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  	"net/http/httptrace"
    14  	"net/http/internal"
    15  	"net/http/internal/ascii"
    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 any) (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, io.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  //
   204  // In other words, this delay will not normally affect anybody, and there
   205  // are workarounds if it does.
   206  func (t *transferWriter) probeRequestBody() {
   207  	t.ByteReadCh = make(chan readResult, 1)
   208  	go func(body io.Reader) {
   209  		var buf [1]byte
   210  		var rres readResult
   211  		rres.n, rres.err = body.Read(buf[:])
   212  		if rres.n == 1 {
   213  			rres.b = buf[0]
   214  		}
   215  		t.ByteReadCh <- rres
   216  		close(t.ByteReadCh)
   217  	}(t.Body)
   218  	timer := time.NewTimer(200 * time.Millisecond)
   219  	select {
   220  	case rres := <-t.ByteReadCh:
   221  		timer.Stop()
   222  		if rres.n == 0 && rres.err == io.EOF {
   223  			// It was empty.
   224  			t.Body = nil
   225  			t.ContentLength = 0
   226  		} else if rres.n == 1 {
   227  			if rres.err != nil {
   228  				t.Body = io.MultiReader(&byteReader{b: rres.b}, errorReader{rres.err})
   229  			} else {
   230  				t.Body = io.MultiReader(&byteReader{b: rres.b}, t.Body)
   231  			}
   232  		} else if rres.err != nil {
   233  			t.Body = errorReader{rres.err}
   234  		}
   235  	case <-timer.C:
   236  		// Too slow. Don't wait. Read it later, and keep
   237  		// assuming that this is ContentLength == -1
   238  		// (unknown), which means we'll send a
   239  		// "Transfer-Encoding: chunked" header.
   240  		t.Body = io.MultiReader(finishAsyncByteRead{t}, t.Body)
   241  		// Request that Request.Write flush the headers to the
   242  		// network before writing the body, since our body may not
   243  		// become readable until it's seen the response headers.
   244  		t.FlushHeaders = true
   245  	}
   246  }
   247  
   248  func noResponseBodyExpected(requestMethod string) bool {
   249  	return requestMethod == "HEAD"
   250  }
   251  
   252  func (t *transferWriter) shouldSendContentLength() bool {
   253  	if chunked(t.TransferEncoding) {
   254  		return false
   255  	}
   256  	if t.ContentLength > 0 {
   257  		return true
   258  	}
   259  	if t.ContentLength < 0 {
   260  		return false
   261  	}
   262  	// Many servers expect a Content-Length for these methods
   263  	if t.Method == "POST" || t.Method == "PUT" || t.Method == "PATCH" {
   264  		return true
   265  	}
   266  	if t.ContentLength == 0 && isIdentity(t.TransferEncoding) {
   267  		if t.Method == "GET" || t.Method == "HEAD" {
   268  			return false
   269  		}
   270  		return true
   271  	}
   272  
   273  	return false
   274  }
   275  
   276  func (t *transferWriter) writeHeader(w io.Writer, trace *httptrace.ClientTrace) error {
   277  	if t.Close && !hasToken(t.Header.get("Connection"), "close") {
   278  		if _, err := io.WriteString(w, "Connection: close\r\n"); err != nil {
   279  			return err
   280  		}
   281  		if trace != nil && trace.WroteHeaderField != nil {
   282  			trace.WroteHeaderField("Connection", []string{"close"})
   283  		}
   284  	}
   285  
   286  	// Write Content-Length and/or Transfer-Encoding whose values are a
   287  	// function of the sanitized field triple (Body, ContentLength,
   288  	// TransferEncoding)
   289  	if t.shouldSendContentLength() {
   290  		if _, err := io.WriteString(w, "Content-Length: "); err != nil {
   291  			return err
   292  		}
   293  		if _, err := io.WriteString(w, strconv.FormatInt(t.ContentLength, 10)+"\r\n"); err != nil {
   294  			return err
   295  		}
   296  		if trace != nil && trace.WroteHeaderField != nil {
   297  			trace.WroteHeaderField("Content-Length", []string{strconv.FormatInt(t.ContentLength, 10)})
   298  		}
   299  	} else if chunked(t.TransferEncoding) {
   300  		if _, err := io.WriteString(w, "Transfer-Encoding: chunked\r\n"); err != nil {
   301  			return err
   302  		}
   303  		if trace != nil && trace.WroteHeaderField != nil {
   304  			trace.WroteHeaderField("Transfer-Encoding", []string{"chunked"})
   305  		}
   306  	}
   307  
   308  	// Write Trailer header
   309  	if t.Trailer != nil {
   310  		keys := make([]string, 0, len(t.Trailer))
   311  		for k := range t.Trailer {
   312  			k = CanonicalHeaderKey(k)
   313  			switch k {
   314  			case "Transfer-Encoding", "Trailer", "Content-Length":
   315  				return badStringError("invalid Trailer key", k)
   316  			}
   317  			keys = append(keys, k)
   318  		}
   319  		if len(keys) > 0 {
   320  			sort.Strings(keys)
   321  			// TODO: could do better allocation-wise here, but trailers are rare,
   322  			// so being lazy for now.
   323  			if _, err := io.WriteString(w, "Trailer: "+strings.Join(keys, ",")+"\r\n"); err != nil {
   324  				return err
   325  			}
   326  			if trace != nil && trace.WroteHeaderField != nil {
   327  				trace.WroteHeaderField("Trailer", keys)
   328  			}
   329  		}
   330  	}
   331  
   332  	return nil
   333  }
   334  
   335  // always closes t.BodyCloser
   336  func (t *transferWriter) writeBody(w io.Writer) (err error) {
   337  	var ncopy int64
   338  	closed := false
   339  	defer func() {
   340  		if closed || t.BodyCloser == nil {
   341  			return
   342  		}
   343  		if closeErr := t.BodyCloser.Close(); closeErr != nil && err == nil {
   344  			err = closeErr
   345  		}
   346  	}()
   347  
   348  	// Write body. We "unwrap" the body first if it was wrapped in a
   349  	// nopCloser or readTrackingBody. This is to ensure that we can take advantage of
   350  	// OS-level optimizations in the event that the body is an
   351  	// *os.File.
   352  	if t.Body != nil {
   353  		var body = t.unwrapBody()
   354  		if chunked(t.TransferEncoding) {
   355  			if bw, ok := w.(*bufio.Writer); ok && !t.IsResponse {
   356  				w = &internal.FlushAfterChunkWriter{Writer: bw}
   357  			}
   358  			cw := internal.NewChunkedWriter(w)
   359  			_, err = t.doBodyCopy(cw, body)
   360  			if err == nil {
   361  				err = cw.Close()
   362  			}
   363  		} else if t.ContentLength == -1 {
   364  			dst := w
   365  			if t.Method == "CONNECT" {
   366  				dst = bufioFlushWriter{dst}
   367  			}
   368  			ncopy, err = t.doBodyCopy(dst, body)
   369  		} else {
   370  			ncopy, err = t.doBodyCopy(w, io.LimitReader(body, t.ContentLength))
   371  			if err != nil {
   372  				return err
   373  			}
   374  			var nextra int64
   375  			nextra, err = t.doBodyCopy(io.Discard, body)
   376  			ncopy += nextra
   377  		}
   378  		if err != nil {
   379  			return err
   380  		}
   381  	}
   382  	if t.BodyCloser != nil {
   383  		closed = true
   384  		if err := t.BodyCloser.Close(); err != nil {
   385  			return err
   386  		}
   387  	}
   388  
   389  	if !t.ResponseToHEAD && t.ContentLength != -1 && t.ContentLength != ncopy {
   390  		return fmt.Errorf("http: ContentLength=%d with Body length %d",
   391  			t.ContentLength, ncopy)
   392  	}
   393  
   394  	if chunked(t.TransferEncoding) {
   395  		// Write Trailer header
   396  		if t.Trailer != nil {
   397  			if err := t.Trailer.Write(w); err != nil {
   398  				return err
   399  			}
   400  		}
   401  		// Last chunk, empty trailer
   402  		_, err = io.WriteString(w, "\r\n")
   403  	}
   404  	return err
   405  }
   406  
   407  // doBodyCopy wraps a copy operation, with any resulting error also
   408  // being saved in bodyReadError.
   409  //
   410  // This function is only intended for use in writeBody.
   411  func (t *transferWriter) doBodyCopy(dst io.Writer, src io.Reader) (n int64, err error) {
   412  	n, err = io.Copy(dst, src)
   413  	if err != nil && err != io.EOF {
   414  		t.bodyReadError = err
   415  	}
   416  	return
   417  }
   418  
   419  // unwrapBodyReader unwraps the body's inner reader if it's a
   420  // nopCloser. This is to ensure that body writes sourced from local
   421  // files (*os.File types) are properly optimized.
   422  //
   423  // This function is only intended for use in writeBody.
   424  func (t *transferWriter) unwrapBody() io.Reader {
   425  	if r, ok := unwrapNopCloser(t.Body); ok {
   426  		return r
   427  	}
   428  	if r, ok := t.Body.(*readTrackingBody); ok {
   429  		r.didRead = true
   430  		return r.ReadCloser
   431  	}
   432  	return t.Body
   433  }
   434  
   435  type transferReader struct {
   436  	// Input
   437  	Header        Header
   438  	StatusCode    int
   439  	RequestMethod string
   440  	ProtoMajor    int
   441  	ProtoMinor    int
   442  	// Output
   443  	Body          io.ReadCloser
   444  	ContentLength int64
   445  	Chunked       bool
   446  	Close         bool
   447  	Trailer       Header
   448  }
   449  
   450  func (t *transferReader) protoAtLeast(m, n int) bool {
   451  	return t.ProtoMajor > m || (t.ProtoMajor == m && t.ProtoMinor >= n)
   452  }
   453  
   454  // bodyAllowedForStatus reports whether a given response status code
   455  // permits a body. See RFC 7230, section 3.3.
   456  func bodyAllowedForStatus(status int) bool {
   457  	switch {
   458  	case status >= 100 && status <= 199:
   459  		return false
   460  	case status == 204:
   461  		return false
   462  	case status == 304:
   463  		return false
   464  	}
   465  	return true
   466  }
   467  
   468  var (
   469  	suppressedHeaders304    = []string{"Content-Type", "Content-Length", "Transfer-Encoding"}
   470  	suppressedHeadersNoBody = []string{"Content-Length", "Transfer-Encoding"}
   471  	excludedHeadersNoBody   = map[string]bool{"Content-Length": true, "Transfer-Encoding": true}
   472  )
   473  
   474  func suppressedHeaders(status int) []string {
   475  	switch {
   476  	case status == 304:
   477  		// RFC 7232 section 4.1
   478  		return suppressedHeaders304
   479  	case !bodyAllowedForStatus(status):
   480  		return suppressedHeadersNoBody
   481  	}
   482  	return nil
   483  }
   484  
   485  // msg is *Request or *Response.
   486  func readTransfer(msg any, r *bufio.Reader) (err error) {
   487  	t := &transferReader{RequestMethod: "GET"}
   488  
   489  	// Unify input
   490  	isResponse := false
   491  	switch rr := msg.(type) {
   492  	case *Response:
   493  		t.Header = rr.Header
   494  		t.StatusCode = rr.StatusCode
   495  		t.ProtoMajor = rr.ProtoMajor
   496  		t.ProtoMinor = rr.ProtoMinor
   497  		t.Close = shouldClose(t.ProtoMajor, t.ProtoMinor, t.Header, true)
   498  		isResponse = true
   499  		if rr.Request != nil {
   500  			t.RequestMethod = rr.Request.Method
   501  		}
   502  	case *Request:
   503  		t.Header = rr.Header
   504  		t.RequestMethod = rr.Method
   505  		t.ProtoMajor = rr.ProtoMajor
   506  		t.ProtoMinor = rr.ProtoMinor
   507  		// Transfer semantics for Requests are exactly like those for
   508  		// Responses with status code 200, responding to a GET method
   509  		t.StatusCode = 200
   510  		t.Close = rr.Close
   511  	default:
   512  		panic("unexpected type")
   513  	}
   514  
   515  	// Default to HTTP/1.1
   516  	if t.ProtoMajor == 0 && t.ProtoMinor == 0 {
   517  		t.ProtoMajor, t.ProtoMinor = 1, 1
   518  	}
   519  
   520  	// Transfer-Encoding: chunked, and overriding Content-Length.
   521  	if err := t.parseTransferEncoding(); err != nil {
   522  		return err
   523  	}
   524  
   525  	realLength, err := fixLength(isResponse, t.StatusCode, t.RequestMethod, t.Header, t.Chunked)
   526  	if err != nil {
   527  		return err
   528  	}
   529  	if isResponse && t.RequestMethod == "HEAD" {
   530  		if n, err := parseContentLength(t.Header.get("Content-Length")); err != nil {
   531  			return err
   532  		} else {
   533  			t.ContentLength = n
   534  		}
   535  	} else {
   536  		t.ContentLength = realLength
   537  	}
   538  
   539  	// Trailer
   540  	t.Trailer, err = fixTrailer(t.Header, t.Chunked)
   541  	if err != nil {
   542  		return err
   543  	}
   544  
   545  	// If there is no Content-Length or chunked Transfer-Encoding on a *Response
   546  	// and the status is not 1xx, 204 or 304, then the body is unbounded.
   547  	// See RFC 7230, section 3.3.
   548  	switch msg.(type) {
   549  	case *Response:
   550  		if realLength == -1 && !t.Chunked && bodyAllowedForStatus(t.StatusCode) {
   551  			// Unbounded body.
   552  			t.Close = true
   553  		}
   554  	}
   555  
   556  	// Prepare body reader. ContentLength < 0 means chunked encoding
   557  	// or close connection when finished, since multipart is not supported yet
   558  	switch {
   559  	case t.Chunked:
   560  		if noResponseBodyExpected(t.RequestMethod) || !bodyAllowedForStatus(t.StatusCode) {
   561  			t.Body = NoBody
   562  		} else {
   563  			t.Body = &body{src: internal.NewChunkedReader(r), hdr: msg, r: r, closing: t.Close}
   564  		}
   565  	case realLength == 0:
   566  		t.Body = NoBody
   567  	case realLength > 0:
   568  		t.Body = &body{src: io.LimitReader(r, realLength), closing: t.Close}
   569  	default:
   570  		// realLength < 0, i.e. "Content-Length" not mentioned in header
   571  		if t.Close {
   572  			// Close semantics (i.e. HTTP/1.0)
   573  			t.Body = &body{src: r, closing: t.Close}
   574  		} else {
   575  			// Persistent connection (i.e. HTTP/1.1)
   576  			t.Body = NoBody
   577  		}
   578  	}
   579  
   580  	// Unify output
   581  	switch rr := msg.(type) {
   582  	case *Request:
   583  		rr.Body = t.Body
   584  		rr.ContentLength = t.ContentLength
   585  		if t.Chunked {
   586  			rr.TransferEncoding = []string{"chunked"}
   587  		}
   588  		rr.Close = t.Close
   589  		rr.Trailer = t.Trailer
   590  	case *Response:
   591  		rr.Body = t.Body
   592  		rr.ContentLength = t.ContentLength
   593  		if t.Chunked {
   594  			rr.TransferEncoding = []string{"chunked"}
   595  		}
   596  		rr.Close = t.Close
   597  		rr.Trailer = t.Trailer
   598  	}
   599  
   600  	return nil
   601  }
   602  
   603  // Checks whether chunked is part of the encodings stack
   604  func chunked(te []string) bool { return len(te) > 0 && te[0] == "chunked" }
   605  
   606  // Checks whether the encoding is explicitly "identity".
   607  func isIdentity(te []string) bool { return len(te) == 1 && te[0] == "identity" }
   608  
   609  // unsupportedTEError reports unsupported transfer-encodings.
   610  type unsupportedTEError struct {
   611  	err string
   612  }
   613  
   614  func (uste *unsupportedTEError) Error() string {
   615  	return uste.err
   616  }
   617  
   618  // isUnsupportedTEError checks if the error is of type
   619  // unsupportedTEError. It is usually invoked with a non-nil err.
   620  func isUnsupportedTEError(err error) bool {
   621  	_, ok := err.(*unsupportedTEError)
   622  	return ok
   623  }
   624  
   625  // parseTransferEncoding sets t.Chunked based on the Transfer-Encoding header.
   626  func (t *transferReader) parseTransferEncoding() error {
   627  	raw, present := t.Header["Transfer-Encoding"]
   628  	if !present {
   629  		return nil
   630  	}
   631  	delete(t.Header, "Transfer-Encoding")
   632  
   633  	// Issue 12785; ignore Transfer-Encoding on HTTP/1.0 requests.
   634  	if !t.protoAtLeast(1, 1) {
   635  		return nil
   636  	}
   637  
   638  	// Like nginx, we only support a single Transfer-Encoding header field, and
   639  	// only if set to "chunked". This is one of the most security sensitive
   640  	// surfaces in HTTP/1.1 due to the risk of request smuggling, so we keep it
   641  	// strict and simple.
   642  	if len(raw) != 1 {
   643  		return &unsupportedTEError{fmt.Sprintf("too many transfer encodings: %q", raw)}
   644  	}
   645  	if !ascii.EqualFold(raw[0], "chunked") {
   646  		return &unsupportedTEError{fmt.Sprintf("unsupported transfer encoding: %q", raw[0])}
   647  	}
   648  
   649  	// RFC 7230 3.3.2 says "A sender MUST NOT send a Content-Length header field
   650  	// in any message that contains a Transfer-Encoding header field."
   651  	//
   652  	// but also: "If a message is received with both a Transfer-Encoding and a
   653  	// Content-Length header field, the Transfer-Encoding overrides the
   654  	// Content-Length. Such a message might indicate an attempt to perform
   655  	// request smuggling (Section 9.5) or response splitting (Section 9.4) and
   656  	// ought to be handled as an error. A sender MUST remove the received
   657  	// Content-Length field prior to forwarding such a message downstream."
   658  	//
   659  	// Reportedly, these appear in the wild.
   660  	delete(t.Header, "Content-Length")
   661  
   662  	t.Chunked = true
   663  	return nil
   664  }
   665  
   666  // Determine the expected body length, using RFC 7230 Section 3.3. This
   667  // function is not a method, because ultimately it should be shared by
   668  // ReadResponse and ReadRequest.
   669  func fixLength(isResponse bool, status int, requestMethod string, header Header, chunked bool) (int64, error) {
   670  	isRequest := !isResponse
   671  	contentLens := header["Content-Length"]
   672  
   673  	// Hardening against HTTP request smuggling
   674  	if len(contentLens) > 1 {
   675  		// Per RFC 7230 Section 3.3.2, prevent multiple
   676  		// Content-Length headers if they differ in value.
   677  		// If there are dups of the value, remove the dups.
   678  		// See Issue 16490.
   679  		first := textproto.TrimString(contentLens[0])
   680  		for _, ct := range contentLens[1:] {
   681  			if first != textproto.TrimString(ct) {
   682  				return 0, fmt.Errorf("http: message cannot contain multiple Content-Length headers; got %q", contentLens)
   683  			}
   684  		}
   685  
   686  		// deduplicate Content-Length
   687  		header.Del("Content-Length")
   688  		header.Add("Content-Length", first)
   689  
   690  		contentLens = header["Content-Length"]
   691  	}
   692  
   693  	// Logic based on response type or status
   694  	if noResponseBodyExpected(requestMethod) {
   695  		// For HTTP requests, as part of hardening against request
   696  		// smuggling (RFC 7230), don't allow a Content-Length header for
   697  		// methods which don't permit bodies. As an exception, allow
   698  		// exactly one Content-Length header if its value is "0".
   699  		if isRequest && len(contentLens) > 0 && !(len(contentLens) == 1 && contentLens[0] == "0") {
   700  			return 0, fmt.Errorf("http: method cannot contain a Content-Length; got %q", contentLens)
   701  		}
   702  		return 0, nil
   703  	}
   704  	if status/100 == 1 {
   705  		return 0, nil
   706  	}
   707  	switch status {
   708  	case 204, 304:
   709  		return 0, nil
   710  	}
   711  
   712  	// Logic based on Transfer-Encoding
   713  	if chunked {
   714  		return -1, nil
   715  	}
   716  
   717  	// Logic based on Content-Length
   718  	var cl string
   719  	if len(contentLens) == 1 {
   720  		cl = textproto.TrimString(contentLens[0])
   721  	}
   722  	if cl != "" {
   723  		n, err := parseContentLength(cl)
   724  		if err != nil {
   725  			return -1, err
   726  		}
   727  		return n, nil
   728  	}
   729  	header.Del("Content-Length")
   730  
   731  	if isRequest {
   732  		// RFC 7230 neither explicitly permits nor forbids an
   733  		// entity-body on a GET request so we permit one if
   734  		// declared, but we default to 0 here (not -1 below)
   735  		// if there's no mention of a body.
   736  		// Likewise, all other request methods are assumed to have
   737  		// no body if neither Transfer-Encoding chunked nor a
   738  		// Content-Length are set.
   739  		return 0, nil
   740  	}
   741  
   742  	// Body-EOF logic based on other methods (like closing, or chunked coding)
   743  	return -1, nil
   744  }
   745  
   746  // Determine whether to hang up after sending a request and body, or
   747  // receiving a response and body
   748  // 'header' is the request headers
   749  func shouldClose(major, minor int, header Header, removeCloseHeader bool) bool {
   750  	if major < 1 {
   751  		return true
   752  	}
   753  
   754  	conv := header["Connection"]
   755  	hasClose := httpguts.HeaderValuesContainsToken(conv, "close")
   756  	if major == 1 && minor == 0 {
   757  		return hasClose || !httpguts.HeaderValuesContainsToken(conv, "keep-alive")
   758  	}
   759  
   760  	if hasClose && removeCloseHeader {
   761  		header.Del("Connection")
   762  	}
   763  
   764  	return hasClose
   765  }
   766  
   767  // Parse the trailer header
   768  func fixTrailer(header Header, chunked bool) (Header, error) {
   769  	vv, ok := header["Trailer"]
   770  	if !ok {
   771  		return nil, nil
   772  	}
   773  	if !chunked {
   774  		// Trailer and no chunking:
   775  		// this is an invalid use case for trailer header.
   776  		// Nevertheless, no error will be returned and we
   777  		// let users decide if this is a valid HTTP message.
   778  		// The Trailer header will be kept in Response.Header
   779  		// but not populate Response.Trailer.
   780  		// See issue #27197.
   781  		return nil, nil
   782  	}
   783  	header.Del("Trailer")
   784  
   785  	trailer := make(Header)
   786  	var err error
   787  	for _, v := range vv {
   788  		foreachHeaderElement(v, func(key string) {
   789  			key = CanonicalHeaderKey(key)
   790  			switch key {
   791  			case "Transfer-Encoding", "Trailer", "Content-Length":
   792  				if err == nil {
   793  					err = badStringError("bad trailer key", key)
   794  					return
   795  				}
   796  			}
   797  			trailer[key] = nil
   798  		})
   799  	}
   800  	if err != nil {
   801  		return nil, err
   802  	}
   803  	if len(trailer) == 0 {
   804  		return nil, nil
   805  	}
   806  	return trailer, nil
   807  }
   808  
   809  // body turns a Reader into a ReadCloser.
   810  // Close ensures that the body has been fully read
   811  // and then reads the trailer if necessary.
   812  type body struct {
   813  	src          io.Reader
   814  	hdr          any           // non-nil (Response or Request) value means read trailer
   815  	r            *bufio.Reader // underlying wire-format reader for the trailer
   816  	closing      bool          // is the connection to be closed after reading body?
   817  	doEarlyClose bool          // whether Close should stop early
   818  
   819  	mu         sync.Mutex // guards following, and calls to Read and Close
   820  	sawEOF     bool
   821  	closed     bool
   822  	earlyClose bool   // Close called and we didn't read to the end of src
   823  	onHitEOF   func() // if non-nil, func to call when EOF is Read
   824  }
   825  
   826  // ErrBodyReadAfterClose is returned when reading a Request or Response
   827  // Body after the body has been closed. This typically happens when the body is
   828  // read after an HTTP Handler calls WriteHeader or Write on its
   829  // ResponseWriter.
   830  var ErrBodyReadAfterClose = errors.New("http: invalid Read on closed Body")
   831  
   832  func (b *body) Read(p []byte) (n int, err error) {
   833  	b.mu.Lock()
   834  	defer b.mu.Unlock()
   835  	if b.closed {
   836  		return 0, ErrBodyReadAfterClose
   837  	}
   838  	return b.readLocked(p)
   839  }
   840  
   841  // Must hold b.mu.
   842  func (b *body) readLocked(p []byte) (n int, err error) {
   843  	if b.sawEOF {
   844  		return 0, io.EOF
   845  	}
   846  	n, err = b.src.Read(p)
   847  
   848  	if err == io.EOF {
   849  		b.sawEOF = true
   850  		// Chunked case. Read the trailer.
   851  		if b.hdr != nil {
   852  			if e := b.readTrailer(); e != nil {
   853  				err = e
   854  				// Something went wrong in the trailer, we must not allow any
   855  				// further reads of any kind to succeed from body, nor any
   856  				// subsequent requests on the server connection. See
   857  				// golang.org/issue/12027
   858  				b.sawEOF = false
   859  				b.closed = true
   860  			}
   861  			b.hdr = nil
   862  		} else {
   863  			// If the server declared the Content-Length, our body is a LimitedReader
   864  			// and we need to check whether this EOF arrived early.
   865  			if lr, ok := b.src.(*io.LimitedReader); ok && lr.N > 0 {
   866  				err = io.ErrUnexpectedEOF
   867  			}
   868  		}
   869  	}
   870  
   871  	// If we can return an EOF here along with the read data, do
   872  	// so. This is optional per the io.Reader contract, but doing
   873  	// so helps the HTTP transport code recycle its connection
   874  	// earlier (since it will see this EOF itself), even if the
   875  	// client doesn't do future reads or Close.
   876  	if err == nil && n > 0 {
   877  		if lr, ok := b.src.(*io.LimitedReader); ok && lr.N == 0 {
   878  			err = io.EOF
   879  			b.sawEOF = true
   880  		}
   881  	}
   882  
   883  	if b.sawEOF && b.onHitEOF != nil {
   884  		b.onHitEOF()
   885  	}
   886  
   887  	return n, err
   888  }
   889  
   890  var (
   891  	singleCRLF = []byte("\r\n")
   892  	doubleCRLF = []byte("\r\n\r\n")
   893  )
   894  
   895  func seeUpcomingDoubleCRLF(r *bufio.Reader) bool {
   896  	for peekSize := 4; ; peekSize++ {
   897  		// This loop stops when Peek returns an error,
   898  		// which it does when r's buffer has been filled.
   899  		buf, err := r.Peek(peekSize)
   900  		if bytes.HasSuffix(buf, doubleCRLF) {
   901  			return true
   902  		}
   903  		if err != nil {
   904  			break
   905  		}
   906  	}
   907  	return false
   908  }
   909  
   910  var errTrailerEOF = errors.New("http: unexpected EOF reading trailer")
   911  
   912  func (b *body) readTrailer() error {
   913  	// The common case, since nobody uses trailers.
   914  	buf, err := b.r.Peek(2)
   915  	if bytes.Equal(buf, singleCRLF) {
   916  		b.r.Discard(2)
   917  		return nil
   918  	}
   919  	if len(buf) < 2 {
   920  		return errTrailerEOF
   921  	}
   922  	if err != nil {
   923  		return err
   924  	}
   925  
   926  	// Make sure there's a header terminator coming up, to prevent
   927  	// a DoS with an unbounded size Trailer. It's not easy to
   928  	// slip in a LimitReader here, as textproto.NewReader requires
   929  	// a concrete *bufio.Reader. Also, we can't get all the way
   930  	// back up to our conn's LimitedReader that *might* be backing
   931  	// this bufio.Reader. Instead, a hack: we iteratively Peek up
   932  	// to the bufio.Reader's max size, looking for a double CRLF.
   933  	// This limits the trailer to the underlying buffer size, typically 4kB.
   934  	if !seeUpcomingDoubleCRLF(b.r) {
   935  		return errors.New("http: suspiciously long trailer after chunked body")
   936  	}
   937  
   938  	hdr, err := textproto.NewReader(b.r).ReadMIMEHeader()
   939  	if err != nil {
   940  		if err == io.EOF {
   941  			return errTrailerEOF
   942  		}
   943  		return err
   944  	}
   945  	switch rr := b.hdr.(type) {
   946  	case *Request:
   947  		mergeSetHeader(&rr.Trailer, Header(hdr))
   948  	case *Response:
   949  		mergeSetHeader(&rr.Trailer, Header(hdr))
   950  	}
   951  	return nil
   952  }
   953  
   954  func mergeSetHeader(dst *Header, src Header) {
   955  	if *dst == nil {
   956  		*dst = src
   957  		return
   958  	}
   959  	for k, vv := range src {
   960  		(*dst)[k] = vv
   961  	}
   962  }
   963  
   964  // unreadDataSizeLocked returns the number of bytes of unread input.
   965  // It returns -1 if unknown.
   966  // b.mu must be held.
   967  func (b *body) unreadDataSizeLocked() int64 {
   968  	if lr, ok := b.src.(*io.LimitedReader); ok {
   969  		return lr.N
   970  	}
   971  	return -1
   972  }
   973  
   974  func (b *body) Close() error {
   975  	b.mu.Lock()
   976  	defer b.mu.Unlock()
   977  	if b.closed {
   978  		return nil
   979  	}
   980  	var err error
   981  	switch {
   982  	case b.sawEOF:
   983  		// Already saw EOF, so no need going to look for it.
   984  	case b.hdr == nil && b.closing:
   985  		// no trailer and closing the connection next.
   986  		// no point in reading to EOF.
   987  	case b.doEarlyClose:
   988  		// Read up to maxPostHandlerReadBytes bytes of the body, looking
   989  		// for EOF (and trailers), so we can re-use this connection.
   990  		if lr, ok := b.src.(*io.LimitedReader); ok && lr.N > maxPostHandlerReadBytes {
   991  			// There was a declared Content-Length, and we have more bytes remaining
   992  			// than our maxPostHandlerReadBytes tolerance. So, give up.
   993  			b.earlyClose = true
   994  		} else {
   995  			var n int64
   996  			// Consume the body, or, which will also lead to us reading
   997  			// the trailer headers after the body, if present.
   998  			n, err = io.CopyN(io.Discard, bodyLocked{b}, maxPostHandlerReadBytes)
   999  			if err == io.EOF {
  1000  				err = nil
  1001  			}
  1002  			if n == maxPostHandlerReadBytes {
  1003  				b.earlyClose = true
  1004  			}
  1005  		}
  1006  	default:
  1007  		// Fully consume the body, which will also lead to us reading
  1008  		// the trailer headers after the body, if present.
  1009  		_, err = io.Copy(io.Discard, bodyLocked{b})
  1010  	}
  1011  	b.closed = true
  1012  	return err
  1013  }
  1014  
  1015  func (b *body) didEarlyClose() bool {
  1016  	b.mu.Lock()
  1017  	defer b.mu.Unlock()
  1018  	return b.earlyClose
  1019  }
  1020  
  1021  // bodyRemains reports whether future Read calls might
  1022  // yield data.
  1023  func (b *body) bodyRemains() bool {
  1024  	b.mu.Lock()
  1025  	defer b.mu.Unlock()
  1026  	return !b.sawEOF
  1027  }
  1028  
  1029  func (b *body) registerOnHitEOF(fn func()) {
  1030  	b.mu.Lock()
  1031  	defer b.mu.Unlock()
  1032  	b.onHitEOF = fn
  1033  }
  1034  
  1035  // bodyLocked is an io.Reader reading from a *body when its mutex is
  1036  // already held.
  1037  type bodyLocked struct {
  1038  	b *body
  1039  }
  1040  
  1041  func (bl bodyLocked) Read(p []byte) (n int, err error) {
  1042  	if bl.b.closed {
  1043  		return 0, ErrBodyReadAfterClose
  1044  	}
  1045  	return bl.b.readLocked(p)
  1046  }
  1047  
  1048  // parseContentLength trims whitespace from s and returns -1 if no value
  1049  // is set, or the value if it's >= 0.
  1050  func parseContentLength(cl string) (int64, error) {
  1051  	cl = textproto.TrimString(cl)
  1052  	if cl == "" {
  1053  		return -1, nil
  1054  	}
  1055  	n, err := strconv.ParseUint(cl, 10, 63)
  1056  	if err != nil {
  1057  		return 0, badStringError("bad Content-Length", cl)
  1058  	}
  1059  	return int64(n), nil
  1060  
  1061  }
  1062  
  1063  // finishAsyncByteRead finishes reading the 1-byte sniff
  1064  // from the ContentLength==0, Body!=nil case.
  1065  type finishAsyncByteRead struct {
  1066  	tw *transferWriter
  1067  }
  1068  
  1069  func (fr finishAsyncByteRead) Read(p []byte) (n int, err error) {
  1070  	if len(p) == 0 {
  1071  		return
  1072  	}
  1073  	rres := <-fr.tw.ByteReadCh
  1074  	n, err = rres.n, rres.err
  1075  	if n == 1 {
  1076  		p[0] = rres.b
  1077  	}
  1078  	if err == nil {
  1079  		err = io.EOF
  1080  	}
  1081  	return
  1082  }
  1083  
  1084  var nopCloserType = reflect.TypeOf(io.NopCloser(nil))
  1085  var nopCloserWriterToType = reflect.TypeOf(io.NopCloser(struct {
  1086  	io.Reader
  1087  	io.WriterTo
  1088  }{}))
  1089  
  1090  // unwrapNopCloser return the underlying reader and true if r is a NopCloser
  1091  // else it return false
  1092  func unwrapNopCloser(r io.Reader) (underlyingReader io.Reader, isNopCloser bool) {
  1093  	switch reflect.TypeOf(r) {
  1094  	case nopCloserType, nopCloserWriterToType:
  1095  		return reflect.ValueOf(r).Field(0).Interface().(io.Reader), true
  1096  	default:
  1097  		return nil, false
  1098  	}
  1099  }
  1100  
  1101  // isKnownInMemoryReader reports whether r is a type known to not
  1102  // block on Read. Its caller uses this as an optional optimization to
  1103  // send fewer TCP packets.
  1104  func isKnownInMemoryReader(r io.Reader) bool {
  1105  	switch r.(type) {
  1106  	case *bytes.Reader, *bytes.Buffer, *strings.Reader:
  1107  		return true
  1108  	}
  1109  	if r, ok := unwrapNopCloser(r); ok {
  1110  		return isKnownInMemoryReader(r)
  1111  	}
  1112  	if r, ok := r.(*readTrackingBody); ok {
  1113  		return isKnownInMemoryReader(r.ReadCloser)
  1114  	}
  1115  	return false
  1116  }
  1117  
  1118  // bufioFlushWriter is an io.Writer wrapper that flushes all writes
  1119  // on its wrapped writer if it's a *bufio.Writer.
  1120  type bufioFlushWriter struct{ w io.Writer }
  1121  
  1122  func (fw bufioFlushWriter) Write(p []byte) (n int, err error) {
  1123  	n, err = fw.w.Write(p)
  1124  	if bw, ok := fw.w.(*bufio.Writer); n > 0 && ok {
  1125  		ferr := bw.Flush()
  1126  		if ferr != nil && err == nil {
  1127  			err = ferr
  1128  		}
  1129  	}
  1130  	return
  1131  }
  1132  

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