Source file src/net/http/transfer.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  package http
     6  
     7  import (
     8  	"bufio"
     9  	"bytes"
    10  	"errors"
    11  	"fmt"
    12  	"io"
    13  	"io/ioutil"
    14  	"net/http/internal"
    15  	"net/textproto"
    16  	"sort"
    17  	"strconv"
    18  	"strings"
    19  	"sync"
    20  	"time"
    21  
    22  	"golang_org/x/net/lex/httplex"
    23  )
    24  
    25  // ErrLineTooLong is returned when reading request or response bodies
    26  // with malformed chunked encoding.
    27  var ErrLineTooLong = internal.ErrLineTooLong
    28  
    29  type errorReader struct {
    30  	err error
    31  }
    32  
    33  func (r errorReader) Read(p []byte) (n int, err error) {
    34  	return 0, r.err
    35  }
    36  
    37  type byteReader struct {
    38  	b    byte
    39  	done bool
    40  }
    41  
    42  func (br *byteReader) Read(p []byte) (n int, err error) {
    43  	if br.done {
    44  		return 0, io.EOF
    45  	}
    46  	if len(p) == 0 {
    47  		return 0, nil
    48  	}
    49  	br.done = true
    50  	p[0] = br.b
    51  	return 1, io.EOF
    52  }
    53  
    54  // transferBodyReader is an io.Reader that reads from tw.Body
    55  // and records any non-EOF error in tw.bodyReadError.
    56  // It is exactly 1 pointer wide to avoid allocations into interfaces.
    57  type transferBodyReader struct{ tw *transferWriter }
    58  
    59  func (br transferBodyReader) Read(p []byte) (n int, err error) {
    60  	n, err = br.tw.Body.Read(p)
    61  	if err != nil && err != io.EOF {
    62  		br.tw.bodyReadError = err
    63  	}
    64  	return
    65  }
    66  
    67  // transferWriter inspects the fields of a user-supplied Request or Response,
    68  // sanitizes them without changing the user object and provides methods for
    69  // writing the respective header, body and trailer in wire format.
    70  type transferWriter struct {
    71  	Method           string
    72  	Body             io.Reader
    73  	BodyCloser       io.Closer
    74  	ResponseToHEAD   bool
    75  	ContentLength    int64 // -1 means unknown, 0 means exactly none
    76  	Close            bool
    77  	TransferEncoding []string
    78  	Header           Header
    79  	Trailer          Header
    80  	IsResponse       bool
    81  	bodyReadError    error // any non-EOF error from reading Body
    82  
    83  	FlushHeaders bool            // flush headers to network before body
    84  	ByteReadCh   chan readResult // non-nil if probeRequestBody called
    85  }
    86  
    87  func newTransferWriter(r interface{}) (t *transferWriter, err error) {
    88  	t = &transferWriter{}
    89  
    90  	// Extract relevant fields
    91  	atLeastHTTP11 := false
    92  	switch rr := r.(type) {
    93  	case *Request:
    94  		if rr.ContentLength != 0 && rr.Body == nil {
    95  			return nil, fmt.Errorf("http: Request.ContentLength=%d with nil Body", rr.ContentLength)
    96  		}
    97  		t.Method = valueOrDefault(rr.Method, "GET")
    98  		t.Close = rr.Close
    99  		t.TransferEncoding = rr.TransferEncoding
   100  		t.Header = rr.Header
   101  		t.Trailer = rr.Trailer
   102  		t.Body = rr.Body
   103  		t.BodyCloser = rr.Body
   104  		t.ContentLength = rr.outgoingLength()
   105  		if t.ContentLength < 0 && len(t.TransferEncoding) == 0 && t.shouldSendChunkedRequestBody() {
   106  			t.TransferEncoding = []string{"chunked"}
   107  		}
   108  		atLeastHTTP11 = true // Transport requests are always 1.1 or 2.0
   109  	case *Response:
   110  		t.IsResponse = true
   111  		if rr.Request != nil {
   112  			t.Method = rr.Request.Method
   113  		}
   114  		t.Body = rr.Body
   115  		t.BodyCloser = rr.Body
   116  		t.ContentLength = rr.ContentLength
   117  		t.Close = rr.Close
   118  		t.TransferEncoding = rr.TransferEncoding
   119  		t.Header = rr.Header
   120  		t.Trailer = rr.Trailer
   121  		atLeastHTTP11 = rr.ProtoAtLeast(1, 1)
   122  		t.ResponseToHEAD = noResponseBodyExpected(t.Method)
   123  	}
   124  
   125  	// Sanitize Body,ContentLength,TransferEncoding
   126  	if t.ResponseToHEAD {
   127  		t.Body = nil
   128  		if chunked(t.TransferEncoding) {
   129  			t.ContentLength = -1
   130  		}
   131  	} else {
   132  		if !atLeastHTTP11 || t.Body == nil {
   133  			t.TransferEncoding = nil
   134  		}
   135  		if chunked(t.TransferEncoding) {
   136  			t.ContentLength = -1
   137  		} else if t.Body == nil { // no chunking, no body
   138  			t.ContentLength = 0
   139  		}
   140  	}
   141  
   142  	// Sanitize Trailer
   143  	if !chunked(t.TransferEncoding) {
   144  		t.Trailer = nil
   145  	}
   146  
   147  	return t, nil
   148  }
   149  
   150  // shouldSendChunkedRequestBody reports whether we should try to send a
   151  // chunked request body to the server. In particular, the case we really
   152  // want to prevent is sending a GET or other typically-bodyless request to a
   153  // server with a chunked body when the body has zero bytes, since GETs with
   154  // bodies (while acceptable according to specs), even zero-byte chunked
   155  // bodies, are approximately never seen in the wild and confuse most
   156  // servers. See Issue 18257, as one example.
   157  //
   158  // The only reason we'd send such a request is if the user set the Body to a
   159  // non-nil value (say, ioutil.NopCloser(bytes.NewReader(nil))) and didn't
   160  // set ContentLength, or NewRequest set it to -1 (unknown), so then we assume
   161  // there's bytes to send.
   162  //
   163  // This code tries to read a byte from the Request.Body in such cases to see
   164  // whether the body actually has content (super rare) or is actually just
   165  // a non-nil content-less ReadCloser (the more common case). In that more
   166  // common case, we act as if their Body were nil instead, and don't send
   167  // a body.
   168  func (t *transferWriter) shouldSendChunkedRequestBody() bool {
   169  	// Note that t.ContentLength is the corrected content length
   170  	// from rr.outgoingLength, so 0 actually means zero, not unknown.
   171  	if t.ContentLength >= 0 || t.Body == nil { // redundant checks; caller did them
   172  		return false
   173  	}
   174  	if requestMethodUsuallyLacksBody(t.Method) {
   175  		// Only probe the Request.Body for GET/HEAD/DELETE/etc
   176  		// requests, because it's only those types of requests
   177  		// that confuse servers.
   178  		t.probeRequestBody() // adjusts t.Body, t.ContentLength
   179  		return t.Body != nil
   180  	}
   181  	// For all other request types (PUT, POST, PATCH, or anything
   182  	// made-up we've never heard of), assume it's normal and the server
   183  	// can deal with a chunked request body. Maybe we'll adjust this
   184  	// later.
   185  	return true
   186  }
   187  
   188  // probeRequestBody reads a byte from t.Body to see whether it's empty
   189  // (returns io.EOF right away).
   190  //
   191  // But because we've had problems with this blocking users in the past
   192  // (issue 17480) when the body is a pipe (perhaps waiting on the response
   193  // headers before the pipe is fed data), we need to be careful and bound how
   194  // long we wait for it. This delay will only affect users if all the following
   195  // are true:
   196  //   * the request body blocks
   197  //   * the content length is not set (or set to -1)
   198  //   * the method doesn't usually have a body (GET, HEAD, DELETE, ...)
   199  //   * there is no transfer-encoding=chunked already set.
   200  // In other words, this delay will not normally affect anybody, and there
   201  // are workarounds if it does.
   202  func (t *transferWriter) probeRequestBody() {
   203  	t.ByteReadCh = make(chan readResult, 1)
   204  	go func(body io.Reader) {
   205  		var buf [1]byte
   206  		var rres readResult
   207  		rres.n, rres.err = body.Read(buf[:])
   208  		if rres.n == 1 {
   209  			rres.b = buf[0]
   210  		}
   211  		t.ByteReadCh <- rres
   212  	}(t.Body)
   213  	timer := time.NewTimer(200 * time.Millisecond)
   214  	select {
   215  	case rres := <-t.ByteReadCh:
   216  		timer.Stop()
   217  		if rres.n == 0 && rres.err == io.EOF {
   218  			// It was empty.
   219  			t.Body = nil
   220  			t.ContentLength = 0
   221  		} else if rres.n == 1 {
   222  			if rres.err != nil {
   223  				t.Body = io.MultiReader(&byteReader{b: rres.b}, errorReader{rres.err})
   224  			} else {
   225  				t.Body = io.MultiReader(&byteReader{b: rres.b}, t.Body)
   226  			}
   227  		} else if rres.err != nil {
   228  			t.Body = errorReader{rres.err}
   229  		}
   230  	case <-timer.C:
   231  		// Too slow. Don't wait. Read it later, and keep
   232  		// assuming that this is ContentLength == -1
   233  		// (unknown), which means we'll send a
   234  		// "Transfer-Encoding: chunked" header.
   235  		t.Body = io.MultiReader(finishAsyncByteRead{t}, t.Body)
   236  		// Request that Request.Write flush the headers to the
   237  		// network before writing the body, since our body may not
   238  		// become readable until it's seen the response headers.
   239  		t.FlushHeaders = true
   240  	}
   241  }
   242  
   243  func noResponseBodyExpected(requestMethod string) bool {
   244  	return requestMethod == "HEAD"
   245  }
   246  
   247  func (t *transferWriter) shouldSendContentLength() bool {
   248  	if chunked(t.TransferEncoding) {
   249  		return false
   250  	}
   251  	if t.ContentLength > 0 {
   252  		return true
   253  	}
   254  	if t.ContentLength < 0 {
   255  		return false
   256  	}
   257  	// Many servers expect a Content-Length for these methods
   258  	if t.Method == "POST" || t.Method == "PUT" {
   259  		return true
   260  	}
   261  	if t.ContentLength == 0 && isIdentity(t.TransferEncoding) {
   262  		if t.Method == "GET" || t.Method == "HEAD" {
   263  			return false
   264  		}
   265  		return true
   266  	}
   267  
   268  	return false
   269  }
   270  
   271  func (t *transferWriter) WriteHeader(w io.Writer) error {
   272  	if t.Close && !hasToken(t.Header.get("Connection"), "close") {
   273  		if _, err := io.WriteString(w, "Connection: close\r\n"); err != nil {
   274  			return err
   275  		}
   276  	}
   277  
   278  	// Write Content-Length and/or Transfer-Encoding whose values are a
   279  	// function of the sanitized field triple (Body, ContentLength,
   280  	// TransferEncoding)
   281  	if t.shouldSendContentLength() {
   282  		if _, err := io.WriteString(w, "Content-Length: "); err != nil {
   283  			return err
   284  		}
   285  		if _, err := io.WriteString(w, strconv.FormatInt(t.ContentLength, 10)+"\r\n"); err != nil {
   286  			return err
   287  		}
   288  	} else if chunked(t.TransferEncoding) {
   289  		if _, err := io.WriteString(w, "Transfer-Encoding: chunked\r\n"); err != nil {
   290  			return err
   291  		}
   292  	}
   293  
   294  	// Write Trailer header
   295  	if t.Trailer != nil {
   296  		keys := make([]string, 0, len(t.Trailer))
   297  		for k := range t.Trailer {
   298  			k = CanonicalHeaderKey(k)
   299  			switch k {
   300  			case "Transfer-Encoding", "Trailer", "Content-Length":
   301  				return &badStringError{"invalid Trailer key", k}
   302  			}
   303  			keys = append(keys, k)
   304  		}
   305  		if len(keys) > 0 {
   306  			sort.Strings(keys)
   307  			// TODO: could do better allocation-wise here, but trailers are rare,
   308  			// so being lazy for now.
   309  			if _, err := io.WriteString(w, "Trailer: "+strings.Join(keys, ",")+"\r\n"); err != nil {
   310  				return err
   311  			}
   312  		}
   313  	}
   314  
   315  	return nil
   316  }
   317  
   318  func (t *transferWriter) WriteBody(w io.Writer) error {
   319  	var err error
   320  	var ncopy int64
   321  
   322  	// Write body
   323  	if t.Body != nil {
   324  		var body = transferBodyReader{t}
   325  		if chunked(t.TransferEncoding) {
   326  			if bw, ok := w.(*bufio.Writer); ok && !t.IsResponse {
   327  				w = &internal.FlushAfterChunkWriter{Writer: bw}
   328  			}
   329  			cw := internal.NewChunkedWriter(w)
   330  			_, err = io.Copy(cw, body)
   331  			if err == nil {
   332  				err = cw.Close()
   333  			}
   334  		} else if t.ContentLength == -1 {
   335  			ncopy, err = io.Copy(w, body)
   336  		} else {
   337  			ncopy, err = io.Copy(w, io.LimitReader(body, t.ContentLength))
   338  			if err != nil {
   339  				return err
   340  			}
   341  			var nextra int64
   342  			nextra, err = io.Copy(ioutil.Discard, body)
   343  			ncopy += nextra
   344  		}
   345  		if err != nil {
   346  			return err
   347  		}
   348  	}
   349  	if t.BodyCloser != nil {
   350  		if err := t.BodyCloser.Close(); err != nil {
   351  			return err
   352  		}
   353  	}
   354  
   355  	if !t.ResponseToHEAD && t.ContentLength != -1 && t.ContentLength != ncopy {
   356  		return fmt.Errorf("http: ContentLength=%d with Body length %d",
   357  			t.ContentLength, ncopy)
   358  	}
   359  
   360  	if chunked(t.TransferEncoding) {
   361  		// Write Trailer header
   362  		if t.Trailer != nil {
   363  			if err := t.Trailer.Write(w); err != nil {
   364  				return err
   365  			}
   366  		}
   367  		// Last chunk, empty trailer
   368  		_, err = io.WriteString(w, "\r\n")
   369  	}
   370  	return err
   371  }
   372  
   373  type transferReader struct {
   374  	// Input
   375  	Header        Header
   376  	StatusCode    int
   377  	RequestMethod string
   378  	ProtoMajor    int
   379  	ProtoMinor    int
   380  	// Output
   381  	Body             io.ReadCloser
   382  	ContentLength    int64
   383  	TransferEncoding []string
   384  	Close            bool
   385  	Trailer          Header
   386  }
   387  
   388  func (t *transferReader) protoAtLeast(m, n int) bool {
   389  	return t.ProtoMajor > m || (t.ProtoMajor == m && t.ProtoMinor >= n)
   390  }
   391  
   392  // bodyAllowedForStatus reports whether a given response status code
   393  // permits a body. See RFC 2616, section 4.4.
   394  func bodyAllowedForStatus(status int) bool {
   395  	switch {
   396  	case status >= 100 && status <= 199:
   397  		return false
   398  	case status == 204:
   399  		return false
   400  	case status == 304:
   401  		return false
   402  	}
   403  	return true
   404  }
   405  
   406  var (
   407  	suppressedHeaders304    = []string{"Content-Type", "Content-Length", "Transfer-Encoding"}
   408  	suppressedHeadersNoBody = []string{"Content-Length", "Transfer-Encoding"}
   409  )
   410  
   411  func suppressedHeaders(status int) []string {
   412  	switch {
   413  	case status == 304:
   414  		// RFC 2616 section 10.3.5: "the response MUST NOT include other entity-headers"
   415  		return suppressedHeaders304
   416  	case !bodyAllowedForStatus(status):
   417  		return suppressedHeadersNoBody
   418  	}
   419  	return nil
   420  }
   421  
   422  // msg is *Request or *Response.
   423  func readTransfer(msg interface{}, r *bufio.Reader) (err error) {
   424  	t := &transferReader{RequestMethod: "GET"}
   425  
   426  	// Unify input
   427  	isResponse := false
   428  	switch rr := msg.(type) {
   429  	case *Response:
   430  		t.Header = rr.Header
   431  		t.StatusCode = rr.StatusCode
   432  		t.ProtoMajor = rr.ProtoMajor
   433  		t.ProtoMinor = rr.ProtoMinor
   434  		t.Close = shouldClose(t.ProtoMajor, t.ProtoMinor, t.Header, true)
   435  		isResponse = true
   436  		if rr.Request != nil {
   437  			t.RequestMethod = rr.Request.Method
   438  		}
   439  	case *Request:
   440  		t.Header = rr.Header
   441  		t.RequestMethod = rr.Method
   442  		t.ProtoMajor = rr.ProtoMajor
   443  		t.ProtoMinor = rr.ProtoMinor
   444  		// Transfer semantics for Requests are exactly like those for
   445  		// Responses with status code 200, responding to a GET method
   446  		t.StatusCode = 200
   447  		t.Close = rr.Close
   448  	default:
   449  		panic("unexpected type")
   450  	}
   451  
   452  	// Default to HTTP/1.1
   453  	if t.ProtoMajor == 0 && t.ProtoMinor == 0 {
   454  		t.ProtoMajor, t.ProtoMinor = 1, 1
   455  	}
   456  
   457  	// Transfer encoding, content length
   458  	err = t.fixTransferEncoding()
   459  	if err != nil {
   460  		return err
   461  	}
   462  
   463  	realLength, err := fixLength(isResponse, t.StatusCode, t.RequestMethod, t.Header, t.TransferEncoding)
   464  	if err != nil {
   465  		return err
   466  	}
   467  	if isResponse && t.RequestMethod == "HEAD" {
   468  		if n, err := parseContentLength(t.Header.get("Content-Length")); err != nil {
   469  			return err
   470  		} else {
   471  			t.ContentLength = n
   472  		}
   473  	} else {
   474  		t.ContentLength = realLength
   475  	}
   476  
   477  	// Trailer
   478  	t.Trailer, err = fixTrailer(t.Header, t.TransferEncoding)
   479  	if err != nil {
   480  		return err
   481  	}
   482  
   483  	// If there is no Content-Length or chunked Transfer-Encoding on a *Response
   484  	// and the status is not 1xx, 204 or 304, then the body is unbounded.
   485  	// See RFC 2616, section 4.4.
   486  	switch msg.(type) {
   487  	case *Response:
   488  		if realLength == -1 &&
   489  			!chunked(t.TransferEncoding) &&
   490  			bodyAllowedForStatus(t.StatusCode) {
   491  			// Unbounded body.
   492  			t.Close = true
   493  		}
   494  	}
   495  
   496  	// Prepare body reader. ContentLength < 0 means chunked encoding
   497  	// or close connection when finished, since multipart is not supported yet
   498  	switch {
   499  	case chunked(t.TransferEncoding):
   500  		if noResponseBodyExpected(t.RequestMethod) || !bodyAllowedForStatus(t.StatusCode) {
   501  			t.Body = NoBody
   502  		} else {
   503  			t.Body = &body{src: internal.NewChunkedReader(r), hdr: msg, r: r, closing: t.Close}
   504  		}
   505  	case realLength == 0:
   506  		t.Body = NoBody
   507  	case realLength > 0:
   508  		t.Body = &body{src: io.LimitReader(r, realLength), closing: t.Close}
   509  	default:
   510  		// realLength < 0, i.e. "Content-Length" not mentioned in header
   511  		if t.Close {
   512  			// Close semantics (i.e. HTTP/1.0)
   513  			t.Body = &body{src: r, closing: t.Close}
   514  		} else {
   515  			// Persistent connection (i.e. HTTP/1.1)
   516  			t.Body = NoBody
   517  		}
   518  	}
   519  
   520  	// Unify output
   521  	switch rr := msg.(type) {
   522  	case *Request:
   523  		rr.Body = t.Body
   524  		rr.ContentLength = t.ContentLength
   525  		rr.TransferEncoding = t.TransferEncoding
   526  		rr.Close = t.Close
   527  		rr.Trailer = t.Trailer
   528  	case *Response:
   529  		rr.Body = t.Body
   530  		rr.ContentLength = t.ContentLength
   531  		rr.TransferEncoding = t.TransferEncoding
   532  		rr.Close = t.Close
   533  		rr.Trailer = t.Trailer
   534  	}
   535  
   536  	return nil
   537  }
   538  
   539  // Checks whether chunked is part of the encodings stack
   540  func chunked(te []string) bool { return len(te) > 0 && te[0] == "chunked" }
   541  
   542  // Checks whether the encoding is explicitly "identity".
   543  func isIdentity(te []string) bool { return len(te) == 1 && te[0] == "identity" }
   544  
   545  // fixTransferEncoding sanitizes t.TransferEncoding, if needed.
   546  func (t *transferReader) fixTransferEncoding() error {
   547  	raw, present := t.Header["Transfer-Encoding"]
   548  	if !present {
   549  		return nil
   550  	}
   551  	delete(t.Header, "Transfer-Encoding")
   552  
   553  	// Issue 12785; ignore Transfer-Encoding on HTTP/1.0 requests.
   554  	if !t.protoAtLeast(1, 1) {
   555  		return nil
   556  	}
   557  
   558  	encodings := strings.Split(raw[0], ",")
   559  	te := make([]string, 0, len(encodings))
   560  	// TODO: Even though we only support "identity" and "chunked"
   561  	// encodings, the loop below is designed with foresight. One
   562  	// invariant that must be maintained is that, if present,
   563  	// chunked encoding must always come first.
   564  	for _, encoding := range encodings {
   565  		encoding = strings.ToLower(strings.TrimSpace(encoding))
   566  		// "identity" encoding is not recorded
   567  		if encoding == "identity" {
   568  			break
   569  		}
   570  		if encoding != "chunked" {
   571  			return &badStringError{"unsupported transfer encoding", encoding}
   572  		}
   573  		te = te[0 : len(te)+1]
   574  		te[len(te)-1] = encoding
   575  	}
   576  	if len(te) > 1 {
   577  		return &badStringError{"too many transfer encodings", strings.Join(te, ",")}
   578  	}
   579  	if len(te) > 0 {
   580  		// RFC 7230 3.3.2 says "A sender MUST NOT send a
   581  		// Content-Length header field in any message that
   582  		// contains a Transfer-Encoding header field."
   583  		//
   584  		// but also:
   585  		// "If a message is received with both a
   586  		// Transfer-Encoding and a Content-Length header
   587  		// field, the Transfer-Encoding overrides the
   588  		// Content-Length. Such a message might indicate an
   589  		// attempt to perform request smuggling (Section 9.5)
   590  		// or response splitting (Section 9.4) and ought to be
   591  		// handled as an error. A sender MUST remove the
   592  		// received Content-Length field prior to forwarding
   593  		// such a message downstream."
   594  		//
   595  		// Reportedly, these appear in the wild.
   596  		delete(t.Header, "Content-Length")
   597  		t.TransferEncoding = te
   598  		return nil
   599  	}
   600  
   601  	return nil
   602  }
   603  
   604  // Determine the expected body length, using RFC 2616 Section 4.4. This
   605  // function is not a method, because ultimately it should be shared by
   606  // ReadResponse and ReadRequest.
   607  func fixLength(isResponse bool, status int, requestMethod string, header Header, te []string) (int64, error) {
   608  	isRequest := !isResponse
   609  	contentLens := header["Content-Length"]
   610  
   611  	// Hardening against HTTP request smuggling
   612  	if len(contentLens) > 1 {
   613  		// Per RFC 7230 Section 3.3.2, prevent multiple
   614  		// Content-Length headers if they differ in value.
   615  		// If there are dups of the value, remove the dups.
   616  		// See Issue 16490.
   617  		first := strings.TrimSpace(contentLens[0])
   618  		for _, ct := range contentLens[1:] {
   619  			if first != strings.TrimSpace(ct) {
   620  				return 0, fmt.Errorf("http: message cannot contain multiple Content-Length headers; got %q", contentLens)
   621  			}
   622  		}
   623  
   624  		// deduplicate Content-Length
   625  		header.Del("Content-Length")
   626  		header.Add("Content-Length", first)
   627  
   628  		contentLens = header["Content-Length"]
   629  	}
   630  
   631  	// Logic based on response type or status
   632  	if noResponseBodyExpected(requestMethod) {
   633  		// For HTTP requests, as part of hardening against request
   634  		// smuggling (RFC 7230), don't allow a Content-Length header for
   635  		// methods which don't permit bodies. As an exception, allow
   636  		// exactly one Content-Length header if its value is "0".
   637  		if isRequest && len(contentLens) > 0 && !(len(contentLens) == 1 && contentLens[0] == "0") {
   638  			return 0, fmt.Errorf("http: method cannot contain a Content-Length; got %q", contentLens)
   639  		}
   640  		return 0, nil
   641  	}
   642  	if status/100 == 1 {
   643  		return 0, nil
   644  	}
   645  	switch status {
   646  	case 204, 304:
   647  		return 0, nil
   648  	}
   649  
   650  	// Logic based on Transfer-Encoding
   651  	if chunked(te) {
   652  		return -1, nil
   653  	}
   654  
   655  	// Logic based on Content-Length
   656  	var cl string
   657  	if len(contentLens) == 1 {
   658  		cl = strings.TrimSpace(contentLens[0])
   659  	}
   660  	if cl != "" {
   661  		n, err := parseContentLength(cl)
   662  		if err != nil {
   663  			return -1, err
   664  		}
   665  		return n, nil
   666  	}
   667  	header.Del("Content-Length")
   668  
   669  	if isRequest {
   670  		// RFC 2616 neither explicitly permits nor forbids an
   671  		// entity-body on a GET request so we permit one if
   672  		// declared, but we default to 0 here (not -1 below)
   673  		// if there's no mention of a body.
   674  		// Likewise, all other request methods are assumed to have
   675  		// no body if neither Transfer-Encoding chunked nor a
   676  		// Content-Length are set.
   677  		return 0, nil
   678  	}
   679  
   680  	// Body-EOF logic based on other methods (like closing, or chunked coding)
   681  	return -1, nil
   682  }
   683  
   684  // Determine whether to hang up after sending a request and body, or
   685  // receiving a response and body
   686  // 'header' is the request headers
   687  func shouldClose(major, minor int, header Header, removeCloseHeader bool) bool {
   688  	if major < 1 {
   689  		return true
   690  	}
   691  
   692  	conv := header["Connection"]
   693  	hasClose := httplex.HeaderValuesContainsToken(conv, "close")
   694  	if major == 1 && minor == 0 {
   695  		return hasClose || !httplex.HeaderValuesContainsToken(conv, "keep-alive")
   696  	}
   697  
   698  	if hasClose && removeCloseHeader {
   699  		header.Del("Connection")
   700  	}
   701  
   702  	return hasClose
   703  }
   704  
   705  // Parse the trailer header
   706  func fixTrailer(header Header, te []string) (Header, error) {
   707  	vv, ok := header["Trailer"]
   708  	if !ok {
   709  		return nil, nil
   710  	}
   711  	header.Del("Trailer")
   712  
   713  	trailer := make(Header)
   714  	var err error
   715  	for _, v := range vv {
   716  		foreachHeaderElement(v, func(key string) {
   717  			key = CanonicalHeaderKey(key)
   718  			switch key {
   719  			case "Transfer-Encoding", "Trailer", "Content-Length":
   720  				if err == nil {
   721  					err = &badStringError{"bad trailer key", key}
   722  					return
   723  				}
   724  			}
   725  			trailer[key] = nil
   726  		})
   727  	}
   728  	if err != nil {
   729  		return nil, err
   730  	}
   731  	if len(trailer) == 0 {
   732  		return nil, nil
   733  	}
   734  	if !chunked(te) {
   735  		// Trailer and no chunking
   736  		return nil, ErrUnexpectedTrailer
   737  	}
   738  	return trailer, nil
   739  }
   740  
   741  // body turns a Reader into a ReadCloser.
   742  // Close ensures that the body has been fully read
   743  // and then reads the trailer if necessary.
   744  type body struct {
   745  	src          io.Reader
   746  	hdr          interface{}   // non-nil (Response or Request) value means read trailer
   747  	r            *bufio.Reader // underlying wire-format reader for the trailer
   748  	closing      bool          // is the connection to be closed after reading body?
   749  	doEarlyClose bool          // whether Close should stop early
   750  
   751  	mu         sync.Mutex // guards following, and calls to Read and Close
   752  	sawEOF     bool
   753  	closed     bool
   754  	earlyClose bool   // Close called and we didn't read to the end of src
   755  	onHitEOF   func() // if non-nil, func to call when EOF is Read
   756  }
   757  
   758  // ErrBodyReadAfterClose is returned when reading a Request or Response
   759  // Body after the body has been closed. This typically happens when the body is
   760  // read after an HTTP Handler calls WriteHeader or Write on its
   761  // ResponseWriter.
   762  var ErrBodyReadAfterClose = errors.New("http: invalid Read on closed Body")
   763  
   764  func (b *body) Read(p []byte) (n int, err error) {
   765  	b.mu.Lock()
   766  	defer b.mu.Unlock()
   767  	if b.closed {
   768  		return 0, ErrBodyReadAfterClose
   769  	}
   770  	return b.readLocked(p)
   771  }
   772  
   773  // Must hold b.mu.
   774  func (b *body) readLocked(p []byte) (n int, err error) {
   775  	if b.sawEOF {
   776  		return 0, io.EOF
   777  	}
   778  	n, err = b.src.Read(p)
   779  
   780  	if err == io.EOF {
   781  		b.sawEOF = true
   782  		// Chunked case. Read the trailer.
   783  		if b.hdr != nil {
   784  			if e := b.readTrailer(); e != nil {
   785  				err = e
   786  				// Something went wrong in the trailer, we must not allow any
   787  				// further reads of any kind to succeed from body, nor any
   788  				// subsequent requests on the server connection. See
   789  				// golang.org/issue/12027
   790  				b.sawEOF = false
   791  				b.closed = true
   792  			}
   793  			b.hdr = nil
   794  		} else {
   795  			// If the server declared the Content-Length, our body is a LimitedReader
   796  			// and we need to check whether this EOF arrived early.
   797  			if lr, ok := b.src.(*io.LimitedReader); ok && lr.N > 0 {
   798  				err = io.ErrUnexpectedEOF
   799  			}
   800  		}
   801  	}
   802  
   803  	// If we can return an EOF here along with the read data, do
   804  	// so. This is optional per the io.Reader contract, but doing
   805  	// so helps the HTTP transport code recycle its connection
   806  	// earlier (since it will see this EOF itself), even if the
   807  	// client doesn't do future reads or Close.
   808  	if err == nil && n > 0 {
   809  		if lr, ok := b.src.(*io.LimitedReader); ok && lr.N == 0 {
   810  			err = io.EOF
   811  			b.sawEOF = true
   812  		}
   813  	}
   814  
   815  	if b.sawEOF && b.onHitEOF != nil {
   816  		b.onHitEOF()
   817  	}
   818  
   819  	return n, err
   820  }
   821  
   822  var (
   823  	singleCRLF = []byte("\r\n")
   824  	doubleCRLF = []byte("\r\n\r\n")
   825  )
   826  
   827  func seeUpcomingDoubleCRLF(r *bufio.Reader) bool {
   828  	for peekSize := 4; ; peekSize++ {
   829  		// This loop stops when Peek returns an error,
   830  		// which it does when r's buffer has been filled.
   831  		buf, err := r.Peek(peekSize)
   832  		if bytes.HasSuffix(buf, doubleCRLF) {
   833  			return true
   834  		}
   835  		if err != nil {
   836  			break
   837  		}
   838  	}
   839  	return false
   840  }
   841  
   842  var errTrailerEOF = errors.New("http: unexpected EOF reading trailer")
   843  
   844  func (b *body) readTrailer() error {
   845  	// The common case, since nobody uses trailers.
   846  	buf, err := b.r.Peek(2)
   847  	if bytes.Equal(buf, singleCRLF) {
   848  		b.r.Discard(2)
   849  		return nil
   850  	}
   851  	if len(buf) < 2 {
   852  		return errTrailerEOF
   853  	}
   854  	if err != nil {
   855  		return err
   856  	}
   857  
   858  	// Make sure there's a header terminator coming up, to prevent
   859  	// a DoS with an unbounded size Trailer. It's not easy to
   860  	// slip in a LimitReader here, as textproto.NewReader requires
   861  	// a concrete *bufio.Reader. Also, we can't get all the way
   862  	// back up to our conn's LimitedReader that *might* be backing
   863  	// this bufio.Reader. Instead, a hack: we iteratively Peek up
   864  	// to the bufio.Reader's max size, looking for a double CRLF.
   865  	// This limits the trailer to the underlying buffer size, typically 4kB.
   866  	if !seeUpcomingDoubleCRLF(b.r) {
   867  		return errors.New("http: suspiciously long trailer after chunked body")
   868  	}
   869  
   870  	hdr, err := textproto.NewReader(b.r).ReadMIMEHeader()
   871  	if err != nil {
   872  		if err == io.EOF {
   873  			return errTrailerEOF
   874  		}
   875  		return err
   876  	}
   877  	switch rr := b.hdr.(type) {
   878  	case *Request:
   879  		mergeSetHeader(&rr.Trailer, Header(hdr))
   880  	case *Response:
   881  		mergeSetHeader(&rr.Trailer, Header(hdr))
   882  	}
   883  	return nil
   884  }
   885  
   886  func mergeSetHeader(dst *Header, src Header) {
   887  	if *dst == nil {
   888  		*dst = src
   889  		return
   890  	}
   891  	for k, vv := range src {
   892  		(*dst)[k] = vv
   893  	}
   894  }
   895  
   896  // unreadDataSizeLocked returns the number of bytes of unread input.
   897  // It returns -1 if unknown.
   898  // b.mu must be held.
   899  func (b *body) unreadDataSizeLocked() int64 {
   900  	if lr, ok := b.src.(*io.LimitedReader); ok {
   901  		return lr.N
   902  	}
   903  	return -1
   904  }
   905  
   906  func (b *body) Close() error {
   907  	b.mu.Lock()
   908  	defer b.mu.Unlock()
   909  	if b.closed {
   910  		return nil
   911  	}
   912  	var err error
   913  	switch {
   914  	case b.sawEOF:
   915  		// Already saw EOF, so no need going to look for it.
   916  	case b.hdr == nil && b.closing:
   917  		// no trailer and closing the connection next.
   918  		// no point in reading to EOF.
   919  	case b.doEarlyClose:
   920  		// Read up to maxPostHandlerReadBytes bytes of the body, looking for
   921  		// for EOF (and trailers), so we can re-use this connection.
   922  		if lr, ok := b.src.(*io.LimitedReader); ok && lr.N > maxPostHandlerReadBytes {
   923  			// There was a declared Content-Length, and we have more bytes remaining
   924  			// than our maxPostHandlerReadBytes tolerance. So, give up.
   925  			b.earlyClose = true
   926  		} else {
   927  			var n int64
   928  			// Consume the body, or, which will also lead to us reading
   929  			// the trailer headers after the body, if present.
   930  			n, err = io.CopyN(ioutil.Discard, bodyLocked{b}, maxPostHandlerReadBytes)
   931  			if err == io.EOF {
   932  				err = nil
   933  			}
   934  			if n == maxPostHandlerReadBytes {
   935  				b.earlyClose = true
   936  			}
   937  		}
   938  	default:
   939  		// Fully consume the body, which will also lead to us reading
   940  		// the trailer headers after the body, if present.
   941  		_, err = io.Copy(ioutil.Discard, bodyLocked{b})
   942  	}
   943  	b.closed = true
   944  	return err
   945  }
   946  
   947  func (b *body) didEarlyClose() bool {
   948  	b.mu.Lock()
   949  	defer b.mu.Unlock()
   950  	return b.earlyClose
   951  }
   952  
   953  // bodyRemains reports whether future Read calls might
   954  // yield data.
   955  func (b *body) bodyRemains() bool {
   956  	b.mu.Lock()
   957  	defer b.mu.Unlock()
   958  	return !b.sawEOF
   959  }
   960  
   961  func (b *body) registerOnHitEOF(fn func()) {
   962  	b.mu.Lock()
   963  	defer b.mu.Unlock()
   964  	b.onHitEOF = fn
   965  }
   966  
   967  // bodyLocked is a io.Reader reading from a *body when its mutex is
   968  // already held.
   969  type bodyLocked struct {
   970  	b *body
   971  }
   972  
   973  func (bl bodyLocked) Read(p []byte) (n int, err error) {
   974  	if bl.b.closed {
   975  		return 0, ErrBodyReadAfterClose
   976  	}
   977  	return bl.b.readLocked(p)
   978  }
   979  
   980  // parseContentLength trims whitespace from s and returns -1 if no value
   981  // is set, or the value if it's >= 0.
   982  func parseContentLength(cl string) (int64, error) {
   983  	cl = strings.TrimSpace(cl)
   984  	if cl == "" {
   985  		return -1, nil
   986  	}
   987  	n, err := strconv.ParseInt(cl, 10, 64)
   988  	if err != nil || n < 0 {
   989  		return 0, &badStringError{"bad Content-Length", cl}
   990  	}
   991  	return n, nil
   992  
   993  }
   994  
   995  // finishAsyncByteRead finishes reading the 1-byte sniff
   996  // from the ContentLength==0, Body!=nil case.
   997  type finishAsyncByteRead struct {
   998  	tw *transferWriter
   999  }
  1000  
  1001  func (fr finishAsyncByteRead) Read(p []byte) (n int, err error) {
  1002  	if len(p) == 0 {
  1003  		return
  1004  	}
  1005  	rres := <-fr.tw.ByteReadCh
  1006  	n, err = rres.n, rres.err
  1007  	if n == 1 {
  1008  		p[0] = rres.b
  1009  	}
  1010  	return
  1011  }
  1012  

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