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  	"path"
    27  	"runtime"
    28  	"slices"
    29  	"strconv"
    30  	"strings"
    31  	"sync"
    32  	"sync/atomic"
    33  	"time"
    34  	_ "unsafe" // for linkname
    35  
    36  	"golang.org/x/net/http/httpguts"
    37  )
    38  
    39  // Errors used by the HTTP server.
    40  var (
    41  	// ErrBodyNotAllowed is returned by ResponseWriter.Write calls
    42  	// when the HTTP method or response code does not permit a
    43  	// body.
    44  	ErrBodyNotAllowed = internal.ErrBodyNotAllowed
    45  
    46  	// ErrHijacked is returned by ResponseWriter.Write calls when
    47  	// the underlying connection has been hijacked using the
    48  	// Hijacker interface. A zero-byte write on a hijacked
    49  	// connection will return ErrHijacked without any other side
    50  	// effects.
    51  	ErrHijacked = errors.New("http: connection has been hijacked")
    52  
    53  	// ErrContentLength is returned by ResponseWriter.Write calls
    54  	// when a Handler set a Content-Length response header with a
    55  	// declared size and then attempted to write more bytes than
    56  	// declared.
    57  	ErrContentLength = errors.New("http: wrote more than the declared Content-Length")
    58  
    59  	// Deprecated: ErrWriteAfterFlush is no longer returned by
    60  	// anything in the net/http package. Callers should not
    61  	// compare errors against this variable.
    62  	ErrWriteAfterFlush = errors.New("unused")
    63  )
    64  
    65  // A Handler responds to an HTTP request.
    66  //
    67  // [Handler.ServeHTTP] should write reply headers and data to the [ResponseWriter]
    68  // and then return. Returning signals that the request is finished; it
    69  // is not valid to use the [ResponseWriter] or read from the
    70  // [Request.Body] after or concurrently with the completion of the
    71  // ServeHTTP call.
    72  //
    73  // Depending on the HTTP client software, HTTP protocol version, and
    74  // any intermediaries between the client and the Go server, it may not
    75  // be possible to read from the [Request.Body] after writing to the
    76  // [ResponseWriter]. Cautious handlers should read the [Request.Body]
    77  // first, and then reply.
    78  //
    79  // Except for reading the body, handlers should not modify the
    80  // provided Request.
    81  //
    82  // If ServeHTTP panics, the server (the caller of ServeHTTP) assumes
    83  // that the effect of the panic was isolated to the active request.
    84  // It recovers the panic, logs a stack trace to the server error log,
    85  // and either closes the network connection or sends an HTTP/2
    86  // RST_STREAM, depending on the HTTP protocol. To abort a handler so
    87  // the client sees an interrupted response but the server doesn't log
    88  // an error, panic with the value [ErrAbortHandler].
    89  type Handler interface {
    90  	ServeHTTP(ResponseWriter, *Request)
    91  }
    92  
    93  // A ResponseWriter interface is used by an HTTP handler to
    94  // construct an HTTP response.
    95  //
    96  // A ResponseWriter may not be used after [Handler.ServeHTTP] has returned.
    97  type ResponseWriter interface {
    98  	// Header returns the header map that will be sent by
    99  	// [ResponseWriter.WriteHeader]. The [Header] map also is the mechanism with which
   100  	// [Handler] implementations can set HTTP trailers.
   101  	//
   102  	// Changing the header map after a call to [ResponseWriter.WriteHeader] (or
   103  	// [ResponseWriter.Write]) has no effect unless the HTTP status code was of the
   104  	// 1xx class or the modified headers are trailers.
   105  	//
   106  	// There are two ways to set Trailers. The preferred way is to
   107  	// predeclare in the headers which trailers you will later
   108  	// send by setting the "Trailer" header to the names of the
   109  	// trailer keys which will come later. In this case, those
   110  	// keys of the Header map are treated as if they were
   111  	// trailers. See the example. The second way, for trailer
   112  	// keys not known to the [Handler] until after the first [ResponseWriter.Write],
   113  	// is to prefix the [Header] map keys with the [TrailerPrefix]
   114  	// constant value.
   115  	//
   116  	// To suppress automatic response headers (such as "Date"), set
   117  	// their value to nil.
   118  	Header() Header
   119  
   120  	// Write writes the data to the connection as part of an HTTP reply.
   121  	//
   122  	// If [ResponseWriter.WriteHeader] has not yet been called, Write calls
   123  	// WriteHeader(http.StatusOK) before writing the data. If the Header
   124  	// does not contain a Content-Type line, Write adds a Content-Type set
   125  	// to the result of passing the initial 512 bytes of written data to
   126  	// [DetectContentType]. Additionally, if the total size of all written
   127  	// data is under a few KB and there are no Flush calls, the
   128  	// Content-Length header is added automatically.
   129  	//
   130  	// Depending on the HTTP protocol version and the client, calling
   131  	// Write or WriteHeader may prevent future reads on the
   132  	// Request.Body. For HTTP/1.x requests, handlers should read any
   133  	// needed request body data before writing the response. Once the
   134  	// headers have been flushed (due to either an explicit Flusher.Flush
   135  	// call or writing enough data to trigger a flush), the request body
   136  	// may be unavailable. For HTTP/2 requests, the Go HTTP server permits
   137  	// handlers to continue to read the request body while concurrently
   138  	// writing the response. However, such behavior may not be supported
   139  	// by all HTTP/2 clients. Handlers should read before writing if
   140  	// possible to maximize compatibility.
   141  	Write([]byte) (int, error)
   142  
   143  	// WriteHeader sends an HTTP response header with the provided
   144  	// status code.
   145  	//
   146  	// If WriteHeader is not called explicitly, the first call to Write
   147  	// will trigger an implicit WriteHeader(http.StatusOK).
   148  	// Thus explicit calls to WriteHeader are mainly used to
   149  	// send error codes or 1xx informational responses.
   150  	//
   151  	// The provided code must be a valid HTTP 1xx-5xx status code.
   152  	// Any number of 1xx headers may be written, followed by at most
   153  	// one 2xx-5xx header. 1xx headers are sent immediately, but 2xx-5xx
   154  	// headers may be buffered. Use the Flusher interface to send
   155  	// buffered data. The header map is cleared when 2xx-5xx headers are
   156  	// sent, but not with 1xx headers.
   157  	//
   158  	// The server will automatically send a 100 (Continue) header
   159  	// on the first read from the request body if the request has
   160  	// an "Expect: 100-continue" header.
   161  	WriteHeader(statusCode int)
   162  }
   163  
   164  // The Flusher interface is implemented by ResponseWriters that allow
   165  // an HTTP handler to flush buffered data to the client.
   166  //
   167  // The default HTTP/1.x and HTTP/2 [ResponseWriter] implementations
   168  // support [Flusher], but ResponseWriter wrappers may not. Handlers
   169  // should always test for this ability at runtime.
   170  //
   171  // Note that even for ResponseWriters that support Flush,
   172  // if the client is connected through an HTTP proxy,
   173  // the buffered data may not reach the client until the response
   174  // completes.
   175  type Flusher interface {
   176  	// Flush sends any buffered data to the client.
   177  	Flush()
   178  }
   179  
   180  // The Hijacker interface is implemented by ResponseWriters that allow
   181  // an HTTP handler to take over the connection.
   182  //
   183  // The default [ResponseWriter] for HTTP/1.x connections supports
   184  // Hijacker, but HTTP/2 connections intentionally do not.
   185  // ResponseWriter wrappers may also not support Hijacker. Handlers
   186  // should always test for this ability at runtime.
   187  type Hijacker interface {
   188  	// Hijack lets the caller take over the connection.
   189  	// After a call to Hijack the HTTP server library
   190  	// will not do anything else with the connection.
   191  	//
   192  	// It becomes the caller's responsibility to manage
   193  	// and close the connection.
   194  	//
   195  	// The returned net.Conn may have read or write deadlines
   196  	// already set, depending on the configuration of the
   197  	// Server. It is the caller's responsibility to set
   198  	// or clear those deadlines as needed.
   199  	//
   200  	// The returned bufio.Reader may contain unprocessed buffered
   201  	// data from the client.
   202  	//
   203  	// After a call to Hijack, the original Request.Body must not
   204  	// be used. The original Request's Context remains valid and
   205  	// is not canceled until the Request's ServeHTTP method
   206  	// returns.
   207  	Hijack() (net.Conn, *bufio.ReadWriter, error)
   208  }
   209  
   210  // The CloseNotifier interface is implemented by ResponseWriters which
   211  // allow detecting when the underlying connection has gone away.
   212  //
   213  // This mechanism can be used to cancel long operations on the server
   214  // if the client has disconnected before the response is ready.
   215  //
   216  // Deprecated: the CloseNotifier interface predates Go's context package.
   217  // New code should use [Request.Context] instead.
   218  type CloseNotifier interface {
   219  	// CloseNotify returns a channel that receives at most a
   220  	// single value (true) when the client connection has gone
   221  	// away.
   222  	//
   223  	// CloseNotify may wait to notify until Request.Body has been
   224  	// fully read.
   225  	//
   226  	// After the Handler has returned, there is no guarantee
   227  	// that the channel receives a value.
   228  	//
   229  	// If the protocol is HTTP/1.1 and CloseNotify is called while
   230  	// processing an idempotent request (such as GET) while
   231  	// HTTP/1.1 pipelining is in use, the arrival of a subsequent
   232  	// pipelined request may cause a value to be sent on the
   233  	// returned channel. In practice HTTP/1.1 pipelining is not
   234  	// enabled in browsers and not seen often in the wild. If this
   235  	// is a problem, use HTTP/2 or only use CloseNotify on methods
   236  	// such as POST.
   237  	CloseNotify() <-chan bool
   238  }
   239  
   240  var (
   241  	// ServerContextKey is a context key. It can be used in HTTP
   242  	// handlers with Context.Value to access the server that
   243  	// started the handler. The associated value will be of
   244  	// type *Server.
   245  	ServerContextKey = &contextKey{"http-server"}
   246  
   247  	// LocalAddrContextKey is a context key. It can be used in
   248  	// HTTP handlers with Context.Value to access the local
   249  	// address the connection arrived on.
   250  	// The associated value will be of type net.Addr.
   251  	LocalAddrContextKey = &contextKey{"local-addr"}
   252  )
   253  
   254  // A conn represents the server side of an HTTP connection.
   255  type conn struct {
   256  	// server is the server on which the connection arrived.
   257  	// Immutable; never nil.
   258  	server *Server
   259  
   260  	// cancelCtx cancels the connection-level context.
   261  	cancelCtx context.CancelFunc
   262  
   263  	// rwc is the underlying network connection.
   264  	// This is never wrapped by other types and is the value given out
   265  	// to [Hijacker] callers. It is usually of type *net.TCPConn or
   266  	// *tls.Conn.
   267  	rwc net.Conn
   268  
   269  	// remoteAddr is rwc.RemoteAddr().String(). It is not populated synchronously
   270  	// inside the Listener's Accept goroutine, as some implementations block.
   271  	// It is populated immediately inside the (*conn).serve goroutine.
   272  	// This is the value of a Handler's (*Request).RemoteAddr.
   273  	remoteAddr string
   274  
   275  	// tlsState is the TLS connection state when using TLS.
   276  	// nil means not TLS.
   277  	tlsState *tls.ConnectionState
   278  
   279  	// werr is set to the first write error to rwc.
   280  	// It is set via checkConnErrorWriter{w}, where bufw writes.
   281  	werr error
   282  
   283  	// r is bufr's read source. It's a wrapper around rwc that provides
   284  	// io.LimitedReader-style limiting (while reading request headers)
   285  	// and functionality to support CloseNotifier. See *connReader docs.
   286  	r *connReader
   287  
   288  	// bufr reads from r.
   289  	bufr *bufio.Reader
   290  
   291  	// bufw writes to checkConnErrorWriter{c}, which populates werr on error.
   292  	bufw *bufio.Writer
   293  
   294  	// lastMethod is the method of the most recent request
   295  	// on this connection, if any.
   296  	lastMethod string
   297  
   298  	curReq atomic.Pointer[response] // (which has a Request in it)
   299  
   300  	curState atomic.Uint64 // packed (unixtime<<8|uint8(ConnState))
   301  
   302  	// mu guards hijackedv
   303  	mu sync.Mutex
   304  
   305  	// hijackedv is whether this connection has been hijacked
   306  	// by a Handler with the Hijacker interface.
   307  	// It is guarded by mu.
   308  	hijackedv bool
   309  }
   310  
   311  func (c *conn) hijacked() bool {
   312  	c.mu.Lock()
   313  	defer c.mu.Unlock()
   314  	return c.hijackedv
   315  }
   316  
   317  // c.mu must be held.
   318  func (c *conn) hijackLocked() (rwc net.Conn, buf *bufio.ReadWriter, err error) {
   319  	if c.hijackedv {
   320  		return nil, nil, ErrHijacked
   321  	}
   322  	c.r.abortPendingRead()
   323  
   324  	c.hijackedv = true
   325  	rwc = c.rwc
   326  	rwc.SetDeadline(time.Time{})
   327  
   328  	if c.r.hasByte {
   329  		if _, err := c.bufr.Peek(c.bufr.Buffered() + 1); err != nil {
   330  			return nil, nil, fmt.Errorf("unexpected Peek failure reading buffered byte: %v", err)
   331  		}
   332  	}
   333  	c.bufw.Reset(rwc)
   334  	buf = bufio.NewReadWriter(c.bufr, c.bufw)
   335  
   336  	c.setState(rwc, StateHijacked, runHooks)
   337  	return
   338  }
   339  
   340  // This should be >= 512 bytes for DetectContentType,
   341  // but otherwise it's somewhat arbitrary.
   342  const bufferBeforeChunkingSize = 2048
   343  
   344  // chunkWriter writes to a response's conn buffer, and is the writer
   345  // wrapped by the response.w buffered writer.
   346  //
   347  // chunkWriter also is responsible for finalizing the Header, including
   348  // conditionally setting the Content-Type and setting a Content-Length
   349  // in cases where the handler's final output is smaller than the buffer
   350  // size. It also conditionally adds chunk headers, when in chunking mode.
   351  //
   352  // See the comment above (*response).Write for the entire write flow.
   353  type chunkWriter struct {
   354  	res *response
   355  
   356  	// header is either nil or a deep clone of res.handlerHeader
   357  	// at the time of res.writeHeader, if res.writeHeader is
   358  	// called and extra buffering is being done to calculate
   359  	// Content-Type and/or Content-Length.
   360  	header Header
   361  
   362  	// wroteHeader tells whether the header's been written to "the
   363  	// wire" (or rather: w.conn.buf). this is unlike
   364  	// (*response).wroteHeader, which tells only whether it was
   365  	// logically written.
   366  	wroteHeader bool
   367  
   368  	// set by the writeHeader method:
   369  	chunking bool // using chunked transfer encoding for reply body
   370  }
   371  
   372  var (
   373  	crlf       = []byte("\r\n")
   374  	colonSpace = []byte(": ")
   375  )
   376  
   377  func (cw *chunkWriter) Write(p []byte) (n int, err error) {
   378  	if !cw.wroteHeader {
   379  		cw.writeHeader(p)
   380  	}
   381  	if cw.res.req.Method == "HEAD" {
   382  		// Eat writes.
   383  		return len(p), nil
   384  	}
   385  	if cw.chunking {
   386  		_, err = fmt.Fprintf(cw.res.conn.bufw, "%x\r\n", len(p))
   387  		if err != nil {
   388  			cw.res.conn.rwc.Close()
   389  			return
   390  		}
   391  	}
   392  	n, err = cw.res.conn.bufw.Write(p)
   393  	if cw.chunking && err == nil {
   394  		_, err = cw.res.conn.bufw.Write(crlf)
   395  	}
   396  	if err != nil {
   397  		cw.res.conn.rwc.Close()
   398  	}
   399  	return
   400  }
   401  
   402  func (cw *chunkWriter) flush() error {
   403  	if !cw.wroteHeader {
   404  		cw.writeHeader(nil)
   405  	}
   406  	return cw.res.conn.bufw.Flush()
   407  }
   408  
   409  func (cw *chunkWriter) close() {
   410  	if !cw.wroteHeader {
   411  		cw.writeHeader(nil)
   412  	}
   413  	if cw.chunking {
   414  		bw := cw.res.conn.bufw // conn's bufio writer
   415  		// zero chunk to mark EOF
   416  		bw.WriteString("0\r\n")
   417  		if trailers := cw.res.finalTrailers(); trailers != nil {
   418  			trailers.Write(bw) // the writer handles noting errors
   419  		}
   420  		// final blank line after the trailers (whether
   421  		// present or not)
   422  		bw.WriteString("\r\n")
   423  	}
   424  }
   425  
   426  // A response represents the server side of an HTTP response.
   427  type response struct {
   428  	conn             *conn
   429  	req              *Request // request for this response
   430  	reqBody          io.ReadCloser
   431  	cancelCtx        context.CancelFunc // when ServeHTTP exits
   432  	wroteHeader      bool               // a non-1xx header has been (logically) written
   433  	wants10KeepAlive bool               // HTTP/1.0 w/ Connection "keep-alive"
   434  	wantsClose       bool               // HTTP request has Connection "close"
   435  
   436  	// canWriteContinue is an atomic boolean that says whether or
   437  	// not a 100 Continue header can be written to the
   438  	// connection.
   439  	// writeContinueMu must be held while writing the header.
   440  	// These two fields together synchronize the body reader (the
   441  	// expectContinueReader, which wants to write 100 Continue)
   442  	// against the main writer.
   443  	writeContinueMu  sync.Mutex
   444  	canWriteContinue atomic.Bool
   445  
   446  	w  *bufio.Writer // buffers output in chunks to chunkWriter
   447  	cw chunkWriter
   448  
   449  	// handlerHeader is the Header that Handlers get access to,
   450  	// which may be retained and mutated even after WriteHeader.
   451  	// handlerHeader is copied into cw.header at WriteHeader
   452  	// time, and privately mutated thereafter.
   453  	handlerHeader Header
   454  	calledHeader  bool // handler accessed handlerHeader via Header
   455  
   456  	written       int64 // number of bytes written in body
   457  	contentLength int64 // explicitly-declared Content-Length; or -1
   458  	status        int   // status code passed to WriteHeader
   459  
   460  	// close connection after this reply.  set on request and
   461  	// updated after response from handler if there's a
   462  	// "Connection: keep-alive" response header and a
   463  	// Content-Length.
   464  	closeAfterReply bool
   465  
   466  	// When fullDuplex is false (the default), we consume any remaining
   467  	// request body before starting to write a response.
   468  	fullDuplex bool
   469  
   470  	// requestBodyLimitHit is set by requestTooLarge when
   471  	// maxBytesReader hits its max size. It is checked in
   472  	// WriteHeader, to make sure we don't consume the
   473  	// remaining request body to try to advance to the next HTTP
   474  	// request. Instead, when this is set, we stop reading
   475  	// subsequent requests on this connection and stop reading
   476  	// input from it.
   477  	requestBodyLimitHit bool
   478  
   479  	// trailers are the headers to be sent after the handler
   480  	// finishes writing the body. This field is initialized from
   481  	// the Trailer response header when the response header is
   482  	// written.
   483  	trailers []string
   484  
   485  	handlerDone atomic.Bool // set true when the handler exits
   486  
   487  	// Buffers for Date, Content-Length, and status code
   488  	dateBuf   [len(TimeFormat)]byte
   489  	clenBuf   [10]byte
   490  	statusBuf [3]byte
   491  
   492  	// lazyCloseNotifyMu protects closeNotifyCh and closeNotifyTriggered.
   493  	lazyCloseNotifyMu sync.Mutex
   494  	// closeNotifyCh is the channel returned by CloseNotify.
   495  	closeNotifyCh chan bool
   496  	// closeNotifyTriggered tracks prior closeNotify calls.
   497  	closeNotifyTriggered bool
   498  }
   499  
   500  func (c *response) SetReadDeadline(deadline time.Time) error {
   501  	return c.conn.rwc.SetReadDeadline(deadline)
   502  }
   503  
   504  func (c *response) SetWriteDeadline(deadline time.Time) error {
   505  	return c.conn.rwc.SetWriteDeadline(deadline)
   506  }
   507  
   508  func (c *response) EnableFullDuplex() error {
   509  	c.fullDuplex = true
   510  	return nil
   511  }
   512  
   513  // TrailerPrefix is a magic prefix for [ResponseWriter.Header] map keys
   514  // that, if present, signals that the map entry is actually for
   515  // the response trailers, and not the response headers. The prefix
   516  // is stripped after the ServeHTTP call finishes and the values are
   517  // sent in the trailers.
   518  //
   519  // This mechanism is intended only for trailers that are not known
   520  // prior to the headers being written. If the set of trailers is fixed
   521  // or known before the header is written, the normal Go trailers mechanism
   522  // is preferred:
   523  //
   524  //	https://pkg.go.dev/net/http#ResponseWriter
   525  //	https://pkg.go.dev/net/http#example-ResponseWriter-Trailers
   526  const TrailerPrefix = "Trailer:"
   527  
   528  // finalTrailers is called after the Handler exits and returns a non-nil
   529  // value if the Handler set any trailers.
   530  func (w *response) finalTrailers() Header {
   531  	var t Header
   532  	for k, vv := range w.handlerHeader {
   533  		if kk, found := strings.CutPrefix(k, TrailerPrefix); found {
   534  			if t == nil {
   535  				t = make(Header)
   536  			}
   537  			t[kk] = vv
   538  		}
   539  	}
   540  	for _, k := range w.trailers {
   541  		if t == nil {
   542  			t = make(Header)
   543  		}
   544  		for _, v := range w.handlerHeader[k] {
   545  			t.Add(k, v)
   546  		}
   547  	}
   548  	return t
   549  }
   550  
   551  // declareTrailer is called for each Trailer header when the
   552  // response header is written. It notes that a header will need to be
   553  // written in the trailers at the end of the response.
   554  func (w *response) declareTrailer(k string) {
   555  	k = CanonicalHeaderKey(k)
   556  	if !httpguts.ValidTrailerHeader(k) {
   557  		// Forbidden by RFC 7230, section 4.1.2
   558  		return
   559  	}
   560  	w.trailers = append(w.trailers, k)
   561  }
   562  
   563  // requestTooLarge is called by maxBytesReader when too much input has
   564  // been read from the client.
   565  func (w *response) requestTooLarge() {
   566  	w.closeAfterReply = true
   567  	w.requestBodyLimitHit = true
   568  	if !w.wroteHeader {
   569  		w.Header().Set("Connection", "close")
   570  	}
   571  }
   572  
   573  // disableWriteContinue stops Request.Body.Read from sending an automatic 100-Continue.
   574  // If a 100-Continue is being written, it waits for it to complete before continuing.
   575  func (w *response) disableWriteContinue() {
   576  	w.writeContinueMu.Lock()
   577  	w.canWriteContinue.Store(false)
   578  	w.writeContinueMu.Unlock()
   579  }
   580  
   581  // writerOnly hides an io.Writer value's optional ReadFrom method
   582  // from io.Copy.
   583  type writerOnly struct {
   584  	io.Writer
   585  }
   586  
   587  // ReadFrom is here to optimize copying from an [*os.File] regular file
   588  // to a [*net.TCPConn] with sendfile, or from a supported src type such
   589  // as a *net.TCPConn on Linux with splice.
   590  func (w *response) ReadFrom(src io.Reader) (n int64, err error) {
   591  	buf := getCopyBuf()
   592  	defer putCopyBuf(buf)
   593  
   594  	// Our underlying w.conn.rwc is usually a *TCPConn (with its
   595  	// own ReadFrom method). If not, just fall back to the normal
   596  	// copy method.
   597  	rf, ok := w.conn.rwc.(io.ReaderFrom)
   598  	if !ok {
   599  		return io.CopyBuffer(writerOnly{w}, src, buf)
   600  	}
   601  
   602  	// Copy the first sniffLen bytes before switching to ReadFrom.
   603  	// This ensures we don't start writing the response before the
   604  	// source is available (see golang.org/issue/5660) and provides
   605  	// enough bytes to perform Content-Type sniffing when required.
   606  	if !w.cw.wroteHeader {
   607  		n0, err := io.CopyBuffer(writerOnly{w}, io.LimitReader(src, internal.SniffLen), buf)
   608  		n += n0
   609  		if err != nil || n0 < internal.SniffLen {
   610  			return n, err
   611  		}
   612  	}
   613  
   614  	w.w.Flush()  // get rid of any previous writes
   615  	w.cw.flush() // make sure Header is written; flush data to rwc
   616  
   617  	// Now that cw has been flushed, its chunking field is guaranteed initialized.
   618  	if !w.cw.chunking && w.bodyAllowed() && w.req.Method != "HEAD" {
   619  		n0, err := rf.ReadFrom(src)
   620  		n += n0
   621  		w.written += n0
   622  		return n, err
   623  	}
   624  
   625  	n0, err := io.CopyBuffer(writerOnly{w}, src, buf)
   626  	n += n0
   627  	return n, err
   628  }
   629  
   630  // debugServerConnections controls whether all server connections are wrapped
   631  // with a verbose logging wrapper.
   632  const debugServerConnections = false
   633  
   634  // Create new connection from rwc.
   635  func (s *Server) newConn(rwc net.Conn) *conn {
   636  	c := &conn{
   637  		server: s,
   638  		rwc:    rwc,
   639  	}
   640  	if debugServerConnections {
   641  		c.rwc = newLoggingConn("server", c.rwc)
   642  	}
   643  	return c
   644  }
   645  
   646  type readResult struct {
   647  	_   incomparable
   648  	n   int
   649  	err error
   650  	b   byte // byte read, if n == 1
   651  }
   652  
   653  // connReader is the io.Reader wrapper used by *conn. It combines a
   654  // selectively-activated io.LimitedReader (to bound request header
   655  // read sizes) with support for selectively keeping an io.Reader.Read
   656  // call blocked in a background goroutine to wait for activity and
   657  // trigger a CloseNotifier channel.
   658  // After a Handler has hijacked the conn and exited, connReader behaves like a
   659  // proxy for the net.Conn and the aforementioned behavior is bypassed.
   660  type connReader struct {
   661  	rwc net.Conn // rwc is the underlying network connection.
   662  
   663  	mu      sync.Mutex // guards following
   664  	conn    *conn      // conn is nil after handler exit.
   665  	hasByte bool
   666  	byteBuf [1]byte
   667  	cond    *sync.Cond
   668  	inRead  bool
   669  	aborted bool  // set true before conn.rwc deadline is set to past
   670  	remain  int64 // bytes remaining
   671  }
   672  
   673  func (cr *connReader) lock() {
   674  	cr.mu.Lock()
   675  	if cr.cond == nil {
   676  		cr.cond = sync.NewCond(&cr.mu)
   677  	}
   678  }
   679  
   680  func (cr *connReader) unlock() { cr.mu.Unlock() }
   681  
   682  func (cr *connReader) releaseConn() {
   683  	cr.lock()
   684  	defer cr.unlock()
   685  	cr.conn = nil
   686  }
   687  
   688  func (cr *connReader) startBackgroundRead() {
   689  	cr.lock()
   690  	defer cr.unlock()
   691  	if cr.inRead {
   692  		panic("invalid concurrent Body.Read call")
   693  	}
   694  	if cr.hasByte {
   695  		return
   696  	}
   697  	cr.inRead = true
   698  	cr.rwc.SetReadDeadline(time.Time{})
   699  	go cr.backgroundRead()
   700  }
   701  
   702  func (cr *connReader) backgroundRead() {
   703  	n, err := cr.rwc.Read(cr.byteBuf[:])
   704  	cr.lock()
   705  	if n == 1 {
   706  		cr.hasByte = true
   707  		// We were past the end of the previous request's body already
   708  		// (since we wouldn't be in a background read otherwise), so
   709  		// this is a pipelined HTTP request. Prior to Go 1.11 we used to
   710  		// send on the CloseNotify channel and cancel the context here,
   711  		// but the behavior was documented as only "may", and we only
   712  		// did that because that's how CloseNotify accidentally behaved
   713  		// in very early Go releases prior to context support. Once we
   714  		// added context support, people used a Handler's
   715  		// Request.Context() and passed it along. Having that context
   716  		// cancel on pipelined HTTP requests caused problems.
   717  		// Fortunately, almost nothing uses HTTP/1.x pipelining.
   718  		// Unfortunately, apt-get does, or sometimes does.
   719  		// New Go 1.11 behavior: don't fire CloseNotify or cancel
   720  		// contexts on pipelined requests. Shouldn't affect people, but
   721  		// fixes cases like Issue 23921. This does mean that a client
   722  		// closing their TCP connection after sending a pipelined
   723  		// request won't cancel the context, but we'll catch that on any
   724  		// write failure (in checkConnErrorWriter.Write).
   725  		// If the server never writes, yes, there are still contrived
   726  		// server & client behaviors where this fails to ever cancel the
   727  		// context, but that's kinda why HTTP/1.x pipelining died
   728  		// anyway.
   729  	}
   730  	if ne, ok := err.(net.Error); ok && cr.aborted && ne.Timeout() {
   731  		// Ignore this error. It's the expected error from
   732  		// another goroutine calling abortPendingRead.
   733  	} else if err != nil {
   734  		cr.handleReadErrorLocked(err)
   735  	}
   736  	cr.aborted = false
   737  	cr.inRead = false
   738  	cr.unlock()
   739  	cr.cond.Broadcast()
   740  }
   741  
   742  func (cr *connReader) abortPendingRead() {
   743  	cr.lock()
   744  	defer cr.unlock()
   745  	if !cr.inRead {
   746  		return
   747  	}
   748  	cr.aborted = true
   749  	cr.rwc.SetReadDeadline(aLongTimeAgo)
   750  	for cr.inRead {
   751  		cr.cond.Wait()
   752  	}
   753  	cr.rwc.SetReadDeadline(time.Time{})
   754  }
   755  
   756  func (cr *connReader) setReadLimit(remain int64) { cr.remain = remain }
   757  func (cr *connReader) setInfiniteReadLimit()     { cr.remain = maxInt64 }
   758  func (cr *connReader) hitReadLimit() bool        { return cr.remain <= 0 }
   759  
   760  // handleReadErrorLocked is called whenever a Read from the client returns a
   761  // non-nil error.
   762  //
   763  // The provided non-nil err is almost always io.EOF or a "use of
   764  // closed network connection". In any case, the error is not
   765  // particularly interesting, except perhaps for debugging during
   766  // development. Any error means the connection is dead and we should
   767  // down its context.
   768  //
   769  // The caller must hold connReader.mu.
   770  func (cr *connReader) handleReadErrorLocked(_ error) {
   771  	if cr.conn == nil {
   772  		return
   773  	}
   774  	cr.conn.cancelCtx()
   775  	if res := cr.conn.curReq.Load(); res != nil {
   776  		res.closeNotify()
   777  	}
   778  }
   779  
   780  func (cr *connReader) Read(p []byte) (n int, err error) {
   781  	cr.lock()
   782  	if cr.conn == nil {
   783  		cr.unlock()
   784  		return cr.rwc.Read(p)
   785  	}
   786  	if cr.inRead {
   787  		hijacked := cr.conn.hijacked()
   788  		cr.unlock()
   789  		if hijacked {
   790  			panic("invalid Body.Read call. After hijacked, the original Request must not be used")
   791  		}
   792  		panic("invalid concurrent Body.Read call")
   793  	}
   794  	if cr.hitReadLimit() {
   795  		cr.unlock()
   796  		return 0, io.EOF
   797  	}
   798  	if len(p) == 0 {
   799  		cr.unlock()
   800  		return 0, nil
   801  	}
   802  	if int64(len(p)) > cr.remain {
   803  		p = p[:cr.remain]
   804  	}
   805  	if cr.hasByte {
   806  		p[0] = cr.byteBuf[0]
   807  		cr.hasByte = false
   808  		cr.unlock()
   809  		return 1, nil
   810  	}
   811  	cr.inRead = true
   812  	cr.unlock()
   813  	n, err = cr.rwc.Read(p)
   814  
   815  	cr.lock()
   816  	cr.inRead = false
   817  	if err != nil {
   818  		cr.handleReadErrorLocked(err)
   819  	}
   820  	cr.remain -= int64(n)
   821  	cr.unlock()
   822  
   823  	cr.cond.Broadcast()
   824  	return n, err
   825  }
   826  
   827  var (
   828  	bufioReaderPool   sync.Pool
   829  	bufioWriter2kPool sync.Pool
   830  	bufioWriter4kPool sync.Pool
   831  )
   832  
   833  const copyBufPoolSize = 32 * 1024
   834  
   835  var copyBufPool = sync.Pool{New: func() any { return new([copyBufPoolSize]byte) }}
   836  
   837  func getCopyBuf() []byte {
   838  	return copyBufPool.Get().(*[copyBufPoolSize]byte)[:]
   839  }
   840  
   841  func putCopyBuf(b []byte) {
   842  	if len(b) != copyBufPoolSize {
   843  		panic("trying to put back buffer of the wrong size in the copyBufPool")
   844  	}
   845  	copyBufPool.Put((*[copyBufPoolSize]byte)(b))
   846  }
   847  
   848  func bufioWriterPool(size int) *sync.Pool {
   849  	switch size {
   850  	case 2 << 10:
   851  		return &bufioWriter2kPool
   852  	case 4 << 10:
   853  		return &bufioWriter4kPool
   854  	}
   855  	return nil
   856  }
   857  
   858  func newBufioReader(r io.Reader) *bufio.Reader {
   859  	if v := bufioReaderPool.Get(); v != nil {
   860  		br := v.(*bufio.Reader)
   861  		br.Reset(r)
   862  		return br
   863  	}
   864  	// Note: if this reader size is ever changed, update
   865  	// TestHandlerBodyClose's assumptions.
   866  	return bufio.NewReader(r)
   867  }
   868  
   869  func putBufioReader(br *bufio.Reader) {
   870  	br.Reset(nil)
   871  	bufioReaderPool.Put(br)
   872  }
   873  
   874  func newBufioWriterSize(w io.Writer, size int) *bufio.Writer {
   875  	pool := bufioWriterPool(size)
   876  	if pool != nil {
   877  		if v := pool.Get(); v != nil {
   878  			bw := v.(*bufio.Writer)
   879  			bw.Reset(w)
   880  			return bw
   881  		}
   882  	}
   883  	return bufio.NewWriterSize(w, size)
   884  }
   885  
   886  func putBufioWriter(bw *bufio.Writer) {
   887  	bw.Reset(nil)
   888  	if pool := bufioWriterPool(bw.Available()); pool != nil {
   889  		pool.Put(bw)
   890  	}
   891  }
   892  
   893  // DefaultMaxHeaderBytes is the maximum permitted size of the headers
   894  // in an HTTP request.
   895  // This can be overridden by setting [Server.MaxHeaderBytes].
   896  const DefaultMaxHeaderBytes = 1 << 20 // 1 MB
   897  
   898  func (s *Server) maxHeaderBytes() int {
   899  	if s.MaxHeaderBytes > 0 {
   900  		return s.MaxHeaderBytes
   901  	}
   902  	return DefaultMaxHeaderBytes
   903  }
   904  
   905  func (s *Server) initialReadLimitSize() int64 {
   906  	return int64(s.maxHeaderBytes()) + 4096 // bufio slop
   907  }
   908  
   909  // tlsHandshakeTimeout returns the time limit permitted for the TLS
   910  // handshake, or zero for unlimited.
   911  //
   912  // It returns the minimum of any positive ReadHeaderTimeout,
   913  // ReadTimeout, or WriteTimeout.
   914  func (s *Server) tlsHandshakeTimeout() time.Duration {
   915  	var ret time.Duration
   916  	for _, v := range [...]time.Duration{
   917  		s.ReadHeaderTimeout,
   918  		s.ReadTimeout,
   919  		s.WriteTimeout,
   920  	} {
   921  		if v <= 0 {
   922  			continue
   923  		}
   924  		if ret == 0 || v < ret {
   925  			ret = v
   926  		}
   927  	}
   928  	return ret
   929  }
   930  
   931  // wrapper around io.ReadCloser which on first read, sends an
   932  // HTTP/1.1 100 Continue header
   933  type expectContinueReader struct {
   934  	resp       *response
   935  	readCloser io.ReadCloser
   936  	closed     atomic.Bool
   937  	sawEOF     atomic.Bool
   938  }
   939  
   940  func (ecr *expectContinueReader) Read(p []byte) (n int, err error) {
   941  	if ecr.closed.Load() {
   942  		return 0, ErrBodyReadAfterClose
   943  	}
   944  	w := ecr.resp
   945  	if w.canWriteContinue.Load() {
   946  		w.writeContinueMu.Lock()
   947  		if w.canWriteContinue.Load() {
   948  			w.conn.bufw.WriteString("HTTP/1.1 100 Continue\r\n\r\n")
   949  			w.conn.bufw.Flush()
   950  			w.canWriteContinue.Store(false)
   951  		}
   952  		w.writeContinueMu.Unlock()
   953  	}
   954  	n, err = ecr.readCloser.Read(p)
   955  	if err == io.EOF {
   956  		ecr.sawEOF.Store(true)
   957  	}
   958  	return
   959  }
   960  
   961  func (ecr *expectContinueReader) Close() error {
   962  	ecr.closed.Store(true)
   963  	return ecr.readCloser.Close()
   964  }
   965  
   966  // TimeFormat is the time format to use when generating times in HTTP
   967  // headers. It is like [time.RFC1123] but hard-codes GMT as the time
   968  // zone. The time being formatted must be in UTC for Format to
   969  // generate the correct format.
   970  //
   971  // For parsing this time format, see [ParseTime].
   972  const TimeFormat = "Mon, 02 Jan 2006 15:04:05 GMT"
   973  
   974  var errTooLarge = errors.New("http: request too large")
   975  
   976  // Read next request from connection.
   977  func (c *conn) readRequest(ctx context.Context) (w *response, err error) {
   978  	if c.hijacked() {
   979  		return nil, ErrHijacked
   980  	}
   981  
   982  	var (
   983  		wholeReqDeadline time.Time // or zero if none
   984  		hdrDeadline      time.Time // or zero if none
   985  	)
   986  	t0 := time.Now()
   987  	if d := c.server.readHeaderTimeout(); d > 0 {
   988  		hdrDeadline = t0.Add(d)
   989  	}
   990  	if d := c.server.ReadTimeout; d > 0 {
   991  		wholeReqDeadline = t0.Add(d)
   992  	}
   993  	c.rwc.SetReadDeadline(hdrDeadline)
   994  	if d := c.server.WriteTimeout; d > 0 {
   995  		defer func() {
   996  			c.rwc.SetWriteDeadline(time.Now().Add(d))
   997  		}()
   998  	}
   999  
  1000  	c.r.setReadLimit(c.server.initialReadLimitSize())
  1001  	if c.lastMethod == "POST" {
  1002  		// RFC 7230 section 3 tolerance for old buggy clients.
  1003  		peek, _ := c.bufr.Peek(4) // ReadRequest will get err below
  1004  		c.bufr.Discard(numLeadingCRorLF(peek))
  1005  	}
  1006  	req, err := readRequest(c.bufr)
  1007  	if err != nil {
  1008  		if c.r.hitReadLimit() {
  1009  			return nil, errTooLarge
  1010  		}
  1011  		return nil, err
  1012  	}
  1013  
  1014  	if !http1ServerSupportsRequest(req) {
  1015  		return nil, statusError{StatusHTTPVersionNotSupported, "unsupported protocol version"}
  1016  	}
  1017  
  1018  	c.lastMethod = req.Method
  1019  	c.r.setInfiniteReadLimit()
  1020  
  1021  	hosts, haveHost := req.Header["Host"]
  1022  	isH2Upgrade := req.isH2Upgrade()
  1023  	if req.ProtoAtLeast(1, 1) && (!haveHost || len(hosts) == 0) && !isH2Upgrade && req.Method != "CONNECT" {
  1024  		return nil, badRequestError("missing required Host header")
  1025  	}
  1026  	if len(hosts) == 1 && !httpguts.ValidHostHeader(hosts[0]) {
  1027  		return nil, badRequestError("malformed Host header")
  1028  	}
  1029  	for k, vv := range req.Header {
  1030  		if !httpguts.ValidHeaderFieldName(k) {
  1031  			return nil, badRequestError("invalid header name")
  1032  		}
  1033  		for _, v := range vv {
  1034  			if !httpguts.ValidHeaderFieldValue(v) {
  1035  				return nil, badRequestError("invalid header value")
  1036  			}
  1037  		}
  1038  	}
  1039  	delete(req.Header, "Host")
  1040  
  1041  	ctx, cancelCtx := context.WithCancel(ctx)
  1042  	req.ctx = ctx
  1043  	req.RemoteAddr = c.remoteAddr
  1044  	req.TLS = c.tlsState
  1045  	if body, ok := req.Body.(*body); ok {
  1046  		body.doEarlyClose = true
  1047  	}
  1048  
  1049  	// Adjust the read deadline if necessary.
  1050  	if !hdrDeadline.Equal(wholeReqDeadline) {
  1051  		c.rwc.SetReadDeadline(wholeReqDeadline)
  1052  	}
  1053  
  1054  	w = &response{
  1055  		conn:          c,
  1056  		cancelCtx:     cancelCtx,
  1057  		req:           req,
  1058  		reqBody:       req.Body,
  1059  		handlerHeader: make(Header),
  1060  		contentLength: -1,
  1061  
  1062  		// We populate these ahead of time so we're not
  1063  		// reading from req.Header after their Handler starts
  1064  		// and maybe mutates it (Issue 14940)
  1065  		wants10KeepAlive: req.wantsHttp10KeepAlive(),
  1066  		wantsClose:       req.wantsClose(),
  1067  	}
  1068  	if isH2Upgrade {
  1069  		w.closeAfterReply = true
  1070  	}
  1071  	w.cw.res = w
  1072  	w.w = newBufioWriterSize(&w.cw, bufferBeforeChunkingSize)
  1073  	return w, nil
  1074  }
  1075  
  1076  // http1ServerSupportsRequest reports whether Go's HTTP/1.x server
  1077  // supports the given request.
  1078  func http1ServerSupportsRequest(req *Request) bool {
  1079  	if req.ProtoMajor == 1 {
  1080  		return true
  1081  	}
  1082  	// Accept "PRI * HTTP/2.0" upgrade requests, so Handlers can
  1083  	// wire up their own HTTP/2 upgrades.
  1084  	if req.ProtoMajor == 2 && req.ProtoMinor == 0 &&
  1085  		req.Method == "PRI" && req.RequestURI == "*" {
  1086  		return true
  1087  	}
  1088  	// Reject HTTP/0.x, and all other HTTP/2+ requests (which
  1089  	// aren't encoded in ASCII anyway).
  1090  	return false
  1091  }
  1092  
  1093  func (w *response) Header() Header {
  1094  	if w.cw.header == nil && w.wroteHeader && !w.cw.wroteHeader {
  1095  		// Accessing the header between logically writing it
  1096  		// and physically writing it means we need to allocate
  1097  		// a clone to snapshot the logically written state.
  1098  		w.cw.header = w.handlerHeader.Clone()
  1099  	}
  1100  	w.calledHeader = true
  1101  	return w.handlerHeader
  1102  }
  1103  
  1104  // maxPostHandlerReadBytes is the max number of Request.Body bytes not
  1105  // consumed by a handler that the server will read from the client
  1106  // in order to keep a connection alive. If there are more bytes
  1107  // than this, the server, to be paranoid, instead sends a
  1108  // "Connection close" response.
  1109  //
  1110  // This number is approximately what a typical machine's TCP buffer
  1111  // size is anyway.  (if we have the bytes on the machine, we might as
  1112  // well read them)
  1113  const maxPostHandlerReadBytes = 256 << 10
  1114  
  1115  func checkWriteHeaderCode(code int) {
  1116  	// Issue 22880: require valid WriteHeader status codes.
  1117  	// For now we only enforce that it's three digits.
  1118  	// In the future we might block things over 599 (600 and above aren't defined
  1119  	// at https://httpwg.org/specs/rfc7231.html#status.codes).
  1120  	// But for now any three digits.
  1121  	//
  1122  	// We used to send "HTTP/1.1 000 0" on the wire in responses but there's
  1123  	// no equivalent bogus thing we can realistically send in HTTP/2,
  1124  	// so we'll consistently panic instead and help people find their bugs
  1125  	// early. (We can't return an error from WriteHeader even if we wanted to.)
  1126  	if code < 100 || code > 999 {
  1127  		panic(fmt.Sprintf("invalid WriteHeader code %v", code))
  1128  	}
  1129  }
  1130  
  1131  // relevantCaller searches the call stack for the first function outside of net/http.
  1132  // The purpose of this function is to provide more helpful error messages.
  1133  func relevantCaller() runtime.Frame {
  1134  	pc := make([]uintptr, 16)
  1135  	n := runtime.Callers(1, pc)
  1136  	frames := runtime.CallersFrames(pc[:n])
  1137  	var frame runtime.Frame
  1138  	for {
  1139  		frame, more := frames.Next()
  1140  		if !strings.HasPrefix(frame.Function, "net/http.") {
  1141  			return frame
  1142  		}
  1143  		if !more {
  1144  			break
  1145  		}
  1146  	}
  1147  	return frame
  1148  }
  1149  
  1150  func (w *response) WriteHeader(code int) {
  1151  	if w.conn.hijacked() {
  1152  		caller := relevantCaller()
  1153  		w.conn.server.logf("http: response.WriteHeader on hijacked connection from %s (%s:%d)", caller.Function, path.Base(caller.File), caller.Line)
  1154  		return
  1155  	}
  1156  	if w.wroteHeader {
  1157  		caller := relevantCaller()
  1158  		w.conn.server.logf("http: superfluous response.WriteHeader call from %s (%s:%d)", caller.Function, path.Base(caller.File), caller.Line)
  1159  		return
  1160  	}
  1161  	checkWriteHeaderCode(code)
  1162  
  1163  	if code < 101 || code > 199 {
  1164  		// Sending a 100 Continue or any non-1xx header disables the
  1165  		// automatically-sent 100 Continue from Request.Body.Read.
  1166  		w.disableWriteContinue()
  1167  	}
  1168  
  1169  	// Handle informational headers.
  1170  	//
  1171  	// We shouldn't send any further headers after 101 Switching Protocols,
  1172  	// so it takes the non-informational path.
  1173  	if code >= 100 && code <= 199 && code != StatusSwitchingProtocols {
  1174  		writeStatusLine(w.conn.bufw, w.req.ProtoAtLeast(1, 1), code, w.statusBuf[:])
  1175  
  1176  		// Per RFC 8297 we must not clear the current header map
  1177  		w.handlerHeader.WriteSubset(w.conn.bufw, excludedHeadersNoBody)
  1178  		w.conn.bufw.Write(crlf)
  1179  		w.conn.bufw.Flush()
  1180  
  1181  		return
  1182  	}
  1183  
  1184  	w.wroteHeader = true
  1185  	w.status = code
  1186  
  1187  	if w.calledHeader && w.cw.header == nil {
  1188  		w.cw.header = w.handlerHeader.Clone()
  1189  	}
  1190  
  1191  	if cl := w.handlerHeader.get("Content-Length"); cl != "" {
  1192  		v, err := strconv.ParseInt(cl, 10, 64)
  1193  		if err == nil && v >= 0 {
  1194  			w.contentLength = v
  1195  		} else {
  1196  			w.conn.server.logf("http: invalid Content-Length of %q", cl)
  1197  			w.handlerHeader.Del("Content-Length")
  1198  		}
  1199  	}
  1200  }
  1201  
  1202  // extraHeader is the set of headers sometimes added by chunkWriter.writeHeader.
  1203  // This type is used to avoid extra allocations from cloning and/or populating
  1204  // the response Header map and all its 1-element slices.
  1205  type extraHeader struct {
  1206  	contentType      string
  1207  	connection       string
  1208  	transferEncoding string
  1209  	date             []byte // written if not nil
  1210  	contentLength    []byte // written if not nil
  1211  }
  1212  
  1213  // Sorted the same as extraHeader.Write's loop.
  1214  var extraHeaderKeys = [][]byte{
  1215  	[]byte("Content-Type"),
  1216  	[]byte("Connection"),
  1217  	[]byte("Transfer-Encoding"),
  1218  }
  1219  
  1220  var (
  1221  	headerContentLength = []byte("Content-Length: ")
  1222  	headerDate          = []byte("Date: ")
  1223  )
  1224  
  1225  // Write writes the headers described in h to w.
  1226  //
  1227  // This method has a value receiver, despite the somewhat large size
  1228  // of h, because it prevents an allocation. The escape analysis isn't
  1229  // smart enough to realize this function doesn't mutate h.
  1230  func (h extraHeader) Write(w *bufio.Writer) {
  1231  	if h.date != nil {
  1232  		w.Write(headerDate)
  1233  		w.Write(h.date)
  1234  		w.Write(crlf)
  1235  	}
  1236  	if h.contentLength != nil {
  1237  		w.Write(headerContentLength)
  1238  		w.Write(h.contentLength)
  1239  		w.Write(crlf)
  1240  	}
  1241  	for i, v := range []string{h.contentType, h.connection, h.transferEncoding} {
  1242  		if v != "" {
  1243  			w.Write(extraHeaderKeys[i])
  1244  			w.Write(colonSpace)
  1245  			w.WriteString(v)
  1246  			w.Write(crlf)
  1247  		}
  1248  	}
  1249  }
  1250  
  1251  // writeHeader finalizes the header sent to the client and writes it
  1252  // to cw.res.conn.bufw.
  1253  //
  1254  // p is not written by writeHeader, but is the first chunk of the body
  1255  // that will be written. It is sniffed for a Content-Type if none is
  1256  // set explicitly. It's also used to set the Content-Length, if the
  1257  // total body size was small and the handler has already finished
  1258  // running.
  1259  func (cw *chunkWriter) writeHeader(p []byte) {
  1260  	if cw.wroteHeader {
  1261  		return
  1262  	}
  1263  	cw.wroteHeader = true
  1264  
  1265  	w := cw.res
  1266  	keepAlivesEnabled := w.conn.server.doKeepAlives()
  1267  	isHEAD := w.req.Method == "HEAD"
  1268  
  1269  	// header is written out to w.conn.buf below. Depending on the
  1270  	// state of the handler, we either own the map or not. If we
  1271  	// don't own it, the exclude map is created lazily for
  1272  	// WriteSubset to remove headers. The setHeader struct holds
  1273  	// headers we need to add.
  1274  	header := cw.header
  1275  	owned := header != nil
  1276  	if !owned {
  1277  		header = w.handlerHeader
  1278  	}
  1279  	var excludeHeader map[string]bool
  1280  	delHeader := func(key string) {
  1281  		if owned {
  1282  			header.Del(key)
  1283  			return
  1284  		}
  1285  		if _, ok := header[key]; !ok {
  1286  			return
  1287  		}
  1288  		if excludeHeader == nil {
  1289  			excludeHeader = make(map[string]bool)
  1290  		}
  1291  		excludeHeader[key] = true
  1292  	}
  1293  	var setHeader extraHeader
  1294  
  1295  	// Don't write out the fake "Trailer:foo" keys. See TrailerPrefix.
  1296  	trailers := false
  1297  	for k := range cw.header {
  1298  		if strings.HasPrefix(k, TrailerPrefix) {
  1299  			if excludeHeader == nil {
  1300  				excludeHeader = make(map[string]bool)
  1301  			}
  1302  			excludeHeader[k] = true
  1303  			trailers = true
  1304  		}
  1305  	}
  1306  	for _, v := range cw.header["Trailer"] {
  1307  		trailers = true
  1308  		foreachHeaderElement(v, cw.res.declareTrailer)
  1309  	}
  1310  
  1311  	te := header.get("Transfer-Encoding")
  1312  	hasTE := te != ""
  1313  
  1314  	// If the handler is done but never sent a Content-Length
  1315  	// response header and this is our first (and last) write, set
  1316  	// it, even to zero. This helps HTTP/1.0 clients keep their
  1317  	// "keep-alive" connections alive.
  1318  	// Exceptions: 304/204/1xx responses never get Content-Length, and if
  1319  	// it was a HEAD request, we don't know the difference between
  1320  	// 0 actual bytes and 0 bytes because the handler noticed it
  1321  	// was a HEAD request and chose not to write anything. So for
  1322  	// HEAD, the handler should either write the Content-Length or
  1323  	// write non-zero bytes. If it's actually 0 bytes and the
  1324  	// handler never looked at the Request.Method, we just don't
  1325  	// send a Content-Length header.
  1326  	// Further, we don't send an automatic Content-Length if they
  1327  	// set a Transfer-Encoding, because they're generally incompatible.
  1328  	if w.handlerDone.Load() && !trailers && !hasTE && bodyAllowedForStatus(w.status) && !header.has("Content-Length") && (!isHEAD || len(p) > 0) {
  1329  		w.contentLength = int64(len(p))
  1330  		setHeader.contentLength = strconv.AppendInt(cw.res.clenBuf[:0], int64(len(p)), 10)
  1331  	}
  1332  
  1333  	// If this was an HTTP/1.0 request with keep-alive and we sent a
  1334  	// Content-Length back, we can make this a keep-alive response ...
  1335  	if w.wants10KeepAlive && keepAlivesEnabled {
  1336  		sentLength := header.get("Content-Length") != ""
  1337  		if sentLength && header.get("Connection") == "keep-alive" {
  1338  			w.closeAfterReply = false
  1339  		}
  1340  	}
  1341  
  1342  	// Check for an explicit (and valid) Content-Length header.
  1343  	hasCL := w.contentLength != -1
  1344  
  1345  	if w.wants10KeepAlive && (isHEAD || hasCL || !bodyAllowedForStatus(w.status)) {
  1346  		_, connectionHeaderSet := header["Connection"]
  1347  		if !connectionHeaderSet {
  1348  			setHeader.connection = "keep-alive"
  1349  		}
  1350  	} else if !w.req.ProtoAtLeast(1, 1) || w.wantsClose {
  1351  		w.closeAfterReply = true
  1352  	}
  1353  
  1354  	if header.get("Connection") == "close" || !keepAlivesEnabled {
  1355  		w.closeAfterReply = true
  1356  	}
  1357  
  1358  	// If the client wanted a 100-continue but we never sent it to
  1359  	// them (or, more strictly: we never finished reading their
  1360  	// request body), don't reuse this connection.
  1361  	//
  1362  	// This behavior was first added on the theory that we don't know
  1363  	// if the next bytes on the wire are going to be the remainder of
  1364  	// the request body or the subsequent request (see issue 11549),
  1365  	// but that's not correct: If we keep using the connection,
  1366  	// the client is required to send the request body whether we
  1367  	// asked for it or not.
  1368  	//
  1369  	// We probably do want to skip reusing the connection in most cases,
  1370  	// however. If the client is offering a large request body that we
  1371  	// don't intend to use, then it's better to close the connection
  1372  	// than to read the body. For now, assume that if we're sending
  1373  	// headers, the handler is done reading the body and we should
  1374  	// drop the connection if we haven't seen EOF.
  1375  	if ecr, ok := w.req.Body.(*expectContinueReader); ok && !ecr.sawEOF.Load() {
  1376  		w.closeAfterReply = true
  1377  	}
  1378  
  1379  	// We do this by default because there are a number of clients that
  1380  	// send a full request before starting to read the response, and they
  1381  	// can deadlock if we start writing the response with unconsumed body
  1382  	// remaining. See Issue 15527 for some history.
  1383  	//
  1384  	// If full duplex mode has been enabled with ResponseController.EnableFullDuplex,
  1385  	// then leave the request body alone.
  1386  	//
  1387  	// We don't take this path when w.closeAfterReply is set.
  1388  	// We may not need to consume the request to get ready for the next one
  1389  	// (since we're closing the conn), but a client which sends a full request
  1390  	// before reading a response may deadlock in this case.
  1391  	// This behavior has been present since CL 5268043 (2011), however,
  1392  	// so it doesn't seem to be causing problems.
  1393  	if w.req.ContentLength != 0 && !w.closeAfterReply && !w.fullDuplex {
  1394  		var discard, tooBig bool
  1395  
  1396  		switch bdy := w.req.Body.(type) {
  1397  		case *expectContinueReader:
  1398  			// We only get here if we have already fully consumed the request body
  1399  			// (see above).
  1400  		case *body:
  1401  			bdy.mu.Lock()
  1402  			switch {
  1403  			case bdy.closed:
  1404  				if !bdy.sawEOF {
  1405  					// Body was closed in handler with non-EOF error.
  1406  					w.closeAfterReply = true
  1407  				}
  1408  			case bdy.unreadDataSizeLocked() >= maxPostHandlerReadBytes:
  1409  				tooBig = true
  1410  			default:
  1411  				discard = true
  1412  			}
  1413  			bdy.mu.Unlock()
  1414  		default:
  1415  			discard = true
  1416  		}
  1417  
  1418  		if discard {
  1419  			_, err := io.CopyN(io.Discard, w.reqBody, maxPostHandlerReadBytes+1)
  1420  			switch err {
  1421  			case nil:
  1422  				// There must be even more data left over.
  1423  				tooBig = true
  1424  			case ErrBodyReadAfterClose:
  1425  				// Body was already consumed and closed.
  1426  			case io.EOF:
  1427  				// The remaining body was just consumed, close it.
  1428  				err = w.reqBody.Close()
  1429  				if err != nil {
  1430  					w.closeAfterReply = true
  1431  				}
  1432  			default:
  1433  				// Some other kind of error occurred, like a read timeout, or
  1434  				// corrupt chunked encoding. In any case, whatever remains
  1435  				// on the wire must not be parsed as another HTTP request.
  1436  				w.closeAfterReply = true
  1437  			}
  1438  		}
  1439  
  1440  		if tooBig {
  1441  			w.requestTooLarge()
  1442  			delHeader("Connection")
  1443  			setHeader.connection = "close"
  1444  		}
  1445  	}
  1446  
  1447  	code := w.status
  1448  	if bodyAllowedForStatus(code) {
  1449  		// If no content type, apply sniffing algorithm to body.
  1450  		_, haveType := header["Content-Type"]
  1451  
  1452  		// If the Content-Encoding was set and is non-blank,
  1453  		// we shouldn't sniff the body. See Issue 31753.
  1454  		ce := header.Get("Content-Encoding")
  1455  		hasCE := len(ce) > 0
  1456  		if !hasCE && !haveType && !hasTE && len(p) > 0 {
  1457  			setHeader.contentType = DetectContentType(p)
  1458  		}
  1459  	} else {
  1460  		for _, k := range suppressedHeaders(code) {
  1461  			delHeader(k)
  1462  		}
  1463  	}
  1464  
  1465  	if !header.has("Date") {
  1466  		setHeader.date = time.Now().UTC().AppendFormat(cw.res.dateBuf[:0], TimeFormat)
  1467  	}
  1468  
  1469  	if hasCL && hasTE && te != "identity" {
  1470  		// TODO: return an error if WriteHeader gets a return parameter
  1471  		// For now just ignore the Content-Length.
  1472  		w.conn.server.logf("http: WriteHeader called with both Transfer-Encoding of %q and a Content-Length of %d",
  1473  			te, w.contentLength)
  1474  		delHeader("Content-Length")
  1475  		hasCL = false
  1476  	}
  1477  
  1478  	if w.req.Method == "HEAD" || !bodyAllowedForStatus(code) || code == StatusNoContent {
  1479  		// Response has no body.
  1480  		delHeader("Transfer-Encoding")
  1481  	} else if hasCL {
  1482  		// Content-Length has been provided, so no chunking is to be done.
  1483  		delHeader("Transfer-Encoding")
  1484  	} else if w.req.ProtoAtLeast(1, 1) {
  1485  		// HTTP/1.1 or greater: Transfer-Encoding has been set to identity, and no
  1486  		// content-length has been provided. The connection must be closed after the
  1487  		// reply is written, and no chunking is to be done. This is the setup
  1488  		// recommended in the Server-Sent Events candidate recommendation 11,
  1489  		// section 8.
  1490  		if hasTE && te == "identity" {
  1491  			cw.chunking = false
  1492  			w.closeAfterReply = true
  1493  			delHeader("Transfer-Encoding")
  1494  		} else {
  1495  			// HTTP/1.1 or greater: use chunked transfer encoding
  1496  			// to avoid closing the connection at EOF.
  1497  			cw.chunking = true
  1498  			setHeader.transferEncoding = "chunked"
  1499  			if hasTE && te == "chunked" {
  1500  				// We will send the chunked Transfer-Encoding header later.
  1501  				delHeader("Transfer-Encoding")
  1502  			}
  1503  		}
  1504  	} else {
  1505  		// HTTP version < 1.1: cannot do chunked transfer
  1506  		// encoding and we don't know the Content-Length so
  1507  		// signal EOF by closing connection.
  1508  		w.closeAfterReply = true
  1509  		delHeader("Transfer-Encoding") // in case already set
  1510  	}
  1511  
  1512  	// Cannot use Content-Length with non-identity Transfer-Encoding.
  1513  	if cw.chunking {
  1514  		delHeader("Content-Length")
  1515  	}
  1516  	if !w.req.ProtoAtLeast(1, 0) {
  1517  		return
  1518  	}
  1519  
  1520  	// Only override the Connection header if it is not a successful
  1521  	// protocol switch response and if KeepAlives are not enabled.
  1522  	// See https://golang.org/issue/36381.
  1523  	delConnectionHeader := w.closeAfterReply &&
  1524  		(!keepAlivesEnabled || !hasToken(cw.header.get("Connection"), "close")) &&
  1525  		!isProtocolSwitchResponse(w.status, header)
  1526  	if delConnectionHeader {
  1527  		delHeader("Connection")
  1528  		if w.req.ProtoAtLeast(1, 1) {
  1529  			setHeader.connection = "close"
  1530  		}
  1531  	}
  1532  
  1533  	writeStatusLine(w.conn.bufw, w.req.ProtoAtLeast(1, 1), code, w.statusBuf[:])
  1534  	cw.header.WriteSubset(w.conn.bufw, excludeHeader)
  1535  	setHeader.Write(w.conn.bufw)
  1536  	w.conn.bufw.Write(crlf)
  1537  }
  1538  
  1539  // foreachHeaderElement splits v according to the "#rule" construction
  1540  // in RFC 7230 section 7 and calls fn for each non-empty element.
  1541  func foreachHeaderElement(v string, fn func(string)) {
  1542  	v = textproto.TrimString(v)
  1543  	if v == "" {
  1544  		return
  1545  	}
  1546  	if !strings.Contains(v, ",") {
  1547  		fn(v)
  1548  		return
  1549  	}
  1550  	for f := range strings.SplitSeq(v, ",") {
  1551  		if f = textproto.TrimString(f); f != "" {
  1552  			fn(f)
  1553  		}
  1554  	}
  1555  }
  1556  
  1557  // writeStatusLine writes an HTTP/1.x Status-Line (RFC 7230 Section 3.1.2)
  1558  // to bw. is11 is whether the HTTP request is HTTP/1.1. false means HTTP/1.0.
  1559  // code is the response status code.
  1560  // scratch is an optional scratch buffer. If it has at least capacity 3, it's used.
  1561  func writeStatusLine(bw *bufio.Writer, is11 bool, code int, scratch []byte) {
  1562  	if is11 {
  1563  		bw.WriteString("HTTP/1.1 ")
  1564  	} else {
  1565  		bw.WriteString("HTTP/1.0 ")
  1566  	}
  1567  	if text := StatusText(code); text != "" {
  1568  		bw.Write(strconv.AppendInt(scratch[:0], int64(code), 10))
  1569  		bw.WriteByte(' ')
  1570  		bw.WriteString(text)
  1571  		bw.WriteString("\r\n")
  1572  	} else {
  1573  		// don't worry about performance
  1574  		fmt.Fprintf(bw, "%03d status code %d\r\n", code, code)
  1575  	}
  1576  }
  1577  
  1578  // bodyAllowed reports whether a Write is allowed for this response type.
  1579  // It's illegal to call this before the header has been flushed.
  1580  func (w *response) bodyAllowed() bool {
  1581  	if !w.wroteHeader {
  1582  		panic("net/http: bodyAllowed called before the header was written")
  1583  	}
  1584  	return bodyAllowedForStatus(w.status)
  1585  }
  1586  
  1587  // The Life Of A Write is like this:
  1588  //
  1589  // Handler starts. No header has been sent. The handler can either
  1590  // write a header, or just start writing. Writing before sending a header
  1591  // sends an implicitly empty 200 OK header.
  1592  //
  1593  // If the handler didn't declare a Content-Length up front, we either
  1594  // go into chunking mode or, if the handler finishes running before
  1595  // the chunking buffer size, we compute a Content-Length and send that
  1596  // in the header instead.
  1597  //
  1598  // Likewise, if the handler didn't set a Content-Type, we sniff that
  1599  // from the initial chunk of output.
  1600  //
  1601  // The Writers are wired together like:
  1602  //
  1603  //  1. *response (the ResponseWriter) ->
  1604  //  2. (*response).w, a [*bufio.Writer] of bufferBeforeChunkingSize bytes ->
  1605  //  3. chunkWriter.Writer (whose writeHeader finalizes Content-Length/Type)
  1606  //     and which writes the chunk headers, if needed ->
  1607  //  4. conn.bufw, a *bufio.Writer of default (4kB) bytes, writing to ->
  1608  //  5. checkConnErrorWriter{c}, which notes any non-nil error on Write
  1609  //     and populates c.werr with it if so, but otherwise writes to ->
  1610  //  6. the rwc, the [net.Conn].
  1611  //
  1612  // TODO(bradfitz): short-circuit some of the buffering when the
  1613  // initial header contains both a Content-Type and Content-Length.
  1614  // Also short-circuit in (1) when the header's been sent and not in
  1615  // chunking mode, writing directly to (4) instead, if (2) has no
  1616  // buffered data. More generally, we could short-circuit from (1) to
  1617  // (3) even in chunking mode if the write size from (1) is over some
  1618  // threshold and nothing is in (2).  The answer might be mostly making
  1619  // bufferBeforeChunkingSize smaller and having bufio's fast-paths deal
  1620  // with this instead.
  1621  func (w *response) Write(data []byte) (n int, err error) {
  1622  	return w.write(len(data), data, "")
  1623  }
  1624  
  1625  func (w *response) WriteString(data string) (n int, err error) {
  1626  	return w.write(len(data), nil, data)
  1627  }
  1628  
  1629  // either dataB or dataS is non-zero.
  1630  func (w *response) write(lenData int, dataB []byte, dataS string) (n int, err error) {
  1631  	if w.conn.hijacked() {
  1632  		if lenData > 0 {
  1633  			caller := relevantCaller()
  1634  			w.conn.server.logf("http: response.Write on hijacked connection from %s (%s:%d)", caller.Function, path.Base(caller.File), caller.Line)
  1635  		}
  1636  		return 0, ErrHijacked
  1637  	}
  1638  
  1639  	if w.canWriteContinue.Load() {
  1640  		// Body reader wants to write 100 Continue but hasn't yet. Tell it not to.
  1641  		w.disableWriteContinue()
  1642  	}
  1643  
  1644  	if !w.wroteHeader {
  1645  		w.WriteHeader(StatusOK)
  1646  	}
  1647  	if lenData == 0 {
  1648  		return 0, nil
  1649  	}
  1650  	if !w.bodyAllowed() {
  1651  		return 0, ErrBodyNotAllowed
  1652  	}
  1653  
  1654  	w.written += int64(lenData) // ignoring errors, for errorKludge
  1655  	if w.contentLength != -1 && w.written > w.contentLength {
  1656  		return 0, ErrContentLength
  1657  	}
  1658  	if dataB != nil {
  1659  		return w.w.Write(dataB)
  1660  	} else {
  1661  		return w.w.WriteString(dataS)
  1662  	}
  1663  }
  1664  
  1665  func (w *response) finishRequest() {
  1666  	w.handlerDone.Store(true)
  1667  
  1668  	if !w.wroteHeader {
  1669  		w.WriteHeader(StatusOK)
  1670  	}
  1671  
  1672  	w.w.Flush()
  1673  	putBufioWriter(w.w)
  1674  	w.cw.close()
  1675  	w.conn.bufw.Flush()
  1676  
  1677  	w.conn.r.abortPendingRead()
  1678  
  1679  	// Close the body (regardless of w.closeAfterReply) so we can
  1680  	// re-use its bufio.Reader later safely.
  1681  	w.reqBody.Close()
  1682  
  1683  	if w.req.MultipartForm != nil {
  1684  		w.req.MultipartForm.RemoveAll()
  1685  	}
  1686  }
  1687  
  1688  // shouldReuseConnection reports whether the underlying TCP connection can be reused.
  1689  // It must only be called after the handler is done executing.
  1690  func (w *response) shouldReuseConnection() bool {
  1691  	if w.closeAfterReply {
  1692  		// The request or something set while executing the
  1693  		// handler indicated we shouldn't reuse this
  1694  		// connection.
  1695  		return false
  1696  	}
  1697  
  1698  	if w.req.Method != "HEAD" && w.contentLength != -1 && w.bodyAllowed() && w.contentLength != w.written {
  1699  		// Did not write enough. Avoid getting out of sync.
  1700  		return false
  1701  	}
  1702  
  1703  	// There was some error writing to the underlying connection
  1704  	// during the request, so don't re-use this conn.
  1705  	if w.conn.werr != nil {
  1706  		return false
  1707  	}
  1708  
  1709  	if w.closedRequestBodyEarly() {
  1710  		return false
  1711  	}
  1712  
  1713  	return true
  1714  }
  1715  
  1716  func (w *response) closedRequestBodyEarly() bool {
  1717  	body, ok := w.req.Body.(*body)
  1718  	return ok && body.didEarlyClose()
  1719  }
  1720  
  1721  func (w *response) Flush() {
  1722  	w.FlushError()
  1723  }
  1724  
  1725  func (w *response) FlushError() error {
  1726  	if !w.wroteHeader {
  1727  		w.WriteHeader(StatusOK)
  1728  	}
  1729  	err := w.w.Flush()
  1730  	e2 := w.cw.flush()
  1731  	if err == nil {
  1732  		err = e2
  1733  	}
  1734  	return err
  1735  }
  1736  
  1737  func (c *conn) finalFlush() {
  1738  	if c.bufr != nil {
  1739  		// Steal the bufio.Reader (~4KB worth of memory) and its associated
  1740  		// reader for a future connection.
  1741  		putBufioReader(c.bufr)
  1742  		c.bufr = nil
  1743  	}
  1744  
  1745  	if c.bufw != nil {
  1746  		c.bufw.Flush()
  1747  		// Steal the bufio.Writer (~4KB worth of memory) and its associated
  1748  		// writer for a future connection.
  1749  		putBufioWriter(c.bufw)
  1750  		c.bufw = nil
  1751  	}
  1752  }
  1753  
  1754  // Close the connection.
  1755  func (c *conn) close() {
  1756  	c.finalFlush()
  1757  	c.rwc.Close()
  1758  }
  1759  
  1760  // rstAvoidanceDelay is the amount of time we sleep after closing the
  1761  // write side of a TCP connection before closing the entire socket.
  1762  // By sleeping, we increase the chances that the client sees our FIN
  1763  // and processes its final data before they process the subsequent RST
  1764  // from closing a connection with known unread data.
  1765  // This RST seems to occur mostly on BSD systems. (And Windows?)
  1766  // This timeout is somewhat arbitrary (~latency around the planet),
  1767  // and may be modified by tests.
  1768  //
  1769  // TODO(bcmills): This should arguably be a server configuration parameter,
  1770  // not a hard-coded value.
  1771  var rstAvoidanceDelay = 500 * time.Millisecond
  1772  
  1773  type closeWriter interface {
  1774  	CloseWrite() error
  1775  }
  1776  
  1777  var _ closeWriter = (*net.TCPConn)(nil)
  1778  
  1779  // closeWriteAndWait flushes any outstanding data and sends a FIN packet (if
  1780  // client is connected via TCP), signaling that we're done. We then
  1781  // pause for a bit, hoping the client processes it before any
  1782  // subsequent RST.
  1783  //
  1784  // See https://golang.org/issue/3595
  1785  func (c *conn) closeWriteAndWait() {
  1786  	c.finalFlush()
  1787  	if tcp, ok := c.rwc.(closeWriter); ok {
  1788  		tcp.CloseWrite()
  1789  	}
  1790  
  1791  	// When we return from closeWriteAndWait, the caller will fully close the
  1792  	// connection. If client is still writing to the connection, this will cause
  1793  	// the write to fail with ECONNRESET or similar. Unfortunately, many TCP
  1794  	// implementations will also drop unread packets from the client's read buffer
  1795  	// when a write fails, causing our final response to be truncated away too.
  1796  	//
  1797  	// As a result, https://www.rfc-editor.org/rfc/rfc7230#section-6.6 recommends
  1798  	// that “[t]he server … continues to read from the connection until it
  1799  	// receives a corresponding close by the client, or until the server is
  1800  	// reasonably certain that its own TCP stack has received the client's
  1801  	// acknowledgement of the packet(s) containing the server's last response.”
  1802  	//
  1803  	// Unfortunately, we have no straightforward way to be “reasonably certain”
  1804  	// that we have received the client's ACK, and at any rate we don't want to
  1805  	// allow a misbehaving client to soak up server connections indefinitely by
  1806  	// withholding an ACK, nor do we want to go through the complexity or overhead
  1807  	// of using low-level APIs to figure out when a TCP round-trip has completed.
  1808  	//
  1809  	// Instead, we declare that we are “reasonably certain” that we received the
  1810  	// ACK if maxRSTAvoidanceDelay has elapsed.
  1811  	time.Sleep(rstAvoidanceDelay)
  1812  }
  1813  
  1814  // validNextProto reports whether the proto is a valid ALPN protocol name.
  1815  // Everything is valid except the empty string and built-in protocol types,
  1816  // so that those can't be overridden with alternate implementations.
  1817  func validNextProto(proto string) bool {
  1818  	switch proto {
  1819  	case "", "http/1.1", "http/1.0":
  1820  		return false
  1821  	}
  1822  	return true
  1823  }
  1824  
  1825  const (
  1826  	runHooks  = true
  1827  	skipHooks = false
  1828  )
  1829  
  1830  func (c *conn) setState(nc net.Conn, state ConnState, runHook bool) {
  1831  	srv := c.server
  1832  	switch state {
  1833  	case StateNew:
  1834  		srv.trackConn(c, true)
  1835  	case StateHijacked, StateClosed:
  1836  		srv.trackConn(c, false)
  1837  	}
  1838  	if state > 0xff || state < 0 {
  1839  		panic("internal error")
  1840  	}
  1841  	packedState := uint64(time.Now().Unix()<<8) | uint64(state)
  1842  	c.curState.Store(packedState)
  1843  	if !runHook {
  1844  		return
  1845  	}
  1846  	if hook := srv.ConnState; hook != nil {
  1847  		hook(nc, state)
  1848  	}
  1849  }
  1850  
  1851  func (c *conn) getState() (state ConnState, unixSec int64) {
  1852  	packedState := c.curState.Load()
  1853  	return ConnState(packedState & 0xff), int64(packedState >> 8)
  1854  }
  1855  
  1856  // badRequestError is a literal string (used by in the server in HTML,
  1857  // unescaped) to tell the user why their request was bad. It should
  1858  // be plain text without user info or other embedded errors.
  1859  func badRequestError(e string) error { return statusError{StatusBadRequest, e} }
  1860  
  1861  // statusError is an error used to respond to a request with an HTTP status.
  1862  // The text should be plain text without user info or other embedded errors.
  1863  type statusError struct {
  1864  	code int
  1865  	text string
  1866  }
  1867  
  1868  func (e statusError) Error() string { return StatusText(e.code) + ": " + e.text }
  1869  
  1870  // ErrAbortHandler is a sentinel panic value to abort a handler.
  1871  // While any panic from ServeHTTP aborts the response to the client,
  1872  // panicking with ErrAbortHandler also suppresses logging of a stack
  1873  // trace to the server's error log.
  1874  var ErrAbortHandler = internal.ErrAbortHandler
  1875  
  1876  // isCommonNetReadError reports whether err is a common error
  1877  // encountered during reading a request off the network when the
  1878  // client has gone away or had its read fail somehow. This is used to
  1879  // determine which logs are interesting enough to log about.
  1880  func isCommonNetReadError(err error) bool {
  1881  	if err == io.EOF {
  1882  		return true
  1883  	}
  1884  	if neterr, ok := err.(net.Error); ok && neterr.Timeout() {
  1885  		return true
  1886  	}
  1887  	if oe, ok := err.(*net.OpError); ok && oe.Op == "read" {
  1888  		return true
  1889  	}
  1890  	return false
  1891  }
  1892  
  1893  type connectionStater interface {
  1894  	ConnectionState() tls.ConnectionState
  1895  }
  1896  
  1897  // Serve a new connection.
  1898  func (c *conn) serve(ctx context.Context) {
  1899  	if ra := c.rwc.RemoteAddr(); ra != nil {
  1900  		c.remoteAddr = ra.String()
  1901  	}
  1902  	ctx = context.WithValue(ctx, LocalAddrContextKey, c.rwc.LocalAddr())
  1903  	var inFlightResponse *response
  1904  	defer func() {
  1905  		if err := recover(); err != nil && err != ErrAbortHandler {
  1906  			const size = 64 << 10
  1907  			buf := make([]byte, size)
  1908  			buf = buf[:runtime.Stack(buf, false)]
  1909  			c.server.logf("http: panic serving %v: %v\n%s", c.remoteAddr, err, buf)
  1910  		}
  1911  		if inFlightResponse != nil {
  1912  			inFlightResponse.cancelCtx()
  1913  			inFlightResponse.disableWriteContinue()
  1914  		}
  1915  		if !c.hijacked() {
  1916  			if inFlightResponse != nil {
  1917  				inFlightResponse.conn.r.abortPendingRead()
  1918  				inFlightResponse.reqBody.Close()
  1919  			}
  1920  			c.close()
  1921  			c.setState(c.rwc, StateClosed, runHooks)
  1922  		}
  1923  	}()
  1924  
  1925  	if tlsConn, ok := c.rwc.(*tls.Conn); ok {
  1926  		tlsTO := c.server.tlsHandshakeTimeout()
  1927  		if tlsTO > 0 {
  1928  			dl := time.Now().Add(tlsTO)
  1929  			c.rwc.SetReadDeadline(dl)
  1930  			c.rwc.SetWriteDeadline(dl)
  1931  		}
  1932  		if err := tlsConn.HandshakeContext(ctx); err != nil {
  1933  			// If the handshake failed due to the client not speaking
  1934  			// TLS, assume they're speaking plaintext HTTP and write a
  1935  			// 400 response on the TLS conn's underlying net.Conn.
  1936  			var reason string
  1937  			if re, ok := err.(tls.RecordHeaderError); ok && re.Conn != nil && tlsRecordHeaderLooksLikeHTTP(re.RecordHeader) {
  1938  				io.WriteString(re.Conn, "HTTP/1.0 400 Bad Request\r\n\r\nClient sent an HTTP request to an HTTPS server.\n")
  1939  				re.Conn.Close()
  1940  				reason = "client sent an HTTP request to an HTTPS server"
  1941  			} else {
  1942  				reason = err.Error()
  1943  			}
  1944  			c.server.logf("http: TLS handshake error from %s: %v", c.rwc.RemoteAddr(), reason)
  1945  			return
  1946  		}
  1947  		// Restore Conn-level deadlines.
  1948  		if tlsTO > 0 {
  1949  			c.rwc.SetReadDeadline(time.Time{})
  1950  			c.rwc.SetWriteDeadline(time.Time{})
  1951  		}
  1952  		c.tlsState = new(tls.ConnectionState)
  1953  		*c.tlsState = tlsConn.ConnectionState()
  1954  		if proto := c.tlsState.NegotiatedProtocol; validNextProto(proto) {
  1955  			if fn := c.server.TLSNextProto[proto]; fn != nil {
  1956  				h := initALPNRequest{ctx, tlsConn, serverHandler{c.server}}
  1957  				// Mark freshly created HTTP/2 as active and prevent any server state hooks
  1958  				// from being run on these connections. This prevents closeIdleConns from
  1959  				// closing such connections. See issue https://golang.org/issue/39776.
  1960  				c.setState(c.rwc, StateActive, skipHooks)
  1961  				fn(c.server, tlsConn, h)
  1962  			}
  1963  			return
  1964  		}
  1965  	}
  1966  
  1967  	// HTTP/1.x from here on.
  1968  
  1969  	// Set Request.TLS if the conn is not a *tls.Conn, but implements ConnectionState.
  1970  	if c.tlsState == nil {
  1971  		if tc, ok := c.rwc.(connectionStater); ok {
  1972  			c.tlsState = new(tls.ConnectionState)
  1973  			*c.tlsState = tc.ConnectionState()
  1974  		}
  1975  	}
  1976  
  1977  	ctx, cancelCtx := context.WithCancel(ctx)
  1978  	c.cancelCtx = cancelCtx
  1979  	defer cancelCtx()
  1980  
  1981  	c.r = &connReader{conn: c, rwc: c.rwc}
  1982  	c.bufr = newBufioReader(c.r)
  1983  	c.bufw = newBufioWriterSize(checkConnErrorWriter{c}, 4<<10)
  1984  
  1985  	protos := c.server.protocols()
  1986  	if c.tlsState == nil && protos.UnencryptedHTTP2() {
  1987  		if c.maybeServeUnencryptedHTTP2(ctx) {
  1988  			return
  1989  		}
  1990  	}
  1991  	if !protos.HTTP1() {
  1992  		return
  1993  	}
  1994  
  1995  	for {
  1996  		w, err := c.readRequest(ctx)
  1997  		if c.r.remain != c.server.initialReadLimitSize() {
  1998  			// If we read any bytes off the wire, we're active.
  1999  			c.setState(c.rwc, StateActive, runHooks)
  2000  		}
  2001  		if c.server.shuttingDown() {
  2002  			return
  2003  		}
  2004  		if err != nil {
  2005  			const errorHeaders = "\r\nContent-Type: text/plain; charset=utf-8\r\nConnection: close\r\n\r\n"
  2006  
  2007  			switch {
  2008  			case err == errTooLarge:
  2009  				// Their HTTP client may or may not be
  2010  				// able to read this if we're
  2011  				// responding to them and hanging up
  2012  				// while they're still writing their
  2013  				// request. Undefined behavior.
  2014  				const publicErr = "431 Request Header Fields Too Large"
  2015  				fmt.Fprintf(c.rwc, "HTTP/1.1 "+publicErr+errorHeaders+publicErr)
  2016  				c.closeWriteAndWait()
  2017  				return
  2018  
  2019  			case isUnsupportedTEError(err):
  2020  				// Respond as per RFC 7230 Section 3.3.1 which says,
  2021  				//      A server that receives a request message with a
  2022  				//      transfer coding it does not understand SHOULD
  2023  				//      respond with 501 (Unimplemented).
  2024  				code := StatusNotImplemented
  2025  
  2026  				// We purposefully aren't echoing back the transfer-encoding's value,
  2027  				// so as to mitigate the risk of cross side scripting by an attacker.
  2028  				fmt.Fprintf(c.rwc, "HTTP/1.1 %d %s%sUnsupported transfer encoding", code, StatusText(code), errorHeaders)
  2029  				return
  2030  
  2031  			case isCommonNetReadError(err):
  2032  				return // don't reply
  2033  
  2034  			default:
  2035  				if v, ok := err.(statusError); ok {
  2036  					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)
  2037  					return
  2038  				}
  2039  				const publicErr = "400 Bad Request"
  2040  				fmt.Fprintf(c.rwc, "HTTP/1.1 "+publicErr+errorHeaders+publicErr)
  2041  				return
  2042  			}
  2043  		}
  2044  
  2045  		// Expect 100 Continue support
  2046  		req := w.req
  2047  		if req.expectsContinue() {
  2048  			if req.ProtoAtLeast(1, 1) && req.ContentLength != 0 {
  2049  				// Wrap the Body reader with one that replies on the connection
  2050  				req.Body = &expectContinueReader{readCloser: req.Body, resp: w}
  2051  				w.canWriteContinue.Store(true)
  2052  			}
  2053  		} else if req.Header.get("Expect") != "" {
  2054  			w.sendExpectationFailed()
  2055  			return
  2056  		}
  2057  
  2058  		c.curReq.Store(w)
  2059  
  2060  		if requestBodyRemains(req.Body) {
  2061  			registerOnHitEOF(req.Body, w.conn.r.startBackgroundRead)
  2062  		} else {
  2063  			w.conn.r.startBackgroundRead()
  2064  		}
  2065  
  2066  		// HTTP cannot have multiple simultaneous active requests.[*]
  2067  		// Until the server replies to this request, it can't read another,
  2068  		// so we might as well run the handler in this goroutine.
  2069  		// [*] Not strictly true: HTTP pipelining. We could let them all process
  2070  		// in parallel even if their responses need to be serialized.
  2071  		// But we're not going to implement HTTP pipelining because it
  2072  		// was never deployed in the wild and the answer is HTTP/2.
  2073  		inFlightResponse = w
  2074  		serverHandler{c.server}.ServeHTTP(w, w.req)
  2075  		inFlightResponse = nil
  2076  		w.cancelCtx()
  2077  		if c.hijacked() {
  2078  			c.r.releaseConn()
  2079  			return
  2080  		}
  2081  		w.finishRequest()
  2082  		c.rwc.SetWriteDeadline(time.Time{})
  2083  		if !w.shouldReuseConnection() {
  2084  			if w.requestBodyLimitHit || w.closedRequestBodyEarly() {
  2085  				c.closeWriteAndWait()
  2086  			}
  2087  			return
  2088  		}
  2089  		c.setState(c.rwc, StateIdle, runHooks)
  2090  		c.curReq.Store(nil)
  2091  
  2092  		if !w.conn.server.doKeepAlives() {
  2093  			// We're in shutdown mode. We might've replied
  2094  			// to the user without "Connection: close" and
  2095  			// they might think they can send another
  2096  			// request, but such is life with HTTP/1.1.
  2097  			return
  2098  		}
  2099  
  2100  		if d := c.server.idleTimeout(); d > 0 {
  2101  			c.rwc.SetReadDeadline(time.Now().Add(d))
  2102  		} else {
  2103  			c.rwc.SetReadDeadline(time.Time{})
  2104  		}
  2105  
  2106  		// Wait for the connection to become readable again before trying to
  2107  		// read the next request. This prevents a ReadHeaderTimeout or
  2108  		// ReadTimeout from starting until the first bytes of the next request
  2109  		// have been received.
  2110  		if _, err := c.bufr.Peek(4); err != nil {
  2111  			return
  2112  		}
  2113  
  2114  		c.rwc.SetReadDeadline(time.Time{})
  2115  	}
  2116  }
  2117  
  2118  // unencryptedHTTP2Request is an HTTP handler that initializes
  2119  // certain uninitialized fields in its *Request.
  2120  //
  2121  // It's the unencrypted version of initALPNRequest.
  2122  type unencryptedHTTP2Request struct {
  2123  	ctx context.Context
  2124  	c   net.Conn
  2125  	h   serverHandler
  2126  }
  2127  
  2128  func (h unencryptedHTTP2Request) BaseContext() context.Context { return h.ctx }
  2129  
  2130  func (h unencryptedHTTP2Request) ServeHTTP(rw ResponseWriter, req *Request) {
  2131  	if req.Body == nil {
  2132  		req.Body = NoBody
  2133  	}
  2134  	if req.RemoteAddr == "" {
  2135  		req.RemoteAddr = h.c.RemoteAddr().String()
  2136  	}
  2137  	h.h.ServeHTTP(rw, req)
  2138  }
  2139  
  2140  // unencryptedNetConnInTLSConn is used to pass an unencrypted net.Conn to
  2141  // functions that only accept a *tls.Conn.
  2142  type unencryptedNetConnInTLSConn struct {
  2143  	net.Conn // panic on all net.Conn methods
  2144  	conn     net.Conn
  2145  }
  2146  
  2147  func (c unencryptedNetConnInTLSConn) UnencryptedNetConn() net.Conn {
  2148  	return c.conn
  2149  }
  2150  
  2151  func unencryptedTLSConn(c net.Conn) *tls.Conn {
  2152  	return tls.Client(unencryptedNetConnInTLSConn{conn: c}, nil)
  2153  }
  2154  
  2155  // TLSNextProto key to use for unencrypted HTTP/2 connections.
  2156  // Not actually a TLS-negotiated protocol.
  2157  const nextProtoUnencryptedHTTP2 = "unencrypted_http2"
  2158  
  2159  func (c *conn) maybeServeUnencryptedHTTP2(ctx context.Context) bool {
  2160  	fn, ok := c.server.TLSNextProto[nextProtoUnencryptedHTTP2]
  2161  	if !ok {
  2162  		return false
  2163  	}
  2164  	hasPreface := func(c *conn, preface []byte) bool {
  2165  		c.r.setReadLimit(int64(len(preface)) - int64(c.bufr.Buffered()))
  2166  		got, err := c.bufr.Peek(len(preface))
  2167  		c.r.setInfiniteReadLimit()
  2168  		return err == nil && bytes.Equal(got, preface)
  2169  	}
  2170  	if !hasPreface(c, []byte("PRI * HTTP/2.0")) {
  2171  		return false
  2172  	}
  2173  	if !hasPreface(c, []byte("PRI * HTTP/2.0\r\n\r\nSM\r\n\r\n")) {
  2174  		return false
  2175  	}
  2176  	c.setState(c.rwc, StateActive, skipHooks)
  2177  	h := unencryptedHTTP2Request{ctx, c.rwc, serverHandler{c.server}}
  2178  	fn(c.server, unencryptedTLSConn(c.rwc), h)
  2179  	return true
  2180  }
  2181  
  2182  func (w *response) sendExpectationFailed() {
  2183  	// TODO(bradfitz): let ServeHTTP handlers handle
  2184  	// requests with non-standard expectation[s]? Seems
  2185  	// theoretical at best, and doesn't fit into the
  2186  	// current ServeHTTP model anyway. We'd need to
  2187  	// make the ResponseWriter an optional
  2188  	// "ExpectReplier" interface or something.
  2189  	//
  2190  	// For now we'll just obey RFC 7231 5.1.1 which says
  2191  	// "A server that receives an Expect field-value other
  2192  	// than 100-continue MAY respond with a 417 (Expectation
  2193  	// Failed) status code to indicate that the unexpected
  2194  	// expectation cannot be met."
  2195  	w.Header().Set("Connection", "close")
  2196  	w.WriteHeader(StatusExpectationFailed)
  2197  	w.finishRequest()
  2198  }
  2199  
  2200  // Hijack implements the [Hijacker.Hijack] method. Our response is both a [ResponseWriter]
  2201  // and a [Hijacker].
  2202  func (w *response) Hijack() (rwc net.Conn, buf *bufio.ReadWriter, err error) {
  2203  	if w.handlerDone.Load() {
  2204  		panic("net/http: Hijack called after ServeHTTP finished")
  2205  	}
  2206  	w.disableWriteContinue()
  2207  	if w.wroteHeader {
  2208  		w.cw.flush()
  2209  	}
  2210  
  2211  	c := w.conn
  2212  	c.mu.Lock()
  2213  	defer c.mu.Unlock()
  2214  
  2215  	// Release the bufioWriter that writes to the chunk writer, it is not
  2216  	// used after a connection has been hijacked.
  2217  	rwc, buf, err = c.hijackLocked()
  2218  	if err == nil {
  2219  		putBufioWriter(w.w)
  2220  		w.w = nil
  2221  	}
  2222  	return rwc, buf, err
  2223  }
  2224  
  2225  func (w *response) CloseNotify() <-chan bool {
  2226  	w.lazyCloseNotifyMu.Lock()
  2227  	defer w.lazyCloseNotifyMu.Unlock()
  2228  	if w.handlerDone.Load() {
  2229  		panic("net/http: CloseNotify called after ServeHTTP finished")
  2230  	}
  2231  	if w.closeNotifyCh == nil {
  2232  		w.closeNotifyCh = make(chan bool, 1)
  2233  		if w.closeNotifyTriggered {
  2234  			w.closeNotifyCh <- true // action prior closeNotify call
  2235  		}
  2236  	}
  2237  	return w.closeNotifyCh
  2238  }
  2239  
  2240  func (w *response) closeNotify() {
  2241  	w.lazyCloseNotifyMu.Lock()
  2242  	defer w.lazyCloseNotifyMu.Unlock()
  2243  	if w.closeNotifyTriggered {
  2244  		return // already triggered
  2245  	}
  2246  	w.closeNotifyTriggered = true
  2247  	if w.closeNotifyCh != nil {
  2248  		w.closeNotifyCh <- true
  2249  	}
  2250  }
  2251  
  2252  func registerOnHitEOF(rc io.ReadCloser, fn func()) {
  2253  	switch v := rc.(type) {
  2254  	case *expectContinueReader:
  2255  		registerOnHitEOF(v.readCloser, fn)
  2256  	case *body:
  2257  		v.registerOnHitEOF(fn)
  2258  	default:
  2259  		panic("unexpected type " + fmt.Sprintf("%T", rc))
  2260  	}
  2261  }
  2262  
  2263  // requestBodyRemains reports whether future calls to Read
  2264  // on rc might yield more data.
  2265  func requestBodyRemains(rc io.ReadCloser) bool {
  2266  	if rc == NoBody {
  2267  		return false
  2268  	}
  2269  	switch v := rc.(type) {
  2270  	case *expectContinueReader:
  2271  		return requestBodyRemains(v.readCloser)
  2272  	case *body:
  2273  		return v.bodyRemains()
  2274  	default:
  2275  		panic("unexpected type " + fmt.Sprintf("%T", rc))
  2276  	}
  2277  }
  2278  
  2279  // The HandlerFunc type is an adapter to allow the use of
  2280  // ordinary functions as HTTP handlers. If f is a function
  2281  // with the appropriate signature, HandlerFunc(f) is a
  2282  // [Handler] that calls f.
  2283  type HandlerFunc func(ResponseWriter, *Request)
  2284  
  2285  // ServeHTTP calls f(w, r).
  2286  func (f HandlerFunc) ServeHTTP(w ResponseWriter, r *Request) {
  2287  	f(w, r)
  2288  }
  2289  
  2290  // Helper handlers
  2291  
  2292  // Error replies to the request with the specified error message and HTTP code.
  2293  // It does not otherwise end the request; the caller should ensure no further
  2294  // writes are done to w.
  2295  // The error message should be plain text.
  2296  //
  2297  // Error deletes the Content-Length header,
  2298  // sets Content-Type to “text/plain; charset=utf-8”,
  2299  // and sets X-Content-Type-Options to “nosniff”.
  2300  // This configures the header properly for the error message,
  2301  // in case the caller had set it up expecting a successful output.
  2302  func Error(w ResponseWriter, error string, code int) {
  2303  	h := w.Header()
  2304  
  2305  	// Delete the Content-Length header, which might be for some other content.
  2306  	// Assuming the error string fits in the writer's buffer, we'll figure
  2307  	// out the correct Content-Length for it later.
  2308  	//
  2309  	// We don't delete Content-Encoding, because some middleware sets
  2310  	// Content-Encoding: gzip and wraps the ResponseWriter to compress on-the-fly.
  2311  	// See https://go.dev/issue/66343.
  2312  	h.Del("Content-Length")
  2313  
  2314  	// There might be content type already set, but we reset it to
  2315  	// text/plain for the error message.
  2316  	h.Set("Content-Type", "text/plain; charset=utf-8")
  2317  	h.Set("X-Content-Type-Options", "nosniff")
  2318  	w.WriteHeader(code)
  2319  	fmt.Fprintln(w, error)
  2320  }
  2321  
  2322  // NotFound replies to the request with an HTTP 404 not found error.
  2323  func NotFound(w ResponseWriter, r *Request) { Error(w, "404 page not found", StatusNotFound) }
  2324  
  2325  // NotFoundHandler returns a simple request handler
  2326  // that replies to each request with a “404 page not found” reply.
  2327  func NotFoundHandler() Handler { return HandlerFunc(NotFound) }
  2328  
  2329  // StripPrefix returns a handler that serves HTTP requests by removing the
  2330  // given prefix from the request URL's Path (and RawPath if set) and invoking
  2331  // the handler h. StripPrefix handles a request for a path that doesn't begin
  2332  // with prefix by replying with an HTTP 404 not found error. The prefix must
  2333  // match exactly: if the prefix in the request contains escaped characters
  2334  // the reply is also an HTTP 404 not found error.
  2335  func StripPrefix(prefix string, h Handler) Handler {
  2336  	if prefix == "" {
  2337  		return h
  2338  	}
  2339  	return HandlerFunc(func(w ResponseWriter, r *Request) {
  2340  		p := strings.TrimPrefix(r.URL.Path, prefix)
  2341  		rp := strings.TrimPrefix(r.URL.RawPath, prefix)
  2342  		if len(p) < len(r.URL.Path) && (r.URL.RawPath == "" || len(rp) < len(r.URL.RawPath)) {
  2343  			r2 := new(Request)
  2344  			*r2 = *r
  2345  			r2.URL = new(url.URL)
  2346  			*r2.URL = *r.URL
  2347  			r2.URL.Path = p
  2348  			r2.URL.RawPath = rp
  2349  			h.ServeHTTP(w, r2)
  2350  		} else {
  2351  			NotFound(w, r)
  2352  		}
  2353  	})
  2354  }
  2355  
  2356  // Redirect replies to the request with a redirect to url,
  2357  // which may be a path relative to the request path.
  2358  // Any non-ASCII characters in url will be percent-encoded,
  2359  // but existing percent encodings will not be changed.
  2360  //
  2361  // The provided code should be in the 3xx range and is usually
  2362  // [StatusMovedPermanently], [StatusFound] or [StatusSeeOther].
  2363  //
  2364  // If the Content-Type header has not been set, [Redirect] sets it
  2365  // to "text/html; charset=utf-8" and writes a small HTML body.
  2366  // Setting the Content-Type header to any value, including nil,
  2367  // disables that behavior.
  2368  func Redirect(w ResponseWriter, r *Request, url string, code int) {
  2369  	if u, err := urlpkg.Parse(url); err == nil {
  2370  		// If url was relative, make its path absolute by
  2371  		// combining with request path.
  2372  		// The client would probably do this for us,
  2373  		// but doing it ourselves is more reliable.
  2374  		// See RFC 7231, section 7.1.2
  2375  		if u.Scheme == "" && u.Host == "" {
  2376  			oldpath := r.URL.EscapedPath()
  2377  			if oldpath == "" { // should not happen, but avoid a crash if it does
  2378  				oldpath = "/"
  2379  			}
  2380  
  2381  			// no leading http://server
  2382  			if url == "" || url[0] != '/' {
  2383  				// make relative path absolute
  2384  				olddir, _ := path.Split(oldpath)
  2385  				url = olddir + url
  2386  			}
  2387  
  2388  			var query string
  2389  			if i := strings.Index(url, "?"); i != -1 {
  2390  				url, query = url[:i], url[i:]
  2391  			}
  2392  
  2393  			// clean up but preserve trailing slash
  2394  			trailing := strings.HasSuffix(url, "/")
  2395  			url = path.Clean(url)
  2396  			if trailing && !strings.HasSuffix(url, "/") {
  2397  				url += "/"
  2398  			}
  2399  			url += query
  2400  		}
  2401  	}
  2402  
  2403  	h := w.Header()
  2404  
  2405  	// RFC 7231 notes that a short HTML body is usually included in
  2406  	// the response because older user agents may not understand 301/307.
  2407  	// Do it only if the request didn't already have a Content-Type header.
  2408  	_, hadCT := h["Content-Type"]
  2409  
  2410  	h.Set("Location", hexEscapeNonASCII(url))
  2411  	if !hadCT && (r.Method == "GET" || r.Method == "HEAD") {
  2412  		h.Set("Content-Type", "text/html; charset=utf-8")
  2413  	}
  2414  	w.WriteHeader(code)
  2415  
  2416  	// Shouldn't send the body for POST or HEAD; that leaves GET.
  2417  	if !hadCT && r.Method == "GET" {
  2418  		body := "<a href=\"" + htmlEscape(url) + "\">" + StatusText(code) + "</a>.\n"
  2419  		fmt.Fprintln(w, body)
  2420  	}
  2421  }
  2422  
  2423  var htmlReplacer = strings.NewReplacer(
  2424  	"&", "&amp;",
  2425  	"<", "&lt;",
  2426  	">", "&gt;",
  2427  	// "&#34;" is shorter than "&quot;".
  2428  	`"`, "&#34;",
  2429  	// "&#39;" is shorter than "&apos;" and apos was not in HTML until HTML5.
  2430  	"'", "&#39;",
  2431  )
  2432  
  2433  func htmlEscape(s string) string {
  2434  	return htmlReplacer.Replace(s)
  2435  }
  2436  
  2437  // Redirect to a fixed URL
  2438  type redirectHandler struct {
  2439  	url  string
  2440  	code int
  2441  }
  2442  
  2443  func (rh *redirectHandler) ServeHTTP(w ResponseWriter, r *Request) {
  2444  	Redirect(w, r, rh.url, rh.code)
  2445  }
  2446  
  2447  // RedirectHandler returns a request handler that redirects
  2448  // each request it receives to the given url using the given
  2449  // status code.
  2450  //
  2451  // The provided code should be in the 3xx range and is usually
  2452  // [StatusMovedPermanently], [StatusFound] or [StatusSeeOther].
  2453  func RedirectHandler(url string, code int) Handler {
  2454  	return &redirectHandler{url, code}
  2455  }
  2456  
  2457  // ServeMux is an HTTP request multiplexer.
  2458  // It matches the URL of each incoming request against a list of registered
  2459  // patterns and calls the handler for the pattern that
  2460  // most closely matches the URL.
  2461  //
  2462  // # Patterns
  2463  //
  2464  // Patterns can match the method, host and path of a request.
  2465  // Some examples:
  2466  //
  2467  //   - "/index.html" matches the path "/index.html" for any host and method.
  2468  //   - "GET /static/" matches a GET request whose path begins with "/static/".
  2469  //   - "example.com/" matches any request to the host "example.com".
  2470  //   - "example.com/{$}" matches requests with host "example.com" and path "/".
  2471  //   - "/b/{bucket}/o/{objectname...}" matches paths whose first segment is "b"
  2472  //     and whose third segment is "o". The name "bucket" denotes the second
  2473  //     segment and "objectname" denotes the remainder of the path.
  2474  //
  2475  // In general, a pattern looks like
  2476  //
  2477  //	[METHOD ][HOST]/[PATH]
  2478  //
  2479  // All three parts are optional; "/" is a valid pattern.
  2480  // If METHOD is present, it must be followed by at least one space or tab.
  2481  //
  2482  // Literal (that is, non-wildcard) parts of a pattern match
  2483  // the corresponding parts of a request case-sensitively.
  2484  //
  2485  // A pattern with no method matches every method. A pattern
  2486  // with the method GET matches both GET and HEAD requests.
  2487  // Otherwise, the method must match exactly.
  2488  //
  2489  // A pattern with no host matches every host.
  2490  // A pattern with a host matches URLs on that host only.
  2491  //
  2492  // A path can include wildcard segments of the form {NAME} or {NAME...}.
  2493  // For example, "/b/{bucket}/o/{objectname...}".
  2494  // The wildcard name must be a valid Go identifier.
  2495  // Wildcards must be full path segments: they must be preceded by a slash and followed by
  2496  // either a slash or the end of the string.
  2497  // For example, "/b_{bucket}" is not a valid pattern.
  2498  //
  2499  // Normally a wildcard matches only a single path segment,
  2500  // ending at the next literal slash (not %2F) in the request URL.
  2501  // But if the "..." is present, then the wildcard matches the remainder of the URL path, including slashes.
  2502  // (Therefore it is invalid for a "..." wildcard to appear anywhere but at the end of a pattern.)
  2503  // The match for a wildcard can be obtained by calling [Request.PathValue] with the wildcard's name.
  2504  // A trailing slash in a path acts as an anonymous "..." wildcard.
  2505  //
  2506  // The special wildcard {$} matches only the end of the URL.
  2507  // For example, the pattern "/{$}" matches only the path "/",
  2508  // whereas the pattern "/" matches every path.
  2509  //
  2510  // For matching, both pattern paths and incoming request paths are unescaped segment by segment.
  2511  // So, for example, the path "/a%2Fb/100%25" is treated as having two segments, "a/b" and "100%".
  2512  // The pattern "/a%2fb/" matches it, but the pattern "/a/b/" does not.
  2513  //
  2514  // # Precedence
  2515  //
  2516  // If two or more patterns match a request, then the most specific pattern takes precedence.
  2517  // A pattern P1 is more specific than P2 if P1 matches a strict subset of P2’s requests;
  2518  // that is, if P2 matches all the requests of P1 and more.
  2519  // If neither is more specific, then the patterns conflict.
  2520  // There is one exception to this rule, for backwards compatibility:
  2521  // if two patterns would otherwise conflict and one has a host while the other does not,
  2522  // then the pattern with the host takes precedence.
  2523  // If a pattern passed to [ServeMux.Handle] or [ServeMux.HandleFunc] conflicts with
  2524  // another pattern that is already registered, those functions panic.
  2525  //
  2526  // As an example of the general rule, "/images/thumbnails/" is more specific than "/images/",
  2527  // so both can be registered.
  2528  // The former matches paths beginning with "/images/thumbnails/"
  2529  // and the latter will match any other path in the "/images/" subtree.
  2530  //
  2531  // As another example, consider the patterns "GET /" and "/index.html":
  2532  // both match a GET request for "/index.html", but the former pattern
  2533  // matches all other GET and HEAD requests, while the latter matches any
  2534  // request for "/index.html" that uses a different method.
  2535  // The patterns conflict.
  2536  //
  2537  // # Trailing-slash redirection
  2538  //
  2539  // Consider a [ServeMux] with a handler for a subtree, registered using a trailing slash or "..." wildcard.
  2540  // If the ServeMux receives a request for the subtree root without a trailing slash,
  2541  // it redirects the request by adding the trailing slash.
  2542  // This behavior can be overridden with a separate registration for the path without
  2543  // the trailing slash or "..." wildcard. For example, registering "/images/" causes ServeMux
  2544  // to redirect a request for "/images" to "/images/", unless "/images" has
  2545  // been registered separately.
  2546  //
  2547  // # Request sanitizing
  2548  //
  2549  // ServeMux also takes care of sanitizing the URL request path and the Host
  2550  // header, stripping the port number and redirecting any request containing . or
  2551  // .. segments or repeated slashes to an equivalent, cleaner URL.
  2552  // Escaped path elements such as "%2e" for "." and "%2f" for "/" are preserved
  2553  // and aren't considered separators for request routing.
  2554  //
  2555  // # Compatibility
  2556  //
  2557  // The pattern syntax and matching behavior of ServeMux changed significantly
  2558  // in Go 1.22. To restore the old behavior, set the GODEBUG environment variable
  2559  // to "httpmuxgo121=1". This setting is read once, at program startup; changes
  2560  // during execution will be ignored.
  2561  //
  2562  // The backwards-incompatible changes include:
  2563  //   - Wildcards are just ordinary literal path segments in 1.21.
  2564  //     For example, the pattern "/{x}" will match only that path in 1.21,
  2565  //     but will match any one-segment path in 1.22.
  2566  //   - In 1.21, no pattern was rejected, unless it was empty or conflicted with an existing pattern.
  2567  //     In 1.22, syntactically invalid patterns will cause [ServeMux.Handle] and [ServeMux.HandleFunc] to panic.
  2568  //     For example, in 1.21, the patterns "/{"  and "/a{x}" match themselves,
  2569  //     but in 1.22 they are invalid and will cause a panic when registered.
  2570  //   - In 1.22, each segment of a pattern is unescaped; this was not done in 1.21.
  2571  //     For example, in 1.22 the pattern "/%61" matches the path "/a" ("%61" being the URL escape sequence for "a"),
  2572  //     but in 1.21 it would match only the path "/%2561" (where "%25" is the escape for the percent sign).
  2573  //   - When matching patterns to paths, in 1.22 each segment of the path is unescaped; in 1.21, the entire path is unescaped.
  2574  //     This change mostly affects how paths with %2F escapes adjacent to slashes are treated.
  2575  //     See https://go.dev/issue/21955 for details.
  2576  type ServeMux struct {
  2577  	mu     sync.RWMutex
  2578  	tree   routingNode
  2579  	index  routingIndex
  2580  	mux121 serveMux121 // used only when GODEBUG=httpmuxgo121=1
  2581  }
  2582  
  2583  // NewServeMux allocates and returns a new [ServeMux].
  2584  func NewServeMux() *ServeMux {
  2585  	return &ServeMux{}
  2586  }
  2587  
  2588  // DefaultServeMux is the default [ServeMux] used by [Serve].
  2589  var DefaultServeMux = &defaultServeMux
  2590  
  2591  var defaultServeMux ServeMux
  2592  
  2593  // cleanPath returns the canonical path for p, eliminating . and .. elements.
  2594  func cleanPath(p string) string {
  2595  	if p == "" {
  2596  		return "/"
  2597  	}
  2598  	if p[0] != '/' {
  2599  		p = "/" + p
  2600  	}
  2601  	np := path.Clean(p)
  2602  	// path.Clean removes trailing slash except for root;
  2603  	// put the trailing slash back if necessary.
  2604  	if p[len(p)-1] == '/' && np != "/" {
  2605  		// Fast path for common case of p being the string we want:
  2606  		if len(p) == len(np)+1 && strings.HasPrefix(p, np) {
  2607  			np = p
  2608  		} else {
  2609  			np += "/"
  2610  		}
  2611  	}
  2612  	return np
  2613  }
  2614  
  2615  // stripHostPort returns h without any trailing ":<port>".
  2616  func stripHostPort(h string) string {
  2617  	// If no port on host, return unchanged
  2618  	if !strings.Contains(h, ":") {
  2619  		return h
  2620  	}
  2621  	host, _, err := net.SplitHostPort(h)
  2622  	if err != nil {
  2623  		return h // on error, return unchanged
  2624  	}
  2625  	return host
  2626  }
  2627  
  2628  // Handler returns the handler to use for the given request,
  2629  // consulting r.Method, r.Host, and r.URL.Path. It always returns
  2630  // a non-nil handler. If the path is not in its canonical form, the
  2631  // handler will be an internally-generated handler that redirects
  2632  // to the canonical path. If the host contains a port, it is ignored
  2633  // when matching handlers.
  2634  //
  2635  // The path and host are used unchanged for CONNECT requests.
  2636  //
  2637  // Handler also returns the registered pattern that matches the
  2638  // request or, in the case of internally-generated redirects,
  2639  // the path that will match after following the redirect.
  2640  //
  2641  // If there is no registered handler that applies to the request,
  2642  // Handler returns a “page not found” or “method not supported”
  2643  // handler and an empty pattern.
  2644  //
  2645  // Handler does not modify its argument. In particular, it does not
  2646  // populate named path wildcards, so r.PathValue will always return
  2647  // the empty string.
  2648  func (mux *ServeMux) Handler(r *Request) (h Handler, pattern string) {
  2649  	if use121 {
  2650  		return mux.mux121.findHandler(r)
  2651  	}
  2652  	h, p, _, _ := mux.findHandler(r)
  2653  	return h, p
  2654  }
  2655  
  2656  // findHandler finds a handler for a request.
  2657  // If there is a matching handler, it returns it and the pattern that matched.
  2658  // Otherwise it returns a Redirect or NotFound handler with the path that would match
  2659  // after the redirect.
  2660  func (mux *ServeMux) findHandler(r *Request) (h Handler, patStr string, _ *pattern, matches []string) {
  2661  	var n *routingNode
  2662  	host := r.URL.Host
  2663  	escapedPath := r.URL.EscapedPath()
  2664  	path := escapedPath
  2665  	// CONNECT requests are not canonicalized.
  2666  	if r.Method == "CONNECT" {
  2667  		// If r.URL.Path is /tree and its handler is not registered,
  2668  		// the /tree -> /tree/ redirect applies to CONNECT requests
  2669  		// but the path canonicalization does not.
  2670  		_, _, u := mux.matchOrRedirect(host, r.Method, path, r.URL)
  2671  		if u != nil {
  2672  			return RedirectHandler(u.String(), StatusTemporaryRedirect), u.Path, nil, nil
  2673  		}
  2674  		// Redo the match, this time with r.Host instead of r.URL.Host.
  2675  		// Pass a nil URL to skip the trailing-slash redirect logic.
  2676  		n, matches, _ = mux.matchOrRedirect(r.Host, r.Method, path, nil)
  2677  	} else {
  2678  		// All other requests have any port stripped and path cleaned
  2679  		// before passing to mux.handler.
  2680  		host = stripHostPort(r.Host)
  2681  		path = cleanPath(path)
  2682  
  2683  		// If the given path is /tree and its handler is not registered,
  2684  		// redirect for /tree/.
  2685  		var u *url.URL
  2686  		n, matches, u = mux.matchOrRedirect(host, r.Method, path, r.URL)
  2687  		if u != nil {
  2688  			return RedirectHandler(u.String(), StatusTemporaryRedirect), n.pattern.String(), nil, nil
  2689  		}
  2690  		if path != escapedPath {
  2691  			// Redirect to cleaned path.
  2692  			patStr := ""
  2693  			if n != nil {
  2694  				patStr = n.pattern.String()
  2695  			}
  2696  			u := &url.URL{Path: path, RawQuery: r.URL.RawQuery}
  2697  			return RedirectHandler(u.String(), StatusTemporaryRedirect), patStr, nil, nil
  2698  		}
  2699  	}
  2700  	if n == nil {
  2701  		// We didn't find a match with the request method. To distinguish between
  2702  		// Not Found and Method Not Allowed, see if there is another pattern that
  2703  		// matches except for the method.
  2704  		allowedMethods := mux.matchingMethods(host, path)
  2705  		if len(allowedMethods) > 0 {
  2706  			return HandlerFunc(func(w ResponseWriter, r *Request) {
  2707  				w.Header().Set("Allow", strings.Join(allowedMethods, ", "))
  2708  				Error(w, StatusText(StatusMethodNotAllowed), StatusMethodNotAllowed)
  2709  			}), "", nil, nil
  2710  		}
  2711  		return NotFoundHandler(), "", nil, nil
  2712  	}
  2713  	return n.handler, n.pattern.String(), n.pattern, matches
  2714  }
  2715  
  2716  // matchOrRedirect looks up a node in the tree that matches the host, method and path.
  2717  //
  2718  // If the url argument is non-nil, handler also deals with trailing-slash
  2719  // redirection: when a path doesn't match exactly, the match is tried again
  2720  // after appending "/" to the path. If that second match succeeds, the last
  2721  // return value is the URL to redirect to.
  2722  func (mux *ServeMux) matchOrRedirect(host, method, path string, u *url.URL) (_ *routingNode, matches []string, redirectTo *url.URL) {
  2723  	mux.mu.RLock()
  2724  	defer mux.mu.RUnlock()
  2725  
  2726  	n, matches := mux.tree.match(host, method, path)
  2727  	// We can terminate here if any of the following is true:
  2728  	// - We have an exact match already.
  2729  	// - We were asked not to try trailing slash redirection.
  2730  	// - The URL already has a trailing slash.
  2731  	// - The URL is an empty string.
  2732  	if !exactMatch(n, path) && u != nil && !strings.HasSuffix(path, "/") && path != "" {
  2733  		// If there is an exact match with a trailing slash, then redirect.
  2734  		path += "/"
  2735  		n2, _ := mux.tree.match(host, method, path)
  2736  		if exactMatch(n2, path) {
  2737  			// It is safe to return n2 here: it is used only in the second RedirectHandler case
  2738  			// of findHandler, and that method returns before it does the "n == nil" check where
  2739  			// the first return value matters. We return it here only to make the pattern available
  2740  			// to findHandler.
  2741  			return n2, nil, &url.URL{Path: cleanPath(u.Path) + "/", RawQuery: u.RawQuery}
  2742  		}
  2743  	}
  2744  	return n, matches, nil
  2745  }
  2746  
  2747  // exactMatch reports whether the node's pattern exactly matches the path.
  2748  // As a special case, if the node is nil, exactMatch return false.
  2749  //
  2750  // Before wildcards were introduced, it was clear that an exact match meant
  2751  // that the pattern and path were the same string. The only other possibility
  2752  // was that a trailing-slash pattern, like "/", matched a path longer than
  2753  // it, like "/a".
  2754  //
  2755  // With wildcards, we define an inexact match as any one where a multi wildcard
  2756  // matches a non-empty string. All other matches are exact.
  2757  // For example, these are all exact matches:
  2758  //
  2759  //	pattern   path
  2760  //	/a        /a
  2761  //	/{x}      /a
  2762  //	/a/{$}    /a/
  2763  //	/a/       /a/
  2764  //
  2765  // The last case has a multi wildcard (implicitly), but the match is exact because
  2766  // the wildcard matches the empty string.
  2767  //
  2768  // Examples of matches that are not exact:
  2769  //
  2770  //	pattern   path
  2771  //	/         /a
  2772  //	/a/{x...} /a/b
  2773  func exactMatch(n *routingNode, path string) bool {
  2774  	if n == nil {
  2775  		return false
  2776  	}
  2777  	// We can't directly implement the definition (empty match for multi
  2778  	// wildcard) because we don't record a match for anonymous multis.
  2779  
  2780  	// If there is no multi, the match is exact.
  2781  	if !n.pattern.lastSegment().multi {
  2782  		return true
  2783  	}
  2784  
  2785  	// If the path doesn't end in a trailing slash, then the multi match
  2786  	// is non-empty.
  2787  	if len(path) > 0 && path[len(path)-1] != '/' {
  2788  		return false
  2789  	}
  2790  	// Only patterns ending in {$} or a multi wildcard can
  2791  	// match a path with a trailing slash.
  2792  	// For the match to be exact, the number of pattern
  2793  	// segments should be the same as the number of slashes in the path.
  2794  	// E.g. "/a/b/{$}" and "/a/b/{...}" exactly match "/a/b/", but "/a/" does not.
  2795  	return len(n.pattern.segments) == strings.Count(path, "/")
  2796  }
  2797  
  2798  // matchingMethods return a sorted list of all methods that would match with the given host and path.
  2799  func (mux *ServeMux) matchingMethods(host, path string) []string {
  2800  	// Hold the read lock for the entire method so that the two matches are done
  2801  	// on the same set of registered patterns.
  2802  	mux.mu.RLock()
  2803  	defer mux.mu.RUnlock()
  2804  	ms := map[string]bool{}
  2805  	mux.tree.matchingMethods(host, path, ms)
  2806  	// matchOrRedirect will try appending a trailing slash if there is no match.
  2807  	if !strings.HasSuffix(path, "/") {
  2808  		mux.tree.matchingMethods(host, path+"/", ms)
  2809  	}
  2810  	return slices.Sorted(maps.Keys(ms))
  2811  }
  2812  
  2813  // ServeHTTP dispatches the request to the handler whose
  2814  // pattern most closely matches the request URL.
  2815  func (mux *ServeMux) ServeHTTP(w ResponseWriter, r *Request) {
  2816  	if r.RequestURI == "*" {
  2817  		if r.ProtoAtLeast(1, 1) {
  2818  			w.Header().Set("Connection", "close")
  2819  		}
  2820  		w.WriteHeader(StatusBadRequest)
  2821  		return
  2822  	}
  2823  	var h Handler
  2824  	if use121 {
  2825  		h, _ = mux.mux121.findHandler(r)
  2826  	} else {
  2827  		h, r.Pattern, r.pat, r.matches = mux.findHandler(r)
  2828  	}
  2829  	h.ServeHTTP(w, r)
  2830  }
  2831  
  2832  // The four functions below all call ServeMux.register so that callerLocation
  2833  // always refers to user code.
  2834  
  2835  // Handle registers the handler for the given pattern.
  2836  // If the given pattern conflicts with one that is already registered
  2837  // or if the pattern is invalid, Handle panics.
  2838  //
  2839  // See [ServeMux] for details on valid patterns and conflict rules.
  2840  func (mux *ServeMux) Handle(pattern string, handler Handler) {
  2841  	if use121 {
  2842  		mux.mux121.handle(pattern, handler)
  2843  	} else {
  2844  		mux.register(pattern, handler)
  2845  	}
  2846  }
  2847  
  2848  // HandleFunc registers the handler function for the given pattern.
  2849  // If the given pattern conflicts with one that is already registered
  2850  // or if the pattern is invalid, HandleFunc panics.
  2851  //
  2852  // See [ServeMux] for details on valid patterns and conflict rules.
  2853  func (mux *ServeMux) HandleFunc(pattern string, handler func(ResponseWriter, *Request)) {
  2854  	if use121 {
  2855  		mux.mux121.handleFunc(pattern, handler)
  2856  	} else {
  2857  		mux.register(pattern, HandlerFunc(handler))
  2858  	}
  2859  }
  2860  
  2861  // Handle registers the handler for the given pattern in [DefaultServeMux].
  2862  // The documentation for [ServeMux] explains how patterns are matched.
  2863  func Handle(pattern string, handler Handler) {
  2864  	if use121 {
  2865  		DefaultServeMux.mux121.handle(pattern, handler)
  2866  	} else {
  2867  		DefaultServeMux.register(pattern, handler)
  2868  	}
  2869  }
  2870  
  2871  // HandleFunc registers the handler function for the given pattern in [DefaultServeMux].
  2872  // The documentation for [ServeMux] explains how patterns are matched.
  2873  func HandleFunc(pattern string, handler func(ResponseWriter, *Request)) {
  2874  	if use121 {
  2875  		DefaultServeMux.mux121.handleFunc(pattern, handler)
  2876  	} else {
  2877  		DefaultServeMux.register(pattern, HandlerFunc(handler))
  2878  	}
  2879  }
  2880  
  2881  func (mux *ServeMux) register(pattern string, handler Handler) {
  2882  	if err := mux.registerErr(pattern, handler); err != nil {
  2883  		panic(err)
  2884  	}
  2885  }
  2886  
  2887  func (mux *ServeMux) registerErr(patstr string, handler Handler) error {
  2888  	if patstr == "" {
  2889  		return errors.New("http: invalid pattern")
  2890  	}
  2891  	if handler == nil {
  2892  		return errors.New("http: nil handler")
  2893  	}
  2894  	if f, ok := handler.(HandlerFunc); ok && f == nil {
  2895  		return errors.New("http: nil handler")
  2896  	}
  2897  
  2898  	pat, err := parsePattern(patstr)
  2899  	if err != nil {
  2900  		return fmt.Errorf("parsing %q: %w", patstr, err)
  2901  	}
  2902  
  2903  	// Get the caller's location, for better conflict error messages.
  2904  	// Skip register and whatever calls it.
  2905  	_, file, line, ok := runtime.Caller(3)
  2906  	if !ok {
  2907  		pat.loc = "unknown location"
  2908  	} else {
  2909  		pat.loc = fmt.Sprintf("%s:%d", file, line)
  2910  	}
  2911  
  2912  	mux.mu.Lock()
  2913  	defer mux.mu.Unlock()
  2914  	// Check for conflict.
  2915  	if err := mux.index.possiblyConflictingPatterns(pat, func(pat2 *pattern) error {
  2916  		if pat.conflictsWith(pat2) {
  2917  			d := describeConflict(pat, pat2)
  2918  			return fmt.Errorf("pattern %q (registered at %s) conflicts with pattern %q (registered at %s):\n%s",
  2919  				pat, pat.loc, pat2, pat2.loc, d)
  2920  		}
  2921  		return nil
  2922  	}); err != nil {
  2923  		return err
  2924  	}
  2925  	mux.tree.addPattern(pat, handler)
  2926  	mux.index.addPattern(pat)
  2927  	return nil
  2928  }
  2929  
  2930  // Serve accepts incoming HTTP connections on the listener l,
  2931  // creating a new service goroutine for each. The service goroutines
  2932  // read requests and then call handler to reply to them.
  2933  //
  2934  // The handler is typically nil, in which case [DefaultServeMux] is used.
  2935  //
  2936  // HTTP/2 support is only enabled if the Listener returns [*tls.Conn]
  2937  // connections and they were configured with "h2" in the TLS
  2938  // Config.NextProtos.
  2939  //
  2940  // Serve always returns a non-nil error.
  2941  func Serve(l net.Listener, handler Handler) error {
  2942  	srv := &Server{Handler: handler}
  2943  	return srv.Serve(l)
  2944  }
  2945  
  2946  // ServeTLS accepts incoming HTTPS connections on the listener l,
  2947  // creating a new service goroutine for each. The service goroutines
  2948  // read requests and then call handler to reply to them.
  2949  //
  2950  // The handler is typically nil, in which case [DefaultServeMux] is used.
  2951  //
  2952  // Additionally, files containing a certificate and matching private key
  2953  // for the server must be provided. If the certificate is signed by a
  2954  // certificate authority, the certFile should be the concatenation
  2955  // of the server's certificate, any intermediates, and the CA's certificate.
  2956  //
  2957  // ServeTLS always returns a non-nil error.
  2958  func ServeTLS(l net.Listener, handler Handler, certFile, keyFile string) error {
  2959  	srv := &Server{Handler: handler}
  2960  	return srv.ServeTLS(l, certFile, keyFile)
  2961  }
  2962  
  2963  // A Server defines parameters for running an HTTP server.
  2964  // The zero value for Server is a valid configuration.
  2965  type Server struct {
  2966  	// Addr optionally specifies the TCP address for the server to listen on,
  2967  	// in the form "host:port". If empty, ":http" (port 80) is used.
  2968  	// The service names are defined in RFC 6335 and assigned by IANA.
  2969  	// See net.Dial for details of the address format.
  2970  	Addr string
  2971  
  2972  	Handler Handler // handler to invoke, http.DefaultServeMux if nil
  2973  
  2974  	// DisableGeneralOptionsHandler, if true, passes "OPTIONS *" requests to the Handler,
  2975  	// otherwise responds with 200 OK and Content-Length: 0.
  2976  	DisableGeneralOptionsHandler bool
  2977  
  2978  	// TLSConfig optionally provides a TLS configuration for use
  2979  	// by ServeTLS and ListenAndServeTLS. Note that this value is
  2980  	// cloned by ServeTLS and ListenAndServeTLS, so it's not
  2981  	// possible to modify the configuration with methods like
  2982  	// tls.Config.SetSessionTicketKeys. To use
  2983  	// SetSessionTicketKeys, use Server.Serve with a TLS Listener
  2984  	// instead.
  2985  	TLSConfig *tls.Config
  2986  
  2987  	// ReadTimeout is the maximum duration for reading the entire
  2988  	// request, including the body. A zero or negative value means
  2989  	// there will be no timeout.
  2990  	//
  2991  	// Because ReadTimeout does not let Handlers make per-request
  2992  	// decisions on each request body's acceptable deadline or
  2993  	// upload rate, most users will prefer to use
  2994  	// ReadHeaderTimeout. It is valid to use them both.
  2995  	ReadTimeout time.Duration
  2996  
  2997  	// ReadHeaderTimeout is the amount of time allowed to read
  2998  	// request headers. The connection's read deadline is reset
  2999  	// after reading the headers and the Handler can decide what
  3000  	// is considered too slow for the body. If zero, the value of
  3001  	// ReadTimeout is used. If negative, or if zero and ReadTimeout
  3002  	// is zero or negative, there is no timeout.
  3003  	ReadHeaderTimeout time.Duration
  3004  
  3005  	// WriteTimeout is the maximum duration before timing out
  3006  	// writes of the response. It is reset whenever a new
  3007  	// request's header is read. Like ReadTimeout, it does not
  3008  	// let Handlers make decisions on a per-request basis.
  3009  	// A zero or negative value means there will be no timeout.
  3010  	WriteTimeout time.Duration
  3011  
  3012  	// IdleTimeout is the maximum amount of time to wait for the
  3013  	// next request when keep-alives are enabled. If zero, the value
  3014  	// of ReadTimeout is used. If negative, or if zero and ReadTimeout
  3015  	// is zero or negative, there is no timeout.
  3016  	IdleTimeout time.Duration
  3017  
  3018  	// MaxHeaderBytes controls the maximum number of bytes the
  3019  	// server will read parsing the request header's keys and
  3020  	// values, including the request line. It does not limit the
  3021  	// size of the request body.
  3022  	// If zero, DefaultMaxHeaderBytes is used.
  3023  	MaxHeaderBytes int
  3024  
  3025  	// TLSNextProto optionally specifies a function to take over
  3026  	// ownership of the provided TLS connection when an ALPN
  3027  	// protocol upgrade has occurred. The map key is the protocol
  3028  	// name negotiated. The Handler argument should be used to
  3029  	// handle HTTP requests and will initialize the Request's TLS
  3030  	// and RemoteAddr if not already set. The connection is
  3031  	// automatically closed when the function returns.
  3032  	// If TLSNextProto is not nil, HTTP/2 support is not enabled
  3033  	// automatically.
  3034  	//
  3035  	// Historically, TLSNextProto was used to disable HTTP/2 support.
  3036  	// The Server.Protocols field now provides a simpler way to do this.
  3037  	TLSNextProto map[string]func(*Server, *tls.Conn, Handler)
  3038  
  3039  	// ConnState specifies an optional callback function that is
  3040  	// called when a client connection changes state. See the
  3041  	// ConnState type and associated constants for details.
  3042  	ConnState func(net.Conn, ConnState)
  3043  
  3044  	// ErrorLog specifies an optional logger for errors accepting
  3045  	// connections, unexpected behavior from handlers, and
  3046  	// underlying FileSystem errors.
  3047  	// If nil, logging is done via the log package's standard logger.
  3048  	ErrorLog *log.Logger
  3049  
  3050  	// BaseContext optionally specifies a function that returns
  3051  	// the base context for incoming requests on this server.
  3052  	// The provided Listener is the specific Listener that's
  3053  	// about to start accepting requests.
  3054  	// If BaseContext is nil, the default is context.Background().
  3055  	// If non-nil, it must return a non-nil context.
  3056  	BaseContext func(net.Listener) context.Context
  3057  
  3058  	// ConnContext optionally specifies a function that modifies
  3059  	// the context used for a new connection c. The provided ctx
  3060  	// is derived from the base context and has a ServerContextKey
  3061  	// value.
  3062  	ConnContext func(ctx context.Context, c net.Conn) context.Context
  3063  
  3064  	// HTTP2 configures HTTP/2 connections.
  3065  	HTTP2 *HTTP2Config
  3066  
  3067  	// Protocols is the set of protocols accepted by the server.
  3068  	//
  3069  	// If Protocols includes UnencryptedHTTP2, the server will accept
  3070  	// unencrypted HTTP/2 connections. The server can serve both
  3071  	// HTTP/1 and unencrypted HTTP/2 on the same address and port.
  3072  	//
  3073  	// If Protocols is nil, the default is usually HTTP/1 and HTTP/2.
  3074  	// If TLSNextProto is non-nil and does not contain an "h2" entry,
  3075  	// the default is HTTP/1 only.
  3076  	Protocols *Protocols
  3077  
  3078  	// DisableClientPriority specifies whether client-specified priority, as
  3079  	// specified in RFC 9218, should be respected or not.
  3080  	//
  3081  	// This field only takes effect if using HTTP/2, and if no custom write
  3082  	// scheduler is defined for the HTTP/2 server. Otherwise, this field is a
  3083  	// no-op.
  3084  	//
  3085  	// If set to true, requests will be served in a round-robin manner, without
  3086  	// prioritization.
  3087  	DisableClientPriority bool
  3088  
  3089  	inShutdown atomic.Bool // true when server is in shutdown
  3090  
  3091  	disableKeepAlives atomic.Bool
  3092  	nextProtoOnce     sync.Once // guards setupHTTP2_* init
  3093  	nextProtoErr      error     // result of http2.ConfigureServer if used
  3094  
  3095  	mu         sync.Mutex
  3096  	listeners  map[*net.Listener]struct{}
  3097  	activeConn map[*conn]struct{}
  3098  	onShutdown []func()
  3099  	h2         *http2Server
  3100  
  3101  	listenerGroup sync.WaitGroup
  3102  }
  3103  
  3104  // Close immediately closes all active net.Listeners and any
  3105  // connections in state [StateNew], [StateActive], or [StateIdle]. For a
  3106  // graceful shutdown, use [Server.Shutdown].
  3107  //
  3108  // Close does not attempt to close (and does not even know about)
  3109  // any hijacked connections, such as WebSockets.
  3110  //
  3111  // Close returns any error returned from closing the [Server]'s
  3112  // underlying Listener(s).
  3113  func (s *Server) Close() error {
  3114  	s.inShutdown.Store(true)
  3115  	s.mu.Lock()
  3116  	defer s.mu.Unlock()
  3117  	err := s.closeListenersLocked()
  3118  
  3119  	// Unlock s.mu while waiting for listenerGroup.
  3120  	// The group Add and Done calls are made with s.mu held,
  3121  	// to avoid adding a new listener in the window between
  3122  	// us setting inShutdown above and waiting here.
  3123  	s.mu.Unlock()
  3124  	s.listenerGroup.Wait()
  3125  	s.mu.Lock()
  3126  
  3127  	for c := range s.activeConn {
  3128  		c.rwc.Close()
  3129  		delete(s.activeConn, c)
  3130  	}
  3131  	return err
  3132  }
  3133  
  3134  // shutdownPollIntervalMax is the max polling interval when checking
  3135  // quiescence during Server.Shutdown. Polling starts with a small
  3136  // interval and backs off to the max.
  3137  // Ideally we could find a solution that doesn't involve polling,
  3138  // but which also doesn't have a high runtime cost (and doesn't
  3139  // involve any contentious mutexes), but that is left as an
  3140  // exercise for the reader.
  3141  const shutdownPollIntervalMax = 500 * time.Millisecond
  3142  
  3143  // Shutdown gracefully shuts down the server without interrupting any
  3144  // active connections. Shutdown works by first closing all open
  3145  // listeners, then closing all idle connections, and then waiting
  3146  // indefinitely for connections to return to idle and then shut down.
  3147  // If the provided context expires before the shutdown is complete,
  3148  // Shutdown returns the context's error, otherwise it returns any
  3149  // error returned from closing the [Server]'s underlying Listener(s).
  3150  //
  3151  // When Shutdown is called, [Serve], [ServeTLS], [ListenAndServe], and
  3152  // [ListenAndServeTLS] immediately return [ErrServerClosed]. Make sure the
  3153  // program doesn't exit and waits instead for Shutdown to return.
  3154  //
  3155  // Shutdown does not attempt to close nor wait for hijacked
  3156  // connections such as WebSockets. The caller of Shutdown should
  3157  // separately notify such long-lived connections of shutdown and wait
  3158  // for them to close, if desired. See [Server.RegisterOnShutdown] for a way to
  3159  // register shutdown notification functions.
  3160  //
  3161  // Once Shutdown has been called on a server, it may not be reused;
  3162  // future calls to methods such as Serve will return ErrServerClosed.
  3163  func (s *Server) Shutdown(ctx context.Context) error {
  3164  	s.inShutdown.Store(true)
  3165  
  3166  	s.mu.Lock()
  3167  	lnerr := s.closeListenersLocked()
  3168  	for _, f := range s.onShutdown {
  3169  		go f()
  3170  	}
  3171  	s.mu.Unlock()
  3172  	s.listenerGroup.Wait()
  3173  
  3174  	pollIntervalBase := time.Millisecond
  3175  	nextPollInterval := func() time.Duration {
  3176  		// Add 10% jitter.
  3177  		interval := pollIntervalBase + time.Duration(rand.IntN(int(pollIntervalBase/10)))
  3178  		// Double and clamp for next time.
  3179  		pollIntervalBase *= 2
  3180  		if pollIntervalBase > shutdownPollIntervalMax {
  3181  			pollIntervalBase = shutdownPollIntervalMax
  3182  		}
  3183  		return interval
  3184  	}
  3185  
  3186  	timer := time.NewTimer(nextPollInterval())
  3187  	defer timer.Stop()
  3188  	for {
  3189  		if s.closeIdleConns() {
  3190  			return lnerr
  3191  		}
  3192  		select {
  3193  		case <-ctx.Done():
  3194  			return ctx.Err()
  3195  		case <-timer.C:
  3196  			timer.Reset(nextPollInterval())
  3197  		}
  3198  	}
  3199  }
  3200  
  3201  // RegisterOnShutdown registers a function to call on [Server.Shutdown].
  3202  // This can be used to gracefully shutdown connections that have
  3203  // undergone ALPN protocol upgrade or that have been hijacked.
  3204  // This function should start protocol-specific graceful shutdown,
  3205  // but should not wait for shutdown to complete.
  3206  func (s *Server) RegisterOnShutdown(f func()) {
  3207  	s.mu.Lock()
  3208  	s.onShutdown = append(s.onShutdown, f)
  3209  	s.mu.Unlock()
  3210  }
  3211  
  3212  // closeIdleConns closes all idle connections and reports whether the
  3213  // server is quiescent.
  3214  func (s *Server) closeIdleConns() bool {
  3215  	s.mu.Lock()
  3216  	defer s.mu.Unlock()
  3217  	quiescent := true
  3218  	for c := range s.activeConn {
  3219  		st, unixSec := c.getState()
  3220  		// Issue 22682: treat StateNew connections as if
  3221  		// they're idle if we haven't read the first request's
  3222  		// header in over 5 seconds.
  3223  		if st == StateNew && unixSec < time.Now().Unix()-5 {
  3224  			st = StateIdle
  3225  		}
  3226  		if st != StateIdle || unixSec == 0 {
  3227  			// Assume unixSec == 0 means it's a very new
  3228  			// connection, without state set yet.
  3229  			quiescent = false
  3230  			continue
  3231  		}
  3232  		c.rwc.Close()
  3233  		delete(s.activeConn, c)
  3234  	}
  3235  	return quiescent
  3236  }
  3237  
  3238  func (s *Server) closeListenersLocked() error {
  3239  	var err error
  3240  	for ln := range s.listeners {
  3241  		if cerr := (*ln).Close(); cerr != nil && err == nil {
  3242  			err = cerr
  3243  		}
  3244  	}
  3245  	return err
  3246  }
  3247  
  3248  // A ConnState represents the state of a client connection to a server.
  3249  // It's used by the optional [Server.ConnState] hook.
  3250  type ConnState int
  3251  
  3252  const (
  3253  	// StateNew represents a new connection that is expected to
  3254  	// send a request immediately. Connections begin at this
  3255  	// state and then transition to either StateActive or
  3256  	// StateClosed.
  3257  	StateNew ConnState = iota
  3258  
  3259  	// StateActive represents a connection that has read 1 or more
  3260  	// bytes of a request. The Server.ConnState hook for
  3261  	// StateActive fires before the request has entered a handler
  3262  	// and doesn't fire again until the request has been
  3263  	// handled. After the request is handled, the state
  3264  	// transitions to StateClosed, StateHijacked, or StateIdle.
  3265  	// For HTTP/2, StateActive fires on the transition from zero
  3266  	// to one active request, and only transitions away once all
  3267  	// active requests are complete. That means that ConnState
  3268  	// cannot be used to do per-request work; ConnState only notes
  3269  	// the overall state of the connection.
  3270  	StateActive
  3271  
  3272  	// StateIdle represents a connection that has finished
  3273  	// handling a request and is in the keep-alive state, waiting
  3274  	// for a new request. Connections transition from StateIdle
  3275  	// to either StateActive or StateClosed.
  3276  	StateIdle
  3277  
  3278  	// StateHijacked represents a hijacked connection.
  3279  	// This is a terminal state. It does not transition to StateClosed.
  3280  	StateHijacked
  3281  
  3282  	// StateClosed represents a closed connection.
  3283  	// This is a terminal state. Hijacked connections do not
  3284  	// transition to StateClosed.
  3285  	StateClosed
  3286  )
  3287  
  3288  var stateName = map[ConnState]string{
  3289  	StateNew:      "new",
  3290  	StateActive:   "active",
  3291  	StateIdle:     "idle",
  3292  	StateHijacked: "hijacked",
  3293  	StateClosed:   "closed",
  3294  }
  3295  
  3296  func (c ConnState) String() string {
  3297  	return stateName[c]
  3298  }
  3299  
  3300  // serverHandler delegates to either the server's Handler or
  3301  // DefaultServeMux and also handles "OPTIONS *" requests.
  3302  type serverHandler struct {
  3303  	srv *Server
  3304  }
  3305  
  3306  // ServeHTTP should be an internal detail,
  3307  // but widely used packages access it using linkname.
  3308  // Notable members of the hall of shame include:
  3309  //   - github.com/erda-project/erda-infra
  3310  //
  3311  // Do not remove or change the type signature.
  3312  // See go.dev/issue/67401.
  3313  //
  3314  //go:linkname badServeHTTP net/http.serverHandler.ServeHTTP
  3315  func (sh serverHandler) ServeHTTP(rw ResponseWriter, req *Request) {
  3316  	handler := sh.srv.Handler
  3317  	if handler == nil {
  3318  		handler = DefaultServeMux
  3319  	}
  3320  	if !sh.srv.DisableGeneralOptionsHandler && req.RequestURI == "*" && req.Method == "OPTIONS" {
  3321  		handler = globalOptionsHandler{}
  3322  	}
  3323  
  3324  	handler.ServeHTTP(rw, req)
  3325  }
  3326  
  3327  func badServeHTTP(serverHandler, ResponseWriter, *Request)
  3328  
  3329  // AllowQuerySemicolons returns a handler that serves requests by converting any
  3330  // unescaped semicolons in the URL query to ampersands, and invoking the handler h.
  3331  //
  3332  // This restores the pre-Go 1.17 behavior of splitting query parameters on both
  3333  // semicolons and ampersands. (See golang.org/issue/25192). Note that this
  3334  // behavior doesn't match that of many proxies, and the mismatch can lead to
  3335  // security issues.
  3336  //
  3337  // AllowQuerySemicolons should be invoked before [Request.ParseForm] is called.
  3338  func AllowQuerySemicolons(h Handler) Handler {
  3339  	return HandlerFunc(func(w ResponseWriter, r *Request) {
  3340  		if strings.Contains(r.URL.RawQuery, ";") {
  3341  			r2 := new(Request)
  3342  			*r2 = *r
  3343  			r2.URL = new(url.URL)
  3344  			*r2.URL = *r.URL
  3345  			r2.URL.RawQuery = strings.ReplaceAll(r.URL.RawQuery, ";", "&")
  3346  			h.ServeHTTP(w, r2)
  3347  		} else {
  3348  			h.ServeHTTP(w, r)
  3349  		}
  3350  	})
  3351  }
  3352  
  3353  // ListenAndServe listens on the TCP network address s.Addr and then
  3354  // calls [Serve] to handle requests on incoming connections.
  3355  // Accepted connections are configured to enable TCP keep-alives.
  3356  //
  3357  // If s.Addr is blank, ":http" is used.
  3358  //
  3359  // ListenAndServe always returns a non-nil error. After [Server.Shutdown] or [Server.Close],
  3360  // the returned error is [ErrServerClosed].
  3361  func (s *Server) ListenAndServe() error {
  3362  	if s.shuttingDown() {
  3363  		return ErrServerClosed
  3364  	}
  3365  	addr := s.Addr
  3366  	if addr == "" {
  3367  		addr = ":http"
  3368  	}
  3369  	ln, err := net.Listen("tcp", addr)
  3370  	if err != nil {
  3371  		return err
  3372  	}
  3373  	return s.Serve(ln)
  3374  }
  3375  
  3376  var testHookServerServe func(*Server, net.Listener) // used if non-nil
  3377  
  3378  // shouldConfigureHTTP2ForServe reports whether Server.Serve should configure
  3379  // automatic HTTP/2. (which sets up the s.TLSNextProto map)
  3380  func (s *Server) shouldConfigureHTTP2ForServe() bool {
  3381  	if s.TLSConfig == nil {
  3382  		// Compatibility with Go 1.6:
  3383  		// If there's no TLSConfig, it's possible that the user just
  3384  		// didn't set it on the http.Server, but did pass it to
  3385  		// tls.NewListener and passed that listener to Serve.
  3386  		// So we should configure HTTP/2 (to set up s.TLSNextProto)
  3387  		// in case the listener returns an "h2" *tls.Conn.
  3388  		return true
  3389  	}
  3390  	if s.protocols().UnencryptedHTTP2() {
  3391  		return true
  3392  	}
  3393  	// The user specified a TLSConfig on their http.Server.
  3394  	// In this, case, only configure HTTP/2 if their tls.Config
  3395  	// explicitly mentions "h2". Otherwise http2.ConfigureServer
  3396  	// would modify the tls.Config to add it, but they probably already
  3397  	// passed this tls.Config to tls.NewListener. And if they did,
  3398  	// it's too late anyway to fix it. It would only be potentially racy.
  3399  	// See Issue 15908.
  3400  	return slices.Contains(s.TLSConfig.NextProtos, "h2")
  3401  }
  3402  
  3403  // ErrServerClosed is returned by the [Server.Serve], [ServeTLS], [ListenAndServe],
  3404  // and [ListenAndServeTLS] methods after a call to [Server.Shutdown] or [Server.Close].
  3405  var ErrServerClosed = errors.New("http: Server closed")
  3406  
  3407  // Serve accepts incoming connections on the Listener l, creating a
  3408  // new service goroutine for each. The service goroutines read requests and
  3409  // then call s.Handler to reply to them.
  3410  //
  3411  // HTTP/2 support is only enabled if the Listener returns [*tls.Conn]
  3412  // connections and they were configured with "h2" in the TLS
  3413  // Config.NextProtos.
  3414  //
  3415  // Serve always returns a non-nil error and closes l.
  3416  // After [Server.Shutdown] or [Server.Close], the returned error is [ErrServerClosed].
  3417  func (s *Server) Serve(l net.Listener) error {
  3418  	if fn := testHookServerServe; fn != nil {
  3419  		fn(s, l) // call hook with unwrapped listener
  3420  	}
  3421  
  3422  	origListener := l
  3423  	l = &onceCloseListener{Listener: l}
  3424  	defer l.Close()
  3425  
  3426  	if err := s.setupHTTP2_Serve(); err != nil {
  3427  		return err
  3428  	}
  3429  
  3430  	if !s.trackListener(&l, true) {
  3431  		return ErrServerClosed
  3432  	}
  3433  	defer s.trackListener(&l, false)
  3434  
  3435  	baseCtx := context.Background()
  3436  	if s.BaseContext != nil {
  3437  		baseCtx = s.BaseContext(origListener)
  3438  		if baseCtx == nil {
  3439  			panic("BaseContext returned a nil context")
  3440  		}
  3441  	}
  3442  
  3443  	var tempDelay time.Duration // how long to sleep on accept failure
  3444  
  3445  	ctx := context.WithValue(baseCtx, ServerContextKey, s)
  3446  	for {
  3447  		rw, err := l.Accept()
  3448  		if err != nil {
  3449  			if s.shuttingDown() {
  3450  				return ErrServerClosed
  3451  			}
  3452  			if ne, ok := err.(net.Error); ok && ne.Temporary() {
  3453  				if tempDelay == 0 {
  3454  					tempDelay = 5 * time.Millisecond
  3455  				} else {
  3456  					tempDelay *= 2
  3457  				}
  3458  				if max := 1 * time.Second; tempDelay > max {
  3459  					tempDelay = max
  3460  				}
  3461  				s.logf("http: Accept error: %v; retrying in %v", err, tempDelay)
  3462  				time.Sleep(tempDelay)
  3463  				continue
  3464  			}
  3465  			return err
  3466  		}
  3467  		connCtx := ctx
  3468  		if cc := s.ConnContext; cc != nil {
  3469  			connCtx = cc(connCtx, rw)
  3470  			if connCtx == nil {
  3471  				panic("ConnContext returned nil")
  3472  			}
  3473  		}
  3474  		tempDelay = 0
  3475  		c := s.newConn(rw)
  3476  		c.setState(c.rwc, StateNew, runHooks) // before Serve can return
  3477  		go c.serve(connCtx)
  3478  	}
  3479  }
  3480  
  3481  func (s *Server) setupTLSConfig(certFile, keyFile string, nextProtos []string) (*tls.Config, error) {
  3482  	config := cloneTLSConfig(s.TLSConfig)
  3483  	config.NextProtos = nextProtos
  3484  
  3485  	configHasCert := len(config.Certificates) > 0 || config.GetCertificate != nil || config.GetConfigForClient != nil
  3486  	if !configHasCert || certFile != "" || keyFile != "" {
  3487  		var err error
  3488  		config.Certificates = make([]tls.Certificate, 1)
  3489  		config.Certificates[0], err = tls.LoadX509KeyPair(certFile, keyFile)
  3490  		if err != nil {
  3491  			return nil, err
  3492  		}
  3493  	}
  3494  	return config, nil
  3495  }
  3496  
  3497  // ServeTLS accepts incoming connections on the Listener l, creating a
  3498  // new service goroutine for each. The service goroutines perform TLS
  3499  // setup and then read requests, calling s.Handler to reply to them.
  3500  //
  3501  // Files containing a certificate and matching private key for the
  3502  // server must be provided if neither the [Server]'s
  3503  // TLSConfig.Certificates, TLSConfig.GetCertificate nor
  3504  // config.GetConfigForClient are populated.
  3505  // If the certificate is signed by a certificate authority, the
  3506  // certFile should be the concatenation of the server's certificate,
  3507  // any intermediates, and the CA's certificate.
  3508  //
  3509  // ServeTLS always returns a non-nil error. After [Server.Shutdown] or [Server.Close], the
  3510  // returned error is [ErrServerClosed].
  3511  func (s *Server) ServeTLS(l net.Listener, certFile, keyFile string) error {
  3512  	// Setup HTTP/2 before s.Serve, to initialize s.TLSConfig
  3513  	// before we clone it and create the TLS Listener.
  3514  	if err := s.setupHTTP2_ServeTLS(); err != nil {
  3515  		return err
  3516  	}
  3517  
  3518  	config, err := s.setupTLSConfig(certFile, keyFile, adjustNextProtos(s.TLSConfig.NextProtos, s.protocols()))
  3519  	if err != nil {
  3520  		return err
  3521  	}
  3522  
  3523  	tlsListener := tls.NewListener(l, config)
  3524  	return s.Serve(tlsListener)
  3525  }
  3526  
  3527  func (s *Server) protocols() Protocols {
  3528  	if s.Protocols != nil {
  3529  		// Historically, even when Protocols for a Server was set to be empty,
  3530  		// the Server can still run normally with just HTTP/1.
  3531  		// To keep backward-compatibility, the zero value of Protocols is
  3532  		// defined as having only HTTP/1 enabled.
  3533  		if s.Protocols.empty() {
  3534  			var p Protocols
  3535  			p.SetHTTP1(true)
  3536  			return p
  3537  		}
  3538  		return *s.Protocols // user-configured set
  3539  	}
  3540  
  3541  	// The historic way of disabling HTTP/2 is to set TLSNextProto to
  3542  	// a non-nil map with no "h2" entry.
  3543  	_, hasH2 := s.TLSNextProto["h2"]
  3544  	http2Disabled := s.TLSNextProto != nil && !hasH2
  3545  
  3546  	// If GODEBUG=http2server=0, then HTTP/2 is disabled unless
  3547  	// the user has manually added an "h2" entry to TLSNextProto
  3548  	// (probably by using x/net/http2 directly).
  3549  	if http2server.Value() == "0" && !hasH2 {
  3550  		http2Disabled = true
  3551  	}
  3552  
  3553  	var p Protocols
  3554  	p.SetHTTP1(true) // default always includes HTTP/1
  3555  	if !http2Disabled {
  3556  		p.SetHTTP2(true)
  3557  	}
  3558  	return p
  3559  }
  3560  
  3561  // adjustNextProtos adds or removes "http/1.1" and "h2" entries from
  3562  // a tls.Config.NextProtos list, according to the set of protocols in protos.
  3563  func adjustNextProtos(nextProtos []string, protos Protocols) []string {
  3564  	// Make a copy of NextProtos since it might be shared with some other tls.Config.
  3565  	// (tls.Config.Clone doesn't do a deep copy.)
  3566  	//
  3567  	// We could avoid an allocation in the common case by checking to see if the slice
  3568  	// is already in order, but this is just one small allocation per connection.
  3569  	nextProtos = slices.Clone(nextProtos)
  3570  	var have Protocols
  3571  	nextProtos = slices.DeleteFunc(nextProtos, func(s string) bool {
  3572  		switch s {
  3573  		case "http/1.1":
  3574  			if !protos.HTTP1() {
  3575  				return true
  3576  			}
  3577  			have.SetHTTP1(true)
  3578  		case "h2":
  3579  			if !protos.HTTP2() {
  3580  				return true
  3581  			}
  3582  			have.SetHTTP2(true)
  3583  		}
  3584  		return false
  3585  	})
  3586  	if protos.HTTP2() && !have.HTTP2() {
  3587  		nextProtos = append(nextProtos, "h2")
  3588  	}
  3589  	if protos.HTTP1() && !have.HTTP1() {
  3590  		nextProtos = append(nextProtos, "http/1.1")
  3591  	}
  3592  	return nextProtos
  3593  }
  3594  
  3595  // trackListener adds or removes a net.Listener to the set of tracked
  3596  // listeners.
  3597  //
  3598  // We store a pointer to interface in the map set, in case the
  3599  // net.Listener is not comparable. This is safe because we only call
  3600  // trackListener via Serve and can track+defer untrack the same
  3601  // pointer to local variable there. We never need to compare a
  3602  // Listener from another caller.
  3603  //
  3604  // It reports whether the server is still up (not Shutdown or Closed).
  3605  func (s *Server) trackListener(ln *net.Listener, add bool) bool {
  3606  	s.mu.Lock()
  3607  	defer s.mu.Unlock()
  3608  	if s.listeners == nil {
  3609  		s.listeners = make(map[*net.Listener]struct{})
  3610  	}
  3611  	if add {
  3612  		if s.shuttingDown() {
  3613  			return false
  3614  		}
  3615  		s.listeners[ln] = struct{}{}
  3616  		s.listenerGroup.Add(1)
  3617  	} else {
  3618  		delete(s.listeners, ln)
  3619  		s.listenerGroup.Done()
  3620  	}
  3621  	return true
  3622  }
  3623  
  3624  func (s *Server) trackConn(c *conn, add bool) {
  3625  	s.mu.Lock()
  3626  	defer s.mu.Unlock()
  3627  	if s.activeConn == nil {
  3628  		s.activeConn = make(map[*conn]struct{})
  3629  	}
  3630  	if add {
  3631  		s.activeConn[c] = struct{}{}
  3632  	} else {
  3633  		delete(s.activeConn, c)
  3634  	}
  3635  }
  3636  
  3637  func (s *Server) idleTimeout() time.Duration {
  3638  	if s.IdleTimeout != 0 {
  3639  		return s.IdleTimeout
  3640  	}
  3641  	return s.ReadTimeout
  3642  }
  3643  
  3644  func (s *Server) readHeaderTimeout() time.Duration {
  3645  	if s.ReadHeaderTimeout != 0 {
  3646  		return s.ReadHeaderTimeout
  3647  	}
  3648  	return s.ReadTimeout
  3649  }
  3650  
  3651  func (s *Server) doKeepAlives() bool {
  3652  	return !s.disableKeepAlives.Load() && !s.shuttingDown()
  3653  }
  3654  
  3655  func (s *Server) shuttingDown() bool {
  3656  	return s.inShutdown.Load()
  3657  }
  3658  
  3659  // SetKeepAlivesEnabled controls whether HTTP keep-alives are enabled.
  3660  // By default, keep-alives are always enabled. Only very
  3661  // resource-constrained environments or servers in the process of
  3662  // shutting down should disable them.
  3663  func (s *Server) SetKeepAlivesEnabled(v bool) {
  3664  	if v {
  3665  		s.disableKeepAlives.Store(false)
  3666  		return
  3667  	}
  3668  	s.disableKeepAlives.Store(true)
  3669  
  3670  	// Close idle HTTP/1 conns:
  3671  	s.closeIdleConns()
  3672  
  3673  	// TODO: Issue 26303: close HTTP/2 conns as soon as they become idle.
  3674  }
  3675  
  3676  func (s *Server) logf(format string, args ...any) {
  3677  	if s.ErrorLog != nil {
  3678  		s.ErrorLog.Printf(format, args...)
  3679  	} else {
  3680  		log.Printf(format, args...)
  3681  	}
  3682  }
  3683  
  3684  // logf prints to the ErrorLog of the *Server associated with request r
  3685  // via ServerContextKey. If there's no associated server, or if ErrorLog
  3686  // is nil, logging is done via the log package's standard logger.
  3687  func logf(r *Request, format string, args ...any) {
  3688  	s, _ := r.Context().Value(ServerContextKey).(*Server)
  3689  	if s != nil && s.ErrorLog != nil {
  3690  		s.ErrorLog.Printf(format, args...)
  3691  	} else {
  3692  		log.Printf(format, args...)
  3693  	}
  3694  }
  3695  
  3696  // ListenAndServe listens on the TCP network address addr and then calls
  3697  // [Serve] with handler to handle requests on incoming connections.
  3698  // Accepted connections are configured to enable TCP keep-alives.
  3699  //
  3700  // The handler is typically nil, in which case [DefaultServeMux] is used.
  3701  //
  3702  // ListenAndServe always returns a non-nil error.
  3703  func ListenAndServe(addr string, handler Handler) error {
  3704  	server := &Server{Addr: addr, Handler: handler}
  3705  	return server.ListenAndServe()
  3706  }
  3707  
  3708  // ListenAndServeTLS acts identically to [ListenAndServe], except that it
  3709  // expects HTTPS connections. Additionally, files containing a certificate and
  3710  // matching private key for the server must be provided. If the certificate
  3711  // is signed by a certificate authority, the certFile should be the concatenation
  3712  // of the server's certificate, any intermediates, and the CA's certificate.
  3713  func ListenAndServeTLS(addr, certFile, keyFile string, handler Handler) error {
  3714  	server := &Server{Addr: addr, Handler: handler}
  3715  	return server.ListenAndServeTLS(certFile, keyFile)
  3716  }
  3717  
  3718  // http3ServerHandler implements an interface in an external library that
  3719  // supports HTTP/3, allowing an external implementation of HTTP/3 to be used
  3720  // via net/http. See https://go.dev/issue/77440 for details.
  3721  //
  3722  // This is currently only used with golang.org/x/net/internal/http3, to allow
  3723  // us to test our HTTP/3 implementation againts tests in net/http. HTTP/3 is
  3724  // not yet accessible to end-users.
  3725  type http3ServerHandler struct {
  3726  	handler   serverHandler
  3727  	tlsConfig *tls.Config
  3728  	baseCtx   context.Context
  3729  	errc      chan error
  3730  }
  3731  
  3732  // ServeHTTP ensures that http3ServerHandler implements the Handler interface,
  3733  // and gives an HTTP/3 server implementation access to the net/http handler.
  3734  func (h http3ServerHandler) ServeHTTP(w ResponseWriter, r *Request) {
  3735  	h.handler.ServeHTTP(w, r)
  3736  }
  3737  
  3738  // Addr gives an HTTP/3 server implementation the address that it should listen
  3739  // on.
  3740  func (h http3ServerHandler) Addr() string {
  3741  	return h.handler.srv.Addr
  3742  }
  3743  
  3744  // TLSConfig gives an HTTP/3 server implementation the *tls.Config that it
  3745  // should use.
  3746  func (h http3ServerHandler) TLSConfig() *tls.Config {
  3747  	return h.tlsConfig
  3748  }
  3749  
  3750  // BaseContext gives an HTTP/3 server implementation the base context to use
  3751  // for server requests.
  3752  func (h http3ServerHandler) BaseContext() context.Context {
  3753  	return h.baseCtx
  3754  }
  3755  
  3756  // ListenErrHook should be called by an HTTP/3 server implementation to
  3757  // propagate any error it encounters when trying to listen, if any, to
  3758  // net/http.
  3759  func (h http3ServerHandler) ListenErrHook(err error) {
  3760  	h.errc <- err
  3761  }
  3762  
  3763  // ListenAndServeTLS listens on the TCP network address s.Addr and
  3764  // then calls [ServeTLS] to handle requests on incoming TLS connections.
  3765  // Accepted connections are configured to enable TCP keep-alives.
  3766  //
  3767  // Filenames containing a certificate and matching private key for the
  3768  // server must be provided if neither the [Server]'s TLSConfig.Certificates
  3769  // nor TLSConfig.GetCertificate are populated. If the certificate is
  3770  // signed by a certificate authority, the certFile should be the
  3771  // concatenation of the server's certificate, any intermediates, and
  3772  // the CA's certificate.
  3773  //
  3774  // If s.Addr is blank, ":https" is used.
  3775  //
  3776  // ListenAndServeTLS always returns a non-nil error. After [Server.Shutdown] or
  3777  // [Server.Close], the returned error is [ErrServerClosed].
  3778  func (s *Server) ListenAndServeTLS(certFile, keyFile string) error {
  3779  	if s.shuttingDown() {
  3780  		return ErrServerClosed
  3781  	}
  3782  	addr := s.Addr
  3783  	if addr == "" {
  3784  		addr = ":https"
  3785  	}
  3786  
  3787  	p := s.protocols()
  3788  	if p.http3() {
  3789  		fn, ok := s.TLSNextProto["http/3"]
  3790  		if !ok {
  3791  			return errors.New("http: Server.Protocols contains HTTP3, but Server does not support HTTP/3")
  3792  		}
  3793  		config, err := s.setupTLSConfig(certFile, keyFile, []string{"h3"})
  3794  		if err != nil {
  3795  			return err
  3796  		}
  3797  		errc := make(chan error, 1)
  3798  		go fn(s, nil, http3ServerHandler{
  3799  			handler:   serverHandler{s},
  3800  			tlsConfig: config,
  3801  			baseCtx:   context.WithValue(context.Background(), ServerContextKey, s),
  3802  			errc:      errc,
  3803  		})
  3804  		if err := <-errc; err != nil {
  3805  			return err
  3806  		}
  3807  	}
  3808  
  3809  	// Only start a TCP listener if HTTP/1 or HTTP/2 is used.
  3810  	if !p.HTTP1() && !p.HTTP2() && !p.UnencryptedHTTP2() {
  3811  		return nil
  3812  	}
  3813  	ln, err := net.Listen("tcp", addr)
  3814  	if err != nil {
  3815  		return err
  3816  	}
  3817  	defer ln.Close()
  3818  	return s.ServeTLS(ln, certFile, keyFile)
  3819  }
  3820  
  3821  // setupHTTP2_ServeTLS conditionally configures HTTP/2 on
  3822  // s and reports whether there was an error setting it up. If it is
  3823  // not configured for policy reasons, nil is returned.
  3824  func (s *Server) setupHTTP2_ServeTLS() error {
  3825  	s.nextProtoOnce.Do(s.onceSetNextProtoDefaults)
  3826  	return s.nextProtoErr
  3827  }
  3828  
  3829  // setupHTTP2_Serve is called from (*Server).Serve and conditionally
  3830  // configures HTTP/2 on s using a more conservative policy than
  3831  // setupHTTP2_ServeTLS because Serve is called after tls.Listen,
  3832  // and may be called concurrently. See shouldConfigureHTTP2ForServe.
  3833  //
  3834  // The tests named TestTransportAutomaticHTTP2* and
  3835  // TestConcurrentServerServe in server_test.go demonstrate some
  3836  // of the supported use cases and motivations.
  3837  func (s *Server) setupHTTP2_Serve() error {
  3838  	s.nextProtoOnce.Do(s.onceSetNextProtoDefaults_Serve)
  3839  	return s.nextProtoErr
  3840  }
  3841  
  3842  func (s *Server) onceSetNextProtoDefaults_Serve() {
  3843  	if s.shouldConfigureHTTP2ForServe() {
  3844  		s.onceSetNextProtoDefaults()
  3845  	}
  3846  }
  3847  
  3848  var http2server = godebug.New("http2server")
  3849  
  3850  // onceSetNextProtoDefaults configures HTTP/2, if the user hasn't
  3851  // configured otherwise. (by setting s.TLSNextProto non-nil)
  3852  // It must only be called via s.nextProtoOnce (use s.setupHTTP2_*).
  3853  func (s *Server) onceSetNextProtoDefaults() {
  3854  	if omitBundledHTTP2 {
  3855  		return
  3856  	}
  3857  	p := s.protocols()
  3858  	if !p.HTTP2() && !p.UnencryptedHTTP2() {
  3859  		return
  3860  	}
  3861  	if http2server.Value() == "0" {
  3862  		http2server.IncNonDefault()
  3863  		return
  3864  	}
  3865  	if _, ok := s.TLSNextProto["h2"]; ok {
  3866  		// TLSNextProto already contains an HTTP/2 implementation.
  3867  		// The user probably called golang.org/x/net/http2.ConfigureServer
  3868  		// to add it.
  3869  		return
  3870  	}
  3871  	s.configureHTTP2()
  3872  }
  3873  
  3874  // TimeoutHandler returns a [Handler] that runs h with the given time limit.
  3875  //
  3876  // The new Handler calls h.ServeHTTP to handle each request, but if a
  3877  // call runs for longer than its time limit, the handler responds with
  3878  // a 503 Service Unavailable error and the given message in its body.
  3879  // (If msg is empty, a suitable default message will be sent.)
  3880  // After such a timeout, writes by h to its [ResponseWriter] will return
  3881  // [ErrHandlerTimeout].
  3882  //
  3883  // TimeoutHandler supports the [Pusher] interface but does not support
  3884  // the [Hijacker] or [Flusher] interfaces.
  3885  func TimeoutHandler(h Handler, dt time.Duration, msg string) Handler {
  3886  	return &timeoutHandler{
  3887  		handler: h,
  3888  		body:    msg,
  3889  		dt:      dt,
  3890  	}
  3891  }
  3892  
  3893  // ErrHandlerTimeout is returned on [ResponseWriter] Write calls
  3894  // in handlers which have timed out.
  3895  var ErrHandlerTimeout = errors.New("http: Handler timeout")
  3896  
  3897  type timeoutHandler struct {
  3898  	handler Handler
  3899  	body    string
  3900  	dt      time.Duration
  3901  
  3902  	// When set, no context will be created and this context will
  3903  	// be used instead.
  3904  	testContext context.Context
  3905  }
  3906  
  3907  func (h *timeoutHandler) errorBody() string {
  3908  	if h.body != "" {
  3909  		return h.body
  3910  	}
  3911  	return "<html><head><title>Timeout</title></head><body><h1>Timeout</h1></body></html>"
  3912  }
  3913  
  3914  func (h *timeoutHandler) ServeHTTP(w ResponseWriter, r *Request) {
  3915  	ctx := h.testContext
  3916  	if ctx == nil {
  3917  		var cancelCtx context.CancelFunc
  3918  		ctx, cancelCtx = context.WithTimeout(r.Context(), h.dt)
  3919  		defer cancelCtx()
  3920  	}
  3921  	r = r.WithContext(ctx)
  3922  	done := make(chan struct{})
  3923  	tw := &timeoutWriter{
  3924  		w:   w,
  3925  		h:   make(Header),
  3926  		req: r,
  3927  	}
  3928  	panicChan := make(chan any, 1)
  3929  	go func() {
  3930  		defer func() {
  3931  			if p := recover(); p != nil {
  3932  				panicChan <- p
  3933  			}
  3934  		}()
  3935  		h.handler.ServeHTTP(tw, r)
  3936  		close(done)
  3937  	}()
  3938  	select {
  3939  	case p := <-panicChan:
  3940  		panic(p)
  3941  	case <-done:
  3942  		tw.mu.Lock()
  3943  		defer tw.mu.Unlock()
  3944  		dst := w.Header()
  3945  		maps.Copy(dst, tw.h)
  3946  		if !tw.wroteHeader {
  3947  			tw.code = StatusOK
  3948  		}
  3949  		w.WriteHeader(tw.code)
  3950  		w.Write(tw.wbuf.Bytes())
  3951  	case <-ctx.Done():
  3952  		tw.mu.Lock()
  3953  		defer tw.mu.Unlock()
  3954  		switch err := ctx.Err(); err {
  3955  		case context.DeadlineExceeded:
  3956  			w.WriteHeader(StatusServiceUnavailable)
  3957  			io.WriteString(w, h.errorBody())
  3958  			tw.err = ErrHandlerTimeout
  3959  		default:
  3960  			w.WriteHeader(StatusServiceUnavailable)
  3961  			tw.err = err
  3962  		}
  3963  	}
  3964  }
  3965  
  3966  type timeoutWriter struct {
  3967  	w    ResponseWriter
  3968  	h    Header
  3969  	wbuf bytes.Buffer
  3970  	req  *Request
  3971  
  3972  	mu          sync.Mutex
  3973  	err         error
  3974  	wroteHeader bool
  3975  	code        int
  3976  }
  3977  
  3978  var _ Pusher = (*timeoutWriter)(nil)
  3979  
  3980  // Push implements the [Pusher] interface.
  3981  func (tw *timeoutWriter) Push(target string, opts *PushOptions) error {
  3982  	if pusher, ok := tw.w.(Pusher); ok {
  3983  		return pusher.Push(target, opts)
  3984  	}
  3985  	return ErrNotSupported
  3986  }
  3987  
  3988  func (tw *timeoutWriter) Header() Header { return tw.h }
  3989  
  3990  func (tw *timeoutWriter) Write(p []byte) (int, error) {
  3991  	tw.mu.Lock()
  3992  	defer tw.mu.Unlock()
  3993  	if tw.err != nil {
  3994  		return 0, tw.err
  3995  	}
  3996  	if !tw.wroteHeader {
  3997  		tw.writeHeaderLocked(StatusOK)
  3998  	}
  3999  	return tw.wbuf.Write(p)
  4000  }
  4001  
  4002  func (tw *timeoutWriter) writeHeaderLocked(code int) {
  4003  	checkWriteHeaderCode(code)
  4004  
  4005  	switch {
  4006  	case tw.err != nil:
  4007  		return
  4008  	case tw.wroteHeader:
  4009  		if tw.req != nil {
  4010  			caller := relevantCaller()
  4011  			logf(tw.req, "http: superfluous response.WriteHeader call from %s (%s:%d)", caller.Function, path.Base(caller.File), caller.Line)
  4012  		}
  4013  	default:
  4014  		tw.wroteHeader = true
  4015  		tw.code = code
  4016  	}
  4017  }
  4018  
  4019  func (tw *timeoutWriter) WriteHeader(code int) {
  4020  	tw.mu.Lock()
  4021  	defer tw.mu.Unlock()
  4022  	tw.writeHeaderLocked(code)
  4023  }
  4024  
  4025  // onceCloseListener wraps a net.Listener, protecting it from
  4026  // multiple Close calls.
  4027  type onceCloseListener struct {
  4028  	net.Listener
  4029  	once     sync.Once
  4030  	closeErr error
  4031  }
  4032  
  4033  func (oc *onceCloseListener) Close() error {
  4034  	oc.once.Do(oc.close)
  4035  	return oc.closeErr
  4036  }
  4037  
  4038  func (oc *onceCloseListener) close() { oc.closeErr = oc.Listener.Close() }
  4039  
  4040  // globalOptionsHandler responds to "OPTIONS *" requests.
  4041  type globalOptionsHandler struct{}
  4042  
  4043  func (globalOptionsHandler) ServeHTTP(w ResponseWriter, r *Request) {
  4044  	w.Header().Set("Content-Length", "0")
  4045  	if r.ContentLength != 0 {
  4046  		// Read up to 4KB of OPTIONS body (as mentioned in the
  4047  		// spec as being reserved for future use), but anything
  4048  		// over that is considered a waste of server resources
  4049  		// (or an attack) and we abort and close the connection,
  4050  		// courtesy of MaxBytesReader's EOF behavior.
  4051  		mb := MaxBytesReader(w, r.Body, 4<<10)
  4052  		io.Copy(io.Discard, mb)
  4053  	}
  4054  }
  4055  
  4056  // initALPNRequest is an HTTP handler that initializes certain
  4057  // uninitialized fields in its *Request. Such partially-initialized
  4058  // Requests come from ALPN protocol handlers.
  4059  type initALPNRequest struct {
  4060  	ctx context.Context
  4061  	c   *tls.Conn
  4062  	h   serverHandler
  4063  }
  4064  
  4065  // BaseContext is an exported but unadvertised [http.Handler] method
  4066  // recognized by x/net/http2 to pass down a context; the TLSNextProto
  4067  // API predates context support so we shoehorn through the only
  4068  // interface we have available.
  4069  func (h initALPNRequest) BaseContext() context.Context { return h.ctx }
  4070  
  4071  func (h initALPNRequest) ServeHTTP(rw ResponseWriter, req *Request) {
  4072  	if req.TLS == nil {
  4073  		req.TLS = &tls.ConnectionState{}
  4074  		*req.TLS = h.c.ConnectionState()
  4075  	}
  4076  	if req.Body == nil {
  4077  		req.Body = NoBody
  4078  	}
  4079  	if req.RemoteAddr == "" {
  4080  		req.RemoteAddr = h.c.RemoteAddr().String()
  4081  	}
  4082  	h.h.ServeHTTP(rw, req)
  4083  }
  4084  
  4085  // loggingConn is used for debugging.
  4086  type loggingConn struct {
  4087  	name string
  4088  	net.Conn
  4089  }
  4090  
  4091  var (
  4092  	uniqNameMu   sync.Mutex
  4093  	uniqNameNext = make(map[string]int)
  4094  )
  4095  
  4096  func newLoggingConn(baseName string, c net.Conn) net.Conn {
  4097  	uniqNameMu.Lock()
  4098  	defer uniqNameMu.Unlock()
  4099  	uniqNameNext[baseName]++
  4100  	return &loggingConn{
  4101  		name: fmt.Sprintf("%s-%d", baseName, uniqNameNext[baseName]),
  4102  		Conn: c,
  4103  	}
  4104  }
  4105  
  4106  func (c *loggingConn) Write(p []byte) (n int, err error) {
  4107  	log.Printf("%s.Write(%d) = ....", c.name, len(p))
  4108  	n, err = c.Conn.Write(p)
  4109  	log.Printf("%s.Write(%d) = %d, %v", c.name, len(p), n, err)
  4110  	return
  4111  }
  4112  
  4113  func (c *loggingConn) Read(p []byte) (n int, err error) {
  4114  	log.Printf("%s.Read(%d) = ....", c.name, len(p))
  4115  	n, err = c.Conn.Read(p)
  4116  	log.Printf("%s.Read(%d) = %d, %v", c.name, len(p), n, err)
  4117  	return
  4118  }
  4119  
  4120  func (c *loggingConn) Close() (err error) {
  4121  	log.Printf("%s.Close() = ...", c.name)
  4122  	err = c.Conn.Close()
  4123  	log.Printf("%s.Close() = %v", c.name, err)
  4124  	return
  4125  }
  4126  
  4127  // checkConnErrorWriter writes to c.rwc and records any write errors to c.werr.
  4128  // It only contains one field (and a pointer field at that), so it
  4129  // fits in an interface value without an extra allocation.
  4130  type checkConnErrorWriter struct {
  4131  	c *conn
  4132  }
  4133  
  4134  func (w checkConnErrorWriter) Write(p []byte) (n int, err error) {
  4135  	n, err = w.c.rwc.Write(p)
  4136  	if err != nil && w.c.werr == nil {
  4137  		w.c.werr = err
  4138  		w.c.cancelCtx()
  4139  	}
  4140  	return
  4141  }
  4142  
  4143  func numLeadingCRorLF(v []byte) (n int) {
  4144  	for _, b := range v {
  4145  		if b == '\r' || b == '\n' {
  4146  			n++
  4147  			continue
  4148  		}
  4149  		break
  4150  	}
  4151  	return
  4152  }
  4153  
  4154  // tlsRecordHeaderLooksLikeHTTP reports whether a TLS record header
  4155  // looks like it might've been a misdirected plaintext HTTP request.
  4156  func tlsRecordHeaderLooksLikeHTTP(hdr [5]byte) bool {
  4157  	switch string(hdr[:]) {
  4158  	case "GET /", "HEAD ", "POST ", "PUT /", "OPTIO":
  4159  		return true
  4160  	}
  4161  	return false
  4162  }
  4163  
  4164  // MaxBytesHandler returns a [Handler] that runs h with its [ResponseWriter] and [Request.Body] wrapped by a MaxBytesReader.
  4165  func MaxBytesHandler(h Handler, n int64) Handler {
  4166  	return HandlerFunc(func(w ResponseWriter, r *Request) {
  4167  		r2 := *r
  4168  		r2.Body = MaxBytesReader(w, r.Body, n)
  4169  		h.ServeHTTP(w, &r2)
  4170  	})
  4171  }
  4172  

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