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Source file src/pkg/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/textproto"
    15		"sort"
    16		"strconv"
    17		"strings"
    18		"sync"
    19	)
    20	
    21	type errorReader struct {
    22		err error
    23	}
    24	
    25	func (r *errorReader) Read(p []byte) (n int, err error) {
    26		return 0, r.err
    27	}
    28	
    29	// transferWriter inspects the fields of a user-supplied Request or Response,
    30	// sanitizes them without changing the user object and provides methods for
    31	// writing the respective header, body and trailer in wire format.
    32	type transferWriter struct {
    33		Method           string
    34		Body             io.Reader
    35		BodyCloser       io.Closer
    36		ResponseToHEAD   bool
    37		ContentLength    int64 // -1 means unknown, 0 means exactly none
    38		Close            bool
    39		TransferEncoding []string
    40		Trailer          Header
    41	}
    42	
    43	func newTransferWriter(r interface{}) (t *transferWriter, err error) {
    44		t = &transferWriter{}
    45	
    46		// Extract relevant fields
    47		atLeastHTTP11 := false
    48		switch rr := r.(type) {
    49		case *Request:
    50			if rr.ContentLength != 0 && rr.Body == nil {
    51				return nil, fmt.Errorf("http: Request.ContentLength=%d with nil Body", rr.ContentLength)
    52			}
    53			t.Method = rr.Method
    54			t.Body = rr.Body
    55			t.BodyCloser = rr.Body
    56			t.ContentLength = rr.ContentLength
    57			t.Close = rr.Close
    58			t.TransferEncoding = rr.TransferEncoding
    59			t.Trailer = rr.Trailer
    60			atLeastHTTP11 = rr.ProtoAtLeast(1, 1)
    61			if t.Body != nil && len(t.TransferEncoding) == 0 && atLeastHTTP11 {
    62				if t.ContentLength == 0 {
    63					// Test to see if it's actually zero or just unset.
    64					var buf [1]byte
    65					n, rerr := io.ReadFull(t.Body, buf[:])
    66					if rerr != nil && rerr != io.EOF {
    67						t.ContentLength = -1
    68						t.Body = &errorReader{rerr}
    69					} else if n == 1 {
    70						// Oh, guess there is data in this Body Reader after all.
    71						// The ContentLength field just wasn't set.
    72						// Stich the Body back together again, re-attaching our
    73						// consumed byte.
    74						t.ContentLength = -1
    75						t.Body = io.MultiReader(bytes.NewReader(buf[:]), t.Body)
    76					} else {
    77						// Body is actually empty.
    78						t.Body = nil
    79						t.BodyCloser = nil
    80					}
    81				}
    82				if t.ContentLength < 0 {
    83					t.TransferEncoding = []string{"chunked"}
    84				}
    85			}
    86		case *Response:
    87			if rr.Request != nil {
    88				t.Method = rr.Request.Method
    89			}
    90			t.Body = rr.Body
    91			t.BodyCloser = rr.Body
    92			t.ContentLength = rr.ContentLength
    93			t.Close = rr.Close
    94			t.TransferEncoding = rr.TransferEncoding
    95			t.Trailer = rr.Trailer
    96			atLeastHTTP11 = rr.ProtoAtLeast(1, 1)
    97			t.ResponseToHEAD = noBodyExpected(t.Method)
    98		}
    99	
   100		// Sanitize Body,ContentLength,TransferEncoding
   101		if t.ResponseToHEAD {
   102			t.Body = nil
   103			if chunked(t.TransferEncoding) {
   104				t.ContentLength = -1
   105			}
   106		} else {
   107			if !atLeastHTTP11 || t.Body == nil {
   108				t.TransferEncoding = nil
   109			}
   110			if chunked(t.TransferEncoding) {
   111				t.ContentLength = -1
   112			} else if t.Body == nil { // no chunking, no body
   113				t.ContentLength = 0
   114			}
   115		}
   116	
   117		// Sanitize Trailer
   118		if !chunked(t.TransferEncoding) {
   119			t.Trailer = nil
   120		}
   121	
   122		return t, nil
   123	}
   124	
   125	func noBodyExpected(requestMethod string) bool {
   126		return requestMethod == "HEAD"
   127	}
   128	
   129	func (t *transferWriter) shouldSendContentLength() bool {
   130		if chunked(t.TransferEncoding) {
   131			return false
   132		}
   133		if t.ContentLength > 0 {
   134			return true
   135		}
   136		// Many servers expect a Content-Length for these methods
   137		if t.Method == "POST" || t.Method == "PUT" {
   138			return true
   139		}
   140		if t.ContentLength == 0 && isIdentity(t.TransferEncoding) {
   141			return true
   142		}
   143	
   144		return false
   145	}
   146	
   147	func (t *transferWriter) WriteHeader(w io.Writer) error {
   148		if t.Close {
   149			if _, err := io.WriteString(w, "Connection: close\r\n"); err != nil {
   150				return err
   151			}
   152		}
   153	
   154		// Write Content-Length and/or Transfer-Encoding whose values are a
   155		// function of the sanitized field triple (Body, ContentLength,
   156		// TransferEncoding)
   157		if t.shouldSendContentLength() {
   158			if _, err := io.WriteString(w, "Content-Length: "); err != nil {
   159				return err
   160			}
   161			if _, err := io.WriteString(w, strconv.FormatInt(t.ContentLength, 10)+"\r\n"); err != nil {
   162				return err
   163			}
   164		} else if chunked(t.TransferEncoding) {
   165			if _, err := io.WriteString(w, "Transfer-Encoding: chunked\r\n"); err != nil {
   166				return err
   167			}
   168		}
   169	
   170		// Write Trailer header
   171		if t.Trailer != nil {
   172			keys := make([]string, 0, len(t.Trailer))
   173			for k := range t.Trailer {
   174				k = CanonicalHeaderKey(k)
   175				switch k {
   176				case "Transfer-Encoding", "Trailer", "Content-Length":
   177					return &badStringError{"invalid Trailer key", k}
   178				}
   179				keys = append(keys, k)
   180			}
   181			if len(keys) > 0 {
   182				sort.Strings(keys)
   183				// TODO: could do better allocation-wise here, but trailers are rare,
   184				// so being lazy for now.
   185				if _, err := io.WriteString(w, "Trailer: "+strings.Join(keys, ",")+"\r\n"); err != nil {
   186					return err
   187				}
   188			}
   189		}
   190	
   191		return nil
   192	}
   193	
   194	func (t *transferWriter) WriteBody(w io.Writer) error {
   195		var err error
   196		var ncopy int64
   197	
   198		// Write body
   199		if t.Body != nil {
   200			if chunked(t.TransferEncoding) {
   201				cw := newChunkedWriter(w)
   202				_, err = io.Copy(cw, t.Body)
   203				if err == nil {
   204					err = cw.Close()
   205				}
   206			} else if t.ContentLength == -1 {
   207				ncopy, err = io.Copy(w, t.Body)
   208			} else {
   209				ncopy, err = io.Copy(w, io.LimitReader(t.Body, t.ContentLength))
   210				if err != nil {
   211					return err
   212				}
   213				var nextra int64
   214				nextra, err = io.Copy(ioutil.Discard, t.Body)
   215				ncopy += nextra
   216			}
   217			if err != nil {
   218				return err
   219			}
   220			if err = t.BodyCloser.Close(); err != nil {
   221				return err
   222			}
   223		}
   224	
   225		if !t.ResponseToHEAD && t.ContentLength != -1 && t.ContentLength != ncopy {
   226			return fmt.Errorf("http: Request.ContentLength=%d with Body length %d",
   227				t.ContentLength, ncopy)
   228		}
   229	
   230		// TODO(petar): Place trailer writer code here.
   231		if chunked(t.TransferEncoding) {
   232			// Write Trailer header
   233			if t.Trailer != nil {
   234				if err := t.Trailer.Write(w); err != nil {
   235					return err
   236				}
   237			}
   238			// Last chunk, empty trailer
   239			_, err = io.WriteString(w, "\r\n")
   240		}
   241		return err
   242	}
   243	
   244	type transferReader struct {
   245		// Input
   246		Header        Header
   247		StatusCode    int
   248		RequestMethod string
   249		ProtoMajor    int
   250		ProtoMinor    int
   251		// Output
   252		Body             io.ReadCloser
   253		ContentLength    int64
   254		TransferEncoding []string
   255		Close            bool
   256		Trailer          Header
   257	}
   258	
   259	// bodyAllowedForStatus reports whether a given response status code
   260	// permits a body.  See RFC2616, section 4.4.
   261	func bodyAllowedForStatus(status int) bool {
   262		switch {
   263		case status >= 100 && status <= 199:
   264			return false
   265		case status == 204:
   266			return false
   267		case status == 304:
   268			return false
   269		}
   270		return true
   271	}
   272	
   273	var (
   274		suppressedHeaders304    = []string{"Content-Type", "Content-Length", "Transfer-Encoding"}
   275		suppressedHeadersNoBody = []string{"Content-Length", "Transfer-Encoding"}
   276	)
   277	
   278	func suppressedHeaders(status int) []string {
   279		switch {
   280		case status == 304:
   281			// RFC 2616 section 10.3.5: "the response MUST NOT include other entity-headers"
   282			return suppressedHeaders304
   283		case !bodyAllowedForStatus(status):
   284			return suppressedHeadersNoBody
   285		}
   286		return nil
   287	}
   288	
   289	// msg is *Request or *Response.
   290	func readTransfer(msg interface{}, r *bufio.Reader) (err error) {
   291		t := &transferReader{RequestMethod: "GET"}
   292	
   293		// Unify input
   294		isResponse := false
   295		switch rr := msg.(type) {
   296		case *Response:
   297			t.Header = rr.Header
   298			t.StatusCode = rr.StatusCode
   299			t.ProtoMajor = rr.ProtoMajor
   300			t.ProtoMinor = rr.ProtoMinor
   301			t.Close = shouldClose(t.ProtoMajor, t.ProtoMinor, t.Header)
   302			isResponse = true
   303			if rr.Request != nil {
   304				t.RequestMethod = rr.Request.Method
   305			}
   306		case *Request:
   307			t.Header = rr.Header
   308			t.ProtoMajor = rr.ProtoMajor
   309			t.ProtoMinor = rr.ProtoMinor
   310			// Transfer semantics for Requests are exactly like those for
   311			// Responses with status code 200, responding to a GET method
   312			t.StatusCode = 200
   313		default:
   314			panic("unexpected type")
   315		}
   316	
   317		// Default to HTTP/1.1
   318		if t.ProtoMajor == 0 && t.ProtoMinor == 0 {
   319			t.ProtoMajor, t.ProtoMinor = 1, 1
   320		}
   321	
   322		// Transfer encoding, content length
   323		t.TransferEncoding, err = fixTransferEncoding(t.RequestMethod, t.Header)
   324		if err != nil {
   325			return err
   326		}
   327	
   328		realLength, err := fixLength(isResponse, t.StatusCode, t.RequestMethod, t.Header, t.TransferEncoding)
   329		if err != nil {
   330			return err
   331		}
   332		if isResponse && t.RequestMethod == "HEAD" {
   333			if n, err := parseContentLength(t.Header.get("Content-Length")); err != nil {
   334				return err
   335			} else {
   336				t.ContentLength = n
   337			}
   338		} else {
   339			t.ContentLength = realLength
   340		}
   341	
   342		// Trailer
   343		t.Trailer, err = fixTrailer(t.Header, t.TransferEncoding)
   344		if err != nil {
   345			return err
   346		}
   347	
   348		// If there is no Content-Length or chunked Transfer-Encoding on a *Response
   349		// and the status is not 1xx, 204 or 304, then the body is unbounded.
   350		// See RFC2616, section 4.4.
   351		switch msg.(type) {
   352		case *Response:
   353			if realLength == -1 &&
   354				!chunked(t.TransferEncoding) &&
   355				bodyAllowedForStatus(t.StatusCode) {
   356				// Unbounded body.
   357				t.Close = true
   358			}
   359		}
   360	
   361		// Prepare body reader.  ContentLength < 0 means chunked encoding
   362		// or close connection when finished, since multipart is not supported yet
   363		switch {
   364		case chunked(t.TransferEncoding):
   365			if noBodyExpected(t.RequestMethod) {
   366				t.Body = eofReader
   367			} else {
   368				t.Body = &body{src: newChunkedReader(r), hdr: msg, r: r, closing: t.Close}
   369			}
   370		case realLength == 0:
   371			t.Body = eofReader
   372		case realLength > 0:
   373			t.Body = &body{src: io.LimitReader(r, realLength), closing: t.Close}
   374		default:
   375			// realLength < 0, i.e. "Content-Length" not mentioned in header
   376			if t.Close {
   377				// Close semantics (i.e. HTTP/1.0)
   378				t.Body = &body{src: r, closing: t.Close}
   379			} else {
   380				// Persistent connection (i.e. HTTP/1.1)
   381				t.Body = eofReader
   382			}
   383		}
   384	
   385		// Unify output
   386		switch rr := msg.(type) {
   387		case *Request:
   388			rr.Body = t.Body
   389			rr.ContentLength = t.ContentLength
   390			rr.TransferEncoding = t.TransferEncoding
   391			rr.Close = t.Close
   392			rr.Trailer = t.Trailer
   393		case *Response:
   394			rr.Body = t.Body
   395			rr.ContentLength = t.ContentLength
   396			rr.TransferEncoding = t.TransferEncoding
   397			rr.Close = t.Close
   398			rr.Trailer = t.Trailer
   399		}
   400	
   401		return nil
   402	}
   403	
   404	// Checks whether chunked is part of the encodings stack
   405	func chunked(te []string) bool { return len(te) > 0 && te[0] == "chunked" }
   406	
   407	// Checks whether the encoding is explicitly "identity".
   408	func isIdentity(te []string) bool { return len(te) == 1 && te[0] == "identity" }
   409	
   410	// Sanitize transfer encoding
   411	func fixTransferEncoding(requestMethod string, header Header) ([]string, error) {
   412		raw, present := header["Transfer-Encoding"]
   413		if !present {
   414			return nil, nil
   415		}
   416	
   417		delete(header, "Transfer-Encoding")
   418	
   419		encodings := strings.Split(raw[0], ",")
   420		te := make([]string, 0, len(encodings))
   421		// TODO: Even though we only support "identity" and "chunked"
   422		// encodings, the loop below is designed with foresight. One
   423		// invariant that must be maintained is that, if present,
   424		// chunked encoding must always come first.
   425		for _, encoding := range encodings {
   426			encoding = strings.ToLower(strings.TrimSpace(encoding))
   427			// "identity" encoding is not recorded
   428			if encoding == "identity" {
   429				break
   430			}
   431			if encoding != "chunked" {
   432				return nil, &badStringError{"unsupported transfer encoding", encoding}
   433			}
   434			te = te[0 : len(te)+1]
   435			te[len(te)-1] = encoding
   436		}
   437		if len(te) > 1 {
   438			return nil, &badStringError{"too many transfer encodings", strings.Join(te, ",")}
   439		}
   440		if len(te) > 0 {
   441			// Chunked encoding trumps Content-Length. See RFC 2616
   442			// Section 4.4. Currently len(te) > 0 implies chunked
   443			// encoding.
   444			delete(header, "Content-Length")
   445			return te, nil
   446		}
   447	
   448		return nil, nil
   449	}
   450	
   451	// Determine the expected body length, using RFC 2616 Section 4.4. This
   452	// function is not a method, because ultimately it should be shared by
   453	// ReadResponse and ReadRequest.
   454	func fixLength(isResponse bool, status int, requestMethod string, header Header, te []string) (int64, error) {
   455	
   456		// Logic based on response type or status
   457		if noBodyExpected(requestMethod) {
   458			return 0, nil
   459		}
   460		if status/100 == 1 {
   461			return 0, nil
   462		}
   463		switch status {
   464		case 204, 304:
   465			return 0, nil
   466		}
   467	
   468		// Logic based on Transfer-Encoding
   469		if chunked(te) {
   470			return -1, nil
   471		}
   472	
   473		// Logic based on Content-Length
   474		cl := strings.TrimSpace(header.get("Content-Length"))
   475		if cl != "" {
   476			n, err := parseContentLength(cl)
   477			if err != nil {
   478				return -1, err
   479			}
   480			return n, nil
   481		} else {
   482			header.Del("Content-Length")
   483		}
   484	
   485		if !isResponse && requestMethod == "GET" {
   486			// RFC 2616 doesn't explicitly permit nor forbid an
   487			// entity-body on a GET request so we permit one if
   488			// declared, but we default to 0 here (not -1 below)
   489			// if there's no mention of a body.
   490			return 0, nil
   491		}
   492	
   493		// Body-EOF logic based on other methods (like closing, or chunked coding)
   494		return -1, nil
   495	}
   496	
   497	// Determine whether to hang up after sending a request and body, or
   498	// receiving a response and body
   499	// 'header' is the request headers
   500	func shouldClose(major, minor int, header Header) bool {
   501		if major < 1 {
   502			return true
   503		} else if major == 1 && minor == 0 {
   504			if !strings.Contains(strings.ToLower(header.get("Connection")), "keep-alive") {
   505				return true
   506			}
   507			return false
   508		} else {
   509			// TODO: Should split on commas, toss surrounding white space,
   510			// and check each field.
   511			if strings.ToLower(header.get("Connection")) == "close" {
   512				header.Del("Connection")
   513				return true
   514			}
   515		}
   516		return false
   517	}
   518	
   519	// Parse the trailer header
   520	func fixTrailer(header Header, te []string) (Header, error) {
   521		raw := header.get("Trailer")
   522		if raw == "" {
   523			return nil, nil
   524		}
   525	
   526		header.Del("Trailer")
   527		trailer := make(Header)
   528		keys := strings.Split(raw, ",")
   529		for _, key := range keys {
   530			key = CanonicalHeaderKey(strings.TrimSpace(key))
   531			switch key {
   532			case "Transfer-Encoding", "Trailer", "Content-Length":
   533				return nil, &badStringError{"bad trailer key", key}
   534			}
   535			trailer[key] = nil
   536		}
   537		if len(trailer) == 0 {
   538			return nil, nil
   539		}
   540		if !chunked(te) {
   541			// Trailer and no chunking
   542			return nil, ErrUnexpectedTrailer
   543		}
   544		return trailer, nil
   545	}
   546	
   547	// body turns a Reader into a ReadCloser.
   548	// Close ensures that the body has been fully read
   549	// and then reads the trailer if necessary.
   550	type body struct {
   551		src     io.Reader
   552		hdr     interface{}   // non-nil (Response or Request) value means read trailer
   553		r       *bufio.Reader // underlying wire-format reader for the trailer
   554		closing bool          // is the connection to be closed after reading body?
   555	
   556		mu     sync.Mutex // guards closed, and calls to Read and Close
   557		closed bool
   558	}
   559	
   560	// ErrBodyReadAfterClose is returned when reading a Request or Response
   561	// Body after the body has been closed. This typically happens when the body is
   562	// read after an HTTP Handler calls WriteHeader or Write on its
   563	// ResponseWriter.
   564	var ErrBodyReadAfterClose = errors.New("http: invalid Read on closed Body")
   565	
   566	func (b *body) Read(p []byte) (n int, err error) {
   567		b.mu.Lock()
   568		defer b.mu.Unlock()
   569		if b.closed {
   570			return 0, ErrBodyReadAfterClose
   571		}
   572		return b.readLocked(p)
   573	}
   574	
   575	// Must hold b.mu.
   576	func (b *body) readLocked(p []byte) (n int, err error) {
   577		n, err = b.src.Read(p)
   578	
   579		if err == io.EOF {
   580			// Chunked case. Read the trailer.
   581			if b.hdr != nil {
   582				if e := b.readTrailer(); e != nil {
   583					err = e
   584				}
   585				b.hdr = nil
   586			} else {
   587				// If the server declared the Content-Length, our body is a LimitedReader
   588				// and we need to check whether this EOF arrived early.
   589				if lr, ok := b.src.(*io.LimitedReader); ok && lr.N > 0 {
   590					err = io.ErrUnexpectedEOF
   591				}
   592			}
   593		}
   594	
   595		// If we can return an EOF here along with the read data, do
   596		// so. This is optional per the io.Reader contract, but doing
   597		// so helps the HTTP transport code recycle its connection
   598		// earlier (since it will see this EOF itself), even if the
   599		// client doesn't do future reads or Close.
   600		if err == nil && n > 0 {
   601			if lr, ok := b.src.(*io.LimitedReader); ok && lr.N == 0 {
   602				err = io.EOF
   603			}
   604		}
   605	
   606		return n, err
   607	}
   608	
   609	var (
   610		singleCRLF = []byte("\r\n")
   611		doubleCRLF = []byte("\r\n\r\n")
   612	)
   613	
   614	func seeUpcomingDoubleCRLF(r *bufio.Reader) bool {
   615		for peekSize := 4; ; peekSize++ {
   616			// This loop stops when Peek returns an error,
   617			// which it does when r's buffer has been filled.
   618			buf, err := r.Peek(peekSize)
   619			if bytes.HasSuffix(buf, doubleCRLF) {
   620				return true
   621			}
   622			if err != nil {
   623				break
   624			}
   625		}
   626		return false
   627	}
   628	
   629	var errTrailerEOF = errors.New("http: unexpected EOF reading trailer")
   630	
   631	func (b *body) readTrailer() error {
   632		// The common case, since nobody uses trailers.
   633		buf, err := b.r.Peek(2)
   634		if bytes.Equal(buf, singleCRLF) {
   635			b.r.ReadByte()
   636			b.r.ReadByte()
   637			return nil
   638		}
   639		if len(buf) < 2 {
   640			return errTrailerEOF
   641		}
   642		if err != nil {
   643			return err
   644		}
   645	
   646		// Make sure there's a header terminator coming up, to prevent
   647		// a DoS with an unbounded size Trailer.  It's not easy to
   648		// slip in a LimitReader here, as textproto.NewReader requires
   649		// a concrete *bufio.Reader.  Also, we can't get all the way
   650		// back up to our conn's LimitedReader that *might* be backing
   651		// this bufio.Reader.  Instead, a hack: we iteratively Peek up
   652		// to the bufio.Reader's max size, looking for a double CRLF.
   653		// This limits the trailer to the underlying buffer size, typically 4kB.
   654		if !seeUpcomingDoubleCRLF(b.r) {
   655			return errors.New("http: suspiciously long trailer after chunked body")
   656		}
   657	
   658		hdr, err := textproto.NewReader(b.r).ReadMIMEHeader()
   659		if err != nil {
   660			if err == io.EOF {
   661				return errTrailerEOF
   662			}
   663			return err
   664		}
   665		switch rr := b.hdr.(type) {
   666		case *Request:
   667			mergeSetHeader(&rr.Trailer, Header(hdr))
   668		case *Response:
   669			mergeSetHeader(&rr.Trailer, Header(hdr))
   670		}
   671		return nil
   672	}
   673	
   674	func mergeSetHeader(dst *Header, src Header) {
   675		if *dst == nil {
   676			*dst = src
   677			return
   678		}
   679		for k, vv := range src {
   680			(*dst)[k] = vv
   681		}
   682	}
   683	
   684	func (b *body) Close() error {
   685		b.mu.Lock()
   686		defer b.mu.Unlock()
   687		if b.closed {
   688			return nil
   689		}
   690		var err error
   691		switch {
   692		case b.hdr == nil && b.closing:
   693			// no trailer and closing the connection next.
   694			// no point in reading to EOF.
   695		default:
   696			// Fully consume the body, which will also lead to us reading
   697			// the trailer headers after the body, if present.
   698			_, err = io.Copy(ioutil.Discard, bodyLocked{b})
   699		}
   700		b.closed = true
   701		return err
   702	}
   703	
   704	// bodyLocked is a io.Reader reading from a *body when its mutex is
   705	// already held.
   706	type bodyLocked struct {
   707		b *body
   708	}
   709	
   710	func (bl bodyLocked) Read(p []byte) (n int, err error) {
   711		if bl.b.closed {
   712			return 0, ErrBodyReadAfterClose
   713		}
   714		return bl.b.readLocked(p)
   715	}
   716	
   717	// parseContentLength trims whitespace from s and returns -1 if no value
   718	// is set, or the value if it's >= 0.
   719	func parseContentLength(cl string) (int64, error) {
   720		cl = strings.TrimSpace(cl)
   721		if cl == "" {
   722			return -1, nil
   723		}
   724		n, err := strconv.ParseInt(cl, 10, 64)
   725		if err != nil || n < 0 {
   726			return 0, &badStringError{"bad Content-Length", cl}
   727		}
   728		return n, nil
   729	
   730	}
   731	

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