Source file src/net/http/server.go

Documentation: net/http

     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  	"io"
    17  	"io/ioutil"
    18  	"log"
    19  	"net"
    20  	"net/textproto"
    21  	"net/url"
    22  	"os"
    23  	"path"
    24  	"runtime"
    25  	"sort"
    26  	"strconv"
    27  	"strings"
    28  	"sync"
    29  	"sync/atomic"
    30  	"time"
    31  
    32  	"golang.org/x/net/http/httpguts"
    33  )
    34  
    35  // Errors used by the HTTP server.
    36  var (
    37  	// ErrBodyNotAllowed is returned by ResponseWriter.Write calls
    38  	// when the HTTP method or response code does not permit a
    39  	// body.
    40  	ErrBodyNotAllowed = errors.New("http: request method or response status code does not allow body")
    41  
    42  	// ErrHijacked is returned by ResponseWriter.Write calls when
    43  	// the underlying connection has been hijacked using the
    44  	// Hijacker interface. A zero-byte write on a hijacked
    45  	// connection will return ErrHijacked without any other side
    46  	// effects.
    47  	ErrHijacked = errors.New("http: connection has been hijacked")
    48  
    49  	// ErrContentLength is returned by ResponseWriter.Write calls
    50  	// when a Handler set a Content-Length response header with a
    51  	// declared size and then attempted to write more bytes than
    52  	// declared.
    53  	ErrContentLength = errors.New("http: wrote more than the declared Content-Length")
    54  
    55  	// Deprecated: ErrWriteAfterFlush is no longer returned by
    56  	// anything in the net/http package. Callers should not
    57  	// compare errors against this variable.
    58  	ErrWriteAfterFlush = errors.New("unused")
    59  )
    60  
    61  // A Handler responds to an HTTP request.
    62  //
    63  // ServeHTTP should write reply headers and data to the ResponseWriter
    64  // and then return. Returning signals that the request is finished; it
    65  // is not valid to use the ResponseWriter or read from the
    66  // Request.Body after or concurrently with the completion of the
    67  // ServeHTTP call.
    68  //
    69  // Depending on the HTTP client software, HTTP protocol version, and
    70  // any intermediaries between the client and the Go server, it may not
    71  // be possible to read from the Request.Body after writing to the
    72  // ResponseWriter. Cautious handlers should read the Request.Body
    73  // first, and then reply.
    74  //
    75  // Except for reading the body, handlers should not modify the
    76  // provided Request.
    77  //
    78  // If ServeHTTP panics, the server (the caller of ServeHTTP) assumes
    79  // that the effect of the panic was isolated to the active request.
    80  // It recovers the panic, logs a stack trace to the server error log,
    81  // and either closes the network connection or sends an HTTP/2
    82  // RST_STREAM, depending on the HTTP protocol. To abort a handler so
    83  // the client sees an interrupted response but the server doesn't log
    84  // an error, panic with the value ErrAbortHandler.
    85  type Handler interface {
    86  	ServeHTTP(ResponseWriter, *Request)
    87  }
    88  
    89  // A ResponseWriter interface is used by an HTTP handler to
    90  // construct an HTTP response.
    91  //
    92  // A ResponseWriter may not be used after the Handler.ServeHTTP method
    93  // has returned.
    94  type ResponseWriter interface {
    95  	// Header returns the header map that will be sent by
    96  	// WriteHeader. The Header map also is the mechanism with which
    97  	// Handlers can set HTTP trailers.
    98  	//
    99  	// Changing the header map after a call to WriteHeader (or
   100  	// Write) has no effect unless the modified headers are
   101  	// trailers.
   102  	//
   103  	// There are two ways to set Trailers. The preferred way is to
   104  	// predeclare in the headers which trailers you will later
   105  	// send by setting the "Trailer" header to the names of the
   106  	// trailer keys which will come later. In this case, those
   107  	// keys of the Header map are treated as if they were
   108  	// trailers. See the example. The second way, for trailer
   109  	// keys not known to the Handler until after the first Write,
   110  	// is to prefix the Header map keys with the TrailerPrefix
   111  	// constant value. See TrailerPrefix.
   112  	//
   113  	// To suppress automatic response headers (such as "Date"), set
   114  	// their value to nil.
   115  	Header() Header
   116  
   117  	// Write writes the data to the connection as part of an HTTP reply.
   118  	//
   119  	// If WriteHeader has not yet been called, Write calls
   120  	// WriteHeader(http.StatusOK) before writing the data. If the Header
   121  	// does not contain a Content-Type line, Write adds a Content-Type set
   122  	// to the result of passing the initial 512 bytes of written data to
   123  	// DetectContentType. Additionally, if the total size of all written
   124  	// data is under a few KB and there are no Flush calls, the
   125  	// Content-Length header is added automatically.
   126  	//
   127  	// Depending on the HTTP protocol version and the client, calling
   128  	// Write or WriteHeader may prevent future reads on the
   129  	// Request.Body. For HTTP/1.x requests, handlers should read any
   130  	// needed request body data before writing the response. Once the
   131  	// headers have been flushed (due to either an explicit Flusher.Flush
   132  	// call or writing enough data to trigger a flush), the request body
   133  	// may be unavailable. For HTTP/2 requests, the Go HTTP server permits
   134  	// handlers to continue to read the request body while concurrently
   135  	// writing the response. However, such behavior may not be supported
   136  	// by all HTTP/2 clients. Handlers should read before writing if
   137  	// possible to maximize compatibility.
   138  	Write([]byte) (int, error)
   139  
   140  	// WriteHeader sends an HTTP response header with the provided
   141  	// status code.
   142  	//
   143  	// If WriteHeader is not called explicitly, the first call to Write
   144  	// will trigger an implicit WriteHeader(http.StatusOK).
   145  	// Thus explicit calls to WriteHeader are mainly used to
   146  	// send error codes.
   147  	//
   148  	// The provided code must be a valid HTTP 1xx-5xx status code.
   149  	// Only one header may be written. Go does not currently
   150  	// support sending user-defined 1xx informational headers,
   151  	// with the exception of 100-continue response header that the
   152  	// Server sends automatically when the Request.Body is read.
   153  	WriteHeader(statusCode int)
   154  }
   155  
   156  // The Flusher interface is implemented by ResponseWriters that allow
   157  // an HTTP handler to flush buffered data to the client.
   158  //
   159  // The default HTTP/1.x and HTTP/2 ResponseWriter implementations
   160  // support Flusher, but ResponseWriter wrappers may not. Handlers
   161  // should always test for this ability at runtime.
   162  //
   163  // Note that even for ResponseWriters that support Flush,
   164  // if the client is connected through an HTTP proxy,
   165  // the buffered data may not reach the client until the response
   166  // completes.
   167  type Flusher interface {
   168  	// Flush sends any buffered data to the client.
   169  	Flush()
   170  }
   171  
   172  // The Hijacker interface is implemented by ResponseWriters that allow
   173  // an HTTP handler to take over the connection.
   174  //
   175  // The default ResponseWriter for HTTP/1.x connections supports
   176  // Hijacker, but HTTP/2 connections intentionally do not.
   177  // ResponseWriter wrappers may also not support Hijacker. Handlers
   178  // should always test for this ability at runtime.
   179  type Hijacker interface {
   180  	// Hijack lets the caller take over the connection.
   181  	// After a call to Hijack the HTTP server library
   182  	// will not do anything else with the connection.
   183  	//
   184  	// It becomes the caller's responsibility to manage
   185  	// and close the connection.
   186  	//
   187  	// The returned net.Conn may have read or write deadlines
   188  	// already set, depending on the configuration of the
   189  	// Server. It is the caller's responsibility to set
   190  	// or clear those deadlines as needed.
   191  	//
   192  	// The returned bufio.Reader may contain unprocessed buffered
   193  	// data from the client.
   194  	//
   195  	// After a call to Hijack, the original Request.Body must not
   196  	// be used. The original Request's Context remains valid and
   197  	// is not canceled until the Request's ServeHTTP method
   198  	// returns.
   199  	Hijack() (net.Conn, *bufio.ReadWriter, error)
   200  }
   201  
   202  // The CloseNotifier interface is implemented by ResponseWriters which
   203  // allow detecting when the underlying connection has gone away.
   204  //
   205  // This mechanism can be used to cancel long operations on the server
   206  // if the client has disconnected before the response is ready.
   207  //
   208  // Deprecated: the CloseNotifier interface predates Go's context package.
   209  // New code should use Request.Context instead.
   210  type CloseNotifier interface {
   211  	// CloseNotify returns a channel that receives at most a
   212  	// single value (true) when the client connection has gone
   213  	// away.
   214  	//
   215  	// CloseNotify may wait to notify until Request.Body has been
   216  	// fully read.
   217  	//
   218  	// After the Handler has returned, there is no guarantee
   219  	// that the channel receives a value.
   220  	//
   221  	// If the protocol is HTTP/1.1 and CloseNotify is called while
   222  	// processing an idempotent request (such a GET) while
   223  	// HTTP/1.1 pipelining is in use, the arrival of a subsequent
   224  	// pipelined request may cause a value to be sent on the
   225  	// returned channel. In practice HTTP/1.1 pipelining is not
   226  	// enabled in browsers and not seen often in the wild. If this
   227  	// is a problem, use HTTP/2 or only use CloseNotify on methods
   228  	// such as POST.
   229  	CloseNotify() <-chan bool
   230  }
   231  
   232  var (
   233  	// ServerContextKey is a context key. It can be used in HTTP
   234  	// handlers with Context.Value to access the server that
   235  	// started the handler. The associated value will be of
   236  	// type *Server.
   237  	ServerContextKey = &contextKey{"http-server"}
   238  
   239  	// LocalAddrContextKey is a context key. It can be used in
   240  	// HTTP handlers with Context.Value to access the local
   241  	// address the connection arrived on.
   242  	// The associated value will be of type net.Addr.
   243  	LocalAddrContextKey = &contextKey{"local-addr"}
   244  )
   245  
   246  // A conn represents the server side of an HTTP connection.
   247  type conn struct {
   248  	// server is the server on which the connection arrived.
   249  	// Immutable; never nil.
   250  	server *Server
   251  
   252  	// cancelCtx cancels the connection-level context.
   253  	cancelCtx context.CancelFunc
   254  
   255  	// rwc is the underlying network connection.
   256  	// This is never wrapped by other types and is the value given out
   257  	// to CloseNotifier callers. It is usually of type *net.TCPConn or
   258  	// *tls.Conn.
   259  	rwc net.Conn
   260  
   261  	// remoteAddr is rwc.RemoteAddr().String(). It is not populated synchronously
   262  	// inside the Listener's Accept goroutine, as some implementations block.
   263  	// It is populated immediately inside the (*conn).serve goroutine.
   264  	// This is the value of a Handler's (*Request).RemoteAddr.
   265  	remoteAddr string
   266  
   267  	// tlsState is the TLS connection state when using TLS.
   268  	// nil means not TLS.
   269  	tlsState *tls.ConnectionState
   270  
   271  	// werr is set to the first write error to rwc.
   272  	// It is set via checkConnErrorWriter{w}, where bufw writes.
   273  	werr error
   274  
   275  	// r is bufr's read source. It's a wrapper around rwc that provides
   276  	// io.LimitedReader-style limiting (while reading request headers)
   277  	// and functionality to support CloseNotifier. See *connReader docs.
   278  	r *connReader
   279  
   280  	// bufr reads from r.
   281  	bufr *bufio.Reader
   282  
   283  	// bufw writes to checkConnErrorWriter{c}, which populates werr on error.
   284  	bufw *bufio.Writer
   285  
   286  	// lastMethod is the method of the most recent request
   287  	// on this connection, if any.
   288  	lastMethod string
   289  
   290  	curReq atomic.Value // of *response (which has a Request in it)
   291  
   292  	curState struct{ atomic uint64 } // packed (unixtime<<8|uint8(ConnState))
   293  
   294  	// mu guards hijackedv
   295  	mu sync.Mutex
   296  
   297  	// hijackedv is whether this connection has been hijacked
   298  	// by a Handler with the Hijacker interface.
   299  	// It is guarded by mu.
   300  	hijackedv bool
   301  }
   302  
   303  func (c *conn) hijacked() bool {
   304  	c.mu.Lock()
   305  	defer c.mu.Unlock()
   306  	return c.hijackedv
   307  }
   308  
   309  // c.mu must be held.
   310  func (c *conn) hijackLocked() (rwc net.Conn, buf *bufio.ReadWriter, err error) {
   311  	if c.hijackedv {
   312  		return nil, nil, ErrHijacked
   313  	}
   314  	c.r.abortPendingRead()
   315  
   316  	c.hijackedv = true
   317  	rwc = c.rwc
   318  	rwc.SetDeadline(time.Time{})
   319  
   320  	buf = bufio.NewReadWriter(c.bufr, bufio.NewWriter(rwc))
   321  	if c.r.hasByte {
   322  		if _, err := c.bufr.Peek(c.bufr.Buffered() + 1); err != nil {
   323  			return nil, nil, fmt.Errorf("unexpected Peek failure reading buffered byte: %v", err)
   324  		}
   325  	}
   326  	c.setState(rwc, StateHijacked)
   327  	return
   328  }
   329  
   330  // This should be >= 512 bytes for DetectContentType,
   331  // but otherwise it's somewhat arbitrary.
   332  const bufferBeforeChunkingSize = 2048
   333  
   334  // chunkWriter writes to a response's conn buffer, and is the writer
   335  // wrapped by the response.bufw buffered writer.
   336  //
   337  // chunkWriter also is responsible for finalizing the Header, including
   338  // conditionally setting the Content-Type and setting a Content-Length
   339  // in cases where the handler's final output is smaller than the buffer
   340  // size. It also conditionally adds chunk headers, when in chunking mode.
   341  //
   342  // See the comment above (*response).Write for the entire write flow.
   343  type chunkWriter struct {
   344  	res *response
   345  
   346  	// header is either nil or a deep clone of res.handlerHeader
   347  	// at the time of res.writeHeader, if res.writeHeader is
   348  	// called and extra buffering is being done to calculate
   349  	// Content-Type and/or Content-Length.
   350  	header Header
   351  
   352  	// wroteHeader tells whether the header's been written to "the
   353  	// wire" (or rather: w.conn.buf). this is unlike
   354  	// (*response).wroteHeader, which tells only whether it was
   355  	// logically written.
   356  	wroteHeader bool
   357  
   358  	// set by the writeHeader method:
   359  	chunking bool // using chunked transfer encoding for reply body
   360  }
   361  
   362  var (
   363  	crlf       = []byte("\r\n")
   364  	colonSpace = []byte(": ")
   365  )
   366  
   367  func (cw *chunkWriter) Write(p []byte) (n int, err error) {
   368  	if !cw.wroteHeader {
   369  		cw.writeHeader(p)
   370  	}
   371  	if cw.res.req.Method == "HEAD" {
   372  		// Eat writes.
   373  		return len(p), nil
   374  	}
   375  	if cw.chunking {
   376  		_, err = fmt.Fprintf(cw.res.conn.bufw, "%x\r\n", len(p))
   377  		if err != nil {
   378  			cw.res.conn.rwc.Close()
   379  			return
   380  		}
   381  	}
   382  	n, err = cw.res.conn.bufw.Write(p)
   383  	if cw.chunking && err == nil {
   384  		_, err = cw.res.conn.bufw.Write(crlf)
   385  	}
   386  	if err != nil {
   387  		cw.res.conn.rwc.Close()
   388  	}
   389  	return
   390  }
   391  
   392  func (cw *chunkWriter) flush() {
   393  	if !cw.wroteHeader {
   394  		cw.writeHeader(nil)
   395  	}
   396  	cw.res.conn.bufw.Flush()
   397  }
   398  
   399  func (cw *chunkWriter) close() {
   400  	if !cw.wroteHeader {
   401  		cw.writeHeader(nil)
   402  	}
   403  	if cw.chunking {
   404  		bw := cw.res.conn.bufw // conn's bufio writer
   405  		// zero chunk to mark EOF
   406  		bw.WriteString("0\r\n")
   407  		if trailers := cw.res.finalTrailers(); trailers != nil {
   408  			trailers.Write(bw) // the writer handles noting errors
   409  		}
   410  		// final blank line after the trailers (whether
   411  		// present or not)
   412  		bw.WriteString("\r\n")
   413  	}
   414  }
   415  
   416  // A response represents the server side of an HTTP response.
   417  type response struct {
   418  	conn             *conn
   419  	req              *Request // request for this response
   420  	reqBody          io.ReadCloser
   421  	cancelCtx        context.CancelFunc // when ServeHTTP exits
   422  	wroteHeader      bool               // reply header has been (logically) written
   423  	wroteContinue    bool               // 100 Continue response was written
   424  	wants10KeepAlive bool               // HTTP/1.0 w/ Connection "keep-alive"
   425  	wantsClose       bool               // HTTP request has Connection "close"
   426  
   427  	w  *bufio.Writer // buffers output in chunks to chunkWriter
   428  	cw chunkWriter
   429  
   430  	// handlerHeader is the Header that Handlers get access to,
   431  	// which may be retained and mutated even after WriteHeader.
   432  	// handlerHeader is copied into cw.header at WriteHeader
   433  	// time, and privately mutated thereafter.
   434  	handlerHeader Header
   435  	calledHeader  bool // handler accessed handlerHeader via Header
   436  
   437  	written       int64 // number of bytes written in body
   438  	contentLength int64 // explicitly-declared Content-Length; or -1
   439  	status        int   // status code passed to WriteHeader
   440  
   441  	// close connection after this reply.  set on request and
   442  	// updated after response from handler if there's a
   443  	// "Connection: keep-alive" response header and a
   444  	// Content-Length.
   445  	closeAfterReply bool
   446  
   447  	// requestBodyLimitHit is set by requestTooLarge when
   448  	// maxBytesReader hits its max size. It is checked in
   449  	// WriteHeader, to make sure we don't consume the
   450  	// remaining request body to try to advance to the next HTTP
   451  	// request. Instead, when this is set, we stop reading
   452  	// subsequent requests on this connection and stop reading
   453  	// input from it.
   454  	requestBodyLimitHit bool
   455  
   456  	// trailers are the headers to be sent after the handler
   457  	// finishes writing the body. This field is initialized from
   458  	// the Trailer response header when the response header is
   459  	// written.
   460  	trailers []string
   461  
   462  	handlerDone atomicBool // set true when the handler exits
   463  
   464  	// Buffers for Date, Content-Length, and status code
   465  	dateBuf   [len(TimeFormat)]byte
   466  	clenBuf   [10]byte
   467  	statusBuf [3]byte
   468  
   469  	// closeNotifyCh is the channel returned by CloseNotify.
   470  	// TODO(bradfitz): this is currently (for Go 1.8) always
   471  	// non-nil. Make this lazily-created again as it used to be?
   472  	closeNotifyCh  chan bool
   473  	didCloseNotify int32 // atomic (only 0->1 winner should send)
   474  }
   475  
   476  // TrailerPrefix is a magic prefix for ResponseWriter.Header map keys
   477  // that, if present, signals that the map entry is actually for
   478  // the response trailers, and not the response headers. The prefix
   479  // is stripped after the ServeHTTP call finishes and the values are
   480  // sent in the trailers.
   481  //
   482  // This mechanism is intended only for trailers that are not known
   483  // prior to the headers being written. If the set of trailers is fixed
   484  // or known before the header is written, the normal Go trailers mechanism
   485  // is preferred:
   486  //    https://golang.org/pkg/net/http/#ResponseWriter
   487  //    https://golang.org/pkg/net/http/#example_ResponseWriter_trailers
   488  const TrailerPrefix = "Trailer:"
   489  
   490  // finalTrailers is called after the Handler exits and returns a non-nil
   491  // value if the Handler set any trailers.
   492  func (w *response) finalTrailers() Header {
   493  	var t Header
   494  	for k, vv := range w.handlerHeader {
   495  		if strings.HasPrefix(k, TrailerPrefix) {
   496  			if t == nil {
   497  				t = make(Header)
   498  			}
   499  			t[strings.TrimPrefix(k, TrailerPrefix)] = vv
   500  		}
   501  	}
   502  	for _, k := range w.trailers {
   503  		if t == nil {
   504  			t = make(Header)
   505  		}
   506  		for _, v := range w.handlerHeader[k] {
   507  			t.Add(k, v)
   508  		}
   509  	}
   510  	return t
   511  }
   512  
   513  type atomicBool int32
   514  
   515  func (b *atomicBool) isSet() bool { return atomic.LoadInt32((*int32)(b)) != 0 }
   516  func (b *atomicBool) setTrue()    { atomic.StoreInt32((*int32)(b), 1) }
   517  
   518  // declareTrailer is called for each Trailer header when the
   519  // response header is written. It notes that a header will need to be
   520  // written in the trailers at the end of the response.
   521  func (w *response) declareTrailer(k string) {
   522  	k = CanonicalHeaderKey(k)
   523  	if !httpguts.ValidTrailerHeader(k) {
   524  		// Forbidden by RFC 7230, section 4.1.2
   525  		return
   526  	}
   527  	w.trailers = append(w.trailers, k)
   528  }
   529  
   530  // requestTooLarge is called by maxBytesReader when too much input has
   531  // been read from the client.
   532  func (w *response) requestTooLarge() {
   533  	w.closeAfterReply = true
   534  	w.requestBodyLimitHit = true
   535  	if !w.wroteHeader {
   536  		w.Header().Set("Connection", "close")
   537  	}
   538  }
   539  
   540  // needsSniff reports whether a Content-Type still needs to be sniffed.
   541  func (w *response) needsSniff() bool {
   542  	_, haveType := w.handlerHeader["Content-Type"]
   543  	return !w.cw.wroteHeader && !haveType && w.written < sniffLen
   544  }
   545  
   546  // writerOnly hides an io.Writer value's optional ReadFrom method
   547  // from io.Copy.
   548  type writerOnly struct {
   549  	io.Writer
   550  }
   551  
   552  func srcIsRegularFile(src io.Reader) (isRegular bool, err error) {
   553  	switch v := src.(type) {
   554  	case *os.File:
   555  		fi, err := v.Stat()
   556  		if err != nil {
   557  			return false, err
   558  		}
   559  		return fi.Mode().IsRegular(), nil
   560  	case *io.LimitedReader:
   561  		return srcIsRegularFile(v.R)
   562  	default:
   563  		return
   564  	}
   565  }
   566  
   567  // ReadFrom is here to optimize copying from an *os.File regular file
   568  // to a *net.TCPConn with sendfile.
   569  func (w *response) ReadFrom(src io.Reader) (n int64, err error) {
   570  	// Our underlying w.conn.rwc is usually a *TCPConn (with its
   571  	// own ReadFrom method). If not, or if our src isn't a regular
   572  	// file, just fall back to the normal copy method.
   573  	rf, ok := w.conn.rwc.(io.ReaderFrom)
   574  	regFile, err := srcIsRegularFile(src)
   575  	if err != nil {
   576  		return 0, err
   577  	}
   578  	if !ok || !regFile {
   579  		bufp := copyBufPool.Get().(*[]byte)
   580  		defer copyBufPool.Put(bufp)
   581  		return io.CopyBuffer(writerOnly{w}, src, *bufp)
   582  	}
   583  
   584  	// sendfile path:
   585  
   586  	if !w.wroteHeader {
   587  		w.WriteHeader(StatusOK)
   588  	}
   589  
   590  	if w.needsSniff() {
   591  		n0, err := io.Copy(writerOnly{w}, io.LimitReader(src, sniffLen))
   592  		n += n0
   593  		if err != nil {
   594  			return n, err
   595  		}
   596  	}
   597  
   598  	w.w.Flush()  // get rid of any previous writes
   599  	w.cw.flush() // make sure Header is written; flush data to rwc
   600  
   601  	// Now that cw has been flushed, its chunking field is guaranteed initialized.
   602  	if !w.cw.chunking && w.bodyAllowed() {
   603  		n0, err := rf.ReadFrom(src)
   604  		n += n0
   605  		w.written += n0
   606  		return n, err
   607  	}
   608  
   609  	n0, err := io.Copy(writerOnly{w}, src)
   610  	n += n0
   611  	return n, err
   612  }
   613  
   614  // debugServerConnections controls whether all server connections are wrapped
   615  // with a verbose logging wrapper.
   616  const debugServerConnections = false
   617  
   618  // Create new connection from rwc.
   619  func (srv *Server) newConn(rwc net.Conn) *conn {
   620  	c := &conn{
   621  		server: srv,
   622  		rwc:    rwc,
   623  	}
   624  	if debugServerConnections {
   625  		c.rwc = newLoggingConn("server", c.rwc)
   626  	}
   627  	return c
   628  }
   629  
   630  type readResult struct {
   631  	n   int
   632  	err error
   633  	b   byte // byte read, if n == 1
   634  }
   635  
   636  // connReader is the io.Reader wrapper used by *conn. It combines a
   637  // selectively-activated io.LimitedReader (to bound request header
   638  // read sizes) with support for selectively keeping an io.Reader.Read
   639  // call blocked in a background goroutine to wait for activity and
   640  // trigger a CloseNotifier channel.
   641  type connReader struct {
   642  	conn *conn
   643  
   644  	mu      sync.Mutex // guards following
   645  	hasByte bool
   646  	byteBuf [1]byte
   647  	cond    *sync.Cond
   648  	inRead  bool
   649  	aborted bool  // set true before conn.rwc deadline is set to past
   650  	remain  int64 // bytes remaining
   651  }
   652  
   653  func (cr *connReader) lock() {
   654  	cr.mu.Lock()
   655  	if cr.cond == nil {
   656  		cr.cond = sync.NewCond(&cr.mu)
   657  	}
   658  }
   659  
   660  func (cr *connReader) unlock() { cr.mu.Unlock() }
   661  
   662  func (cr *connReader) startBackgroundRead() {
   663  	cr.lock()
   664  	defer cr.unlock()
   665  	if cr.inRead {
   666  		panic("invalid concurrent Body.Read call")
   667  	}
   668  	if cr.hasByte {
   669  		return
   670  	}
   671  	cr.inRead = true
   672  	cr.conn.rwc.SetReadDeadline(time.Time{})
   673  	go cr.backgroundRead()
   674  }
   675  
   676  func (cr *connReader) backgroundRead() {
   677  	n, err := cr.conn.rwc.Read(cr.byteBuf[:])
   678  	cr.lock()
   679  	if n == 1 {
   680  		cr.hasByte = true
   681  		// We were past the end of the previous request's body already
   682  		// (since we wouldn't be in a background read otherwise), so
   683  		// this is a pipelined HTTP request. Prior to Go 1.11 we used to
   684  		// send on the CloseNotify channel and cancel the context here,
   685  		// but the behavior was documented as only "may", and we only
   686  		// did that because that's how CloseNotify accidentally behaved
   687  		// in very early Go releases prior to context support. Once we
   688  		// added context support, people used a Handler's
   689  		// Request.Context() and passed it along. Having that context
   690  		// cancel on pipelined HTTP requests caused problems.
   691  		// Fortunately, almost nothing uses HTTP/1.x pipelining.
   692  		// Unfortunately, apt-get does, or sometimes does.
   693  		// New Go 1.11 behavior: don't fire CloseNotify or cancel
   694  		// contexts on pipelined requests. Shouldn't affect people, but
   695  		// fixes cases like Issue 23921. This does mean that a client
   696  		// closing their TCP connection after sending a pipelined
   697  		// request won't cancel the context, but we'll catch that on any
   698  		// write failure (in checkConnErrorWriter.Write).
   699  		// If the server never writes, yes, there are still contrived
   700  		// server & client behaviors where this fails to ever cancel the
   701  		// context, but that's kinda why HTTP/1.x pipelining died
   702  		// anyway.
   703  	}
   704  	if ne, ok := err.(net.Error); ok && cr.aborted && ne.Timeout() {
   705  		// Ignore this error. It's the expected error from
   706  		// another goroutine calling abortPendingRead.
   707  	} else if err != nil {
   708  		cr.handleReadError(err)
   709  	}
   710  	cr.aborted = false
   711  	cr.inRead = false
   712  	cr.unlock()
   713  	cr.cond.Broadcast()
   714  }
   715  
   716  func (cr *connReader) abortPendingRead() {
   717  	cr.lock()
   718  	defer cr.unlock()
   719  	if !cr.inRead {
   720  		return
   721  	}
   722  	cr.aborted = true
   723  	cr.conn.rwc.SetReadDeadline(aLongTimeAgo)
   724  	for cr.inRead {
   725  		cr.cond.Wait()
   726  	}
   727  	cr.conn.rwc.SetReadDeadline(time.Time{})
   728  }
   729  
   730  func (cr *connReader) setReadLimit(remain int64) { cr.remain = remain }
   731  func (cr *connReader) setInfiniteReadLimit()     { cr.remain = maxInt64 }
   732  func (cr *connReader) hitReadLimit() bool        { return cr.remain <= 0 }
   733  
   734  // handleReadError is called whenever a Read from the client returns a
   735  // non-nil error.
   736  //
   737  // The provided non-nil err is almost always io.EOF or a "use of
   738  // closed network connection". In any case, the error is not
   739  // particularly interesting, except perhaps for debugging during
   740  // development. Any error means the connection is dead and we should
   741  // down its context.
   742  //
   743  // It may be called from multiple goroutines.
   744  func (cr *connReader) handleReadError(_ error) {
   745  	cr.conn.cancelCtx()
   746  	cr.closeNotify()
   747  }
   748  
   749  // may be called from multiple goroutines.
   750  func (cr *connReader) closeNotify() {
   751  	res, _ := cr.conn.curReq.Load().(*response)
   752  	if res != nil && atomic.CompareAndSwapInt32(&res.didCloseNotify, 0, 1) {
   753  		res.closeNotifyCh <- true
   754  	}
   755  }
   756  
   757  func (cr *connReader) Read(p []byte) (n int, err error) {
   758  	cr.lock()
   759  	if cr.inRead {
   760  		cr.unlock()
   761  		if cr.conn.hijacked() {
   762  			panic("invalid Body.Read call. After hijacked, the original Request must not be used")
   763  		}
   764  		panic("invalid concurrent Body.Read call")
   765  	}
   766  	if cr.hitReadLimit() {
   767  		cr.unlock()
   768  		return 0, io.EOF
   769  	}
   770  	if len(p) == 0 {
   771  		cr.unlock()
   772  		return 0, nil
   773  	}
   774  	if int64(len(p)) > cr.remain {
   775  		p = p[:cr.remain]
   776  	}
   777  	if cr.hasByte {
   778  		p[0] = cr.byteBuf[0]
   779  		cr.hasByte = false
   780  		cr.unlock()
   781  		return 1, nil
   782  	}
   783  	cr.inRead = true
   784  	cr.unlock()
   785  	n, err = cr.conn.rwc.Read(p)
   786  
   787  	cr.lock()
   788  	cr.inRead = false
   789  	if err != nil {
   790  		cr.handleReadError(err)
   791  	}
   792  	cr.remain -= int64(n)
   793  	cr.unlock()
   794  
   795  	cr.cond.Broadcast()
   796  	return n, err
   797  }
   798  
   799  var (
   800  	bufioReaderPool   sync.Pool
   801  	bufioWriter2kPool sync.Pool
   802  	bufioWriter4kPool sync.Pool
   803  )
   804  
   805  var copyBufPool = sync.Pool{
   806  	New: func() interface{} {
   807  		b := make([]byte, 32*1024)
   808  		return &b
   809  	},
   810  }
   811  
   812  func bufioWriterPool(size int) *sync.Pool {
   813  	switch size {
   814  	case 2 << 10:
   815  		return &bufioWriter2kPool
   816  	case 4 << 10:
   817  		return &bufioWriter4kPool
   818  	}
   819  	return nil
   820  }
   821  
   822  func newBufioReader(r io.Reader) *bufio.Reader {
   823  	if v := bufioReaderPool.Get(); v != nil {
   824  		br := v.(*bufio.Reader)
   825  		br.Reset(r)
   826  		return br
   827  	}
   828  	// Note: if this reader size is ever changed, update
   829  	// TestHandlerBodyClose's assumptions.
   830  	return bufio.NewReader(r)
   831  }
   832  
   833  func putBufioReader(br *bufio.Reader) {
   834  	br.Reset(nil)
   835  	bufioReaderPool.Put(br)
   836  }
   837  
   838  func newBufioWriterSize(w io.Writer, size int) *bufio.Writer {
   839  	pool := bufioWriterPool(size)
   840  	if pool != nil {
   841  		if v := pool.Get(); v != nil {
   842  			bw := v.(*bufio.Writer)
   843  			bw.Reset(w)
   844  			return bw
   845  		}
   846  	}
   847  	return bufio.NewWriterSize(w, size)
   848  }
   849  
   850  func putBufioWriter(bw *bufio.Writer) {
   851  	bw.Reset(nil)
   852  	if pool := bufioWriterPool(bw.Available()); pool != nil {
   853  		pool.Put(bw)
   854  	}
   855  }
   856  
   857  // DefaultMaxHeaderBytes is the maximum permitted size of the headers
   858  // in an HTTP request.
   859  // This can be overridden by setting Server.MaxHeaderBytes.
   860  const DefaultMaxHeaderBytes = 1 << 20 // 1 MB
   861  
   862  func (srv *Server) maxHeaderBytes() int {
   863  	if srv.MaxHeaderBytes > 0 {
   864  		return srv.MaxHeaderBytes
   865  	}
   866  	return DefaultMaxHeaderBytes
   867  }
   868  
   869  func (srv *Server) initialReadLimitSize() int64 {
   870  	return int64(srv.maxHeaderBytes()) + 4096 // bufio slop
   871  }
   872  
   873  // wrapper around io.ReadCloser which on first read, sends an
   874  // HTTP/1.1 100 Continue header
   875  type expectContinueReader struct {
   876  	resp       *response
   877  	readCloser io.ReadCloser
   878  	closed     bool
   879  	sawEOF     bool
   880  }
   881  
   882  func (ecr *expectContinueReader) Read(p []byte) (n int, err error) {
   883  	if ecr.closed {
   884  		return 0, ErrBodyReadAfterClose
   885  	}
   886  	if !ecr.resp.wroteContinue && !ecr.resp.conn.hijacked() {
   887  		ecr.resp.wroteContinue = true
   888  		ecr.resp.conn.bufw.WriteString("HTTP/1.1 100 Continue\r\n\r\n")
   889  		ecr.resp.conn.bufw.Flush()
   890  	}
   891  	n, err = ecr.readCloser.Read(p)
   892  	if err == io.EOF {
   893  		ecr.sawEOF = true
   894  	}
   895  	return
   896  }
   897  
   898  func (ecr *expectContinueReader) Close() error {
   899  	ecr.closed = true
   900  	return ecr.readCloser.Close()
   901  }
   902  
   903  // TimeFormat is the time format to use when generating times in HTTP
   904  // headers. It is like time.RFC1123 but hard-codes GMT as the time
   905  // zone. The time being formatted must be in UTC for Format to
   906  // generate the correct format.
   907  //
   908  // For parsing this time format, see ParseTime.
   909  const TimeFormat = "Mon, 02 Jan 2006 15:04:05 GMT"
   910  
   911  // appendTime is a non-allocating version of []byte(t.UTC().Format(TimeFormat))
   912  func appendTime(b []byte, t time.Time) []byte {
   913  	const days = "SunMonTueWedThuFriSat"
   914  	const months = "JanFebMarAprMayJunJulAugSepOctNovDec"
   915  
   916  	t = t.UTC()
   917  	yy, mm, dd := t.Date()
   918  	hh, mn, ss := t.Clock()
   919  	day := days[3*t.Weekday():]
   920  	mon := months[3*(mm-1):]
   921  
   922  	return append(b,
   923  		day[0], day[1], day[2], ',', ' ',
   924  		byte('0'+dd/10), byte('0'+dd%10), ' ',
   925  		mon[0], mon[1], mon[2], ' ',
   926  		byte('0'+yy/1000), byte('0'+(yy/100)%10), byte('0'+(yy/10)%10), byte('0'+yy%10), ' ',
   927  		byte('0'+hh/10), byte('0'+hh%10), ':',
   928  		byte('0'+mn/10), byte('0'+mn%10), ':',
   929  		byte('0'+ss/10), byte('0'+ss%10), ' ',
   930  		'G', 'M', 'T')
   931  }
   932  
   933  var errTooLarge = errors.New("http: request too large")
   934  
   935  // Read next request from connection.
   936  func (c *conn) readRequest(ctx context.Context) (w *response, err error) {
   937  	if c.hijacked() {
   938  		return nil, ErrHijacked
   939  	}
   940  
   941  	var (
   942  		wholeReqDeadline time.Time // or zero if none
   943  		hdrDeadline      time.Time // or zero if none
   944  	)
   945  	t0 := time.Now()
   946  	if d := c.server.readHeaderTimeout(); d != 0 {
   947  		hdrDeadline = t0.Add(d)
   948  	}
   949  	if d := c.server.ReadTimeout; d != 0 {
   950  		wholeReqDeadline = t0.Add(d)
   951  	}
   952  	c.rwc.SetReadDeadline(hdrDeadline)
   953  	if d := c.server.WriteTimeout; d != 0 {
   954  		defer func() {
   955  			c.rwc.SetWriteDeadline(time.Now().Add(d))
   956  		}()
   957  	}
   958  
   959  	c.r.setReadLimit(c.server.initialReadLimitSize())
   960  	if c.lastMethod == "POST" {
   961  		// RFC 7230 section 3 tolerance for old buggy clients.
   962  		peek, _ := c.bufr.Peek(4) // ReadRequest will get err below
   963  		c.bufr.Discard(numLeadingCRorLF(peek))
   964  	}
   965  	req, err := readRequest(c.bufr, keepHostHeader)
   966  	if err != nil {
   967  		if c.r.hitReadLimit() {
   968  			return nil, errTooLarge
   969  		}
   970  		return nil, err
   971  	}
   972  
   973  	if !http1ServerSupportsRequest(req) {
   974  		return nil, badRequestError("unsupported protocol version")
   975  	}
   976  
   977  	c.lastMethod = req.Method
   978  	c.r.setInfiniteReadLimit()
   979  
   980  	hosts, haveHost := req.Header["Host"]
   981  	isH2Upgrade := req.isH2Upgrade()
   982  	if req.ProtoAtLeast(1, 1) && (!haveHost || len(hosts) == 0) && !isH2Upgrade && req.Method != "CONNECT" {
   983  		return nil, badRequestError("missing required Host header")
   984  	}
   985  	if len(hosts) > 1 {
   986  		return nil, badRequestError("too many Host headers")
   987  	}
   988  	if len(hosts) == 1 && !httpguts.ValidHostHeader(hosts[0]) {
   989  		return nil, badRequestError("malformed Host header")
   990  	}
   991  	for k, vv := range req.Header {
   992  		if !httpguts.ValidHeaderFieldName(k) {
   993  			return nil, badRequestError("invalid header name")
   994  		}
   995  		for _, v := range vv {
   996  			if !httpguts.ValidHeaderFieldValue(v) {
   997  				return nil, badRequestError("invalid header value")
   998  			}
   999  		}
  1000  	}
  1001  	delete(req.Header, "Host")
  1002  
  1003  	ctx, cancelCtx := context.WithCancel(ctx)
  1004  	req.ctx = ctx
  1005  	req.RemoteAddr = c.remoteAddr
  1006  	req.TLS = c.tlsState
  1007  	if body, ok := req.Body.(*body); ok {
  1008  		body.doEarlyClose = true
  1009  	}
  1010  
  1011  	// Adjust the read deadline if necessary.
  1012  	if !hdrDeadline.Equal(wholeReqDeadline) {
  1013  		c.rwc.SetReadDeadline(wholeReqDeadline)
  1014  	}
  1015  
  1016  	w = &response{
  1017  		conn:          c,
  1018  		cancelCtx:     cancelCtx,
  1019  		req:           req,
  1020  		reqBody:       req.Body,
  1021  		handlerHeader: make(Header),
  1022  		contentLength: -1,
  1023  		closeNotifyCh: make(chan bool, 1),
  1024  
  1025  		// We populate these ahead of time so we're not
  1026  		// reading from req.Header after their Handler starts
  1027  		// and maybe mutates it (Issue 14940)
  1028  		wants10KeepAlive: req.wantsHttp10KeepAlive(),
  1029  		wantsClose:       req.wantsClose(),
  1030  	}
  1031  	if isH2Upgrade {
  1032  		w.closeAfterReply = true
  1033  	}
  1034  	w.cw.res = w
  1035  	w.w = newBufioWriterSize(&w.cw, bufferBeforeChunkingSize)
  1036  	return w, nil
  1037  }
  1038  
  1039  // http1ServerSupportsRequest reports whether Go's HTTP/1.x server
  1040  // supports the given request.
  1041  func http1ServerSupportsRequest(req *Request) bool {
  1042  	if req.ProtoMajor == 1 {
  1043  		return true
  1044  	}
  1045  	// Accept "PRI * HTTP/2.0" upgrade requests, so Handlers can
  1046  	// wire up their own HTTP/2 upgrades.
  1047  	if req.ProtoMajor == 2 && req.ProtoMinor == 0 &&
  1048  		req.Method == "PRI" && req.RequestURI == "*" {
  1049  		return true
  1050  	}
  1051  	// Reject HTTP/0.x, and all other HTTP/2+ requests (which
  1052  	// aren't encoded in ASCII anyway).
  1053  	return false
  1054  }
  1055  
  1056  func (w *response) Header() Header {
  1057  	if w.cw.header == nil && w.wroteHeader && !w.cw.wroteHeader {
  1058  		// Accessing the header between logically writing it
  1059  		// and physically writing it means we need to allocate
  1060  		// a clone to snapshot the logically written state.
  1061  		w.cw.header = w.handlerHeader.Clone()
  1062  	}
  1063  	w.calledHeader = true
  1064  	return w.handlerHeader
  1065  }
  1066  
  1067  // maxPostHandlerReadBytes is the max number of Request.Body bytes not
  1068  // consumed by a handler that the server will read from the client
  1069  // in order to keep a connection alive. If there are more bytes than
  1070  // this then the server to be paranoid instead sends a "Connection:
  1071  // close" response.
  1072  //
  1073  // This number is approximately what a typical machine's TCP buffer
  1074  // size is anyway.  (if we have the bytes on the machine, we might as
  1075  // well read them)
  1076  const maxPostHandlerReadBytes = 256 << 10
  1077  
  1078  func checkWriteHeaderCode(code int) {
  1079  	// Issue 22880: require valid WriteHeader status codes.
  1080  	// For now we only enforce that it's three digits.
  1081  	// In the future we might block things over 599 (600 and above aren't defined
  1082  	// at https://httpwg.org/specs/rfc7231.html#status.codes)
  1083  	// and we might block under 200 (once we have more mature 1xx support).
  1084  	// But for now any three digits.
  1085  	//
  1086  	// We used to send "HTTP/1.1 000 0" on the wire in responses but there's
  1087  	// no equivalent bogus thing we can realistically send in HTTP/2,
  1088  	// so we'll consistently panic instead and help people find their bugs
  1089  	// early. (We can't return an error from WriteHeader even if we wanted to.)
  1090  	if code < 100 || code > 999 {
  1091  		panic(fmt.Sprintf("invalid WriteHeader code %v", code))
  1092  	}
  1093  }
  1094  
  1095  // relevantCaller searches the call stack for the first function outside of net/http.
  1096  // The purpose of this function is to provide more helpful error messages.
  1097  func relevantCaller() runtime.Frame {
  1098  	pc := make([]uintptr, 16)
  1099  	n := runtime.Callers(1, pc)
  1100  	frames := runtime.CallersFrames(pc[:n])
  1101  	var frame runtime.Frame
  1102  	for {
  1103  		frame, more := frames.Next()
  1104  		if !strings.HasPrefix(frame.Function, "net/http.") {
  1105  			return frame
  1106  		}
  1107  		if !more {
  1108  			break
  1109  		}
  1110  	}
  1111  	return frame
  1112  }
  1113  
  1114  func (w *response) WriteHeader(code int) {
  1115  	if w.conn.hijacked() {
  1116  		caller := relevantCaller()
  1117  		w.conn.server.logf("http: response.WriteHeader on hijacked connection from %s (%s:%d)", caller.Function, path.Base(caller.File), caller.Line)
  1118  		return
  1119  	}
  1120  	if w.wroteHeader {
  1121  		caller := relevantCaller()
  1122  		w.conn.server.logf("http: superfluous response.WriteHeader call from %s (%s:%d)", caller.Function, path.Base(caller.File), caller.Line)
  1123  		return
  1124  	}
  1125  	checkWriteHeaderCode(code)
  1126  	w.wroteHeader = true
  1127  	w.status = code
  1128  
  1129  	if w.calledHeader && w.cw.header == nil {
  1130  		w.cw.header = w.handlerHeader.Clone()
  1131  	}
  1132  
  1133  	if cl := w.handlerHeader.get("Content-Length"); cl != "" {
  1134  		v, err := strconv.ParseInt(cl, 10, 64)
  1135  		if err == nil && v >= 0 {
  1136  			w.contentLength = v
  1137  		} else {
  1138  			w.conn.server.logf("http: invalid Content-Length of %q", cl)
  1139  			w.handlerHeader.Del("Content-Length")
  1140  		}
  1141  	}
  1142  }
  1143  
  1144  // extraHeader is the set of headers sometimes added by chunkWriter.writeHeader.
  1145  // This type is used to avoid extra allocations from cloning and/or populating
  1146  // the response Header map and all its 1-element slices.
  1147  type extraHeader struct {
  1148  	contentType      string
  1149  	connection       string
  1150  	transferEncoding string
  1151  	date             []byte // written if not nil
  1152  	contentLength    []byte // written if not nil
  1153  }
  1154  
  1155  // Sorted the same as extraHeader.Write's loop.
  1156  var extraHeaderKeys = [][]byte{
  1157  	[]byte("Content-Type"),
  1158  	[]byte("Connection"),
  1159  	[]byte("Transfer-Encoding"),
  1160  }
  1161  
  1162  var (
  1163  	headerContentLength = []byte("Content-Length: ")
  1164  	headerDate          = []byte("Date: ")
  1165  )
  1166  
  1167  // Write writes the headers described in h to w.
  1168  //
  1169  // This method has a value receiver, despite the somewhat large size
  1170  // of h, because it prevents an allocation. The escape analysis isn't
  1171  // smart enough to realize this function doesn't mutate h.
  1172  func (h extraHeader) Write(w *bufio.Writer) {
  1173  	if h.date != nil {
  1174  		w.Write(headerDate)
  1175  		w.Write(h.date)
  1176  		w.Write(crlf)
  1177  	}
  1178  	if h.contentLength != nil {
  1179  		w.Write(headerContentLength)
  1180  		w.Write(h.contentLength)
  1181  		w.Write(crlf)
  1182  	}
  1183  	for i, v := range []string{h.contentType, h.connection, h.transferEncoding} {
  1184  		if v != "" {
  1185  			w.Write(extraHeaderKeys[i])
  1186  			w.Write(colonSpace)
  1187  			w.WriteString(v)
  1188  			w.Write(crlf)
  1189  		}
  1190  	}
  1191  }
  1192  
  1193  // writeHeader finalizes the header sent to the client and writes it
  1194  // to cw.res.conn.bufw.
  1195  //
  1196  // p is not written by writeHeader, but is the first chunk of the body
  1197  // that will be written. It is sniffed for a Content-Type if none is
  1198  // set explicitly. It's also used to set the Content-Length, if the
  1199  // total body size was small and the handler has already finished
  1200  // running.
  1201  func (cw *chunkWriter) writeHeader(p []byte) {
  1202  	if cw.wroteHeader {
  1203  		return
  1204  	}
  1205  	cw.wroteHeader = true
  1206  
  1207  	w := cw.res
  1208  	keepAlivesEnabled := w.conn.server.doKeepAlives()
  1209  	isHEAD := w.req.Method == "HEAD"
  1210  
  1211  	// header is written out to w.conn.buf below. Depending on the
  1212  	// state of the handler, we either own the map or not. If we
  1213  	// don't own it, the exclude map is created lazily for
  1214  	// WriteSubset to remove headers. The setHeader struct holds
  1215  	// headers we need to add.
  1216  	header := cw.header
  1217  	owned := header != nil
  1218  	if !owned {
  1219  		header = w.handlerHeader
  1220  	}
  1221  	var excludeHeader map[string]bool
  1222  	delHeader := func(key string) {
  1223  		if owned {
  1224  			header.Del(key)
  1225  			return
  1226  		}
  1227  		if _, ok := header[key]; !ok {
  1228  			return
  1229  		}
  1230  		if excludeHeader == nil {
  1231  			excludeHeader = make(map[string]bool)
  1232  		}
  1233  		excludeHeader[key] = true
  1234  	}
  1235  	var setHeader extraHeader
  1236  
  1237  	// Don't write out the fake "Trailer:foo" keys. See TrailerPrefix.
  1238  	trailers := false
  1239  	for k := range cw.header {
  1240  		if strings.HasPrefix(k, TrailerPrefix) {
  1241  			if excludeHeader == nil {
  1242  				excludeHeader = make(map[string]bool)
  1243  			}
  1244  			excludeHeader[k] = true
  1245  			trailers = true
  1246  		}
  1247  	}
  1248  	for _, v := range cw.header["Trailer"] {
  1249  		trailers = true
  1250  		foreachHeaderElement(v, cw.res.declareTrailer)
  1251  	}
  1252  
  1253  	te := header.get("Transfer-Encoding")
  1254  	hasTE := te != ""
  1255  
  1256  	// If the handler is done but never sent a Content-Length
  1257  	// response header and this is our first (and last) write, set
  1258  	// it, even to zero. This helps HTTP/1.0 clients keep their
  1259  	// "keep-alive" connections alive.
  1260  	// Exceptions: 304/204/1xx responses never get Content-Length, and if
  1261  	// it was a HEAD request, we don't know the difference between
  1262  	// 0 actual bytes and 0 bytes because the handler noticed it
  1263  	// was a HEAD request and chose not to write anything. So for
  1264  	// HEAD, the handler should either write the Content-Length or
  1265  	// write non-zero bytes. If it's actually 0 bytes and the
  1266  	// handler never looked at the Request.Method, we just don't
  1267  	// send a Content-Length header.
  1268  	// Further, we don't send an automatic Content-Length if they
  1269  	// set a Transfer-Encoding, because they're generally incompatible.
  1270  	if w.handlerDone.isSet() && !trailers && !hasTE && bodyAllowedForStatus(w.status) && header.get("Content-Length") == "" && (!isHEAD || len(p) > 0) {
  1271  		w.contentLength = int64(len(p))
  1272  		setHeader.contentLength = strconv.AppendInt(cw.res.clenBuf[:0], int64(len(p)), 10)
  1273  	}
  1274  
  1275  	// If this was an HTTP/1.0 request with keep-alive and we sent a
  1276  	// Content-Length back, we can make this a keep-alive response ...
  1277  	if w.wants10KeepAlive && keepAlivesEnabled {
  1278  		sentLength := header.get("Content-Length") != ""
  1279  		if sentLength && header.get("Connection") == "keep-alive" {
  1280  			w.closeAfterReply = false
  1281  		}
  1282  	}
  1283  
  1284  	// Check for an explicit (and valid) Content-Length header.
  1285  	hasCL := w.contentLength != -1
  1286  
  1287  	if w.wants10KeepAlive && (isHEAD || hasCL || !bodyAllowedForStatus(w.status)) {
  1288  		_, connectionHeaderSet := header["Connection"]
  1289  		if !connectionHeaderSet {
  1290  			setHeader.connection = "keep-alive"
  1291  		}
  1292  	} else if !w.req.ProtoAtLeast(1, 1) || w.wantsClose {
  1293  		w.closeAfterReply = true
  1294  	}
  1295  
  1296  	if header.get("Connection") == "close" || !keepAlivesEnabled {
  1297  		w.closeAfterReply = true
  1298  	}
  1299  
  1300  	// If the client wanted a 100-continue but we never sent it to
  1301  	// them (or, more strictly: we never finished reading their
  1302  	// request body), don't reuse this connection because it's now
  1303  	// in an unknown state: we might be sending this response at
  1304  	// the same time the client is now sending its request body
  1305  	// after a timeout.  (Some HTTP clients send Expect:
  1306  	// 100-continue but knowing that some servers don't support
  1307  	// it, the clients set a timer and send the body later anyway)
  1308  	// If we haven't seen EOF, we can't skip over the unread body
  1309  	// because we don't know if the next bytes on the wire will be
  1310  	// the body-following-the-timer or the subsequent request.
  1311  	// See Issue 11549.
  1312  	if ecr, ok := w.req.Body.(*expectContinueReader); ok && !ecr.sawEOF {
  1313  		w.closeAfterReply = true
  1314  	}
  1315  
  1316  	// Per RFC 2616, we should consume the request body before
  1317  	// replying, if the handler hasn't already done so. But we
  1318  	// don't want to do an unbounded amount of reading here for
  1319  	// DoS reasons, so we only try up to a threshold.
  1320  	// TODO(bradfitz): where does RFC 2616 say that? See Issue 15527
  1321  	// about HTTP/1.x Handlers concurrently reading and writing, like
  1322  	// HTTP/2 handlers can do. Maybe this code should be relaxed?
  1323  	if w.req.ContentLength != 0 && !w.closeAfterReply {
  1324  		var discard, tooBig bool
  1325  
  1326  		switch bdy := w.req.Body.(type) {
  1327  		case *expectContinueReader:
  1328  			if bdy.resp.wroteContinue {
  1329  				discard = true
  1330  			}
  1331  		case *body:
  1332  			bdy.mu.Lock()
  1333  			switch {
  1334  			case bdy.closed:
  1335  				if !bdy.sawEOF {
  1336  					// Body was closed in handler with non-EOF error.
  1337  					w.closeAfterReply = true
  1338  				}
  1339  			case bdy.unreadDataSizeLocked() >= maxPostHandlerReadBytes:
  1340  				tooBig = true
  1341  			default:
  1342  				discard = true
  1343  			}
  1344  			bdy.mu.Unlock()
  1345  		default:
  1346  			discard = true
  1347  		}
  1348  
  1349  		if discard {
  1350  			_, err := io.CopyN(ioutil.Discard, w.reqBody, maxPostHandlerReadBytes+1)
  1351  			switch err {
  1352  			case nil:
  1353  				// There must be even more data left over.
  1354  				tooBig = true
  1355  			case ErrBodyReadAfterClose:
  1356  				// Body was already consumed and closed.
  1357  			case io.EOF:
  1358  				// The remaining body was just consumed, close it.
  1359  				err = w.reqBody.Close()
  1360  				if err != nil {
  1361  					w.closeAfterReply = true
  1362  				}
  1363  			default:
  1364  				// Some other kind of error occurred, like a read timeout, or
  1365  				// corrupt chunked encoding. In any case, whatever remains
  1366  				// on the wire must not be parsed as another HTTP request.
  1367  				w.closeAfterReply = true
  1368  			}
  1369  		}
  1370  
  1371  		if tooBig {
  1372  			w.requestTooLarge()
  1373  			delHeader("Connection")
  1374  			setHeader.connection = "close"
  1375  		}
  1376  	}
  1377  
  1378  	code := w.status
  1379  	if bodyAllowedForStatus(code) {
  1380  		// If no content type, apply sniffing algorithm to body.
  1381  		_, haveType := header["Content-Type"]
  1382  		if !haveType && !hasTE && len(p) > 0 {
  1383  			setHeader.contentType = DetectContentType(p)
  1384  		}
  1385  	} else {
  1386  		for _, k := range suppressedHeaders(code) {
  1387  			delHeader(k)
  1388  		}
  1389  	}
  1390  
  1391  	if !header.has("Date") {
  1392  		setHeader.date = appendTime(cw.res.dateBuf[:0], time.Now())
  1393  	}
  1394  
  1395  	if hasCL && hasTE && te != "identity" {
  1396  		// TODO: return an error if WriteHeader gets a return parameter
  1397  		// For now just ignore the Content-Length.
  1398  		w.conn.server.logf("http: WriteHeader called with both Transfer-Encoding of %q and a Content-Length of %d",
  1399  			te, w.contentLength)
  1400  		delHeader("Content-Length")
  1401  		hasCL = false
  1402  	}
  1403  
  1404  	if w.req.Method == "HEAD" || !bodyAllowedForStatus(code) {
  1405  		// do nothing
  1406  	} else if code == StatusNoContent {
  1407  		delHeader("Transfer-Encoding")
  1408  	} else if hasCL {
  1409  		delHeader("Transfer-Encoding")
  1410  	} else if w.req.ProtoAtLeast(1, 1) {
  1411  		// HTTP/1.1 or greater: Transfer-Encoding has been set to identity, and no
  1412  		// content-length has been provided. The connection must be closed after the
  1413  		// reply is written, and no chunking is to be done. This is the setup
  1414  		// recommended in the Server-Sent Events candidate recommendation 11,
  1415  		// section 8.
  1416  		if hasTE && te == "identity" {
  1417  			cw.chunking = false
  1418  			w.closeAfterReply = true
  1419  		} else {
  1420  			// HTTP/1.1 or greater: use chunked transfer encoding
  1421  			// to avoid closing the connection at EOF.
  1422  			cw.chunking = true
  1423  			setHeader.transferEncoding = "chunked"
  1424  			if hasTE && te == "chunked" {
  1425  				// We will send the chunked Transfer-Encoding header later.
  1426  				delHeader("Transfer-Encoding")
  1427  			}
  1428  		}
  1429  	} else {
  1430  		// HTTP version < 1.1: cannot do chunked transfer
  1431  		// encoding and we don't know the Content-Length so
  1432  		// signal EOF by closing connection.
  1433  		w.closeAfterReply = true
  1434  		delHeader("Transfer-Encoding") // in case already set
  1435  	}
  1436  
  1437  	// Cannot use Content-Length with non-identity Transfer-Encoding.
  1438  	if cw.chunking {
  1439  		delHeader("Content-Length")
  1440  	}
  1441  	if !w.req.ProtoAtLeast(1, 0) {
  1442  		return
  1443  	}
  1444  
  1445  	if w.closeAfterReply && (!keepAlivesEnabled || !hasToken(cw.header.get("Connection"), "close")) {
  1446  		delHeader("Connection")
  1447  		if w.req.ProtoAtLeast(1, 1) {
  1448  			setHeader.connection = "close"
  1449  		}
  1450  	}
  1451  
  1452  	writeStatusLine(w.conn.bufw, w.req.ProtoAtLeast(1, 1), code, w.statusBuf[:])
  1453  	cw.header.WriteSubset(w.conn.bufw, excludeHeader)
  1454  	setHeader.Write(w.conn.bufw)
  1455  	w.conn.bufw.Write(crlf)
  1456  }
  1457  
  1458  // foreachHeaderElement splits v according to the "#rule" construction
  1459  // in RFC 7230 section 7 and calls fn for each non-empty element.
  1460  func foreachHeaderElement(v string, fn func(string)) {
  1461  	v = textproto.TrimString(v)
  1462  	if v == "" {
  1463  		return
  1464  	}
  1465  	if !strings.Contains(v, ",") {
  1466  		fn(v)
  1467  		return
  1468  	}
  1469  	for _, f := range strings.Split(v, ",") {
  1470  		if f = textproto.TrimString(f); f != "" {
  1471  			fn(f)
  1472  		}
  1473  	}
  1474  }
  1475  
  1476  // writeStatusLine writes an HTTP/1.x Status-Line (RFC 7230 Section 3.1.2)
  1477  // to bw. is11 is whether the HTTP request is HTTP/1.1. false means HTTP/1.0.
  1478  // code is the response status code.
  1479  // scratch is an optional scratch buffer. If it has at least capacity 3, it's used.
  1480  func writeStatusLine(bw *bufio.Writer, is11 bool, code int, scratch []byte) {
  1481  	if is11 {
  1482  		bw.WriteString("HTTP/1.1 ")
  1483  	} else {
  1484  		bw.WriteString("HTTP/1.0 ")
  1485  	}
  1486  	if text, ok := statusText[code]; ok {
  1487  		bw.Write(strconv.AppendInt(scratch[:0], int64(code), 10))
  1488  		bw.WriteByte(' ')
  1489  		bw.WriteString(text)
  1490  		bw.WriteString("\r\n")
  1491  	} else {
  1492  		// don't worry about performance
  1493  		fmt.Fprintf(bw, "%03d status code %d\r\n", code, code)
  1494  	}
  1495  }
  1496  
  1497  // bodyAllowed reports whether a Write is allowed for this response type.
  1498  // It's illegal to call this before the header has been flushed.
  1499  func (w *response) bodyAllowed() bool {
  1500  	if !w.wroteHeader {
  1501  		panic("")
  1502  	}
  1503  	return bodyAllowedForStatus(w.status)
  1504  }
  1505  
  1506  // The Life Of A Write is like this:
  1507  //
  1508  // Handler starts. No header has been sent. The handler can either
  1509  // write a header, or just start writing. Writing before sending a header
  1510  // sends an implicitly empty 200 OK header.
  1511  //
  1512  // If the handler didn't declare a Content-Length up front, we either
  1513  // go into chunking mode or, if the handler finishes running before
  1514  // the chunking buffer size, we compute a Content-Length and send that
  1515  // in the header instead.
  1516  //
  1517  // Likewise, if the handler didn't set a Content-Type, we sniff that
  1518  // from the initial chunk of output.
  1519  //
  1520  // The Writers are wired together like:
  1521  //
  1522  // 1. *response (the ResponseWriter) ->
  1523  // 2. (*response).w, a *bufio.Writer of bufferBeforeChunkingSize bytes
  1524  // 3. chunkWriter.Writer (whose writeHeader finalizes Content-Length/Type)
  1525  //    and which writes the chunk headers, if needed.
  1526  // 4. conn.buf, a bufio.Writer of default (4kB) bytes, writing to ->
  1527  // 5. checkConnErrorWriter{c}, which notes any non-nil error on Write
  1528  //    and populates c.werr with it if so. but otherwise writes to:
  1529  // 6. the rwc, the net.Conn.
  1530  //
  1531  // TODO(bradfitz): short-circuit some of the buffering when the
  1532  // initial header contains both a Content-Type and Content-Length.
  1533  // Also short-circuit in (1) when the header's been sent and not in
  1534  // chunking mode, writing directly to (4) instead, if (2) has no
  1535  // buffered data. More generally, we could short-circuit from (1) to
  1536  // (3) even in chunking mode if the write size from (1) is over some
  1537  // threshold and nothing is in (2).  The answer might be mostly making
  1538  // bufferBeforeChunkingSize smaller and having bufio's fast-paths deal
  1539  // with this instead.
  1540  func (w *response) Write(data []byte) (n int, err error) {
  1541  	return w.write(len(data), data, "")
  1542  }
  1543  
  1544  func (w *response) WriteString(data string) (n int, err error) {
  1545  	return w.write(len(data), nil, data)
  1546  }
  1547  
  1548  // either dataB or dataS is non-zero.
  1549  func (w *response) write(lenData int, dataB []byte, dataS string) (n int, err error) {
  1550  	if w.conn.hijacked() {
  1551  		if lenData > 0 {
  1552  			caller := relevantCaller()
  1553  			w.conn.server.logf("http: response.Write on hijacked connection from %s (%s:%d)", caller.Function, path.Base(caller.File), caller.Line)
  1554  		}
  1555  		return 0, ErrHijacked
  1556  	}
  1557  	if !w.wroteHeader {
  1558  		w.WriteHeader(StatusOK)
  1559  	}
  1560  	if lenData == 0 {
  1561  		return 0, nil
  1562  	}
  1563  	if !w.bodyAllowed() {
  1564  		return 0, ErrBodyNotAllowed
  1565  	}
  1566  
  1567  	w.written += int64(lenData) // ignoring errors, for errorKludge
  1568  	if w.contentLength != -1 && w.written > w.contentLength {
  1569  		return 0, ErrContentLength
  1570  	}
  1571  	if dataB != nil {
  1572  		return w.w.Write(dataB)
  1573  	} else {
  1574  		return w.w.WriteString(dataS)
  1575  	}
  1576  }
  1577  
  1578  func (w *response) finishRequest() {
  1579  	w.handlerDone.setTrue()
  1580  
  1581  	if !w.wroteHeader {
  1582  		w.WriteHeader(StatusOK)
  1583  	}
  1584  
  1585  	w.w.Flush()
  1586  	putBufioWriter(w.w)
  1587  	w.cw.close()
  1588  	w.conn.bufw.Flush()
  1589  
  1590  	w.conn.r.abortPendingRead()
  1591  
  1592  	// Close the body (regardless of w.closeAfterReply) so we can
  1593  	// re-use its bufio.Reader later safely.
  1594  	w.reqBody.Close()
  1595  
  1596  	if w.req.MultipartForm != nil {
  1597  		w.req.MultipartForm.RemoveAll()
  1598  	}
  1599  }
  1600  
  1601  // shouldReuseConnection reports whether the underlying TCP connection can be reused.
  1602  // It must only be called after the handler is done executing.
  1603  func (w *response) shouldReuseConnection() bool {
  1604  	if w.closeAfterReply {
  1605  		// The request or something set while executing the
  1606  		// handler indicated we shouldn't reuse this
  1607  		// connection.
  1608  		return false
  1609  	}
  1610  
  1611  	if w.req.Method != "HEAD" && w.contentLength != -1 && w.bodyAllowed() && w.contentLength != w.written {
  1612  		// Did not write enough. Avoid getting out of sync.
  1613  		return false
  1614  	}
  1615  
  1616  	// There was some error writing to the underlying connection
  1617  	// during the request, so don't re-use this conn.
  1618  	if w.conn.werr != nil {
  1619  		return false
  1620  	}
  1621  
  1622  	if w.closedRequestBodyEarly() {
  1623  		return false
  1624  	}
  1625  
  1626  	return true
  1627  }
  1628  
  1629  func (w *response) closedRequestBodyEarly() bool {
  1630  	body, ok := w.req.Body.(*body)
  1631  	return ok && body.didEarlyClose()
  1632  }
  1633  
  1634  func (w *response) Flush() {
  1635  	if !w.wroteHeader {
  1636  		w.WriteHeader(StatusOK)
  1637  	}
  1638  	w.w.Flush()
  1639  	w.cw.flush()
  1640  }
  1641  
  1642  func (c *conn) finalFlush() {
  1643  	if c.bufr != nil {
  1644  		// Steal the bufio.Reader (~4KB worth of memory) and its associated
  1645  		// reader for a future connection.
  1646  		putBufioReader(c.bufr)
  1647  		c.bufr = nil
  1648  	}
  1649  
  1650  	if c.bufw != nil {
  1651  		c.bufw.Flush()
  1652  		// Steal the bufio.Writer (~4KB worth of memory) and its associated
  1653  		// writer for a future connection.
  1654  		putBufioWriter(c.bufw)
  1655  		c.bufw = nil
  1656  	}
  1657  }
  1658  
  1659  // Close the connection.
  1660  func (c *conn) close() {
  1661  	c.finalFlush()
  1662  	c.rwc.Close()
  1663  }
  1664  
  1665  // rstAvoidanceDelay is the amount of time we sleep after closing the
  1666  // write side of a TCP connection before closing the entire socket.
  1667  // By sleeping, we increase the chances that the client sees our FIN
  1668  // and processes its final data before they process the subsequent RST
  1669  // from closing a connection with known unread data.
  1670  // This RST seems to occur mostly on BSD systems. (And Windows?)
  1671  // This timeout is somewhat arbitrary (~latency around the planet).
  1672  const rstAvoidanceDelay = 500 * time.Millisecond
  1673  
  1674  type closeWriter interface {
  1675  	CloseWrite() error
  1676  }
  1677  
  1678  var _ closeWriter = (*net.TCPConn)(nil)
  1679  
  1680  // closeWrite flushes any outstanding data and sends a FIN packet (if
  1681  // client is connected via TCP), signalling that we're done. We then
  1682  // pause for a bit, hoping the client processes it before any
  1683  // subsequent RST.
  1684  //
  1685  // See https://golang.org/issue/3595
  1686  func (c *conn) closeWriteAndWait() {
  1687  	c.finalFlush()
  1688  	if tcp, ok := c.rwc.(closeWriter); ok {
  1689  		tcp.CloseWrite()
  1690  	}
  1691  	time.Sleep(rstAvoidanceDelay)
  1692  }
  1693  
  1694  // validNPN reports whether the proto is not a blacklisted Next
  1695  // Protocol Negotiation protocol. Empty and built-in protocol types
  1696  // are blacklisted and can't be overridden with alternate
  1697  // implementations.
  1698  func validNPN(proto string) bool {
  1699  	switch proto {
  1700  	case "", "http/1.1", "http/1.0":
  1701  		return false
  1702  	}
  1703  	return true
  1704  }
  1705  
  1706  func (c *conn) setState(nc net.Conn, state ConnState) {
  1707  	srv := c.server
  1708  	switch state {
  1709  	case StateNew:
  1710  		srv.trackConn(c, true)
  1711  	case StateHijacked, StateClosed:
  1712  		srv.trackConn(c, false)
  1713  	}
  1714  	if state > 0xff || state < 0 {
  1715  		panic("internal error")
  1716  	}
  1717  	packedState := uint64(time.Now().Unix()<<8) | uint64(state)
  1718  	atomic.StoreUint64(&c.curState.atomic, packedState)
  1719  	if hook := srv.ConnState; hook != nil {
  1720  		hook(nc, state)
  1721  	}
  1722  }
  1723  
  1724  func (c *conn) getState() (state ConnState, unixSec int64) {
  1725  	packedState := atomic.LoadUint64(&c.curState.atomic)
  1726  	return ConnState(packedState & 0xff), int64(packedState >> 8)
  1727  }
  1728  
  1729  // badRequestError is a literal string (used by in the server in HTML,
  1730  // unescaped) to tell the user why their request was bad. It should
  1731  // be plain text without user info or other embedded errors.
  1732  type badRequestError string
  1733  
  1734  func (e badRequestError) Error() string { return "Bad Request: " + string(e) }
  1735  
  1736  // ErrAbortHandler is a sentinel panic value to abort a handler.
  1737  // While any panic from ServeHTTP aborts the response to the client,
  1738  // panicking with ErrAbortHandler also suppresses logging of a stack
  1739  // trace to the server's error log.
  1740  var ErrAbortHandler = errors.New("net/http: abort Handler")
  1741  
  1742  // isCommonNetReadError reports whether err is a common error
  1743  // encountered during reading a request off the network when the
  1744  // client has gone away or had its read fail somehow. This is used to
  1745  // determine which logs are interesting enough to log about.
  1746  func isCommonNetReadError(err error) bool {
  1747  	if err == io.EOF {
  1748  		return true
  1749  	}
  1750  	if neterr, ok := err.(net.Error); ok && neterr.Timeout() {
  1751  		return true
  1752  	}
  1753  	if oe, ok := err.(*net.OpError); ok && oe.Op == "read" {
  1754  		return true
  1755  	}
  1756  	return false
  1757  }
  1758  
  1759  // Serve a new connection.
  1760  func (c *conn) serve(ctx context.Context) {
  1761  	c.remoteAddr = c.rwc.RemoteAddr().String()
  1762  	ctx = context.WithValue(ctx, LocalAddrContextKey, c.rwc.LocalAddr())
  1763  	defer func() {
  1764  		if err := recover(); err != nil && err != ErrAbortHandler {
  1765  			const size = 64 << 10
  1766  			buf := make([]byte, size)
  1767  			buf = buf[:runtime.Stack(buf, false)]
  1768  			c.server.logf("http: panic serving %v: %v\n%s", c.remoteAddr, err, buf)
  1769  		}
  1770  		if !c.hijacked() {
  1771  			c.close()
  1772  			c.setState(c.rwc, StateClosed)
  1773  		}
  1774  	}()
  1775  
  1776  	if tlsConn, ok := c.rwc.(*tls.Conn); ok {
  1777  		if d := c.server.ReadTimeout; d != 0 {
  1778  			c.rwc.SetReadDeadline(time.Now().Add(d))
  1779  		}
  1780  		if d := c.server.WriteTimeout; d != 0 {
  1781  			c.rwc.SetWriteDeadline(time.Now().Add(d))
  1782  		}
  1783  		if err := tlsConn.Handshake(); err != nil {
  1784  			// If the handshake failed due to the client not speaking
  1785  			// TLS, assume they're speaking plaintext HTTP and write a
  1786  			// 400 response on the TLS conn's underlying net.Conn.
  1787  			if re, ok := err.(tls.RecordHeaderError); ok && re.Conn != nil && tlsRecordHeaderLooksLikeHTTP(re.RecordHeader) {
  1788  				io.WriteString(re.Conn, "HTTP/1.0 400 Bad Request\r\n\r\nClient sent an HTTP request to an HTTPS server.\n")
  1789  				re.Conn.Close()
  1790  				return
  1791  			}
  1792  			c.server.logf("http: TLS handshake error from %s: %v", c.rwc.RemoteAddr(), err)
  1793  			return
  1794  		}
  1795  		c.tlsState = new(tls.ConnectionState)
  1796  		*c.tlsState = tlsConn.ConnectionState()
  1797  		if proto := c.tlsState.NegotiatedProtocol; validNPN(proto) {
  1798  			if fn := c.server.TLSNextProto[proto]; fn != nil {
  1799  				h := initNPNRequest{ctx, tlsConn, serverHandler{c.server}}
  1800  				fn(c.server, tlsConn, h)
  1801  			}
  1802  			return
  1803  		}
  1804  	}
  1805  
  1806  	// HTTP/1.x from here on.
  1807  
  1808  	ctx, cancelCtx := context.WithCancel(ctx)
  1809  	c.cancelCtx = cancelCtx
  1810  	defer cancelCtx()
  1811  
  1812  	c.r = &connReader{conn: c}
  1813  	c.bufr = newBufioReader(c.r)
  1814  	c.bufw = newBufioWriterSize(checkConnErrorWriter{c}, 4<<10)
  1815  
  1816  	for {
  1817  		w, err := c.readRequest(ctx)
  1818  		if c.r.remain != c.server.initialReadLimitSize() {
  1819  			// If we read any bytes off the wire, we're active.
  1820  			c.setState(c.rwc, StateActive)
  1821  		}
  1822  		if err != nil {
  1823  			const errorHeaders = "\r\nContent-Type: text/plain; charset=utf-8\r\nConnection: close\r\n\r\n"
  1824  
  1825  			switch {
  1826  			case err == errTooLarge:
  1827  				// Their HTTP client may or may not be
  1828  				// able to read this if we're
  1829  				// responding to them and hanging up
  1830  				// while they're still writing their
  1831  				// request. Undefined behavior.
  1832  				const publicErr = "431 Request Header Fields Too Large"
  1833  				fmt.Fprintf(c.rwc, "HTTP/1.1 "+publicErr+errorHeaders+publicErr)
  1834  				c.closeWriteAndWait()
  1835  				return
  1836  
  1837  			case isUnsupportedTEError(err):
  1838  				// Respond as per RFC 7230 Section 3.3.1 which says,
  1839  				//      A server that receives a request message with a
  1840  				//      transfer coding it does not understand SHOULD
  1841  				//      respond with 501 (Unimplemented).
  1842  				code := StatusNotImplemented
  1843  
  1844  				// We purposefully aren't echoing back the transfer-encoding's value,
  1845  				// so as to mitigate the risk of cross side scripting by an attacker.
  1846  				fmt.Fprintf(c.rwc, "HTTP/1.1 %d %s%sUnsupported transfer encoding", code, StatusText(code), errorHeaders)
  1847  				return
  1848  
  1849  			case isCommonNetReadError(err):
  1850  				return // don't reply
  1851  
  1852  			default:
  1853  				publicErr := "400 Bad Request"
  1854  				if v, ok := err.(badRequestError); ok {
  1855  					publicErr = publicErr + ": " + string(v)
  1856  				}
  1857  
  1858  				fmt.Fprintf(c.rwc, "HTTP/1.1 "+publicErr+errorHeaders+publicErr)
  1859  				return
  1860  			}
  1861  		}
  1862  
  1863  		// Expect 100 Continue support
  1864  		req := w.req
  1865  		if req.expectsContinue() {
  1866  			if req.ProtoAtLeast(1, 1) && req.ContentLength != 0 {
  1867  				// Wrap the Body reader with one that replies on the connection
  1868  				req.Body = &expectContinueReader{readCloser: req.Body, resp: w}
  1869  			}
  1870  		} else if req.Header.get("Expect") != "" {
  1871  			w.sendExpectationFailed()
  1872  			return
  1873  		}
  1874  
  1875  		c.curReq.Store(w)
  1876  
  1877  		if requestBodyRemains(req.Body) {
  1878  			registerOnHitEOF(req.Body, w.conn.r.startBackgroundRead)
  1879  		} else {
  1880  			w.conn.r.startBackgroundRead()
  1881  		}
  1882  
  1883  		// HTTP cannot have multiple simultaneous active requests.[*]
  1884  		// Until the server replies to this request, it can't read another,
  1885  		// so we might as well run the handler in this goroutine.
  1886  		// [*] Not strictly true: HTTP pipelining. We could let them all process
  1887  		// in parallel even if their responses need to be serialized.
  1888  		// But we're not going to implement HTTP pipelining because it
  1889  		// was never deployed in the wild and the answer is HTTP/2.
  1890  		serverHandler{c.server}.ServeHTTP(w, w.req)
  1891  		w.cancelCtx()
  1892  		if c.hijacked() {
  1893  			return
  1894  		}
  1895  		w.finishRequest()
  1896  		if !w.shouldReuseConnection() {
  1897  			if w.requestBodyLimitHit || w.closedRequestBodyEarly() {
  1898  				c.closeWriteAndWait()
  1899  			}
  1900  			return
  1901  		}
  1902  		c.setState(c.rwc, StateIdle)
  1903  		c.curReq.Store((*response)(nil))
  1904  
  1905  		if !w.conn.server.doKeepAlives() {
  1906  			// We're in shutdown mode. We might've replied
  1907  			// to the user without "Connection: close" and
  1908  			// they might think they can send another
  1909  			// request, but such is life with HTTP/1.1.
  1910  			return
  1911  		}
  1912  
  1913  		if d := c.server.idleTimeout(); d != 0 {
  1914  			c.rwc.SetReadDeadline(time.Now().Add(d))
  1915  			if _, err := c.bufr.Peek(4); err != nil {
  1916  				return
  1917  			}
  1918  		}
  1919  		c.rwc.SetReadDeadline(time.Time{})
  1920  	}
  1921  }
  1922  
  1923  func (w *response) sendExpectationFailed() {
  1924  	// TODO(bradfitz): let ServeHTTP handlers handle
  1925  	// requests with non-standard expectation[s]? Seems
  1926  	// theoretical at best, and doesn't fit into the
  1927  	// current ServeHTTP model anyway. We'd need to
  1928  	// make the ResponseWriter an optional
  1929  	// "ExpectReplier" interface or something.
  1930  	//
  1931  	// For now we'll just obey RFC 7231 5.1.1 which says
  1932  	// "A server that receives an Expect field-value other
  1933  	// than 100-continue MAY respond with a 417 (Expectation
  1934  	// Failed) status code to indicate that the unexpected
  1935  	// expectation cannot be met."
  1936  	w.Header().Set("Connection", "close")
  1937  	w.WriteHeader(StatusExpectationFailed)
  1938  	w.finishRequest()
  1939  }
  1940  
  1941  // Hijack implements the Hijacker.Hijack method. Our response is both a ResponseWriter
  1942  // and a Hijacker.
  1943  func (w *response) Hijack() (rwc net.Conn, buf *bufio.ReadWriter, err error) {
  1944  	if w.handlerDone.isSet() {
  1945  		panic("net/http: Hijack called after ServeHTTP finished")
  1946  	}
  1947  	if w.wroteHeader {
  1948  		w.cw.flush()
  1949  	}
  1950  
  1951  	c := w.conn
  1952  	c.mu.Lock()
  1953  	defer c.mu.Unlock()
  1954  
  1955  	// Release the bufioWriter that writes to the chunk writer, it is not
  1956  	// used after a connection has been hijacked.
  1957  	rwc, buf, err = c.hijackLocked()
  1958  	if err == nil {
  1959  		putBufioWriter(w.w)
  1960  		w.w = nil
  1961  	}
  1962  	return rwc, buf, err
  1963  }
  1964  
  1965  func (w *response) CloseNotify() <-chan bool {
  1966  	if w.handlerDone.isSet() {
  1967  		panic("net/http: CloseNotify called after ServeHTTP finished")
  1968  	}
  1969  	return w.closeNotifyCh
  1970  }
  1971  
  1972  func registerOnHitEOF(rc io.ReadCloser, fn func()) {
  1973  	switch v := rc.(type) {
  1974  	case *expectContinueReader:
  1975  		registerOnHitEOF(v.readCloser, fn)
  1976  	case *body:
  1977  		v.registerOnHitEOF(fn)
  1978  	default:
  1979  		panic("unexpected type " + fmt.Sprintf("%T", rc))
  1980  	}
  1981  }
  1982  
  1983  // requestBodyRemains reports whether future calls to Read
  1984  // on rc might yield more data.
  1985  func requestBodyRemains(rc io.ReadCloser) bool {
  1986  	if rc == NoBody {
  1987  		return false
  1988  	}
  1989  	switch v := rc.(type) {
  1990  	case *expectContinueReader:
  1991  		return requestBodyRemains(v.readCloser)
  1992  	case *body:
  1993  		return v.bodyRemains()
  1994  	default:
  1995  		panic("unexpected type " + fmt.Sprintf("%T", rc))
  1996  	}
  1997  }
  1998  
  1999  // The HandlerFunc type is an adapter to allow the use of
  2000  // ordinary functions as HTTP handlers. If f is a function
  2001  // with the appropriate signature, HandlerFunc(f) is a
  2002  // Handler that calls f.
  2003  type HandlerFunc func(ResponseWriter, *Request)
  2004  
  2005  // ServeHTTP calls f(w, r).
  2006  func (f HandlerFunc) ServeHTTP(w ResponseWriter, r *Request) {
  2007  	f(w, r)
  2008  }
  2009  
  2010  // Helper handlers
  2011  
  2012  // Error replies to the request with the specified error message and HTTP code.
  2013  // It does not otherwise end the request; the caller should ensure no further
  2014  // writes are done to w.
  2015  // The error message should be plain text.
  2016  func Error(w ResponseWriter, error string, code int) {
  2017  	w.Header().Set("Content-Type", "text/plain; charset=utf-8")
  2018  	w.Header().Set("X-Content-Type-Options", "nosniff")
  2019  	w.WriteHeader(code)
  2020  	fmt.Fprintln(w, error)
  2021  }
  2022  
  2023  // NotFound replies to the request with an HTTP 404 not found error.
  2024  func NotFound(w ResponseWriter, r *Request) { Error(w, "404 page not found", StatusNotFound) }
  2025  
  2026  // NotFoundHandler returns a simple request handler
  2027  // that replies to each request with a ``404 page not found'' reply.
  2028  func NotFoundHandler() Handler { return HandlerFunc(NotFound) }
  2029  
  2030  // StripPrefix returns a handler that serves HTTP requests
  2031  // by removing the given prefix from the request URL's Path
  2032  // and invoking the handler h. StripPrefix handles a
  2033  // request for a path that doesn't begin with prefix by
  2034  // replying with an HTTP 404 not found error.
  2035  func StripPrefix(prefix string, h Handler) Handler {
  2036  	if prefix == "" {
  2037  		return h
  2038  	}
  2039  	return HandlerFunc(func(w ResponseWriter, r *Request) {
  2040  		if p := strings.TrimPrefix(r.URL.Path, prefix); len(p) < len(r.URL.Path) {
  2041  			r2 := new(Request)
  2042  			*r2 = *r
  2043  			r2.URL = new(url.URL)
  2044  			*r2.URL = *r.URL
  2045  			r2.URL.Path = p
  2046  			h.ServeHTTP(w, r2)
  2047  		} else {
  2048  			NotFound(w, r)
  2049  		}
  2050  	})
  2051  }
  2052  
  2053  // Redirect replies to the request with a redirect to url,
  2054  // which may be a path relative to the request path.
  2055  //
  2056  // The provided code should be in the 3xx range and is usually
  2057  // StatusMovedPermanently, StatusFound or StatusSeeOther.
  2058  //
  2059  // If the Content-Type header has not been set, Redirect sets it
  2060  // to "text/html; charset=utf-8" and writes a small HTML body.
  2061  // Setting the Content-Type header to any value, including nil,
  2062  // disables that behavior.
  2063  func Redirect(w ResponseWriter, r *Request, url string, code int) {
  2064  	// parseURL is just url.Parse (url is shadowed for godoc).
  2065  	if u, err := parseURL(url); err == nil {
  2066  		// If url was relative, make its path absolute by
  2067  		// combining with request path.
  2068  		// The client would probably do this for us,
  2069  		// but doing it ourselves is more reliable.
  2070  		// See RFC 7231, section 7.1.2
  2071  		if u.Scheme == "" && u.Host == "" {
  2072  			oldpath := r.URL.Path
  2073  			if oldpath == "" { // should not happen, but avoid a crash if it does
  2074  				oldpath = "/"
  2075  			}
  2076  
  2077  			// no leading http://server
  2078  			if url == "" || url[0] != '/' {
  2079  				// make relative path absolute
  2080  				olddir, _ := path.Split(oldpath)
  2081  				url = olddir + url
  2082  			}
  2083  
  2084  			var query string
  2085  			if i := strings.Index(url, "?"); i != -1 {
  2086  				url, query = url[:i], url[i:]
  2087  			}
  2088  
  2089  			// clean up but preserve trailing slash
  2090  			trailing := strings.HasSuffix(url, "/")
  2091  			url = path.Clean(url)
  2092  			if trailing && !strings.HasSuffix(url, "/") {
  2093  				url += "/"
  2094  			}
  2095  			url += query
  2096  		}
  2097  	}
  2098  
  2099  	h := w.Header()
  2100  
  2101  	// RFC 7231 notes that a short HTML body is usually included in
  2102  	// the response because older user agents may not understand 301/307.
  2103  	// Do it only if the request didn't already have a Content-Type header.
  2104  	_, hadCT := h["Content-Type"]
  2105  
  2106  	h.Set("Location", hexEscapeNonASCII(url))
  2107  	if !hadCT && (r.Method == "GET" || r.Method == "HEAD") {
  2108  		h.Set("Content-Type", "text/html; charset=utf-8")
  2109  	}
  2110  	w.WriteHeader(code)
  2111  
  2112  	// Shouldn't send the body for POST or HEAD; that leaves GET.
  2113  	if !hadCT && r.Method == "GET" {
  2114  		body := "<a href=\"" + htmlEscape(url) + "\">" + statusText[code] + "</a>.\n"
  2115  		fmt.Fprintln(w, body)
  2116  	}
  2117  }
  2118  
  2119  // parseURL is just url.Parse. It exists only so that url.Parse can be called
  2120  // in places where url is shadowed for godoc. See https://golang.org/cl/49930.
  2121  var parseURL = url.Parse
  2122  
  2123  var htmlReplacer = strings.NewReplacer(
  2124  	"&", "&amp;",
  2125  	"<", "&lt;",
  2126  	">", "&gt;",
  2127  	// "&#34;" is shorter than "&quot;".
  2128  	`"`, "&#34;",
  2129  	// "&#39;" is shorter than "&apos;" and apos was not in HTML until HTML5.
  2130  	"'", "&#39;",
  2131  )
  2132  
  2133  func htmlEscape(s string) string {
  2134  	return htmlReplacer.Replace(s)
  2135  }
  2136  
  2137  // Redirect to a fixed URL
  2138  type redirectHandler struct {
  2139  	url  string
  2140  	code int
  2141  }
  2142  
  2143  func (rh *redirectHandler) ServeHTTP(w ResponseWriter, r *Request) {
  2144  	Redirect(w, r, rh.url, rh.code)
  2145  }
  2146  
  2147  // RedirectHandler returns a request handler that redirects
  2148  // each request it receives to the given url using the given
  2149  // status code.
  2150  //
  2151  // The provided code should be in the 3xx range and is usually
  2152  // StatusMovedPermanently, StatusFound or StatusSeeOther.
  2153  func RedirectHandler(url string, code int) Handler {
  2154  	return &redirectHandler{url, code}
  2155  }
  2156  
  2157  // ServeMux is an HTTP request multiplexer.
  2158  // It matches the URL of each incoming request against a list of registered
  2159  // patterns and calls the handler for the pattern that
  2160  // most closely matches the URL.
  2161  //
  2162  // Patterns name fixed, rooted paths, like "/favicon.ico",
  2163  // or rooted subtrees, like "/images/" (note the trailing slash).
  2164  // Longer patterns take precedence over shorter ones, so that
  2165  // if there are handlers registered for both "/images/"
  2166  // and "/images/thumbnails/", the latter handler will be
  2167  // called for paths beginning "/images/thumbnails/" and the
  2168  // former will receive requests for any other paths in the
  2169  // "/images/" subtree.
  2170  //
  2171  // Note that since a pattern ending in a slash names a rooted subtree,
  2172  // the pattern "/" matches all paths not matched by other registered
  2173  // patterns, not just the URL with Path == "/".
  2174  //
  2175  // If a subtree has been registered and a request is received naming the
  2176  // subtree root without its trailing slash, ServeMux redirects that
  2177  // request to the subtree root (adding the trailing slash). This behavior can
  2178  // be overridden with a separate registration for the path without
  2179  // the trailing slash. For example, registering "/images/" causes ServeMux
  2180  // to redirect a request for "/images" to "/images/", unless "/images" has
  2181  // been registered separately.
  2182  //
  2183  // Patterns may optionally begin with a host name, restricting matches to
  2184  // URLs on that host only. Host-specific patterns take precedence over
  2185  // general patterns, so that a handler might register for the two patterns
  2186  // "/codesearch" and "codesearch.google.com/" without also taking over
  2187  // requests for "http://www.google.com/".
  2188  //
  2189  // ServeMux also takes care of sanitizing the URL request path and the Host
  2190  // header, stripping the port number and redirecting any request containing . or
  2191  // .. elements or repeated slashes to an equivalent, cleaner URL.
  2192  type ServeMux struct {
  2193  	mu    sync.RWMutex
  2194  	m     map[string]muxEntry
  2195  	es    []muxEntry // slice of entries sorted from longest to shortest.
  2196  	hosts bool       // whether any patterns contain hostnames
  2197  }
  2198  
  2199  type muxEntry struct {
  2200  	h       Handler
  2201  	pattern string
  2202  }
  2203  
  2204  // NewServeMux allocates and returns a new ServeMux.
  2205  func NewServeMux() *ServeMux { return new(ServeMux) }
  2206  
  2207  // DefaultServeMux is the default ServeMux used by Serve.
  2208  var DefaultServeMux = &defaultServeMux
  2209  
  2210  var defaultServeMux ServeMux
  2211  
  2212  // cleanPath returns the canonical path for p, eliminating . and .. elements.
  2213  func cleanPath(p string) string {
  2214  	if p == "" {
  2215  		return "/"
  2216  	}
  2217  	if p[0] != '/' {
  2218  		p = "/" + p
  2219  	}
  2220  	np := path.Clean(p)
  2221  	// path.Clean removes trailing slash except for root;
  2222  	// put the trailing slash back if necessary.
  2223  	if p[len(p)-1] == '/' && np != "/" {
  2224  		// Fast path for common case of p being the string we want:
  2225  		if len(p) == len(np)+1 && strings.HasPrefix(p, np) {
  2226  			np = p
  2227  		} else {
  2228  			np += "/"
  2229  		}
  2230  	}
  2231  	return np
  2232  }
  2233  
  2234  // stripHostPort returns h without any trailing ":<port>".
  2235  func stripHostPort(h string) string {
  2236  	// If no port on host, return unchanged
  2237  	if strings.IndexByte(h, ':') == -1 {
  2238  		return h
  2239  	}
  2240  	host, _, err := net.SplitHostPort(h)
  2241  	if err != nil {
  2242  		return h // on error, return unchanged
  2243  	}
  2244  	return host
  2245  }
  2246  
  2247  // Find a handler on a handler map given a path string.
  2248  // Most-specific (longest) pattern wins.
  2249  func (mux *ServeMux) match(path string) (h Handler, pattern string) {
  2250  	// Check for exact match first.
  2251  	v, ok := mux.m[path]
  2252  	if ok {
  2253  		return v.h, v.pattern
  2254  	}
  2255  
  2256  	// Check for longest valid match.  mux.es contains all patterns
  2257  	// that end in / sorted from longest to shortest.
  2258  	for _, e := range mux.es {
  2259  		if strings.HasPrefix(path, e.pattern) {
  2260  			return e.h, e.pattern
  2261  		}
  2262  	}
  2263  	return nil, ""
  2264  }
  2265  
  2266  // redirectToPathSlash determines if the given path needs appending "/" to it.
  2267  // This occurs when a handler for path + "/" was already registered, but
  2268  // not for path itself. If the path needs appending to, it creates a new
  2269  // URL, setting the path to u.Path + "/" and returning true to indicate so.
  2270  func (mux *ServeMux) redirectToPathSlash(host, path string, u *url.URL) (*url.URL, bool) {
  2271  	mux.mu.RLock()
  2272  	shouldRedirect := mux.shouldRedirectRLocked(host, path)
  2273  	mux.mu.RUnlock()
  2274  	if !shouldRedirect {
  2275  		return u, false
  2276  	}
  2277  	path = path + "/"
  2278  	u = &url.URL{Path: path, RawQuery: u.RawQuery}
  2279  	return u, true
  2280  }
  2281  
  2282  // shouldRedirectRLocked reports whether the given path and host should be redirected to
  2283  // path+"/". This should happen if a handler is registered for path+"/" but
  2284  // not path -- see comments at ServeMux.
  2285  func (mux *ServeMux) shouldRedirectRLocked(host, path string) bool {
  2286  	p := []string{path, host + path}
  2287  
  2288  	for _, c := range p {
  2289  		if _, exist := mux.m[c]; exist {
  2290  			return false
  2291  		}
  2292  	}
  2293  
  2294  	n := len(path)
  2295  	if n == 0 {
  2296  		return false
  2297  	}
  2298  	for _, c := range p {
  2299  		if _, exist := mux.m[c+"/"]; exist {
  2300  			return path[n-1] != '/'
  2301  		}
  2302  	}
  2303  
  2304  	return false
  2305  }
  2306  
  2307  // Handler returns the handler to use for the given request,
  2308  // consulting r.Method, r.Host, and r.URL.Path. It always returns
  2309  // a non-nil handler. If the path is not in its canonical form, the
  2310  // handler will be an internally-generated handler that redirects
  2311  // to the canonical path. If the host contains a port, it is ignored
  2312  // when matching handlers.
  2313  //
  2314  // The path and host are used unchanged for CONNECT requests.
  2315  //
  2316  // Handler also returns the registered pattern that matches the
  2317  // request or, in the case of internally-generated redirects,
  2318  // the pattern that will match after following the redirect.
  2319  //
  2320  // If there is no registered handler that applies to the request,
  2321  // Handler returns a ``page not found'' handler and an empty pattern.
  2322  func (mux *ServeMux) Handler(r *Request) (h Handler, pattern string) {
  2323  
  2324  	// CONNECT requests are not canonicalized.
  2325  	if r.Method == "CONNECT" {
  2326  		// If r.URL.Path is /tree and its handler is not registered,
  2327  		// the /tree -> /tree/ redirect applies to CONNECT requests
  2328  		// but the path canonicalization does not.
  2329  		if u, ok := mux.redirectToPathSlash(r.URL.Host, r.URL.Path, r.URL); ok {
  2330  			return RedirectHandler(u.String(), StatusMovedPermanently), u.Path
  2331  		}
  2332  
  2333  		return mux.handler(r.Host, r.URL.Path)
  2334  	}
  2335  
  2336  	// All other requests have any port stripped and path cleaned
  2337  	// before passing to mux.handler.
  2338  	host := stripHostPort(r.Host)
  2339  	path := cleanPath(r.URL.Path)
  2340  
  2341  	// If the given path is /tree and its handler is not registered,
  2342  	// redirect for /tree/.
  2343  	if u, ok := mux.redirectToPathSlash(host, path, r.URL); ok {
  2344  		return RedirectHandler(u.String(), StatusMovedPermanently), u.Path
  2345  	}
  2346  
  2347  	if path != r.URL.Path {
  2348  		_, pattern = mux.handler(host, path)
  2349  		url := *r.URL
  2350  		url.Path = path
  2351  		return RedirectHandler(url.String(), StatusMovedPermanently), pattern
  2352  	}
  2353  
  2354  	return mux.handler(host, r.URL.Path)
  2355  }
  2356  
  2357  // handler is the main implementation of Handler.
  2358  // The path is known to be in canonical form, except for CONNECT methods.
  2359  func (mux *ServeMux) handler(host, path string) (h Handler, pattern string) {
  2360  	mux.mu.RLock()
  2361  	defer mux.mu.RUnlock()
  2362  
  2363  	// Host-specific pattern takes precedence over generic ones
  2364  	if mux.hosts {
  2365  		h, pattern = mux.match(host + path)
  2366  	}
  2367  	if h == nil {
  2368  		h, pattern = mux.match(path)
  2369  	}
  2370  	if h == nil {
  2371  		h, pattern = NotFoundHandler(), ""
  2372  	}
  2373  	return
  2374  }
  2375  
  2376  // ServeHTTP dispatches the request to the handler whose
  2377  // pattern most closely matches the request URL.
  2378  func (mux *ServeMux) ServeHTTP(w ResponseWriter, r *Request) {
  2379  	if r.RequestURI == "*" {
  2380  		if r.ProtoAtLeast(1, 1) {
  2381  			w.Header().Set("Connection", "close")
  2382  		}
  2383  		w.WriteHeader(StatusBadRequest)
  2384  		return
  2385  	}
  2386  	h, _ := mux.Handler(r)
  2387  	h.ServeHTTP(w, r)
  2388  }
  2389  
  2390  // Handle registers the handler for the given pattern.
  2391  // If a handler already exists for pattern, Handle panics.
  2392  func (mux *ServeMux) Handle(pattern string, handler Handler) {
  2393  	mux.mu.Lock()
  2394  	defer mux.mu.Unlock()
  2395  
  2396  	if pattern == "" {
  2397  		panic("http: invalid pattern")
  2398  	}
  2399  	if handler == nil {
  2400  		panic("http: nil handler")
  2401  	}
  2402  	if _, exist := mux.m[pattern]; exist {
  2403  		panic("http: multiple registrations for " + pattern)
  2404  	}
  2405  
  2406  	if mux.m == nil {
  2407  		mux.m = make(map[string]muxEntry)
  2408  	}
  2409  	e := muxEntry{h: handler, pattern: pattern}
  2410  	mux.m[pattern] = e
  2411  	if pattern[len(pattern)-1] == '/' {
  2412  		mux.es = appendSorted(mux.es, e)
  2413  	}
  2414  
  2415  	if pattern[0] != '/' {
  2416  		mux.hosts = true
  2417  	}
  2418  }
  2419  
  2420  func appendSorted(es []muxEntry, e muxEntry) []muxEntry {
  2421  	n := len(es)
  2422  	i := sort.Search(n, func(i int) bool {
  2423  		return len(es[i].pattern) < len(e.pattern)
  2424  	})
  2425  	if i == n {
  2426  		return append(es, e)
  2427  	}
  2428  	// we now know that i points at where we want to insert
  2429  	es = append(es, muxEntry{}) // try to grow the slice in place, any entry works.
  2430  	copy(es[i+1:], es[i:])      // Move shorter entries down
  2431  	es[i] = e
  2432  	return es
  2433  }
  2434  
  2435  // HandleFunc registers the handler function for the given pattern.
  2436  func (mux *ServeMux) HandleFunc(pattern string, handler func(ResponseWriter, *Request)) {
  2437  	if handler == nil {
  2438  		panic("http: nil handler")
  2439  	}
  2440  	mux.Handle(pattern, HandlerFunc(handler))
  2441  }
  2442  
  2443  // Handle registers the handler for the given pattern
  2444  // in the DefaultServeMux.
  2445  // The documentation for ServeMux explains how patterns are matched.
  2446  func Handle(pattern string, handler Handler) { DefaultServeMux.Handle(pattern, handler) }
  2447  
  2448  // HandleFunc registers the handler function for the given pattern
  2449  // in the DefaultServeMux.
  2450  // The documentation for ServeMux explains how patterns are matched.
  2451  func HandleFunc(pattern string, handler func(ResponseWriter, *Request)) {
  2452  	DefaultServeMux.HandleFunc(pattern, handler)
  2453  }
  2454  
  2455  // Serve accepts incoming HTTP connections on the listener l,
  2456  // creating a new service goroutine for each. The service goroutines
  2457  // read requests and then call handler to reply to them.
  2458  //
  2459  // The handler is typically nil, in which case the DefaultServeMux is used.
  2460  //
  2461  // HTTP/2 support is only enabled if the Listener returns *tls.Conn
  2462  // connections and they were configured with "h2" in the TLS
  2463  // Config.NextProtos.
  2464  //
  2465  // Serve always returns a non-nil error.
  2466  func Serve(l net.Listener, handler Handler) error {
  2467  	srv := &Server{Handler: handler}
  2468  	return srv.Serve(l)
  2469  }
  2470  
  2471  // ServeTLS accepts incoming HTTPS connections on the listener l,
  2472  // creating a new service goroutine for each. The service goroutines
  2473  // read requests and then call handler to reply to them.
  2474  //
  2475  // The handler is typically nil, in which case the DefaultServeMux is used.
  2476  //
  2477  // Additionally, files containing a certificate and matching private key
  2478  // for the server must be provided. If the certificate is signed by a
  2479  // certificate authority, the certFile should be the concatenation
  2480  // of the server's certificate, any intermediates, and the CA's certificate.
  2481  //
  2482  // ServeTLS always returns a non-nil error.
  2483  func ServeTLS(l net.Listener, handler Handler, certFile, keyFile string) error {
  2484  	srv := &Server{Handler: handler}
  2485  	return srv.ServeTLS(l, certFile, keyFile)
  2486  }
  2487  
  2488  // A Server defines parameters for running an HTTP server.
  2489  // The zero value for Server is a valid configuration.
  2490  type Server struct {
  2491  	Addr    string  // TCP address to listen on, ":http" if empty
  2492  	Handler Handler // handler to invoke, http.DefaultServeMux if nil
  2493  
  2494  	// TLSConfig optionally provides a TLS configuration for use
  2495  	// by ServeTLS and ListenAndServeTLS. Note that this value is
  2496  	// cloned by ServeTLS and ListenAndServeTLS, so it's not
  2497  	// possible to modify the configuration with methods like
  2498  	// tls.Config.SetSessionTicketKeys. To use
  2499  	// SetSessionTicketKeys, use Server.Serve with a TLS Listener
  2500  	// instead.
  2501  	TLSConfig *tls.Config
  2502  
  2503  	// ReadTimeout is the maximum duration for reading the entire
  2504  	// request, including the body.
  2505  	//
  2506  	// Because ReadTimeout does not let Handlers make per-request
  2507  	// decisions on each request body's acceptable deadline or
  2508  	// upload rate, most users will prefer to use
  2509  	// ReadHeaderTimeout. It is valid to use them both.
  2510  	ReadTimeout time.Duration
  2511  
  2512  	// ReadHeaderTimeout is the amount of time allowed to read
  2513  	// request headers. The connection's read deadline is reset
  2514  	// after reading the headers and the Handler can decide what
  2515  	// is considered too slow for the body. If ReadHeaderTimeout
  2516  	// is zero, the value of ReadTimeout is used. If both are
  2517  	// zero, there is no timeout.
  2518  	ReadHeaderTimeout time.Duration
  2519  
  2520  	// WriteTimeout is the maximum duration before timing out
  2521  	// writes of the response. It is reset whenever a new
  2522  	// request's header is read. Like ReadTimeout, it does not
  2523  	// let Handlers make decisions on a per-request basis.
  2524  	WriteTimeout time.Duration
  2525  
  2526  	// IdleTimeout is the maximum amount of time to wait for the
  2527  	// next request when keep-alives are enabled. If IdleTimeout
  2528  	// is zero, the value of ReadTimeout is used. If both are
  2529  	// zero, there is no timeout.
  2530  	IdleTimeout time.Duration
  2531  
  2532  	// MaxHeaderBytes controls the maximum number of bytes the
  2533  	// server will read parsing the request header's keys and
  2534  	// values, including the request line. It does not limit the
  2535  	// size of the request body.
  2536  	// If zero, DefaultMaxHeaderBytes is used.
  2537  	MaxHeaderBytes int
  2538  
  2539  	// TLSNextProto optionally specifies a function to take over
  2540  	// ownership of the provided TLS connection when an NPN/ALPN
  2541  	// protocol upgrade has occurred. The map key is the protocol
  2542  	// name negotiated. The Handler argument should be used to
  2543  	// handle HTTP requests and will initialize the Request's TLS
  2544  	// and RemoteAddr if not already set. The connection is
  2545  	// automatically closed when the function returns.
  2546  	// If TLSNextProto is not nil, HTTP/2 support is not enabled
  2547  	// automatically.
  2548  	TLSNextProto map[string]func(*Server, *tls.Conn, Handler)
  2549  
  2550  	// ConnState specifies an optional callback function that is
  2551  	// called when a client connection changes state. See the
  2552  	// ConnState type and associated constants for details.
  2553  	ConnState func(net.Conn, ConnState)
  2554  
  2555  	// ErrorLog specifies an optional logger for errors accepting
  2556  	// connections, unexpected behavior from handlers, and
  2557  	// underlying FileSystem errors.
  2558  	// If nil, logging is done via the log package's standard logger.
  2559  	ErrorLog *log.Logger
  2560  
  2561  	// BaseContext optionally specifies a function that returns
  2562  	// the base context for incoming requests on this server.
  2563  	// The provided Listener is the specific Listener that's
  2564  	// about to start accepting requests.
  2565  	// If BaseContext is nil, the default is context.Background().
  2566  	// If non-nil, it must return a non-nil context.
  2567  	BaseContext func(net.Listener) context.Context
  2568  
  2569  	// ConnContext optionally specifies a function that modifies
  2570  	// the context used for a new connection c. The provided ctx
  2571  	// is derived from the base context and has a ServerContextKey
  2572  	// value.
  2573  	ConnContext func(ctx context.Context, c net.Conn) context.Context
  2574  
  2575  	disableKeepAlives int32     // accessed atomically.
  2576  	inShutdown        int32     // accessed atomically (non-zero means we're in Shutdown)
  2577  	nextProtoOnce     sync.Once // guards setupHTTP2_* init
  2578  	nextProtoErr      error     // result of http2.ConfigureServer if used
  2579  
  2580  	mu         sync.Mutex
  2581  	listeners  map[*net.Listener]struct{}
  2582  	activeConn map[*conn]struct{}
  2583  	doneChan   chan struct{}
  2584  	onShutdown []func()
  2585  }
  2586  
  2587  func (s *Server) getDoneChan() <-chan struct{} {
  2588  	s.mu.Lock()
  2589  	defer s.mu.Unlock()
  2590  	return s.getDoneChanLocked()
  2591  }
  2592  
  2593  func (s *Server) getDoneChanLocked() chan struct{} {
  2594  	if s.doneChan == nil {
  2595  		s.doneChan = make(chan struct{})
  2596  	}
  2597  	return s.doneChan
  2598  }
  2599  
  2600  func (s *Server) closeDoneChanLocked() {
  2601  	ch := s.getDoneChanLocked()
  2602  	select {
  2603  	case <-ch:
  2604  		// Already closed. Don't close again.
  2605  	default:
  2606  		// Safe to close here. We're the only closer, guarded
  2607  		// by s.mu.
  2608  		close(ch)
  2609  	}
  2610  }
  2611  
  2612  // Close immediately closes all active net.Listeners and any
  2613  // connections in state StateNew, StateActive, or StateIdle. For a
  2614  // graceful shutdown, use Shutdown.
  2615  //
  2616  // Close does not attempt to close (and does not even know about)
  2617  // any hijacked connections, such as WebSockets.
  2618  //
  2619  // Close returns any error returned from closing the Server's
  2620  // underlying Listener(s).
  2621  func (srv *Server) Close() error {
  2622  	atomic.StoreInt32(&srv.inShutdown, 1)
  2623  	srv.mu.Lock()
  2624  	defer srv.mu.Unlock()
  2625  	srv.closeDoneChanLocked()
  2626  	err := srv.closeListenersLocked()
  2627  	for c := range srv.activeConn {
  2628  		c.rwc.Close()
  2629  		delete(srv.activeConn, c)
  2630  	}
  2631  	return err
  2632  }
  2633  
  2634  // shutdownPollInterval is how often we poll for quiescence
  2635  // during Server.Shutdown. This is lower during tests, to
  2636  // speed up tests.
  2637  // Ideally we could find a solution that doesn't involve polling,
  2638  // but which also doesn't have a high runtime cost (and doesn't
  2639  // involve any contentious mutexes), but that is left as an
  2640  // exercise for the reader.
  2641  var shutdownPollInterval = 500 * time.Millisecond
  2642  
  2643  // Shutdown gracefully shuts down the server without interrupting any
  2644  // active connections. Shutdown works by first closing all open
  2645  // listeners, then closing all idle connections, and then waiting
  2646  // indefinitely for connections to return to idle and then shut down.
  2647  // If the provided context expires before the shutdown is complete,
  2648  // Shutdown returns the context's error, otherwise it returns any
  2649  // error returned from closing the Server's underlying Listener(s).
  2650  //
  2651  // When Shutdown is called, Serve, ListenAndServe, and
  2652  // ListenAndServeTLS immediately return ErrServerClosed. Make sure the
  2653  // program doesn't exit and waits instead for Shutdown to return.
  2654  //
  2655  // Shutdown does not attempt to close nor wait for hijacked
  2656  // connections such as WebSockets. The caller of Shutdown should
  2657  // separately notify such long-lived connections of shutdown and wait
  2658  // for them to close, if desired. See RegisterOnShutdown for a way to
  2659  // register shutdown notification functions.
  2660  //
  2661  // Once Shutdown has been called on a server, it may not be reused;
  2662  // future calls to methods such as Serve will return ErrServerClosed.
  2663  func (srv *Server) Shutdown(ctx context.Context) error {
  2664  	atomic.StoreInt32(&srv.inShutdown, 1)
  2665  
  2666  	srv.mu.Lock()
  2667  	lnerr := srv.closeListenersLocked()
  2668  	srv.closeDoneChanLocked()
  2669  	for _, f := range srv.onShutdown {
  2670  		go f()
  2671  	}
  2672  	srv.mu.Unlock()
  2673  
  2674  	ticker := time.NewTicker(shutdownPollInterval)
  2675  	defer ticker.Stop()
  2676  	for {
  2677  		if srv.closeIdleConns() {
  2678  			return lnerr
  2679  		}
  2680  		select {
  2681  		case <-ctx.Done():
  2682  			return ctx.Err()
  2683  		case <-ticker.C:
  2684  		}
  2685  	}
  2686  }
  2687  
  2688  // RegisterOnShutdown registers a function to call on Shutdown.
  2689  // This can be used to gracefully shutdown connections that have
  2690  // undergone NPN/ALPN protocol upgrade or that have been hijacked.
  2691  // This function should start protocol-specific graceful shutdown,
  2692  // but should not wait for shutdown to complete.
  2693  func (srv *Server) RegisterOnShutdown(f func()) {
  2694  	srv.mu.Lock()
  2695  	srv.onShutdown = append(srv.onShutdown, f)
  2696  	srv.mu.Unlock()
  2697  }
  2698  
  2699  // closeIdleConns closes all idle connections and reports whether the
  2700  // server is quiescent.
  2701  func (s *Server) closeIdleConns() bool {
  2702  	s.mu.Lock()
  2703  	defer s.mu.Unlock()
  2704  	quiescent := true
  2705  	for c := range s.activeConn {
  2706  		st, unixSec := c.getState()
  2707  		// Issue 22682: treat StateNew connections as if
  2708  		// they're idle if we haven't read the first request's
  2709  		// header in over 5 seconds.
  2710  		if st == StateNew && unixSec < time.Now().Unix()-5 {
  2711  			st = StateIdle
  2712  		}
  2713  		if st != StateIdle || unixSec == 0 {
  2714  			// Assume unixSec == 0 means it's a very new
  2715  			// connection, without state set yet.
  2716  			quiescent = false
  2717  			continue
  2718  		}
  2719  		c.rwc.Close()
  2720  		delete(s.activeConn, c)
  2721  	}
  2722  	return quiescent
  2723  }
  2724  
  2725  func (s *Server) closeListenersLocked() error {
  2726  	var err error
  2727  	for ln := range s.listeners {
  2728  		if cerr := (*ln).Close(); cerr != nil && err == nil {
  2729  			err = cerr
  2730  		}
  2731  		delete(s.listeners, ln)
  2732  	}
  2733  	return err
  2734  }
  2735  
  2736  // A ConnState represents the state of a client connection to a server.
  2737  // It's used by the optional Server.ConnState hook.
  2738  type ConnState int
  2739  
  2740  const (
  2741  	// StateNew represents a new connection that is expected to
  2742  	// send a request immediately. Connections begin at this
  2743  	// state and then transition to either StateActive or
  2744  	// StateClosed.
  2745  	StateNew ConnState = iota
  2746  
  2747  	// StateActive represents a connection that has read 1 or more
  2748  	// bytes of a request. The Server.ConnState hook for
  2749  	// StateActive fires before the request has entered a handler
  2750  	// and doesn't fire again until the request has been
  2751  	// handled. After the request is handled, the state
  2752  	// transitions to StateClosed, StateHijacked, or StateIdle.
  2753  	// For HTTP/2, StateActive fires on the transition from zero
  2754  	// to one active request, and only transitions away once all
  2755  	// active requests are complete. That means that ConnState
  2756  	// cannot be used to do per-request work; ConnState only notes
  2757  	// the overall state of the connection.
  2758  	StateActive
  2759  
  2760  	// StateIdle represents a connection that has finished
  2761  	// handling a request and is in the keep-alive state, waiting
  2762  	// for a new request. Connections transition from StateIdle
  2763  	// to either StateActive or StateClosed.
  2764  	StateIdle
  2765  
  2766  	// StateHijacked represents a hijacked connection.
  2767  	// This is a terminal state. It does not transition to StateClosed.
  2768  	StateHijacked
  2769  
  2770  	// StateClosed represents a closed connection.
  2771  	// This is a terminal state. Hijacked connections do not
  2772  	// transition to StateClosed.
  2773  	StateClosed
  2774  )
  2775  
  2776  var stateName = map[ConnState]string{
  2777  	StateNew:      "new",
  2778  	StateActive:   "active",
  2779  	StateIdle:     "idle",
  2780  	StateHijacked: "hijacked",
  2781  	StateClosed:   "closed",
  2782  }
  2783  
  2784  func (c ConnState) String() string {
  2785  	return stateName[c]
  2786  }
  2787  
  2788  // serverHandler delegates to either the server's Handler or
  2789  // DefaultServeMux and also handles "OPTIONS *" requests.
  2790  type serverHandler struct {
  2791  	srv *Server
  2792  }
  2793  
  2794  func (sh serverHandler) ServeHTTP(rw ResponseWriter, req *Request) {
  2795  	handler := sh.srv.Handler
  2796  	if handler == nil {
  2797  		handler = DefaultServeMux
  2798  	}
  2799  	if req.RequestURI == "*" && req.Method == "OPTIONS" {
  2800  		handler = globalOptionsHandler{}
  2801  	}
  2802  	handler.ServeHTTP(rw, req)
  2803  }
  2804  
  2805  // ListenAndServe listens on the TCP network address srv.Addr and then
  2806  // calls Serve to handle requests on incoming connections.
  2807  // Accepted connections are configured to enable TCP keep-alives.
  2808  //
  2809  // If srv.Addr is blank, ":http" is used.
  2810  //
  2811  // ListenAndServe always returns a non-nil error. After Shutdown or Close,
  2812  // the returned error is ErrServerClosed.
  2813  func (srv *Server) ListenAndServe() error {
  2814  	if srv.shuttingDown() {
  2815  		return ErrServerClosed
  2816  	}
  2817  	addr := srv.Addr
  2818  	if addr == "" {
  2819  		addr = ":http"
  2820  	}
  2821  	ln, err := net.Listen("tcp", addr)
  2822  	if err != nil {
  2823  		return err
  2824  	}
  2825  	return srv.Serve(ln)
  2826  }
  2827  
  2828  var testHookServerServe func(*Server, net.Listener) // used if non-nil
  2829  
  2830  // shouldDoServeHTTP2 reports whether Server.Serve should configure
  2831  // automatic HTTP/2. (which sets up the srv.TLSNextProto map)
  2832  func (srv *Server) shouldConfigureHTTP2ForServe() bool {
  2833  	if srv.TLSConfig == nil {
  2834  		// Compatibility with Go 1.6:
  2835  		// If there's no TLSConfig, it's possible that the user just
  2836  		// didn't set it on the http.Server, but did pass it to
  2837  		// tls.NewListener and passed that listener to Serve.
  2838  		// So we should configure HTTP/2 (to set up srv.TLSNextProto)
  2839  		// in case the listener returns an "h2" *tls.Conn.
  2840  		return true
  2841  	}
  2842  	// The user specified a TLSConfig on their http.Server.
  2843  	// In this, case, only configure HTTP/2 if their tls.Config
  2844  	// explicitly mentions "h2". Otherwise http2.ConfigureServer
  2845  	// would modify the tls.Config to add it, but they probably already
  2846  	// passed this tls.Config to tls.NewListener. And if they did,
  2847  	// it's too late anyway to fix it. It would only be potentially racy.
  2848  	// See Issue 15908.
  2849  	return strSliceContains(srv.TLSConfig.NextProtos, http2NextProtoTLS)
  2850  }
  2851  
  2852  // ErrServerClosed is returned by the Server's Serve, ServeTLS, ListenAndServe,
  2853  // and ListenAndServeTLS methods after a call to Shutdown or Close.
  2854  var ErrServerClosed = errors.New("http: Server closed")
  2855  
  2856  // Serve accepts incoming connections on the Listener l, creating a
  2857  // new service goroutine for each. The service goroutines read requests and
  2858  // then call srv.Handler to reply to them.
  2859  //
  2860  // HTTP/2 support is only enabled if the Listener returns *tls.Conn
  2861  // connections and they were configured with "h2" in the TLS
  2862  // Config.NextProtos.
  2863  //
  2864  // Serve always returns a non-nil error and closes l.
  2865  // After Shutdown or Close, the returned error is ErrServerClosed.
  2866  func (srv *Server) Serve(l net.Listener) error {
  2867  	if fn := testHookServerServe; fn != nil {
  2868  		fn(srv, l) // call hook with unwrapped listener
  2869  	}
  2870  
  2871  	origListener := l
  2872  	l = &onceCloseListener{Listener: l}
  2873  	defer l.Close()
  2874  
  2875  	if err := srv.setupHTTP2_Serve(); err != nil {
  2876  		return err
  2877  	}
  2878  
  2879  	if !srv.trackListener(&l, true) {
  2880  		return ErrServerClosed
  2881  	}
  2882  	defer srv.trackListener(&l, false)
  2883  
  2884  	var tempDelay time.Duration // how long to sleep on accept failure
  2885  
  2886  	baseCtx := context.Background()
  2887  	if srv.BaseContext != nil {
  2888  		baseCtx = srv.BaseContext(origListener)
  2889  		if baseCtx == nil {
  2890  			panic("BaseContext returned a nil context")
  2891  		}
  2892  	}
  2893  
  2894  	ctx := context.WithValue(baseCtx, ServerContextKey, srv)
  2895  	for {
  2896  		rw, e := l.Accept()
  2897  		if e != nil {
  2898  			select {
  2899  			case <-srv.getDoneChan():
  2900  				return ErrServerClosed
  2901  			default:
  2902  			}
  2903  			if ne, ok := e.(net.Error); ok && ne.Temporary() {
  2904  				if tempDelay == 0 {
  2905  					tempDelay = 5 * time.Millisecond
  2906  				} else {
  2907  					tempDelay *= 2
  2908  				}
  2909  				if max := 1 * time.Second; tempDelay > max {
  2910  					tempDelay = max
  2911  				}
  2912  				srv.logf("http: Accept error: %v; retrying in %v", e, tempDelay)
  2913  				time.Sleep(tempDelay)
  2914  				continue
  2915  			}
  2916  			return e
  2917  		}
  2918  		if cc := srv.ConnContext; cc != nil {
  2919  			ctx = cc(ctx, rw)
  2920  			if ctx == nil {
  2921  				panic("ConnContext returned nil")
  2922  			}
  2923  		}
  2924  		tempDelay = 0
  2925  		c := srv.newConn(rw)
  2926  		c.setState(c.rwc, StateNew) // before Serve can return
  2927  		go c.serve(ctx)
  2928  	}
  2929  }
  2930  
  2931  // ServeTLS accepts incoming connections on the Listener l, creating a
  2932  // new service goroutine for each. The service goroutines perform TLS
  2933  // setup and then read requests, calling srv.Handler to reply to them.
  2934  //
  2935  // Files containing a certificate and matching private key for the
  2936  // server must be provided if neither the Server's
  2937  // TLSConfig.Certificates nor TLSConfig.GetCertificate are populated.
  2938  // If the certificate is signed by a certificate authority, the
  2939  // certFile should be the concatenation of the server's certificate,
  2940  // any intermediates, and the CA's certificate.
  2941  //
  2942  // ServeTLS always returns a non-nil error. After Shutdown or Close, the
  2943  // returned error is ErrServerClosed.
  2944  func (srv *Server) ServeTLS(l net.Listener, certFile, keyFile string) error {
  2945  	// Setup HTTP/2 before srv.Serve, to initialize srv.TLSConfig
  2946  	// before we clone it and create the TLS Listener.
  2947  	if err := srv.setupHTTP2_ServeTLS(); err != nil {
  2948  		return err
  2949  	}
  2950  
  2951  	config := cloneTLSConfig(srv.TLSConfig)
  2952  	if !strSliceContains(config.NextProtos, "http/1.1") {
  2953  		config.NextProtos = append(config.NextProtos, "http/1.1")
  2954  	}
  2955  
  2956  	configHasCert := len(config.Certificates) > 0 || config.GetCertificate != nil
  2957  	if !configHasCert || certFile != "" || keyFile != "" {
  2958  		var err error
  2959  		config.Certificates = make([]tls.Certificate, 1)
  2960  		config.Certificates[0], err = tls.LoadX509KeyPair(certFile, keyFile)
  2961  		if err != nil {
  2962  			return err
  2963  		}
  2964  	}
  2965  
  2966  	tlsListener := tls.NewListener(l, config)
  2967  	return srv.Serve(tlsListener)
  2968  }
  2969  
  2970  // trackListener adds or removes a net.Listener to the set of tracked
  2971  // listeners.
  2972  //
  2973  // We store a pointer to interface in the map set, in case the
  2974  // net.Listener is not comparable. This is safe because we only call
  2975  // trackListener via Serve and can track+defer untrack the same
  2976  // pointer to local variable there. We never need to compare a
  2977  // Listener from another caller.
  2978  //
  2979  // It reports whether the server is still up (not Shutdown or Closed).
  2980  func (s *Server) trackListener(ln *net.Listener, add bool) bool {
  2981  	s.mu.Lock()
  2982  	defer s.mu.Unlock()
  2983  	if s.listeners == nil {
  2984  		s.listeners = make(map[*net.Listener]struct{})
  2985  	}
  2986  	if add {
  2987  		if s.shuttingDown() {
  2988  			return false
  2989  		}
  2990  		s.listeners[ln] = struct{}{}
  2991  	} else {
  2992  		delete(s.listeners, ln)
  2993  	}
  2994  	return true
  2995  }
  2996  
  2997  func (s *Server) trackConn(c *conn, add bool) {
  2998  	s.mu.Lock()
  2999  	defer s.mu.Unlock()
  3000  	if s.activeConn == nil {
  3001  		s.activeConn = make(map[*conn]struct{})
  3002  	}
  3003  	if add {
  3004  		s.activeConn[c] = struct{}{}
  3005  	} else {
  3006  		delete(s.activeConn, c)
  3007  	}
  3008  }
  3009  
  3010  func (s *Server) idleTimeout() time.Duration {
  3011  	if s.IdleTimeout != 0 {
  3012  		return s.IdleTimeout
  3013  	}
  3014  	return s.ReadTimeout
  3015  }
  3016  
  3017  func (s *Server) readHeaderTimeout() time.Duration {
  3018  	if s.ReadHeaderTimeout != 0 {
  3019  		return s.ReadHeaderTimeout
  3020  	}
  3021  	return s.ReadTimeout
  3022  }
  3023  
  3024  func (s *Server) doKeepAlives() bool {
  3025  	return atomic.LoadInt32(&s.disableKeepAlives) == 0 && !s.shuttingDown()
  3026  }
  3027  
  3028  func (s *Server) shuttingDown() bool {
  3029  	// TODO: replace inShutdown with the existing atomicBool type;
  3030  	// see https://github.com/golang/go/issues/20239#issuecomment-381434582
  3031  	return atomic.LoadInt32(&s.inShutdown) != 0
  3032  }
  3033  
  3034  // SetKeepAlivesEnabled controls whether HTTP keep-alives are enabled.
  3035  // By default, keep-alives are always enabled. Only very
  3036  // resource-constrained environments or servers in the process of
  3037  // shutting down should disable them.
  3038  func (srv *Server) SetKeepAlivesEnabled(v bool) {
  3039  	if v {
  3040  		atomic.StoreInt32(&srv.disableKeepAlives, 0)
  3041  		return
  3042  	}
  3043  	atomic.StoreInt32(&srv.disableKeepAlives, 1)
  3044  
  3045  	// Close idle HTTP/1 conns:
  3046  	srv.closeIdleConns()
  3047  
  3048  	// TODO: Issue 26303: close HTTP/2 conns as soon as they become idle.
  3049  }
  3050  
  3051  func (s *Server) logf(format string, args ...interface{}) {
  3052  	if s.ErrorLog != nil {
  3053  		s.ErrorLog.Printf(format, args...)
  3054  	} else {
  3055  		log.Printf(format, args...)
  3056  	}
  3057  }
  3058  
  3059  // logf prints to the ErrorLog of the *Server associated with request r
  3060  // via ServerContextKey. If there's no associated server, or if ErrorLog
  3061  // is nil, logging is done via the log package's standard logger.
  3062  func logf(r *Request, format string, args ...interface{}) {
  3063  	s, _ := r.Context().Value(ServerContextKey).(*Server)
  3064  	if s != nil && s.ErrorLog != nil {
  3065  		s.ErrorLog.Printf(format, args...)
  3066  	} else {
  3067  		log.Printf(format, args...)
  3068  	}
  3069  }
  3070  
  3071  // ListenAndServe listens on the TCP network address addr and then calls
  3072  // Serve with handler to handle requests on incoming connections.
  3073  // Accepted connections are configured to enable TCP keep-alives.
  3074  //
  3075  // The handler is typically nil, in which case the DefaultServeMux is used.
  3076  //
  3077  // ListenAndServe always returns a non-nil error.
  3078  func ListenAndServe(addr string, handler Handler) error {
  3079  	server := &Server{Addr: addr, Handler: handler}
  3080  	return server.ListenAndServe()
  3081  }
  3082  
  3083  // ListenAndServeTLS acts identically to ListenAndServe, except that it
  3084  // expects HTTPS connections. Additionally, files containing a certificate and
  3085  // matching private key for the server must be provided. If the certificate
  3086  // is signed by a certificate authority, the certFile should be the concatenation
  3087  // of the server's certificate, any intermediates, and the CA's certificate.
  3088  func ListenAndServeTLS(addr, certFile, keyFile string, handler Handler) error {
  3089  	server := &Server{Addr: addr, Handler: handler}
  3090  	return server.ListenAndServeTLS(certFile, keyFile)
  3091  }
  3092  
  3093  // ListenAndServeTLS listens on the TCP network address srv.Addr and
  3094  // then calls ServeTLS to handle requests on incoming TLS connections.
  3095  // Accepted connections are configured to enable TCP keep-alives.
  3096  //
  3097  // Filenames containing a certificate and matching private key for the
  3098  // server must be provided if neither the Server's TLSConfig.Certificates
  3099  // nor TLSConfig.GetCertificate are populated. If the certificate is
  3100  // signed by a certificate authority, the certFile should be the
  3101  // concatenation of the server's certificate, any intermediates, and
  3102  // the CA's certificate.
  3103  //
  3104  // If srv.Addr is blank, ":https" is used.
  3105  //
  3106  // ListenAndServeTLS always returns a non-nil error. After Shutdown or
  3107  // Close, the returned error is ErrServerClosed.
  3108  func (srv *Server) ListenAndServeTLS(certFile, keyFile string) error {
  3109  	if srv.shuttingDown() {
  3110  		return ErrServerClosed
  3111  	}
  3112  	addr := srv.Addr
  3113  	if addr == "" {
  3114  		addr = ":https"
  3115  	}
  3116  
  3117  	ln, err := net.Listen("tcp", addr)
  3118  	if err != nil {
  3119  		return err
  3120  	}
  3121  
  3122  	defer ln.Close()
  3123  
  3124  	return srv.ServeTLS(ln, certFile, keyFile)
  3125  }
  3126  
  3127  // setupHTTP2_ServeTLS conditionally configures HTTP/2 on
  3128  // srv and reports whether there was an error setting it up. If it is
  3129  // not configured for policy reasons, nil is returned.
  3130  func (srv *Server) setupHTTP2_ServeTLS() error {
  3131  	srv.nextProtoOnce.Do(srv.onceSetNextProtoDefaults)
  3132  	return srv.nextProtoErr
  3133  }
  3134  
  3135  // setupHTTP2_Serve is called from (*Server).Serve and conditionally
  3136  // configures HTTP/2 on srv using a more conservative policy than
  3137  // setupHTTP2_ServeTLS because Serve is called after tls.Listen,
  3138  // and may be called concurrently. See shouldConfigureHTTP2ForServe.
  3139  //
  3140  // The tests named TestTransportAutomaticHTTP2* and
  3141  // TestConcurrentServerServe in server_test.go demonstrate some
  3142  // of the supported use cases and motivations.
  3143  func (srv *Server) setupHTTP2_Serve() error {
  3144  	srv.nextProtoOnce.Do(srv.onceSetNextProtoDefaults_Serve)
  3145  	return srv.nextProtoErr
  3146  }
  3147  
  3148  func (srv *Server) onceSetNextProtoDefaults_Serve() {
  3149  	if srv.shouldConfigureHTTP2ForServe() {
  3150  		srv.onceSetNextProtoDefaults()
  3151  	}
  3152  }
  3153  
  3154  // onceSetNextProtoDefaults configures HTTP/2, if the user hasn't
  3155  // configured otherwise. (by setting srv.TLSNextProto non-nil)
  3156  // It must only be called via srv.nextProtoOnce (use srv.setupHTTP2_*).
  3157  func (srv *Server) onceSetNextProtoDefaults() {
  3158  	if strings.Contains(os.Getenv("GODEBUG"), "http2server=0") {
  3159  		return
  3160  	}
  3161  	// Enable HTTP/2 by default if the user hasn't otherwise
  3162  	// configured their TLSNextProto map.
  3163  	if srv.TLSNextProto == nil {
  3164  		conf := &http2Server{
  3165  			NewWriteScheduler: func() http2WriteScheduler { return http2NewPriorityWriteScheduler(nil) },
  3166  		}
  3167  		srv.nextProtoErr = http2ConfigureServer(srv, conf)
  3168  	}
  3169  }
  3170  
  3171  // TimeoutHandler returns a Handler that runs h with the given time limit.
  3172  //
  3173  // The new Handler calls h.ServeHTTP to handle each request, but if a
  3174  // call runs for longer than its time limit, the handler responds with
  3175  // a 503 Service Unavailable error and the given message in its body.
  3176  // (If msg is empty, a suitable default message will be sent.)
  3177  // After such a timeout, writes by h to its ResponseWriter will return
  3178  // ErrHandlerTimeout.
  3179  //
  3180  // TimeoutHandler supports the Flusher and Pusher interfaces but does not
  3181  // support the Hijacker interface.
  3182  func TimeoutHandler(h Handler, dt time.Duration, msg string) Handler {
  3183  	return &timeoutHandler{
  3184  		handler: h,
  3185  		body:    msg,
  3186  		dt:      dt,
  3187  	}
  3188  }
  3189  
  3190  // ErrHandlerTimeout is returned on ResponseWriter Write calls
  3191  // in handlers which have timed out.
  3192  var ErrHandlerTimeout = errors.New("http: Handler timeout")
  3193  
  3194  type timeoutHandler struct {
  3195  	handler Handler
  3196  	body    string
  3197  	dt      time.Duration
  3198  
  3199  	// When set, no context will be created and this context will
  3200  	// be used instead.
  3201  	testContext context.Context
  3202  }
  3203  
  3204  func (h *timeoutHandler) errorBody() string {
  3205  	if h.body != "" {
  3206  		return h.body
  3207  	}
  3208  	return "<html><head><title>Timeout</title></head><body><h1>Timeout</h1></body></html>"
  3209  }
  3210  
  3211  func (h *timeoutHandler) ServeHTTP(w ResponseWriter, r *Request) {
  3212  	ctx := h.testContext
  3213  	if ctx == nil {
  3214  		var cancelCtx context.CancelFunc
  3215  		ctx, cancelCtx = context.WithTimeout(r.Context(), h.dt)
  3216  		defer cancelCtx()
  3217  	}
  3218  	r = r.WithContext(ctx)
  3219  	done := make(chan struct{})
  3220  	tw := &timeoutWriter{
  3221  		w: w,
  3222  		h: make(Header),
  3223  	}
  3224  	panicChan := make(chan interface{}, 1)
  3225  	go func() {
  3226  		defer func() {
  3227  			if p := recover(); p != nil {
  3228  				panicChan <- p
  3229  			}
  3230  		}()
  3231  		h.handler.ServeHTTP(tw, r)
  3232  		close(done)
  3233  	}()
  3234  	select {
  3235  	case p := <-panicChan:
  3236  		panic(p)
  3237  	case <-done:
  3238  		tw.mu.Lock()
  3239  		defer tw.mu.Unlock()
  3240  		dst := w.Header()
  3241  		for k, vv := range tw.h {
  3242  			dst[k] = vv
  3243  		}
  3244  		if !tw.wroteHeader {
  3245  			tw.code = StatusOK
  3246  		}
  3247  		w.WriteHeader(tw.code)
  3248  		w.Write(tw.wbuf.Bytes())
  3249  	case <-ctx.Done():
  3250  		tw.mu.Lock()
  3251  		defer tw.mu.Unlock()
  3252  		w.WriteHeader(StatusServiceUnavailable)
  3253  		io.WriteString(w, h.errorBody())
  3254  		tw.timedOut = true
  3255  	}
  3256  }
  3257  
  3258  type timeoutWriter struct {
  3259  	w    ResponseWriter
  3260  	h    Header
  3261  	wbuf bytes.Buffer
  3262  
  3263  	mu          sync.Mutex
  3264  	timedOut    bool
  3265  	wroteHeader bool
  3266  	code        int
  3267  }
  3268  
  3269  var _ Pusher = (*timeoutWriter)(nil)
  3270  
  3271  // Push implements the Pusher interface.
  3272  func (tw *timeoutWriter) Push(target string, opts *PushOptions) error {
  3273  	if pusher, ok := tw.w.(Pusher); ok {
  3274  		return pusher.Push(target, opts)
  3275  	}
  3276  	return ErrNotSupported
  3277  }
  3278  
  3279  func (tw *timeoutWriter) Header() Header { return tw.h }
  3280  
  3281  func (tw *timeoutWriter) Write(p []byte) (int, error) {
  3282  	tw.mu.Lock()
  3283  	defer tw.mu.Unlock()
  3284  	if tw.timedOut {
  3285  		return 0, ErrHandlerTimeout
  3286  	}
  3287  	if !tw.wroteHeader {
  3288  		tw.writeHeader(StatusOK)
  3289  	}
  3290  	return tw.wbuf.Write(p)
  3291  }
  3292  
  3293  func (tw *timeoutWriter) WriteHeader(code int) {
  3294  	checkWriteHeaderCode(code)
  3295  	tw.mu.Lock()
  3296  	defer tw.mu.Unlock()
  3297  	if tw.timedOut || tw.wroteHeader {
  3298  		return
  3299  	}
  3300  	tw.writeHeader(code)
  3301  }
  3302  
  3303  func (tw *timeoutWriter) writeHeader(code int) {
  3304  	tw.wroteHeader = true
  3305  	tw.code = code
  3306  }
  3307  
  3308  // onceCloseListener wraps a net.Listener, protecting it from
  3309  // multiple Close calls.
  3310  type onceCloseListener struct {
  3311  	net.Listener
  3312  	once     sync.Once
  3313  	closeErr error
  3314  }
  3315  
  3316  func (oc *onceCloseListener) Close() error {
  3317  	oc.once.Do(oc.close)
  3318  	return oc.closeErr
  3319  }
  3320  
  3321  func (oc *onceCloseListener) close() { oc.closeErr = oc.Listener.Close() }
  3322  
  3323  // globalOptionsHandler responds to "OPTIONS *" requests.
  3324  type globalOptionsHandler struct{}
  3325  
  3326  func (globalOptionsHandler) ServeHTTP(w ResponseWriter, r *Request) {
  3327  	w.Header().Set("Content-Length", "0")
  3328  	if r.ContentLength != 0 {
  3329  		// Read up to 4KB of OPTIONS body (as mentioned in the
  3330  		// spec as being reserved for future use), but anything
  3331  		// over that is considered a waste of server resources
  3332  		// (or an attack) and we abort and close the connection,
  3333  		// courtesy of MaxBytesReader's EOF behavior.
  3334  		mb := MaxBytesReader(w, r.Body, 4<<10)
  3335  		io.Copy(ioutil.Discard, mb)
  3336  	}
  3337  }
  3338  
  3339  // initNPNRequest is an HTTP handler that initializes certain
  3340  // uninitialized fields in its *Request. Such partially-initialized
  3341  // Requests come from NPN protocol handlers.
  3342  type initNPNRequest struct {
  3343  	ctx context.Context
  3344  	c   *tls.Conn
  3345  	h   serverHandler
  3346  }
  3347  
  3348  // BaseContext is an exported but unadvertised http.Handler method
  3349  // recognized by x/net/http2 to pass down a context; the TLSNextProto
  3350  // API predates context support so we shoehorn through the only
  3351  // interface we have available.
  3352  func (h initNPNRequest) BaseContext() context.Context { return h.ctx }
  3353  
  3354  func (h initNPNRequest) ServeHTTP(rw ResponseWriter, req *Request) {
  3355  	if req.TLS == nil {
  3356  		req.TLS = &tls.ConnectionState{}
  3357  		*req.TLS = h.c.ConnectionState()
  3358  	}
  3359  	if req.Body == nil {
  3360  		req.Body = NoBody
  3361  	}
  3362  	if req.RemoteAddr == "" {
  3363  		req.RemoteAddr = h.c.RemoteAddr().String()
  3364  	}
  3365  	h.h.ServeHTTP(rw, req)
  3366  }
  3367  
  3368  // loggingConn is used for debugging.
  3369  type loggingConn struct {
  3370  	name string
  3371  	net.Conn
  3372  }
  3373  
  3374  var (
  3375  	uniqNameMu   sync.Mutex
  3376  	uniqNameNext = make(map[string]int)
  3377  )
  3378  
  3379  func newLoggingConn(baseName string, c net.Conn) net.Conn {
  3380  	uniqNameMu.Lock()
  3381  	defer uniqNameMu.Unlock()
  3382  	uniqNameNext[baseName]++
  3383  	return &loggingConn{
  3384  		name: fmt.Sprintf("%s-%d", baseName, uniqNameNext[baseName]),
  3385  		Conn: c,
  3386  	}
  3387  }
  3388  
  3389  func (c *loggingConn) Write(p []byte) (n int, err error) {
  3390  	log.Printf("%s.Write(%d) = ....", c.name, len(p))
  3391  	n, err = c.Conn.Write(p)
  3392  	log.Printf("%s.Write(%d) = %d, %v", c.name, len(p), n, err)
  3393  	return
  3394  }
  3395  
  3396  func (c *loggingConn) Read(p []byte) (n int, err error) {
  3397  	log.Printf("%s.Read(%d) = ....", c.name, len(p))
  3398  	n, err = c.Conn.Read(p)
  3399  	log.Printf("%s.Read(%d) = %d, %v", c.name, len(p), n, err)
  3400  	return
  3401  }
  3402  
  3403  func (c *loggingConn) Close() (err error) {
  3404  	log.Printf("%s.Close() = ...", c.name)
  3405  	err = c.Conn.Close()
  3406  	log.Printf("%s.Close() = %v", c.name, err)
  3407  	return
  3408  }
  3409  
  3410  // checkConnErrorWriter writes to c.rwc and records any write errors to c.werr.
  3411  // It only contains one field (and a pointer field at that), so it
  3412  // fits in an interface value without an extra allocation.
  3413  type checkConnErrorWriter struct {
  3414  	c *conn
  3415  }
  3416  
  3417  func (w checkConnErrorWriter) Write(p []byte) (n int, err error) {
  3418  	n, err = w.c.rwc.Write(p)
  3419  	if err != nil && w.c.werr == nil {
  3420  		w.c.werr = err
  3421  		w.c.cancelCtx()
  3422  	}
  3423  	return
  3424  }
  3425  
  3426  func numLeadingCRorLF(v []byte) (n int) {
  3427  	for _, b := range v {
  3428  		if b == '\r' || b == '\n' {
  3429  			n++
  3430  			continue
  3431  		}
  3432  		break
  3433  	}
  3434  	return
  3435  
  3436  }
  3437  
  3438  func strSliceContains(ss []string, s string) bool {
  3439  	for _, v := range ss {
  3440  		if v == s {
  3441  			return true
  3442  		}
  3443  	}
  3444  	return false
  3445  }
  3446  
  3447  // tlsRecordHeaderLooksLikeHTTP reports whether a TLS record header
  3448  // looks like it might've been a misdirected plaintext HTTP request.
  3449  func tlsRecordHeaderLooksLikeHTTP(hdr [5]byte) bool {
  3450  	switch string(hdr[:]) {
  3451  	case "GET /", "HEAD ", "POST ", "PUT /", "OPTIO":
  3452  		return true
  3453  	}
  3454  	return false
  3455  }
  3456  

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