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/httptrace"
    15  	"net/http/internal"
    16  	"net/textproto"
    17  	"reflect"
    18  	"sort"
    19  	"strconv"
    20  	"strings"
    21  	"sync"
    22  	"time"
    23  
    24  	"golang.org/x/net/http/httpguts"
    25  )
    26  
    27  // ErrLineTooLong is returned when reading request or response bodies
    28  // with malformed chunked encoding.
    29  var ErrLineTooLong = internal.ErrLineTooLong
    30  
    31  type errorReader struct {
    32  	err error
    33  }
    34  
    35  func (r errorReader) Read(p []byte) (n int, err error) {
    36  	return 0, r.err
    37  }
    38  
    39  type byteReader struct {
    40  	b    byte
    41  	done bool
    42  }
    43  
    44  func (br *byteReader) Read(p []byte) (n int, err error) {
    45  	if br.done {
    46  		return 0, io.EOF
    47  	}
    48  	if len(p) == 0 {
    49  		return 0, nil
    50  	}
    51  	br.done = true
    52  	p[0] = br.b
    53  	return 1, io.EOF
    54  }
    55  
    56  // transferWriter inspects the fields of a user-supplied Request or Response,
    57  // sanitizes them without changing the user object and provides methods for
    58  // writing the respective header, body and trailer in wire format.
    59  type transferWriter struct {
    60  	Method           string
    61  	Body             io.Reader
    62  	BodyCloser       io.Closer
    63  	ResponseToHEAD   bool
    64  	ContentLength    int64 // -1 means unknown, 0 means exactly none
    65  	Close            bool
    66  	TransferEncoding []string
    67  	Header           Header
    68  	Trailer          Header
    69  	IsResponse       bool
    70  	bodyReadError    error // any non-EOF error from reading Body
    71  
    72  	FlushHeaders bool            // flush headers to network before body
    73  	ByteReadCh   chan readResult // non-nil if probeRequestBody called
    74  }
    75  
    76  func newTransferWriter(r interface{}) (t *transferWriter, err error) {
    77  	t = &transferWriter{}
    78  
    79  	// Extract relevant fields
    80  	atLeastHTTP11 := false
    81  	switch rr := r.(type) {
    82  	case *Request:
    83  		if rr.ContentLength != 0 && rr.Body == nil {
    84  			return nil, fmt.Errorf("http: Request.ContentLength=%d with nil Body", rr.ContentLength)
    85  		}
    86  		t.Method = valueOrDefault(rr.Method, "GET")
    87  		t.Close = rr.Close
    88  		t.TransferEncoding = rr.TransferEncoding
    89  		t.Header = rr.Header
    90  		t.Trailer = rr.Trailer
    91  		t.Body = rr.Body
    92  		t.BodyCloser = rr.Body
    93  		t.ContentLength = rr.outgoingLength()
    94  		if t.ContentLength < 0 && len(t.TransferEncoding) == 0 && t.shouldSendChunkedRequestBody() {
    95  			t.TransferEncoding = []string{"chunked"}
    96  		}
    97  		// If there's a body, conservatively flush the headers
    98  		// to any bufio.Writer we're writing to, just in case
    99  		// the server needs the headers early, before we copy
   100  		// the body and possibly block. We make an exception
   101  		// for the common standard library in-memory types,
   102  		// though, to avoid unnecessary TCP packets on the
   103  		// wire. (Issue 22088.)
   104  		if t.ContentLength != 0 && !isKnownInMemoryReader(t.Body) {
   105  			t.FlushHeaders = true
   106  		}
   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 t.Method == "CONNECT" {
   175  		return false
   176  	}
   177  	if requestMethodUsuallyLacksBody(t.Method) {
   178  		// Only probe the Request.Body for GET/HEAD/DELETE/etc
   179  		// requests, because it's only those types of requests
   180  		// that confuse servers.
   181  		t.probeRequestBody() // adjusts t.Body, t.ContentLength
   182  		return t.Body != nil
   183  	}
   184  	// For all other request types (PUT, POST, PATCH, or anything
   185  	// made-up we've never heard of), assume it's normal and the server
   186  	// can deal with a chunked request body. Maybe we'll adjust this
   187  	// later.
   188  	return true
   189  }
   190  
   191  // probeRequestBody reads a byte from t.Body to see whether it's empty
   192  // (returns io.EOF right away).
   193  //
   194  // But because we've had problems with this blocking users in the past
   195  // (issue 17480) when the body is a pipe (perhaps waiting on the response
   196  // headers before the pipe is fed data), we need to be careful and bound how
   197  // long we wait for it. This delay will only affect users if all the following
   198  // are true:
   199  //   * the request body blocks
   200  //   * the content length is not set (or set to -1)
   201  //   * the method doesn't usually have a body (GET, HEAD, DELETE, ...)
   202  //   * there is no transfer-encoding=chunked already set.
   203  // In other words, this delay will not normally affect anybody, and there
   204  // are workarounds if it does.
   205  func (t *transferWriter) probeRequestBody() {
   206  	t.ByteReadCh = make(chan readResult, 1)
   207  	go func(body io.Reader) {
   208  		var buf [1]byte
   209  		var rres readResult
   210  		rres.n, rres.err = body.Read(buf[:])
   211  		if rres.n == 1 {
   212  			rres.b = buf[0]
   213  		}
   214  		t.ByteReadCh <- rres
   215  	}(t.Body)
   216  	timer := time.NewTimer(200 * time.Millisecond)
   217  	select {
   218  	case rres := <-t.ByteReadCh:
   219  		timer.Stop()
   220  		if rres.n == 0 && rres.err == io.EOF {
   221  			// It was empty.
   222  			t.Body = nil
   223  			t.ContentLength = 0
   224  		} else if rres.n == 1 {
   225  			if rres.err != nil {
   226  				t.Body = io.MultiReader(&byteReader{b: rres.b}, errorReader{rres.err})
   227  			} else {
   228  				t.Body = io.MultiReader(&byteReader{b: rres.b}, t.Body)
   229  			}
   230  		} else if rres.err != nil {
   231  			t.Body = errorReader{rres.err}
   232  		}
   233  	case <-timer.C:
   234  		// Too slow. Don't wait. Read it later, and keep
   235  		// assuming that this is ContentLength == -1
   236  		// (unknown), which means we'll send a
   237  		// "Transfer-Encoding: chunked" header.
   238  		t.Body = io.MultiReader(finishAsyncByteRead{t}, t.Body)
   239  		// Request that Request.Write flush the headers to the
   240  		// network before writing the body, since our body may not
   241  		// become readable until it's seen the response headers.
   242  		t.FlushHeaders = true
   243  	}
   244  }
   245  
   246  func noResponseBodyExpected(requestMethod string) bool {
   247  	return requestMethod == "HEAD"
   248  }
   249  
   250  func (t *transferWriter) shouldSendContentLength() bool {
   251  	if chunked(t.TransferEncoding) {
   252  		return false
   253  	}
   254  	if t.ContentLength > 0 {
   255  		return true
   256  	}
   257  	if t.ContentLength < 0 {
   258  		return false
   259  	}
   260  	// Many servers expect a Content-Length for these methods
   261  	if t.Method == "POST" || t.Method == "PUT" {
   262  		return true
   263  	}
   264  	if t.ContentLength == 0 && isIdentity(t.TransferEncoding) {
   265  		if t.Method == "GET" || t.Method == "HEAD" {
   266  			return false
   267  		}
   268  		return true
   269  	}
   270  
   271  	return false
   272  }
   273  
   274  func (t *transferWriter) writeHeader(w io.Writer, trace *httptrace.ClientTrace) error {
   275  	if t.Close && !hasToken(t.Header.get("Connection"), "close") {
   276  		if _, err := io.WriteString(w, "Connection: close\r\n"); err != nil {
   277  			return err
   278  		}
   279  		if trace != nil && trace.WroteHeaderField != nil {
   280  			trace.WroteHeaderField("Connection", []string{"close"})
   281  		}
   282  	}
   283  
   284  	// Write Content-Length and/or Transfer-Encoding whose values are a
   285  	// function of the sanitized field triple (Body, ContentLength,
   286  	// TransferEncoding)
   287  	if t.shouldSendContentLength() {
   288  		if _, err := io.WriteString(w, "Content-Length: "); err != nil {
   289  			return err
   290  		}
   291  		if _, err := io.WriteString(w, strconv.FormatInt(t.ContentLength, 10)+"\r\n"); err != nil {
   292  			return err
   293  		}
   294  		if trace != nil && trace.WroteHeaderField != nil {
   295  			trace.WroteHeaderField("Content-Length", []string{strconv.FormatInt(t.ContentLength, 10)})
   296  		}
   297  	} else if chunked(t.TransferEncoding) {
   298  		if _, err := io.WriteString(w, "Transfer-Encoding: chunked\r\n"); err != nil {
   299  			return err
   300  		}
   301  		if trace != nil && trace.WroteHeaderField != nil {
   302  			trace.WroteHeaderField("Transfer-Encoding", []string{"chunked"})
   303  		}
   304  	}
   305  
   306  	// Write Trailer header
   307  	if t.Trailer != nil {
   308  		keys := make([]string, 0, len(t.Trailer))
   309  		for k := range t.Trailer {
   310  			k = CanonicalHeaderKey(k)
   311  			switch k {
   312  			case "Transfer-Encoding", "Trailer", "Content-Length":
   313  				return &badStringError{"invalid Trailer key", k}
   314  			}
   315  			keys = append(keys, k)
   316  		}
   317  		if len(keys) > 0 {
   318  			sort.Strings(keys)
   319  			// TODO: could do better allocation-wise here, but trailers are rare,
   320  			// so being lazy for now.
   321  			if _, err := io.WriteString(w, "Trailer: "+strings.Join(keys, ",")+"\r\n"); err != nil {
   322  				return err
   323  			}
   324  			if trace != nil && trace.WroteHeaderField != nil {
   325  				trace.WroteHeaderField("Trailer", keys)
   326  			}
   327  		}
   328  	}
   329  
   330  	return nil
   331  }
   332  
   333  func (t *transferWriter) writeBody(w io.Writer) error {
   334  	var err error
   335  	var ncopy int64
   336  
   337  	// Write body. We "unwrap" the body first if it was wrapped in a
   338  	// nopCloser. This is to ensure that we can take advantage of
   339  	// OS-level optimizations in the event that the body is an
   340  	// *os.File.
   341  	if t.Body != nil {
   342  		var body = t.unwrapBody()
   343  		if chunked(t.TransferEncoding) {
   344  			if bw, ok := w.(*bufio.Writer); ok && !t.IsResponse {
   345  				w = &internal.FlushAfterChunkWriter{Writer: bw}
   346  			}
   347  			cw := internal.NewChunkedWriter(w)
   348  			_, err = t.doBodyCopy(cw, body)
   349  			if err == nil {
   350  				err = cw.Close()
   351  			}
   352  		} else if t.ContentLength == -1 {
   353  			dst := w
   354  			if t.Method == "CONNECT" {
   355  				dst = bufioFlushWriter{dst}
   356  			}
   357  			ncopy, err = t.doBodyCopy(dst, body)
   358  		} else {
   359  			ncopy, err = t.doBodyCopy(w, io.LimitReader(body, t.ContentLength))
   360  			if err != nil {
   361  				return err
   362  			}
   363  			var nextra int64
   364  			nextra, err = t.doBodyCopy(ioutil.Discard, body)
   365  			ncopy += nextra
   366  		}
   367  		if err != nil {
   368  			return err
   369  		}
   370  	}
   371  	if t.BodyCloser != nil {
   372  		if err := t.BodyCloser.Close(); err != nil {
   373  			return err
   374  		}
   375  	}
   376  
   377  	if !t.ResponseToHEAD && t.ContentLength != -1 && t.ContentLength != ncopy {
   378  		return fmt.Errorf("http: ContentLength=%d with Body length %d",
   379  			t.ContentLength, ncopy)
   380  	}
   381  
   382  	if chunked(t.TransferEncoding) {
   383  		// Write Trailer header
   384  		if t.Trailer != nil {
   385  			if err := t.Trailer.Write(w); err != nil {
   386  				return err
   387  			}
   388  		}
   389  		// Last chunk, empty trailer
   390  		_, err = io.WriteString(w, "\r\n")
   391  	}
   392  	return err
   393  }
   394  
   395  // doBodyCopy wraps a copy operation, with any resulting error also
   396  // being saved in bodyReadError.
   397  //
   398  // This function is only intended for use in writeBody.
   399  func (t *transferWriter) doBodyCopy(dst io.Writer, src io.Reader) (n int64, err error) {
   400  	n, err = io.Copy(dst, src)
   401  	if err != nil && err != io.EOF {
   402  		t.bodyReadError = err
   403  	}
   404  	return
   405  }
   406  
   407  // unwrapBodyReader unwraps the body's inner reader if it's a
   408  // nopCloser. This is to ensure that body writes sourced from local
   409  // files (*os.File types) are properly optimized.
   410  //
   411  // This function is only intended for use in writeBody.
   412  func (t *transferWriter) unwrapBody() io.Reader {
   413  	if reflect.TypeOf(t.Body) == nopCloserType {
   414  		return reflect.ValueOf(t.Body).Field(0).Interface().(io.Reader)
   415  	}
   416  
   417  	return t.Body
   418  }
   419  
   420  type transferReader struct {
   421  	// Input
   422  	Header        Header
   423  	StatusCode    int
   424  	RequestMethod string
   425  	ProtoMajor    int
   426  	ProtoMinor    int
   427  	// Output
   428  	Body             io.ReadCloser
   429  	ContentLength    int64
   430  	TransferEncoding []string
   431  	Close            bool
   432  	Trailer          Header
   433  }
   434  
   435  func (t *transferReader) protoAtLeast(m, n int) bool {
   436  	return t.ProtoMajor > m || (t.ProtoMajor == m && t.ProtoMinor >= n)
   437  }
   438  
   439  // bodyAllowedForStatus reports whether a given response status code
   440  // permits a body. See RFC 7230, section 3.3.
   441  func bodyAllowedForStatus(status int) bool {
   442  	switch {
   443  	case status >= 100 && status <= 199:
   444  		return false
   445  	case status == 204:
   446  		return false
   447  	case status == 304:
   448  		return false
   449  	}
   450  	return true
   451  }
   452  
   453  var (
   454  	suppressedHeaders304    = []string{"Content-Type", "Content-Length", "Transfer-Encoding"}
   455  	suppressedHeadersNoBody = []string{"Content-Length", "Transfer-Encoding"}
   456  )
   457  
   458  func suppressedHeaders(status int) []string {
   459  	switch {
   460  	case status == 304:
   461  		// RFC 7232 section 4.1
   462  		return suppressedHeaders304
   463  	case !bodyAllowedForStatus(status):
   464  		return suppressedHeadersNoBody
   465  	}
   466  	return nil
   467  }
   468  
   469  // msg is *Request or *Response.
   470  func readTransfer(msg interface{}, r *bufio.Reader) (err error) {
   471  	t := &transferReader{RequestMethod: "GET"}
   472  
   473  	// Unify input
   474  	isResponse := false
   475  	switch rr := msg.(type) {
   476  	case *Response:
   477  		t.Header = rr.Header
   478  		t.StatusCode = rr.StatusCode
   479  		t.ProtoMajor = rr.ProtoMajor
   480  		t.ProtoMinor = rr.ProtoMinor
   481  		t.Close = shouldClose(t.ProtoMajor, t.ProtoMinor, t.Header, true)
   482  		isResponse = true
   483  		if rr.Request != nil {
   484  			t.RequestMethod = rr.Request.Method
   485  		}
   486  	case *Request:
   487  		t.Header = rr.Header
   488  		t.RequestMethod = rr.Method
   489  		t.ProtoMajor = rr.ProtoMajor
   490  		t.ProtoMinor = rr.ProtoMinor
   491  		// Transfer semantics for Requests are exactly like those for
   492  		// Responses with status code 200, responding to a GET method
   493  		t.StatusCode = 200
   494  		t.Close = rr.Close
   495  	default:
   496  		panic("unexpected type")
   497  	}
   498  
   499  	// Default to HTTP/1.1
   500  	if t.ProtoMajor == 0 && t.ProtoMinor == 0 {
   501  		t.ProtoMajor, t.ProtoMinor = 1, 1
   502  	}
   503  
   504  	// Transfer encoding, content length
   505  	err = t.fixTransferEncoding()
   506  	if err != nil {
   507  		return err
   508  	}
   509  
   510  	realLength, err := fixLength(isResponse, t.StatusCode, t.RequestMethod, t.Header, t.TransferEncoding)
   511  	if err != nil {
   512  		return err
   513  	}
   514  	if isResponse && t.RequestMethod == "HEAD" {
   515  		if n, err := parseContentLength(t.Header.get("Content-Length")); err != nil {
   516  			return err
   517  		} else {
   518  			t.ContentLength = n
   519  		}
   520  	} else {
   521  		t.ContentLength = realLength
   522  	}
   523  
   524  	// Trailer
   525  	t.Trailer, err = fixTrailer(t.Header, t.TransferEncoding)
   526  	if err != nil {
   527  		return err
   528  	}
   529  
   530  	// If there is no Content-Length or chunked Transfer-Encoding on a *Response
   531  	// and the status is not 1xx, 204 or 304, then the body is unbounded.
   532  	// See RFC 7230, section 3.3.
   533  	switch msg.(type) {
   534  	case *Response:
   535  		if realLength == -1 &&
   536  			!chunked(t.TransferEncoding) &&
   537  			bodyAllowedForStatus(t.StatusCode) {
   538  			// Unbounded body.
   539  			t.Close = true
   540  		}
   541  	}
   542  
   543  	// Prepare body reader. ContentLength < 0 means chunked encoding
   544  	// or close connection when finished, since multipart is not supported yet
   545  	switch {
   546  	case chunked(t.TransferEncoding):
   547  		if noResponseBodyExpected(t.RequestMethod) || !bodyAllowedForStatus(t.StatusCode) {
   548  			t.Body = NoBody
   549  		} else {
   550  			t.Body = &body{src: internal.NewChunkedReader(r), hdr: msg, r: r, closing: t.Close}
   551  		}
   552  	case realLength == 0:
   553  		t.Body = NoBody
   554  	case realLength > 0:
   555  		t.Body = &body{src: io.LimitReader(r, realLength), closing: t.Close}
   556  	default:
   557  		// realLength < 0, i.e. "Content-Length" not mentioned in header
   558  		if t.Close {
   559  			// Close semantics (i.e. HTTP/1.0)
   560  			t.Body = &body{src: r, closing: t.Close}
   561  		} else {
   562  			// Persistent connection (i.e. HTTP/1.1)
   563  			t.Body = NoBody
   564  		}
   565  	}
   566  
   567  	// Unify output
   568  	switch rr := msg.(type) {
   569  	case *Request:
   570  		rr.Body = t.Body
   571  		rr.ContentLength = t.ContentLength
   572  		rr.TransferEncoding = t.TransferEncoding
   573  		rr.Close = t.Close
   574  		rr.Trailer = t.Trailer
   575  	case *Response:
   576  		rr.Body = t.Body
   577  		rr.ContentLength = t.ContentLength
   578  		rr.TransferEncoding = t.TransferEncoding
   579  		rr.Close = t.Close
   580  		rr.Trailer = t.Trailer
   581  	}
   582  
   583  	return nil
   584  }
   585  
   586  // Checks whether chunked is part of the encodings stack
   587  func chunked(te []string) bool { return len(te) > 0 && te[0] == "chunked" }
   588  
   589  // Checks whether the encoding is explicitly "identity".
   590  func isIdentity(te []string) bool { return len(te) == 1 && te[0] == "identity" }
   591  
   592  // unsupportedTEError reports unsupported transfer-encodings.
   593  type unsupportedTEError struct {
   594  	err string
   595  }
   596  
   597  func (uste *unsupportedTEError) Error() string {
   598  	return uste.err
   599  }
   600  
   601  // isUnsupportedTEError checks if the error is of type
   602  // unsupportedTEError. It is usually invoked with a non-nil err.
   603  func isUnsupportedTEError(err error) bool {
   604  	_, ok := err.(*unsupportedTEError)
   605  	return ok
   606  }
   607  
   608  // fixTransferEncoding sanitizes t.TransferEncoding, if needed.
   609  func (t *transferReader) fixTransferEncoding() error {
   610  	raw, present := t.Header["Transfer-Encoding"]
   611  	if !present {
   612  		return nil
   613  	}
   614  	delete(t.Header, "Transfer-Encoding")
   615  
   616  	// Issue 12785; ignore Transfer-Encoding on HTTP/1.0 requests.
   617  	if !t.protoAtLeast(1, 1) {
   618  		return nil
   619  	}
   620  
   621  	encodings := strings.Split(raw[0], ",")
   622  	te := make([]string, 0, len(encodings))
   623  	// TODO: Even though we only support "identity" and "chunked"
   624  	// encodings, the loop below is designed with foresight. One
   625  	// invariant that must be maintained is that, if present,
   626  	// chunked encoding must always come first.
   627  	for _, encoding := range encodings {
   628  		encoding = strings.ToLower(strings.TrimSpace(encoding))
   629  		// "identity" encoding is not recorded
   630  		if encoding == "identity" {
   631  			break
   632  		}
   633  		if encoding != "chunked" {
   634  			return &unsupportedTEError{fmt.Sprintf("unsupported transfer encoding: %q", encoding)}
   635  		}
   636  		te = te[0 : len(te)+1]
   637  		te[len(te)-1] = encoding
   638  	}
   639  	if len(te) > 1 {
   640  		return &badStringError{"too many transfer encodings", strings.Join(te, ",")}
   641  	}
   642  	if len(te) > 0 {
   643  		// RFC 7230 3.3.2 says "A sender MUST NOT send a
   644  		// Content-Length header field in any message that
   645  		// contains a Transfer-Encoding header field."
   646  		//
   647  		// but also:
   648  		// "If a message is received with both a
   649  		// Transfer-Encoding and a Content-Length header
   650  		// field, the Transfer-Encoding overrides the
   651  		// Content-Length. Such a message might indicate an
   652  		// attempt to perform request smuggling (Section 9.5)
   653  		// or response splitting (Section 9.4) and ought to be
   654  		// handled as an error. A sender MUST remove the
   655  		// received Content-Length field prior to forwarding
   656  		// such a message downstream."
   657  		//
   658  		// Reportedly, these appear in the wild.
   659  		delete(t.Header, "Content-Length")
   660  		t.TransferEncoding = te
   661  		return nil
   662  	}
   663  
   664  	return nil
   665  }
   666  
   667  // Determine the expected body length, using RFC 7230 Section 3.3. This
   668  // function is not a method, because ultimately it should be shared by
   669  // ReadResponse and ReadRequest.
   670  func fixLength(isResponse bool, status int, requestMethod string, header Header, te []string) (int64, error) {
   671  	isRequest := !isResponse
   672  	contentLens := header["Content-Length"]
   673  
   674  	// Hardening against HTTP request smuggling
   675  	if len(contentLens) > 1 {
   676  		// Per RFC 7230 Section 3.3.2, prevent multiple
   677  		// Content-Length headers if they differ in value.
   678  		// If there are dups of the value, remove the dups.
   679  		// See Issue 16490.
   680  		first := strings.TrimSpace(contentLens[0])
   681  		for _, ct := range contentLens[1:] {
   682  			if first != strings.TrimSpace(ct) {
   683  				return 0, fmt.Errorf("http: message cannot contain multiple Content-Length headers; got %q", contentLens)
   684  			}
   685  		}
   686  
   687  		// deduplicate Content-Length
   688  		header.Del("Content-Length")
   689  		header.Add("Content-Length", first)
   690  
   691  		contentLens = header["Content-Length"]
   692  	}
   693  
   694  	// Logic based on response type or status
   695  	if noResponseBodyExpected(requestMethod) {
   696  		// For HTTP requests, as part of hardening against request
   697  		// smuggling (RFC 7230), don't allow a Content-Length header for
   698  		// methods which don't permit bodies. As an exception, allow
   699  		// exactly one Content-Length header if its value is "0".
   700  		if isRequest && len(contentLens) > 0 && !(len(contentLens) == 1 && contentLens[0] == "0") {
   701  			return 0, fmt.Errorf("http: method cannot contain a Content-Length; got %q", contentLens)
   702  		}
   703  		return 0, nil
   704  	}
   705  	if status/100 == 1 {
   706  		return 0, nil
   707  	}
   708  	switch status {
   709  	case 204, 304:
   710  		return 0, nil
   711  	}
   712  
   713  	// Logic based on Transfer-Encoding
   714  	if chunked(te) {
   715  		return -1, nil
   716  	}
   717  
   718  	// Logic based on Content-Length
   719  	var cl string
   720  	if len(contentLens) == 1 {
   721  		cl = strings.TrimSpace(contentLens[0])
   722  	}
   723  	if cl != "" {
   724  		n, err := parseContentLength(cl)
   725  		if err != nil {
   726  			return -1, err
   727  		}
   728  		return n, nil
   729  	}
   730  	header.Del("Content-Length")
   731  
   732  	if isRequest {
   733  		// RFC 7230 neither explicitly permits nor forbids an
   734  		// entity-body on a GET request so we permit one if
   735  		// declared, but we default to 0 here (not -1 below)
   736  		// if there's no mention of a body.
   737  		// Likewise, all other request methods are assumed to have
   738  		// no body if neither Transfer-Encoding chunked nor a
   739  		// Content-Length are set.
   740  		return 0, nil
   741  	}
   742  
   743  	// Body-EOF logic based on other methods (like closing, or chunked coding)
   744  	return -1, nil
   745  }
   746  
   747  // Determine whether to hang up after sending a request and body, or
   748  // receiving a response and body
   749  // 'header' is the request headers
   750  func shouldClose(major, minor int, header Header, removeCloseHeader bool) bool {
   751  	if major < 1 {
   752  		return true
   753  	}
   754  
   755  	conv := header["Connection"]
   756  	hasClose := httpguts.HeaderValuesContainsToken(conv, "close")
   757  	if major == 1 && minor == 0 {
   758  		return hasClose || !httpguts.HeaderValuesContainsToken(conv, "keep-alive")
   759  	}
   760  
   761  	if hasClose && removeCloseHeader {
   762  		header.Del("Connection")
   763  	}
   764  
   765  	return hasClose
   766  }
   767  
   768  // Parse the trailer header
   769  func fixTrailer(header Header, te []string) (Header, error) {
   770  	vv, ok := header["Trailer"]
   771  	if !ok {
   772  		return nil, nil
   773  	}
   774  	if !chunked(te) {
   775  		// Trailer and no chunking:
   776  		// this is an invalid use case for trailer header.
   777  		// Nevertheless, no error will be returned and we
   778  		// let users decide if this is a valid HTTP message.
   779  		// The Trailer header will be kept in Response.Header
   780  		// but not populate Response.Trailer.
   781  		// See issue #27197.
   782  		return nil, nil
   783  	}
   784  	header.Del("Trailer")
   785  
   786  	trailer := make(Header)
   787  	var err error
   788  	for _, v := range vv {
   789  		foreachHeaderElement(v, func(key string) {
   790  			key = CanonicalHeaderKey(key)
   791  			switch key {
   792  			case "Transfer-Encoding", "Trailer", "Content-Length":
   793  				if err == nil {
   794  					err = &badStringError{"bad trailer key", key}
   795  					return
   796  				}
   797  			}
   798  			trailer[key] = nil
   799  		})
   800  	}
   801  	if err != nil {
   802  		return nil, err
   803  	}
   804  	if len(trailer) == 0 {
   805  		return nil, nil
   806  	}
   807  	return trailer, nil
   808  }
   809  
   810  // body turns a Reader into a ReadCloser.
   811  // Close ensures that the body has been fully read
   812  // and then reads the trailer if necessary.
   813  type body struct {
   814  	src          io.Reader
   815  	hdr          interface{}   // non-nil (Response or Request) value means read trailer
   816  	r            *bufio.Reader // underlying wire-format reader for the trailer
   817  	closing      bool          // is the connection to be closed after reading body?
   818  	doEarlyClose bool          // whether Close should stop early
   819  
   820  	mu         sync.Mutex // guards following, and calls to Read and Close
   821  	sawEOF     bool
   822  	closed     bool
   823  	earlyClose bool   // Close called and we didn't read to the end of src
   824  	onHitEOF   func() // if non-nil, func to call when EOF is Read
   825  }
   826  
   827  // ErrBodyReadAfterClose is returned when reading a Request or Response
   828  // Body after the body has been closed. This typically happens when the body is
   829  // read after an HTTP Handler calls WriteHeader or Write on its
   830  // ResponseWriter.
   831  var ErrBodyReadAfterClose = errors.New("http: invalid Read on closed Body")
   832  
   833  func (b *body) Read(p []byte) (n int, err error) {
   834  	b.mu.Lock()
   835  	defer b.mu.Unlock()
   836  	if b.closed {
   837  		return 0, ErrBodyReadAfterClose
   838  	}
   839  	return b.readLocked(p)
   840  }
   841  
   842  // Must hold b.mu.
   843  func (b *body) readLocked(p []byte) (n int, err error) {
   844  	if b.sawEOF {
   845  		return 0, io.EOF
   846  	}
   847  	n, err = b.src.Read(p)
   848  
   849  	if err == io.EOF {
   850  		b.sawEOF = true
   851  		// Chunked case. Read the trailer.
   852  		if b.hdr != nil {
   853  			if e := b.readTrailer(); e != nil {
   854  				err = e
   855  				// Something went wrong in the trailer, we must not allow any
   856  				// further reads of any kind to succeed from body, nor any
   857  				// subsequent requests on the server connection. See
   858  				// golang.org/issue/12027
   859  				b.sawEOF = false
   860  				b.closed = true
   861  			}
   862  			b.hdr = nil
   863  		} else {
   864  			// If the server declared the Content-Length, our body is a LimitedReader
   865  			// and we need to check whether this EOF arrived early.
   866  			if lr, ok := b.src.(*io.LimitedReader); ok && lr.N > 0 {
   867  				err = io.ErrUnexpectedEOF
   868  			}
   869  		}
   870  	}
   871  
   872  	// If we can return an EOF here along with the read data, do
   873  	// so. This is optional per the io.Reader contract, but doing
   874  	// so helps the HTTP transport code recycle its connection
   875  	// earlier (since it will see this EOF itself), even if the
   876  	// client doesn't do future reads or Close.
   877  	if err == nil && n > 0 {
   878  		if lr, ok := b.src.(*io.LimitedReader); ok && lr.N == 0 {
   879  			err = io.EOF
   880  			b.sawEOF = true
   881  		}
   882  	}
   883  
   884  	if b.sawEOF && b.onHitEOF != nil {
   885  		b.onHitEOF()
   886  	}
   887  
   888  	return n, err
   889  }
   890  
   891  var (
   892  	singleCRLF = []byte("\r\n")
   893  	doubleCRLF = []byte("\r\n\r\n")
   894  )
   895  
   896  func seeUpcomingDoubleCRLF(r *bufio.Reader) bool {
   897  	for peekSize := 4; ; peekSize++ {
   898  		// This loop stops when Peek returns an error,
   899  		// which it does when r's buffer has been filled.
   900  		buf, err := r.Peek(peekSize)
   901  		if bytes.HasSuffix(buf, doubleCRLF) {
   902  			return true
   903  		}
   904  		if err != nil {
   905  			break
   906  		}
   907  	}
   908  	return false
   909  }
   910  
   911  var errTrailerEOF = errors.New("http: unexpected EOF reading trailer")
   912  
   913  func (b *body) readTrailer() error {
   914  	// The common case, since nobody uses trailers.
   915  	buf, err := b.r.Peek(2)
   916  	if bytes.Equal(buf, singleCRLF) {
   917  		b.r.Discard(2)
   918  		return nil
   919  	}
   920  	if len(buf) < 2 {
   921  		return errTrailerEOF
   922  	}
   923  	if err != nil {
   924  		return err
   925  	}
   926  
   927  	// Make sure there's a header terminator coming up, to prevent
   928  	// a DoS with an unbounded size Trailer. It's not easy to
   929  	// slip in a LimitReader here, as textproto.NewReader requires
   930  	// a concrete *bufio.Reader. Also, we can't get all the way
   931  	// back up to our conn's LimitedReader that *might* be backing
   932  	// this bufio.Reader. Instead, a hack: we iteratively Peek up
   933  	// to the bufio.Reader's max size, looking for a double CRLF.
   934  	// This limits the trailer to the underlying buffer size, typically 4kB.
   935  	if !seeUpcomingDoubleCRLF(b.r) {
   936  		return errors.New("http: suspiciously long trailer after chunked body")
   937  	}
   938  
   939  	hdr, err := textproto.NewReader(b.r).ReadMIMEHeader()
   940  	if err != nil {
   941  		if err == io.EOF {
   942  			return errTrailerEOF
   943  		}
   944  		return err
   945  	}
   946  	switch rr := b.hdr.(type) {
   947  	case *Request:
   948  		mergeSetHeader(&rr.Trailer, Header(hdr))
   949  	case *Response:
   950  		mergeSetHeader(&rr.Trailer, Header(hdr))
   951  	}
   952  	return nil
   953  }
   954  
   955  func mergeSetHeader(dst *Header, src Header) {
   956  	if *dst == nil {
   957  		*dst = src
   958  		return
   959  	}
   960  	for k, vv := range src {
   961  		(*dst)[k] = vv
   962  	}
   963  }
   964  
   965  // unreadDataSizeLocked returns the number of bytes of unread input.
   966  // It returns -1 if unknown.
   967  // b.mu must be held.
   968  func (b *body) unreadDataSizeLocked() int64 {
   969  	if lr, ok := b.src.(*io.LimitedReader); ok {
   970  		return lr.N
   971  	}
   972  	return -1
   973  }
   974  
   975  func (b *body) Close() error {
   976  	b.mu.Lock()
   977  	defer b.mu.Unlock()
   978  	if b.closed {
   979  		return nil
   980  	}
   981  	var err error
   982  	switch {
   983  	case b.sawEOF:
   984  		// Already saw EOF, so no need going to look for it.
   985  	case b.hdr == nil && b.closing:
   986  		// no trailer and closing the connection next.
   987  		// no point in reading to EOF.
   988  	case b.doEarlyClose:
   989  		// Read up to maxPostHandlerReadBytes bytes of the body, looking
   990  		// for EOF (and trailers), so we can re-use this connection.
   991  		if lr, ok := b.src.(*io.LimitedReader); ok && lr.N > maxPostHandlerReadBytes {
   992  			// There was a declared Content-Length, and we have more bytes remaining
   993  			// than our maxPostHandlerReadBytes tolerance. So, give up.
   994  			b.earlyClose = true
   995  		} else {
   996  			var n int64
   997  			// Consume the body, or, which will also lead to us reading
   998  			// the trailer headers after the body, if present.
   999  			n, err = io.CopyN(ioutil.Discard, bodyLocked{b}, maxPostHandlerReadBytes)
  1000  			if err == io.EOF {
  1001  				err = nil
  1002  			}
  1003  			if n == maxPostHandlerReadBytes {
  1004  				b.earlyClose = true
  1005  			}
  1006  		}
  1007  	default:
  1008  		// Fully consume the body, which will also lead to us reading
  1009  		// the trailer headers after the body, if present.
  1010  		_, err = io.Copy(ioutil.Discard, bodyLocked{b})
  1011  	}
  1012  	b.closed = true
  1013  	return err
  1014  }
  1015  
  1016  func (b *body) didEarlyClose() bool {
  1017  	b.mu.Lock()
  1018  	defer b.mu.Unlock()
  1019  	return b.earlyClose
  1020  }
  1021  
  1022  // bodyRemains reports whether future Read calls might
  1023  // yield data.
  1024  func (b *body) bodyRemains() bool {
  1025  	b.mu.Lock()
  1026  	defer b.mu.Unlock()
  1027  	return !b.sawEOF
  1028  }
  1029  
  1030  func (b *body) registerOnHitEOF(fn func()) {
  1031  	b.mu.Lock()
  1032  	defer b.mu.Unlock()
  1033  	b.onHitEOF = fn
  1034  }
  1035  
  1036  // bodyLocked is a io.Reader reading from a *body when its mutex is
  1037  // already held.
  1038  type bodyLocked struct {
  1039  	b *body
  1040  }
  1041  
  1042  func (bl bodyLocked) Read(p []byte) (n int, err error) {
  1043  	if bl.b.closed {
  1044  		return 0, ErrBodyReadAfterClose
  1045  	}
  1046  	return bl.b.readLocked(p)
  1047  }
  1048  
  1049  // parseContentLength trims whitespace from s and returns -1 if no value
  1050  // is set, or the value if it's >= 0.
  1051  func parseContentLength(cl string) (int64, error) {
  1052  	cl = strings.TrimSpace(cl)
  1053  	if cl == "" {
  1054  		return -1, nil
  1055  	}
  1056  	n, err := strconv.ParseInt(cl, 10, 64)
  1057  	if err != nil || n < 0 {
  1058  		return 0, &badStringError{"bad Content-Length", cl}
  1059  	}
  1060  	return n, nil
  1061  
  1062  }
  1063  
  1064  // finishAsyncByteRead finishes reading the 1-byte sniff
  1065  // from the ContentLength==0, Body!=nil case.
  1066  type finishAsyncByteRead struct {
  1067  	tw *transferWriter
  1068  }
  1069  
  1070  func (fr finishAsyncByteRead) Read(p []byte) (n int, err error) {
  1071  	if len(p) == 0 {
  1072  		return
  1073  	}
  1074  	rres := <-fr.tw.ByteReadCh
  1075  	n, err = rres.n, rres.err
  1076  	if n == 1 {
  1077  		p[0] = rres.b
  1078  	}
  1079  	return
  1080  }
  1081  
  1082  var nopCloserType = reflect.TypeOf(ioutil.NopCloser(nil))
  1083  
  1084  // isKnownInMemoryReader reports whether r is a type known to not
  1085  // block on Read. Its caller uses this as an optional optimization to
  1086  // send fewer TCP packets.
  1087  func isKnownInMemoryReader(r io.Reader) bool {
  1088  	switch r.(type) {
  1089  	case *bytes.Reader, *bytes.Buffer, *strings.Reader:
  1090  		return true
  1091  	}
  1092  	if reflect.TypeOf(r) == nopCloserType {
  1093  		return isKnownInMemoryReader(reflect.ValueOf(r).Field(0).Interface().(io.Reader))
  1094  	}
  1095  	return false
  1096  }
  1097  
  1098  // bufioFlushWriter is an io.Writer wrapper that flushes all writes
  1099  // on its wrapped writer if it's a *bufio.Writer.
  1100  type bufioFlushWriter struct{ w io.Writer }
  1101  
  1102  func (fw bufioFlushWriter) Write(p []byte) (n int, err error) {
  1103  	n, err = fw.w.Write(p)
  1104  	if bw, ok := fw.w.(*bufio.Writer); n > 0 && ok {
  1105  		ferr := bw.Flush()
  1106  		if ferr != nil && err == nil {
  1107  			err = ferr
  1108  		}
  1109  	}
  1110  	return
  1111  }
  1112  

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