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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 2616.
     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  	"strconv"
    26  	"strings"
    27  	"sync"
    28  	"sync/atomic"
    29  	"time"
    30  
    31  	"golang_org/x/net/lex/httplex"
    32  )
    33  
    34  // Errors used by the HTTP server.
    35  var (
    36  	// ErrBodyNotAllowed is returned by ResponseWriter.Write calls
    37  	// when the HTTP method or response code does not permit a
    38  	// body.
    39  	ErrBodyNotAllowed = errors.New("http: request method or response status code does not allow body")
    40  
    41  	// ErrHijacked is returned by ResponseWriter.Write calls when
    42  	// the underlying connection has been hijacked using the
    43  	// Hijacker interface. A zero-byte write on a hijacked
    44  	// connection will return ErrHijacked without any other side
    45  	// effects.
    46  	ErrHijacked = errors.New("http: connection has been hijacked")
    47  
    48  	// ErrContentLength is returned by ResponseWriter.Write calls
    49  	// when a Handler set a Content-Length response header with a
    50  	// declared size and then attempted to write more bytes than
    51  	// declared.
    52  	ErrContentLength = errors.New("http: wrote more than the declared Content-Length")
    53  
    54  	// Deprecated: ErrWriteAfterFlush is no longer used.
    55  	ErrWriteAfterFlush = errors.New("unused")
    56  )
    57  
    58  // A Handler responds to an HTTP request.
    59  //
    60  // ServeHTTP should write reply headers and data to the ResponseWriter
    61  // and then return. Returning signals that the request is finished; it
    62  // is not valid to use the ResponseWriter or read from the
    63  // Request.Body after or concurrently with the completion of the
    64  // ServeHTTP call.
    65  //
    66  // Depending on the HTTP client software, HTTP protocol version, and
    67  // any intermediaries between the client and the Go server, it may not
    68  // be possible to read from the Request.Body after writing to the
    69  // ResponseWriter. Cautious handlers should read the Request.Body
    70  // first, and then reply.
    71  //
    72  // Except for reading the body, handlers should not modify the
    73  // provided Request.
    74  //
    75  // If ServeHTTP panics, the server (the caller of ServeHTTP) assumes
    76  // that the effect of the panic was isolated to the active request.
    77  // It recovers the panic, logs a stack trace to the server error log,
    78  // and either closes the network connection or sends an HTTP/2
    79  // RST_STREAM, depending on the HTTP protocol. To abort a handler so
    80  // the client sees an interrupted response but the server doesn't log
    81  // an error, panic with the value ErrAbortHandler.
    82  type Handler interface {
    83  	ServeHTTP(ResponseWriter, *Request)
    84  }
    85  
    86  // A ResponseWriter interface is used by an HTTP handler to
    87  // construct an HTTP response.
    88  //
    89  // A ResponseWriter may not be used after the Handler.ServeHTTP method
    90  // has returned.
    91  type ResponseWriter interface {
    92  	// Header returns the header map that will be sent by
    93  	// WriteHeader. The Header map also is the mechanism with which
    94  	// Handlers can set HTTP trailers.
    95  	//
    96  	// Changing the header map after a call to WriteHeader (or
    97  	// Write) has no effect unless the modified headers are
    98  	// trailers.
    99  	//
   100  	// There are two ways to set Trailers. The preferred way is to
   101  	// predeclare in the headers which trailers you will later
   102  	// send by setting the "Trailer" header to the names of the
   103  	// trailer keys which will come later. In this case, those
   104  	// keys of the Header map are treated as if they were
   105  	// trailers. See the example. The second way, for trailer
   106  	// keys not known to the Handler until after the first Write,
   107  	// is to prefix the Header map keys with the TrailerPrefix
   108  	// constant value. See TrailerPrefix.
   109  	//
   110  	// To suppress implicit response headers (such as "Date"), set
   111  	// their value to nil.
   112  	Header() Header
   113  
   114  	// Write writes the data to the connection as part of an HTTP reply.
   115  	//
   116  	// If WriteHeader has not yet been called, Write calls
   117  	// WriteHeader(http.StatusOK) before writing the data. If the Header
   118  	// does not contain a Content-Type line, Write adds a Content-Type set
   119  	// to the result of passing the initial 512 bytes of written data to
   120  	// DetectContentType.
   121  	//
   122  	// Depending on the HTTP protocol version and the client, calling
   123  	// Write or WriteHeader may prevent future reads on the
   124  	// Request.Body. For HTTP/1.x requests, handlers should read any
   125  	// needed request body data before writing the response. Once the
   126  	// headers have been flushed (due to either an explicit Flusher.Flush
   127  	// call or writing enough data to trigger a flush), the request body
   128  	// may be unavailable. For HTTP/2 requests, the Go HTTP server permits
   129  	// handlers to continue to read the request body while concurrently
   130  	// writing the response. However, such behavior may not be supported
   131  	// by all HTTP/2 clients. Handlers should read before writing if
   132  	// possible to maximize compatibility.
   133  	Write([]byte) (int, error)
   134  
   135  	// WriteHeader sends an HTTP response header with the provided
   136  	// status code.
   137  	//
   138  	// If WriteHeader is not called explicitly, the first call to Write
   139  	// will trigger an implicit WriteHeader(http.StatusOK).
   140  	// Thus explicit calls to WriteHeader are mainly used to
   141  	// send error codes.
   142  	//
   143  	// The provided code must be a valid HTTP 1xx-5xx status code.
   144  	// Only one header may be written. Go does not currently
   145  	// support sending user-defined 1xx informational headers,
   146  	// with the exception of 100-continue response header that the
   147  	// Server sends automatically when the Request.Body is read.
   148  	WriteHeader(statusCode int)
   149  }
   150  
   151  // The Flusher interface is implemented by ResponseWriters that allow
   152  // an HTTP handler to flush buffered data to the client.
   153  //
   154  // The default HTTP/1.x and HTTP/2 ResponseWriter implementations
   155  // support Flusher, but ResponseWriter wrappers may not. Handlers
   156  // should always test for this ability at runtime.
   157  //
   158  // Note that even for ResponseWriters that support Flush,
   159  // if the client is connected through an HTTP proxy,
   160  // the buffered data may not reach the client until the response
   161  // completes.
   162  type Flusher interface {
   163  	// Flush sends any buffered data to the client.
   164  	Flush()
   165  }
   166  
   167  // The Hijacker interface is implemented by ResponseWriters that allow
   168  // an HTTP handler to take over the connection.
   169  //
   170  // The default ResponseWriter for HTTP/1.x connections supports
   171  // Hijacker, but HTTP/2 connections intentionally do not.
   172  // ResponseWriter wrappers may also not support Hijacker. Handlers
   173  // should always test for this ability at runtime.
   174  type Hijacker interface {
   175  	// Hijack lets the caller take over the connection.
   176  	// After a call to Hijack the HTTP server library
   177  	// will not do anything else with the connection.
   178  	//
   179  	// It becomes the caller's responsibility to manage
   180  	// and close the connection.
   181  	//
   182  	// The returned net.Conn may have read or write deadlines
   183  	// already set, depending on the configuration of the
   184  	// Server. It is the caller's responsibility to set
   185  	// or clear those deadlines as needed.
   186  	//
   187  	// The returned bufio.Reader may contain unprocessed buffered
   188  	// data from the client.
   189  	//
   190  	// After a call to Hijack, the original Request.Body must
   191  	// not be used.
   192  	Hijack() (net.Conn, *bufio.ReadWriter, error)
   193  }
   194  
   195  // The CloseNotifier interface is implemented by ResponseWriters which
   196  // allow detecting when the underlying connection has gone away.
   197  //
   198  // This mechanism can be used to cancel long operations on the server
   199  // if the client has disconnected before the response is ready.
   200  type CloseNotifier interface {
   201  	// CloseNotify returns a channel that receives at most a
   202  	// single value (true) when the client connection has gone
   203  	// away.
   204  	//
   205  	// CloseNotify may wait to notify until Request.Body has been
   206  	// fully read.
   207  	//
   208  	// After the Handler has returned, there is no guarantee
   209  	// that the channel receives a value.
   210  	//
   211  	// If the protocol is HTTP/1.1 and CloseNotify is called while
   212  	// processing an idempotent request (such a GET) while
   213  	// HTTP/1.1 pipelining is in use, the arrival of a subsequent
   214  	// pipelined request may cause a value to be sent on the
   215  	// returned channel. In practice HTTP/1.1 pipelining is not
   216  	// enabled in browsers and not seen often in the wild. If this
   217  	// is a problem, use HTTP/2 or only use CloseNotify on methods
   218  	// such as POST.
   219  	CloseNotify() <-chan bool
   220  }
   221  
   222  var (
   223  	// ServerContextKey is a context key. It can be used in HTTP
   224  	// handlers with context.WithValue to access the server that
   225  	// started the handler. The associated value will be of
   226  	// type *Server.
   227  	ServerContextKey = &contextKey{"http-server"}
   228  
   229  	// LocalAddrContextKey is a context key. It can be used in
   230  	// HTTP handlers with context.WithValue to access the address
   231  	// the local address the connection arrived on.
   232  	// The associated value will be of type net.Addr.
   233  	LocalAddrContextKey = &contextKey{"local-addr"}
   234  )
   235  
   236  // A conn represents the server side of an HTTP connection.
   237  type conn struct {
   238  	// server is the server on which the connection arrived.
   239  	// Immutable; never nil.
   240  	server *Server
   241  
   242  	// cancelCtx cancels the connection-level context.
   243  	cancelCtx context.CancelFunc
   244  
   245  	// rwc is the underlying network connection.
   246  	// This is never wrapped by other types and is the value given out
   247  	// to CloseNotifier callers. It is usually of type *net.TCPConn or
   248  	// *tls.Conn.
   249  	rwc net.Conn
   250  
   251  	// remoteAddr is rwc.RemoteAddr().String(). It is not populated synchronously
   252  	// inside the Listener's Accept goroutine, as some implementations block.
   253  	// It is populated immediately inside the (*conn).serve goroutine.
   254  	// This is the value of a Handler's (*Request).RemoteAddr.
   255  	remoteAddr string
   256  
   257  	// tlsState is the TLS connection state when using TLS.
   258  	// nil means not TLS.
   259  	tlsState *tls.ConnectionState
   260  
   261  	// werr is set to the first write error to rwc.
   262  	// It is set via checkConnErrorWriter{w}, where bufw writes.
   263  	werr error
   264  
   265  	// r is bufr's read source. It's a wrapper around rwc that provides
   266  	// io.LimitedReader-style limiting (while reading request headers)
   267  	// and functionality to support CloseNotifier. See *connReader docs.
   268  	r *connReader
   269  
   270  	// bufr reads from r.
   271  	bufr *bufio.Reader
   272  
   273  	// bufw writes to checkConnErrorWriter{c}, which populates werr on error.
   274  	bufw *bufio.Writer
   275  
   276  	// lastMethod is the method of the most recent request
   277  	// on this connection, if any.
   278  	lastMethod string
   279  
   280  	curReq atomic.Value // of *response (which has a Request in it)
   281  
   282  	curState atomic.Value // of ConnState
   283  
   284  	// mu guards hijackedv
   285  	mu sync.Mutex
   286  
   287  	// hijackedv is whether this connection has been hijacked
   288  	// by a Handler with the Hijacker interface.
   289  	// It is guarded by mu.
   290  	hijackedv bool
   291  }
   292  
   293  func (c *conn) hijacked() bool {
   294  	c.mu.Lock()
   295  	defer c.mu.Unlock()
   296  	return c.hijackedv
   297  }
   298  
   299  // c.mu must be held.
   300  func (c *conn) hijackLocked() (rwc net.Conn, buf *bufio.ReadWriter, err error) {
   301  	if c.hijackedv {
   302  		return nil, nil, ErrHijacked
   303  	}
   304  	c.r.abortPendingRead()
   305  
   306  	c.hijackedv = true
   307  	rwc = c.rwc
   308  	rwc.SetDeadline(time.Time{})
   309  
   310  	buf = bufio.NewReadWriter(c.bufr, bufio.NewWriter(rwc))
   311  	if c.r.hasByte {
   312  		if _, err := c.bufr.Peek(c.bufr.Buffered() + 1); err != nil {
   313  			return nil, nil, fmt.Errorf("unexpected Peek failure reading buffered byte: %v", err)
   314  		}
   315  	}
   316  	c.setState(rwc, StateHijacked)
   317  	return
   318  }
   319  
   320  // This should be >= 512 bytes for DetectContentType,
   321  // but otherwise it's somewhat arbitrary.
   322  const bufferBeforeChunkingSize = 2048
   323  
   324  // chunkWriter writes to a response's conn buffer, and is the writer
   325  // wrapped by the response.bufw buffered writer.
   326  //
   327  // chunkWriter also is responsible for finalizing the Header, including
   328  // conditionally setting the Content-Type and setting a Content-Length
   329  // in cases where the handler's final output is smaller than the buffer
   330  // size. It also conditionally adds chunk headers, when in chunking mode.
   331  //
   332  // See the comment above (*response).Write for the entire write flow.
   333  type chunkWriter struct {
   334  	res *response
   335  
   336  	// header is either nil or a deep clone of res.handlerHeader
   337  	// at the time of res.WriteHeader, if res.WriteHeader is
   338  	// called and extra buffering is being done to calculate
   339  	// Content-Type and/or Content-Length.
   340  	header Header
   341  
   342  	// wroteHeader tells whether the header's been written to "the
   343  	// wire" (or rather: w.conn.buf). this is unlike
   344  	// (*response).wroteHeader, which tells only whether it was
   345  	// logically written.
   346  	wroteHeader bool
   347  
   348  	// set by the writeHeader method:
   349  	chunking bool // using chunked transfer encoding for reply body
   350  }
   351  
   352  var (
   353  	crlf       = []byte("\r\n")
   354  	colonSpace = []byte(": ")
   355  )
   356  
   357  func (cw *chunkWriter) Write(p []byte) (n int, err error) {
   358  	if !cw.wroteHeader {
   359  		cw.writeHeader(p)
   360  	}
   361  	if cw.res.req.Method == "HEAD" {
   362  		// Eat writes.
   363  		return len(p), nil
   364  	}
   365  	if cw.chunking {
   366  		_, err = fmt.Fprintf(cw.res.conn.bufw, "%x\r\n", len(p))
   367  		if err != nil {
   368  			cw.res.conn.rwc.Close()
   369  			return
   370  		}
   371  	}
   372  	n, err = cw.res.conn.bufw.Write(p)
   373  	if cw.chunking && err == nil {
   374  		_, err = cw.res.conn.bufw.Write(crlf)
   375  	}
   376  	if err != nil {
   377  		cw.res.conn.rwc.Close()
   378  	}
   379  	return
   380  }
   381  
   382  func (cw *chunkWriter) flush() {
   383  	if !cw.wroteHeader {
   384  		cw.writeHeader(nil)
   385  	}
   386  	cw.res.conn.bufw.Flush()
   387  }
   388  
   389  func (cw *chunkWriter) close() {
   390  	if !cw.wroteHeader {
   391  		cw.writeHeader(nil)
   392  	}
   393  	if cw.chunking {
   394  		bw := cw.res.conn.bufw // conn's bufio writer
   395  		// zero chunk to mark EOF
   396  		bw.WriteString("0\r\n")
   397  		if trailers := cw.res.finalTrailers(); trailers != nil {
   398  			trailers.Write(bw) // the writer handles noting errors
   399  		}
   400  		// final blank line after the trailers (whether
   401  		// present or not)
   402  		bw.WriteString("\r\n")
   403  	}
   404  }
   405  
   406  // A response represents the server side of an HTTP response.
   407  type response struct {
   408  	conn             *conn
   409  	req              *Request // request for this response
   410  	reqBody          io.ReadCloser
   411  	cancelCtx        context.CancelFunc // when ServeHTTP exits
   412  	wroteHeader      bool               // reply header has been (logically) written
   413  	wroteContinue    bool               // 100 Continue response was written
   414  	wants10KeepAlive bool               // HTTP/1.0 w/ Connection "keep-alive"
   415  	wantsClose       bool               // HTTP request has Connection "close"
   416  
   417  	w  *bufio.Writer // buffers output in chunks to chunkWriter
   418  	cw chunkWriter
   419  
   420  	// handlerHeader is the Header that Handlers get access to,
   421  	// which may be retained and mutated even after WriteHeader.
   422  	// handlerHeader is copied into cw.header at WriteHeader
   423  	// time, and privately mutated thereafter.
   424  	handlerHeader Header
   425  	calledHeader  bool // handler accessed handlerHeader via Header
   426  
   427  	written       int64 // number of bytes written in body
   428  	contentLength int64 // explicitly-declared Content-Length; or -1
   429  	status        int   // status code passed to WriteHeader
   430  
   431  	// close connection after this reply.  set on request and
   432  	// updated after response from handler if there's a
   433  	// "Connection: keep-alive" response header and a
   434  	// Content-Length.
   435  	closeAfterReply bool
   436  
   437  	// requestBodyLimitHit is set by requestTooLarge when
   438  	// maxBytesReader hits its max size. It is checked in
   439  	// WriteHeader, to make sure we don't consume the
   440  	// remaining request body to try to advance to the next HTTP
   441  	// request. Instead, when this is set, we stop reading
   442  	// subsequent requests on this connection and stop reading
   443  	// input from it.
   444  	requestBodyLimitHit bool
   445  
   446  	// trailers are the headers to be sent after the handler
   447  	// finishes writing the body. This field is initialized from
   448  	// the Trailer response header when the response header is
   449  	// written.
   450  	trailers []string
   451  
   452  	handlerDone atomicBool // set true when the handler exits
   453  
   454  	// Buffers for Date, Content-Length, and status code
   455  	dateBuf   [len(TimeFormat)]byte
   456  	clenBuf   [10]byte
   457  	statusBuf [3]byte
   458  
   459  	// closeNotifyCh is the channel returned by CloseNotify.
   460  	// TODO(bradfitz): this is currently (for Go 1.8) always
   461  	// non-nil. Make this lazily-created again as it used to be?
   462  	closeNotifyCh  chan bool
   463  	didCloseNotify int32 // atomic (only 0->1 winner should send)
   464  }
   465  
   466  // TrailerPrefix is a magic prefix for ResponseWriter.Header map keys
   467  // that, if present, signals that the map entry is actually for
   468  // the response trailers, and not the response headers. The prefix
   469  // is stripped after the ServeHTTP call finishes and the values are
   470  // sent in the trailers.
   471  //
   472  // This mechanism is intended only for trailers that are not known
   473  // prior to the headers being written. If the set of trailers is fixed
   474  // or known before the header is written, the normal Go trailers mechanism
   475  // is preferred:
   476  //    https://golang.org/pkg/net/http/#ResponseWriter
   477  //    https://golang.org/pkg/net/http/#example_ResponseWriter_trailers
   478  const TrailerPrefix = "Trailer:"
   479  
   480  // finalTrailers is called after the Handler exits and returns a non-nil
   481  // value if the Handler set any trailers.
   482  func (w *response) finalTrailers() Header {
   483  	var t Header
   484  	for k, vv := range w.handlerHeader {
   485  		if strings.HasPrefix(k, TrailerPrefix) {
   486  			if t == nil {
   487  				t = make(Header)
   488  			}
   489  			t[strings.TrimPrefix(k, TrailerPrefix)] = vv
   490  		}
   491  	}
   492  	for _, k := range w.trailers {
   493  		if t == nil {
   494  			t = make(Header)
   495  		}
   496  		for _, v := range w.handlerHeader[k] {
   497  			t.Add(k, v)
   498  		}
   499  	}
   500  	return t
   501  }
   502  
   503  type atomicBool int32
   504  
   505  func (b *atomicBool) isSet() bool { return atomic.LoadInt32((*int32)(b)) != 0 }
   506  func (b *atomicBool) setTrue()    { atomic.StoreInt32((*int32)(b), 1) }
   507  
   508  // declareTrailer is called for each Trailer header when the
   509  // response header is written. It notes that a header will need to be
   510  // written in the trailers at the end of the response.
   511  func (w *response) declareTrailer(k string) {
   512  	k = CanonicalHeaderKey(k)
   513  	switch k {
   514  	case "Transfer-Encoding", "Content-Length", "Trailer":
   515  		// Forbidden by RFC 2616 14.40.
   516  		return
   517  	}
   518  	w.trailers = append(w.trailers, k)
   519  }
   520  
   521  // requestTooLarge is called by maxBytesReader when too much input has
   522  // been read from the client.
   523  func (w *response) requestTooLarge() {
   524  	w.closeAfterReply = true
   525  	w.requestBodyLimitHit = true
   526  	if !w.wroteHeader {
   527  		w.Header().Set("Connection", "close")
   528  	}
   529  }
   530  
   531  // needsSniff reports whether a Content-Type still needs to be sniffed.
   532  func (w *response) needsSniff() bool {
   533  	_, haveType := w.handlerHeader["Content-Type"]
   534  	return !w.cw.wroteHeader && !haveType && w.written < sniffLen
   535  }
   536  
   537  // writerOnly hides an io.Writer value's optional ReadFrom method
   538  // from io.Copy.
   539  type writerOnly struct {
   540  	io.Writer
   541  }
   542  
   543  func srcIsRegularFile(src io.Reader) (isRegular bool, err error) {
   544  	switch v := src.(type) {
   545  	case *os.File:
   546  		fi, err := v.Stat()
   547  		if err != nil {
   548  			return false, err
   549  		}
   550  		return fi.Mode().IsRegular(), nil
   551  	case *io.LimitedReader:
   552  		return srcIsRegularFile(v.R)
   553  	default:
   554  		return
   555  	}
   556  }
   557  
   558  // ReadFrom is here to optimize copying from an *os.File regular file
   559  // to a *net.TCPConn with sendfile.
   560  func (w *response) ReadFrom(src io.Reader) (n int64, err error) {
   561  	// Our underlying w.conn.rwc is usually a *TCPConn (with its
   562  	// own ReadFrom method). If not, or if our src isn't a regular
   563  	// file, just fall back to the normal copy method.
   564  	rf, ok := w.conn.rwc.(io.ReaderFrom)
   565  	regFile, err := srcIsRegularFile(src)
   566  	if err != nil {
   567  		return 0, err
   568  	}
   569  	if !ok || !regFile {
   570  		bufp := copyBufPool.Get().(*[]byte)
   571  		defer copyBufPool.Put(bufp)
   572  		return io.CopyBuffer(writerOnly{w}, src, *bufp)
   573  	}
   574  
   575  	// sendfile path:
   576  
   577  	if !w.wroteHeader {
   578  		w.WriteHeader(StatusOK)
   579  	}
   580  
   581  	if w.needsSniff() {
   582  		n0, err := io.Copy(writerOnly{w}, io.LimitReader(src, sniffLen))
   583  		n += n0
   584  		if err != nil {
   585  			return n, err
   586  		}
   587  	}
   588  
   589  	w.w.Flush()  // get rid of any previous writes
   590  	w.cw.flush() // make sure Header is written; flush data to rwc
   591  
   592  	// Now that cw has been flushed, its chunking field is guaranteed initialized.
   593  	if !w.cw.chunking && w.bodyAllowed() {
   594  		n0, err := rf.ReadFrom(src)
   595  		n += n0
   596  		w.written += n0
   597  		return n, err
   598  	}
   599  
   600  	n0, err := io.Copy(writerOnly{w}, src)
   601  	n += n0
   602  	return n, err
   603  }
   604  
   605  // debugServerConnections controls whether all server connections are wrapped
   606  // with a verbose logging wrapper.
   607  const debugServerConnections = false
   608  
   609  // Create new connection from rwc.
   610  func (srv *Server) newConn(rwc net.Conn) *conn {
   611  	c := &conn{
   612  		server: srv,
   613  		rwc:    rwc,
   614  	}
   615  	if debugServerConnections {
   616  		c.rwc = newLoggingConn("server", c.rwc)
   617  	}
   618  	return c
   619  }
   620  
   621  type readResult struct {
   622  	n   int
   623  	err error
   624  	b   byte // byte read, if n == 1
   625  }
   626  
   627  // connReader is the io.Reader wrapper used by *conn. It combines a
   628  // selectively-activated io.LimitedReader (to bound request header
   629  // read sizes) with support for selectively keeping an io.Reader.Read
   630  // call blocked in a background goroutine to wait for activity and
   631  // trigger a CloseNotifier channel.
   632  type connReader struct {
   633  	conn *conn
   634  
   635  	mu      sync.Mutex // guards following
   636  	hasByte bool
   637  	byteBuf [1]byte
   638  	cond    *sync.Cond
   639  	inRead  bool
   640  	aborted bool  // set true before conn.rwc deadline is set to past
   641  	remain  int64 // bytes remaining
   642  }
   643  
   644  func (cr *connReader) lock() {
   645  	cr.mu.Lock()
   646  	if cr.cond == nil {
   647  		cr.cond = sync.NewCond(&cr.mu)
   648  	}
   649  }
   650  
   651  func (cr *connReader) unlock() { cr.mu.Unlock() }
   652  
   653  func (cr *connReader) startBackgroundRead() {
   654  	cr.lock()
   655  	defer cr.unlock()
   656  	if cr.inRead {
   657  		panic("invalid concurrent Body.Read call")
   658  	}
   659  	if cr.hasByte {
   660  		return
   661  	}
   662  	cr.inRead = true
   663  	cr.conn.rwc.SetReadDeadline(time.Time{})
   664  	go cr.backgroundRead()
   665  }
   666  
   667  func (cr *connReader) backgroundRead() {
   668  	n, err := cr.conn.rwc.Read(cr.byteBuf[:])
   669  	cr.lock()
   670  	if n == 1 {
   671  		cr.hasByte = true
   672  		// We were at EOF already (since we wouldn't be in a
   673  		// background read otherwise), so this is a pipelined
   674  		// HTTP request.
   675  		cr.closeNotifyFromPipelinedRequest()
   676  	}
   677  	if ne, ok := err.(net.Error); ok && cr.aborted && ne.Timeout() {
   678  		// Ignore this error. It's the expected error from
   679  		// another goroutine calling abortPendingRead.
   680  	} else if err != nil {
   681  		cr.handleReadError(err)
   682  	}
   683  	cr.aborted = false
   684  	cr.inRead = false
   685  	cr.unlock()
   686  	cr.cond.Broadcast()
   687  }
   688  
   689  func (cr *connReader) abortPendingRead() {
   690  	cr.lock()
   691  	defer cr.unlock()
   692  	if !cr.inRead {
   693  		return
   694  	}
   695  	cr.aborted = true
   696  	cr.conn.rwc.SetReadDeadline(aLongTimeAgo)
   697  	for cr.inRead {
   698  		cr.cond.Wait()
   699  	}
   700  	cr.conn.rwc.SetReadDeadline(time.Time{})
   701  }
   702  
   703  func (cr *connReader) setReadLimit(remain int64) { cr.remain = remain }
   704  func (cr *connReader) setInfiniteReadLimit()     { cr.remain = maxInt64 }
   705  func (cr *connReader) hitReadLimit() bool        { return cr.remain <= 0 }
   706  
   707  // may be called from multiple goroutines.
   708  func (cr *connReader) handleReadError(err error) {
   709  	cr.conn.cancelCtx()
   710  	cr.closeNotify()
   711  }
   712  
   713  // closeNotifyFromPipelinedRequest simply calls closeNotify.
   714  //
   715  // This method wrapper is here for documentation. The callers are the
   716  // cases where we send on the closenotify channel because of a
   717  // pipelined HTTP request, per the previous Go behavior and
   718  // documentation (that this "MAY" happen).
   719  //
   720  // TODO: consider changing this behavior and making context
   721  // cancelation and closenotify work the same.
   722  func (cr *connReader) closeNotifyFromPipelinedRequest() {
   723  	cr.closeNotify()
   724  }
   725  
   726  // may be called from multiple goroutines.
   727  func (cr *connReader) closeNotify() {
   728  	res, _ := cr.conn.curReq.Load().(*response)
   729  	if res != nil {
   730  		if atomic.CompareAndSwapInt32(&res.didCloseNotify, 0, 1) {
   731  			res.closeNotifyCh <- true
   732  		}
   733  	}
   734  }
   735  
   736  func (cr *connReader) Read(p []byte) (n int, err error) {
   737  	cr.lock()
   738  	if cr.inRead {
   739  		cr.unlock()
   740  		if cr.conn.hijacked() {
   741  			panic("invalid Body.Read call. After hijacked, the original Request must not be used")
   742  		}
   743  		panic("invalid concurrent Body.Read call")
   744  	}
   745  	if cr.hitReadLimit() {
   746  		cr.unlock()
   747  		return 0, io.EOF
   748  	}
   749  	if len(p) == 0 {
   750  		cr.unlock()
   751  		return 0, nil
   752  	}
   753  	if int64(len(p)) > cr.remain {
   754  		p = p[:cr.remain]
   755  	}
   756  	if cr.hasByte {
   757  		p[0] = cr.byteBuf[0]
   758  		cr.hasByte = false
   759  		cr.unlock()
   760  		return 1, nil
   761  	}
   762  	cr.inRead = true
   763  	cr.unlock()
   764  	n, err = cr.conn.rwc.Read(p)
   765  
   766  	cr.lock()
   767  	cr.inRead = false
   768  	if err != nil {
   769  		cr.handleReadError(err)
   770  	}
   771  	cr.remain -= int64(n)
   772  	cr.unlock()
   773  
   774  	cr.cond.Broadcast()
   775  	return n, err
   776  }
   777  
   778  var (
   779  	bufioReaderPool   sync.Pool
   780  	bufioWriter2kPool sync.Pool
   781  	bufioWriter4kPool sync.Pool
   782  )
   783  
   784  var copyBufPool = sync.Pool{
   785  	New: func() interface{} {
   786  		b := make([]byte, 32*1024)
   787  		return &b
   788  	},
   789  }
   790  
   791  func bufioWriterPool(size int) *sync.Pool {
   792  	switch size {
   793  	case 2 << 10:
   794  		return &bufioWriter2kPool
   795  	case 4 << 10:
   796  		return &bufioWriter4kPool
   797  	}
   798  	return nil
   799  }
   800  
   801  func newBufioReader(r io.Reader) *bufio.Reader {
   802  	if v := bufioReaderPool.Get(); v != nil {
   803  		br := v.(*bufio.Reader)
   804  		br.Reset(r)
   805  		return br
   806  	}
   807  	// Note: if this reader size is ever changed, update
   808  	// TestHandlerBodyClose's assumptions.
   809  	return bufio.NewReader(r)
   810  }
   811  
   812  func putBufioReader(br *bufio.Reader) {
   813  	br.Reset(nil)
   814  	bufioReaderPool.Put(br)
   815  }
   816  
   817  func newBufioWriterSize(w io.Writer, size int) *bufio.Writer {
   818  	pool := bufioWriterPool(size)
   819  	if pool != nil {
   820  		if v := pool.Get(); v != nil {
   821  			bw := v.(*bufio.Writer)
   822  			bw.Reset(w)
   823  			return bw
   824  		}
   825  	}
   826  	return bufio.NewWriterSize(w, size)
   827  }
   828  
   829  func putBufioWriter(bw *bufio.Writer) {
   830  	bw.Reset(nil)
   831  	if pool := bufioWriterPool(bw.Available()); pool != nil {
   832  		pool.Put(bw)
   833  	}
   834  }
   835  
   836  // DefaultMaxHeaderBytes is the maximum permitted size of the headers
   837  // in an HTTP request.
   838  // This can be overridden by setting Server.MaxHeaderBytes.
   839  const DefaultMaxHeaderBytes = 1 << 20 // 1 MB
   840  
   841  func (srv *Server) maxHeaderBytes() int {
   842  	if srv.MaxHeaderBytes > 0 {
   843  		return srv.MaxHeaderBytes
   844  	}
   845  	return DefaultMaxHeaderBytes
   846  }
   847  
   848  func (srv *Server) initialReadLimitSize() int64 {
   849  	return int64(srv.maxHeaderBytes()) + 4096 // bufio slop
   850  }
   851  
   852  // wrapper around io.ReadCloser which on first read, sends an
   853  // HTTP/1.1 100 Continue header
   854  type expectContinueReader struct {
   855  	resp       *response
   856  	readCloser io.ReadCloser
   857  	closed     bool
   858  	sawEOF     bool
   859  }
   860  
   861  func (ecr *expectContinueReader) Read(p []byte) (n int, err error) {
   862  	if ecr.closed {
   863  		return 0, ErrBodyReadAfterClose
   864  	}
   865  	if !ecr.resp.wroteContinue && !ecr.resp.conn.hijacked() {
   866  		ecr.resp.wroteContinue = true
   867  		ecr.resp.conn.bufw.WriteString("HTTP/1.1 100 Continue\r\n\r\n")
   868  		ecr.resp.conn.bufw.Flush()
   869  	}
   870  	n, err = ecr.readCloser.Read(p)
   871  	if err == io.EOF {
   872  		ecr.sawEOF = true
   873  	}
   874  	return
   875  }
   876  
   877  func (ecr *expectContinueReader) Close() error {
   878  	ecr.closed = true
   879  	return ecr.readCloser.Close()
   880  }
   881  
   882  // TimeFormat is the time format to use when generating times in HTTP
   883  // headers. It is like time.RFC1123 but hard-codes GMT as the time
   884  // zone. The time being formatted must be in UTC for Format to
   885  // generate the correct format.
   886  //
   887  // For parsing this time format, see ParseTime.
   888  const TimeFormat = "Mon, 02 Jan 2006 15:04:05 GMT"
   889  
   890  // appendTime is a non-allocating version of []byte(t.UTC().Format(TimeFormat))
   891  func appendTime(b []byte, t time.Time) []byte {
   892  	const days = "SunMonTueWedThuFriSat"
   893  	const months = "JanFebMarAprMayJunJulAugSepOctNovDec"
   894  
   895  	t = t.UTC()
   896  	yy, mm, dd := t.Date()
   897  	hh, mn, ss := t.Clock()
   898  	day := days[3*t.Weekday():]
   899  	mon := months[3*(mm-1):]
   900  
   901  	return append(b,
   902  		day[0], day[1], day[2], ',', ' ',
   903  		byte('0'+dd/10), byte('0'+dd%10), ' ',
   904  		mon[0], mon[1], mon[2], ' ',
   905  		byte('0'+yy/1000), byte('0'+(yy/100)%10), byte('0'+(yy/10)%10), byte('0'+yy%10), ' ',
   906  		byte('0'+hh/10), byte('0'+hh%10), ':',
   907  		byte('0'+mn/10), byte('0'+mn%10), ':',
   908  		byte('0'+ss/10), byte('0'+ss%10), ' ',
   909  		'G', 'M', 'T')
   910  }
   911  
   912  var errTooLarge = errors.New("http: request too large")
   913  
   914  // Read next request from connection.
   915  func (c *conn) readRequest(ctx context.Context) (w *response, err error) {
   916  	if c.hijacked() {
   917  		return nil, ErrHijacked
   918  	}
   919  
   920  	var (
   921  		wholeReqDeadline time.Time // or zero if none
   922  		hdrDeadline      time.Time // or zero if none
   923  	)
   924  	t0 := time.Now()
   925  	if d := c.server.readHeaderTimeout(); d != 0 {
   926  		hdrDeadline = t0.Add(d)
   927  	}
   928  	if d := c.server.ReadTimeout; d != 0 {
   929  		wholeReqDeadline = t0.Add(d)
   930  	}
   931  	c.rwc.SetReadDeadline(hdrDeadline)
   932  	if d := c.server.WriteTimeout; d != 0 {
   933  		defer func() {
   934  			c.rwc.SetWriteDeadline(time.Now().Add(d))
   935  		}()
   936  	}
   937  
   938  	c.r.setReadLimit(c.server.initialReadLimitSize())
   939  	if c.lastMethod == "POST" {
   940  		// RFC 2616 section 4.1 tolerance for old buggy clients.
   941  		peek, _ := c.bufr.Peek(4) // ReadRequest will get err below
   942  		c.bufr.Discard(numLeadingCRorLF(peek))
   943  	}
   944  	req, err := readRequest(c.bufr, keepHostHeader)
   945  	if err != nil {
   946  		if c.r.hitReadLimit() {
   947  			return nil, errTooLarge
   948  		}
   949  		return nil, err
   950  	}
   951  
   952  	if !http1ServerSupportsRequest(req) {
   953  		return nil, badRequestError("unsupported protocol version")
   954  	}
   955  
   956  	c.lastMethod = req.Method
   957  	c.r.setInfiniteReadLimit()
   958  
   959  	hosts, haveHost := req.Header["Host"]
   960  	isH2Upgrade := req.isH2Upgrade()
   961  	if req.ProtoAtLeast(1, 1) && (!haveHost || len(hosts) == 0) && !isH2Upgrade && req.Method != "CONNECT" {
   962  		return nil, badRequestError("missing required Host header")
   963  	}
   964  	if len(hosts) > 1 {
   965  		return nil, badRequestError("too many Host headers")
   966  	}
   967  	if len(hosts) == 1 && !httplex.ValidHostHeader(hosts[0]) {
   968  		return nil, badRequestError("malformed Host header")
   969  	}
   970  	for k, vv := range req.Header {
   971  		if !httplex.ValidHeaderFieldName(k) {
   972  			return nil, badRequestError("invalid header name")
   973  		}
   974  		for _, v := range vv {
   975  			if !httplex.ValidHeaderFieldValue(v) {
   976  				return nil, badRequestError("invalid header value")
   977  			}
   978  		}
   979  	}
   980  	delete(req.Header, "Host")
   981  
   982  	ctx, cancelCtx := context.WithCancel(ctx)
   983  	req.ctx = ctx
   984  	req.RemoteAddr = c.remoteAddr
   985  	req.TLS = c.tlsState
   986  	if body, ok := req.Body.(*body); ok {
   987  		body.doEarlyClose = true
   988  	}
   989  
   990  	// Adjust the read deadline if necessary.
   991  	if !hdrDeadline.Equal(wholeReqDeadline) {
   992  		c.rwc.SetReadDeadline(wholeReqDeadline)
   993  	}
   994  
   995  	w = &response{
   996  		conn:          c,
   997  		cancelCtx:     cancelCtx,
   998  		req:           req,
   999  		reqBody:       req.Body,
  1000  		handlerHeader: make(Header),
  1001  		contentLength: -1,
  1002  		closeNotifyCh: make(chan bool, 1),
  1003  
  1004  		// We populate these ahead of time so we're not
  1005  		// reading from req.Header after their Handler starts
  1006  		// and maybe mutates it (Issue 14940)
  1007  		wants10KeepAlive: req.wantsHttp10KeepAlive(),
  1008  		wantsClose:       req.wantsClose(),
  1009  	}
  1010  	if isH2Upgrade {
  1011  		w.closeAfterReply = true
  1012  	}
  1013  	w.cw.res = w
  1014  	w.w = newBufioWriterSize(&w.cw, bufferBeforeChunkingSize)
  1015  	return w, nil
  1016  }
  1017  
  1018  // http1ServerSupportsRequest reports whether Go's HTTP/1.x server
  1019  // supports the given request.
  1020  func http1ServerSupportsRequest(req *Request) bool {
  1021  	if req.ProtoMajor == 1 {
  1022  		return true
  1023  	}
  1024  	// Accept "PRI * HTTP/2.0" upgrade requests, so Handlers can
  1025  	// wire up their own HTTP/2 upgrades.
  1026  	if req.ProtoMajor == 2 && req.ProtoMinor == 0 &&
  1027  		req.Method == "PRI" && req.RequestURI == "*" {
  1028  		return true
  1029  	}
  1030  	// Reject HTTP/0.x, and all other HTTP/2+ requests (which
  1031  	// aren't encoded in ASCII anyway).
  1032  	return false
  1033  }
  1034  
  1035  func (w *response) Header() Header {
  1036  	if w.cw.header == nil && w.wroteHeader && !w.cw.wroteHeader {
  1037  		// Accessing the header between logically writing it
  1038  		// and physically writing it means we need to allocate
  1039  		// a clone to snapshot the logically written state.
  1040  		w.cw.header = w.handlerHeader.clone()
  1041  	}
  1042  	w.calledHeader = true
  1043  	return w.handlerHeader
  1044  }
  1045  
  1046  // maxPostHandlerReadBytes is the max number of Request.Body bytes not
  1047  // consumed by a handler that the server will read from the client
  1048  // in order to keep a connection alive. If there are more bytes than
  1049  // this then the server to be paranoid instead sends a "Connection:
  1050  // close" response.
  1051  //
  1052  // This number is approximately what a typical machine's TCP buffer
  1053  // size is anyway.  (if we have the bytes on the machine, we might as
  1054  // well read them)
  1055  const maxPostHandlerReadBytes = 256 << 10
  1056  
  1057  func checkWriteHeaderCode(code int) {
  1058  	// Issue 22880: require valid WriteHeader status codes.
  1059  	// For now we only enforce that it's three digits.
  1060  	// In the future we might block things over 599 (600 and above aren't defined
  1061  	// at http://httpwg.org/specs/rfc7231.html#status.codes)
  1062  	// and we might block under 200 (once we have more mature 1xx support).
  1063  	// But for now any three digits.
  1064  	//
  1065  	// We used to send "HTTP/1.1 000 0" on the wire in responses but there's
  1066  	// no equivalent bogus thing we can realistically send in HTTP/2,
  1067  	// so we'll consistently panic instead and help people find their bugs
  1068  	// early. (We can't return an error from WriteHeader even if we wanted to.)
  1069  	if code < 100 || code > 999 {
  1070  		panic(fmt.Sprintf("invalid WriteHeader code %v", code))
  1071  	}
  1072  }
  1073  
  1074  func (w *response) WriteHeader(code int) {
  1075  	if w.conn.hijacked() {
  1076  		w.conn.server.logf("http: response.WriteHeader on hijacked connection")
  1077  		return
  1078  	}
  1079  	if w.wroteHeader {
  1080  		w.conn.server.logf("http: multiple response.WriteHeader calls")
  1081  		return
  1082  	}
  1083  	checkWriteHeaderCode(code)
  1084  	w.wroteHeader = true
  1085  	w.status = code
  1086  
  1087  	if w.calledHeader && w.cw.header == nil {
  1088  		w.cw.header = w.handlerHeader.clone()
  1089  	}
  1090  
  1091  	if cl := w.handlerHeader.get("Content-Length"); cl != "" {
  1092  		v, err := strconv.ParseInt(cl, 10, 64)
  1093  		if err == nil && v >= 0 {
  1094  			w.contentLength = v
  1095  		} else {
  1096  			w.conn.server.logf("http: invalid Content-Length of %q", cl)
  1097  			w.handlerHeader.Del("Content-Length")
  1098  		}
  1099  	}
  1100  }
  1101  
  1102  // extraHeader is the set of headers sometimes added by chunkWriter.writeHeader.
  1103  // This type is used to avoid extra allocations from cloning and/or populating
  1104  // the response Header map and all its 1-element slices.
  1105  type extraHeader struct {
  1106  	contentType      string
  1107  	connection       string
  1108  	transferEncoding string
  1109  	date             []byte // written if not nil
  1110  	contentLength    []byte // written if not nil
  1111  }
  1112  
  1113  // Sorted the same as extraHeader.Write's loop.
  1114  var extraHeaderKeys = [][]byte{
  1115  	[]byte("Content-Type"),
  1116  	[]byte("Connection"),
  1117  	[]byte("Transfer-Encoding"),
  1118  }
  1119  
  1120  var (
  1121  	headerContentLength = []byte("Content-Length: ")
  1122  	headerDate          = []byte("Date: ")
  1123  )
  1124  
  1125  // Write writes the headers described in h to w.
  1126  //
  1127  // This method has a value receiver, despite the somewhat large size
  1128  // of h, because it prevents an allocation. The escape analysis isn't
  1129  // smart enough to realize this function doesn't mutate h.
  1130  func (h extraHeader) Write(w *bufio.Writer) {
  1131  	if h.date != nil {
  1132  		w.Write(headerDate)
  1133  		w.Write(h.date)
  1134  		w.Write(crlf)
  1135  	}
  1136  	if h.contentLength != nil {
  1137  		w.Write(headerContentLength)
  1138  		w.Write(h.contentLength)
  1139  		w.Write(crlf)
  1140  	}
  1141  	for i, v := range []string{h.contentType, h.connection, h.transferEncoding} {
  1142  		if v != "" {
  1143  			w.Write(extraHeaderKeys[i])
  1144  			w.Write(colonSpace)
  1145  			w.WriteString(v)
  1146  			w.Write(crlf)
  1147  		}
  1148  	}
  1149  }
  1150  
  1151  // writeHeader finalizes the header sent to the client and writes it
  1152  // to cw.res.conn.bufw.
  1153  //
  1154  // p is not written by writeHeader, but is the first chunk of the body
  1155  // that will be written. It is sniffed for a Content-Type if none is
  1156  // set explicitly. It's also used to set the Content-Length, if the
  1157  // total body size was small and the handler has already finished
  1158  // running.
  1159  func (cw *chunkWriter) writeHeader(p []byte) {
  1160  	if cw.wroteHeader {
  1161  		return
  1162  	}
  1163  	cw.wroteHeader = true
  1164  
  1165  	w := cw.res
  1166  	keepAlivesEnabled := w.conn.server.doKeepAlives()
  1167  	isHEAD := w.req.Method == "HEAD"
  1168  
  1169  	// header is written out to w.conn.buf below. Depending on the
  1170  	// state of the handler, we either own the map or not. If we
  1171  	// don't own it, the exclude map is created lazily for
  1172  	// WriteSubset to remove headers. The setHeader struct holds
  1173  	// headers we need to add.
  1174  	header := cw.header
  1175  	owned := header != nil
  1176  	if !owned {
  1177  		header = w.handlerHeader
  1178  	}
  1179  	var excludeHeader map[string]bool
  1180  	delHeader := func(key string) {
  1181  		if owned {
  1182  			header.Del(key)
  1183  			return
  1184  		}
  1185  		if _, ok := header[key]; !ok {
  1186  			return
  1187  		}
  1188  		if excludeHeader == nil {
  1189  			excludeHeader = make(map[string]bool)
  1190  		}
  1191  		excludeHeader[key] = true
  1192  	}
  1193  	var setHeader extraHeader
  1194  
  1195  	// Don't write out the fake "Trailer:foo" keys. See TrailerPrefix.
  1196  	trailers := false
  1197  	for k := range cw.header {
  1198  		if strings.HasPrefix(k, TrailerPrefix) {
  1199  			if excludeHeader == nil {
  1200  				excludeHeader = make(map[string]bool)
  1201  			}
  1202  			excludeHeader[k] = true
  1203  			trailers = true
  1204  		}
  1205  	}
  1206  	for _, v := range cw.header["Trailer"] {
  1207  		trailers = true
  1208  		foreachHeaderElement(v, cw.res.declareTrailer)
  1209  	}
  1210  
  1211  	te := header.get("Transfer-Encoding")
  1212  	hasTE := te != ""
  1213  
  1214  	// If the handler is done but never sent a Content-Length
  1215  	// response header and this is our first (and last) write, set
  1216  	// it, even to zero. This helps HTTP/1.0 clients keep their
  1217  	// "keep-alive" connections alive.
  1218  	// Exceptions: 304/204/1xx responses never get Content-Length, and if
  1219  	// it was a HEAD request, we don't know the difference between
  1220  	// 0 actual bytes and 0 bytes because the handler noticed it
  1221  	// was a HEAD request and chose not to write anything. So for
  1222  	// HEAD, the handler should either write the Content-Length or
  1223  	// write non-zero bytes. If it's actually 0 bytes and the
  1224  	// handler never looked at the Request.Method, we just don't
  1225  	// send a Content-Length header.
  1226  	// Further, we don't send an automatic Content-Length if they
  1227  	// set a Transfer-Encoding, because they're generally incompatible.
  1228  	if w.handlerDone.isSet() && !trailers && !hasTE && bodyAllowedForStatus(w.status) && header.get("Content-Length") == "" && (!isHEAD || len(p) > 0) {
  1229  		w.contentLength = int64(len(p))
  1230  		setHeader.contentLength = strconv.AppendInt(cw.res.clenBuf[:0], int64(len(p)), 10)
  1231  	}
  1232  
  1233  	// If this was an HTTP/1.0 request with keep-alive and we sent a
  1234  	// Content-Length back, we can make this a keep-alive response ...
  1235  	if w.wants10KeepAlive && keepAlivesEnabled {
  1236  		sentLength := header.get("Content-Length") != ""
  1237  		if sentLength && header.get("Connection") == "keep-alive" {
  1238  			w.closeAfterReply = false
  1239  		}
  1240  	}
  1241  
  1242  	// Check for an explicit (and valid) Content-Length header.
  1243  	hasCL := w.contentLength != -1
  1244  
  1245  	if w.wants10KeepAlive && (isHEAD || hasCL || !bodyAllowedForStatus(w.status)) {
  1246  		_, connectionHeaderSet := header["Connection"]
  1247  		if !connectionHeaderSet {
  1248  			setHeader.connection = "keep-alive"
  1249  		}
  1250  	} else if !w.req.ProtoAtLeast(1, 1) || w.wantsClose {
  1251  		w.closeAfterReply = true
  1252  	}
  1253  
  1254  	if header.get("Connection") == "close" || !keepAlivesEnabled {
  1255  		w.closeAfterReply = true
  1256  	}
  1257  
  1258  	// If the client wanted a 100-continue but we never sent it to
  1259  	// them (or, more strictly: we never finished reading their
  1260  	// request body), don't reuse this connection because it's now
  1261  	// in an unknown state: we might be sending this response at
  1262  	// the same time the client is now sending its request body
  1263  	// after a timeout.  (Some HTTP clients send Expect:
  1264  	// 100-continue but knowing that some servers don't support
  1265  	// it, the clients set a timer and send the body later anyway)
  1266  	// If we haven't seen EOF, we can't skip over the unread body
  1267  	// because we don't know if the next bytes on the wire will be
  1268  	// the body-following-the-timer or the subsequent request.
  1269  	// See Issue 11549.
  1270  	if ecr, ok := w.req.Body.(*expectContinueReader); ok && !ecr.sawEOF {
  1271  		w.closeAfterReply = true
  1272  	}
  1273  
  1274  	// Per RFC 2616, we should consume the request body before
  1275  	// replying, if the handler hasn't already done so. But we
  1276  	// don't want to do an unbounded amount of reading here for
  1277  	// DoS reasons, so we only try up to a threshold.
  1278  	// TODO(bradfitz): where does RFC 2616 say that? See Issue 15527
  1279  	// about HTTP/1.x Handlers concurrently reading and writing, like
  1280  	// HTTP/2 handlers can do. Maybe this code should be relaxed?
  1281  	if w.req.ContentLength != 0 && !w.closeAfterReply {
  1282  		var discard, tooBig bool
  1283  
  1284  		switch bdy := w.req.Body.(type) {
  1285  		case *expectContinueReader:
  1286  			if bdy.resp.wroteContinue {
  1287  				discard = true
  1288  			}
  1289  		case *body:
  1290  			bdy.mu.Lock()
  1291  			switch {
  1292  			case bdy.closed:
  1293  				if !bdy.sawEOF {
  1294  					// Body was closed in handler with non-EOF error.
  1295  					w.closeAfterReply = true
  1296  				}
  1297  			case bdy.unreadDataSizeLocked() >= maxPostHandlerReadBytes:
  1298  				tooBig = true
  1299  			default:
  1300  				discard = true
  1301  			}
  1302  			bdy.mu.Unlock()
  1303  		default:
  1304  			discard = true
  1305  		}
  1306  
  1307  		if discard {
  1308  			_, err := io.CopyN(ioutil.Discard, w.reqBody, maxPostHandlerReadBytes+1)
  1309  			switch err {
  1310  			case nil:
  1311  				// There must be even more data left over.
  1312  				tooBig = true
  1313  			case ErrBodyReadAfterClose:
  1314  				// Body was already consumed and closed.
  1315  			case io.EOF:
  1316  				// The remaining body was just consumed, close it.
  1317  				err = w.reqBody.Close()
  1318  				if err != nil {
  1319  					w.closeAfterReply = true
  1320  				}
  1321  			default:
  1322  				// Some other kind of error occurred, like a read timeout, or
  1323  				// corrupt chunked encoding. In any case, whatever remains
  1324  				// on the wire must not be parsed as another HTTP request.
  1325  				w.closeAfterReply = true
  1326  			}
  1327  		}
  1328  
  1329  		if tooBig {
  1330  			w.requestTooLarge()
  1331  			delHeader("Connection")
  1332  			setHeader.connection = "close"
  1333  		}
  1334  	}
  1335  
  1336  	code := w.status
  1337  	if bodyAllowedForStatus(code) {
  1338  		// If no content type, apply sniffing algorithm to body.
  1339  		_, haveType := header["Content-Type"]
  1340  		if !haveType && !hasTE && len(p) > 0 {
  1341  			setHeader.contentType = DetectContentType(p)
  1342  		}
  1343  	} else {
  1344  		for _, k := range suppressedHeaders(code) {
  1345  			delHeader(k)
  1346  		}
  1347  	}
  1348  
  1349  	if _, ok := header["Date"]; !ok {
  1350  		setHeader.date = appendTime(cw.res.dateBuf[:0], time.Now())
  1351  	}
  1352  
  1353  	if hasCL && hasTE && te != "identity" {
  1354  		// TODO: return an error if WriteHeader gets a return parameter
  1355  		// For now just ignore the Content-Length.
  1356  		w.conn.server.logf("http: WriteHeader called with both Transfer-Encoding of %q and a Content-Length of %d",
  1357  			te, w.contentLength)
  1358  		delHeader("Content-Length")
  1359  		hasCL = false
  1360  	}
  1361  
  1362  	if w.req.Method == "HEAD" || !bodyAllowedForStatus(code) {
  1363  		// do nothing
  1364  	} else if code == StatusNoContent {
  1365  		delHeader("Transfer-Encoding")
  1366  	} else if hasCL {
  1367  		delHeader("Transfer-Encoding")
  1368  	} else if w.req.ProtoAtLeast(1, 1) {
  1369  		// HTTP/1.1 or greater: Transfer-Encoding has been set to identity, and no
  1370  		// content-length has been provided. The connection must be closed after the
  1371  		// reply is written, and no chunking is to be done. This is the setup
  1372  		// recommended in the Server-Sent Events candidate recommendation 11,
  1373  		// section 8.
  1374  		if hasTE && te == "identity" {
  1375  			cw.chunking = false
  1376  			w.closeAfterReply = true
  1377  		} else {
  1378  			// HTTP/1.1 or greater: use chunked transfer encoding
  1379  			// to avoid closing the connection at EOF.
  1380  			cw.chunking = true
  1381  			setHeader.transferEncoding = "chunked"
  1382  			if hasTE && te == "chunked" {
  1383  				// We will send the chunked Transfer-Encoding header later.
  1384  				delHeader("Transfer-Encoding")
  1385  			}
  1386  		}
  1387  	} else {
  1388  		// HTTP version < 1.1: cannot do chunked transfer
  1389  		// encoding and we don't know the Content-Length so
  1390  		// signal EOF by closing connection.
  1391  		w.closeAfterReply = true
  1392  		delHeader("Transfer-Encoding") // in case already set
  1393  	}
  1394  
  1395  	// Cannot use Content-Length with non-identity Transfer-Encoding.
  1396  	if cw.chunking {
  1397  		delHeader("Content-Length")
  1398  	}
  1399  	if !w.req.ProtoAtLeast(1, 0) {
  1400  		return
  1401  	}
  1402  
  1403  	if w.closeAfterReply && (!keepAlivesEnabled || !hasToken(cw.header.get("Connection"), "close")) {
  1404  		delHeader("Connection")
  1405  		if w.req.ProtoAtLeast(1, 1) {
  1406  			setHeader.connection = "close"
  1407  		}
  1408  	}
  1409  
  1410  	writeStatusLine(w.conn.bufw, w.req.ProtoAtLeast(1, 1), code, w.statusBuf[:])
  1411  	cw.header.WriteSubset(w.conn.bufw, excludeHeader)
  1412  	setHeader.Write(w.conn.bufw)
  1413  	w.conn.bufw.Write(crlf)
  1414  }
  1415  
  1416  // foreachHeaderElement splits v according to the "#rule" construction
  1417  // in RFC 2616 section 2.1 and calls fn for each non-empty element.
  1418  func foreachHeaderElement(v string, fn func(string)) {
  1419  	v = textproto.TrimString(v)
  1420  	if v == "" {
  1421  		return
  1422  	}
  1423  	if !strings.Contains(v, ",") {
  1424  		fn(v)
  1425  		return
  1426  	}
  1427  	for _, f := range strings.Split(v, ",") {
  1428  		if f = textproto.TrimString(f); f != "" {
  1429  			fn(f)
  1430  		}
  1431  	}
  1432  }
  1433  
  1434  // writeStatusLine writes an HTTP/1.x Status-Line (RFC 2616 Section 6.1)
  1435  // to bw. is11 is whether the HTTP request is HTTP/1.1. false means HTTP/1.0.
  1436  // code is the response status code.
  1437  // scratch is an optional scratch buffer. If it has at least capacity 3, it's used.
  1438  func writeStatusLine(bw *bufio.Writer, is11 bool, code int, scratch []byte) {
  1439  	if is11 {
  1440  		bw.WriteString("HTTP/1.1 ")
  1441  	} else {
  1442  		bw.WriteString("HTTP/1.0 ")
  1443  	}
  1444  	if text, ok := statusText[code]; ok {
  1445  		bw.Write(strconv.AppendInt(scratch[:0], int64(code), 10))
  1446  		bw.WriteByte(' ')
  1447  		bw.WriteString(text)
  1448  		bw.WriteString("\r\n")
  1449  	} else {
  1450  		// don't worry about performance
  1451  		fmt.Fprintf(bw, "%03d status code %d\r\n", code, code)
  1452  	}
  1453  }
  1454  
  1455  // bodyAllowed reports whether a Write is allowed for this response type.
  1456  // It's illegal to call this before the header has been flushed.
  1457  func (w *response) bodyAllowed() bool {
  1458  	if !w.wroteHeader {
  1459  		panic("")
  1460  	}
  1461  	return bodyAllowedForStatus(w.status)
  1462  }
  1463  
  1464  // The Life Of A Write is like this:
  1465  //
  1466  // Handler starts. No header has been sent. The handler can either
  1467  // write a header, or just start writing. Writing before sending a header
  1468  // sends an implicitly empty 200 OK header.
  1469  //
  1470  // If the handler didn't declare a Content-Length up front, we either
  1471  // go into chunking mode or, if the handler finishes running before
  1472  // the chunking buffer size, we compute a Content-Length and send that
  1473  // in the header instead.
  1474  //
  1475  // Likewise, if the handler didn't set a Content-Type, we sniff that
  1476  // from the initial chunk of output.
  1477  //
  1478  // The Writers are wired together like:
  1479  //
  1480  // 1. *response (the ResponseWriter) ->
  1481  // 2. (*response).w, a *bufio.Writer of bufferBeforeChunkingSize bytes
  1482  // 3. chunkWriter.Writer (whose writeHeader finalizes Content-Length/Type)
  1483  //    and which writes the chunk headers, if needed.
  1484  // 4. conn.buf, a bufio.Writer of default (4kB) bytes, writing to ->
  1485  // 5. checkConnErrorWriter{c}, which notes any non-nil error on Write
  1486  //    and populates c.werr with it if so. but otherwise writes to:
  1487  // 6. the rwc, the net.Conn.
  1488  //
  1489  // TODO(bradfitz): short-circuit some of the buffering when the
  1490  // initial header contains both a Content-Type and Content-Length.
  1491  // Also short-circuit in (1) when the header's been sent and not in
  1492  // chunking mode, writing directly to (4) instead, if (2) has no
  1493  // buffered data. More generally, we could short-circuit from (1) to
  1494  // (3) even in chunking mode if the write size from (1) is over some
  1495  // threshold and nothing is in (2).  The answer might be mostly making
  1496  // bufferBeforeChunkingSize smaller and having bufio's fast-paths deal
  1497  // with this instead.
  1498  func (w *response) Write(data []byte) (n int, err error) {
  1499  	return w.write(len(data), data, "")
  1500  }
  1501  
  1502  func (w *response) WriteString(data string) (n int, err error) {
  1503  	return w.write(len(data), nil, data)
  1504  }
  1505  
  1506  // either dataB or dataS is non-zero.
  1507  func (w *response) write(lenData int, dataB []byte, dataS string) (n int, err error) {
  1508  	if w.conn.hijacked() {
  1509  		if lenData > 0 {
  1510  			w.conn.server.logf("http: response.Write on hijacked connection")
  1511  		}
  1512  		return 0, ErrHijacked
  1513  	}
  1514  	if !w.wroteHeader {
  1515  		w.WriteHeader(StatusOK)
  1516  	}
  1517  	if lenData == 0 {
  1518  		return 0, nil
  1519  	}
  1520  	if !w.bodyAllowed() {
  1521  		return 0, ErrBodyNotAllowed
  1522  	}
  1523  
  1524  	w.written += int64(lenData) // ignoring errors, for errorKludge
  1525  	if w.contentLength != -1 && w.written > w.contentLength {
  1526  		return 0, ErrContentLength
  1527  	}
  1528  	if dataB != nil {
  1529  		return w.w.Write(dataB)
  1530  	} else {
  1531  		return w.w.WriteString(dataS)
  1532  	}
  1533  }
  1534  
  1535  func (w *response) finishRequest() {
  1536  	w.handlerDone.setTrue()
  1537  
  1538  	if !w.wroteHeader {
  1539  		w.WriteHeader(StatusOK)
  1540  	}
  1541  
  1542  	w.w.Flush()
  1543  	putBufioWriter(w.w)
  1544  	w.cw.close()
  1545  	w.conn.bufw.Flush()
  1546  
  1547  	w.conn.r.abortPendingRead()
  1548  
  1549  	// Close the body (regardless of w.closeAfterReply) so we can
  1550  	// re-use its bufio.Reader later safely.
  1551  	w.reqBody.Close()
  1552  
  1553  	if w.req.MultipartForm != nil {
  1554  		w.req.MultipartForm.RemoveAll()
  1555  	}
  1556  }
  1557  
  1558  // shouldReuseConnection reports whether the underlying TCP connection can be reused.
  1559  // It must only be called after the handler is done executing.
  1560  func (w *response) shouldReuseConnection() bool {
  1561  	if w.closeAfterReply {
  1562  		// The request or something set while executing the
  1563  		// handler indicated we shouldn't reuse this
  1564  		// connection.
  1565  		return false
  1566  	}
  1567  
  1568  	if w.req.Method != "HEAD" && w.contentLength != -1 && w.bodyAllowed() && w.contentLength != w.written {
  1569  		// Did not write enough. Avoid getting out of sync.
  1570  		return false
  1571  	}
  1572  
  1573  	// There was some error writing to the underlying connection
  1574  	// during the request, so don't re-use this conn.
  1575  	if w.conn.werr != nil {
  1576  		return false
  1577  	}
  1578  
  1579  	if w.closedRequestBodyEarly() {
  1580  		return false
  1581  	}
  1582  
  1583  	return true
  1584  }
  1585  
  1586  func (w *response) closedRequestBodyEarly() bool {
  1587  	body, ok := w.req.Body.(*body)
  1588  	return ok && body.didEarlyClose()
  1589  }
  1590  
  1591  func (w *response) Flush() {
  1592  	if !w.wroteHeader {
  1593  		w.WriteHeader(StatusOK)
  1594  	}
  1595  	w.w.Flush()
  1596  	w.cw.flush()
  1597  }
  1598  
  1599  func (c *conn) finalFlush() {
  1600  	if c.bufr != nil {
  1601  		// Steal the bufio.Reader (~4KB worth of memory) and its associated
  1602  		// reader for a future connection.
  1603  		putBufioReader(c.bufr)
  1604  		c.bufr = nil
  1605  	}
  1606  
  1607  	if c.bufw != nil {
  1608  		c.bufw.Flush()
  1609  		// Steal the bufio.Writer (~4KB worth of memory) and its associated
  1610  		// writer for a future connection.
  1611  		putBufioWriter(c.bufw)
  1612  		c.bufw = nil
  1613  	}
  1614  }
  1615  
  1616  // Close the connection.
  1617  func (c *conn) close() {
  1618  	c.finalFlush()
  1619  	c.rwc.Close()
  1620  }
  1621  
  1622  // rstAvoidanceDelay is the amount of time we sleep after closing the
  1623  // write side of a TCP connection before closing the entire socket.
  1624  // By sleeping, we increase the chances that the client sees our FIN
  1625  // and processes its final data before they process the subsequent RST
  1626  // from closing a connection with known unread data.
  1627  // This RST seems to occur mostly on BSD systems. (And Windows?)
  1628  // This timeout is somewhat arbitrary (~latency around the planet).
  1629  const rstAvoidanceDelay = 500 * time.Millisecond
  1630  
  1631  type closeWriter interface {
  1632  	CloseWrite() error
  1633  }
  1634  
  1635  var _ closeWriter = (*net.TCPConn)(nil)
  1636  
  1637  // closeWrite flushes any outstanding data and sends a FIN packet (if
  1638  // client is connected via TCP), signalling that we're done. We then
  1639  // pause for a bit, hoping the client processes it before any
  1640  // subsequent RST.
  1641  //
  1642  // See https://golang.org/issue/3595
  1643  func (c *conn) closeWriteAndWait() {
  1644  	c.finalFlush()
  1645  	if tcp, ok := c.rwc.(closeWriter); ok {
  1646  		tcp.CloseWrite()
  1647  	}
  1648  	time.Sleep(rstAvoidanceDelay)
  1649  }
  1650  
  1651  // validNPN reports whether the proto is not a blacklisted Next
  1652  // Protocol Negotiation protocol. Empty and built-in protocol types
  1653  // are blacklisted and can't be overridden with alternate
  1654  // implementations.
  1655  func validNPN(proto string) bool {
  1656  	switch proto {
  1657  	case "", "http/1.1", "http/1.0":
  1658  		return false
  1659  	}
  1660  	return true
  1661  }
  1662  
  1663  func (c *conn) setState(nc net.Conn, state ConnState) {
  1664  	srv := c.server
  1665  	switch state {
  1666  	case StateNew:
  1667  		srv.trackConn(c, true)
  1668  	case StateHijacked, StateClosed:
  1669  		srv.trackConn(c, false)
  1670  	}
  1671  	c.curState.Store(connStateInterface[state])
  1672  	if hook := srv.ConnState; hook != nil {
  1673  		hook(nc, state)
  1674  	}
  1675  }
  1676  
  1677  // connStateInterface is an array of the interface{} versions of
  1678  // ConnState values, so we can use them in atomic.Values later without
  1679  // paying the cost of shoving their integers in an interface{}.
  1680  var connStateInterface = [...]interface{}{
  1681  	StateNew:      StateNew,
  1682  	StateActive:   StateActive,
  1683  	StateIdle:     StateIdle,
  1684  	StateHijacked: StateHijacked,
  1685  	StateClosed:   StateClosed,
  1686  }
  1687  
  1688  // badRequestError is a literal string (used by in the server in HTML,
  1689  // unescaped) to tell the user why their request was bad. It should
  1690  // be plain text without user info or other embedded errors.
  1691  type badRequestError string
  1692  
  1693  func (e badRequestError) Error() string { return "Bad Request: " + string(e) }
  1694  
  1695  // ErrAbortHandler is a sentinel panic value to abort a handler.
  1696  // While any panic from ServeHTTP aborts the response to the client,
  1697  // panicking with ErrAbortHandler also suppresses logging of a stack
  1698  // trace to the server's error log.
  1699  var ErrAbortHandler = errors.New("net/http: abort Handler")
  1700  
  1701  // isCommonNetReadError reports whether err is a common error
  1702  // encountered during reading a request off the network when the
  1703  // client has gone away or had its read fail somehow. This is used to
  1704  // determine which logs are interesting enough to log about.
  1705  func isCommonNetReadError(err error) bool {
  1706  	if err == io.EOF {
  1707  		return true
  1708  	}
  1709  	if neterr, ok := err.(net.Error); ok && neterr.Timeout() {
  1710  		return true
  1711  	}
  1712  	if oe, ok := err.(*net.OpError); ok && oe.Op == "read" {
  1713  		return true
  1714  	}
  1715  	return false
  1716  }
  1717  
  1718  // Serve a new connection.
  1719  func (c *conn) serve(ctx context.Context) {
  1720  	c.remoteAddr = c.rwc.RemoteAddr().String()
  1721  	ctx = context.WithValue(ctx, LocalAddrContextKey, c.rwc.LocalAddr())
  1722  	defer func() {
  1723  		if err := recover(); err != nil && err != ErrAbortHandler {
  1724  			const size = 64 << 10
  1725  			buf := make([]byte, size)
  1726  			buf = buf[:runtime.Stack(buf, false)]
  1727  			c.server.logf("http: panic serving %v: %v\n%s", c.remoteAddr, err, buf)
  1728  		}
  1729  		if !c.hijacked() {
  1730  			c.close()
  1731  			c.setState(c.rwc, StateClosed)
  1732  		}
  1733  	}()
  1734  
  1735  	if tlsConn, ok := c.rwc.(*tls.Conn); ok {
  1736  		if d := c.server.ReadTimeout; d != 0 {
  1737  			c.rwc.SetReadDeadline(time.Now().Add(d))
  1738  		}
  1739  		if d := c.server.WriteTimeout; d != 0 {
  1740  			c.rwc.SetWriteDeadline(time.Now().Add(d))
  1741  		}
  1742  		if err := tlsConn.Handshake(); err != nil {
  1743  			c.server.logf("http: TLS handshake error from %s: %v", c.rwc.RemoteAddr(), err)
  1744  			return
  1745  		}
  1746  		c.tlsState = new(tls.ConnectionState)
  1747  		*c.tlsState = tlsConn.ConnectionState()
  1748  		if proto := c.tlsState.NegotiatedProtocol; validNPN(proto) {
  1749  			if fn := c.server.TLSNextProto[proto]; fn != nil {
  1750  				h := initNPNRequest{tlsConn, serverHandler{c.server}}
  1751  				fn(c.server, tlsConn, h)
  1752  			}
  1753  			return
  1754  		}
  1755  	}
  1756  
  1757  	// HTTP/1.x from here on.
  1758  
  1759  	ctx, cancelCtx := context.WithCancel(ctx)
  1760  	c.cancelCtx = cancelCtx
  1761  	defer cancelCtx()
  1762  
  1763  	c.r = &connReader{conn: c}
  1764  	c.bufr = newBufioReader(c.r)
  1765  	c.bufw = newBufioWriterSize(checkConnErrorWriter{c}, 4<<10)
  1766  
  1767  	for {
  1768  		w, err := c.readRequest(ctx)
  1769  		if c.r.remain != c.server.initialReadLimitSize() {
  1770  			// If we read any bytes off the wire, we're active.
  1771  			c.setState(c.rwc, StateActive)
  1772  		}
  1773  		if err != nil {
  1774  			const errorHeaders = "\r\nContent-Type: text/plain; charset=utf-8\r\nConnection: close\r\n\r\n"
  1775  
  1776  			if err == errTooLarge {
  1777  				// Their HTTP client may or may not be
  1778  				// able to read this if we're
  1779  				// responding to them and hanging up
  1780  				// while they're still writing their
  1781  				// request. Undefined behavior.
  1782  				const publicErr = "431 Request Header Fields Too Large"
  1783  				fmt.Fprintf(c.rwc, "HTTP/1.1 "+publicErr+errorHeaders+publicErr)
  1784  				c.closeWriteAndWait()
  1785  				return
  1786  			}
  1787  			if isCommonNetReadError(err) {
  1788  				return // don't reply
  1789  			}
  1790  
  1791  			publicErr := "400 Bad Request"
  1792  			if v, ok := err.(badRequestError); ok {
  1793  				publicErr = publicErr + ": " + string(v)
  1794  			}
  1795  
  1796  			fmt.Fprintf(c.rwc, "HTTP/1.1 "+publicErr+errorHeaders+publicErr)
  1797  			return
  1798  		}
  1799  
  1800  		// Expect 100 Continue support
  1801  		req := w.req
  1802  		if req.expectsContinue() {
  1803  			if req.ProtoAtLeast(1, 1) && req.ContentLength != 0 {
  1804  				// Wrap the Body reader with one that replies on the connection
  1805  				req.Body = &expectContinueReader{readCloser: req.Body, resp: w}
  1806  			}
  1807  		} else if req.Header.get("Expect") != "" {
  1808  			w.sendExpectationFailed()
  1809  			return
  1810  		}
  1811  
  1812  		c.curReq.Store(w)
  1813  
  1814  		if requestBodyRemains(req.Body) {
  1815  			registerOnHitEOF(req.Body, w.conn.r.startBackgroundRead)
  1816  		} else {
  1817  			if w.conn.bufr.Buffered() > 0 {
  1818  				w.conn.r.closeNotifyFromPipelinedRequest()
  1819  			}
  1820  			w.conn.r.startBackgroundRead()
  1821  		}
  1822  
  1823  		// HTTP cannot have multiple simultaneous active requests.[*]
  1824  		// Until the server replies to this request, it can't read another,
  1825  		// so we might as well run the handler in this goroutine.
  1826  		// [*] Not strictly true: HTTP pipelining. We could let them all process
  1827  		// in parallel even if their responses need to be serialized.
  1828  		// But we're not going to implement HTTP pipelining because it
  1829  		// was never deployed in the wild and the answer is HTTP/2.
  1830  		serverHandler{c.server}.ServeHTTP(w, w.req)
  1831  		w.cancelCtx()
  1832  		if c.hijacked() {
  1833  			return
  1834  		}
  1835  		w.finishRequest()
  1836  		if !w.shouldReuseConnection() {
  1837  			if w.requestBodyLimitHit || w.closedRequestBodyEarly() {
  1838  				c.closeWriteAndWait()
  1839  			}
  1840  			return
  1841  		}
  1842  		c.setState(c.rwc, StateIdle)
  1843  		c.curReq.Store((*response)(nil))
  1844  
  1845  		if !w.conn.server.doKeepAlives() {
  1846  			// We're in shutdown mode. We might've replied
  1847  			// to the user without "Connection: close" and
  1848  			// they might think they can send another
  1849  			// request, but such is life with HTTP/1.1.
  1850  			return
  1851  		}
  1852  
  1853  		if d := c.server.idleTimeout(); d != 0 {
  1854  			c.rwc.SetReadDeadline(time.Now().Add(d))
  1855  			if _, err := c.bufr.Peek(4); err != nil {
  1856  				return
  1857  			}
  1858  		}
  1859  		c.rwc.SetReadDeadline(time.Time{})
  1860  	}
  1861  }
  1862  
  1863  func (w *response) sendExpectationFailed() {
  1864  	// TODO(bradfitz): let ServeHTTP handlers handle
  1865  	// requests with non-standard expectation[s]? Seems
  1866  	// theoretical at best, and doesn't fit into the
  1867  	// current ServeHTTP model anyway. We'd need to
  1868  	// make the ResponseWriter an optional
  1869  	// "ExpectReplier" interface or something.
  1870  	//
  1871  	// For now we'll just obey RFC 2616 14.20 which says
  1872  	// "If a server receives a request containing an
  1873  	// Expect field that includes an expectation-
  1874  	// extension that it does not support, it MUST
  1875  	// respond with a 417 (Expectation Failed) status."
  1876  	w.Header().Set("Connection", "close")
  1877  	w.WriteHeader(StatusExpectationFailed)
  1878  	w.finishRequest()
  1879  }
  1880  
  1881  // Hijack implements the Hijacker.Hijack method. Our response is both a ResponseWriter
  1882  // and a Hijacker.
  1883  func (w *response) Hijack() (rwc net.Conn, buf *bufio.ReadWriter, err error) {
  1884  	if w.handlerDone.isSet() {
  1885  		panic("net/http: Hijack called after ServeHTTP finished")
  1886  	}
  1887  	if w.wroteHeader {
  1888  		w.cw.flush()
  1889  	}
  1890  
  1891  	c := w.conn
  1892  	c.mu.Lock()
  1893  	defer c.mu.Unlock()
  1894  
  1895  	// Release the bufioWriter that writes to the chunk writer, it is not
  1896  	// used after a connection has been hijacked.
  1897  	rwc, buf, err = c.hijackLocked()
  1898  	if err == nil {
  1899  		putBufioWriter(w.w)
  1900  		w.w = nil
  1901  	}
  1902  	return rwc, buf, err
  1903  }
  1904  
  1905  func (w *response) CloseNotify() <-chan bool {
  1906  	if w.handlerDone.isSet() {
  1907  		panic("net/http: CloseNotify called after ServeHTTP finished")
  1908  	}
  1909  	return w.closeNotifyCh
  1910  }
  1911  
  1912  func registerOnHitEOF(rc io.ReadCloser, fn func()) {
  1913  	switch v := rc.(type) {
  1914  	case *expectContinueReader:
  1915  		registerOnHitEOF(v.readCloser, fn)
  1916  	case *body:
  1917  		v.registerOnHitEOF(fn)
  1918  	default:
  1919  		panic("unexpected type " + fmt.Sprintf("%T", rc))
  1920  	}
  1921  }
  1922  
  1923  // requestBodyRemains reports whether future calls to Read
  1924  // on rc might yield more data.
  1925  func requestBodyRemains(rc io.ReadCloser) bool {
  1926  	if rc == NoBody {
  1927  		return false
  1928  	}
  1929  	switch v := rc.(type) {
  1930  	case *expectContinueReader:
  1931  		return requestBodyRemains(v.readCloser)
  1932  	case *body:
  1933  		return v.bodyRemains()
  1934  	default:
  1935  		panic("unexpected type " + fmt.Sprintf("%T", rc))
  1936  	}
  1937  }
  1938  
  1939  // The HandlerFunc type is an adapter to allow the use of
  1940  // ordinary functions as HTTP handlers. If f is a function
  1941  // with the appropriate signature, HandlerFunc(f) is a
  1942  // Handler that calls f.
  1943  type HandlerFunc func(ResponseWriter, *Request)
  1944  
  1945  // ServeHTTP calls f(w, r).
  1946  func (f HandlerFunc) ServeHTTP(w ResponseWriter, r *Request) {
  1947  	f(w, r)
  1948  }
  1949  
  1950  // Helper handlers
  1951  
  1952  // Error replies to the request with the specified error message and HTTP code.
  1953  // It does not otherwise end the request; the caller should ensure no further
  1954  // writes are done to w.
  1955  // The error message should be plain text.
  1956  func Error(w ResponseWriter, error string, code int) {
  1957  	w.Header().Set("Content-Type", "text/plain; charset=utf-8")
  1958  	w.Header().Set("X-Content-Type-Options", "nosniff")
  1959  	w.WriteHeader(code)
  1960  	fmt.Fprintln(w, error)
  1961  }
  1962  
  1963  // NotFound replies to the request with an HTTP 404 not found error.
  1964  func NotFound(w ResponseWriter, r *Request) { Error(w, "404 page not found", StatusNotFound) }
  1965  
  1966  // NotFoundHandler returns a simple request handler
  1967  // that replies to each request with a ``404 page not found'' reply.
  1968  func NotFoundHandler() Handler { return HandlerFunc(NotFound) }
  1969  
  1970  // StripPrefix returns a handler that serves HTTP requests
  1971  // by removing the given prefix from the request URL's Path
  1972  // and invoking the handler h. StripPrefix handles a
  1973  // request for a path that doesn't begin with prefix by
  1974  // replying with an HTTP 404 not found error.
  1975  func StripPrefix(prefix string, h Handler) Handler {
  1976  	if prefix == "" {
  1977  		return h
  1978  	}
  1979  	return HandlerFunc(func(w ResponseWriter, r *Request) {
  1980  		if p := strings.TrimPrefix(r.URL.Path, prefix); len(p) < len(r.URL.Path) {
  1981  			r2 := new(Request)
  1982  			*r2 = *r
  1983  			r2.URL = new(url.URL)
  1984  			*r2.URL = *r.URL
  1985  			r2.URL.Path = p
  1986  			h.ServeHTTP(w, r2)
  1987  		} else {
  1988  			NotFound(w, r)
  1989  		}
  1990  	})
  1991  }
  1992  
  1993  // Redirect replies to the request with a redirect to url,
  1994  // which may be a path relative to the request path.
  1995  //
  1996  // The provided code should be in the 3xx range and is usually
  1997  // StatusMovedPermanently, StatusFound or StatusSeeOther.
  1998  func Redirect(w ResponseWriter, r *Request, url string, code int) {
  1999  	// parseURL is just url.Parse (url is shadowed for godoc).
  2000  	if u, err := parseURL(url); err == nil {
  2001  		// If url was relative, make absolute by
  2002  		// combining with request path.
  2003  		// The browser would probably do this for us,
  2004  		// but doing it ourselves is more reliable.
  2005  
  2006  		// NOTE(rsc): RFC 2616 says that the Location
  2007  		// line must be an absolute URI, like
  2008  		// "http://www.google.com/redirect/",
  2009  		// not a path like "/redirect/".
  2010  		// Unfortunately, we don't know what to
  2011  		// put in the host name section to get the
  2012  		// client to connect to us again, so we can't
  2013  		// know the right absolute URI to send back.
  2014  		// Because of this problem, no one pays attention
  2015  		// to the RFC; they all send back just a new path.
  2016  		// So do we.
  2017  		if u.Scheme == "" && u.Host == "" {
  2018  			oldpath := r.URL.Path
  2019  			if oldpath == "" { // should not happen, but avoid a crash if it does
  2020  				oldpath = "/"
  2021  			}
  2022  
  2023  			// no leading http://server
  2024  			if url == "" || url[0] != '/' {
  2025  				// make relative path absolute
  2026  				olddir, _ := path.Split(oldpath)
  2027  				url = olddir + url
  2028  			}
  2029  
  2030  			var query string
  2031  			if i := strings.Index(url, "?"); i != -1 {
  2032  				url, query = url[:i], url[i:]
  2033  			}
  2034  
  2035  			// clean up but preserve trailing slash
  2036  			trailing := strings.HasSuffix(url, "/")
  2037  			url = path.Clean(url)
  2038  			if trailing && !strings.HasSuffix(url, "/") {
  2039  				url += "/"
  2040  			}
  2041  			url += query
  2042  		}
  2043  	}
  2044  
  2045  	w.Header().Set("Location", hexEscapeNonASCII(url))
  2046  	if r.Method == "GET" || r.Method == "HEAD" {
  2047  		w.Header().Set("Content-Type", "text/html; charset=utf-8")
  2048  	}
  2049  	w.WriteHeader(code)
  2050  
  2051  	// RFC 2616 recommends that a short note "SHOULD" be included in the
  2052  	// response because older user agents may not understand 301/307.
  2053  	// Shouldn't send the response for POST or HEAD; that leaves GET.
  2054  	if r.Method == "GET" {
  2055  		note := "<a href=\"" + htmlEscape(url) + "\">" + statusText[code] + "</a>.\n"
  2056  		fmt.Fprintln(w, note)
  2057  	}
  2058  }
  2059  
  2060  // parseURL is just url.Parse. It exists only so that url.Parse can be called
  2061  // in places where url is shadowed for godoc. See https://golang.org/cl/49930.
  2062  var parseURL = url.Parse
  2063  
  2064  var htmlReplacer = strings.NewReplacer(
  2065  	"&", "&amp;",
  2066  	"<", "&lt;",
  2067  	">", "&gt;",
  2068  	// "&#34;" is shorter than "&quot;".
  2069  	`"`, "&#34;",
  2070  	// "&#39;" is shorter than "&apos;" and apos was not in HTML until HTML5.
  2071  	"'", "&#39;",
  2072  )
  2073  
  2074  func htmlEscape(s string) string {
  2075  	return htmlReplacer.Replace(s)
  2076  }
  2077  
  2078  // Redirect to a fixed URL
  2079  type redirectHandler struct {
  2080  	url  string
  2081  	code int
  2082  }
  2083  
  2084  func (rh *redirectHandler) ServeHTTP(w ResponseWriter, r *Request) {
  2085  	Redirect(w, r, rh.url, rh.code)
  2086  }
  2087  
  2088  // RedirectHandler returns a request handler that redirects
  2089  // each request it receives to the given url using the given
  2090  // status code.
  2091  //
  2092  // The provided code should be in the 3xx range and is usually
  2093  // StatusMovedPermanently, StatusFound or StatusSeeOther.
  2094  func RedirectHandler(url string, code int) Handler {
  2095  	return &redirectHandler{url, code}
  2096  }
  2097  
  2098  // ServeMux is an HTTP request multiplexer.
  2099  // It matches the URL of each incoming request against a list of registered
  2100  // patterns and calls the handler for the pattern that
  2101  // most closely matches the URL.
  2102  //
  2103  // Patterns name fixed, rooted paths, like "/favicon.ico",
  2104  // or rooted subtrees, like "/images/" (note the trailing slash).
  2105  // Longer patterns take precedence over shorter ones, so that
  2106  // if there are handlers registered for both "/images/"
  2107  // and "/images/thumbnails/", the latter handler will be
  2108  // called for paths beginning "/images/thumbnails/" and the
  2109  // former will receive requests for any other paths in the
  2110  // "/images/" subtree.
  2111  //
  2112  // Note that since a pattern ending in a slash names a rooted subtree,
  2113  // the pattern "/" matches all paths not matched by other registered
  2114  // patterns, not just the URL with Path == "/".
  2115  //
  2116  // If a subtree has been registered and a request is received naming the
  2117  // subtree root without its trailing slash, ServeMux redirects that
  2118  // request to the subtree root (adding the trailing slash). This behavior can
  2119  // be overridden with a separate registration for the path without
  2120  // the trailing slash. For example, registering "/images/" causes ServeMux
  2121  // to redirect a request for "/images" to "/images/", unless "/images" has
  2122  // been registered separately.
  2123  //
  2124  // Patterns may optionally begin with a host name, restricting matches to
  2125  // URLs on that host only. Host-specific patterns take precedence over
  2126  // general patterns, so that a handler might register for the two patterns
  2127  // "/codesearch" and "codesearch.google.com/" without also taking over
  2128  // requests for "http://www.google.com/".
  2129  //
  2130  // ServeMux also takes care of sanitizing the URL request path,
  2131  // redirecting any request containing . or .. elements or repeated slashes
  2132  // to an equivalent, cleaner URL.
  2133  type ServeMux struct {
  2134  	mu    sync.RWMutex
  2135  	m     map[string]muxEntry
  2136  	hosts bool // whether any patterns contain hostnames
  2137  }
  2138  
  2139  type muxEntry struct {
  2140  	h       Handler
  2141  	pattern string
  2142  }
  2143  
  2144  // NewServeMux allocates and returns a new ServeMux.
  2145  func NewServeMux() *ServeMux { return new(ServeMux) }
  2146  
  2147  // DefaultServeMux is the default ServeMux used by Serve.
  2148  var DefaultServeMux = &defaultServeMux
  2149  
  2150  var defaultServeMux ServeMux
  2151  
  2152  // Does path match pattern?
  2153  func pathMatch(pattern, path string) bool {
  2154  	if len(pattern) == 0 {
  2155  		// should not happen
  2156  		return false
  2157  	}
  2158  	n := len(pattern)
  2159  	if pattern[n-1] != '/' {
  2160  		return pattern == path
  2161  	}
  2162  	return len(path) >= n && path[0:n] == pattern
  2163  }
  2164  
  2165  // Return the canonical path for p, eliminating . and .. elements.
  2166  func cleanPath(p string) string {
  2167  	if p == "" {
  2168  		return "/"
  2169  	}
  2170  	if p[0] != '/' {
  2171  		p = "/" + p
  2172  	}
  2173  	np := path.Clean(p)
  2174  	// path.Clean removes trailing slash except for root;
  2175  	// put the trailing slash back if necessary.
  2176  	if p[len(p)-1] == '/' && np != "/" {
  2177  		np += "/"
  2178  	}
  2179  	return np
  2180  }
  2181  
  2182  // stripHostPort returns h without any trailing ":<port>".
  2183  func stripHostPort(h string) string {
  2184  	// If no port on host, return unchanged
  2185  	if strings.IndexByte(h, ':') == -1 {
  2186  		return h
  2187  	}
  2188  	host, _, err := net.SplitHostPort(h)
  2189  	if err != nil {
  2190  		return h // on error, return unchanged
  2191  	}
  2192  	return host
  2193  }
  2194  
  2195  // Find a handler on a handler map given a path string.
  2196  // Most-specific (longest) pattern wins.
  2197  func (mux *ServeMux) match(path string) (h Handler, pattern string) {
  2198  	// Check for exact match first.
  2199  	v, ok := mux.m[path]
  2200  	if ok {
  2201  		return v.h, v.pattern
  2202  	}
  2203  
  2204  	// Check for longest valid match.
  2205  	var n = 0
  2206  	for k, v := range mux.m {
  2207  		if !pathMatch(k, path) {
  2208  			continue
  2209  		}
  2210  		if h == nil || len(k) > n {
  2211  			n = len(k)
  2212  			h = v.h
  2213  			pattern = v.pattern
  2214  		}
  2215  	}
  2216  	return
  2217  }
  2218  
  2219  // redirectToPathSlash determines if the given path needs appending "/" to it.
  2220  // This occurs when a handler for path + "/" was already registered, but
  2221  // not for path itself. If the path needs appending to, it creates a new
  2222  // URL, setting the path to u.Path + "/" and returning true to indicate so.
  2223  func (mux *ServeMux) redirectToPathSlash(host, path string, u *url.URL) (*url.URL, bool) {
  2224  	if !mux.shouldRedirect(host, path) {
  2225  		return u, false
  2226  	}
  2227  	path = path + "/"
  2228  	u = &url.URL{Path: path, RawQuery: u.RawQuery}
  2229  	return u, true
  2230  }
  2231  
  2232  // shouldRedirect reports whether the given path and host should be redirected to
  2233  // path+"/". This should happen if a handler is registered for path+"/" but
  2234  // not path -- see comments at ServeMux.
  2235  func (mux *ServeMux) shouldRedirect(host, path string) bool {
  2236  	p := []string{path, host + path}
  2237  
  2238  	for _, c := range p {
  2239  		if _, exist := mux.m[c]; exist {
  2240  			return false
  2241  		}
  2242  	}
  2243  
  2244  	n := len(path)
  2245  	if n == 0 {
  2246  		return false
  2247  	}
  2248  	for _, c := range p {
  2249  		if _, exist := mux.m[c+"/"]; exist {
  2250  			return path[n-1] != '/'
  2251  		}
  2252  	}
  2253  
  2254  	return false
  2255  }
  2256  
  2257  // Handler returns the handler to use for the given request,
  2258  // consulting r.Method, r.Host, and r.URL.Path. It always returns
  2259  // a non-nil handler. If the path is not in its canonical form, the
  2260  // handler will be an internally-generated handler that redirects
  2261  // to the canonical path. If the host contains a port, it is ignored
  2262  // when matching handlers.
  2263  //
  2264  // The path and host are used unchanged for CONNECT requests.
  2265  //
  2266  // Handler also returns the registered pattern that matches the
  2267  // request or, in the case of internally-generated redirects,
  2268  // the pattern that will match after following the redirect.
  2269  //
  2270  // If there is no registered handler that applies to the request,
  2271  // Handler returns a ``page not found'' handler and an empty pattern.
  2272  func (mux *ServeMux) Handler(r *Request) (h Handler, pattern string) {
  2273  
  2274  	// CONNECT requests are not canonicalized.
  2275  	if r.Method == "CONNECT" {
  2276  		// If r.URL.Path is /tree and its handler is not registered,
  2277  		// the /tree -> /tree/ redirect applies to CONNECT requests
  2278  		// but the path canonicalization does not.
  2279  		if u, ok := mux.redirectToPathSlash(r.URL.Host, r.URL.Path, r.URL); ok {
  2280  			return RedirectHandler(u.String(), StatusMovedPermanently), u.Path
  2281  		}
  2282  
  2283  		return mux.handler(r.Host, r.URL.Path)
  2284  	}
  2285  
  2286  	// All other requests have any port stripped and path cleaned
  2287  	// before passing to mux.handler.
  2288  	host := stripHostPort(r.Host)
  2289  	path := cleanPath(r.URL.Path)
  2290  
  2291  	// If the given path is /tree and its handler is not registered,
  2292  	// redirect for /tree/.
  2293  	if u, ok := mux.redirectToPathSlash(host, path, r.URL); ok {
  2294  		return RedirectHandler(u.String(), StatusMovedPermanently), u.Path
  2295  	}
  2296  
  2297  	if path != r.URL.Path {
  2298  		_, pattern = mux.handler(host, path)
  2299  		url := *r.URL
  2300  		url.Path = path
  2301  		return RedirectHandler(url.String(), StatusMovedPermanently), pattern
  2302  	}
  2303  
  2304  	return mux.handler(host, r.URL.Path)
  2305  }
  2306  
  2307  // handler is the main implementation of Handler.
  2308  // The path is known to be in canonical form, except for CONNECT methods.
  2309  func (mux *ServeMux) handler(host, path string) (h Handler, pattern string) {
  2310  	mux.mu.RLock()
  2311  	defer mux.mu.RUnlock()
  2312  
  2313  	// Host-specific pattern takes precedence over generic ones
  2314  	if mux.hosts {
  2315  		h, pattern = mux.match(host + path)
  2316  	}
  2317  	if h == nil {
  2318  		h, pattern = mux.match(path)
  2319  	}
  2320  	if h == nil {
  2321  		h, pattern = NotFoundHandler(), ""
  2322  	}
  2323  	return
  2324  }
  2325  
  2326  // ServeHTTP dispatches the request to the handler whose
  2327  // pattern most closely matches the request URL.
  2328  func (mux *ServeMux) ServeHTTP(w ResponseWriter, r *Request) {
  2329  	if r.RequestURI == "*" {
  2330  		if r.ProtoAtLeast(1, 1) {
  2331  			w.Header().Set("Connection", "close")
  2332  		}
  2333  		w.WriteHeader(StatusBadRequest)
  2334  		return
  2335  	}
  2336  	h, _ := mux.Handler(r)
  2337  	h.ServeHTTP(w, r)
  2338  }
  2339  
  2340  // Handle registers the handler for the given pattern.
  2341  // If a handler already exists for pattern, Handle panics.
  2342  func (mux *ServeMux) Handle(pattern string, handler Handler) {
  2343  	mux.mu.Lock()
  2344  	defer mux.mu.Unlock()
  2345  
  2346  	if pattern == "" {
  2347  		panic("http: invalid pattern")
  2348  	}
  2349  	if handler == nil {
  2350  		panic("http: nil handler")
  2351  	}
  2352  	if _, exist := mux.m[pattern]; exist {
  2353  		panic("http: multiple registrations for " + pattern)
  2354  	}
  2355  
  2356  	if mux.m == nil {
  2357  		mux.m = make(map[string]muxEntry)
  2358  	}
  2359  	mux.m[pattern] = muxEntry{h: handler, pattern: pattern}
  2360  
  2361  	if pattern[0] != '/' {
  2362  		mux.hosts = true
  2363  	}
  2364  }
  2365  
  2366  // HandleFunc registers the handler function for the given pattern.
  2367  func (mux *ServeMux) HandleFunc(pattern string, handler func(ResponseWriter, *Request)) {
  2368  	mux.Handle(pattern, HandlerFunc(handler))
  2369  }
  2370  
  2371  // Handle registers the handler for the given pattern
  2372  // in the DefaultServeMux.
  2373  // The documentation for ServeMux explains how patterns are matched.
  2374  func Handle(pattern string, handler Handler) { DefaultServeMux.Handle(pattern, handler) }
  2375  
  2376  // HandleFunc registers the handler function for the given pattern
  2377  // in the DefaultServeMux.
  2378  // The documentation for ServeMux explains how patterns are matched.
  2379  func HandleFunc(pattern string, handler func(ResponseWriter, *Request)) {
  2380  	DefaultServeMux.HandleFunc(pattern, handler)
  2381  }
  2382  
  2383  // Serve accepts incoming HTTP connections on the listener l,
  2384  // creating a new service goroutine for each. The service goroutines
  2385  // read requests and then call handler to reply to them.
  2386  // Handler is typically nil, in which case the DefaultServeMux is used.
  2387  func Serve(l net.Listener, handler Handler) error {
  2388  	srv := &Server{Handler: handler}
  2389  	return srv.Serve(l)
  2390  }
  2391  
  2392  // ServeTLS accepts incoming HTTPS connections on the listener l,
  2393  // creating a new service goroutine for each. The service goroutines
  2394  // read requests and then call handler to reply to them.
  2395  //
  2396  // Handler is typically nil, in which case the DefaultServeMux is used.
  2397  //
  2398  // Additionally, files containing a certificate and matching private key
  2399  // for the server must be provided. If the certificate is signed by a
  2400  // certificate authority, the certFile should be the concatenation
  2401  // of the server's certificate, any intermediates, and the CA's certificate.
  2402  func ServeTLS(l net.Listener, handler Handler, certFile, keyFile string) error {
  2403  	srv := &Server{Handler: handler}
  2404  	return srv.ServeTLS(l, certFile, keyFile)
  2405  }
  2406  
  2407  // A Server defines parameters for running an HTTP server.
  2408  // The zero value for Server is a valid configuration.
  2409  type Server struct {
  2410  	Addr    string  // TCP address to listen on, ":http" if empty
  2411  	Handler Handler // handler to invoke, http.DefaultServeMux if nil
  2412  
  2413  	// TLSConfig optionally provides a TLS configuration for use
  2414  	// by ServeTLS and ListenAndServeTLS. Note that this value is
  2415  	// cloned by ServeTLS and ListenAndServeTLS, so it's not
  2416  	// possible to modify the configuration with methods like
  2417  	// tls.Config.SetSessionTicketKeys. To use
  2418  	// SetSessionTicketKeys, use Server.Serve with a TLS Listener
  2419  	// instead.
  2420  	TLSConfig *tls.Config
  2421  
  2422  	// ReadTimeout is the maximum duration for reading the entire
  2423  	// request, including the body.
  2424  	//
  2425  	// Because ReadTimeout does not let Handlers make per-request
  2426  	// decisions on each request body's acceptable deadline or
  2427  	// upload rate, most users will prefer to use
  2428  	// ReadHeaderTimeout. It is valid to use them both.
  2429  	ReadTimeout time.Duration
  2430  
  2431  	// ReadHeaderTimeout is the amount of time allowed to read
  2432  	// request headers. The connection's read deadline is reset
  2433  	// after reading the headers and the Handler can decide what
  2434  	// is considered too slow for the body.
  2435  	ReadHeaderTimeout time.Duration
  2436  
  2437  	// WriteTimeout is the maximum duration before timing out
  2438  	// writes of the response. It is reset whenever a new
  2439  	// request's header is read. Like ReadTimeout, it does not
  2440  	// let Handlers make decisions on a per-request basis.
  2441  	WriteTimeout time.Duration
  2442  
  2443  	// IdleTimeout is the maximum amount of time to wait for the
  2444  	// next request when keep-alives are enabled. If IdleTimeout
  2445  	// is zero, the value of ReadTimeout is used. If both are
  2446  	// zero, ReadHeaderTimeout is used.
  2447  	IdleTimeout time.Duration
  2448  
  2449  	// MaxHeaderBytes controls the maximum number of bytes the
  2450  	// server will read parsing the request header's keys and
  2451  	// values, including the request line. It does not limit the
  2452  	// size of the request body.
  2453  	// If zero, DefaultMaxHeaderBytes is used.
  2454  	MaxHeaderBytes int
  2455  
  2456  	// TLSNextProto optionally specifies a function to take over
  2457  	// ownership of the provided TLS connection when an NPN/ALPN
  2458  	// protocol upgrade has occurred. The map key is the protocol
  2459  	// name negotiated. The Handler argument should be used to
  2460  	// handle HTTP requests and will initialize the Request's TLS
  2461  	// and RemoteAddr if not already set. The connection is
  2462  	// automatically closed when the function returns.
  2463  	// If TLSNextProto is not nil, HTTP/2 support is not enabled
  2464  	// automatically.
  2465  	TLSNextProto map[string]func(*Server, *tls.Conn, Handler)
  2466  
  2467  	// ConnState specifies an optional callback function that is
  2468  	// called when a client connection changes state. See the
  2469  	// ConnState type and associated constants for details.
  2470  	ConnState func(net.Conn, ConnState)
  2471  
  2472  	// ErrorLog specifies an optional logger for errors accepting
  2473  	// connections, unexpected behavior from handlers, and
  2474  	// underlying FileSystem errors.
  2475  	// If nil, logging is done via the log package's standard logger.
  2476  	ErrorLog *log.Logger
  2477  
  2478  	disableKeepAlives int32     // accessed atomically.
  2479  	inShutdown        int32     // accessed atomically (non-zero means we're in Shutdown)
  2480  	nextProtoOnce     sync.Once // guards setupHTTP2_* init
  2481  	nextProtoErr      error     // result of http2.ConfigureServer if used
  2482  
  2483  	mu         sync.Mutex
  2484  	listeners  map[net.Listener]struct{}
  2485  	activeConn map[*conn]struct{}
  2486  	doneChan   chan struct{}
  2487  	onShutdown []func()
  2488  }
  2489  
  2490  func (s *Server) getDoneChan() <-chan struct{} {
  2491  	s.mu.Lock()
  2492  	defer s.mu.Unlock()
  2493  	return s.getDoneChanLocked()
  2494  }
  2495  
  2496  func (s *Server) getDoneChanLocked() chan struct{} {
  2497  	if s.doneChan == nil {
  2498  		s.doneChan = make(chan struct{})
  2499  	}
  2500  	return s.doneChan
  2501  }
  2502  
  2503  func (s *Server) closeDoneChanLocked() {
  2504  	ch := s.getDoneChanLocked()
  2505  	select {
  2506  	case <-ch:
  2507  		// Already closed. Don't close again.
  2508  	default:
  2509  		// Safe to close here. We're the only closer, guarded
  2510  		// by s.mu.
  2511  		close(ch)
  2512  	}
  2513  }
  2514  
  2515  // Close immediately closes all active net.Listeners and any
  2516  // connections in state StateNew, StateActive, or StateIdle. For a
  2517  // graceful shutdown, use Shutdown.
  2518  //
  2519  // Close does not attempt to close (and does not even know about)
  2520  // any hijacked connections, such as WebSockets.
  2521  //
  2522  // Close returns any error returned from closing the Server's
  2523  // underlying Listener(s).
  2524  func (srv *Server) Close() error {
  2525  	srv.mu.Lock()
  2526  	defer srv.mu.Unlock()
  2527  	srv.closeDoneChanLocked()
  2528  	err := srv.closeListenersLocked()
  2529  	for c := range srv.activeConn {
  2530  		c.rwc.Close()
  2531  		delete(srv.activeConn, c)
  2532  	}
  2533  	return err
  2534  }
  2535  
  2536  // shutdownPollInterval is how often we poll for quiescence
  2537  // during Server.Shutdown. This is lower during tests, to
  2538  // speed up tests.
  2539  // Ideally we could find a solution that doesn't involve polling,
  2540  // but which also doesn't have a high runtime cost (and doesn't
  2541  // involve any contentious mutexes), but that is left as an
  2542  // exercise for the reader.
  2543  var shutdownPollInterval = 500 * time.Millisecond
  2544  
  2545  // Shutdown gracefully shuts down the server without interrupting any
  2546  // active connections. Shutdown works by first closing all open
  2547  // listeners, then closing all idle connections, and then waiting
  2548  // indefinitely for connections to return to idle and then shut down.
  2549  // If the provided context expires before the shutdown is complete,
  2550  // Shutdown returns the context's error, otherwise it returns any
  2551  // error returned from closing the Server's underlying Listener(s).
  2552  //
  2553  // When Shutdown is called, Serve, ListenAndServe, and
  2554  // ListenAndServeTLS immediately return ErrServerClosed. Make sure the
  2555  // program doesn't exit and waits instead for Shutdown to return.
  2556  //
  2557  // Shutdown does not attempt to close nor wait for hijacked
  2558  // connections such as WebSockets. The caller of Shutdown should
  2559  // separately notify such long-lived connections of shutdown and wait
  2560  // for them to close, if desired. See RegisterOnShutdown for a way to
  2561  // register shutdown notification functions.
  2562  func (srv *Server) Shutdown(ctx context.Context) error {
  2563  	atomic.AddInt32(&srv.inShutdown, 1)
  2564  	defer atomic.AddInt32(&srv.inShutdown, -1)
  2565  
  2566  	srv.mu.Lock()
  2567  	lnerr := srv.closeListenersLocked()
  2568  	srv.closeDoneChanLocked()
  2569  	for _, f := range srv.onShutdown {
  2570  		go f()
  2571  	}
  2572  	srv.mu.Unlock()
  2573  
  2574  	ticker := time.NewTicker(shutdownPollInterval)
  2575  	defer ticker.Stop()
  2576  	for {
  2577  		if srv.closeIdleConns() {
  2578  			return lnerr
  2579  		}
  2580  		select {
  2581  		case <-ctx.Done():
  2582  			return ctx.Err()
  2583  		case <-ticker.C:
  2584  		}
  2585  	}
  2586  }
  2587  
  2588  // RegisterOnShutdown registers a function to call on Shutdown.
  2589  // This can be used to gracefully shutdown connections that have
  2590  // undergone NPN/ALPN protocol upgrade or that have been hijacked.
  2591  // This function should start protocol-specific graceful shutdown,
  2592  // but should not wait for shutdown to complete.
  2593  func (srv *Server) RegisterOnShutdown(f func()) {
  2594  	srv.mu.Lock()
  2595  	srv.onShutdown = append(srv.onShutdown, f)
  2596  	srv.mu.Unlock()
  2597  }
  2598  
  2599  // closeIdleConns closes all idle connections and reports whether the
  2600  // server is quiescent.
  2601  func (s *Server) closeIdleConns() bool {
  2602  	s.mu.Lock()
  2603  	defer s.mu.Unlock()
  2604  	quiescent := true
  2605  	for c := range s.activeConn {
  2606  		st, ok := c.curState.Load().(ConnState)
  2607  		if !ok || st != StateIdle {
  2608  			quiescent = false
  2609  			continue
  2610  		}
  2611  		c.rwc.Close()
  2612  		delete(s.activeConn, c)
  2613  	}
  2614  	return quiescent
  2615  }
  2616  
  2617  func (s *Server) closeListenersLocked() error {
  2618  	var err error
  2619  	for ln := range s.listeners {
  2620  		if cerr := ln.Close(); cerr != nil && err == nil {
  2621  			err = cerr
  2622  		}
  2623  		delete(s.listeners, ln)
  2624  	}
  2625  	return err
  2626  }
  2627  
  2628  // A ConnState represents the state of a client connection to a server.
  2629  // It's used by the optional Server.ConnState hook.
  2630  type ConnState int
  2631  
  2632  const (
  2633  	// StateNew represents a new connection that is expected to
  2634  	// send a request immediately. Connections begin at this
  2635  	// state and then transition to either StateActive or
  2636  	// StateClosed.
  2637  	StateNew ConnState = iota
  2638  
  2639  	// StateActive represents a connection that has read 1 or more
  2640  	// bytes of a request. The Server.ConnState hook for
  2641  	// StateActive fires before the request has entered a handler
  2642  	// and doesn't fire again until the request has been
  2643  	// handled. After the request is handled, the state
  2644  	// transitions to StateClosed, StateHijacked, or StateIdle.
  2645  	// For HTTP/2, StateActive fires on the transition from zero
  2646  	// to one active request, and only transitions away once all
  2647  	// active requests are complete. That means that ConnState
  2648  	// cannot be used to do per-request work; ConnState only notes
  2649  	// the overall state of the connection.
  2650  	StateActive
  2651  
  2652  	// StateIdle represents a connection that has finished
  2653  	// handling a request and is in the keep-alive state, waiting
  2654  	// for a new request. Connections transition from StateIdle
  2655  	// to either StateActive or StateClosed.
  2656  	StateIdle
  2657  
  2658  	// StateHijacked represents a hijacked connection.
  2659  	// This is a terminal state. It does not transition to StateClosed.
  2660  	StateHijacked
  2661  
  2662  	// StateClosed represents a closed connection.
  2663  	// This is a terminal state. Hijacked connections do not
  2664  	// transition to StateClosed.
  2665  	StateClosed
  2666  )
  2667  
  2668  var stateName = map[ConnState]string{
  2669  	StateNew:      "new",
  2670  	StateActive:   "active",
  2671  	StateIdle:     "idle",
  2672  	StateHijacked: "hijacked",
  2673  	StateClosed:   "closed",
  2674  }
  2675  
  2676  func (c ConnState) String() string {
  2677  	return stateName[c]
  2678  }
  2679  
  2680  // serverHandler delegates to either the server's Handler or
  2681  // DefaultServeMux and also handles "OPTIONS *" requests.
  2682  type serverHandler struct {
  2683  	srv *Server
  2684  }
  2685  
  2686  func (sh serverHandler) ServeHTTP(rw ResponseWriter, req *Request) {
  2687  	handler := sh.srv.Handler
  2688  	if handler == nil {
  2689  		handler = DefaultServeMux
  2690  	}
  2691  	if req.RequestURI == "*" && req.Method == "OPTIONS" {
  2692  		handler = globalOptionsHandler{}
  2693  	}
  2694  	handler.ServeHTTP(rw, req)
  2695  }
  2696  
  2697  // ListenAndServe listens on the TCP network address srv.Addr and then
  2698  // calls Serve to handle requests on incoming connections.
  2699  // Accepted connections are configured to enable TCP keep-alives.
  2700  // If srv.Addr is blank, ":http" is used.
  2701  // ListenAndServe always returns a non-nil error.
  2702  func (srv *Server) ListenAndServe() error {
  2703  	addr := srv.Addr
  2704  	if addr == "" {
  2705  		addr = ":http"
  2706  	}
  2707  	ln, err := net.Listen("tcp", addr)
  2708  	if err != nil {
  2709  		return err
  2710  	}
  2711  	return srv.Serve(tcpKeepAliveListener{ln.(*net.TCPListener)})
  2712  }
  2713  
  2714  var testHookServerServe func(*Server, net.Listener) // used if non-nil
  2715  
  2716  // shouldDoServeHTTP2 reports whether Server.Serve should configure
  2717  // automatic HTTP/2. (which sets up the srv.TLSNextProto map)
  2718  func (srv *Server) shouldConfigureHTTP2ForServe() bool {
  2719  	if srv.TLSConfig == nil {
  2720  		// Compatibility with Go 1.6:
  2721  		// If there's no TLSConfig, it's possible that the user just
  2722  		// didn't set it on the http.Server, but did pass it to
  2723  		// tls.NewListener and passed that listener to Serve.
  2724  		// So we should configure HTTP/2 (to set up srv.TLSNextProto)
  2725  		// in case the listener returns an "h2" *tls.Conn.
  2726  		return true
  2727  	}
  2728  	// The user specified a TLSConfig on their http.Server.
  2729  	// In this, case, only configure HTTP/2 if their tls.Config
  2730  	// explicitly mentions "h2". Otherwise http2.ConfigureServer
  2731  	// would modify the tls.Config to add it, but they probably already
  2732  	// passed this tls.Config to tls.NewListener. And if they did,
  2733  	// it's too late anyway to fix it. It would only be potentially racy.
  2734  	// See Issue 15908.
  2735  	return strSliceContains(srv.TLSConfig.NextProtos, http2NextProtoTLS)
  2736  }
  2737  
  2738  // ErrServerClosed is returned by the Server's Serve, ServeTLS, ListenAndServe,
  2739  // and ListenAndServeTLS methods after a call to Shutdown or Close.
  2740  var ErrServerClosed = errors.New("http: Server closed")
  2741  
  2742  // Serve accepts incoming connections on the Listener l, creating a
  2743  // new service goroutine for each. The service goroutines read requests and
  2744  // then call srv.Handler to reply to them.
  2745  //
  2746  // For HTTP/2 support, srv.TLSConfig should be initialized to the
  2747  // provided listener's TLS Config before calling Serve. If
  2748  // srv.TLSConfig is non-nil and doesn't include the string "h2" in
  2749  // Config.NextProtos, HTTP/2 support is not enabled.
  2750  //
  2751  // Serve always returns a non-nil error. After Shutdown or Close, the
  2752  // returned error is ErrServerClosed.
  2753  func (srv *Server) Serve(l net.Listener) error {
  2754  	defer l.Close()
  2755  	if fn := testHookServerServe; fn != nil {
  2756  		fn(srv, l)
  2757  	}
  2758  	var tempDelay time.Duration // how long to sleep on accept failure
  2759  
  2760  	if err := srv.setupHTTP2_Serve(); err != nil {
  2761  		return err
  2762  	}
  2763  
  2764  	srv.trackListener(l, true)
  2765  	defer srv.trackListener(l, false)
  2766  
  2767  	baseCtx := context.Background() // base is always background, per Issue 16220
  2768  	ctx := context.WithValue(baseCtx, ServerContextKey, srv)
  2769  	for {
  2770  		rw, e := l.Accept()
  2771  		if e != nil {
  2772  			select {
  2773  			case <-srv.getDoneChan():
  2774  				return ErrServerClosed
  2775  			default:
  2776  			}
  2777  			if ne, ok := e.(net.Error); ok && ne.Temporary() {
  2778  				if tempDelay == 0 {
  2779  					tempDelay = 5 * time.Millisecond
  2780  				} else {
  2781  					tempDelay *= 2
  2782  				}
  2783  				if max := 1 * time.Second; tempDelay > max {
  2784  					tempDelay = max
  2785  				}
  2786  				srv.logf("http: Accept error: %v; retrying in %v", e, tempDelay)
  2787  				time.Sleep(tempDelay)
  2788  				continue
  2789  			}
  2790  			return e
  2791  		}
  2792  		tempDelay = 0
  2793  		c := srv.newConn(rw)
  2794  		c.setState(c.rwc, StateNew) // before Serve can return
  2795  		go c.serve(ctx)
  2796  	}
  2797  }
  2798  
  2799  // ServeTLS accepts incoming connections on the Listener l, creating a
  2800  // new service goroutine for each. The service goroutines read requests and
  2801  // then call srv.Handler to reply to them.
  2802  //
  2803  // Additionally, files containing a certificate and matching private key for
  2804  // the server must be provided if neither the Server's TLSConfig.Certificates
  2805  // nor TLSConfig.GetCertificate are populated.. If the certificate is signed by
  2806  // a certificate authority, the certFile should be the concatenation of the
  2807  // server's certificate, any intermediates, and the CA's certificate.
  2808  //
  2809  // For HTTP/2 support, srv.TLSConfig should be initialized to the
  2810  // provided listener's TLS Config before calling ServeTLS. If
  2811  // srv.TLSConfig is non-nil and doesn't include the string "h2" in
  2812  // Config.NextProtos, HTTP/2 support is not enabled.
  2813  //
  2814  // ServeTLS always returns a non-nil error. After Shutdown or Close, the
  2815  // returned error is ErrServerClosed.
  2816  func (srv *Server) ServeTLS(l net.Listener, certFile, keyFile string) error {
  2817  	// Setup HTTP/2 before srv.Serve, to initialize srv.TLSConfig
  2818  	// before we clone it and create the TLS Listener.
  2819  	if err := srv.setupHTTP2_ServeTLS(); err != nil {
  2820  		return err
  2821  	}
  2822  
  2823  	config := cloneTLSConfig(srv.TLSConfig)
  2824  	if !strSliceContains(config.NextProtos, "http/1.1") {
  2825  		config.NextProtos = append(config.NextProtos, "http/1.1")
  2826  	}
  2827  
  2828  	configHasCert := len(config.Certificates) > 0 || config.GetCertificate != nil
  2829  	if !configHasCert || certFile != "" || keyFile != "" {
  2830  		var err error
  2831  		config.Certificates = make([]tls.Certificate, 1)
  2832  		config.Certificates[0], err = tls.LoadX509KeyPair(certFile, keyFile)
  2833  		if err != nil {
  2834  			return err
  2835  		}
  2836  	}
  2837  
  2838  	tlsListener := tls.NewListener(l, config)
  2839  	return srv.Serve(tlsListener)
  2840  }
  2841  
  2842  func (s *Server) trackListener(ln net.Listener, add bool) {
  2843  	s.mu.Lock()
  2844  	defer s.mu.Unlock()
  2845  	if s.listeners == nil {
  2846  		s.listeners = make(map[net.Listener]struct{})
  2847  	}
  2848  	if add {
  2849  		// If the *Server is being reused after a previous
  2850  		// Close or Shutdown, reset its doneChan:
  2851  		if len(s.listeners) == 0 && len(s.activeConn) == 0 {
  2852  			s.doneChan = nil
  2853  		}
  2854  		s.listeners[ln] = struct{}{}
  2855  	} else {
  2856  		delete(s.listeners, ln)
  2857  	}
  2858  }
  2859  
  2860  func (s *Server) trackConn(c *conn, add bool) {
  2861  	s.mu.Lock()
  2862  	defer s.mu.Unlock()
  2863  	if s.activeConn == nil {
  2864  		s.activeConn = make(map[*conn]struct{})
  2865  	}
  2866  	if add {
  2867  		s.activeConn[c] = struct{}{}
  2868  	} else {
  2869  		delete(s.activeConn, c)
  2870  	}
  2871  }
  2872  
  2873  func (s *Server) idleTimeout() time.Duration {
  2874  	if s.IdleTimeout != 0 {
  2875  		return s.IdleTimeout
  2876  	}
  2877  	return s.ReadTimeout
  2878  }
  2879  
  2880  func (s *Server) readHeaderTimeout() time.Duration {
  2881  	if s.ReadHeaderTimeout != 0 {
  2882  		return s.ReadHeaderTimeout
  2883  	}
  2884  	return s.ReadTimeout
  2885  }
  2886  
  2887  func (s *Server) doKeepAlives() bool {
  2888  	return atomic.LoadInt32(&s.disableKeepAlives) == 0 && !s.shuttingDown()
  2889  }
  2890  
  2891  func (s *Server) shuttingDown() bool {
  2892  	return atomic.LoadInt32(&s.inShutdown) != 0
  2893  }
  2894  
  2895  // SetKeepAlivesEnabled controls whether HTTP keep-alives are enabled.
  2896  // By default, keep-alives are always enabled. Only very
  2897  // resource-constrained environments or servers in the process of
  2898  // shutting down should disable them.
  2899  func (srv *Server) SetKeepAlivesEnabled(v bool) {
  2900  	if v {
  2901  		atomic.StoreInt32(&srv.disableKeepAlives, 0)
  2902  		return
  2903  	}
  2904  	atomic.StoreInt32(&srv.disableKeepAlives, 1)
  2905  
  2906  	// Close idle HTTP/1 conns:
  2907  	srv.closeIdleConns()
  2908  
  2909  	// Close HTTP/2 conns, as soon as they become idle, but reset
  2910  	// the chan so future conns (if the listener is still active)
  2911  	// still work and don't get a GOAWAY immediately, before their
  2912  	// first request:
  2913  	srv.mu.Lock()
  2914  	defer srv.mu.Unlock()
  2915  	srv.closeDoneChanLocked() // closes http2 conns
  2916  	srv.doneChan = nil
  2917  }
  2918  
  2919  func (s *Server) logf(format string, args ...interface{}) {
  2920  	if s.ErrorLog != nil {
  2921  		s.ErrorLog.Printf(format, args...)
  2922  	} else {
  2923  		log.Printf(format, args...)
  2924  	}
  2925  }
  2926  
  2927  // logf prints to the ErrorLog of the *Server associated with request r
  2928  // via ServerContextKey. If there's no associated server, or if ErrorLog
  2929  // is nil, logging is done via the log package's standard logger.
  2930  func logf(r *Request, format string, args ...interface{}) {
  2931  	s, _ := r.Context().Value(ServerContextKey).(*Server)
  2932  	if s != nil && s.ErrorLog != nil {
  2933  		s.ErrorLog.Printf(format, args...)
  2934  	} else {
  2935  		log.Printf(format, args...)
  2936  	}
  2937  }
  2938  
  2939  // ListenAndServe listens on the TCP network address addr
  2940  // and then calls Serve with handler to handle requests
  2941  // on incoming connections.
  2942  // Accepted connections are configured to enable TCP keep-alives.
  2943  // Handler is typically nil, in which case the DefaultServeMux is
  2944  // used.
  2945  //
  2946  // A trivial example server is:
  2947  //
  2948  //	package main
  2949  //
  2950  //	import (
  2951  //		"io"
  2952  //		"net/http"
  2953  //		"log"
  2954  //	)
  2955  //
  2956  //	// hello world, the web server
  2957  //	func HelloServer(w http.ResponseWriter, req *http.Request) {
  2958  //		io.WriteString(w, "hello, world!\n")
  2959  //	}
  2960  //
  2961  //	func main() {
  2962  //		http.HandleFunc("/hello", HelloServer)
  2963  //		log.Fatal(http.ListenAndServe(":12345", nil))
  2964  //	}
  2965  //
  2966  // ListenAndServe always returns a non-nil error.
  2967  func ListenAndServe(addr string, handler Handler) error {
  2968  	server := &Server{Addr: addr, Handler: handler}
  2969  	return server.ListenAndServe()
  2970  }
  2971  
  2972  // ListenAndServeTLS acts identically to ListenAndServe, except that it
  2973  // expects HTTPS connections. Additionally, files containing a certificate and
  2974  // matching private key for the server must be provided. If the certificate
  2975  // is signed by a certificate authority, the certFile should be the concatenation
  2976  // of the server's certificate, any intermediates, and the CA's certificate.
  2977  //
  2978  // A trivial example server is:
  2979  //
  2980  //	import (
  2981  //		"log"
  2982  //		"net/http"
  2983  //	)
  2984  //
  2985  //	func handler(w http.ResponseWriter, req *http.Request) {
  2986  //		w.Header().Set("Content-Type", "text/plain")
  2987  //		w.Write([]byte("This is an example server.\n"))
  2988  //	}
  2989  //
  2990  //	func main() {
  2991  //		http.HandleFunc("/", handler)
  2992  //		log.Printf("About to listen on 10443. Go to https://127.0.0.1:10443/")
  2993  //		err := http.ListenAndServeTLS(":10443", "cert.pem", "key.pem", nil)
  2994  //		log.Fatal(err)
  2995  //	}
  2996  //
  2997  // One can use generate_cert.go in crypto/tls to generate cert.pem and key.pem.
  2998  //
  2999  // ListenAndServeTLS always returns a non-nil error.
  3000  func ListenAndServeTLS(addr, certFile, keyFile string, handler Handler) error {
  3001  	server := &Server{Addr: addr, Handler: handler}
  3002  	return server.ListenAndServeTLS(certFile, keyFile)
  3003  }
  3004  
  3005  // ListenAndServeTLS listens on the TCP network address srv.Addr and
  3006  // then calls Serve to handle requests on incoming TLS connections.
  3007  // Accepted connections are configured to enable TCP keep-alives.
  3008  //
  3009  // Filenames containing a certificate and matching private key for the
  3010  // server must be provided if neither the Server's TLSConfig.Certificates
  3011  // nor TLSConfig.GetCertificate are populated. If the certificate is
  3012  // signed by a certificate authority, the certFile should be the
  3013  // concatenation of the server's certificate, any intermediates, and
  3014  // the CA's certificate.
  3015  //
  3016  // If srv.Addr is blank, ":https" is used.
  3017  //
  3018  // ListenAndServeTLS always returns a non-nil error.
  3019  func (srv *Server) ListenAndServeTLS(certFile, keyFile string) error {
  3020  	addr := srv.Addr
  3021  	if addr == "" {
  3022  		addr = ":https"
  3023  	}
  3024  
  3025  	ln, err := net.Listen("tcp", addr)
  3026  	if err != nil {
  3027  		return err
  3028  	}
  3029  
  3030  	defer ln.Close()
  3031  
  3032  	return srv.ServeTLS(tcpKeepAliveListener{ln.(*net.TCPListener)}, certFile, keyFile)
  3033  }
  3034  
  3035  // setupHTTP2_ServeTLS conditionally configures HTTP/2 on
  3036  // srv and returns whether there was an error setting it up. If it is
  3037  // not configured for policy reasons, nil is returned.
  3038  func (srv *Server) setupHTTP2_ServeTLS() error {
  3039  	srv.nextProtoOnce.Do(srv.onceSetNextProtoDefaults)
  3040  	return srv.nextProtoErr
  3041  }
  3042  
  3043  // setupHTTP2_Serve is called from (*Server).Serve and conditionally
  3044  // configures HTTP/2 on srv using a more conservative policy than
  3045  // setupHTTP2_ServeTLS because Serve may be called
  3046  // concurrently.
  3047  //
  3048  // The tests named TestTransportAutomaticHTTP2* and
  3049  // TestConcurrentServerServe in server_test.go demonstrate some
  3050  // of the supported use cases and motivations.
  3051  func (srv *Server) setupHTTP2_Serve() error {
  3052  	srv.nextProtoOnce.Do(srv.onceSetNextProtoDefaults_Serve)
  3053  	return srv.nextProtoErr
  3054  }
  3055  
  3056  func (srv *Server) onceSetNextProtoDefaults_Serve() {
  3057  	if srv.shouldConfigureHTTP2ForServe() {
  3058  		srv.onceSetNextProtoDefaults()
  3059  	}
  3060  }
  3061  
  3062  // onceSetNextProtoDefaults configures HTTP/2, if the user hasn't
  3063  // configured otherwise. (by setting srv.TLSNextProto non-nil)
  3064  // It must only be called via srv.nextProtoOnce (use srv.setupHTTP2_*).
  3065  func (srv *Server) onceSetNextProtoDefaults() {
  3066  	if strings.Contains(os.Getenv("GODEBUG"), "http2server=0") {
  3067  		return
  3068  	}
  3069  	// Enable HTTP/2 by default if the user hasn't otherwise
  3070  	// configured their TLSNextProto map.
  3071  	if srv.TLSNextProto == nil {
  3072  		conf := &http2Server{
  3073  			NewWriteScheduler: func() http2WriteScheduler { return http2NewPriorityWriteScheduler(nil) },
  3074  		}
  3075  		srv.nextProtoErr = http2ConfigureServer(srv, conf)
  3076  	}
  3077  }
  3078  
  3079  // TimeoutHandler returns a Handler that runs h with the given time limit.
  3080  //
  3081  // The new Handler calls h.ServeHTTP to handle each request, but if a
  3082  // call runs for longer than its time limit, the handler responds with
  3083  // a 503 Service Unavailable error and the given message in its body.
  3084  // (If msg is empty, a suitable default message will be sent.)
  3085  // After such a timeout, writes by h to its ResponseWriter will return
  3086  // ErrHandlerTimeout.
  3087  //
  3088  // TimeoutHandler buffers all Handler writes to memory and does not
  3089  // support the Hijacker or Flusher interfaces.
  3090  func TimeoutHandler(h Handler, dt time.Duration, msg string) Handler {
  3091  	return &timeoutHandler{
  3092  		handler: h,
  3093  		body:    msg,
  3094  		dt:      dt,
  3095  	}
  3096  }
  3097  
  3098  // ErrHandlerTimeout is returned on ResponseWriter Write calls
  3099  // in handlers which have timed out.
  3100  var ErrHandlerTimeout = errors.New("http: Handler timeout")
  3101  
  3102  type timeoutHandler struct {
  3103  	handler Handler
  3104  	body    string
  3105  	dt      time.Duration
  3106  
  3107  	// When set, no context will be created and this context will
  3108  	// be used instead.
  3109  	testContext context.Context
  3110  }
  3111  
  3112  func (h *timeoutHandler) errorBody() string {
  3113  	if h.body != "" {
  3114  		return h.body
  3115  	}
  3116  	return "<html><head><title>Timeout</title></head><body><h1>Timeout</h1></body></html>"
  3117  }
  3118  
  3119  func (h *timeoutHandler) ServeHTTP(w ResponseWriter, r *Request) {
  3120  	ctx := h.testContext
  3121  	if ctx == nil {
  3122  		var cancelCtx context.CancelFunc
  3123  		ctx, cancelCtx = context.WithTimeout(r.Context(), h.dt)
  3124  		defer cancelCtx()
  3125  	}
  3126  	r = r.WithContext(ctx)
  3127  	done := make(chan struct{})
  3128  	tw := &timeoutWriter{
  3129  		w: w,
  3130  		h: make(Header),
  3131  	}
  3132  	panicChan := make(chan interface{}, 1)
  3133  	go func() {
  3134  		defer func() {
  3135  			if p := recover(); p != nil {
  3136  				panicChan <- p
  3137  			}
  3138  		}()
  3139  		h.handler.ServeHTTP(tw, r)
  3140  		close(done)
  3141  	}()
  3142  	select {
  3143  	case p := <-panicChan:
  3144  		panic(p)
  3145  	case <-done:
  3146  		tw.mu.Lock()
  3147  		defer tw.mu.Unlock()
  3148  		dst := w.Header()
  3149  		for k, vv := range tw.h {
  3150  			dst[k] = vv
  3151  		}
  3152  		if !tw.wroteHeader {
  3153  			tw.code = StatusOK
  3154  		}
  3155  		w.WriteHeader(tw.code)
  3156  		w.Write(tw.wbuf.Bytes())
  3157  	case <-ctx.Done():
  3158  		tw.mu.Lock()
  3159  		defer tw.mu.Unlock()
  3160  		w.WriteHeader(StatusServiceUnavailable)
  3161  		io.WriteString(w, h.errorBody())
  3162  		tw.timedOut = true
  3163  		return
  3164  	}
  3165  }
  3166  
  3167  type timeoutWriter struct {
  3168  	w    ResponseWriter
  3169  	h    Header
  3170  	wbuf bytes.Buffer
  3171  
  3172  	mu          sync.Mutex
  3173  	timedOut    bool
  3174  	wroteHeader bool
  3175  	code        int
  3176  }
  3177  
  3178  func (tw *timeoutWriter) Header() Header { return tw.h }
  3179  
  3180  func (tw *timeoutWriter) Write(p []byte) (int, error) {
  3181  	tw.mu.Lock()
  3182  	defer tw.mu.Unlock()
  3183  	if tw.timedOut {
  3184  		return 0, ErrHandlerTimeout
  3185  	}
  3186  	if !tw.wroteHeader {
  3187  		tw.writeHeader(StatusOK)
  3188  	}
  3189  	return tw.wbuf.Write(p)
  3190  }
  3191  
  3192  func (tw *timeoutWriter) WriteHeader(code int) {
  3193  	checkWriteHeaderCode(code)
  3194  	tw.mu.Lock()
  3195  	defer tw.mu.Unlock()
  3196  	if tw.timedOut || tw.wroteHeader {
  3197  		return
  3198  	}
  3199  	tw.writeHeader(code)
  3200  }
  3201  
  3202  func (tw *timeoutWriter) writeHeader(code int) {
  3203  	tw.wroteHeader = true
  3204  	tw.code = code
  3205  }
  3206  
  3207  // tcpKeepAliveListener sets TCP keep-alive timeouts on accepted
  3208  // connections. It's used by ListenAndServe and ListenAndServeTLS so
  3209  // dead TCP connections (e.g. closing laptop mid-download) eventually
  3210  // go away.
  3211  type tcpKeepAliveListener struct {
  3212  	*net.TCPListener
  3213  }
  3214  
  3215  func (ln tcpKeepAliveListener) Accept() (net.Conn, error) {
  3216  	tc, err := ln.AcceptTCP()
  3217  	if err != nil {
  3218  		return nil, err
  3219  	}
  3220  	tc.SetKeepAlive(true)
  3221  	tc.SetKeepAlivePeriod(3 * time.Minute)
  3222  	return tc, nil
  3223  }
  3224  
  3225  // globalOptionsHandler responds to "OPTIONS *" requests.
  3226  type globalOptionsHandler struct{}
  3227  
  3228  func (globalOptionsHandler) ServeHTTP(w ResponseWriter, r *Request) {
  3229  	w.Header().Set("Content-Length", "0")
  3230  	if r.ContentLength != 0 {
  3231  		// Read up to 4KB of OPTIONS body (as mentioned in the
  3232  		// spec as being reserved for future use), but anything
  3233  		// over that is considered a waste of server resources
  3234  		// (or an attack) and we abort and close the connection,
  3235  		// courtesy of MaxBytesReader's EOF behavior.
  3236  		mb := MaxBytesReader(w, r.Body, 4<<10)
  3237  		io.Copy(ioutil.Discard, mb)
  3238  	}
  3239  }
  3240  
  3241  // initNPNRequest is an HTTP handler that initializes certain
  3242  // uninitialized fields in its *Request. Such partially-initialized
  3243  // Requests come from NPN protocol handlers.
  3244  type initNPNRequest struct {
  3245  	c *tls.Conn
  3246  	h serverHandler
  3247  }
  3248  
  3249  func (h initNPNRequest) ServeHTTP(rw ResponseWriter, req *Request) {
  3250  	if req.TLS == nil {
  3251  		req.TLS = &tls.ConnectionState{}
  3252  		*req.TLS = h.c.ConnectionState()
  3253  	}
  3254  	if req.Body == nil {
  3255  		req.Body = NoBody
  3256  	}
  3257  	if req.RemoteAddr == "" {
  3258  		req.RemoteAddr = h.c.RemoteAddr().String()
  3259  	}
  3260  	h.h.ServeHTTP(rw, req)
  3261  }
  3262  
  3263  // loggingConn is used for debugging.
  3264  type loggingConn struct {
  3265  	name string
  3266  	net.Conn
  3267  }
  3268  
  3269  var (
  3270  	uniqNameMu   sync.Mutex
  3271  	uniqNameNext = make(map[string]int)
  3272  )
  3273  
  3274  func newLoggingConn(baseName string, c net.Conn) net.Conn {
  3275  	uniqNameMu.Lock()
  3276  	defer uniqNameMu.Unlock()
  3277  	uniqNameNext[baseName]++
  3278  	return &loggingConn{
  3279  		name: fmt.Sprintf("%s-%d", baseName, uniqNameNext[baseName]),
  3280  		Conn: c,
  3281  	}
  3282  }
  3283  
  3284  func (c *loggingConn) Write(p []byte) (n int, err error) {
  3285  	log.Printf("%s.Write(%d) = ....", c.name, len(p))
  3286  	n, err = c.Conn.Write(p)
  3287  	log.Printf("%s.Write(%d) = %d, %v", c.name, len(p), n, err)
  3288  	return
  3289  }
  3290  
  3291  func (c *loggingConn) Read(p []byte) (n int, err error) {
  3292  	log.Printf("%s.Read(%d) = ....", c.name, len(p))
  3293  	n, err = c.Conn.Read(p)
  3294  	log.Printf("%s.Read(%d) = %d, %v", c.name, len(p), n, err)
  3295  	return
  3296  }
  3297  
  3298  func (c *loggingConn) Close() (err error) {
  3299  	log.Printf("%s.Close() = ...", c.name)
  3300  	err = c.Conn.Close()
  3301  	log.Printf("%s.Close() = %v", c.name, err)
  3302  	return
  3303  }
  3304  
  3305  // checkConnErrorWriter writes to c.rwc and records any write errors to c.werr.
  3306  // It only contains one field (and a pointer field at that), so it
  3307  // fits in an interface value without an extra allocation.
  3308  type checkConnErrorWriter struct {
  3309  	c *conn
  3310  }
  3311  
  3312  func (w checkConnErrorWriter) Write(p []byte) (n int, err error) {
  3313  	n, err = w.c.rwc.Write(p)
  3314  	if err != nil && w.c.werr == nil {
  3315  		w.c.werr = err
  3316  		w.c.cancelCtx()
  3317  	}
  3318  	return
  3319  }
  3320  
  3321  func numLeadingCRorLF(v []byte) (n int) {
  3322  	for _, b := range v {
  3323  		if b == '\r' || b == '\n' {
  3324  			n++
  3325  			continue
  3326  		}
  3327  		break
  3328  	}
  3329  	return
  3330  
  3331  }
  3332  
  3333  func strSliceContains(ss []string, s string) bool {
  3334  	for _, v := range ss {
  3335  		if v == s {
  3336  			return true
  3337  		}
  3338  	}
  3339  	return false
  3340  }
  3341  

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