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Source file src/net/http/transfer.go

     1	// Copyright 2009 The Go Authors. All rights reserved.
     2	// Use of this source code is governed by a BSD-style
     3	// license that can be found in the LICENSE file.
     4	
     5	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	
    21		"golang_org/x/net/lex/httplex"
    22	)
    23	
    24	// ErrLineTooLong is returned when reading request or response bodies
    25	// with malformed chunked encoding.
    26	var ErrLineTooLong = internal.ErrLineTooLong
    27	
    28	type errorReader struct {
    29		err error
    30	}
    31	
    32	func (r errorReader) Read(p []byte) (n int, err error) {
    33		return 0, r.err
    34	}
    35	
    36	// transferWriter inspects the fields of a user-supplied Request or Response,
    37	// sanitizes them without changing the user object and provides methods for
    38	// writing the respective header, body and trailer in wire format.
    39	type transferWriter struct {
    40		Method           string
    41		Body             io.Reader
    42		BodyCloser       io.Closer
    43		ResponseToHEAD   bool
    44		ContentLength    int64 // -1 means unknown, 0 means exactly none
    45		Close            bool
    46		TransferEncoding []string
    47		Trailer          Header
    48		IsResponse       bool
    49	}
    50	
    51	func newTransferWriter(r interface{}) (t *transferWriter, err error) {
    52		t = &transferWriter{}
    53	
    54		// Extract relevant fields
    55		atLeastHTTP11 := false
    56		switch rr := r.(type) {
    57		case *Request:
    58			if rr.ContentLength != 0 && rr.Body == nil {
    59				return nil, fmt.Errorf("http: Request.ContentLength=%d with nil Body", rr.ContentLength)
    60			}
    61			t.Method = valueOrDefault(rr.Method, "GET")
    62			t.Body = rr.Body
    63			t.BodyCloser = rr.Body
    64			t.ContentLength = rr.ContentLength
    65			t.Close = rr.Close
    66			t.TransferEncoding = rr.TransferEncoding
    67			t.Trailer = rr.Trailer
    68			atLeastHTTP11 = rr.ProtoAtLeast(1, 1)
    69			if t.Body != nil && len(t.TransferEncoding) == 0 && atLeastHTTP11 {
    70				if t.ContentLength == 0 {
    71					// Test to see if it's actually zero or just unset.
    72					var buf [1]byte
    73					n, rerr := io.ReadFull(t.Body, buf[:])
    74					if rerr != nil && rerr != io.EOF {
    75						t.ContentLength = -1
    76						t.Body = errorReader{rerr}
    77					} else if n == 1 {
    78						// Oh, guess there is data in this Body Reader after all.
    79						// The ContentLength field just wasn't set.
    80						// Stich the Body back together again, re-attaching our
    81						// consumed byte.
    82						t.ContentLength = -1
    83						t.Body = io.MultiReader(bytes.NewReader(buf[:]), t.Body)
    84					} else {
    85						// Body is actually empty.
    86						t.Body = nil
    87						t.BodyCloser = nil
    88					}
    89				}
    90				if t.ContentLength < 0 {
    91					t.TransferEncoding = []string{"chunked"}
    92				}
    93			}
    94		case *Response:
    95			t.IsResponse = true
    96			if rr.Request != nil {
    97				t.Method = rr.Request.Method
    98			}
    99			t.Body = rr.Body
   100			t.BodyCloser = rr.Body
   101			t.ContentLength = rr.ContentLength
   102			t.Close = rr.Close
   103			t.TransferEncoding = rr.TransferEncoding
   104			t.Trailer = rr.Trailer
   105			atLeastHTTP11 = rr.ProtoAtLeast(1, 1)
   106			t.ResponseToHEAD = noBodyExpected(t.Method)
   107		}
   108	
   109		// Sanitize Body,ContentLength,TransferEncoding
   110		if t.ResponseToHEAD {
   111			t.Body = nil
   112			if chunked(t.TransferEncoding) {
   113				t.ContentLength = -1
   114			}
   115		} else {
   116			if !atLeastHTTP11 || t.Body == nil {
   117				t.TransferEncoding = nil
   118			}
   119			if chunked(t.TransferEncoding) {
   120				t.ContentLength = -1
   121			} else if t.Body == nil { // no chunking, no body
   122				t.ContentLength = 0
   123			}
   124		}
   125	
   126		// Sanitize Trailer
   127		if !chunked(t.TransferEncoding) {
   128			t.Trailer = nil
   129		}
   130	
   131		return t, nil
   132	}
   133	
   134	func noBodyExpected(requestMethod string) bool {
   135		return requestMethod == "HEAD"
   136	}
   137	
   138	func (t *transferWriter) shouldSendContentLength() bool {
   139		if chunked(t.TransferEncoding) {
   140			return false
   141		}
   142		if t.ContentLength > 0 {
   143			return true
   144		}
   145		if t.ContentLength < 0 {
   146			return false
   147		}
   148		// Many servers expect a Content-Length for these methods
   149		if t.Method == "POST" || t.Method == "PUT" {
   150			return true
   151		}
   152		if t.ContentLength == 0 && isIdentity(t.TransferEncoding) {
   153			if t.Method == "GET" || t.Method == "HEAD" {
   154				return false
   155			}
   156			return true
   157		}
   158	
   159		return false
   160	}
   161	
   162	func (t *transferWriter) WriteHeader(w io.Writer) error {
   163		if t.Close {
   164			if _, err := io.WriteString(w, "Connection: close\r\n"); err != nil {
   165				return err
   166			}
   167		}
   168	
   169		// Write Content-Length and/or Transfer-Encoding whose values are a
   170		// function of the sanitized field triple (Body, ContentLength,
   171		// TransferEncoding)
   172		if t.shouldSendContentLength() {
   173			if _, err := io.WriteString(w, "Content-Length: "); err != nil {
   174				return err
   175			}
   176			if _, err := io.WriteString(w, strconv.FormatInt(t.ContentLength, 10)+"\r\n"); err != nil {
   177				return err
   178			}
   179		} else if chunked(t.TransferEncoding) {
   180			if _, err := io.WriteString(w, "Transfer-Encoding: chunked\r\n"); err != nil {
   181				return err
   182			}
   183		}
   184	
   185		// Write Trailer header
   186		if t.Trailer != nil {
   187			keys := make([]string, 0, len(t.Trailer))
   188			for k := range t.Trailer {
   189				k = CanonicalHeaderKey(k)
   190				switch k {
   191				case "Transfer-Encoding", "Trailer", "Content-Length":
   192					return &badStringError{"invalid Trailer key", k}
   193				}
   194				keys = append(keys, k)
   195			}
   196			if len(keys) > 0 {
   197				sort.Strings(keys)
   198				// TODO: could do better allocation-wise here, but trailers are rare,
   199				// so being lazy for now.
   200				if _, err := io.WriteString(w, "Trailer: "+strings.Join(keys, ",")+"\r\n"); err != nil {
   201					return err
   202				}
   203			}
   204		}
   205	
   206		return nil
   207	}
   208	
   209	func (t *transferWriter) WriteBody(w io.Writer) error {
   210		var err error
   211		var ncopy int64
   212	
   213		// Write body
   214		if t.Body != nil {
   215			if chunked(t.TransferEncoding) {
   216				if bw, ok := w.(*bufio.Writer); ok && !t.IsResponse {
   217					w = &internal.FlushAfterChunkWriter{bw}
   218				}
   219				cw := internal.NewChunkedWriter(w)
   220				_, err = io.Copy(cw, t.Body)
   221				if err == nil {
   222					err = cw.Close()
   223				}
   224			} else if t.ContentLength == -1 {
   225				ncopy, err = io.Copy(w, t.Body)
   226			} else {
   227				ncopy, err = io.Copy(w, io.LimitReader(t.Body, t.ContentLength))
   228				if err != nil {
   229					return err
   230				}
   231				var nextra int64
   232				nextra, err = io.Copy(ioutil.Discard, t.Body)
   233				ncopy += nextra
   234			}
   235			if err != nil {
   236				return err
   237			}
   238			if err = t.BodyCloser.Close(); err != nil {
   239				return err
   240			}
   241		}
   242	
   243		if !t.ResponseToHEAD && t.ContentLength != -1 && t.ContentLength != ncopy {
   244			return fmt.Errorf("http: ContentLength=%d with Body length %d",
   245				t.ContentLength, ncopy)
   246		}
   247	
   248		if chunked(t.TransferEncoding) {
   249			// Write Trailer header
   250			if t.Trailer != nil {
   251				if err := t.Trailer.Write(w); err != nil {
   252					return err
   253				}
   254			}
   255			// Last chunk, empty trailer
   256			_, err = io.WriteString(w, "\r\n")
   257		}
   258		return err
   259	}
   260	
   261	type transferReader struct {
   262		// Input
   263		Header        Header
   264		StatusCode    int
   265		RequestMethod string
   266		ProtoMajor    int
   267		ProtoMinor    int
   268		// Output
   269		Body             io.ReadCloser
   270		ContentLength    int64
   271		TransferEncoding []string
   272		Close            bool
   273		Trailer          Header
   274	}
   275	
   276	func (t *transferReader) protoAtLeast(m, n int) bool {
   277		return t.ProtoMajor > m || (t.ProtoMajor == m && t.ProtoMinor >= n)
   278	}
   279	
   280	// bodyAllowedForStatus reports whether a given response status code
   281	// permits a body. See RFC 2616, section 4.4.
   282	func bodyAllowedForStatus(status int) bool {
   283		switch {
   284		case status >= 100 && status <= 199:
   285			return false
   286		case status == 204:
   287			return false
   288		case status == 304:
   289			return false
   290		}
   291		return true
   292	}
   293	
   294	var (
   295		suppressedHeaders304    = []string{"Content-Type", "Content-Length", "Transfer-Encoding"}
   296		suppressedHeadersNoBody = []string{"Content-Length", "Transfer-Encoding"}
   297	)
   298	
   299	func suppressedHeaders(status int) []string {
   300		switch {
   301		case status == 304:
   302			// RFC 2616 section 10.3.5: "the response MUST NOT include other entity-headers"
   303			return suppressedHeaders304
   304		case !bodyAllowedForStatus(status):
   305			return suppressedHeadersNoBody
   306		}
   307		return nil
   308	}
   309	
   310	// msg is *Request or *Response.
   311	func readTransfer(msg interface{}, r *bufio.Reader) (err error) {
   312		t := &transferReader{RequestMethod: "GET"}
   313	
   314		// Unify input
   315		isResponse := false
   316		switch rr := msg.(type) {
   317		case *Response:
   318			t.Header = rr.Header
   319			t.StatusCode = rr.StatusCode
   320			t.ProtoMajor = rr.ProtoMajor
   321			t.ProtoMinor = rr.ProtoMinor
   322			t.Close = shouldClose(t.ProtoMajor, t.ProtoMinor, t.Header, true)
   323			isResponse = true
   324			if rr.Request != nil {
   325				t.RequestMethod = rr.Request.Method
   326			}
   327		case *Request:
   328			t.Header = rr.Header
   329			t.RequestMethod = rr.Method
   330			t.ProtoMajor = rr.ProtoMajor
   331			t.ProtoMinor = rr.ProtoMinor
   332			// Transfer semantics for Requests are exactly like those for
   333			// Responses with status code 200, responding to a GET method
   334			t.StatusCode = 200
   335			t.Close = rr.Close
   336		default:
   337			panic("unexpected type")
   338		}
   339	
   340		// Default to HTTP/1.1
   341		if t.ProtoMajor == 0 && t.ProtoMinor == 0 {
   342			t.ProtoMajor, t.ProtoMinor = 1, 1
   343		}
   344	
   345		// Transfer encoding, content length
   346		err = t.fixTransferEncoding()
   347		if err != nil {
   348			return err
   349		}
   350	
   351		realLength, err := fixLength(isResponse, t.StatusCode, t.RequestMethod, t.Header, t.TransferEncoding)
   352		if err != nil {
   353			return err
   354		}
   355		if isResponse && t.RequestMethod == "HEAD" {
   356			if n, err := parseContentLength(t.Header.get("Content-Length")); err != nil {
   357				return err
   358			} else {
   359				t.ContentLength = n
   360			}
   361		} else {
   362			t.ContentLength = realLength
   363		}
   364	
   365		// Trailer
   366		t.Trailer, err = fixTrailer(t.Header, t.TransferEncoding)
   367		if err != nil {
   368			return err
   369		}
   370	
   371		// If there is no Content-Length or chunked Transfer-Encoding on a *Response
   372		// and the status is not 1xx, 204 or 304, then the body is unbounded.
   373		// See RFC 2616, section 4.4.
   374		switch msg.(type) {
   375		case *Response:
   376			if realLength == -1 &&
   377				!chunked(t.TransferEncoding) &&
   378				bodyAllowedForStatus(t.StatusCode) {
   379				// Unbounded body.
   380				t.Close = true
   381			}
   382		}
   383	
   384		// Prepare body reader. ContentLength < 0 means chunked encoding
   385		// or close connection when finished, since multipart is not supported yet
   386		switch {
   387		case chunked(t.TransferEncoding):
   388			if noBodyExpected(t.RequestMethod) {
   389				t.Body = eofReader
   390			} else {
   391				t.Body = &body{src: internal.NewChunkedReader(r), hdr: msg, r: r, closing: t.Close}
   392			}
   393		case realLength == 0:
   394			t.Body = eofReader
   395		case realLength > 0:
   396			t.Body = &body{src: io.LimitReader(r, realLength), closing: t.Close}
   397		default:
   398			// realLength < 0, i.e. "Content-Length" not mentioned in header
   399			if t.Close {
   400				// Close semantics (i.e. HTTP/1.0)
   401				t.Body = &body{src: r, closing: t.Close}
   402			} else {
   403				// Persistent connection (i.e. HTTP/1.1)
   404				t.Body = eofReader
   405			}
   406		}
   407	
   408		// Unify output
   409		switch rr := msg.(type) {
   410		case *Request:
   411			rr.Body = t.Body
   412			rr.ContentLength = t.ContentLength
   413			rr.TransferEncoding = t.TransferEncoding
   414			rr.Close = t.Close
   415			rr.Trailer = t.Trailer
   416		case *Response:
   417			rr.Body = t.Body
   418			rr.ContentLength = t.ContentLength
   419			rr.TransferEncoding = t.TransferEncoding
   420			rr.Close = t.Close
   421			rr.Trailer = t.Trailer
   422		}
   423	
   424		return nil
   425	}
   426	
   427	// Checks whether chunked is part of the encodings stack
   428	func chunked(te []string) bool { return len(te) > 0 && te[0] == "chunked" }
   429	
   430	// Checks whether the encoding is explicitly "identity".
   431	func isIdentity(te []string) bool { return len(te) == 1 && te[0] == "identity" }
   432	
   433	// fixTransferEncoding sanitizes t.TransferEncoding, if needed.
   434	func (t *transferReader) fixTransferEncoding() error {
   435		raw, present := t.Header["Transfer-Encoding"]
   436		if !present {
   437			return nil
   438		}
   439		delete(t.Header, "Transfer-Encoding")
   440	
   441		// Issue 12785; ignore Transfer-Encoding on HTTP/1.0 requests.
   442		if !t.protoAtLeast(1, 1) {
   443			return nil
   444		}
   445	
   446		encodings := strings.Split(raw[0], ",")
   447		te := make([]string, 0, len(encodings))
   448		// TODO: Even though we only support "identity" and "chunked"
   449		// encodings, the loop below is designed with foresight. One
   450		// invariant that must be maintained is that, if present,
   451		// chunked encoding must always come first.
   452		for _, encoding := range encodings {
   453			encoding = strings.ToLower(strings.TrimSpace(encoding))
   454			// "identity" encoding is not recorded
   455			if encoding == "identity" {
   456				break
   457			}
   458			if encoding != "chunked" {
   459				return &badStringError{"unsupported transfer encoding", encoding}
   460			}
   461			te = te[0 : len(te)+1]
   462			te[len(te)-1] = encoding
   463		}
   464		if len(te) > 1 {
   465			return &badStringError{"too many transfer encodings", strings.Join(te, ",")}
   466		}
   467		if len(te) > 0 {
   468			// RFC 7230 3.3.2 says "A sender MUST NOT send a
   469			// Content-Length header field in any message that
   470			// contains a Transfer-Encoding header field."
   471			//
   472			// but also:
   473			// "If a message is received with both a
   474			// Transfer-Encoding and a Content-Length header
   475			// field, the Transfer-Encoding overrides the
   476			// Content-Length. Such a message might indicate an
   477			// attempt to perform request smuggling (Section 9.5)
   478			// or response splitting (Section 9.4) and ought to be
   479			// handled as an error. A sender MUST remove the
   480			// received Content-Length field prior to forwarding
   481			// such a message downstream."
   482			//
   483			// Reportedly, these appear in the wild.
   484			delete(t.Header, "Content-Length")
   485			t.TransferEncoding = te
   486			return nil
   487		}
   488	
   489		return nil
   490	}
   491	
   492	// Determine the expected body length, using RFC 2616 Section 4.4. This
   493	// function is not a method, because ultimately it should be shared by
   494	// ReadResponse and ReadRequest.
   495	func fixLength(isResponse bool, status int, requestMethod string, header Header, te []string) (int64, error) {
   496		contentLens := header["Content-Length"]
   497		isRequest := !isResponse
   498		// Logic based on response type or status
   499		if noBodyExpected(requestMethod) {
   500			// For HTTP requests, as part of hardening against request
   501			// smuggling (RFC 7230), don't allow a Content-Length header for
   502			// methods which don't permit bodies. As an exception, allow
   503			// exactly one Content-Length header if its value is "0".
   504			if isRequest && len(contentLens) > 0 && !(len(contentLens) == 1 && contentLens[0] == "0") {
   505				return 0, fmt.Errorf("http: method cannot contain a Content-Length; got %q", contentLens)
   506			}
   507			return 0, nil
   508		}
   509		if status/100 == 1 {
   510			return 0, nil
   511		}
   512		switch status {
   513		case 204, 304:
   514			return 0, nil
   515		}
   516	
   517		if len(contentLens) > 1 {
   518			// harden against HTTP request smuggling. See RFC 7230.
   519			return 0, errors.New("http: message cannot contain multiple Content-Length headers")
   520		}
   521	
   522		// Logic based on Transfer-Encoding
   523		if chunked(te) {
   524			return -1, nil
   525		}
   526	
   527		// Logic based on Content-Length
   528		var cl string
   529		if len(contentLens) == 1 {
   530			cl = strings.TrimSpace(contentLens[0])
   531		}
   532		if cl != "" {
   533			n, err := parseContentLength(cl)
   534			if err != nil {
   535				return -1, err
   536			}
   537			return n, nil
   538		} else {
   539			header.Del("Content-Length")
   540		}
   541	
   542		if !isResponse {
   543			// RFC 2616 neither explicitly permits nor forbids an
   544			// entity-body on a GET request so we permit one if
   545			// declared, but we default to 0 here (not -1 below)
   546			// if there's no mention of a body.
   547			// Likewise, all other request methods are assumed to have
   548			// no body if neither Transfer-Encoding chunked nor a
   549			// Content-Length are set.
   550			return 0, nil
   551		}
   552	
   553		// Body-EOF logic based on other methods (like closing, or chunked coding)
   554		return -1, nil
   555	}
   556	
   557	// Determine whether to hang up after sending a request and body, or
   558	// receiving a response and body
   559	// 'header' is the request headers
   560	func shouldClose(major, minor int, header Header, removeCloseHeader bool) bool {
   561		if major < 1 {
   562			return true
   563		}
   564	
   565		conv := header["Connection"]
   566		hasClose := httplex.HeaderValuesContainsToken(conv, "close")
   567		if major == 1 && minor == 0 {
   568			return hasClose || !httplex.HeaderValuesContainsToken(conv, "keep-alive")
   569		}
   570	
   571		if hasClose && removeCloseHeader {
   572			header.Del("Connection")
   573		}
   574	
   575		return hasClose
   576	}
   577	
   578	// Parse the trailer header
   579	func fixTrailer(header Header, te []string) (Header, error) {
   580		vv, ok := header["Trailer"]
   581		if !ok {
   582			return nil, nil
   583		}
   584		header.Del("Trailer")
   585	
   586		trailer := make(Header)
   587		var err error
   588		for _, v := range vv {
   589			foreachHeaderElement(v, func(key string) {
   590				key = CanonicalHeaderKey(key)
   591				switch key {
   592				case "Transfer-Encoding", "Trailer", "Content-Length":
   593					if err == nil {
   594						err = &badStringError{"bad trailer key", key}
   595						return
   596					}
   597				}
   598				trailer[key] = nil
   599			})
   600		}
   601		if err != nil {
   602			return nil, err
   603		}
   604		if len(trailer) == 0 {
   605			return nil, nil
   606		}
   607		if !chunked(te) {
   608			// Trailer and no chunking
   609			return nil, ErrUnexpectedTrailer
   610		}
   611		return trailer, nil
   612	}
   613	
   614	// body turns a Reader into a ReadCloser.
   615	// Close ensures that the body has been fully read
   616	// and then reads the trailer if necessary.
   617	type body struct {
   618		src          io.Reader
   619		hdr          interface{}   // non-nil (Response or Request) value means read trailer
   620		r            *bufio.Reader // underlying wire-format reader for the trailer
   621		closing      bool          // is the connection to be closed after reading body?
   622		doEarlyClose bool          // whether Close should stop early
   623	
   624		mu         sync.Mutex // guards following, and calls to Read and Close
   625		sawEOF     bool
   626		closed     bool
   627		earlyClose bool   // Close called and we didn't read to the end of src
   628		onHitEOF   func() // if non-nil, func to call when EOF is Read
   629	}
   630	
   631	// ErrBodyReadAfterClose is returned when reading a Request or Response
   632	// Body after the body has been closed. This typically happens when the body is
   633	// read after an HTTP Handler calls WriteHeader or Write on its
   634	// ResponseWriter.
   635	var ErrBodyReadAfterClose = errors.New("http: invalid Read on closed Body")
   636	
   637	func (b *body) Read(p []byte) (n int, err error) {
   638		b.mu.Lock()
   639		defer b.mu.Unlock()
   640		if b.closed {
   641			return 0, ErrBodyReadAfterClose
   642		}
   643		return b.readLocked(p)
   644	}
   645	
   646	// Must hold b.mu.
   647	func (b *body) readLocked(p []byte) (n int, err error) {
   648		if b.sawEOF {
   649			return 0, io.EOF
   650		}
   651		n, err = b.src.Read(p)
   652	
   653		if err == io.EOF {
   654			b.sawEOF = true
   655			// Chunked case. Read the trailer.
   656			if b.hdr != nil {
   657				if e := b.readTrailer(); e != nil {
   658					err = e
   659					// Something went wrong in the trailer, we must not allow any
   660					// further reads of any kind to succeed from body, nor any
   661					// subsequent requests on the server connection. See
   662					// golang.org/issue/12027
   663					b.sawEOF = false
   664					b.closed = true
   665				}
   666				b.hdr = nil
   667			} else {
   668				// If the server declared the Content-Length, our body is a LimitedReader
   669				// and we need to check whether this EOF arrived early.
   670				if lr, ok := b.src.(*io.LimitedReader); ok && lr.N > 0 {
   671					err = io.ErrUnexpectedEOF
   672				}
   673			}
   674		}
   675	
   676		// If we can return an EOF here along with the read data, do
   677		// so. This is optional per the io.Reader contract, but doing
   678		// so helps the HTTP transport code recycle its connection
   679		// earlier (since it will see this EOF itself), even if the
   680		// client doesn't do future reads or Close.
   681		if err == nil && n > 0 {
   682			if lr, ok := b.src.(*io.LimitedReader); ok && lr.N == 0 {
   683				err = io.EOF
   684				b.sawEOF = true
   685			}
   686		}
   687	
   688		if b.sawEOF && b.onHitEOF != nil {
   689			b.onHitEOF()
   690		}
   691	
   692		return n, err
   693	}
   694	
   695	var (
   696		singleCRLF = []byte("\r\n")
   697		doubleCRLF = []byte("\r\n\r\n")
   698	)
   699	
   700	func seeUpcomingDoubleCRLF(r *bufio.Reader) bool {
   701		for peekSize := 4; ; peekSize++ {
   702			// This loop stops when Peek returns an error,
   703			// which it does when r's buffer has been filled.
   704			buf, err := r.Peek(peekSize)
   705			if bytes.HasSuffix(buf, doubleCRLF) {
   706				return true
   707			}
   708			if err != nil {
   709				break
   710			}
   711		}
   712		return false
   713	}
   714	
   715	var errTrailerEOF = errors.New("http: unexpected EOF reading trailer")
   716	
   717	func (b *body) readTrailer() error {
   718		// The common case, since nobody uses trailers.
   719		buf, err := b.r.Peek(2)
   720		if bytes.Equal(buf, singleCRLF) {
   721			b.r.Discard(2)
   722			return nil
   723		}
   724		if len(buf) < 2 {
   725			return errTrailerEOF
   726		}
   727		if err != nil {
   728			return err
   729		}
   730	
   731		// Make sure there's a header terminator coming up, to prevent
   732		// a DoS with an unbounded size Trailer. It's not easy to
   733		// slip in a LimitReader here, as textproto.NewReader requires
   734		// a concrete *bufio.Reader. Also, we can't get all the way
   735		// back up to our conn's LimitedReader that *might* be backing
   736		// this bufio.Reader. Instead, a hack: we iteratively Peek up
   737		// to the bufio.Reader's max size, looking for a double CRLF.
   738		// This limits the trailer to the underlying buffer size, typically 4kB.
   739		if !seeUpcomingDoubleCRLF(b.r) {
   740			return errors.New("http: suspiciously long trailer after chunked body")
   741		}
   742	
   743		hdr, err := textproto.NewReader(b.r).ReadMIMEHeader()
   744		if err != nil {
   745			if err == io.EOF {
   746				return errTrailerEOF
   747			}
   748			return err
   749		}
   750		switch rr := b.hdr.(type) {
   751		case *Request:
   752			mergeSetHeader(&rr.Trailer, Header(hdr))
   753		case *Response:
   754			mergeSetHeader(&rr.Trailer, Header(hdr))
   755		}
   756		return nil
   757	}
   758	
   759	func mergeSetHeader(dst *Header, src Header) {
   760		if *dst == nil {
   761			*dst = src
   762			return
   763		}
   764		for k, vv := range src {
   765			(*dst)[k] = vv
   766		}
   767	}
   768	
   769	// unreadDataSizeLocked returns the number of bytes of unread input.
   770	// It returns -1 if unknown.
   771	// b.mu must be held.
   772	func (b *body) unreadDataSizeLocked() int64 {
   773		if lr, ok := b.src.(*io.LimitedReader); ok {
   774			return lr.N
   775		}
   776		return -1
   777	}
   778	
   779	func (b *body) Close() error {
   780		b.mu.Lock()
   781		defer b.mu.Unlock()
   782		if b.closed {
   783			return nil
   784		}
   785		var err error
   786		switch {
   787		case b.sawEOF:
   788			// Already saw EOF, so no need going to look for it.
   789		case b.hdr == nil && b.closing:
   790			// no trailer and closing the connection next.
   791			// no point in reading to EOF.
   792		case b.doEarlyClose:
   793			// Read up to maxPostHandlerReadBytes bytes of the body, looking for
   794			// for EOF (and trailers), so we can re-use this connection.
   795			if lr, ok := b.src.(*io.LimitedReader); ok && lr.N > maxPostHandlerReadBytes {
   796				// There was a declared Content-Length, and we have more bytes remaining
   797				// than our maxPostHandlerReadBytes tolerance. So, give up.
   798				b.earlyClose = true
   799			} else {
   800				var n int64
   801				// Consume the body, or, which will also lead to us reading
   802				// the trailer headers after the body, if present.
   803				n, err = io.CopyN(ioutil.Discard, bodyLocked{b}, maxPostHandlerReadBytes)
   804				if err == io.EOF {
   805					err = nil
   806				}
   807				if n == maxPostHandlerReadBytes {
   808					b.earlyClose = true
   809				}
   810			}
   811		default:
   812			// Fully consume the body, which will also lead to us reading
   813			// the trailer headers after the body, if present.
   814			_, err = io.Copy(ioutil.Discard, bodyLocked{b})
   815		}
   816		b.closed = true
   817		return err
   818	}
   819	
   820	func (b *body) didEarlyClose() bool {
   821		b.mu.Lock()
   822		defer b.mu.Unlock()
   823		return b.earlyClose
   824	}
   825	
   826	// bodyRemains reports whether future Read calls might
   827	// yield data.
   828	func (b *body) bodyRemains() bool {
   829		b.mu.Lock()
   830		defer b.mu.Unlock()
   831		return !b.sawEOF
   832	}
   833	
   834	func (b *body) registerOnHitEOF(fn func()) {
   835		b.mu.Lock()
   836		defer b.mu.Unlock()
   837		b.onHitEOF = fn
   838	}
   839	
   840	// bodyLocked is a io.Reader reading from a *body when its mutex is
   841	// already held.
   842	type bodyLocked struct {
   843		b *body
   844	}
   845	
   846	func (bl bodyLocked) Read(p []byte) (n int, err error) {
   847		if bl.b.closed {
   848			return 0, ErrBodyReadAfterClose
   849		}
   850		return bl.b.readLocked(p)
   851	}
   852	
   853	// parseContentLength trims whitespace from s and returns -1 if no value
   854	// is set, or the value if it's >= 0.
   855	func parseContentLength(cl string) (int64, error) {
   856		cl = strings.TrimSpace(cl)
   857		if cl == "" {
   858			return -1, nil
   859		}
   860		n, err := strconv.ParseInt(cl, 10, 64)
   861		if err != nil || n < 0 {
   862			return 0, &badStringError{"bad Content-Length", cl}
   863		}
   864		return n, nil
   865	
   866	}
   867	

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