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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 or readTrackingBody. 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  	if r, ok := t.Body.(*readTrackingBody); ok {
   417  		r.didRead = true
   418  		return r.ReadCloser
   419  	}
   420  	return t.Body
   421  }
   422  
   423  type transferReader struct {
   424  	// Input
   425  	Header        Header
   426  	StatusCode    int
   427  	RequestMethod string
   428  	ProtoMajor    int
   429  	ProtoMinor    int
   430  	// Output
   431  	Body          io.ReadCloser
   432  	ContentLength int64
   433  	Chunked       bool
   434  	Close         bool
   435  	Trailer       Header
   436  }
   437  
   438  func (t *transferReader) protoAtLeast(m, n int) bool {
   439  	return t.ProtoMajor > m || (t.ProtoMajor == m && t.ProtoMinor >= n)
   440  }
   441  
   442  // bodyAllowedForStatus reports whether a given response status code
   443  // permits a body. See RFC 7230, section 3.3.
   444  func bodyAllowedForStatus(status int) bool {
   445  	switch {
   446  	case status >= 100 && status <= 199:
   447  		return false
   448  	case status == 204:
   449  		return false
   450  	case status == 304:
   451  		return false
   452  	}
   453  	return true
   454  }
   455  
   456  var (
   457  	suppressedHeaders304    = []string{"Content-Type", "Content-Length", "Transfer-Encoding"}
   458  	suppressedHeadersNoBody = []string{"Content-Length", "Transfer-Encoding"}
   459  )
   460  
   461  func suppressedHeaders(status int) []string {
   462  	switch {
   463  	case status == 304:
   464  		// RFC 7232 section 4.1
   465  		return suppressedHeaders304
   466  	case !bodyAllowedForStatus(status):
   467  		return suppressedHeadersNoBody
   468  	}
   469  	return nil
   470  }
   471  
   472  // msg is *Request or *Response.
   473  func readTransfer(msg interface{}, r *bufio.Reader) (err error) {
   474  	t := &transferReader{RequestMethod: "GET"}
   475  
   476  	// Unify input
   477  	isResponse := false
   478  	switch rr := msg.(type) {
   479  	case *Response:
   480  		t.Header = rr.Header
   481  		t.StatusCode = rr.StatusCode
   482  		t.ProtoMajor = rr.ProtoMajor
   483  		t.ProtoMinor = rr.ProtoMinor
   484  		t.Close = shouldClose(t.ProtoMajor, t.ProtoMinor, t.Header, true)
   485  		isResponse = true
   486  		if rr.Request != nil {
   487  			t.RequestMethod = rr.Request.Method
   488  		}
   489  	case *Request:
   490  		t.Header = rr.Header
   491  		t.RequestMethod = rr.Method
   492  		t.ProtoMajor = rr.ProtoMajor
   493  		t.ProtoMinor = rr.ProtoMinor
   494  		// Transfer semantics for Requests are exactly like those for
   495  		// Responses with status code 200, responding to a GET method
   496  		t.StatusCode = 200
   497  		t.Close = rr.Close
   498  	default:
   499  		panic("unexpected type")
   500  	}
   501  
   502  	// Default to HTTP/1.1
   503  	if t.ProtoMajor == 0 && t.ProtoMinor == 0 {
   504  		t.ProtoMajor, t.ProtoMinor = 1, 1
   505  	}
   506  
   507  	// Transfer-Encoding: chunked, and overriding Content-Length.
   508  	if err := t.parseTransferEncoding(); err != nil {
   509  		return err
   510  	}
   511  
   512  	realLength, err := fixLength(isResponse, t.StatusCode, t.RequestMethod, t.Header, t.Chunked)
   513  	if err != nil {
   514  		return err
   515  	}
   516  	if isResponse && t.RequestMethod == "HEAD" {
   517  		if n, err := parseContentLength(t.Header.get("Content-Length")); err != nil {
   518  			return err
   519  		} else {
   520  			t.ContentLength = n
   521  		}
   522  	} else {
   523  		t.ContentLength = realLength
   524  	}
   525  
   526  	// Trailer
   527  	t.Trailer, err = fixTrailer(t.Header, t.Chunked)
   528  	if err != nil {
   529  		return err
   530  	}
   531  
   532  	// If there is no Content-Length or chunked Transfer-Encoding on a *Response
   533  	// and the status is not 1xx, 204 or 304, then the body is unbounded.
   534  	// See RFC 7230, section 3.3.
   535  	switch msg.(type) {
   536  	case *Response:
   537  		if realLength == -1 && !t.Chunked && 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 t.Chunked:
   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  		if t.Chunked {
   573  			rr.TransferEncoding = []string{"chunked"}
   574  		}
   575  		rr.Close = t.Close
   576  		rr.Trailer = t.Trailer
   577  	case *Response:
   578  		rr.Body = t.Body
   579  		rr.ContentLength = t.ContentLength
   580  		if t.Chunked {
   581  			rr.TransferEncoding = []string{"chunked"}
   582  		}
   583  		rr.Close = t.Close
   584  		rr.Trailer = t.Trailer
   585  	}
   586  
   587  	return nil
   588  }
   589  
   590  // Checks whether chunked is part of the encodings stack
   591  func chunked(te []string) bool { return len(te) > 0 && te[0] == "chunked" }
   592  
   593  // Checks whether the encoding is explicitly "identity".
   594  func isIdentity(te []string) bool { return len(te) == 1 && te[0] == "identity" }
   595  
   596  // unsupportedTEError reports unsupported transfer-encodings.
   597  type unsupportedTEError struct {
   598  	err string
   599  }
   600  
   601  func (uste *unsupportedTEError) Error() string {
   602  	return uste.err
   603  }
   604  
   605  // isUnsupportedTEError checks if the error is of type
   606  // unsupportedTEError. It is usually invoked with a non-nil err.
   607  func isUnsupportedTEError(err error) bool {
   608  	_, ok := err.(*unsupportedTEError)
   609  	return ok
   610  }
   611  
   612  // parseTransferEncoding sets t.Chunked based on the Transfer-Encoding header.
   613  func (t *transferReader) parseTransferEncoding() error {
   614  	raw, present := t.Header["Transfer-Encoding"]
   615  	if !present {
   616  		return nil
   617  	}
   618  	delete(t.Header, "Transfer-Encoding")
   619  
   620  	// Issue 12785; ignore Transfer-Encoding on HTTP/1.0 requests.
   621  	if !t.protoAtLeast(1, 1) {
   622  		return nil
   623  	}
   624  
   625  	// Like nginx, we only support a single Transfer-Encoding header field, and
   626  	// only if set to "chunked". This is one of the most security sensitive
   627  	// surfaces in HTTP/1.1 due to the risk of request smuggling, so we keep it
   628  	// strict and simple.
   629  	if len(raw) != 1 {
   630  		return &unsupportedTEError{fmt.Sprintf("too many transfer encodings: %q", raw)}
   631  	}
   632  	if strings.ToLower(textproto.TrimString(raw[0])) != "chunked" {
   633  		return &unsupportedTEError{fmt.Sprintf("unsupported transfer encoding: %q", raw[0])}
   634  	}
   635  
   636  	// RFC 7230 3.3.2 says "A sender MUST NOT send a Content-Length header field
   637  	// in any message that contains a Transfer-Encoding header field."
   638  	//
   639  	// but also: "If a message is received with both a Transfer-Encoding and a
   640  	// Content-Length header field, the Transfer-Encoding overrides the
   641  	// Content-Length. Such a message might indicate an attempt to perform
   642  	// request smuggling (Section 9.5) or response splitting (Section 9.4) and
   643  	// ought to be handled as an error. A sender MUST remove the received
   644  	// Content-Length field prior to forwarding such a message downstream."
   645  	//
   646  	// Reportedly, these appear in the wild.
   647  	delete(t.Header, "Content-Length")
   648  
   649  	t.Chunked = true
   650  	return nil
   651  }
   652  
   653  // Determine the expected body length, using RFC 7230 Section 3.3. This
   654  // function is not a method, because ultimately it should be shared by
   655  // ReadResponse and ReadRequest.
   656  func fixLength(isResponse bool, status int, requestMethod string, header Header, chunked bool) (int64, error) {
   657  	isRequest := !isResponse
   658  	contentLens := header["Content-Length"]
   659  
   660  	// Hardening against HTTP request smuggling
   661  	if len(contentLens) > 1 {
   662  		// Per RFC 7230 Section 3.3.2, prevent multiple
   663  		// Content-Length headers if they differ in value.
   664  		// If there are dups of the value, remove the dups.
   665  		// See Issue 16490.
   666  		first := textproto.TrimString(contentLens[0])
   667  		for _, ct := range contentLens[1:] {
   668  			if first != textproto.TrimString(ct) {
   669  				return 0, fmt.Errorf("http: message cannot contain multiple Content-Length headers; got %q", contentLens)
   670  			}
   671  		}
   672  
   673  		// deduplicate Content-Length
   674  		header.Del("Content-Length")
   675  		header.Add("Content-Length", first)
   676  
   677  		contentLens = header["Content-Length"]
   678  	}
   679  
   680  	// Logic based on response type or status
   681  	if noResponseBodyExpected(requestMethod) {
   682  		// For HTTP requests, as part of hardening against request
   683  		// smuggling (RFC 7230), don't allow a Content-Length header for
   684  		// methods which don't permit bodies. As an exception, allow
   685  		// exactly one Content-Length header if its value is "0".
   686  		if isRequest && len(contentLens) > 0 && !(len(contentLens) == 1 && contentLens[0] == "0") {
   687  			return 0, fmt.Errorf("http: method cannot contain a Content-Length; got %q", contentLens)
   688  		}
   689  		return 0, nil
   690  	}
   691  	if status/100 == 1 {
   692  		return 0, nil
   693  	}
   694  	switch status {
   695  	case 204, 304:
   696  		return 0, nil
   697  	}
   698  
   699  	// Logic based on Transfer-Encoding
   700  	if chunked {
   701  		return -1, nil
   702  	}
   703  
   704  	// Logic based on Content-Length
   705  	var cl string
   706  	if len(contentLens) == 1 {
   707  		cl = textproto.TrimString(contentLens[0])
   708  	}
   709  	if cl != "" {
   710  		n, err := parseContentLength(cl)
   711  		if err != nil {
   712  			return -1, err
   713  		}
   714  		return n, nil
   715  	}
   716  	header.Del("Content-Length")
   717  
   718  	if isRequest {
   719  		// RFC 7230 neither explicitly permits nor forbids an
   720  		// entity-body on a GET request so we permit one if
   721  		// declared, but we default to 0 here (not -1 below)
   722  		// if there's no mention of a body.
   723  		// Likewise, all other request methods are assumed to have
   724  		// no body if neither Transfer-Encoding chunked nor a
   725  		// Content-Length are set.
   726  		return 0, nil
   727  	}
   728  
   729  	// Body-EOF logic based on other methods (like closing, or chunked coding)
   730  	return -1, nil
   731  }
   732  
   733  // Determine whether to hang up after sending a request and body, or
   734  // receiving a response and body
   735  // 'header' is the request headers
   736  func shouldClose(major, minor int, header Header, removeCloseHeader bool) bool {
   737  	if major < 1 {
   738  		return true
   739  	}
   740  
   741  	conv := header["Connection"]
   742  	hasClose := httpguts.HeaderValuesContainsToken(conv, "close")
   743  	if major == 1 && minor == 0 {
   744  		return hasClose || !httpguts.HeaderValuesContainsToken(conv, "keep-alive")
   745  	}
   746  
   747  	if hasClose && removeCloseHeader {
   748  		header.Del("Connection")
   749  	}
   750  
   751  	return hasClose
   752  }
   753  
   754  // Parse the trailer header
   755  func fixTrailer(header Header, chunked bool) (Header, error) {
   756  	vv, ok := header["Trailer"]
   757  	if !ok {
   758  		return nil, nil
   759  	}
   760  	if !chunked {
   761  		// Trailer and no chunking:
   762  		// this is an invalid use case for trailer header.
   763  		// Nevertheless, no error will be returned and we
   764  		// let users decide if this is a valid HTTP message.
   765  		// The Trailer header will be kept in Response.Header
   766  		// but not populate Response.Trailer.
   767  		// See issue #27197.
   768  		return nil, nil
   769  	}
   770  	header.Del("Trailer")
   771  
   772  	trailer := make(Header)
   773  	var err error
   774  	for _, v := range vv {
   775  		foreachHeaderElement(v, func(key string) {
   776  			key = CanonicalHeaderKey(key)
   777  			switch key {
   778  			case "Transfer-Encoding", "Trailer", "Content-Length":
   779  				if err == nil {
   780  					err = badStringError("bad trailer key", key)
   781  					return
   782  				}
   783  			}
   784  			trailer[key] = nil
   785  		})
   786  	}
   787  	if err != nil {
   788  		return nil, err
   789  	}
   790  	if len(trailer) == 0 {
   791  		return nil, nil
   792  	}
   793  	return trailer, nil
   794  }
   795  
   796  // body turns a Reader into a ReadCloser.
   797  // Close ensures that the body has been fully read
   798  // and then reads the trailer if necessary.
   799  type body struct {
   800  	src          io.Reader
   801  	hdr          interface{}   // non-nil (Response or Request) value means read trailer
   802  	r            *bufio.Reader // underlying wire-format reader for the trailer
   803  	closing      bool          // is the connection to be closed after reading body?
   804  	doEarlyClose bool          // whether Close should stop early
   805  
   806  	mu         sync.Mutex // guards following, and calls to Read and Close
   807  	sawEOF     bool
   808  	closed     bool
   809  	earlyClose bool   // Close called and we didn't read to the end of src
   810  	onHitEOF   func() // if non-nil, func to call when EOF is Read
   811  }
   812  
   813  // ErrBodyReadAfterClose is returned when reading a Request or Response
   814  // Body after the body has been closed. This typically happens when the body is
   815  // read after an HTTP Handler calls WriteHeader or Write on its
   816  // ResponseWriter.
   817  var ErrBodyReadAfterClose = errors.New("http: invalid Read on closed Body")
   818  
   819  func (b *body) Read(p []byte) (n int, err error) {
   820  	b.mu.Lock()
   821  	defer b.mu.Unlock()
   822  	if b.closed {
   823  		return 0, ErrBodyReadAfterClose
   824  	}
   825  	return b.readLocked(p)
   826  }
   827  
   828  // Must hold b.mu.
   829  func (b *body) readLocked(p []byte) (n int, err error) {
   830  	if b.sawEOF {
   831  		return 0, io.EOF
   832  	}
   833  	n, err = b.src.Read(p)
   834  
   835  	if err == io.EOF {
   836  		b.sawEOF = true
   837  		// Chunked case. Read the trailer.
   838  		if b.hdr != nil {
   839  			if e := b.readTrailer(); e != nil {
   840  				err = e
   841  				// Something went wrong in the trailer, we must not allow any
   842  				// further reads of any kind to succeed from body, nor any
   843  				// subsequent requests on the server connection. See
   844  				// golang.org/issue/12027
   845  				b.sawEOF = false
   846  				b.closed = true
   847  			}
   848  			b.hdr = nil
   849  		} else {
   850  			// If the server declared the Content-Length, our body is a LimitedReader
   851  			// and we need to check whether this EOF arrived early.
   852  			if lr, ok := b.src.(*io.LimitedReader); ok && lr.N > 0 {
   853  				err = io.ErrUnexpectedEOF
   854  			}
   855  		}
   856  	}
   857  
   858  	// If we can return an EOF here along with the read data, do
   859  	// so. This is optional per the io.Reader contract, but doing
   860  	// so helps the HTTP transport code recycle its connection
   861  	// earlier (since it will see this EOF itself), even if the
   862  	// client doesn't do future reads or Close.
   863  	if err == nil && n > 0 {
   864  		if lr, ok := b.src.(*io.LimitedReader); ok && lr.N == 0 {
   865  			err = io.EOF
   866  			b.sawEOF = true
   867  		}
   868  	}
   869  
   870  	if b.sawEOF && b.onHitEOF != nil {
   871  		b.onHitEOF()
   872  	}
   873  
   874  	return n, err
   875  }
   876  
   877  var (
   878  	singleCRLF = []byte("\r\n")
   879  	doubleCRLF = []byte("\r\n\r\n")
   880  )
   881  
   882  func seeUpcomingDoubleCRLF(r *bufio.Reader) bool {
   883  	for peekSize := 4; ; peekSize++ {
   884  		// This loop stops when Peek returns an error,
   885  		// which it does when r's buffer has been filled.
   886  		buf, err := r.Peek(peekSize)
   887  		if bytes.HasSuffix(buf, doubleCRLF) {
   888  			return true
   889  		}
   890  		if err != nil {
   891  			break
   892  		}
   893  	}
   894  	return false
   895  }
   896  
   897  var errTrailerEOF = errors.New("http: unexpected EOF reading trailer")
   898  
   899  func (b *body) readTrailer() error {
   900  	// The common case, since nobody uses trailers.
   901  	buf, err := b.r.Peek(2)
   902  	if bytes.Equal(buf, singleCRLF) {
   903  		b.r.Discard(2)
   904  		return nil
   905  	}
   906  	if len(buf) < 2 {
   907  		return errTrailerEOF
   908  	}
   909  	if err != nil {
   910  		return err
   911  	}
   912  
   913  	// Make sure there's a header terminator coming up, to prevent
   914  	// a DoS with an unbounded size Trailer. It's not easy to
   915  	// slip in a LimitReader here, as textproto.NewReader requires
   916  	// a concrete *bufio.Reader. Also, we can't get all the way
   917  	// back up to our conn's LimitedReader that *might* be backing
   918  	// this bufio.Reader. Instead, a hack: we iteratively Peek up
   919  	// to the bufio.Reader's max size, looking for a double CRLF.
   920  	// This limits the trailer to the underlying buffer size, typically 4kB.
   921  	if !seeUpcomingDoubleCRLF(b.r) {
   922  		return errors.New("http: suspiciously long trailer after chunked body")
   923  	}
   924  
   925  	hdr, err := textproto.NewReader(b.r).ReadMIMEHeader()
   926  	if err != nil {
   927  		if err == io.EOF {
   928  			return errTrailerEOF
   929  		}
   930  		return err
   931  	}
   932  	switch rr := b.hdr.(type) {
   933  	case *Request:
   934  		mergeSetHeader(&rr.Trailer, Header(hdr))
   935  	case *Response:
   936  		mergeSetHeader(&rr.Trailer, Header(hdr))
   937  	}
   938  	return nil
   939  }
   940  
   941  func mergeSetHeader(dst *Header, src Header) {
   942  	if *dst == nil {
   943  		*dst = src
   944  		return
   945  	}
   946  	for k, vv := range src {
   947  		(*dst)[k] = vv
   948  	}
   949  }
   950  
   951  // unreadDataSizeLocked returns the number of bytes of unread input.
   952  // It returns -1 if unknown.
   953  // b.mu must be held.
   954  func (b *body) unreadDataSizeLocked() int64 {
   955  	if lr, ok := b.src.(*io.LimitedReader); ok {
   956  		return lr.N
   957  	}
   958  	return -1
   959  }
   960  
   961  func (b *body) Close() error {
   962  	b.mu.Lock()
   963  	defer b.mu.Unlock()
   964  	if b.closed {
   965  		return nil
   966  	}
   967  	var err error
   968  	switch {
   969  	case b.sawEOF:
   970  		// Already saw EOF, so no need going to look for it.
   971  	case b.hdr == nil && b.closing:
   972  		// no trailer and closing the connection next.
   973  		// no point in reading to EOF.
   974  	case b.doEarlyClose:
   975  		// Read up to maxPostHandlerReadBytes bytes of the body, looking
   976  		// for EOF (and trailers), so we can re-use this connection.
   977  		if lr, ok := b.src.(*io.LimitedReader); ok && lr.N > maxPostHandlerReadBytes {
   978  			// There was a declared Content-Length, and we have more bytes remaining
   979  			// than our maxPostHandlerReadBytes tolerance. So, give up.
   980  			b.earlyClose = true
   981  		} else {
   982  			var n int64
   983  			// Consume the body, or, which will also lead to us reading
   984  			// the trailer headers after the body, if present.
   985  			n, err = io.CopyN(ioutil.Discard, bodyLocked{b}, maxPostHandlerReadBytes)
   986  			if err == io.EOF {
   987  				err = nil
   988  			}
   989  			if n == maxPostHandlerReadBytes {
   990  				b.earlyClose = true
   991  			}
   992  		}
   993  	default:
   994  		// Fully consume the body, which will also lead to us reading
   995  		// the trailer headers after the body, if present.
   996  		_, err = io.Copy(ioutil.Discard, bodyLocked{b})
   997  	}
   998  	b.closed = true
   999  	return err
  1000  }
  1001  
  1002  func (b *body) didEarlyClose() bool {
  1003  	b.mu.Lock()
  1004  	defer b.mu.Unlock()
  1005  	return b.earlyClose
  1006  }
  1007  
  1008  // bodyRemains reports whether future Read calls might
  1009  // yield data.
  1010  func (b *body) bodyRemains() bool {
  1011  	b.mu.Lock()
  1012  	defer b.mu.Unlock()
  1013  	return !b.sawEOF
  1014  }
  1015  
  1016  func (b *body) registerOnHitEOF(fn func()) {
  1017  	b.mu.Lock()
  1018  	defer b.mu.Unlock()
  1019  	b.onHitEOF = fn
  1020  }
  1021  
  1022  // bodyLocked is a io.Reader reading from a *body when its mutex is
  1023  // already held.
  1024  type bodyLocked struct {
  1025  	b *body
  1026  }
  1027  
  1028  func (bl bodyLocked) Read(p []byte) (n int, err error) {
  1029  	if bl.b.closed {
  1030  		return 0, ErrBodyReadAfterClose
  1031  	}
  1032  	return bl.b.readLocked(p)
  1033  }
  1034  
  1035  // parseContentLength trims whitespace from s and returns -1 if no value
  1036  // is set, or the value if it's >= 0.
  1037  func parseContentLength(cl string) (int64, error) {
  1038  	cl = textproto.TrimString(cl)
  1039  	if cl == "" {
  1040  		return -1, nil
  1041  	}
  1042  	n, err := strconv.ParseUint(cl, 10, 63)
  1043  	if err != nil {
  1044  		return 0, badStringError("bad Content-Length", cl)
  1045  	}
  1046  	return int64(n), nil
  1047  
  1048  }
  1049  
  1050  // finishAsyncByteRead finishes reading the 1-byte sniff
  1051  // from the ContentLength==0, Body!=nil case.
  1052  type finishAsyncByteRead struct {
  1053  	tw *transferWriter
  1054  }
  1055  
  1056  func (fr finishAsyncByteRead) Read(p []byte) (n int, err error) {
  1057  	if len(p) == 0 {
  1058  		return
  1059  	}
  1060  	rres := <-fr.tw.ByteReadCh
  1061  	n, err = rres.n, rres.err
  1062  	if n == 1 {
  1063  		p[0] = rres.b
  1064  	}
  1065  	return
  1066  }
  1067  
  1068  var nopCloserType = reflect.TypeOf(ioutil.NopCloser(nil))
  1069  
  1070  // isKnownInMemoryReader reports whether r is a type known to not
  1071  // block on Read. Its caller uses this as an optional optimization to
  1072  // send fewer TCP packets.
  1073  func isKnownInMemoryReader(r io.Reader) bool {
  1074  	switch r.(type) {
  1075  	case *bytes.Reader, *bytes.Buffer, *strings.Reader:
  1076  		return true
  1077  	}
  1078  	if reflect.TypeOf(r) == nopCloserType {
  1079  		return isKnownInMemoryReader(reflect.ValueOf(r).Field(0).Interface().(io.Reader))
  1080  	}
  1081  	if r, ok := r.(*readTrackingBody); ok {
  1082  		return isKnownInMemoryReader(r.ReadCloser)
  1083  	}
  1084  	return false
  1085  }
  1086  
  1087  // bufioFlushWriter is an io.Writer wrapper that flushes all writes
  1088  // on its wrapped writer if it's a *bufio.Writer.
  1089  type bufioFlushWriter struct{ w io.Writer }
  1090  
  1091  func (fw bufioFlushWriter) Write(p []byte) (n int, err error) {
  1092  	n, err = fw.w.Write(p)
  1093  	if bw, ok := fw.w.(*bufio.Writer); n > 0 && ok {
  1094  		ferr := bw.Flush()
  1095  		if ferr != nil && err == nil {
  1096  			err = ferr
  1097  		}
  1098  	}
  1099  	return
  1100  }
  1101  

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