147  	// If WriteHeader is not called explicitly, the first call to Write
   148  	// will trigger an implicit WriteHeader(http.StatusOK).
   149  	// Thus explicit calls to WriteHeader are mainly used to
   150  	// send error codes or 1xx informational responses.
   151  	//
   152  	// The provided code must be a valid HTTP 1xx-5xx status code.
   153  	// Any number of 1xx headers may be written, followed by at most
   154  	// one 2xx-5xx header. 1xx headers are sent immediately, but 2xx-5xx
   155  	// headers may be buffered. Use the Flusher interface to send
   156  	// buffered data. The header map is cleared when 2xx-5xx headers are
   157  	// sent, but not with 1xx headers.
   158  	//
   159  	// The server will automatically send a 100 (Continue) header
   160  	// on the first read from the request body if the request has
   161  	// an "Expect: 100-continue" header.
   162  	WriteHeader(statusCode int)
   163  }
   164  
   165  // The Flusher interface is implemented by ResponseWriters that allow
   166  // an HTTP handler to flush buffered data to the client.
   167  //
   168  // The default HTTP/1.x and HTTP/2 [ResponseWriter] implementations
   169  // support [Flusher], but ResponseWriter wrappers may not. Handlers
   170  // should always test for this ability at runtime.
   171  //
   172  // Note that even for ResponseWriters that support Flush,
   173  // if the client is connected through an HTTP proxy,
   174  // the buffered data may not reach the client until the response
   175  // completes.
   176  type Flusher interface {
   177  	// Flush sends any buffered data to the client.
   178  	Flush()
   179  }
   180  
   181  // The Hijacker interface is implemented by ResponseWriters that allow
   182  // an HTTP handler to take over the connection.
   183  //
   184  // The default [ResponseWriter] for HTTP/1.x connections supports
   185  // Hijacker, but HTTP/2 connections intentionally do not.
   186  // ResponseWriter wrappers may also not support Hijacker. Handlers
   187  // should always test for this ability at runtime.
   188  type Hijacker interface {
   189  	// Hijack lets the caller take over the connection.
   190  	// After a call to Hijack the HTTP server library
   191  	// will not do anything else with the connection.
   192  	//
   193  	// It becomes the caller's responsibility to manage
   194  	// and close the connection.
   195  	//
   196  	// The returned net.Conn may have read or write deadlines
   197  	// already set, depending on the configuration of the
   198  	// Server. It is the caller's responsibility to set
   199  	// or clear those deadlines as needed.
   200  	//
   201  	// The returned bufio.Reader may contain unprocessed buffered
   202  	// data from the client.
   203  	//
   204  	// After a call to Hijack, the original Request.Body must not
   205  	// be used. The original Request's Context remains valid and
   206  	// is not canceled until the Request's ServeHTTP method
   207  	// returns.
   208  	Hijack() (net.Conn, *bufio.ReadWriter, error)
   209  }
   210  
   211  // The CloseNotifier interface is implemented by ResponseWriters which
   212  // allow detecting when the underlying connection has gone away.
   213  //
   214  // This mechanism can be used to cancel long operations on the server
   215  // if the client has disconnected before the response is ready.
   216  //
   217  // Deprecated: the CloseNotifier interface predates Go's context package.
   218  // New code should use [Request.Context] instead.
   219  type CloseNotifier interface {
   220  	// CloseNotify returns a channel that receives at most a
   221  	// single value (true) when the client connection has gone
   222  	// away.
   223  	//
   224  	// CloseNotify may wait to notify until Request.Body has been
   225  	// fully read.
   226  	//
   227  	// After the Handler has returned, there is no guarantee
   228  	// that the channel receives a value.
   229  	//
   230  	// If the protocol is HTTP/1.1 and CloseNotify is called while
   231  	// processing an idempotent request (such as GET) while
   232  	// HTTP/1.1 pipelining is in use, the arrival of a subsequent
   233  	// pipelined request may cause a value to be sent on the
   234  	// returned channel. In practice HTTP/1.1 pipelining is not
   235  	// enabled in browsers and not seen often in the wild. If this
   236  	// is a problem, use HTTP/2 or only use CloseNotify on methods
   237  	// such as POST.
   238  	CloseNotify() <-chan bool
   239  }
   240  
   241  var (
   242  	// ServerContextKey is a context key. It can be used in HTTP
   243  	// handlers with Context.Value to access the server that
   244  	// started the handler. The associated value will be of
   245  	// type *Server.
   246  	ServerContextKey = &contextKey{"http-server"}
   247  
   248  	// LocalAddrContextKey is a context key. It can be used in
   249  	// HTTP handlers with Context.Value to access the local
   250  	// address the connection arrived on.
   251  	// The associated value will be of type net.Addr.
   252  	LocalAddrContextKey = &contextKey{"local-addr"}
   253  )
   254  
   255  // A conn represents the server side of an HTTP connection.
   256  type conn struct {
   257  	// server is the server on which the connection arrived.
   258  	// Immutable; never nil.
   259  	server *Server
   260  
   261  	// cancelCtx cancels the connection-level context.
   262  	cancelCtx context.CancelFunc
   263  
   264  	// rwc is the underlying network connection.
   265  	// This is never wrapped by other types and is the value given out
   266  	// to [Hijacker] callers. It is usually of type *net.TCPConn or
   267  	// *tls.Conn.
   268  	rwc net.Conn
   269  
   270  	// remoteAddr is rwc.RemoteAddr().String(). It is not populated synchronously
   271  	// inside the Listener's Accept goroutine, as some implementations block.
   272  	// It is populated immediately inside the (*conn).serve goroutine.
   273  	// This is the value of a Handler's (*Request).RemoteAddr.
   274  	remoteAddr string
   275  
   276  	// tlsState is the TLS connection state when using TLS.
   277  	// nil means not TLS.
   278  	tlsState *tls.ConnectionState
   279  
   280  	// werr is set to the first write error to rwc.
   281  	// It is set via checkConnErrorWriter{w}, where bufw writes.
   282  	werr error
   283  
   284  	// r is bufr's read source. It's a wrapper around rwc that provides
   285  	// io.LimitedReader-style limiting (while reading request headers)
   286  	// and functionality to support CloseNotifier. See *connReader docs.
   287  	r *connReader
   288  
   289  	// bufr reads from r.
   290  	bufr *bufio.Reader
   291  
   292  	// bufw writes to checkConnErrorWriter{c}, which populates werr on error.
   293  	bufw *bufio.Writer
   294  
   295  	// lastMethod is the method of the most recent request
   296  	// on this connection, if any.
   297  	lastMethod string
   298  
   299  	curReq atomic.Pointer[response] // (which has a Request in it)
   300  
   301  	curState atomic.Uint64 // packed (unixtime<<8|uint8(ConnState))
   302  
   303  	// mu guards hijackedv
   304  	mu sync.Mutex
   305  
   306  	// hijackedv is whether this connection has been hijacked
   307  	// by a Handler with the Hijacker interface.
   308  	// It is guarded by mu.
   309  	hijackedv bool
   310  }
   311  
   312  func (c *conn) hijacked() bool {
   313  	c.mu.Lock()
   314  	defer c.mu.Unlock()
   315  	return c.hijackedv
   316  }
   317  
   318  // c.mu must be held.
   319  func (c *conn) hijackLocked() (rwc net.Conn, buf *bufio.ReadWriter, err error) {
   320  	if c.hijackedv {
   321  		return nil, nil, ErrHijacked
   322  	}
   323  	c.r.abortPendingRead()
   324  
   325  	c.hijackedv = true
   326  	rwc = c.rwc
   327  	rwc.SetDeadline(time.Time{})
   328  
   329  	if c.r.hasByte {
   330  		if _, err := c.bufr.Peek(c.bufr.Buffered() + 1); err != nil {
   331  			return nil, nil, fmt.Errorf("unexpected Peek failure reading buffered byte: %v", err)
   332  		}
   333  	}
   334  	c.bufw.Reset(rwc)
   335  	buf = bufio.NewReadWriter(c.bufr, c.bufw)
   336  
   337  	c.setState(rwc, StateHijacked, runHooks)
   338  	return
   339  }
   340  
   341  // This should be >= 512 bytes for DetectContentType,
   342  // but otherwise it's somewhat arbitrary.
   343  const bufferBeforeChunkingSize = 2048
   344  
   345  // chunkWriter writes to a response's conn buffer, and is the writer
   346  // wrapped by the response.w buffered writer.
   347  //
   348  // chunkWriter also is responsible for finalizing the Header, including
   349  // conditionally setting the Content-Type and setting a Content-Length
   350  // in cases where the handler's final output is smaller than the buffer
   351  // size. It also conditionally adds chunk headers, when in chunking mode.
   352  //
   353  // See the comment above (*response).Write for the entire write flow.
   354  type chunkWriter struct {
   355  	res *response
   356  
   357  	// header is either nil or a deep clone of res.handlerHeader
   358  	// at the time of res.writeHeader, if res.writeHeader is
   359  	// called and extra buffering is being done to calculate
   360  	// Content-Type and/or Content-Length.
   361  	header Header
   362  
   363  	// wroteHeader tells whether the header's been written to "the
   364  	// wire" (or rather: w.conn.buf). this is unlike
   365  	// (*response).wroteHeader, which tells only whether it was
   366  	// logically written.
   367  	wroteHeader bool
   368  
   369  	// set by the writeHeader method:
   370  	chunking bool // using chunked transfer encoding for reply body
   371  }
   372  
   373  var (
   374  	crlf       = []byte("\r\n")
   375  	colonSpace = []byte(": ")
   376  )
   377  
   378  func (cw *chunkWriter) Write(p []byte) (n int, err error) {
   379  	if !cw.wroteHeader {
   380  		cw.writeHeader(p)
   381  	}
   382  	if cw.res.req.Method == "HEAD" {
   383  		// Eat writes.
   384  		return len(p), nil
   385  	}
   386  	if cw.chunking {
   387  		_, err = fmt.Fprintf(cw.res.conn.bufw, "%x\r\n", len(p))
   388  		if err != nil {
   389  			cw.res.conn.rwc.Close()
   390  			return
   391  		}
   392  	}
   393  	n, err = cw.res.conn.bufw.Write(p)
   394  	if cw.chunking && err == nil {
   395  		_, err = cw.res.conn.bufw.Write(crlf)
   396  	}
   397  	if err != nil {
   398  		cw.res.conn.rwc.Close()
   399  	}
   400  	return
   401  }
   402  
   403  func (cw *chunkWriter) flush() error {
   404  	if !cw.wroteHeader {
   405  		cw.writeHeader(nil)
   406  	}
   407  	return cw.res.conn.bufw.Flush()
   408  }
   409  
   410  func (cw *chunkWriter) close() {
   411  	if !cw.wroteHeader {
   412  		cw.writeHeader(nil)
   413  	}
   414  	if cw.chunking {
   415  		bw := cw.res.conn.bufw // conn's bufio writer
   416  		// zero chunk to mark EOF
   417  		bw.WriteString("0\r\n")
   418  		if trailers := cw.res.finalTrailers(); trailers != nil {
   419  			trailers.Write(bw) // the writer handles noting errors
   420  		}
   421  		// final blank line after the trailers (whether
   422  		// present or not)
   423  		bw.WriteString("\r\n")
   424  	}
   425  }
   426  
   427  // A response represents the server side of an HTTP response.
   428  type response struct {
   429  	conn             *conn
   430  	req              *Request           // request for this response
   431  	reqBody          *body              // nil when NoBody
   432  	cancelCtx        context.CancelFunc // when ServeHTTP exits
   433  	wroteHeader      bool               // a non-1xx header has been (logically) written
   434  	wants10KeepAlive bool               // HTTP/1.0 w/ Connection "keep-alive"
   435  	wantsClose       bool               // HTTP request has Connection "close"
   436  	ecReader         *expectContinueReader
   437  
   438  	// canWriteContinue is an atomic boolean that says whether or
   439  	// not a 100 Continue header can be written to the
   440  	// connection.
   441  	// writeContinueMu must be held while writing the header.
   442  	// These two fields together synchronize the body reader (the
   443  	// expectContinueReader, which wants to write 100 Continue)
   444  	// against the main writer.
   445  	writeContinueMu  sync.Mutex
   446  	canWriteContinue atomic.Bool
   447  
   448  	w  *bufio.Writer // buffers output in chunks to chunkWriter
   449  	cw chunkWriter
   450  
   451  	// handlerHeader is the Header that Handlers get access to,
   452  	// which may be retained and mutated even after WriteHeader.
   453  	// handlerHeader is copied into cw.header at WriteHeader
   454  	// time, and privately mutated thereafter.
   455  	handlerHeader Header
   456  	calledHeader  bool // handler accessed handlerHeader via Header
   457  
   458  	written       int64 // number of bytes written in body
   459  	contentLength int64 // explicitly-declared Content-Length; or -1
   460  	status        int   // status code passed to WriteHeader
   461  
   462  	// close connection after this reply.  set on request and
   463  	// updated after response from handler if there's a
   464  	// "Connection: keep-alive" response header and a
   465  	// Content-Length.
   466  	closeAfterReply bool
   467  
   468  	// When fullDuplex is false (the default), we consume any remaining
   469  	// request body before starting to write a response.
   470  	fullDuplex bool
   471  
   472  	// requestBodyLimitHit is set by requestTooLarge when
   473  	// maxBytesReader hits its max size. It is checked in
   474  	// WriteHeader, to make sure we don't consume the
   475  	// remaining request body to try to advance to the next HTTP
   476  	// request. Instead, when this is set, we stop reading
   477  	// subsequent requests on this connection and stop reading
   478  	// input from it.
   479  	requestBodyLimitHit bool
   480  
   481  	// trailers are the headers to be sent after the handler
   482  	// finishes writing the body. This field is initialized from
   483  	// the Trailer response header when the response header is
   484  	// written.
   485  	trailers []string
   486  
   487  	handlerDone atomic.Bool // set true when the handler exits
   488  
   489  	// Buffers for Date, Content-Length, and status code
   490  	dateBuf   [len(TimeFormat)]byte
   491  	clenBuf   [10]byte
   492  	statusBuf [3]byte
   493  
   494  	// lazyCloseNotifyMu protects closeNotifyCh and closeNotifyTriggered.
   495  	lazyCloseNotifyMu sync.Mutex
   496  	// closeNotifyCh is the channel returned by CloseNotify.
   497  	closeNotifyCh chan bool
   498  	// closeNotifyTriggered tracks prior closeNotify calls.
   499  	closeNotifyTriggered bool
   500  }
   501  
   502  func (c *response) SetReadDeadline(deadline time.Time) error {
   503  	return c.conn.rwc.SetReadDeadline(deadline)
   504  }
   505  
   506  func (c *response) SetWriteDeadline(deadline time.Time) error {
   507  	return c.conn.rwc.SetWriteDeadline(deadline)
   508  }
   509  
   510  func (c *response) EnableFullDuplex() error {
   511  	c.fullDuplex = true
   512  	return nil
   513  }
   514  
   515  // TrailerPrefix is a magic prefix for [ResponseWriter.Header] map keys
   516  // that, if present, signals that the map entry is actually for
   517  // the response trailers, and not the response headers. The prefix
   518  // is stripped after the ServeHTTP call finishes and the values are
   519  // sent in the trailers.
   520  //
   521  // This mechanism is intended only for trailers that are not known
   522  // prior to the headers being written. If the set of trailers is fixed
   523  // or known before the header is written, the normal Go trailers mechanism
   524  // is preferred:
   525  //
   526  //	https://pkg.go.dev/net/http#ResponseWriter
   527  //	https://pkg.go.dev/net/http#example-ResponseWriter-Trailers
   528  const TrailerPrefix = "Trailer:"
   529  
   530  // finalTrailers is called after the Handler exits and returns a non-nil
   531  // value if the Handler set any trailers.
   532  func (w *response) finalTrailers() Header {
   533  	var t Header
   534  	for k, vv := range w.handlerHeader {
   535  		if kk, found := strings.CutPrefix(k, TrailerPrefix); found {
   536  			if t == nil {
   537  				t = make(Header)
   538  			}
   539  			t[kk] = vv
   540  		}
   541  	}
   542  	for _, k := range w.trailers {
   543  		if t == nil {
   544  			t = make(Header)
   545  		}
   546  		for _, v := range w.handlerHeader[k] {
   547  			t.Add(k, v)
   548  		}
   549  	}
   550  	return t
   551  }
   552  
   553  // declareTrailer is called for each Trailer header when the
   554  // response header is written. It notes that a header will need to be
   555  // written in the trailers at the end of the response.
   556  func (w *response) declareTrailer(k string) {
   557  	k = CanonicalHeaderKey(k)
   558  	if !httpguts.ValidTrailerHeader(k) {
   559  		// Forbidden by RFC 7230, section 4.1.2
   560  		return
   561  	}
   562  	w.trailers = append(w.trailers, k)
   563  }
   564  
   565  // requestTooLarge is called by maxBytesReader when too much input has
   566  // been read from the client.
   567  func (w *response) requestTooLarge() {
   568  	w.closeAfterReply = true
   569  	w.requestBodyLimitHit = true
   570  	if !w.wroteHeader {
   571  		w.Header().Set("Connection", "close")
   572  	}
   573  }
   574  
   575  // disableWriteContinue stops Request.Body.Read from sending an automatic
   576  // 100 Continue. As the name implies, it is only useful when the request
   577  // expects a 100 Continue and the body is wrapped in an expectContinueReader;
   578  // otherwise, it is a no-op.
   579  // If a 100-Continue is being written, it waits for it to complete before
   580  // continuing. If skipDrain is true, it also prevents the server from draining
   581  // the request body and flags the connection to be closed after the reply, as
   582  // the client will never send the body.
   583  func (w *response) disableWriteContinue(skipDrain bool) {
   584  	if w.ecReader == nil {
   585  		return
   586  	}
   587  	w.writeContinueMu.Lock()
   588  	if w.canWriteContinue.Load() {
   589  		w.canWriteContinue.Store(false)
   590  		if skipDrain {
   591  			// Make sure that the connection will not be reused by sending
   592  			// "Connection: close" header in the response.
   593  			w.closeAfterReply = true
   594  			// Ensure that the body will not be drained in Close.
   595  			w.ecReader.closed.Store(true)
   596  		}
   597  	}
   598  	w.writeContinueMu.Unlock()
   599  }
   600  
   601  // writerOnly hides an io.Writer value's optional ReadFrom method
   602  // from io.Copy.
   603  type writerOnly struct {
   604  	io.Writer
   605  }
   606  
   607  // ReadFrom is here to optimize copying from an [*os.File] regular file
   608  // to a [*net.TCPConn] with sendfile, or from a supported src type such
   609  // as a *net.TCPConn on Linux with splice.
   610  func (w *response) ReadFrom(src io.Reader) (n int64, err error) {
   611  	buf := getCopyBuf()
   612  	defer putCopyBuf(buf)
   613  
   614  	// Our underlying w.conn.rwc is usually a *TCPConn (with its
   615  	// own ReadFrom method). If not, just fall back to the normal
   616  	// copy method.
   617  	rf, ok := w.conn.rwc.(io.ReaderFrom)
   618  	if !ok {
   619  		return io.CopyBuffer(writerOnly{w}, src, buf)
   620  	}
   621  
   622  	// Copy the first sniffLen bytes before switching to ReadFrom.
   623  	// This ensures we don't start writing the response before the
   624  	// source is available (see golang.org/issue/5660) and provides
   625  	// enough bytes to perform Content-Type sniffing when required.
   626  	if !w.cw.wroteHeader {
   627  		n0, err := io.CopyBuffer(writerOnly{w}, io.LimitReader(src, internal.SniffLen), buf)
   628  		n += n0
   629  		if err != nil || n0 < internal.SniffLen {
   630  			return n, err
   631  		}
   632  	}
   633  
   634  	w.w.Flush()  // get rid of any previous writes
   635  	w.cw.flush() // make sure Header is written; flush data to rwc
   636  
   637  	// Now that cw has been flushed, its chunking field is guaranteed initialized.
   638  	if !w.cw.chunking && w.bodyAllowed() && w.req.Method != "HEAD" {
   639  		// When a content length is declared, but exceeded; any excess bytes
   640  		// from src should be ignored, and ErrContentLength should be returned.
   641  		// This mirrors the behavior of response.Write.
   642  		if w.contentLength != -1 {
   643  			defer func(originalReader io.Reader) {
   644  				if w.written != w.contentLength {
   645  					return
   646  				}
   647  				if n, _ := originalReader.Read([]byte{0}); err == nil && n != 0 {
   648  					err = ErrContentLength
   649  				}
   650  			}(src)
   651  			// src can be an io.LimitedReader already. To avoid unnecessary
   652  			// alloc and having to unnest readers repeatedly in net.sendFile,
   653  			// just adjust the existing LimitedReader N when this is the case.
   654  			if lr, ok := src.(*io.LimitedReader); ok {
   655  				if lenDiff := lr.N - (w.contentLength - w.written); lenDiff > 0 {
   656  					defer func() { lr.N += lenDiff }()
   657  					lr.N -= lenDiff
   658  				}
   659  			} else {
   660  				src = io.LimitReader(src, w.contentLength-w.written)
   661  			}
   662  		}
   663  		n0, err := rf.ReadFrom(src)
   664  		n += n0
   665  		w.written += n0
   666  		return n, err
   667  	}
   668  
   669  	n0, err := io.CopyBuffer(writerOnly{w}, src, buf)
   670  	n += n0
   671  	return n, err
   672  }
   673  
   674  // debugServerConnections controls whether all server connections are wrapped
   675  // with a verbose logging wrapper.
   676  const debugServerConnections = false
   677  
   678  // Create new connection from rwc.
   679  func (s *Server) newConn(rwc net.Conn) *conn {
   680  	c := &conn{
   681  		server: s,
   682  		rwc:    rwc,
   683  	}
   684  	if debugServerConnections {
   685  		c.rwc = newLoggingConn("server", c.rwc)
   686  	}
   687  	return c
   688  }
   689  
   690  type readResult struct {
   691  	_   incomparable
   692  	n   int
   693  	err error
   694  	b   byte // byte read, if n == 1
   695  }
   696  
   697  // connReader is the io.Reader wrapper used by *conn. It combines a
   698  // selectively-activated io.LimitedReader (to bound request header
   699  // read sizes) with support for selectively keeping an io.Reader.Read
   700  // call blocked in a background goroutine to wait for activity and
   701  // trigger a CloseNotifier channel.
   702  // After a Handler has hijacked the conn and exited, connReader behaves like a
   703  // proxy for the net.Conn and the aforementioned behavior is bypassed.
   704  type connReader struct {
   705  	rwc net.Conn // rwc is the underlying network connection.
   706  
   707  	mu      sync.Mutex // guards following
   708  	conn    *conn      // conn is nil after handler exit.
   709  	hasByte bool
   710  	byteBuf [1]byte
   711  	cond    *sync.Cond
   712  	inRead  bool
   713  	aborted bool  // set true before conn.rwc deadline is set to past
   714  	remain  int64 // bytes remaining
   715  }
   716  
   717  func (cr *connReader) lock() {
   718  	cr.mu.Lock()
   719  	if cr.cond == nil {
   720  		cr.cond = sync.NewCond(&cr.mu)
   721  	}
   722  }
   723  
   724  func (cr *connReader) unlock() { cr.mu.Unlock() }
   725  
   726  func (cr *connReader) releaseConn() {
   727  	cr.lock()
   728  	defer cr.unlock()
   729  	cr.conn = nil
   730  }
   731  
   732  func (cr *connReader) startBackgroundRead() {
   733  	cr.lock()
   734  	defer cr.unlock()
   735  	if cr.inRead {
   736  		panic("invalid concurrent Body.Read call")
   737  	}
   738  	if cr.hasByte {
   739  		return
   740  	}
   741  	cr.inRead = true
   742  	cr.rwc.SetReadDeadline(time.Time{})
   743  	go cr.backgroundRead()
   744  }
   745  
   746  func (cr *connReader) backgroundRead() {
   747  	n, err := cr.rwc.Read(cr.byteBuf[:])
   748  	cr.lock()
   749  	if n == 1 {
   750  		cr.hasByte = true
   751  		// We were past the end of the previous request's body already
   752  		// (since we wouldn't be in a background read otherwise), so
   753  		// this is a pipelined HTTP request. Prior to Go 1.11 we used to
   754  		// send on the CloseNotify channel and cancel the context here,
   755  		// but the behavior was documented as only "may", and we only
   756  		// did that because that's how CloseNotify accidentally behaved
   757  		// in very early Go releases prior to context support. Once we
   758  		// added context support, people used a Handler's
   759  		// Request.Context() and passed it along. Having that context
   760  		// cancel on pipelined HTTP requests caused problems.
   761  		// Fortunately, almost nothing uses HTTP/1.x pipelining.
   762  		// Unfortunately, apt-get does, or sometimes does.
   763  		// New Go 1.11 behavior: don't fire CloseNotify or cancel
   764  		// contexts on pipelined requests. Shouldn't affect people, but
   765  		// fixes cases like Issue 23921. This does mean that a client
   766  		// closing their TCP connection after sending a pipelined
   767  		// request won't cancel the context, but we'll catch that on any
   768  		// write failure (in checkConnErrorWriter.Write).
   769  		// If the server never writes, yes, there are still contrived
   770  		// server & client behaviors where this fails to ever cancel the
   771  		// context, but that's kinda why HTTP/1.x pipelining died
   772  		// anyway.
   773  	}
   774  	if ne, ok := err.(net.Error); ok && cr.aborted && ne.Timeout() {
   775  		// Ignore this error. It's the expected error from
   776  		// another goroutine calling abortPendingRead.
   777  	} else if err != nil {
   778  		cr.handleReadErrorLocked(err)
   779  	}
   780  	cr.aborted = false
   781  	cr.inRead = false
   782  	cr.unlock()
   783  	cr.cond.Broadcast()
   784  }
   785  
   786  func (cr *connReader) abortPendingRead() {
   787  	cr.lock()
   788  	defer cr.unlock()
   789  	if !cr.inRead {
   790  		return
   791  	}
   792  	cr.aborted = true
   793  	cr.rwc.SetReadDeadline(aLongTimeAgo)
   794  	for cr.inRead {
   795  		cr.cond.Wait()
   796  	}
   797  	cr.rwc.SetReadDeadline(time.Time{})
   798  }
   799  
   800  func (cr *connReader) setReadLimit(remain int64) { cr.remain = remain }
   801  func (cr *connReader) setInfiniteReadLimit()     { cr.remain = maxInt64 }
   802  func (cr *connReader) hitReadLimit() bool        { return cr.remain <= 0 }
   803  
   804  // handleReadErrorLocked is called whenever a Read from the client returns a
   805  // non-nil error.
   806  //
   807  // The provided non-nil err is almost always io.EOF or a "use of
   808  // closed network connection". Any error means the connection is dead and we
   809  // should shut down its context. An error other than io.EOF or an expired read
   810  // deadline also means the connection is dead for writing, so any response
   811  // write still in flight is aborted.
   812  //
   813  // The caller must hold connReader.mu.
   814  func (cr *connReader) handleReadErrorLocked(err error) {
   815  	if cr.conn == nil {
   816  		return
   817  	}
   818  	// io.EOF means the client half closed and may still be waiting for a
   819  	// response, and an expired read deadline is the server's own doing.
   820  	// Any other error means the connection is gone in both directions, so
   821  	// unblock a response write in flight.
   822  	//
   823  	// This matters because on some systems the poller never reports the
   824  	// socket as writable again once a read has consumed its pending error,
   825  	// so a handler blocked writing a large response would otherwise block
   826  	// forever. See go.dev/issue/78438.
   827  	if err != io.EOF && !errors.Is(err, os.ErrDeadlineExceeded) {
   828  		cr.conn.rwc.SetWriteDeadline(aLongTimeAgo)
   829  	}
   830  	cr.conn.cancelCtx()
   831  	if res := cr.conn.curReq.Load(); res != nil {
   832  		res.closeNotify()
   833  	}
   834  }
   835  
   836  func (cr *connReader) Read(p []byte) (n int, err error) {
   837  	cr.lock()
   838  	if cr.conn == nil {
   839  		cr.unlock()
   840  		return cr.rwc.Read(p)
   841  	}
   842  	if cr.inRead {
   843  		hijacked := cr.conn.hijacked()
   844  		cr.unlock()
   845  		if hijacked {
   846  			panic("invalid Body.Read call. After hijacked, the original Request must not be used")
   847  		}
   848  		panic("invalid concurrent Body.Read call")
   849  	}
   850  	if cr.hitReadLimit() {
   851  		cr.unlock()
   852  		return 0, io.EOF
   853  	}
   854  	if len(p) == 0 {
   855  		cr.unlock()
   856  		return 0, nil
   857  	}
   858  	if int64(len(p)) > cr.remain {
   859  		p = p[:cr.remain]
   860  	}
   861  	if cr.hasByte {
   862  		p[0] = cr.byteBuf[0]
   863  		cr.hasByte = false
   864  		cr.unlock()
   865  		return 1, nil
   866  	}
   867  	cr.inRead = true
   868  	cr.unlock()
   869  	n, err = cr.rwc.Read(p)
   870  
   871  	cr.lock()
   872  	cr.inRead = false
   873  	if err != nil {
   874  		cr.handleReadErrorLocked(err)
   875  	}
   876  	cr.remain -= int64(n)
   877  	cr.unlock()
   878  
   879  	cr.cond.Broadcast()
   880  	return n, err
   881  }
   882  
   883  var (
   884  	bufioReaderPool   sync.Pool
   885  	bufioWriter2kPool sync.Pool
   886  	bufioWriter4kPool sync.Pool
   887  )
   888  
   889  const copyBufPoolSize = 32 * 1024
   890  
   891  var copyBufPool = sync.Pool{New: func() any { return new([copyBufPoolSize]byte) }}
   892  
   893  func getCopyBuf() []byte {
   894  	return copyBufPool.Get().(*[copyBufPoolSize]byte)[:]
   895  }
   896  
   897  func putCopyBuf(b []byte) {
   898  	if len(b) != copyBufPoolSize {
   899  		panic("trying to put back buffer of the wrong size in the copyBufPool")
   900  	}
   901  	copyBufPool.Put((*[copyBufPoolSize]byte)(b))
   902  }
   903  
   904  func bufioWriterPool(size int) *sync.Pool {
   905  	switch size {
   906  	case 2 << 10:
   907  		return &bufioWriter2kPool
   908  	case 4 << 10:
   909  		return &bufioWriter4kPool
   910  	}
   911  	return nil
   912  }
   913  
   914  func newBufioReader(r io.Reader) *bufio.Reader {
   915  	if v := bufioReaderPool.Get(); v != nil {
   916  		br := v.(*bufio.Reader)
   917  		br.Reset(r)
   918  		return br
   919  	}
   920  	// Note: if this reader size is ever changed, update
   921  	// TestHandlerBodyClose's assumptions.
   922  	return bufio.NewReader(r)
   923  }
   924  
   925  func putBufioReader(br *bufio.Reader) {
   926  	br.Reset(nil)
   927  	bufioReaderPool.Put(br)
   928  }
   929  
   930  func newBufioWriterSize(w io.Writer, size int) *bufio.Writer {
   931  	pool := bufioWriterPool(size)
   932  	if pool != nil {
   933  		if v := pool.Get(); v != nil {
   934  			bw := v.(*bufio.Writer)
   935  			bw.Reset(w)
   936  			return bw
   937  		}
   938  	}
   939  	return bufio.NewWriterSize(w, size)
   940  }
   941  
   942  func putBufioWriter(bw *bufio.Writer) {
   943  	bw.Reset(nil)
   944  	if pool := bufioWriterPool(bw.Available()); pool != nil {
   945  		pool.Put(bw)
   946  	}
   947  }
   948  
   949  // DefaultMaxHeaderBytes is the maximum permitted size of the headers
   950  // in an HTTP request.
   951  // This can be overridden by setting [Server.MaxHeaderBytes].
   952  const DefaultMaxHeaderBytes = 1 << 20 // 1 MB
   953  
   954  // DefaultMaxHeaderValueCount is the maximum permitted number of
   955  // header values in an HTTP request.
   956  // This can be overridden by setting [Server.MaxHeaderValueCount].
   957  const DefaultMaxHeaderValueCount = 500
   958  
   959  func (s *Server) maxHeaderBytes() int {
   960  	if s.MaxHeaderBytes > 0 {
   961  		return s.MaxHeaderBytes
   962  	}
   963  	return DefaultMaxHeaderBytes
   964  }
   965  
   966  func (s *Server) maxHeaderValueCount() int {
   967  	if s.MaxHeaderValueCount > 0 {
   968  		return s.MaxHeaderValueCount
   969  	}
   970  	return DefaultMaxHeaderValueCount
   971  }
   972  
   973  func (s *Server) initialReadLimitSize() int64 {
   974  	return int64(s.maxHeaderBytes()) + 4096 // bufio slop
   975  }
   976  
   977  // tlsHandshakeTimeout returns the time limit permitted for the TLS
   978  // handshake, or zero for unlimited.
   979  //
   980  // It returns the minimum of any positive ReadHeaderTimeout,
   981  // ReadTimeout, or WriteTimeout.
   982  func (s *Server) tlsHandshakeTimeout() time.Duration {
   983  	var ret time.Duration
   984  	for _, v := range [...]time.Duration{
   985  		s.ReadHeaderTimeout,
   986  		s.ReadTimeout,
   987  		s.WriteTimeout,
   988  	} {
   989  		if v <= 0 {
   990  			continue
   991  		}
   992  		if ret == 0 || v < ret {
   993  			ret = v
   994  		}
   995  	}
   996  	return ret
   997  }
   998  
   999  // wrapper around io.ReadCloser which on first read, sends an
  1000  // HTTP/1.1 100 Continue header
  1001  type expectContinueReader struct {
  1002  	resp       *response
  1003  	readCloser io.ReadCloser
  1004  	closed     atomic.Bool
  1005  }
  1006  
  1007  func (ecr *expectContinueReader) Read(p []byte) (n int, err error) {
  1008  	if ecr.closed.Load() {
  1009  		return 0, ErrBodyReadAfterClose
  1010  	}
  1011  	w := ecr.resp
  1012  	if w.canWriteContinue.Load() {
  1013  		w.writeContinueMu.Lock()
  1014  		if w.canWriteContinue.Load() {
  1015  			w.conn.bufw.WriteString("HTTP/1.1 100 Continue\r\n\r\n")
  1016  			w.conn.bufw.Flush()
  1017  			w.canWriteContinue.Store(false)
  1018  		}
  1019  		w.writeContinueMu.Unlock()
  1020  	}
  1021  	return ecr.readCloser.Read(p)
  1022  }
  1023  
  1024  func (ecr *expectContinueReader) Close() error {
  1025  	if ecr.resp.canWriteContinue.Load() {
  1026  		ecr.resp.disableWriteContinue(true)
  1027  	}
  1028  	if ecr.closed.Swap(true) {
  1029  		return nil
  1030  	}
  1031  	return ecr.readCloser.Close()
  1032  }
  1033  
  1034  // TimeFormat is the time format to use when generating times in HTTP
  1035  // headers. It is like [time.RFC1123] but hard-codes GMT as the time
  1036  // zone. The time being formatted must be in UTC for Format to
  1037  // generate the correct format.
  1038  //
  1039  // For parsing this time format, see [ParseTime].
  1040  const TimeFormat = "Mon, 02 Jan 2006 15:04:05 GMT"
  1041  
  1042  var errTooLarge = errors.New("http: request too large")
  1043  
  1044  // Read next request from connection.
  1045  func (c *conn) readRequest(ctx context.Context) (w *response, err error) {
  1046  	if c.hijacked() {
  1047  		return nil, ErrHijacked
  1048  	}
  1049  
  1050  	t0 := time.Now()
  1051  	var wholeReqDeadline time.Time // or zero if none
  1052  	if d := c.server.ReadTimeout; d > 0 {
  1053  		wholeReqDeadline = t0.Add(d)
  1054  	}
  1055  	if d := c.server.WriteTimeout; d > 0 {
  1056  		defer func() {
  1057  			c.rwc.SetWriteDeadline(time.Now().Add(d))
  1058  		}()
  1059  	}
  1060  
  1061  	c.r.setReadLimit(c.server.initialReadLimitSize())
  1062  	if c.lastMethod == "POST" {
  1063  		// RFC 7230 section 3 tolerance for old buggy clients.
  1064  		peek, _ := c.bufr.Peek(4) // ReadRequest will get err below
  1065  		c.bufr.Discard(numLeadingCRorLF(peek))
  1066  	}
  1067  	req, err := readRequestLimit(c.bufr, int64(c.server.maxHeaderValueCount()))
  1068  	if err != nil {
  1069  		if c.r.hitReadLimit() {
  1070  			return nil, errTooLarge
  1071  		}
  1072  		return nil, err
  1073  	}
  1074  
  1075  	if !http1ServerSupportsRequest(req) {
  1076  		return nil, statusError{StatusHTTPVersionNotSupported, "unsupported protocol version"}
  1077  	}
  1078  
  1079  	c.lastMethod = req.Method
  1080  	c.r.setInfiniteReadLimit()
  1081  
  1082  	hosts, haveHost := req.Header["Host"]
  1083  	isH2Upgrade := req.isH2Upgrade()
  1084  	if req.ProtoAtLeast(1, 1) && (!haveHost || len(hosts) == 0) && !isH2Upgrade && req.Method != "CONNECT" {
  1085  		return nil, badRequestError("missing required Host header")
  1086  	}
  1087  	if len(hosts) == 1 && !httpguts.ValidHostHeader(hosts[0]) {
  1088  		return nil, badRequestError("malformed Host header")
  1089  	}
  1090  	for k, vv := range req.Header {
  1091  		if !httpguts.ValidHeaderFieldName(k) {
  1092  			return nil, badRequestError("invalid header name")
  1093  		}
  1094  		for _, v := range vv {
  1095  			if !httpguts.ValidHeaderFieldValue(v) {
  1096  				return nil, badRequestError("invalid header value")
  1097  			}
  1098  		}
  1099  	}
  1100  	delete(req.Header, "Host")
  1101  
  1102  	ctx, cancelCtx := context.WithCancel(ctx)
  1103  	req.ctx = ctx
  1104  	req.RemoteAddr = c.remoteAddr
  1105  	req.TLS = c.tlsState
  1106  	var reqBody *body
  1107  	switch b := req.Body.(type) {
  1108  	case noBody:
  1109  	case *body:
  1110  		reqBody = b
  1111  		reqBody.doEarlyClose = true
  1112  	default:
  1113  		panic(fmt.Errorf("http: unexpected request body type %T", req.Body))
  1114  	}
  1115  
  1116  	c.rwc.SetReadDeadline(wholeReqDeadline)
  1117  
  1118  	w = &response{
  1119  		conn:          c,
  1120  		cancelCtx:     cancelCtx,
  1121  		req:           req,
  1122  		reqBody:       reqBody,
  1123  		handlerHeader: make(Header),
  1124  		contentLength: -1,
  1125  
  1126  		// We populate these ahead of time so we're not
  1127  		// reading from req.Header after their Handler starts
  1128  		// and maybe mutates it (Issue 14940)
  1129  		wants10KeepAlive: req.wantsHttp10KeepAlive(),
  1130  		wantsClose:       req.wantsClose(),
  1131  	}
  1132  	if isH2Upgrade {
  1133  		w.closeAfterReply = true
  1134  	}
  1135  	w.cw.res = w
  1136  	w.w = newBufioWriterSize(&w.cw, bufferBeforeChunkingSize)
  1137  	return w, nil
  1138  }
  1139  
  1140  // http1ServerSupportsRequest reports whether Go's HTTP/1.x server
  1141  // supports the given request.
  1142  func http1ServerSupportsRequest(req *Request) bool {
  1143  	if req.ProtoMajor == 1 {
  1144  		return true
  1145  	}
  1146  	// Accept "PRI * HTTP/2.0" upgrade requests, so Handlers can
  1147  	// wire up their own HTTP/2 upgrades.
  1148  	if req.ProtoMajor == 2 && req.ProtoMinor == 0 &&
  1149  		req.Method == "PRI" && req.RequestURI == "*" {
  1150  		return true
  1151  	}
  1152  	// Reject HTTP/0.x, and all other HTTP/2+ requests (which
  1153  	// aren't encoded in ASCII anyway).
  1154  	return false
  1155  }
  1156  
  1157  func (w *response) Header() Header {
  1158  	if w.cw.header == nil && w.wroteHeader && !w.cw.wroteHeader {
  1159  		// Accessing the header between logically writing it
  1160  		// and physically writing it means we need to allocate
  1161  		// a clone to snapshot the logically written state.
  1162  		w.cw.header = w.handlerHeader.Clone()
  1163  	}
  1164  	w.calledHeader = true
  1165  	return w.handlerHeader
  1166  }
  1167  
  1168  // maxPostHandlerReadBytes is the max number of Request.Body bytes not
  1169  // consumed by a handler that the server will read from the client
  1170  // in order to keep a connection alive. If there are more bytes
  1171  // than this, the server, to be paranoid, instead sends a
  1172  // "Connection close" response.
  1173  //
  1174  // This number is approximately what a typical machine's TCP buffer
  1175  // size is anyway.  (if we have the bytes on the machine, we might as
  1176  // well read them)
  1177  const maxPostHandlerReadBytes = 256 << 10
  1178  
  1179  func checkWriteHeaderCode(code int) {
  1180  	// Issue 22880: require valid WriteHeader status codes.
  1181  	// For now we only enforce that it's three digits.
  1182  	// In the future we might block things over 599 (600 and above aren't defined
  1183  	// at https://httpwg.org/specs/rfc7231.html#status.codes).
  1184  	// But for now any three digits.
  1185  	//
  1186  	// We used to send "HTTP/1.1 000 0" on the wire in responses but there's
  1187  	// no equivalent bogus thing we can realistically send in HTTP/2,
  1188  	// so we'll consistently panic instead and help people find their bugs
  1189  	// early. (We can't return an error from WriteHeader even if we wanted to.)
  1190  	if code < 100 || code > 999 {
  1191  		panic(fmt.Sprintf("invalid WriteHeader code %v", code))
  1192  	}
  1193  }
  1194  
  1195  // relevantCaller searches the call stack for the first function outside of net/http.
  1196  // The purpose of this function is to provide more helpful error messages.
  1197  func relevantCaller() runtime.Frame {
  1198  	pc := make([]uintptr, 16)
  1199  	n := runtime.Callers(1, pc)
  1200  	frames := runtime.CallersFrames(pc[:n])
  1201  	var frame runtime.Frame
  1202  	for {
  1203  		var more bool
  1204  		frame, more = frames.Next()
  1205  		if !strings.HasPrefix(frame.Function, "net/http.") {
  1206  			return frame
  1207  		}
  1208  		if !more {
  1209  			break
  1210  		}
  1211  	}
  1212  	return frame
  1213  }
  1214  
  1215  func (w *response) WriteHeader(code int) {
  1216  	if w.conn.hijacked() {
  1217  		caller := relevantCaller()
  1218  		w.conn.server.logf("http: response.WriteHeader on hijacked connection from %s (%s:%d)", caller.Function, path.Base(caller.File), caller.Line)
  1219  		return
  1220  	}
  1221  	if w.wroteHeader {
  1222  		caller := relevantCaller()
  1223  		w.conn.server.logf("http: superfluous response.WriteHeader call from %s (%s:%d)", caller.Function, path.Base(caller.File), caller.Line)
  1224  		return
  1225  	}
  1226  	checkWriteHeaderCode(code)
  1227  
  1228  	// Sending a 100 Continue or any non-1XX header disables the
  1229  	// automatically-sent 100 Continue from Request.Body.Read. If it is a final
  1230  	// response (200 or higher), we skip draining the request body, which the
  1231  	// client will never send.
  1232  	if code == 100 || code >= 200 {
  1233  		w.disableWriteContinue(code >= 200)
  1234  	}
  1235  
  1236  	// Handle informational headers.
  1237  	//
  1238  	// We shouldn't send any further headers after 101 Switching Protocols,
  1239  	// so it takes the non-informational path.
  1240  	if code >= 100 && code <= 199 && code != StatusSwitchingProtocols {
  1241  		w.writeContinueMu.Lock()
  1242  		defer w.writeContinueMu.Unlock()
  1243  		writeStatusLine(w.conn.bufw, w.req.ProtoAtLeast(1, 1), code, w.statusBuf[:])
  1244  
  1245  		// Per RFC 8297 we must not clear the current header map
  1246  		w.handlerHeader.WriteSubset(w.conn.bufw, excludedHeadersNoBody)
  1247  		w.conn.bufw.Write(crlf)
  1248  		w.conn.bufw.Flush()
  1249  
  1250  		return
  1251  	}
  1252  
  1253  	w.wroteHeader = true
  1254  	w.status = code
  1255  
  1256  	if w.calledHeader && w.cw.header == nil {
  1257  		w.cw.header = w.handlerHeader.Clone()
  1258  	}
  1259  
  1260  	if cl := w.handlerHeader.get("Content-Length"); cl != "" {
  1261  		v, err := strconv.ParseInt(cl, 10, 64)
  1262  		if err == nil && v >= 0 {
  1263  			w.contentLength = v
  1264  		} else {
  1265  			w.conn.server.logf("http: invalid Content-Length of %q", cl)
  1266  			w.handlerHeader.Del("Content-Length")
  1267  		}
  1268  	}
  1269  }
  1270  
  1271  // extraHeader is the set of headers sometimes added by chunkWriter.writeHeader.
  1272  // This type is used to avoid extra allocations from cloning and/or populating
  1273  // the response Header map and all its 1-element slices.
  1274  type extraHeader struct {
  1275  	contentType      string
  1276  	connection       string
  1277  	transferEncoding string
  1278  	date             []byte // written if not nil
  1279  	contentLength    []byte // written if not nil
  1280  }
  1281  
  1282  // Sorted the same as extraHeader.Write's loop.
  1283  var extraHeaderKeys = [][]byte{
  1284  	[]byte("Content-Type"),
  1285  	[]byte("Connection"),
  1286  	[]byte("Transfer-Encoding"),
  1287  }
  1288  
  1289  var (
  1290  	headerContentLength = []byte("Content-Length: ")
  1291  	headerDate          = []byte("Date: ")
  1292  )
  1293  
  1294  // Write writes the headers described in h to w.
  1295  //
  1296  // This method has a value receiver, despite the somewhat large size
  1297  // of h, because it prevents an allocation. The escape analysis isn't
  1298  // smart enough to realize this function doesn't mutate h.
  1299  func (h extraHeader) Write(w *bufio.Writer) {
  1300  	if h.date != nil {
  1301  		w.Write(headerDate)
  1302  		w.Write(h.date)
  1303  		w.Write(crlf)
  1304  	}
  1305  	if h.contentLength != nil {
  1306  		w.Write(headerContentLength)
  1307  		w.Write(h.contentLength)
  1308  		w.Write(crlf)
  1309  	}
  1310  	for i, v := range []string{h.contentType, h.connection, h.transferEncoding} {
  1311  		if v != "" {
  1312  			w.Write(extraHeaderKeys[i])
  1313  			w.Write(colonSpace)
  1314  			w.WriteString(v)
  1315  			w.Write(crlf)
  1316  		}
  1317  	}
  1318  }
  1319  
  1320  // writeHeader finalizes the header sent to the client and writes it
  1321  // to cw.res.conn.bufw.
  1322  //
  1323  // p is not written by writeHeader, but is the first chunk of the body
  1324  // that will be written. It is sniffed for a Content-Type if none is
  1325  // set explicitly. It's also used to set the Content-Length, if the
  1326  // total body size was small and the handler has already finished
  1327  // running.
  1328  func (cw *chunkWriter) writeHeader(p []byte) {
  1329  	if cw.wroteHeader {
  1330  		return
  1331  	}
  1332  	cw.wroteHeader = true
  1333  
  1334  	w := cw.res
  1335  	keepAlivesEnabled := w.conn.server.doKeepAlives()
  1336  	isHEAD := w.req.Method == "HEAD"
  1337  
  1338  	// header is written out to w.conn.buf below. Depending on the
  1339  	// state of the handler, we either own the map or not. If we
  1340  	// don't own it, the exclude map is created lazily for
  1341  	// WriteSubset to remove headers. The setHeader struct holds
  1342  	// headers we need to add.
  1343  	header := cw.header
  1344  	owned := header != nil
  1345  	if !owned {
  1346  		header = w.handlerHeader
  1347  	}
  1348  	var excludeHeader map[string]bool
  1349  	delHeader := func(key string) {
  1350  		if owned {
  1351  			header.Del(key)
  1352  			return
  1353  		}
  1354  		if _, ok := header[key]; !ok {
  1355  			return
  1356  		}
  1357  		if excludeHeader == nil {
  1358  			excludeHeader = make(map[string]bool)
  1359  		}
  1360  		excludeHeader[key] = true
  1361  	}
  1362  	var setHeader extraHeader
  1363  
  1364  	// Don't write out the fake "Trailer:foo" keys. See TrailerPrefix.
  1365  	trailers := false
  1366  	for k := range cw.header {
  1367  		if strings.HasPrefix(k, TrailerPrefix) {
  1368  			if excludeHeader == nil {
  1369  				excludeHeader = make(map[string]bool)
  1370  			}
  1371  			excludeHeader[k] = true
  1372  			trailers = true
  1373  		}
  1374  	}
  1375  	for _, v := range cw.header["Trailer"] {
  1376  		trailers = true
  1377  		foreachHeaderElement(v, cw.res.declareTrailer)
  1378  	}
  1379  
  1380  	te := header.get("Transfer-Encoding")
  1381  	hasTE := te != ""
  1382  
  1383  	// If the handler is done but never sent a Content-Length
  1384  	// response header and this is our first (and last) write, set
  1385  	// it, even to zero. This helps HTTP/1.0 clients keep their
  1386  	// "keep-alive" connections alive.
  1387  	// Exceptions: 304/204/1xx responses never get Content-Length, and if
  1388  	// it was a HEAD request, we don't know the difference between
  1389  	// 0 actual bytes and 0 bytes because the handler noticed it
  1390  	// was a HEAD request and chose not to write anything. So for
  1391  	// HEAD, the handler should either write the Content-Length or
  1392  	// write non-zero bytes. If it's actually 0 bytes and the
  1393  	// handler never looked at the Request.Method, we just don't
  1394  	// send a Content-Length header.
  1395  	// Further, we don't send an automatic Content-Length if they
  1396  	// set a Transfer-Encoding, because they're generally incompatible.
  1397  	if w.handlerDone.Load() && !trailers && !hasTE && bodyAllowedForStatus(w.status) && !header.has("Content-Length") && (!isHEAD || len(p) > 0) {
  1398  		w.contentLength = int64(len(p))
  1399  		setHeader.contentLength = strconv.AppendInt(cw.res.clenBuf[:0], int64(len(p)), 10)
  1400  	}
  1401  
  1402  	// If this was an HTTP/1.0 request with keep-alive and we sent a
  1403  	// Content-Length back, we can make this a keep-alive response ...
  1404  	if w.wants10KeepAlive && keepAlivesEnabled {
  1405  		sentLength := header.get("Content-Length") != ""
  1406  		if sentLength && header.get("Connection") == "keep-alive" {
  1407  			w.closeAfterReply = false
  1408  		}
  1409  	}
  1410  
  1411  	// Check for an explicit (and valid) Content-Length header.
  1412  	hasCL := w.contentLength != -1
  1413  
  1414  	if w.wants10KeepAlive && (isHEAD || hasCL || !bodyAllowedForStatus(w.status)) {
  1415  		_, connectionHeaderSet := header["Connection"]
  1416  		if !connectionHeaderSet {
  1417  			setHeader.connection = "keep-alive"
  1418  		}
  1419  	} else if !w.req.ProtoAtLeast(1, 1) || w.wantsClose {
  1420  		w.closeAfterReply = true
  1421  	}
  1422  
  1423  	if header.get("Connection") == "close" || !keepAlivesEnabled {
  1424  		w.closeAfterReply = true
  1425  	}
  1426  
  1427  	// If the client wanted a 100-continue but we never sent it to
  1428  	// them (or, more strictly: we never finished reading their
  1429  	// request body), don't reuse this connection.
  1430  	//
  1431  	// This behavior was first added on the theory that we don't know
  1432  	// if the next bytes on the wire are going to be the remainder of
  1433  	// the request body or the subsequent request (see issue 11549),
  1434  	// but that's not correct: If we keep using the connection,
  1435  	// the client is required to send the request body whether we
  1436  	// asked for it or not.
  1437  	//
  1438  	// We probably do want to skip reusing the connection in most cases,
  1439  	// however. If the client is offering a large request body that we
  1440  	// don't intend to use, then it's better to close the connection
  1441  	// than to read the body. For now, assume that if we're sending
  1442  	// headers, the handler is done reading the body and we should
  1443  	// drop the connection if we haven't seen EOF.
  1444  	if w.ecReader != nil && w.reqBody.bodyRemains() {
  1445  		w.closeAfterReply = true
  1446  	}
  1447  
  1448  	// We do this by default because there are a number of clients that
  1449  	// send a full request before starting to read the response, and they
  1450  	// can deadlock if we start writing the response with unconsumed body
  1451  	// remaining. See Issue 15527 for some history.
  1452  	//
  1453  	// If full duplex mode has been enabled with ResponseController.EnableFullDuplex,
  1454  	// then leave the request body alone.
  1455  	//
  1456  	// We don't take this path when w.closeAfterReply is set.
  1457  	// We may not need to consume the request to get ready for the next one
  1458  	// (since we're closing the conn), but a client which sends a full request
  1459  	// before reading a response may deadlock in this case.
  1460  	// This behavior has been present since CL 5268043 (2011), however,
  1461  	// so it doesn't seem to be causing problems.
  1462  	if w.req.ContentLength != 0 && w.reqBody != nil && !w.closeAfterReply && !w.fullDuplex {
  1463  		var discard, tooBig bool
  1464  		w.reqBody.mu.Lock()
  1465  		switch {
  1466  		case w.reqBody.closed:
  1467  			if !w.reqBody.sawEOF {
  1468  				// Body was closed in handler with non-EOF error.
  1469  				w.closeAfterReply = true
  1470  			}
  1471  		case w.reqBody.unreadDataSizeLocked() >= maxPostHandlerReadBytes:
  1472  			tooBig = true
  1473  		default:
  1474  			discard = true
  1475  		}
  1476  		w.reqBody.mu.Unlock()
  1477  
  1478  		if discard {
  1479  			w.reqBody.Close()
  1480  			if !w.reqBody.consumedEntireBody() {
  1481  				w.closeAfterReply = true
  1482  			}
  1483  		}
  1484  		if tooBig {
  1485  			w.requestTooLarge()
  1486  			delHeader("Connection")
  1487  			setHeader.connection = "close"
  1488  		}
  1489  	}
  1490  
  1491  	code := w.status
  1492  	if bodyAllowedForStatus(code) {
  1493  		// If no content type, apply sniffing algorithm to body.
  1494  		_, haveType := header["Content-Type"]
  1495  
  1496  		// If the Content-Encoding was set and is non-blank,
  1497  		// we shouldn't sniff the body. See Issue 31753.
  1498  		ce := header.Get("Content-Encoding")
  1499  		hasCE := len(ce) > 0
  1500  		if !hasCE && !haveType && !hasTE && len(p) > 0 {
  1501  			setHeader.contentType = DetectContentType(p)
  1502  		}
  1503  	} else {
  1504  		for _, k := range suppressedHeaders(code) {
  1505  			delHeader(k)
  1506  		}
  1507  	}
  1508  
  1509  	if !header.has("Date") {
  1510  		setHeader.date = time.Now().UTC().AppendFormat(cw.res.dateBuf[:0], TimeFormat)
  1511  	}
  1512  
  1513  	if hasCL && hasTE && te != "identity" {
  1514  		// TODO: return an error if WriteHeader gets a return parameter
  1515  		// For now just ignore the Content-Length.
  1516  		w.conn.server.logf("http: WriteHeader called with both Transfer-Encoding of %q and a Content-Length of %d",
  1517  			te, w.contentLength)
  1518  		delHeader("Content-Length")
  1519  		hasCL = false
  1520  	}
  1521  
  1522  	if w.req.Method == "HEAD" || !bodyAllowedForStatus(code) || code == StatusNoContent {
  1523  		// Response has no body.
  1524  		delHeader("Transfer-Encoding")
  1525  	} else if hasCL {
  1526  		// Content-Length has been provided, so no chunking is to be done.
  1527  		delHeader("Transfer-Encoding")
  1528  	} else if w.req.ProtoAtLeast(1, 1) {
  1529  		// HTTP/1.1 or greater: Transfer-Encoding has been set to identity, and no
  1530  		// content-length has been provided. The connection must be closed after the
  1531  		// reply is written, and no chunking is to be done. This is the setup
  1532  		// recommended in the Server-Sent Events candidate recommendation 11,
  1533  		// section 8.
  1534  		if hasTE && te == "identity" {
  1535  			cw.chunking = false
  1536  			w.closeAfterReply = true
  1537  			delHeader("Transfer-Encoding")
  1538  		} else {
  1539  			// HTTP/1.1 or greater: use chunked transfer encoding
  1540  			// to avoid closing the connection at EOF.
  1541  			cw.chunking = true
  1542  			setHeader.transferEncoding = "chunked"
  1543  			if hasTE && te == "chunked" {
  1544  				// We will send the chunked Transfer-Encoding header later.
  1545  				delHeader("Transfer-Encoding")
  1546  			}
  1547  		}
  1548  	} else {
  1549  		// HTTP version < 1.1: cannot do chunked transfer
  1550  		// encoding and we don't know the Content-Length so
  1551  		// signal EOF by closing connection.
  1552  		w.closeAfterReply = true
  1553  		delHeader("Transfer-Encoding") // in case already set
  1554  	}
  1555  
  1556  	// Cannot use Content-Length with non-identity Transfer-Encoding.
  1557  	if cw.chunking {
  1558  		delHeader("Content-Length")
  1559  	}
  1560  	if !w.req.ProtoAtLeast(1, 0) {
  1561  		return
  1562  	}
  1563  
  1564  	// Only override the Connection header if it is not a successful
  1565  	// protocol switch response and if KeepAlives are not enabled.
  1566  	// See https://golang.org/issue/36381.
  1567  	delConnectionHeader := w.closeAfterReply &&
  1568  		(!keepAlivesEnabled || !hasToken(cw.header.get("Connection"), "close")) &&
  1569  		!isProtocolSwitchResponse(w.status, header)
  1570  	if delConnectionHeader {
  1571  		delHeader("Connection")
  1572  		if w.req.ProtoAtLeast(1, 1) {
  1573  			setHeader.connection = "close"
  1574  		}
  1575  	}
  1576  
  1577  	writeStatusLine(w.conn.bufw, w.req.ProtoAtLeast(1, 1), code, w.statusBuf[:])
  1578  	cw.header.WriteSubset(w.conn.bufw, excludeHeader)
  1579  	setHeader.Write(w.conn.bufw)
  1580  	w.conn.bufw.Write(crlf)
  1581  }
  1582  
  1583  // foreachHeaderElement splits v according to the "#rule" construction
  1584  // in RFC 7230 section 7 and calls fn for each non-empty element.
  1585  func foreachHeaderElement(v string, fn func(string)) {
  1586  	v = textproto.TrimString(v)
  1587  	if v == "" {
  1588  		return
  1589  	}
  1590  	if !strings.Contains(v, ",") {
  1591  		fn(v)
  1592  		return
  1593  	}
  1594  	for f := range strings.SplitSeq(v, ",") {
  1595  		if f = textproto.TrimString(f); f != "" {
  1596  			fn(f)
  1597  		}
  1598  	}
  1599  }
  1600  
  1601  // writeStatusLine writes an HTTP/1.x Status-Line (RFC 7230 Section 3.1.2)
  1602  // to bw. is11 is whether the HTTP request is HTTP/1.1. false means HTTP/1.0.
  1603  // code is the response status code.
  1604  // scratch is an optional scratch buffer. If it has at least capacity 3, it's used.
  1605  func writeStatusLine(bw *bufio.Writer, is11 bool, code int, scratch []byte) {
  1606  	if is11 {
  1607  		bw.WriteString("HTTP/1.1 ")
  1608  	} else {
  1609  		bw.WriteString("HTTP/1.0 ")
  1610  	}
  1611  	if text := StatusText(code); text != "" {
  1612  		bw.Write(strconv.AppendInt(scratch[:0], int64(code), 10))
  1613  		bw.WriteByte(' ')
  1614  		bw.WriteString(text)
  1615  		bw.WriteString("\r\n")
  1616  	} else {
  1617  		// don't worry about performance
  1618  		fmt.Fprintf(bw, "%03d status code %d\r\n", code, code)
  1619  	}
  1620  }
  1621  
  1622  // bodyAllowed reports whether a Write is allowed for this response type.
  1623  // It's illegal to call this before the header has been flushed.
  1624  func (w *response) bodyAllowed() bool {
  1625  	if !w.wroteHeader {
  1626  		panic("net/http: bodyAllowed called before the header was written")
  1627  	}
  1628  	return bodyAllowedForStatus(w.status)
  1629  }
  1630  
  1631  // The Life Of A Write is like this:
  1632  //
  1633  // Handler starts. No header has been sent. The handler can either
  1634  // write a header, or just start writing. Writing before sending a header
  1635  // sends an implicitly empty 200 OK header.
  1636  //
  1637  // If the handler didn't declare a Content-Length up front, we either
  1638  // go into chunking mode or, if the handler finishes running before
  1639  // the chunking buffer size, we compute a Content-Length and send that
  1640  // in the header instead.
  1641  //
  1642  // Likewise, if the handler didn't set a Content-Type, we sniff that
  1643  // from the initial chunk of output.
  1644  //
  1645  // The Writers are wired together like:
  1646  //
  1647  //  1. *response (the ResponseWriter) ->
  1648  //  2. (*response).w, a [*bufio.Writer] of bufferBeforeChunkingSize bytes ->
  1649  //  3. chunkWriter.Writer (whose writeHeader finalizes Content-Length/Type)
  1650  //     and which writes the chunk headers, if needed ->
  1651  //  4. conn.bufw, a *bufio.Writer of default (4kB) bytes, writing to ->
  1652  //  5. checkConnErrorWriter{c}, which notes any non-nil error on Write
  1653  //     and populates c.werr with it if so, but otherwise writes to ->
  1654  //  6. the rwc, the [net.Conn].
  1655  //
  1656  // TODO(bradfitz): short-circuit some of the buffering when the
  1657  // initial header contains both a Content-Type and Content-Length.
  1658  // Also short-circuit in (1) when the header's been sent and not in
  1659  // chunking mode, writing directly to (4) instead, if (2) has no
  1660  // buffered data. More generally, we could short-circuit from (1) to
  1661  // (3) even in chunking mode if the write size from (1) is over some
  1662  // threshold and nothing is in (2).  The answer might be mostly making
  1663  // bufferBeforeChunkingSize smaller and having bufio's fast-paths deal
  1664  // with this instead.
  1665  func (w *response) Write(data []byte) (n int, err error) {
  1666  	return w.write(len(data), data, "")
  1667  }
  1668  
  1669  func (w *response) WriteString(data string) (n int, err error) {
  1670  	return w.write(len(data), nil, data)
  1671  }
  1672  
  1673  // either dataB or dataS is non-zero.
  1674  func (w *response) write(lenData int, dataB []byte, dataS string) (n int, err error) {
  1675  	if w.conn.hijacked() {
  1676  		if lenData > 0 {
  1677  			caller := relevantCaller()
  1678  			w.conn.server.logf("http: response.Write on hijacked connection from %s (%s:%d)", caller.Function, path.Base(caller.File), caller.Line)
  1679  		}
  1680  		return 0, ErrHijacked
  1681  	}
  1682  
  1683  	if w.canWriteContinue.Load() {
  1684  		// Body reader wants to write 100 Continue but hasn't yet. Tell it not to.
  1685  		w.disableWriteContinue(true)
  1686  	}
  1687  
  1688  	if !w.wroteHeader {
  1689  		w.WriteHeader(StatusOK)
  1690  	}
  1691  	if lenData == 0 {
  1692  		return 0, nil
  1693  	}
  1694  	if !w.bodyAllowed() {
  1695  		return 0, ErrBodyNotAllowed
  1696  	}
  1697  
  1698  	w.written += int64(lenData) // ignoring errors, for errorKludge
  1699  	if w.contentLength != -1 && w.written > w.contentLength {
  1700  		return 0, ErrContentLength
  1701  	}
  1702  	if dataB != nil {
  1703  		return w.w.Write(dataB)
  1704  	} else {
  1705  		return w.w.WriteString(dataS)
  1706  	}
  1707  }
  1708  
  1709  func (w *response) finishRequest() {
  1710  	w.handlerDone.Store(true)
  1711  
  1712  	if !w.wroteHeader {
  1713  		w.WriteHeader(StatusOK)
  1714  	}
  1715  
  1716  	w.w.Flush()
  1717  	putBufioWriter(w.w)
  1718  	w.cw.close()
  1719  	w.conn.bufw.Flush()
  1720  
  1721  	w.conn.r.abortPendingRead()
  1722  	w.reqBody.registerOnHitEOF(nil) // prevent new background read from starting
  1723  
  1724  	if w.canWriteContinue.Load() {
  1725  		w.disableWriteContinue(true)
  1726  	}
  1727  
  1728  	// Close the body (regardless of w.closeAfterReply) so we can
  1729  	// re-use its bufio.Reader later safely.
  1730  	//
  1731  	// In full-duplex mode, this may also drain the remaining request body.
  1732  	w.reqBody.Close()
  1733  }
  1734  
  1735  // shouldReuseConnection reports whether the underlying TCP connection can be reused.
  1736  // It must only be called after the handler is done executing.
  1737  func (w *response) shouldReuseConnection() bool {
  1738  	if w.closeAfterReply {
  1739  		// The request or something set while executing the
  1740  		// handler indicated we shouldn't reuse this
  1741  		// connection.
  1742  		return false
  1743  	}
  1744  
  1745  	if w.req.Method != "HEAD" && w.contentLength != -1 && w.bodyAllowed() && w.contentLength != w.written {
  1746  		// Did not write enough. Avoid getting out of sync.
  1747  		return false
  1748  	}
  1749  
  1750  	// There was some error writing to the underlying connection
  1751  	// during the request, so don't re-use this conn.
  1752  	if w.conn.werr != nil {
  1753  		return false
  1754  	}
  1755  
  1756  	// We haven't read the entire request body, so we can't reuse the connection.
  1757  	if !w.reqBody.consumedEntireBody() {
  1758  		return false
  1759  	}
  1760  
  1761  	return true
  1762  }
  1763  
  1764  func (w *response) Flush() {
  1765  	w.FlushError()
  1766  }
  1767  
  1768  func (w *response) FlushError() error {
  1769  	if !w.wroteHeader {
  1770  		w.WriteHeader(StatusOK)
  1771  	}
  1772  	err := w.w.Flush()
  1773  	e2 := w.cw.flush()
  1774  	if err == nil {
  1775  		err = e2
  1776  	}
  1777  	return err
  1778  }
  1779  
  1780  func (c *conn) finalFlush() {
  1781  	if c.bufr != nil {
  1782  		// Steal the bufio.Reader (~4KB worth of memory) and its associated
  1783  		// reader for a future connection.
  1784  		putBufioReader(c.bufr)
  1785  		c.bufr = nil
  1786  	}
  1787  
  1788  	if c.bufw != nil {
  1789  		c.bufw.Flush()
  1790  		// Steal the bufio.Writer (~4KB worth of memory) and its associated
  1791  		// writer for a future connection.
  1792  		putBufioWriter(c.bufw)
  1793  		c.bufw = nil
  1794  	}
  1795  }
  1796  
  1797  // Close the connection.
  1798  func (c *conn) close() {
  1799  	c.finalFlush()
  1800  	c.rwc.Close()
  1801  }
  1802  
  1803  // rstAvoidanceDelay is the amount of time we sleep after closing the
  1804  // write side of a TCP connection before closing the entire socket.
  1805  // By sleeping, we increase the chances that the client sees our FIN
  1806  // and processes its final data before they process the subsequent RST
  1807  // from closing a connection with known unread data.
  1808  // This RST seems to occur mostly on BSD systems. (And Windows?)
  1809  // This timeout is somewhat arbitrary (~latency around the planet),
  1810  // and may be modified by tests.
  1811  //
  1812  // TODO(bcmills): This should arguably be a server configuration parameter,
  1813  // not a hard-coded value.
  1814  var rstAvoidanceDelay = 500 * time.Millisecond
  1815  
  1816  type closeWriter interface {
  1817  	CloseWrite() error
  1818  }
  1819  
  1820  var _ closeWriter = (*net.TCPConn)(nil)
  1821  
  1822  // closeWriteAndWait flushes any outstanding data and sends a FIN packet (if
  1823  // client is connected via TCP), signaling that we're done. We then
  1824  // pause for a bit, hoping the client processes it before any
  1825  // subsequent RST.
  1826  //
  1827  // See https://golang.org/issue/3595
  1828  func (c *conn) closeWriteAndWait() {
  1829  	c.finalFlush()
  1830  	if tcp, ok := c.rwc.(closeWriter); ok {
  1831  		tcp.CloseWrite()
  1832  	}
  1833  
  1834  	// When we return from closeWriteAndWait, the caller will fully close the
  1835  	// connection. If client is still writing to the connection, this will cause
  1836  	// the write to fail with ECONNRESET or similar. Unfortunately, many TCP
  1837  	// implementations will also drop unread packets from the client's read buffer
  1838  	// when a write fails, causing our final response to be truncated away too.
  1839  	//
  1840  	// As a result, https://www.rfc-editor.org/rfc/rfc7230#section-6.6 recommends
  1841  	// that “[t]he server … continues to read from the connection until it
  1842  	// receives a corresponding close by the client, or until the server is
  1843  	// reasonably certain that its own TCP stack has received the client's
  1844  	// acknowledgement of the packet(s) containing the server's last response.”
  1845  	//
  1846  	// Unfortunately, we have no straightforward way to be “reasonably certain”
  1847  	// that we have received the client's ACK, and at any rate we don't want to
  1848  	// allow a misbehaving client to soak up server connections indefinitely by
  1849  	// withholding an ACK, nor do we want to go through the complexity or overhead
  1850  	// of using low-level APIs to figure out when a TCP round-trip has completed.
  1851  	//
  1852  	// Instead, we declare that we are “reasonably certain” that we received the
  1853  	// ACK if maxRSTAvoidanceDelay has elapsed.
  1854  	time.Sleep(rstAvoidanceDelay)
  1855  }
  1856  
  1857  // validNextProto reports whether the proto is a valid ALPN protocol name.
  1858  // Everything is valid except the empty string and built-in protocol types,
  1859  // so that those can't be overridden with alternate implementations.
  1860  func validNextProto(proto string) bool {
  1861  	switch proto {
  1862  	case "", "http/1.1", "http/1.0":
  1863  		return false
  1864  	}
  1865  	return true
  1866  }
  1867  
  1868  const (
  1869  	runHooks  = true
  1870  	skipHooks = false
  1871  )
  1872  
  1873  func (c *conn) setState(nc net.Conn, state ConnState, runHook bool) {
  1874  	srv := c.server
  1875  	switch state {
  1876  	case StateNew:
  1877  		srv.trackConn(c, true)
  1878  	case StateHijacked, StateClosed:
  1879  		srv.trackConn(c, false)
  1880  	}
  1881  	if state > 0xff || state < 0 {
  1882  		panic("internal error")
  1883  	}
  1884  	packedState := uint64(time.Now().Unix()<<8) | uint64(state)
  1885  	c.curState.Store(packedState)
  1886  	if !runHook {
  1887  		return
  1888  	}
  1889  	if hook := srv.ConnState; hook != nil {
  1890  		hook(nc, state)
  1891  	}
  1892  }
  1893  
  1894  func (c *conn) getState() (state ConnState, unixSec int64) {
  1895  	packedState := c.curState.Load()
  1896  	return ConnState(packedState & 0xff), int64(packedState >> 8)
  1897  }
  1898  
  1899  // badRequestError is a literal string (used by in the server in HTML,
  1900  // unescaped) to tell the user why their request was bad. It should
  1901  // be plain text without user info or other embedded errors.
  1902  func badRequestError(e string) error { return statusError{StatusBadRequest, e} }
  1903  
  1904  // statusError is an error used to respond to a request with an HTTP status.
  1905  // The text should be plain text without user info or other embedded errors.
  1906  type statusError struct {
  1907  	code int
  1908  	text string
  1909  }
  1910  
  1911  func (e statusError) Error() string { return StatusText(e.code) + ": " + e.text }
  1912  
  1913  // ErrAbortHandler is a sentinel panic value to abort a handler.
  1914  // While any panic from ServeHTTP aborts the response to the client,
  1915  // panicking with ErrAbortHandler also suppresses logging of a stack
  1916  // trace to the server's error log.
  1917  var ErrAbortHandler = internal.ErrAbortHandler
  1918  
  1919  // isCommonNetReadError reports whether err is a common error
  1920  // encountered during reading a request off the network when the
  1921  // client has gone away or had its read fail somehow. This is used to
  1922  // determine which logs are interesting enough to log about.
  1923  func isCommonNetReadError(err error) bool {
  1924  	if err == io.EOF {
  1925  		return true
  1926  	}
  1927  	if neterr, ok := err.(net.Error); ok && neterr.Timeout() {
  1928  		return true
  1929  	}
  1930  	if oe, ok := err.(*net.OpError); ok && oe.Op == "read" {
  1931  		return true
  1932  	}
  1933  	return false
  1934  }
  1935  
  1936  // Serve a new connection.
  1937  func (c *conn) serve(ctx context.Context) {
  1938  	if ra := c.rwc.RemoteAddr(); ra != nil {
  1939  		c.remoteAddr = ra.String()
  1940  	}
  1941  	ctx = context.WithValue(ctx, LocalAddrContextKey, c.rwc.LocalAddr())
  1942  	var inFlightResponse *response
  1943  	defer func() {
  1944  		if err := recover(); err != nil && err != ErrAbortHandler {
  1945  			const size = 64 << 10
  1946  			buf := make([]byte, size)
  1947  			buf = buf[:runtime.Stack(buf, false)]
  1948  			c.server.logf("http: panic serving %v: %v\n%s", c.remoteAddr, err, buf)
  1949  		}
  1950  		if inFlightResponse != nil {
  1951  			inFlightResponse.cancelCtx()
  1952  			inFlightResponse.disableWriteContinue(true)
  1953  		}
  1954  		if !c.hijacked() {
  1955  			if inFlightResponse != nil {
  1956  				inFlightResponse.conn.r.abortPendingRead()
  1957  				inFlightResponse.reqBody.Close()
  1958  			}
  1959  			c.close()
  1960  			c.setState(c.rwc, StateClosed, runHooks)
  1961  		}
  1962  	}()
  1963  
  1964  	type connectionStater interface {
  1965  		ConnectionState() tls.ConnectionState
  1966  	}
  1967  	type handshakeContexter interface {
  1968  		HandshakeContext(ctx context.Context) error
  1969  	}
  1970  	if connStater, ok := c.rwc.(connectionStater); ok {
  1971  		tlsTO := c.server.tlsHandshakeTimeout()
  1972  		if tlsTO > 0 {
  1973  			dl := time.Now().Add(tlsTO)
  1974  			c.rwc.SetReadDeadline(dl)
  1975  			c.rwc.SetWriteDeadline(dl)
  1976  		}
  1977  		var err error
  1978  		if handshaker, ok := c.rwc.(handshakeContexter); ok {
  1979  			err = handshaker.HandshakeContext(ctx)
  1980  		}
  1981  		if err != nil {
  1982  			// If the handshake failed due to the client not speaking
  1983  			// TLS, assume they're speaking plaintext HTTP and write a
  1984  			// 400 response on the TLS conn's underlying net.Conn.
  1985  			var reason string
  1986  			if re, ok := err.(tls.RecordHeaderError); ok && re.Conn != nil && tlsRecordHeaderLooksLikeHTTP(re.RecordHeader) {
  1987  				io.WriteString(re.Conn, "HTTP/1.0 400 Bad Request\r\n\r\nClient sent an HTTP request to an HTTPS server.\n")
  1988  				re.Conn.Close()
  1989  				reason = "client sent an HTTP request to an HTTPS server"
  1990  			} else {
  1991  				reason = err.Error()
  1992  			}
  1993  			c.server.logf("http: TLS handshake error from %s: %v", c.rwc.RemoteAddr(), reason)
  1994  			return
  1995  		}
  1996  		// Restore Conn-level deadlines.
  1997  		if tlsTO > 0 {
  1998  			c.rwc.SetReadDeadline(time.Time{})
  1999  			c.rwc.SetWriteDeadline(time.Time{})
  2000  		}
  2001  		c.tlsState = new(tls.ConnectionState)
  2002  		*c.tlsState = connStater.ConnectionState()
  2003  		proto := c.tlsState.NegotiatedProtocol
  2004  		if proto == "h2" && c.server.h2 != nil {
  2005  			// net/http/internal/http2 path.
  2006  			//
  2007  			// Mark freshly created HTTP/2 as active and prevent any server state hooks
  2008  			// from being run on these connections. This prevents closeIdleConns from
  2009  			// closing such connections. See issue https://golang.org/issue/39776.
  2010  			c.setState(c.rwc, StateActive, skipHooks)
  2011  			const sawClientPreface = false
  2012  			c.server.serveHTTP2Conn(ctx, c.rwc, serverHandler{c.server}, sawClientPreface, nil, nil)
  2013  			return
  2014  		}
  2015  		tlsConn, tlsConnOK := c.rwc.(*tls.Conn)
  2016  		if validNextProto(proto) && tlsConnOK {
  2017  			// Legacy TLSNextProto path.
  2018  			if fn := c.server.TLSNextProto[proto]; fn != nil {
  2019  				h := initALPNRequest{ctx, tlsConn, serverHandler{c.server}}
  2020  				// Mark freshly created HTTP/2 as active (see above).
  2021  				c.setState(c.rwc, StateActive, skipHooks)
  2022  				fn(c.server, tlsConn, h)
  2023  			}
  2024  			return
  2025  		}
  2026  	}
  2027  
  2028  	// HTTP/1.x or unencrypted HTTP/2.
  2029  
  2030  	// Set Request.TLS if the conn is not a *tls.Conn, but implements ConnectionState.
  2031  	if c.tlsState == nil {
  2032  		if tc, ok := c.rwc.(connectionStater); ok {
  2033  			c.tlsState = new(tls.ConnectionState)
  2034  			*c.tlsState = tc.ConnectionState()
  2035  		}
  2036  	}
  2037  
  2038  	ctx, cancelCtx := context.WithCancel(ctx)
  2039  	c.cancelCtx = cancelCtx
  2040  	defer cancelCtx()
  2041  
  2042  	c.r = &connReader{conn: c, rwc: c.rwc}
  2043  	c.bufr = newBufioReader(c.r)
  2044  	c.bufw = newBufioWriterSize(checkConnErrorWriter{c}, 4<<10)
  2045  
  2046  	if d := c.server.readHeaderTimeout(); d > 0 {
  2047  		c.rwc.SetReadDeadline(time.Now().Add(d))
  2048  	}
  2049  
  2050  	protos := c.server.protocols()
  2051  	if c.tlsState == nil && protos.UnencryptedHTTP2() {
  2052  		if c.maybeServeUnencryptedHTTP2(ctx) {
  2053  			return
  2054  		}
  2055  	}
  2056  	if !protos.HTTP1() {
  2057  		return
  2058  	}
  2059  
  2060  	// HTTP/1.x from here on.
  2061  
  2062  	for {
  2063  		w, err := c.readRequest(ctx)
  2064  		if c.r.remain != c.server.initialReadLimitSize() {
  2065  			// If we read any bytes off the wire, we're active.
  2066  			c.setState(c.rwc, StateActive, runHooks)
  2067  		}
  2068  		if c.server.shuttingDown() {
  2069  			return
  2070  		}
  2071  		if err != nil {
  2072  			const errorHeaders = "\r\nContent-Type: text/plain; charset=utf-8\r\nConnection: close\r\n\r\n"
  2073  
  2074  			switch {
  2075  			case err == errTooLarge:
  2076  				// Their HTTP client may or may not be
  2077  				// able to read this if we're
  2078  				// responding to them and hanging up
  2079  				// while they're still writing their
  2080  				// request. Undefined behavior.
  2081  				const publicErr = "431 Request Header Fields Too Large"
  2082  				fmt.Fprintf(c.rwc, "HTTP/1.1 "+publicErr+errorHeaders+publicErr)
  2083  				c.closeWriteAndWait()
  2084  				return
  2085  
  2086  			case isUnsupportedTEError(err):
  2087  				// Respond as per RFC 7230 Section 3.3.1 which says,
  2088  				//      A server that receives a request message with a
  2089  				//      transfer coding it does not understand SHOULD
  2090  				//      respond with 501 (Unimplemented).
  2091  				code := StatusNotImplemented
  2092  
  2093  				// We purposefully aren't echoing back the transfer-encoding's value,
  2094  				// so as to mitigate the risk of cross side scripting by an attacker.
  2095  				fmt.Fprintf(c.rwc, "HTTP/1.1 %d %s%sUnsupported transfer encoding", code, StatusText(code), errorHeaders)
  2096  				return
  2097  
  2098  			case isCommonNetReadError(err):
  2099  				return // don't reply
  2100  
  2101  			default:
  2102  				if v, ok := err.(statusError); ok {
  2103  					fmt.Fprintf(c.rwc, "HTTP/1.1 %d %s: %s%s%d %s: %s", v.code, StatusText(v.code), v.text, errorHeaders, v.code, StatusText(v.code), v.text)
  2104  					return
  2105  				}
  2106  				const publicErr = "400 Bad Request"
  2107  				fmt.Fprintf(c.rwc, "HTTP/1.1 "+publicErr+errorHeaders+publicErr)
  2108  				return
  2109  			}
  2110  		}
  2111  
  2112  		// Expect 100 Continue support
  2113  		req := w.req
  2114  		if req.expectsContinue() {
  2115  			if req.ProtoAtLeast(1, 1) && req.ContentLength != 0 {
  2116  				// Wrap the Body reader with one that replies on the connection
  2117  				w.ecReader = &expectContinueReader{readCloser: req.Body, resp: w}
  2118  				w.canWriteContinue.Store(true)
  2119  				req.Body = w.ecReader
  2120  			}
  2121  		} else if req.Header.get("Expect") != "" {
  2122  			w.sendExpectationFailed()
  2123  			return
  2124  		}
  2125  
  2126  		c.curReq.Store(w)
  2127  
  2128  		// Start background read, which detects when a client has closed its connection
  2129  		// while a request handler is still running. When the request has a body, we
  2130  		// start the background read only after the entire body has been consumed.
  2131  		if w.reqBody.bodyRemains() {
  2132  			w.reqBody.registerOnHitEOF(w.conn.r.startBackgroundRead)
  2133  		} else {
  2134  			w.conn.r.startBackgroundRead()
  2135  		}
  2136  
  2137  		// HTTP cannot have multiple simultaneous active requests.[*]
  2138  		// Until the server replies to this request, it can't read another,
  2139  		// so we might as well run the handler in this goroutine.
  2140  		// [*] Not strictly true: HTTP pipelining. We could let them all process
  2141  		// in parallel even if their responses need to be serialized.
  2142  		// But we're not going to implement HTTP pipelining because it
  2143  		// was never deployed in the wild and the answer is HTTP/2.
  2144  		inFlightResponse = w
  2145  		serverHandler{c.server}.ServeHTTP(w, w.req)
  2146  		inFlightResponse = nil
  2147  		w.cancelCtx()
  2148  		if c.hijacked() {
  2149  			c.r.releaseConn()
  2150  			return
  2151  		}
  2152  		w.finishRequest()
  2153  		c.rwc.SetWriteDeadline(time.Time{})
  2154  		if !w.shouldReuseConnection() {
  2155  			// On some platforms, closing a socket with data in the read buffer
  2156  			// sends a RST. If we do this with data sent by us in flight, the client
  2157  			// might read the RST before reading what we sent. So if we might still
  2158  			// have bytes in our read buffer, CloseWrite the connection (to send a FIN)
  2159  			// and wait a short while before closing it entirely.
  2160  			if w.requestBodyLimitHit || !w.reqBody.consumedEntireBody() {
  2161  				c.closeWriteAndWait()
  2162  			}
  2163  			return
  2164  		}
  2165  		c.setState(c.rwc, StateIdle, runHooks)
  2166  		c.curReq.Store(nil)
  2167  
  2168  		if !w.conn.server.doKeepAlives() {
  2169  			// We're in shutdown mode. We might've replied
  2170  			// to the user without "Connection: close" and
  2171  			// they might think they can send another
  2172  			// request, but such is life with HTTP/1.1.
  2173  			return
  2174  		}
  2175  
  2176  		if d := c.server.idleTimeout(); d > 0 {
  2177  			c.rwc.SetReadDeadline(time.Now().Add(d))
  2178  		} else {
  2179  			c.rwc.SetReadDeadline(time.Time{})
  2180  		}
  2181  
  2182  		// Wait for the connection to become readable again before trying to
  2183  		// read the next request. This prevents a ReadHeaderTimeout or
  2184  		// ReadTimeout from starting until the first bytes of the next request
  2185  		// have been received.
  2186  		if _, err := c.bufr.Peek(4); err != nil {
  2187  			return
  2188  		}
  2189  
  2190  		if d := c.server.readHeaderTimeout(); d > 0 {
  2191  			c.rwc.SetReadDeadline(time.Now().Add(d))
  2192  		} else {
  2193  			c.rwc.SetReadDeadline(time.Time{})
  2194  		}
  2195  	}
  2196  }
  2197  
  2198  // unencryptedHTTP2Request is an HTTP handler that initializes
  2199  // certain uninitialized fields in its *Request.
  2200  //
  2201  // It's the unencrypted version of initALPNRequest.
  2202  type unencryptedHTTP2Request struct {
  2203  	ctx context.Context
  2204  	c   net.Conn
  2205  	h   serverHandler
  2206  }
  2207  
  2208  func (h unencryptedHTTP2Request) BaseContext() context.Context { return h.ctx }
  2209  
  2210  func (h unencryptedHTTP2Request) ServeHTTP(rw ResponseWriter, req *Request) {
  2211  	if req.Body == nil {
  2212  		req.Body = NoBody
  2213  	}
  2214  	if req.RemoteAddr == "" {
  2215  		req.RemoteAddr = h.c.RemoteAddr().String()
  2216  	}
  2217  	h.h.ServeHTTP(rw, req)
  2218  }
  2219  
  2220  // unencryptedNetConnInTLSConn is used to pass an unencrypted net.Conn to
  2221  // functions that only accept a *tls.Conn.
  2222  type unencryptedNetConnInTLSConn struct {
  2223  	net.Conn // panic on all net.Conn methods
  2224  	conn     net.Conn
  2225  }
  2226  
  2227  func (c unencryptedNetConnInTLSConn) UnencryptedNetConn() net.Conn {
  2228  	return c.conn
  2229  }
  2230  
  2231  func unencryptedTLSConn(c net.Conn) *tls.Conn {
  2232  	return tls.Client(unencryptedNetConnInTLSConn{conn: c}, nil)
  2233  }
  2234  
  2235  // TLSNextProto key to use for unencrypted HTTP/2 connections.
  2236  // Not actually a TLS-negotiated protocol.
  2237  const nextProtoUnencryptedHTTP2 = "unencrypted_http2"
  2238  
  2239  func (c *conn) maybeServeUnencryptedHTTP2(ctx context.Context) bool {
  2240  	var nextFunc func(*Server, *tls.Conn, Handler)
  2241  	if c.server.h2 == nil {
  2242  		var ok bool
  2243  		nextFunc, ok = c.server.TLSNextProto[nextProtoUnencryptedHTTP2]
  2244  		if !ok {
  2245  			return false
  2246  		}
  2247  	}
  2248  	hasPreface := func(c *conn, preface []byte) bool {
  2249  		c.r.setReadLimit(int64(len(preface)) - int64(c.bufr.Buffered()))
  2250  		got, err := c.bufr.Peek(len(preface))
  2251  		c.r.setInfiniteReadLimit()
  2252  		return err == nil && bytes.Equal(got, preface)
  2253  	}
  2254  	if !hasPreface(c, []byte("PRI * HTTP/2.0")) {
  2255  		return false
  2256  	}
  2257  	if !hasPreface(c, []byte("PRI * HTTP/2.0\r\n\r\nSM\r\n\r\n")) {
  2258  		return false
  2259  	}
  2260  	c.setState(c.rwc, StateActive, skipHooks)
  2261  	if c.server.h2 != nil {
  2262  		const sawClientPreface = true
  2263  		c.server.serveHTTP2Conn(ctx, c.rwc, serverHandler{c.server}, sawClientPreface, nil, nil)
  2264  	} else {
  2265  		c.rwc.SetReadDeadline(time.Time{})
  2266  		c.rwc.SetWriteDeadline(time.Time{})
  2267  		h := unencryptedHTTP2Request{ctx, c.rwc, serverHandler{c.server}}
  2268  		nextFunc(c.server, unencryptedTLSConn(c.rwc), h)
  2269  	}
  2270  	return true
  2271  }
  2272  
  2273  func (w *response) sendExpectationFailed() {
  2274  	// TODO(bradfitz): let ServeHTTP handlers handle
  2275  	// requests with non-standard expectation[s]? Seems
  2276  	// theoretical at best, and doesn't fit into the
  2277  	// current ServeHTTP model anyway. We'd need to
  2278  	// make the ResponseWriter an optional
  2279  	// "ExpectReplier" interface or something.
  2280  	//
  2281  	// For now we'll just obey RFC 7231 5.1.1 which says
  2282  	// "A server that receives an Expect field-value other
  2283  	// than 100-continue MAY respond with a 417 (Expectation
  2284  	// Failed) status code to indicate that the unexpected
  2285  	// expectation cannot be met."
  2286  	w.Header().Set("Connection", "close")
  2287  	w.WriteHeader(StatusExpectationFailed)
  2288  	w.finishRequest()
  2289  }
  2290  
  2291  // Hijack implements the [Hijacker.Hijack] method. Our response is both a [ResponseWriter]
  2292  // and a [Hijacker].
  2293  func (w *response) Hijack() (rwc net.Conn, buf *bufio.ReadWriter, err error) {
  2294  	if w.handlerDone.Load() {
  2295  		panic("net/http: Hijack called after ServeHTTP finished")
  2296  	}
  2297  	w.disableWriteContinue(false)
  2298  	if w.wroteHeader {
  2299  		w.cw.flush()
  2300  	}
  2301  
  2302  	c := w.conn
  2303  	c.mu.Lock()
  2304  	defer c.mu.Unlock()
  2305  
  2306  	// Release the bufioWriter that writes to the chunk writer, it is not
  2307  	// used after a connection has been hijacked.
  2308  	rwc, buf, err = c.hijackLocked()
  2309  	if err == nil {
  2310  		putBufioWriter(w.w)
  2311  		w.w = nil
  2312  	}
  2313  	return rwc, buf, err
  2314  }
  2315  
  2316  func (w *response) CloseNotify() <-chan bool {
  2317  	w.lazyCloseNotifyMu.Lock()
  2318  	defer w.lazyCloseNotifyMu.Unlock()
  2319  	if w.handlerDone.Load() {
  2320  		panic("net/http: CloseNotify called after ServeHTTP finished")
  2321  	}
  2322  	if w.closeNotifyCh == nil {
  2323  		w.closeNotifyCh = make(chan bool, 1)
  2324  		if w.closeNotifyTriggered {
  2325  			w.closeNotifyCh <- true // action prior closeNotify call
  2326  		}
  2327  	}
  2328  	return w.closeNotifyCh
  2329  }
  2330  
  2331  func (w *response) closeNotify() {
  2332  	w.lazyCloseNotifyMu.Lock()
  2333  	defer w.lazyCloseNotifyMu.Unlock()
  2334  	if w.closeNotifyTriggered {
  2335  		return // already triggered
  2336  	}
  2337  	w.closeNotifyTriggered = true
  2338  	if w.closeNotifyCh != nil {
  2339  		w.closeNotifyCh <- true
  2340  	}
  2341  }
  2342  
  2343  // The HandlerFunc type is an adapter to allow the use of
  2344  // ordinary functions as HTTP handlers. If f is a function
  2345  // with the appropriate signature, HandlerFunc(f) is a
  2346  // [Handler] that calls f.
  2347  type HandlerFunc func(ResponseWriter, *Request)
  2348  
  2349  // ServeHTTP calls f(w, r).
  2350  func (f HandlerFunc) ServeHTTP(w ResponseWriter, r *Request) {
  2351  	f(w, r)
  2352  }
  2353  
  2354  // Helper handlers
  2355  
  2356  // Error replies to the request with the specified error message and HTTP code.
  2357  // It does not otherwise end the request; the caller should ensure no further
  2358  // writes are done to w.
  2359  // The error message should be plain text.
  2360  //
  2361  // Error deletes the Content-Length header,
  2362  // sets Content-Type to “text/plain; charset=utf-8”,
  2363  // and sets X-Content-Type-Options to “nosniff”.
  2364  // This configures the header properly for the error message,
  2365  // in case the caller had set it up expecting a successful output.
  2366  func Error(w ResponseWriter, error string, code int) {
  2367  	h := w.Header()
  2368  
  2369  	// Delete the Content-Length header, which might be for some other content.
  2370  	// Assuming the error string fits in the writer's buffer, we'll figure
  2371  	// out the correct Content-Length for it later.
  2372  	//
  2373  	// We don't delete Content-Encoding, because some middleware sets
  2374  	// Content-Encoding: gzip and wraps the ResponseWriter to compress on-the-fly.
  2375  	// See https://go.dev/issue/66343.
  2376  	h.Del("Content-Length")
  2377  
  2378  	// There might be content type already set, but we reset it to
  2379  	// text/plain for the error message.
  2380  	h.Set("Content-Type", "text/plain; charset=utf-8")
  2381  	h.Set("X-Content-Type-Options", "nosniff")
  2382  	w.WriteHeader(code)
  2383  	fmt.Fprintln(w, error)
  2384  }
  2385  
  2386  // NotFound replies to the request with an HTTP 404 not found error.
  2387  func NotFound(w ResponseWriter, r *Request) { Error(w, "404 page not found", StatusNotFound) }
  2388  
  2389  // NotFoundHandler returns a simple request handler
  2390  // that replies to each request with a “404 page not found” reply.
  2391  func NotFoundHandler() Handler { return HandlerFunc(NotFound) }
  2392  
  2393  // StripPrefix returns a handler that serves HTTP requests by removing the
  2394  // given prefix from the request URL's Path (and RawPath if set) and invoking
  2395  // the handler h. StripPrefix handles a request for a path that doesn't begin
  2396  // with prefix by replying with an HTTP 404 not found error. The prefix must
  2397  // match exactly: if the prefix in the request contains escaped characters
  2398  // the reply is also an HTTP 404 not found error.
  2399  func StripPrefix(prefix string, h Handler) Handler {
  2400  	if prefix == "" {
  2401  		return h
  2402  	}
  2403  	return HandlerFunc(func(w ResponseWriter, r *Request) {
  2404  		p := strings.TrimPrefix(r.URL.Path, prefix)
  2405  		rp := strings.TrimPrefix(r.URL.RawPath, prefix)
  2406  		if len(p) < len(r.URL.Path) && (r.URL.RawPath == "" || len(rp) < len(r.URL.RawPath)) {
  2407  			r2 := new(Request)
  2408  			*r2 = *r
  2409  			r2.URL = new(url.URL)
  2410  			*r2.URL = *r.URL
  2411  			r2.URL.Path = p
  2412  			r2.URL.RawPath = rp
  2413  			h.ServeHTTP(w, r2)
  2414  		} else {
  2415  			NotFound(w, r)
  2416  		}
  2417  	})
  2418  }
  2419  
  2420  // Redirect replies to the request with a redirect to url,
  2421  // which may be a path relative to the request path.
  2422  // Any non-ASCII characters in url will be percent-encoded,
  2423  // but existing percent encodings will not be changed.
  2424  //
  2425  // The provided code should be in the 3xx range and is usually
  2426  // [StatusMovedPermanently], [StatusFound] or [StatusSeeOther].
  2427  //
  2428  // If the Content-Type header has not been set, [Redirect] sets it
  2429  // to "text/html; charset=utf-8" and writes a small HTML body.
  2430  // Setting the Content-Type header to any value, including nil,
  2431  // disables that behavior.
  2432  func Redirect(w ResponseWriter, r *Request, url string, code int) {
  2433  	if u, err := urlpkg.Parse(url); err == nil {
  2434  		// If url was relative, make its path absolute by
  2435  		// combining with request path.
  2436  		// The client would probably do this for us,
  2437  		// but doing it ourselves is more reliable.
  2438  		// See RFC 7231, section 7.1.2
  2439  		if u.Scheme == "" && u.Host == "" {
  2440  			oldpath := r.URL.EscapedPath()
  2441  			if oldpath == "" { // should not happen, but avoid a crash if it does
  2442  				oldpath = "/"
  2443  			}
  2444  
  2445  			// no leading http://server
  2446  			if url == "" || url[0] != '/' {
  2447  				// make relative path absolute
  2448  				olddir, _ := path.Split(oldpath)
  2449  				url = olddir + url
  2450  			}
  2451  
  2452  			var query string
  2453  			if i := strings.Index(url, "?"); i != -1 {
  2454  				url, query = url[:i], url[i:]
  2455  			}
  2456  
  2457  			// clean up but preserve trailing slash
  2458  			trailing := strings.HasSuffix(url, "/")
  2459  			url = path.Clean(url)
  2460  			if trailing && !strings.HasSuffix(url, "/") {
  2461  				url += "/"
  2462  			}
  2463  			url += query
  2464  		}
  2465  	}
  2466  
  2467  	h := w.Header()
  2468  
  2469  	// RFC 7231 notes that a short HTML body is usually included in
  2470  	// the response because older user agents may not understand 301/307.
  2471  	// Do it only if the request didn't already have a Content-Type header.
  2472  	_, hadCT := h["Content-Type"]
  2473  
  2474  	h.Set("Location", hexEscapeNonASCII(url))
  2475  	if !hadCT && (r.Method == "GET" || r.Method == "HEAD") {
  2476  		h.Set("Content-Type", "text/html; charset=utf-8")
  2477  	}
  2478  	w.WriteHeader(code)
  2479  
  2480  	// Shouldn't send the body for POST or HEAD; that leaves GET.
  2481  	if !hadCT && r.Method == "GET" {
  2482  		body := "<a href=\"" + htmlEscape(url) + "\">" + StatusText(code) + "</a>.\n"
  2483  		fmt.Fprintln(w, body)
  2484  	}
  2485  }
  2486  
  2487  var htmlReplacer = strings.NewReplacer(
  2488  	"&", "&amp;",
  2489  	"<", "&lt;",
  2490  	">", "&gt;",
  2491  	// "&#34;" is shorter than "&quot;".
  2492  	`"`, "&#34;",
  2493  	// "&#39;" is shorter than "&apos;" and apos was not in HTML until HTML5.
  2494  	"'", "&#39;",
  2495  )
  2496  
  2497  func htmlEscape(s string) string {
  2498  	return htmlReplacer.Replace(s)
  2499  }
  2500  
  2501  // Redirect to a fixed URL
  2502  type redirectHandler struct {
  2503  	url  string
  2504  	code int
  2505  }
  2506  
  2507  func (rh *redirectHandler) ServeHTTP(w ResponseWriter, r *Request) {
  2508  	Redirect(w, r, rh.url, rh.code)
  2509  }
  2510  
  2511  // RedirectHandler returns a request handler that redirects
  2512  // each request it receives to the given url using the given
  2513  // status code.
  2514  //
  2515  // The provided code should be in the 3xx range and is usually
  2516  // [StatusMovedPermanently], [StatusFound] or [StatusSeeOther].
  2517  func RedirectHandler(url string, code int) Handler {
  2518  	return &redirectHandler{url, code}
  2519  }
  2520  
  2521  // ServeMux is an HTTP request multiplexer.
  2522  // It matches the URL of each incoming request against a list of registered
  2523  // patterns and calls the handler for the pattern that
  2524  // most closely matches the URL.
  2525  //
  2526  // # Patterns
  2527  //
  2528  // Patterns can match the method, host and path of a request.
  2529  // Some examples:
  2530  //
  2531  //   - "/index.html" matches the path "/index.html" for any host and method.
  2532  //   - "GET /static/" matches a GET request whose path begins with "/static/".
  2533  //   - "example.com/" matches any request to the host "example.com".
  2534  //   - "example.com/{$}" matches requests with host "example.com" and path "/".
  2535  //   - "/b/{bucket}/o/{objectname...}" matches paths whose first segment is "b"
  2536  //     and whose third segment is "o". The name "bucket" denotes the second
  2537  //     segment and "objectname" denotes the remainder of the path.
  2538  //
  2539  // In general, a pattern looks like
  2540  //
  2541  //	[METHOD ][HOST]/[PATH]
  2542  //
  2543  // All three parts are optional; "/" is a valid pattern.
  2544  // If METHOD is present, it must be followed by at least one space or tab.
  2545  //
  2546  // Literal (that is, non-wildcard) parts of a pattern match
  2547  // the corresponding parts of a request case-sensitively.
  2548  //
  2549  // A pattern with no method matches every method. A pattern
  2550  // with the method GET matches both GET and HEAD requests.
  2551  // Otherwise, the method must match exactly.
  2552  //
  2553  // A pattern with no host matches every host.
  2554  // A pattern with a host matches URLs on that host only.
  2555  //
  2556  // A path can include wildcard segments of the form {NAME} or {NAME...}.
  2557  // For example, "/b/{bucket}/o/{objectname...}".
  2558  // The wildcard name must be a valid Go identifier.
  2559  // Wildcards must be full path segments: they must be preceded by a slash and followed by
  2560  // either a slash or the end of the string.
  2561  // For example, "/b_{bucket}" is not a valid pattern.
  2562  //
  2563  // Normally a wildcard matches only a single path segment,
  2564  // ending at the next literal slash (not %2F) in the request URL.
  2565  // But if the "..." is present, then the wildcard matches the remainder of the URL path, including slashes.
  2566  // (Therefore it is invalid for a "..." wildcard to appear anywhere but at the end of a pattern.)
  2567  // The match for a wildcard can be obtained by calling [Request.PathValue] with the wildcard's name.
  2568  // A trailing slash in a path acts as an anonymous "..." wildcard.
  2569  //
  2570  // The special wildcard {$} matches only the end of the URL.
  2571  // For example, the pattern "/{$}" matches only the path "/",
  2572  // whereas the pattern "/" matches every path.
  2573  //
  2574  // For matching, both pattern paths and incoming request paths are unescaped segment by segment.
  2575  // So, for example, the path "/a%2Fb/100%25" is treated as having two segments, "a/b" and "100%".
  2576  // The pattern "/a%2fb/" matches it, but the pattern "/a/b/" does not.
  2577  //
  2578  // # Precedence
  2579  //
  2580  // If two or more patterns match a request, then the most specific pattern takes precedence.
  2581  // A pattern P1 is more specific than P2 if P1 matches a strict subset of P2’s requests;
  2582  // that is, if P2 matches all the requests of P1 and more.
  2583  // If neither is more specific, then the patterns conflict.
  2584  // There is one exception to this rule, for backwards compatibility:
  2585  // if two patterns would otherwise conflict and one has a host while the other does not,
  2586  // then the pattern with the host takes precedence.
  2587  // If a pattern passed to [ServeMux.Handle] or [ServeMux.HandleFunc] conflicts with
  2588  // another pattern that is already registered, those functions panic.
  2589  //
  2590  // As an example of the general rule, "/images/thumbnails/" is more specific than "/images/",
  2591  // so both can be registered.
  2592  // The former matches paths beginning with "/images/thumbnails/"
  2593  // and the latter will match any other path in the "/images/" subtree.
  2594  //
  2595  // As another example, consider the patterns "GET /" and "/index.html":
  2596  // both match a GET request for "/index.html", but the former pattern
  2597  // matches all other GET and HEAD requests, while the latter matches any
  2598  // request for "/index.html" that uses a different method.
  2599  // The patterns conflict.
  2600  //
  2601  // # Trailing-slash redirection
  2602  //
  2603  // Consider a [ServeMux] with a handler for a subtree, registered using a trailing slash or "..." wildcard.
  2604  // If the ServeMux receives a request for the subtree root without a trailing slash,
  2605  // it redirects the request by adding the trailing slash.
  2606  // This behavior can be overridden with a separate registration for the path without
  2607  // the trailing slash or "..." wildcard. For example, registering "/images/" causes ServeMux
  2608  // to redirect a request for "/images" to "/images/", unless "/images" has
  2609  // been registered separately.
  2610  //
  2611  // # Request sanitizing
  2612  //
  2613  // ServeMux also takes care of sanitizing the URL request path and the Host
  2614  // header, stripping the port number and redirecting any request containing . or
  2615  // .. segments or repeated slashes to an equivalent, cleaner URL.
  2616  // Escaped path elements such as "%2e" for "." and "%2f" for "/" are preserved
  2617  // and aren't considered separators for request routing.
  2618  //
  2619  // # Compatibility
  2620  //
  2621  // The pattern syntax and matching behavior of ServeMux changed significantly
  2622  // in Go 1.22. To restore the old behavior, set the GODEBUG environment variable
  2623  // to "httpmuxgo121=1". This setting is read once, at program startup; changes
  2624  // during execution will be ignored.
  2625  //
  2626  // The backwards-incompatible changes include:
  2627  //   - Wildcards are just ordinary literal path segments in 1.21.
  2628  //     For example, the pattern "/{x}" will match only that path in 1.21,
  2629  //     but will match any one-segment path in 1.22.
  2630  //   - In 1.21, no pattern was rejected, unless it was empty or conflicted with an existing pattern.
  2631  //     In 1.22, syntactically invalid patterns will cause [ServeMux.Handle] and [ServeMux.HandleFunc] to panic.
  2632  //     For example, in 1.21, the patterns "/{"  and "/a{x}" match themselves,
  2633  //     but in 1.22 they are invalid and will cause a panic when registered.
  2634  //   - In 1.22, each segment of a pattern is unescaped; this was not done in 1.21.
  2635  //     For example, in 1.22 the pattern "/%61" matches the path "/a" ("%61" being the URL escape sequence for "a"),
  2636  //     but in 1.21 it would match only the path "/%2561" (where "%25" is the escape for the percent sign).
  2637  //   - When matching patterns to paths, in 1.22 each segment of the path is unescaped; in 1.21, the entire path is unescaped.
  2638  //     This change mostly affects how paths with %2F escapes adjacent to slashes are treated.
  2639  //     See https://go.dev/issue/21955 for details.
  2640  type ServeMux struct {
  2641  	mu     sync.RWMutex
  2642  	tree   routingNode
  2643  	index  routingIndex
  2644  	mux121 serveMux121 // used only when GODEBUG=httpmuxgo121=1
  2645  }
  2646  
  2647  // NewServeMux allocates and returns a new [ServeMux].
  2648  func NewServeMux() *ServeMux {
  2649  	return &ServeMux{}
  2650  }
  2651  
  2652  // DefaultServeMux is the default [ServeMux] used by [Serve].
  2653  var DefaultServeMux = &defaultServeMux
  2654  
  2655  var defaultServeMux ServeMux
  2656  
  2657  // cleanPath returns the canonical path for p, eliminating . and .. elements.
  2658  func cleanPath(p string) string {
  2659  	if p == "" {
  2660  		return "/"
  2661  	}
  2662  	if p[0] != '/' {
  2663  		p = "/" + p
  2664  	}
  2665  	np := path.Clean(p)
  2666  	// path.Clean removes trailing slash except for root;
  2667  	// put the trailing slash back if necessary.
  2668  	if p[len(p)-1] == '/' && np != "/" {
  2669  		// Fast path for common case of p being the string we want:
  2670  		if len(p) == len(np)+1 && strings.HasPrefix(p, np) {
  2671  			np = p
  2672  		} else {
  2673  			np += "/"
  2674  		}
  2675  	}
  2676  	return np
  2677  }
  2678  
  2679  // stripHostPort returns h without any trailing ":<port>".
  2680  func stripHostPort(h string) string {
  2681  	// If no port on host, return unchanged
  2682  	if !strings.Contains(h, ":") {
  2683  		return h
  2684  	}
  2685  	host, _, err := net.SplitHostPort(h)
  2686  	if err != nil {
  2687  		return h // on error, return unchanged
  2688  	}
  2689  	return host
  2690  }
  2691  
  2692  // Handler returns the handler to use for the given request,
  2693  // consulting r.Method, r.Host, and r.URL.Path. It always returns
  2694  // a non-nil handler. If the path is not in its canonical form, the
  2695  // handler will be an internally-generated handler that redirects
  2696  // to the canonical path. If the host contains a port, it is ignored
  2697  // when matching handlers.
  2698  //
  2699  // The path and host are used unchanged for CONNECT requests.
  2700  //
  2701  // Handler also returns the registered pattern that matches the
  2702  // request or, in the case of internally-generated redirects,
  2703  // the path that will match after following the redirect.
  2704  //
  2705  // If there is no registered handler that applies to the request,
  2706  // Handler returns a “page not found” or “method not supported”
  2707  // handler and an empty pattern.
  2708  //
  2709  // Handler does not modify its argument. In particular, it does not
  2710  // populate named path wildcards, so r.PathValue will always return
  2711  // the empty string.
  2712  func (mux *ServeMux) Handler(r *Request) (h Handler, pattern string) {
  2713  	if use121 {
  2714  		return mux.mux121.findHandler(r)
  2715  	}
  2716  	h, p, _, _ := mux.findHandler(r)
  2717  	return h, p
  2718  }
  2719  
  2720  // findHandler finds a handler for a request.
  2721  // If there is a matching handler, it returns it and the pattern that matched.
  2722  // Otherwise it returns a Redirect or NotFound handler with the path that would match
  2723  // after the redirect.
  2724  func (mux *ServeMux) findHandler(r *Request) (h Handler, patStr string, _ *pattern, matches []string) {
  2725  	var n *routingNode
  2726  	host := r.URL.Host
  2727  	escapedPath := r.URL.EscapedPath()
  2728  	path := escapedPath
  2729  	// CONNECT requests are not canonicalized.
  2730  	if r.Method == "CONNECT" {
  2731  		// If r.URL.Path is /tree and its handler is not registered,
  2732  		// the /tree -> /tree/ redirect applies to CONNECT requests
  2733  		// but the path canonicalization does not.
  2734  		_, _, u := mux.matchOrRedirect(host, r.Method, path, r.URL)
  2735  		if u != nil {
  2736  			return RedirectHandler(u.String(), StatusTemporaryRedirect), u.Path, nil, nil
  2737  		}
  2738  		// Redo the match, this time with r.Host instead of r.URL.Host.
  2739  		// Pass a nil URL to skip the trailing-slash redirect logic.
  2740  		n, matches, _ = mux.matchOrRedirect(r.Host, r.Method, path, nil)
  2741  	} else {
  2742  		// All other requests have any port stripped and path cleaned
  2743  		// before passing to mux.handler.
  2744  		host = stripHostPort(r.Host)
  2745  		path = cleanPath(path)
  2746  
  2747  		// If the given path is /tree and its handler is not registered,
  2748  		// redirect for /tree/.
  2749  		var u *url.URL
  2750  		n, matches, u = mux.matchOrRedirect(host, r.Method, path, r.URL)
  2751  		if u != nil {
  2752  			return RedirectHandler(u.String(), StatusTemporaryRedirect), n.pattern.String(), nil, nil
  2753  		}
  2754  		if path != escapedPath {
  2755  			// Redirect to cleaned path.
  2756  			patStr := ""
  2757  			if n != nil {
  2758  				patStr = n.pattern.String()
  2759  			}
  2760  			u := urlFromEscaped(path, r.URL.RawQuery)
  2761  			return RedirectHandler(u.String(), StatusTemporaryRedirect), patStr, nil, nil
  2762  		}
  2763  	}
  2764  	if n == nil {
  2765  		// We didn't find a match with the request method. To distinguish between
  2766  		// Not Found and Method Not Allowed, see if there is another pattern that
  2767  		// matches except for the method.
  2768  		allowedMethods := mux.matchingMethods(host, path)
  2769  		if len(allowedMethods) > 0 {
  2770  			return HandlerFunc(func(w ResponseWriter, r *Request) {
  2771  				w.Header().Set("Allow", strings.Join(allowedMethods, ", "))
  2772  				Error(w, StatusText(StatusMethodNotAllowed), StatusMethodNotAllowed)
  2773  			}), "", nil, nil
  2774  		}
  2775  		return NotFoundHandler(), "", nil, nil
  2776  	}
  2777  	return n.handler, n.pattern.String(), n.pattern, matches
  2778  }
  2779  
  2780  // matchOrRedirect looks up a node in the tree that matches the host, method and path.
  2781  //
  2782  // If the url argument is non-nil, handler also deals with trailing-slash
  2783  // redirection: when a path doesn't match exactly, the match is tried again
  2784  // after appending "/" to the path. If that second match succeeds, the last
  2785  // return value is the URL to redirect to.
  2786  func (mux *ServeMux) matchOrRedirect(host, method, path string, u *url.URL) (_ *routingNode, matches []string, redirectTo *url.URL) {
  2787  	mux.mu.RLock()
  2788  	defer mux.mu.RUnlock()
  2789  
  2790  	n, matches := mux.tree.match(host, method, path)
  2791  	// We can terminate here if any of the following is true:
  2792  	// - We have an exact match already.
  2793  	// - We were asked not to try trailing slash redirection.
  2794  	// - The URL already has a trailing slash.
  2795  	// - The URL is an empty string.
  2796  	if !exactMatch(n, path) && u != nil && !strings.HasSuffix(path, "/") && path != "" {
  2797  		// If there is an exact match with a trailing slash, then redirect.
  2798  		path += "/"
  2799  		n2, _ := mux.tree.match(host, method, path)
  2800  		if exactMatch(n2, path) {
  2801  			// It is safe to return n2 here: it is used only in the second RedirectHandler case
  2802  			// of findHandler, and that method returns before it does the "n == nil" check where
  2803  			// the first return value matters. We return it here only to make the pattern available
  2804  			// to findHandler.
  2805  			return n2, nil, urlFromEscaped(path, u.RawQuery)
  2806  		}
  2807  	}
  2808  	return n, matches, nil
  2809  }
  2810  
  2811  // urlFromEscaped returns a url.URL constructed from an escaped path and a raw
  2812  // query.
  2813  //
  2814  // It ensures that the Path and RawPath fields are in sync by unescaping the
  2815  // escaped path. Populating only the Path field and leaving RawPath empty (or
  2816  // failing to keep them in sync) can cause url.URL.String to produce a URL with
  2817  // either unexpected escaping (e.g., double-escaping "%" into "%25" in an
  2818  // already escaped path) or a lack thereof (e.g., losing the escaping of "%2f"
  2819  // and turning it into a literal path separator "/").
  2820  func urlFromEscaped(escaped, rawQuery string) *url.URL {
  2821  	unescaped, err := url.PathUnescape(escaped)
  2822  	// Should be impossible, since ServeMux will reject unparsable URLs way
  2823  	// earlier.
  2824  	if err != nil {
  2825  		unescaped = escaped
  2826  	}
  2827  	return &url.URL{
  2828  		Path:     unescaped,
  2829  		RawPath:  escaped,
  2830  		RawQuery: rawQuery,
  2831  	}
  2832  }
  2833  
  2834  // exactMatch reports whether the node's pattern exactly matches the path.
  2835  // As a special case, if the node is nil, exactMatch return false.
  2836  //
  2837  // Before wildcards were introduced, it was clear that an exact match meant
  2838  // that the pattern and path were the same string. The only other possibility
  2839  // was that a trailing-slash pattern, like "/", matched a path longer than
  2840  // it, like "/a".
  2841  //
  2842  // With wildcards, we define an inexact match as any one where a multi wildcard
  2843  // matches a non-empty string. All other matches are exact.
  2844  // For example, these are all exact matches:
  2845  //
  2846  //	pattern   path
  2847  //	/a        /a
  2848  //	/{x}      /a
  2849  //	/a/{$}    /a/
  2850  //	/a/       /a/
  2851  //
  2852  // The last case has a multi wildcard (implicitly), but the match is exact because
  2853  // the wildcard matches the empty string.
  2854  //
  2855  // Examples of matches that are not exact:
  2856  //
  2857  //	pattern   path
  2858  //	/         /a
  2859  //	/a/{x...} /a/b
  2860  func exactMatch(n *routingNode, path string) bool {
  2861  	if n == nil {
  2862  		return false
  2863  	}
  2864  	// We can't directly implement the definition (empty match for multi
  2865  	// wildcard) because we don't record a match for anonymous multis.
  2866  
  2867  	// If there is no multi, the match is exact.
  2868  	if !n.pattern.lastSegment().multi {
  2869  		return true
  2870  	}
  2871  
  2872  	// If the path doesn't end in a trailing slash, then the multi match
  2873  	// is non-empty.
  2874  	if len(path) > 0 && path[len(path)-1] != '/' {
  2875  		return false
  2876  	}
  2877  	// Only patterns ending in {$} or a multi wildcard can
  2878  	// match a path with a trailing slash.
  2879  	// For the match to be exact, the number of pattern
  2880  	// segments should be the same as the number of slashes in the path.
  2881  	// E.g. "/a/b/{$}" and "/a/b/{...}" exactly match "/a/b/", but "/a/" does not.
  2882  	return len(n.pattern.segments) == strings.Count(path, "/")
  2883  }
  2884  
  2885  // matchingMethods return a sorted list of all methods that would match with the given host and path.
  2886  func (mux *ServeMux) matchingMethods(host, path string) []string {
  2887  	// Hold the read lock for the entire method so that the two matches are done
  2888  	// on the same set of registered patterns.
  2889  	mux.mu.RLock()
  2890  	defer mux.mu.RUnlock()
  2891  	ms := map[string]bool{}
  2892  	mux.tree.matchingMethods(host, path, ms)
  2893  	// matchOrRedirect will try appending a trailing slash if there is no match.
  2894  	if !strings.HasSuffix(path, "/") {
  2895  		mux.tree.matchingMethods(host, path+"/", ms)
  2896  	}
  2897  	return slices.Sorted(maps.Keys(ms))
  2898  }
  2899  
  2900  // ServeHTTP dispatches the request to the handler whose
  2901  // pattern most closely matches the request URL.
  2902  func (mux *ServeMux) ServeHTTP(w ResponseWriter, r *Request) {
  2903  	if r.RequestURI == "*" {
  2904  		if r.ProtoAtLeast(1, 1) {
  2905  			w.Header().Set("Connection", "close")
  2906  		}
  2907  		w.WriteHeader(StatusBadRequest)
  2908  		return
  2909  	}
  2910  	var h Handler
  2911  	if use121 {
  2912  		h, _ = mux.mux121.findHandler(r)
  2913  	} else {
  2914  		h, r.Pattern, r.pat, r.matches = mux.findHandler(r)
  2915  	}
  2916  	h.ServeHTTP(w, r)
  2917  }
  2918  
  2919  // The four functions below all call ServeMux.register so that callerLocation
  2920  // always refers to user code.
  2921  
  2922  // Handle registers the handler for the given pattern.
  2923  // If the given pattern conflicts with one that is already registered
  2924  // or if the pattern is invalid, Handle panics.
  2925  //
  2926  // See [ServeMux] for details on valid patterns and conflict rules.
  2927  func (mux *ServeMux) Handle(pattern string, handler Handler) {
  2928  	if use121 {
  2929  		mux.mux121.handle(pattern, handler)
  2930  	} else {
  2931  		mux.register(pattern, handler)
  2932  	}
  2933  }
  2934  
  2935  // HandleFunc registers the handler function for the given pattern.
  2936  // If the given pattern conflicts with one that is already registered
  2937  // or if the pattern is invalid, HandleFunc panics.
  2938  //
  2939  // See [ServeMux] for details on valid patterns and conflict rules.
  2940  func (mux *ServeMux) HandleFunc(pattern string, handler func(ResponseWriter, *Request)) {
  2941  	if use121 {
  2942  		mux.mux121.handleFunc(pattern, handler)
  2943  	} else {
  2944  		mux.register(pattern, HandlerFunc(handler))
  2945  	}
  2946  }
  2947  
  2948  // Handle registers the handler for the given pattern in [DefaultServeMux].
  2949  // The documentation for [ServeMux] explains how patterns are matched.
  2950  func Handle(pattern string, handler Handler) {
  2951  	if use121 {
  2952  		DefaultServeMux.mux121.handle(pattern, handler)
  2953  	} else {
  2954  		DefaultServeMux.register(pattern, handler)
  2955  	}
  2956  }
  2957  
  2958  // HandleFunc registers the handler function for the given pattern in [DefaultServeMux].
  2959  // The documentation for [ServeMux] explains how patterns are matched.
  2960  func HandleFunc(pattern string, handler func(ResponseWriter, *Request)) {
  2961  	if use121 {
  2962  		DefaultServeMux.mux121.handleFunc(pattern, handler)
  2963  	} else {
  2964  		DefaultServeMux.register(pattern, HandlerFunc(handler))
  2965  	}
  2966  }
  2967  
  2968  func (mux *ServeMux) register(pattern string, handler Handler) {
  2969  	if err := mux.registerErr(pattern, handler); err != nil {
  2970  		panic(err)
  2971  	}
  2972  }
  2973  
  2974  func (mux *ServeMux) registerErr(patstr string, handler Handler) error {
  2975  	if patstr == "" {
  2976  		return errors.New("http: invalid pattern")
  2977  	}
  2978  	if handler == nil {
  2979  		return errors.New("http: nil handler")
  2980  	}
  2981  	if f, ok := handler.(HandlerFunc); ok && f == nil {
  2982  		return errors.New("http: nil handler")
  2983  	}
  2984  
  2985  	pat, err := parsePattern(patstr)
  2986  	if err != nil {
  2987  		return fmt.Errorf("parsing %q: %w", patstr, err)
  2988  	}
  2989  
  2990  	// Get the caller's location, for better conflict error messages.
  2991  	// Skip register and whatever calls it.
  2992  	_, file, line, ok := runtime.Caller(3)
  2993  	if !ok {
  2994  		pat.loc = "unknown location"
  2995  	} else {
  2996  		pat.loc = fmt.Sprintf("%s:%d", file, line)
  2997  	}
  2998  
  2999  	mux.mu.Lock()
  3000  	defer mux.mu.Unlock()
  3001  	// Check for conflict.
  3002  	if err := mux.index.possiblyConflictingPatterns(pat, func(pat2 *pattern) error {
  3003  		if pat.conflictsWith(pat2) {
  3004  			d := describeConflict(pat, pat2)
  3005  			return fmt.Errorf("pattern %q (registered at %s) conflicts with pattern %q (registered at %s):\n%s",
  3006  				pat, pat.loc, pat2, pat2.loc, d)
  3007  		}
  3008  		return nil
  3009  	}); err != nil {
  3010  		return err
  3011  	}
  3012  	mux.tree.addPattern(pat, handler)
  3013  	mux.index.addPattern(pat)
  3014  	return nil
  3015  }
  3016  
  3017  // Serve accepts incoming HTTP connections on the listener l,
  3018  // creating a new service goroutine for each. The service goroutines
  3019  // read requests and then call handler to reply to them.
  3020  //
  3021  // The handler is typically nil, in which case [DefaultServeMux] is used.
  3022  //
  3023  // HTTP/2 support is only enabled if the Listener returns [*tls.Conn]
  3024  // connections or connections which implement the same ConnectionState
  3025  // method as *tls.Conn, and the connection state indicates that the "h2"
  3026  // protocol was negotiated by ALPN.
  3027  //
  3028  // Serve always returns a non-nil error.
  3029  func Serve(l net.Listener, handler Handler) error {
  3030  	srv := &Server{Handler: handler}
  3031  	return srv.Serve(l)
  3032  }
  3033  
  3034  // ServeTLS accepts incoming HTTPS connections on the listener l,
  3035  // creating a new service goroutine for each. The service goroutines
  3036  // read requests and then call handler to reply to them.
  3037  //
  3038  // The handler is typically nil, in which case [DefaultServeMux] is used.
  3039  //
  3040  // Additionally, files containing a certificate and matching private key
  3041  // for the server must be provided. If the certificate is signed by a
  3042  // certificate authority, the certFile should be the concatenation
  3043  // of the server's certificate, any intermediates, and the CA's certificate.
  3044  //
  3045  // ServeTLS always returns a non-nil error.
  3046  func ServeTLS(l net.Listener, handler Handler, certFile, keyFile string) error {
  3047  	srv := &Server{Handler: handler}
  3048  	return srv.ServeTLS(l, certFile, keyFile)
  3049  }
  3050  
  3051  // A Server defines parameters for running an HTTP server.
  3052  // The zero value for Server is a valid configuration.
  3053  type Server struct {
  3054  	// Addr optionally specifies the TCP address for the server to listen on,
  3055  	// in the form "host:port". If empty, ":http" (port 80) is used.
  3056  	// The service names are defined in RFC 6335 and assigned by IANA.
  3057  	// See net.Dial for details of the address format.
  3058  	Addr string
  3059  
  3060  	Handler Handler // handler to invoke, http.DefaultServeMux if nil
  3061  
  3062  	// DisableGeneralOptionsHandler, if true, passes "OPTIONS *" requests to the Handler,
  3063  	// otherwise responds with 200 OK and Content-Length: 0.
  3064  	DisableGeneralOptionsHandler bool
  3065  
  3066  	// TLSConfig optionally provides a TLS configuration for use
  3067  	// by ServeTLS and ListenAndServeTLS. Note that this value is
  3068  	// cloned by ServeTLS and ListenAndServeTLS, so it's not
  3069  	// possible to modify the configuration with methods like
  3070  	// tls.Config.SetSessionTicketKeys. To use
  3071  	// SetSessionTicketKeys, use Server.Serve with a TLS Listener
  3072  	// instead.
  3073  	TLSConfig *tls.Config
  3074  
  3075  	// ReadTimeout is the maximum duration for reading the entire
  3076  	// request, including the body. A zero or negative value means
  3077  	// there will be no timeout.
  3078  	//
  3079  	// Because ReadTimeout does not let Handlers make per-request
  3080  	// decisions on each request body's acceptable deadline or
  3081  	// upload rate, most users will prefer to use
  3082  	// ReadHeaderTimeout. It is valid to use them both.
  3083  	ReadTimeout time.Duration
  3084  
  3085  	// ReadHeaderTimeout is the amount of time allowed to read
  3086  	// request headers. The connection's read deadline is reset
  3087  	// after reading the headers and the Handler can decide what
  3088  	// is considered too slow for the body. If zero, the value of
  3089  	// ReadTimeout is used. If negative, or if zero and ReadTimeout
  3090  	// is zero or negative, there is no timeout.
  3091  	ReadHeaderTimeout time.Duration
  3092  
  3093  	// WriteTimeout is the maximum duration before timing out
  3094  	// writes of the response. It is reset whenever a new
  3095  	// request's header is read. Like ReadTimeout, it does not
  3096  	// let Handlers make decisions on a per-request basis.
  3097  	// A zero or negative value means there will be no timeout.
  3098  	WriteTimeout time.Duration
  3099  
  3100  	// IdleTimeout is the maximum amount of time to wait for the
  3101  	// next request when keep-alives are enabled. If zero, the value
  3102  	// of ReadTimeout is used. If negative, or if zero and ReadTimeout
  3103  	// is zero or negative, there is no timeout.
  3104  	IdleTimeout time.Duration
  3105  
  3106  	// MaxHeaderBytes controls the maximum number of bytes the
  3107  	// server will read parsing the request header's keys and
  3108  	// values, including the request line. It does not limit the
  3109  	// size of the request body.
  3110  	// If zero, DefaultMaxHeaderBytes is used.
  3111  	MaxHeaderBytes int
  3112  
  3113  	// MaxHeaderValueCount controls the maximum number of header
  3114  	// values that the server is willing to parse from a request.
  3115  	// If zero, DefaultMaxHeaderValueCount is used.
  3116  	// Note that comma-separated values in a single header line are
  3117  	// counted once, while values sent as multiple header lines are
  3118  	// counted multiple times.
  3119  	MaxHeaderValueCount int
  3120  
  3121  	// TLSNextProto optionally specifies a function to take over
  3122  	// ownership of the provided TLS connection when an ALPN
  3123  	// protocol upgrade has occurred. The map key is the protocol
  3124  	// name negotiated. The Handler argument should be used to
  3125  	// handle HTTP requests and will initialize the Request's TLS
  3126  	// and RemoteAddr if not already set. The connection is
  3127  	// automatically closed when the function returns.
  3128  	// If TLSNextProto is not nil, HTTP/2 support is not enabled
  3129  	// automatically.
  3130  	//
  3131  	// Historically, TLSNextProto was used to disable HTTP/2 support.
  3132  	// The Server.Protocols field now provides a simpler way to do this.
  3133  	TLSNextProto map[string]func(*Server, *tls.Conn, Handler)
  3134  
  3135  	// ConnState specifies an optional callback function that is
  3136  	// called when a client connection changes state. See the
  3137  	// ConnState type and associated constants for details.
  3138  	ConnState func(net.Conn, ConnState)
  3139  
  3140  	// ErrorLog specifies an optional logger for errors accepting
  3141  	// connections, unexpected behavior from handlers, and
  3142  	// underlying FileSystem errors.
  3143  	// If nil, logging is done via the log package's standard logger.
  3144  	ErrorLog *log.Logger
  3145  
  3146  	// BaseContext optionally specifies a function that returns
  3147  	// the base context for incoming requests on this server.
  3148  	// The provided Listener is the specific Listener that's
  3149  	// about to start accepting requests.
  3150  	// If BaseContext is nil, the default is context.Background().
  3151  	// If non-nil, it must return a non-nil context.
  3152  	BaseContext func(net.Listener) context.Context
  3153  
  3154  	// ConnContext optionally specifies a function that modifies
  3155  	// the context used for a new connection c. The provided ctx
  3156  	// is derived from the base context and has a ServerContextKey
  3157  	// value.
  3158  	ConnContext func(ctx context.Context, c net.Conn) context.Context
  3159  
  3160  	// HTTP2 configures HTTP/2 connections.
  3161  	HTTP2 *HTTP2Config
  3162  
  3163  	// Protocols is the set of protocols accepted by the server.
  3164  	//
  3165  	// If Protocols includes UnencryptedHTTP2, the server will accept
  3166  	// unencrypted HTTP/2 connections. The server can serve both
  3167  	// HTTP/1 and unencrypted HTTP/2 on the same address and port.
  3168  	//
  3169  	// If Protocols is nil, the default is usually HTTP/1 and HTTP/2.
  3170  	// If TLSNextProto is non-nil and does not contain an "h2" entry,
  3171  	// the default is HTTP/1 only.
  3172  	Protocols *Protocols
  3173  
  3174  	// DisableClientPriority specifies whether client-specified priority, as
  3175  	// specified in RFC 9218, should be respected or not.
  3176  	//
  3177  	// This field only takes effect if using HTTP/2, and if no custom write
  3178  	// scheduler is defined for the HTTP/2 server. Otherwise, this field is a
  3179  	// no-op.
  3180  	//
  3181  	// If set to true, requests will be served in a round-robin manner, without
  3182  	// prioritization.
  3183  	DisableClientPriority bool
  3184  
  3185  	inShutdown atomic.Bool // true when server is in shutdown
  3186  
  3187  	disableKeepAlives atomic.Bool
  3188  	nextProtoOnce     sync.Once // guards setupHTTP2_* init
  3189  	nextProtoErr      error     // result of http2.ConfigureServer if used
  3190  
  3191  	mu            sync.Mutex
  3192  	listeners     map[*net.Listener]struct{}
  3193  	activeConn    map[*conn]struct{}
  3194  	onShutdown    []func()
  3195  	h2            *http2Server
  3196  	h2Config      http2ExternalServerConfig
  3197  	h2IdleTimeout time.Duration
  3198  	h3Server      http3Server
  3199  
  3200  	listenerGroup sync.WaitGroup
  3201  }
  3202  
  3203  // Close immediately closes all active net.Listeners and any
  3204  // connections in state [StateNew], [StateActive], or [StateIdle]. For a
  3205  // graceful shutdown, use [Server.Shutdown].
  3206  //
  3207  // Close does not attempt to close (and does not even know about)
  3208  // any hijacked connections, such as WebSockets.
  3209  //
  3210  // Close returns any error returned from closing the [Server]'s
  3211  // underlying Listener(s).
  3212  func (s *Server) Close() error {
  3213  	s.inShutdown.Store(true)
  3214  	s.mu.Lock()
  3215  	defer s.mu.Unlock()
  3216  	err := s.closeListenersLocked()
  3217  	if s.h3Server != nil {
  3218  		ctx, cancel := context.WithCancel(context.Background())
  3219  		cancel()
  3220  		go s.h3Server.Shutdown(ctx)
  3221  	}
  3222  
  3223  	// Unlock s.mu while waiting for listenerGroup.
  3224  	// The group Add and Done calls are made with s.mu held,
  3225  	// to avoid adding a new listener in the window between
  3226  	// us setting inShutdown above and waiting here.
  3227  	s.mu.Unlock()
  3228  	s.listenerGroup.Wait()
  3229  	s.mu.Lock()
  3230  
  3231  	for c := range s.activeConn {
  3232  		c.rwc.Close()
  3233  		delete(s.activeConn, c)
  3234  	}
  3235  	return err
  3236  }
  3237  
  3238  // shutdownPollIntervalMax is the max polling interval when checking
  3239  // quiescence during Server.Shutdown. Polling starts with a small
  3240  // interval and backs off to the max.
  3241  // Ideally we could find a solution that doesn't involve polling,
  3242  // but which also doesn't have a high runtime cost (and doesn't
  3243  // involve any contentious mutexes), but that is left as an
  3244  // exercise for the reader.
  3245  const shutdownPollIntervalMax = 500 * time.Millisecond
  3246  
  3247  // Shutdown gracefully shuts down the server without interrupting any
  3248  // active connections. Shutdown works by first closing all open
  3249  // listeners, then closing all idle connections, and then waiting
  3250  // indefinitely for connections to return to idle and then shut down.
  3251  // If the provided context expires before the shutdown is complete,
  3252  // Shutdown returns the context's error, otherwise it returns any
  3253  // error returned from closing the [Server]'s underlying Listener(s).
  3254  //
  3255  // When Shutdown is called, [Serve], [ServeTLS], [ListenAndServe], and
  3256  // [ListenAndServeTLS] immediately return [ErrServerClosed]. Make sure the
  3257  // program doesn't exit and waits instead for Shutdown to return.
  3258  //
  3259  // Shutdown does not attempt to close nor wait for hijacked
  3260  // connections such as WebSockets. The caller of Shutdown should
  3261  // separately notify such long-lived connections of shutdown and wait
  3262  // for them to close, if desired. See [Server.RegisterOnShutdown] for a way to
  3263  // register shutdown notification functions.
  3264  //
  3265  // Once Shutdown has been called on a server, it may not be reused;
  3266  // future calls to methods such as Serve will return ErrServerClosed.
  3267  func (s *Server) Shutdown(ctx context.Context) error {
  3268  	s.inShutdown.Store(true)
  3269  
  3270  	s.mu.Lock()
  3271  	lnerr := s.closeListenersLocked()
  3272  	for _, f := range s.onShutdown {
  3273  		go f()
  3274  	}
  3275  	if s.h3Server != nil {
  3276  		go s.h3Server.Shutdown(ctx)
  3277  	}
  3278  	s.mu.Unlock()
  3279  	s.listenerGroup.Wait()
  3280  
  3281  	pollIntervalBase := time.Millisecond
  3282  	nextPollInterval := func() time.Duration {
  3283  		// Add 10% jitter.
  3284  		interval := pollIntervalBase + time.Duration(rand.IntN(int(pollIntervalBase/10)))
  3285  		// Double and clamp for next time.
  3286  		pollIntervalBase *= 2
  3287  		if pollIntervalBase > shutdownPollIntervalMax {
  3288  			pollIntervalBase = shutdownPollIntervalMax
  3289  		}
  3290  		return interval
  3291  	}
  3292  
  3293  	timer := time.NewTimer(nextPollInterval())
  3294  	defer timer.Stop()
  3295  	for {
  3296  		if s.closeIdleConns() {
  3297  			return lnerr
  3298  		}
  3299  		select {
  3300  		case <-ctx.Done():
  3301  			return ctx.Err()
  3302  		case <-timer.C:
  3303  			timer.Reset(nextPollInterval())
  3304  		}
  3305  	}
  3306  }
  3307  
  3308  // RegisterOnShutdown registers a function to call on [Server.Shutdown].
  3309  // This can be used to gracefully shutdown connections that have
  3310  // undergone ALPN protocol upgrade or that have been hijacked.
  3311  // This function should start protocol-specific graceful shutdown,
  3312  // but should not wait for shutdown to complete.
  3313  func (s *Server) RegisterOnShutdown(f func()) {
  3314  	s.mu.Lock()
  3315  	s.onShutdown = append(s.onShutdown, f)
  3316  	s.mu.Unlock()
  3317  }
  3318  
  3319  // closeIdleConns closes all idle connections and reports whether the
  3320  // server is quiescent.
  3321  func (s *Server) closeIdleConns() bool {
  3322  	s.mu.Lock()
  3323  	defer s.mu.Unlock()
  3324  	quiescent := true
  3325  	for c := range s.activeConn {
  3326  		st, unixSec := c.getState()
  3327  		// Issue 22682: treat StateNew connections as if
  3328  		// they're idle if we haven't read the first request's
  3329  		// header in over 5 seconds.
  3330  		if st == StateNew && unixSec < time.Now().Unix()-5 {
  3331  			st = StateIdle
  3332  		}
  3333  		if st != StateIdle || unixSec == 0 {
  3334  			// Assume unixSec == 0 means it's a very new
  3335  			// connection, without state set yet.
  3336  			quiescent = false
  3337  			continue
  3338  		}
  3339  		c.rwc.Close()
  3340  		delete(s.activeConn, c)
  3341  	}
  3342  	return quiescent
  3343  }
  3344  
  3345  func (s *Server) closeListenersLocked() error {
  3346  	var err error
  3347  	for ln := range s.listeners {
  3348  		if cerr := (*ln).Close(); cerr != nil && err == nil {
  3349  			err = cerr
  3350  		}
  3351  	}
  3352  	return err
  3353  }
  3354  
  3355  // A ConnState represents the state of a client connection to a server.
  3356  // It's used by the optional [Server.ConnState] hook.
  3357  type ConnState int
  3358  
  3359  const (
  3360  	// StateNew represents a new connection that is expected to
  3361  	// send a request immediately. Connections begin at this
  3362  	// state and then transition to either StateActive or
  3363  	// StateClosed.
  3364  	StateNew ConnState = iota
  3365  
  3366  	// StateActive represents a connection that has read 1 or more
  3367  	// bytes of a request. The Server.ConnState hook for
  3368  	// StateActive fires before the request has entered a handler
  3369  	// and doesn't fire again until the request has been
  3370  	// handled. After the request is handled, the state
  3371  	// transitions to StateClosed, StateHijacked, or StateIdle.
  3372  	// For HTTP/2, StateActive fires on the transition from zero
  3373  	// to one active request, and only transitions away once all
  3374  	// active requests are complete. That means that ConnState
  3375  	// cannot be used to do per-request work; ConnState only notes
  3376  	// the overall state of the connection.
  3377  	StateActive
  3378  
  3379  	// StateIdle represents a connection that has finished
  3380  	// handling a request and is in the keep-alive state, waiting
  3381  	// for a new request. Connections transition from StateIdle
  3382  	// to either StateActive or StateClosed.
  3383  	StateIdle
  3384  
  3385  	// StateHijacked represents a hijacked connection.
  3386  	// This is a terminal state. It does not transition to StateClosed.
  3387  	StateHijacked
  3388  
  3389  	// StateClosed represents a closed connection.
  3390  	// This is a terminal state. Hijacked connections do not
  3391  	// transition to StateClosed.
  3392  	StateClosed
  3393  )
  3394  
  3395  var stateName = map[ConnState]string{
  3396  	StateNew:      "new",
  3397  	StateActive:   "active",
  3398  	StateIdle:     "idle",
  3399  	StateHijacked: "hijacked",
  3400  	StateClosed:   "closed",
  3401  }
  3402  
  3403  func (c ConnState) String() string {
  3404  	return stateName[c]
  3405  }
  3406  
  3407  // serverHandler delegates to either the server's Handler or
  3408  // DefaultServeMux and also handles "OPTIONS *" requests.
  3409  type serverHandler struct {
  3410  	srv *Server
  3411  }
  3412  
  3413  // ServeHTTP should be an internal detail,
  3414  // but widely used packages access it using linkname.
  3415  // Notable members of the hall of shame include:
  3416  //   - github.com/erda-project/erda-infra
  3417  //
  3418  // Do not remove or change the type signature.
  3419  // See go.dev/issue/67401.
  3420  //
  3421  //go:linkname badServeHTTP net/http.serverHandler.ServeHTTP
  3422  func (sh serverHandler) ServeHTTP(rw ResponseWriter, req *Request) {
  3423  	handler := sh.srv.Handler
  3424  	if handler == nil {
  3425  		handler = DefaultServeMux
  3426  	}
  3427  	if !sh.srv.DisableGeneralOptionsHandler && req.RequestURI == "*" && req.Method == "OPTIONS" {
  3428  		handler = globalOptionsHandler{}
  3429  	}
  3430  
  3431  	defer func() {
  3432  		if req.MultipartForm != nil {
  3433  			req.MultipartForm.RemoveAll()
  3434  		}
  3435  	}()
  3436  	handler.ServeHTTP(rw, req)
  3437  }
  3438  
  3439  func badServeHTTP(serverHandler, ResponseWriter, *Request)
  3440  
  3441  // AllowQuerySemicolons returns a handler that serves requests by converting any
  3442  // unescaped semicolons in the URL query to ampersands, and invoking the handler h.
  3443  //
  3444  // This restores the pre-Go 1.17 behavior of splitting query parameters on both
  3445  // semicolons and ampersands. (See golang.org/issue/25192). Note that this
  3446  // behavior doesn't match that of many proxies, and the mismatch can lead to
  3447  // security issues.
  3448  //
  3449  // AllowQuerySemicolons should be invoked before [Request.ParseForm] is called.
  3450  func AllowQuerySemicolons(h Handler) Handler {
  3451  	return HandlerFunc(func(w ResponseWriter, r *Request) {
  3452  		if strings.Contains(r.URL.RawQuery, ";") {
  3453  			r2 := new(Request)
  3454  			*r2 = *r
  3455  			r2.URL = new(url.URL)
  3456  			*r2.URL = *r.URL
  3457  			r2.URL.RawQuery = strings.ReplaceAll(r.URL.RawQuery, ";", "&")
  3458  			h.ServeHTTP(w, r2)
  3459  		} else {
  3460  			h.ServeHTTP(w, r)
  3461  		}
  3462  	})
  3463  }
  3464  
  3465  // ListenAndServe listens on the TCP network address s.Addr and then
  3466  // calls [Serve] to handle requests on incoming connections.
  3467  // Accepted connections are configured to enable TCP keep-alives.
  3468  //
  3469  // If s.Addr is blank, ":http" is used.
  3470  //
  3471  // ListenAndServe always returns a non-nil error. After [Server.Shutdown] or [Server.Close],
  3472  // the returned error is [ErrServerClosed].
  3473  func (s *Server) ListenAndServe() error {
  3474  	if s.shuttingDown() {
  3475  		return ErrServerClosed
  3476  	}
  3477  	addr := s.Addr
  3478  	if addr == "" {
  3479  		addr = ":http"
  3480  	}
  3481  	ln, err := net.Listen("tcp", addr)
  3482  	if err != nil {
  3483  		return err
  3484  	}
  3485  	return s.Serve(ln)
  3486  }
  3487  
  3488  var testHookServerServe func(*Server, net.Listener) // used if non-nil
  3489  
  3490  // shouldConfigureHTTP2ForServe reports whether Server.Serve should configure
  3491  // automatic HTTP/2. (which sets up the s.TLSNextProto map)
  3492  func (s *Server) shouldConfigureHTTP2ForServe() bool {
  3493  	if s.TLSConfig == nil {
  3494  		// Compatibility with Go 1.6:
  3495  		// If there's no TLSConfig, it's possible that the user just
  3496  		// didn't set it on the http.Server, but did pass it to
  3497  		// tls.NewListener and passed that listener to Serve.
  3498  		// So we should configure HTTP/2 (to set up s.TLSNextProto)
  3499  		// in case the listener returns an "h2" *tls.Conn.
  3500  		return true
  3501  	}
  3502  	if s.protocols().UnencryptedHTTP2() {
  3503  		return true
  3504  	}
  3505  	// The user specified a TLSConfig on their http.Server.
  3506  	// In this, case, only configure HTTP/2 if their tls.Config
  3507  	// explicitly mentions "h2". Otherwise http2.ConfigureServer
  3508  	// would modify the tls.Config to add it, but they probably already
  3509  	// passed this tls.Config to tls.NewListener. And if they did,
  3510  	// it's too late anyway to fix it. It would only be potentially racy.
  3511  	// See Issue 15908.
  3512  	return slices.Contains(s.TLSConfig.NextProtos, "h2")
  3513  }
  3514  
  3515  // ErrServerClosed is returned by the [Server.Serve], [ServeTLS], [ListenAndServe],
  3516  // and [ListenAndServeTLS] methods after a call to [Server.Shutdown] or [Server.Close].
  3517  var ErrServerClosed = errors.New("http: Server closed")
  3518  
  3519  // Serve accepts incoming connections on the Listener l, creating a
  3520  // new service goroutine for each. The service goroutines read requests and
  3521  // then call s.Handler to reply to them.
  3522  //
  3523  // HTTP/2 support is only enabled if the Listener returns [*tls.Conn]
  3524  // connections and they were configured with "h2" in the TLS
  3525  // Config.NextProtos.
  3526  //
  3527  // Serve always returns a non-nil error and closes l.
  3528  // After [Server.Shutdown] or [Server.Close], the returned error is [ErrServerClosed].
  3529  func (s *Server) Serve(l net.Listener) error {
  3530  	// This is the sneaky path we use to let x/net/http2 wrap an http.Server
  3531  	// and x/net/http3 install an HTTP/3 implementation:
  3532  	// http2.ConfigureServer calls http.Server.Serve with a net.Listener that
  3533  	// implements a certain interface, which we recognize here as an attempt
  3534  	// to associate an http2.Server with us.
  3535  	//
  3536  	// (This is about as principled as the way we (ab)use Transport.RegisterProtocol,
  3537  	// which is to say not at all. It's worth it.)
  3538  	//
  3539  	// Server.Serve never returns a nil error under normal circumstances.
  3540  	// Returning nil on success informs our caller that we support this
  3541  	// sneaky registration mechanism.
  3542  	switch conf := l.(type) {
  3543  	case http2ExternalServerConfig:
  3544  		s.setHTTP2Config(conf)
  3545  		return nil
  3546  	case http3Server:
  3547  		s.setHTTP3Server(conf)
  3548  		return nil
  3549  	}
  3550  
  3551  	if fn := testHookServerServe; fn != nil {
  3552  		fn(s, l) // call hook with unwrapped listener
  3553  	}
  3554  
  3555  	origListener := l
  3556  	l = &onceCloseListener{Listener: l}
  3557  	defer l.Close()
  3558  
  3559  	if err := s.setupHTTP2_Serve(); err != nil {
  3560  		return err
  3561  	}
  3562  
  3563  	if !s.trackListener(&l, true) {
  3564  		return ErrServerClosed
  3565  	}
  3566  	defer s.trackListener(&l, false)
  3567  
  3568  	baseCtx := context.Background()
  3569  	if s.BaseContext != nil {
  3570  		baseCtx = s.BaseContext(origListener)
  3571  		if baseCtx == nil {
  3572  			panic("BaseContext returned a nil context")
  3573  		}
  3574  	}
  3575  
  3576  	var tempDelay time.Duration // how long to sleep on accept failure
  3577  
  3578  	ctx := context.WithValue(baseCtx, ServerContextKey, s)
  3579  	for {
  3580  		rw, err := l.Accept()
  3581  		if err != nil {
  3582  			if s.shuttingDown() {
  3583  				return ErrServerClosed
  3584  			}
  3585  			if ne, ok := err.(net.Error); ok && ne.Temporary() {
  3586  				if tempDelay == 0 {
  3587  					tempDelay = 5 * time.Millisecond
  3588  				} else {
  3589  					tempDelay *= 2
  3590  				}
  3591  				if max := 1 * time.Second; tempDelay > max {
  3592  					tempDelay = max
  3593  				}
  3594  				s.logf("http: Accept error: %v; retrying in %v", err, tempDelay)
  3595  				time.Sleep(tempDelay)
  3596  				continue
  3597  			}
  3598  			return err
  3599  		}
  3600  		connCtx := ctx
  3601  		if cc := s.ConnContext; cc != nil {
  3602  			connCtx = cc(connCtx, rw)
  3603  			if connCtx == nil {
  3604  				panic("ConnContext returned nil")
  3605  			}
  3606  		}
  3607  		tempDelay = 0
  3608  		c := s.newConn(rw)
  3609  		c.setState(c.rwc, StateNew, runHooks) // before Serve can return
  3610  		go c.serve(connCtx)
  3611  	}
  3612  }
  3613  
  3614  func (s *Server) setupTLSConfig(certFile, keyFile string, nextProtos []string) (*tls.Config, error) {
  3615  	config := cloneTLSConfig(s.TLSConfig)
  3616  	config.NextProtos = nextProtos
  3617  
  3618  	configHasCert := len(config.Certificates) > 0 || config.GetCertificate != nil || config.GetConfigForClient != nil
  3619  	if !configHasCert || certFile != "" || keyFile != "" {
  3620  		var err error
  3621  		config.Certificates = make([]tls.Certificate, 1)
  3622  		config.Certificates[0], err = tls.LoadX509KeyPair(certFile, keyFile)
  3623  		if err != nil {
  3624  			return nil, err
  3625  		}
  3626  	}
  3627  	return config, nil
  3628  }
  3629  
  3630  // ServeTLS accepts incoming connections on the Listener l, creating a
  3631  // new service goroutine for each. The service goroutines perform TLS
  3632  // setup and then read requests, calling s.Handler to reply to them.
  3633  //
  3634  // Files containing a certificate and matching private key for the
  3635  // server must be provided if neither the [Server]'s
  3636  // TLSConfig.Certificates, TLSConfig.GetCertificate nor
  3637  // config.GetConfigForClient are populated.
  3638  // If the certificate is signed by a certificate authority, the
  3639  // certFile should be the concatenation of the server's certificate,
  3640  // any intermediates, and the CA's certificate.
  3641  //
  3642  // ServeTLS always returns a non-nil error. After [Server.Shutdown] or [Server.Close], the
  3643  // returned error is [ErrServerClosed].
  3644  func (s *Server) ServeTLS(l net.Listener, certFile, keyFile string) error {
  3645  	// Setup HTTP/2 before s.Serve, to initialize s.TLSConfig
  3646  	// before we clone it and create the TLS Listener.
  3647  	if err := s.setupHTTP2_ServeTLS(); err != nil {
  3648  		return err
  3649  	}
  3650  	if s.h3Server != nil {
  3651  		// Temporary, test-only way to serve HTTP/3 from a PacketConn:
  3652  		// Pass it to ServeTLS wrapped in a net.Listener.
  3653  		// The caller should pass a net.Listener that immediately returns an error
  3654  		// if passed to a Server that doesn't support this path.
  3655  		if x, ok := l.(interface {
  3656  			HTTP3PacketConn() net.PacketConn
  3657  		}); ok {
  3658  			return s.serveHTTP3(x.HTTP3PacketConn(), certFile, keyFile)
  3659  		}
  3660  	}
  3661  
  3662  	var nextProtos []string
  3663  	if s.TLSConfig != nil {
  3664  		nextProtos = s.TLSConfig.NextProtos
  3665  	}
  3666  	config, err := s.setupTLSConfig(certFile, keyFile, adjustNextProtos(nextProtos, s.protocols()))
  3667  	if err != nil {
  3668  		return err
  3669  	}
  3670  
  3671  	tlsListener := tls.NewListener(l, config)
  3672  	return s.Serve(tlsListener)
  3673  }
  3674  
  3675  func (s *Server) protocols() Protocols {
  3676  	if s.Protocols != nil {
  3677  		// Historically, even when Protocols for a Server was set to be empty,
  3678  		// the Server can still run normally with just HTTP/1.
  3679  		// To keep backward-compatibility, the zero value of Protocols is
  3680  		// defined as having only HTTP/1 enabled.
  3681  		if s.Protocols.empty() {
  3682  			var p Protocols
  3683  			p.SetHTTP1(true)
  3684  			return p
  3685  		}
  3686  		return *s.Protocols // user-configured set
  3687  	}
  3688  
  3689  	// The historic way of disabling HTTP/2 is to set TLSNextProto to
  3690  	// a non-nil map with no "h2" entry.
  3691  	_, hasH2 := s.TLSNextProto["h2"]
  3692  	http2Disabled := s.TLSNextProto != nil && !hasH2
  3693  
  3694  	// If GODEBUG=http2server=0, then HTTP/2 is disabled unless
  3695  	// the user has manually added an "h2" entry to TLSNextProto
  3696  	// (probably by using x/net/http2 directly).
  3697  	if http2server.Value() == "0" && !hasH2 {
  3698  		http2Disabled = true
  3699  	}
  3700  
  3701  	var p Protocols
  3702  	p.SetHTTP1(true) // default always includes HTTP/1
  3703  	if !http2Disabled {
  3704  		p.SetHTTP2(true)
  3705  	}
  3706  	return p
  3707  }
  3708  
  3709  // adjustNextProtos adds or removes "http/1.1" and "h2" entries from
  3710  // a tls.Config.NextProtos list, according to the set of protocols in protos.
  3711  func adjustNextProtos(nextProtos []string, protos Protocols) []string {
  3712  	// Make a copy of NextProtos since it might be shared with some other tls.Config.
  3713  	// (tls.Config.Clone doesn't do a deep copy.)
  3714  	//
  3715  	// We could avoid an allocation in the common case by checking to see if the slice
  3716  	// is already in order, but this is just one small allocation per connection.
  3717  	nextProtos = slices.Clone(nextProtos)
  3718  	var have Protocols
  3719  	nextProtos = slices.DeleteFunc(nextProtos, func(s string) bool {
  3720  		switch s {
  3721  		case "http/1.1":
  3722  			if !protos.HTTP1() {
  3723  				return true
  3724  			}
  3725  			have.SetHTTP1(true)
  3726  		case "h2":
  3727  			if !protos.HTTP2() {
  3728  				return true
  3729  			}
  3730  			have.SetHTTP2(true)
  3731  		}
  3732  		return false
  3733  	})
  3734  	if protos.HTTP2() && !have.HTTP2() {
  3735  		nextProtos = append(nextProtos, "h2")
  3736  	}
  3737  	if protos.HTTP1() && !have.HTTP1() {
  3738  		nextProtos = append(nextProtos, "http/1.1")
  3739  	}
  3740  	return nextProtos
  3741  }
  3742  
  3743  // trackListener adds or removes a net.Listener to the set of tracked
  3744  // listeners.
  3745  //
  3746  // We store a pointer to interface in the map set, in case the
  3747  // net.Listener is not comparable. This is safe because we only call
  3748  // trackListener via Serve and can track+defer untrack the same
  3749  // pointer to local variable there. We never need to compare a
  3750  // Listener from another caller.
  3751  //
  3752  // It reports whether the server is still up (not Shutdown or Closed).
  3753  func (s *Server) trackListener(ln *net.Listener, add bool) bool {
  3754  	s.mu.Lock()
  3755  	defer s.mu.Unlock()
  3756  	if s.listeners == nil {
  3757  		s.listeners = make(map[*net.Listener]struct{})
  3758  	}
  3759  	if add {
  3760  		if s.shuttingDown() {
  3761  			return false
  3762  		}
  3763  		s.listeners[ln] = struct{}{}
  3764  		s.listenerGroup.Add(1)
  3765  	} else {
  3766  		delete(s.listeners, ln)
  3767  		s.listenerGroup.Done()
  3768  	}
  3769  	return true
  3770  }
  3771  
  3772  func (s *Server) trackConn(c *conn, add bool) {
  3773  	s.mu.Lock()
  3774  	defer s.mu.Unlock()
  3775  	if s.activeConn == nil {
  3776  		s.activeConn = make(map[*conn]struct{})
  3777  	}
  3778  	if add {
  3779  		s.activeConn[c] = struct{}{}
  3780  	} else {
  3781  		delete(s.activeConn, c)
  3782  	}
  3783  }
  3784  
  3785  func (s *Server) idleTimeout() time.Duration {
  3786  	if s.IdleTimeout != 0 {
  3787  		return s.IdleTimeout
  3788  	}
  3789  	return s.ReadTimeout
  3790  }
  3791  
  3792  func (s *Server) readHeaderTimeout() time.Duration {
  3793  	if s.ReadHeaderTimeout != 0 {
  3794  		return s.ReadHeaderTimeout
  3795  	}
  3796  	return s.ReadTimeout
  3797  }
  3798  
  3799  func (s *Server) doKeepAlives() bool {
  3800  	return !s.disableKeepAlives.Load() && !s.shuttingDown()
  3801  }
  3802  
  3803  func (s *Server) shuttingDown() bool {
  3804  	return s.inShutdown.Load()
  3805  }
  3806  
  3807  // SetKeepAlivesEnabled controls whether HTTP keep-alives are enabled.
  3808  // By default, keep-alives are always enabled. Only very
  3809  // resource-constrained environments or servers in the process of
  3810  // shutting down should disable them.
  3811  func (s *Server) SetKeepAlivesEnabled(v bool) {
  3812  	if v {
  3813  		s.disableKeepAlives.Store(false)
  3814  		return
  3815  	}
  3816  	s.disableKeepAlives.Store(true)
  3817  
  3818  	// Close idle HTTP/1 conns:
  3819  	s.closeIdleConns()
  3820  
  3821  	// TODO: Issue 26303: close HTTP/2 conns as soon as they become idle.
  3822  }
  3823  
  3824  func (s *Server) logf(format string, args ...any) {
  3825  	if s.ErrorLog != nil {
  3826  		s.ErrorLog.Printf(format, args...)
  3827  	} else {
  3828  		log.Printf(format, args...)
  3829  	}
  3830  }
  3831  
  3832  // logf prints to the ErrorLog of the *Server associated with request r
  3833  // via ServerContextKey. If there's no associated server, or if ErrorLog
  3834  // is nil, logging is done via the log package's standard logger.
  3835  func logf(r *Request, format string, args ...any) {
  3836  	s, _ := r.Context().Value(ServerContextKey).(*Server)
  3837  	if s != nil && s.ErrorLog != nil {
  3838  		s.ErrorLog.Printf(format, args...)
  3839  	} else {
  3840  		log.Printf(format, args...)
  3841  	}
  3842  }
  3843  
  3844  // ListenAndServe listens on the TCP network address addr and then calls
  3845  // [Serve] with handler to handle requests on incoming connections.
  3846  // Accepted connections are configured to enable TCP keep-alives.
  3847  //
  3848  // The handler is typically nil, in which case [DefaultServeMux] is used.
  3849  //
  3850  // ListenAndServe always returns a non-nil error.
  3851  func ListenAndServe(addr string, handler Handler) error {
  3852  	server := &Server{Addr: addr, Handler: handler}
  3853  	return server.ListenAndServe()
  3854  }
  3855  
  3856  // ListenAndServeTLS acts identically to [ListenAndServe], except that it
  3857  // expects HTTPS connections. Additionally, files containing a certificate and
  3858  // matching private key for the server must be provided. If the certificate
  3859  // is signed by a certificate authority, the certFile should be the concatenation
  3860  // of the server's certificate, any intermediates, and the CA's certificate.
  3861  func ListenAndServeTLS(addr, certFile, keyFile string, handler Handler) error {
  3862  	server := &Server{Addr: addr, Handler: handler}
  3863  	return server.ListenAndServeTLS(certFile, keyFile)
  3864  }
  3865  
  3866  // http3ServerHandler implements an interface in an external library that
  3867  // supports HTTP/3, allowing an external implementation of HTTP/3 to be used
  3868  // via net/http. See https://go.dev/issue/77440 for details.
  3869  //
  3870  // This is currently only used with golang.org/x/net/internal/http3, to allow
  3871  // us to test our HTTP/3 implementation against tests in net/http. HTTP/3 is
  3872  // not yet accessible to end-users.
  3873  type http3ServerHandler struct {
  3874  	handler     serverHandler
  3875  	tlsConfig   *tls.Config
  3876  	baseCtx     context.Context
  3877  	errc        chan error
  3878  	shutdownCtx context.Context
  3879  }
  3880  
  3881  // ServeHTTP ensures that http3ServerHandler implements the Handler interface,
  3882  // and gives an HTTP/3 server implementation access to the net/http handler.
  3883  func (h *http3ServerHandler) ServeHTTP(w ResponseWriter, r *Request) {
  3884  	h.handler.ServeHTTP(w, r)
  3885  }
  3886  
  3887  // Addr gives an HTTP/3 server implementation the address that it should listen
  3888  // on.
  3889  func (h *http3ServerHandler) Addr() string {
  3890  	return h.handler.srv.Addr
  3891  }
  3892  
  3893  // TLSConfig gives an HTTP/3 server implementation the *tls.Config that it
  3894  // should use.
  3895  func (h *http3ServerHandler) TLSConfig() *tls.Config {
  3896  	return h.tlsConfig
  3897  }
  3898  
  3899  // BaseContext gives an HTTP/3 server implementation the base context to use
  3900  // for server requests.
  3901  func (h *http3ServerHandler) BaseContext() context.Context {
  3902  	return h.baseCtx
  3903  }
  3904  
  3905  // ListenErrHook should be called by an HTTP/3 server implementation to
  3906  // propagate any error it encounters when trying to listen, if any, to
  3907  // net/http.
  3908  func (h *http3ServerHandler) ListenErrHook(err error) {
  3909  	h.errc <- err
  3910  }
  3911  
  3912  // ShutdownContext gives an HTTP/3 server implementation the context that is
  3913  // used when [Server.Shutdown] is called. This allows an HTTP/3 server
  3914  // implementation to know how long it can take to gracefully shutdown in the
  3915  // function it registers with [Server.RegisterOnShutdown]. Callers must not use
  3916  // this method for any other purpose.
  3917  func (h *http3ServerHandler) ShutdownContext() context.Context {
  3918  	return h.shutdownCtx
  3919  }
  3920  
  3921  // ListenAndServeTLS listens on the TCP network address s.Addr and
  3922  // then calls [ServeTLS] to handle requests on incoming TLS connections.
  3923  // Accepted connections are configured to enable TCP keep-alives.
  3924  //
  3925  // Filenames containing a certificate and matching private key for the
  3926  // server must be provided if neither the [Server]'s TLSConfig.Certificates
  3927  // nor TLSConfig.GetCertificate are populated. If the certificate is
  3928  // signed by a certificate authority, the certFile should be the
  3929  // concatenation of the server's certificate, any intermediates, and
  3930  // the CA's certificate.
  3931  //
  3932  // If s.Addr is blank, ":https" is used.
  3933  //
  3934  // ListenAndServeTLS always returns a non-nil error. After [Server.Shutdown] or
  3935  // [Server.Close], the returned error is [ErrServerClosed].
  3936  func (s *Server) ListenAndServeTLS(certFile, keyFile string) error {
  3937  	if s.shuttingDown() {
  3938  		return ErrServerClosed
  3939  	}
  3940  	addr := s.Addr
  3941  	if addr == "" {
  3942  		addr = ":https"
  3943  	}
  3944  
  3945  	p := s.protocols()
  3946  	if p.http3() {
  3947  		// TODO: Support HTTP/3 here.
  3948  		// For now, tests use Server.ServeTLS.
  3949  		return errors.New("http: Server.Protocols contains HTTP3, but Server does not support HTTP/3")
  3950  	}
  3951  	// Only start a TCP listener if HTTP/1 or HTTP/2 is used.
  3952  	if !p.HTTP1() && !p.HTTP2() && !p.UnencryptedHTTP2() {
  3953  		return errors.New("http: no protocols configured")
  3954  	}
  3955  
  3956  	ln, err := net.Listen("tcp", addr)
  3957  	if err != nil {
  3958  		return err
  3959  	}
  3960  	defer ln.Close()
  3961  	return s.ServeTLS(ln, certFile, keyFile)
  3962  }
  3963  
  3964  // setupHTTP2_ServeTLS conditionally configures HTTP/2 on
  3965  // s and reports whether there was an error setting it up. If it is
  3966  // not configured for policy reasons, nil is returned.
  3967  func (s *Server) setupHTTP2_ServeTLS() error {
  3968  	s.nextProtoOnce.Do(s.onceSetNextProtoDefaults)
  3969  	return s.nextProtoErr
  3970  }
  3971  
  3972  // setupHTTP2_Serve is called from (*Server).Serve and conditionally
  3973  // configures HTTP/2 on s using a more conservative policy than
  3974  // setupHTTP2_ServeTLS because Serve is called after tls.Listen,
  3975  // and may be called concurrently. See shouldConfigureHTTP2ForServe.
  3976  //
  3977  // The tests named TestTransportAutomaticHTTP2* and
  3978  // TestConcurrentServerServe in server_test.go demonstrate some
  3979  // of the supported use cases and motivations.
  3980  func (s *Server) setupHTTP2_Serve() error {
  3981  	s.nextProtoOnce.Do(s.onceSetNextProtoDefaults_Serve)
  3982  	return s.nextProtoErr
  3983  }
  3984  
  3985  func (s *Server) onceSetNextProtoDefaults_Serve() {
  3986  	if s.shouldConfigureHTTP2ForServe() {
  3987  		s.onceSetNextProtoDefaults()
  3988  	}
  3989  }
  3990  
  3991  var http2server = godebug.New("http2server")
  3992  
  3993  // onceSetNextProtoDefaults configures HTTP/2, if the user hasn't
  3994  // configured otherwise. (by setting s.TLSNextProto non-nil)
  3995  // It must only be called via s.nextProtoOnce (use s.setupHTTP2_*).
  3996  func (s *Server) onceSetNextProtoDefaults() {
  3997  	if omitBundledHTTP2 {
  3998  		return
  3999  	}
  4000  	p := s.protocols()
  4001  	if !p.HTTP2() && !p.UnencryptedHTTP2() {
  4002  		return
  4003  	}
  4004  	if http2server.Value() == "0" {
  4005  		http2server.IncNonDefault()
  4006  		return
  4007  	}
  4008  	if _, ok := s.TLSNextProto["h2"]; ok {
  4009  		// TLSNextProto already contains an HTTP/2 implementation.
  4010  		// The user probably called golang.org/x/net/http2.ConfigureServer
  4011  		// to add it.
  4012  		return
  4013  	}
  4014  	s.configureHTTP2()
  4015  }
  4016  
  4017  // TimeoutHandler returns a [Handler] that runs h with the given time limit.
  4018  //
  4019  // The new Handler calls h.ServeHTTP to handle each request, but if a
  4020  // call runs for longer than its time limit, the handler responds with
  4021  // a 503 Service Unavailable error and the given message in its body.
  4022  // (If msg is empty, a suitable default message will be sent.)
  4023  // After such a timeout, writes by h to its [ResponseWriter] will return
  4024  // [ErrHandlerTimeout].
  4025  //
  4026  // TimeoutHandler supports the [Pusher] interface but does not support
  4027  // the [Hijacker] or [Flusher] interfaces.
  4028  func TimeoutHandler(h Handler, dt time.Duration, msg string) Handler {
  4029  	return &timeoutHandler{
  4030  		handler: h,
  4031  		body:    msg,
  4032  		dt:      dt,
  4033  	}
  4034  }
  4035  
  4036  // ErrHandlerTimeout is returned on [ResponseWriter] Write calls
  4037  // in handlers which have timed out.
  4038  var ErrHandlerTimeout = errors.New("http: Handler timeout")
  4039  
  4040  type timeoutHandler struct {
  4041  	handler Handler
  4042  	body    string
  4043  	dt      time.Duration
  4044  
  4045  	// When set, no context will be created and this context will
  4046  	// be used instead.
  4047  	testContext context.Context
  4048  }
  4049  
  4050  func (h *timeoutHandler) errorBody() string {
  4051  	if h.body != "" {
  4052  		return h.body
  4053  	}
  4054  	return "<html><head><title>Timeout</title></head><body><h1>Timeout</h1></body></html>"
  4055  }
  4056  
  4057  func (h *timeoutHandler) ServeHTTP(w ResponseWriter, r *Request) {
  4058  	ctx := h.testContext
  4059  	if ctx == nil {
  4060  		var cancelCtx context.CancelFunc
  4061  		ctx, cancelCtx = context.WithTimeout(r.Context(), h.dt)
  4062  		defer cancelCtx()
  4063  	}
  4064  	r = r.WithContext(ctx)
  4065  	done := make(chan struct{})
  4066  	tw := &timeoutWriter{
  4067  		w:   w,
  4068  		h:   make(Header),
  4069  		req: r,
  4070  	}
  4071  	panicChan := make(chan any, 1)
  4072  	go func() {
  4073  		defer func() {
  4074  			if p := recover(); p != nil {
  4075  				panicChan <- p
  4076  			}
  4077  		}()
  4078  		h.handler.ServeHTTP(tw, r)
  4079  		close(done)
  4080  	}()
  4081  	select {
  4082  	case p := <-panicChan:
  4083  		panic(p)
  4084  	case <-done:
  4085  		tw.mu.Lock()
  4086  		defer tw.mu.Unlock()
  4087  		dst := w.Header()
  4088  		maps.Copy(dst, tw.h)
  4089  		if !tw.wroteHeader {
  4090  			tw.code = StatusOK
  4091  		}
  4092  		w.WriteHeader(tw.code)
  4093  		w.Write(tw.wbuf.Bytes())
  4094  	case <-ctx.Done():
  4095  		tw.mu.Lock()
  4096  		defer tw.mu.Unlock()
  4097  		switch err := ctx.Err(); err {
  4098  		case context.DeadlineExceeded:
  4099  			w.WriteHeader(StatusServiceUnavailable)
  4100  			io.WriteString(w, h.errorBody())
  4101  			tw.err = ErrHandlerTimeout
  4102  		default:
  4103  			w.WriteHeader(StatusServiceUnavailable)
  4104  			tw.err = err
  4105  		}
  4106  	}
  4107  }
  4108  
  4109  type timeoutWriter struct {
  4110  	w    ResponseWriter
  4111  	h    Header
  4112  	wbuf bytes.Buffer
  4113  	req  *Request
  4114  
  4115  	mu          sync.Mutex
  4116  	err         error
  4117  	wroteHeader bool
  4118  	code        int
  4119  }
  4120  
  4121  var _ Pusher = (*timeoutWriter)(nil)
  4122  
  4123  // Push implements the [Pusher] interface.
  4124  func (tw *timeoutWriter) Push(target string, opts *PushOptions) error {
  4125  	if pusher, ok := tw.w.(Pusher); ok {
  4126  		return pusher.Push(target, opts)
  4127  	}
  4128  	return ErrNotSupported
  4129  }
  4130  
  4131  func (tw *timeoutWriter) Header() Header { return tw.h }
  4132  
  4133  func (tw *timeoutWriter) Write(p []byte) (int, error) {
  4134  	tw.mu.Lock()
  4135  	defer tw.mu.Unlock()
  4136  	if tw.err != nil {
  4137  		return 0, tw.err
  4138  	}
  4139  	if !tw.wroteHeader {
  4140  		tw.writeHeaderLocked(StatusOK)
  4141  	}
  4142  	return tw.wbuf.Write(p)
  4143  }
  4144  
  4145  func (tw *timeoutWriter) writeHeaderLocked(code int) {
  4146  	checkWriteHeaderCode(code)
  4147  
  4148  	switch {
  4149  	case tw.err != nil:
  4150  		return
  4151  	case tw.wroteHeader:
  4152  		if tw.req != nil {
  4153  			caller := relevantCaller()
  4154  			logf(tw.req, "http: superfluous response.WriteHeader call from %s (%s:%d)", caller.Function, path.Base(caller.File), caller.Line)
  4155  		}
  4156  	default:
  4157  		tw.wroteHeader = true
  4158  		tw.code = code
  4159  	}
  4160  }
  4161  
  4162  func (tw *timeoutWriter) WriteHeader(code int) {
  4163  	tw.mu.Lock()
  4164  	defer tw.mu.Unlock()
  4165  	tw.writeHeaderLocked(code)
  4166  }
  4167  
  4168  // onceCloseListener wraps a net.Listener, protecting it from
  4169  // multiple Close calls.
  4170  type onceCloseListener struct {
  4171  	net.Listener
  4172  	once     sync.Once
  4173  	closeErr error
  4174  }
  4175  
  4176  func (oc *onceCloseListener) Close() error {
  4177  	oc.once.Do(oc.close)
  4178  	return oc.closeErr
  4179  }
  4180  
  4181  func (oc *onceCloseListener) close() { oc.closeErr = oc.Listener.Close() }
  4182  
  4183  // globalOptionsHandler responds to "OPTIONS *" requests.
  4184  type globalOptionsHandler struct{}
  4185  
  4186  func (globalOptionsHandler) ServeHTTP(w ResponseWriter, r *Request) {
  4187  	w.Header().Set("Content-Length", "0")
  4188  	if r.ContentLength != 0 {
  4189  		// Read up to 4KB of OPTIONS body (as mentioned in the
  4190  		// spec as being reserved for future use), but anything
  4191  		// over that is considered a waste of server resources
  4192  		// (or an attack) and we abort and close the connection,
  4193  		// courtesy of MaxBytesReader's EOF behavior.
  4194  		mb := MaxBytesReader(w, r.Body, 4<<10)
  4195  		io.Copy(io.Discard, mb)
  4196  	}
  4197  }
  4198  
  4199  // initALPNRequest is an HTTP handler that initializes certain
  4200  // uninitialized fields in its *Request. Such partially-initialized
  4201  // Requests come from ALPN protocol handlers.
  4202  type initALPNRequest struct {
  4203  	ctx context.Context
  4204  	c   *tls.Conn
  4205  	h   serverHandler
  4206  }
  4207  
  4208  // BaseContext is an exported but unadvertised [http.Handler] method
  4209  // recognized by x/net/http2 to pass down a context; the TLSNextProto
  4210  // API predates context support so we shoehorn through the only
  4211  // interface we have available.
  4212  func (h initALPNRequest) BaseContext() context.Context { return h.ctx }
  4213  
  4214  func (h initALPNRequest) ServeHTTP(rw ResponseWriter, req *Request) {
  4215  	if req.TLS == nil {
  4216  		req.TLS = &tls.ConnectionState{}
  4217  		*req.TLS = h.c.ConnectionState()
  4218  	}
  4219  	if req.Body == nil {
  4220  		req.Body = NoBody
  4221  	}
  4222  	if req.RemoteAddr == "" {
  4223  		req.RemoteAddr = h.c.RemoteAddr().String()
  4224  	}
  4225  	h.h.ServeHTTP(rw, req)
  4226  }
  4227  
  4228  // loggingConn is used for debugging.
  4229  type loggingConn struct {
  4230  	name string
  4231  	net.Conn
  4232  }
  4233  
  4234  var (
  4235  	uniqNameMu   sync.Mutex
  4236  	uniqNameNext = make(map[string]int)
  4237  )
  4238  
  4239  func newLoggingConn(baseName string, c net.Conn) net.Conn {
  4240  	uniqNameMu.Lock()
  4241  	defer uniqNameMu.Unlock()
  4242  	uniqNameNext[baseName]++
  4243  	return &loggingConn{
  4244  		name: fmt.Sprintf("%s-%d", baseName, uniqNameNext[baseName]),
  4245  		Conn: c,
  4246  	}
  4247  }
  4248  
  4249  func (c *loggingConn) Write(p []byte) (n int, err error) {
  4250  	log.Printf("%s.Write(%d) = ....", c.name, len(p))
  4251  	n, err = c.Conn.Write(p)
  4252  	log.Printf("%s.Write(%d) = %d, %v", c.name, len(p), n, err)
  4253  	return
  4254  }
  4255  
  4256  func (c *loggingConn) Read(p []byte) (n int, err error) {
  4257  	log.Printf("%s.Read(%d) = ....", c.name, len(p))
  4258  	n, err = c.Conn.Read(p)
  4259  	log.Printf("%s.Read(%d) = %d, %v", c.name, len(p), n, err)
  4260  	return
  4261  }
  4262  
  4263  func (c *loggingConn) Close() (err error) {
  4264  	log.Printf("%s.Close() = ...", c.name)
  4265  	err = c.Conn.Close()
  4266  	log.Printf("%s.Close() = %v", c.name, err)
  4267  	return
  4268  }
  4269  
  4270  // checkConnErrorWriter writes to c.rwc and records any write errors to c.werr.
  4271  // It only contains one field (and a pointer field at that), so it
  4272  // fits in an interface value without an extra allocation.
  4273  type checkConnErrorWriter struct {
  4274  	c *conn
  4275  }
  4276  
  4277  func (w checkConnErrorWriter) Write(p []byte) (n int, err error) {
  4278  	n, err = w.c.rwc.Write(p)
  4279  	if err != nil && w.c.werr == nil {
  4280  		w.c.werr = err
  4281  		w.c.cancelCtx()
  4282  	}
  4283  	return
  4284  }
  4285  
  4286  func numLeadingCRorLF(v []byte) (n int) {
  4287  	for _, b := range v {
  4288  		if b == '\r' || b == '\n' {
  4289  			n++
  4290  			continue
  4291  		}
  4292  		break
  4293  	}
  4294  	return
  4295  }
  4296  
  4297  // tlsRecordHeaderLooksLikeHTTP reports whether a TLS record header
  4298  // looks like it might've been a misdirected plaintext HTTP request.
  4299  func tlsRecordHeaderLooksLikeHTTP(hdr [5]byte) bool {
  4300  	switch string(hdr[:]) {
  4301  	case "GET /", "HEAD ", "POST ", "PUT /", "OPTIO":
  4302  		return true
  4303  	}
  4304  	return false
  4305  }
  4306  
  4307  // MaxBytesHandler returns a [Handler] that runs h with its [ResponseWriter] and [Request.Body] wrapped by a MaxBytesReader.
  4308  func MaxBytesHandler(h Handler, n int64) Handler {
  4309  	return HandlerFunc(func(w ResponseWriter, r *Request) {
  4310  		r2 := *r
  4311  		r2.Body = MaxBytesReader(w, r.Body, n)
  4312  		h.ServeHTTP(w, &r2)
  4313  	})
  4314  }
  4315  

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