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  	"internal/godebug"
    13  	"io"
    14  	"net/http/httptrace"
    15  	"net/http/internal"
    16  	"net/http/internal/ascii"
    17  	"net/textproto"
    18  	"reflect"
    19  	"sort"
    20  	"strconv"
    21  	"strings"
    22  	"sync"
    23  	"time"
    24  
    25  	"golang.org/x/net/http/httpguts"
    26  )
    27  
    28  // ErrLineTooLong is returned when reading request or response bodies
    29  // with malformed chunked encoding.
    30  var ErrLineTooLong = internal.ErrLineTooLong
    31  
    32  type errorReader struct {
    33  	err error
    34  }
    35  
    36  func (r errorReader) Read(p []byte) (n int, err error) {
    37  	return 0, r.err
    38  }
    39  
    40  type byteReader struct {
    41  	b    byte
    42  	done bool
    43  }
    44  
    45  func (br *byteReader) Read(p []byte) (n int, err error) {
    46  	if br.done {
    47  		return 0, io.EOF
    48  	}
    49  	if len(p) == 0 {
    50  		return 0, nil
    51  	}
    52  	br.done = true
    53  	p[0] = br.b
    54  	return 1, io.EOF
    55  }
    56  
    57  // transferWriter inspects the fields of a user-supplied Request or Response,
    58  // sanitizes them without changing the user object and provides methods for
    59  // writing the respective header, body and trailer in wire format.
    60  type transferWriter struct {
    61  	Method           string
    62  	Body             io.Reader
    63  	BodyCloser       io.Closer
    64  	ResponseToHEAD   bool
    65  	ContentLength    int64 // -1 means unknown, 0 means exactly none
    66  	Close            bool
    67  	TransferEncoding []string
    68  	Header           Header
    69  	Trailer          Header
    70  	IsResponse       bool
    71  	bodyReadError    error // any non-EOF error from reading Body
    72  
    73  	FlushHeaders bool            // flush headers to network before body
    74  	ByteReadCh   chan readResult // non-nil if probeRequestBody called
    75  }
    76  
    77  func newTransferWriter(r any) (t *transferWriter, err error) {
    78  	t = &transferWriter{}
    79  
    80  	// Extract relevant fields
    81  	atLeastHTTP11 := false
    82  	switch rr := r.(type) {
    83  	case *Request:
    84  		if rr.ContentLength != 0 && rr.Body == nil {
    85  			return nil, fmt.Errorf("http: Request.ContentLength=%d with nil Body", rr.ContentLength)
    86  		}
    87  		t.Method = valueOrDefault(rr.Method, "GET")
    88  		t.Close = rr.Close
    89  		t.TransferEncoding = rr.TransferEncoding
    90  		t.Header = rr.Header
    91  		t.Trailer = rr.Trailer
    92  		t.Body = rr.Body
    93  		t.BodyCloser = rr.Body
    94  		t.ContentLength = rr.outgoingLength()
    95  		if t.ContentLength < 0 && len(t.TransferEncoding) == 0 && t.shouldSendChunkedRequestBody() {
    96  			t.TransferEncoding = []string{"chunked"}
    97  		}
    98  		// If there's a body, conservatively flush the headers
    99  		// to any bufio.Writer we're writing to, just in case
   100  		// the server needs the headers early, before we copy
   101  		// the body and possibly block. We make an exception
   102  		// for the common standard library in-memory types,
   103  		// though, to avoid unnecessary TCP packets on the
   104  		// wire. (Issue 22088.)
   105  		if t.ContentLength != 0 && !isKnownInMemoryReader(t.Body) {
   106  			t.FlushHeaders = true
   107  		}
   108  
   109  		atLeastHTTP11 = true // Transport requests are always 1.1 or 2.0
   110  	case *Response:
   111  		t.IsResponse = true
   112  		if rr.Request != nil {
   113  			t.Method = rr.Request.Method
   114  		}
   115  		t.Body = rr.Body
   116  		t.BodyCloser = rr.Body
   117  		t.ContentLength = rr.ContentLength
   118  		t.Close = rr.Close
   119  		t.TransferEncoding = rr.TransferEncoding
   120  		t.Header = rr.Header
   121  		t.Trailer = rr.Trailer
   122  		atLeastHTTP11 = rr.ProtoAtLeast(1, 1)
   123  		t.ResponseToHEAD = noResponseBodyExpected(t.Method)
   124  	}
   125  
   126  	// Sanitize Body,ContentLength,TransferEncoding
   127  	if t.ResponseToHEAD {
   128  		t.Body = nil
   129  		if chunked(t.TransferEncoding) {
   130  			t.ContentLength = -1
   131  		}
   132  	} else {
   133  		if !atLeastHTTP11 || t.Body == nil {
   134  			t.TransferEncoding = nil
   135  		}
   136  		if chunked(t.TransferEncoding) {
   137  			t.ContentLength = -1
   138  		} else if t.Body == nil { // no chunking, no body
   139  			t.ContentLength = 0
   140  		}
   141  	}
   142  
   143  	// Sanitize Trailer
   144  	if !chunked(t.TransferEncoding) {
   145  		t.Trailer = nil
   146  	}
   147  
   148  	return t, nil
   149  }
   150  
   151  // shouldSendChunkedRequestBody reports whether we should try to send a
   152  // chunked request body to the server. In particular, the case we really
   153  // want to prevent is sending a GET or other typically-bodyless request to a
   154  // server with a chunked body when the body has zero bytes, since GETs with
   155  // bodies (while acceptable according to specs), even zero-byte chunked
   156  // bodies, are approximately never seen in the wild and confuse most
   157  // servers. See Issue 18257, as one example.
   158  //
   159  // The only reason we'd send such a request is if the user set the Body to a
   160  // non-nil value (say, io.NopCloser(bytes.NewReader(nil))) and didn't
   161  // set ContentLength, or NewRequest set it to -1 (unknown), so then we assume
   162  // there's bytes to send.
   163  //
   164  // This code tries to read a byte from the Request.Body in such cases to see
   165  // whether the body actually has content (super rare) or is actually just
   166  // a non-nil content-less ReadCloser (the more common case). In that more
   167  // common case, we act as if their Body were nil instead, and don't send
   168  // a body.
   169  func (t *transferWriter) shouldSendChunkedRequestBody() bool {
   170  	// Note that t.ContentLength is the corrected content length
   171  	// from rr.outgoingLength, so 0 actually means zero, not unknown.
   172  	if t.ContentLength >= 0 || t.Body == nil { // redundant checks; caller did them
   173  		return false
   174  	}
   175  	if t.Method == "CONNECT" {
   176  		return false
   177  	}
   178  	if requestMethodUsuallyLacksBody(t.Method) {
   179  		// Only probe the Request.Body for GET/HEAD/DELETE/etc
   180  		// requests, because it's only those types of requests
   181  		// that confuse servers.
   182  		t.probeRequestBody() // adjusts t.Body, t.ContentLength
   183  		return t.Body != nil
   184  	}
   185  	// For all other request types (PUT, POST, PATCH, or anything
   186  	// made-up we've never heard of), assume it's normal and the server
   187  	// can deal with a chunked request body. Maybe we'll adjust this
   188  	// later.
   189  	return true
   190  }
   191  
   192  // probeRequestBody reads a byte from t.Body to see whether it's empty
   193  // (returns io.EOF right away).
   194  //
   195  // But because we've had problems with this blocking users in the past
   196  // (issue 17480) when the body is a pipe (perhaps waiting on the response
   197  // headers before the pipe is fed data), we need to be careful and bound how
   198  // long we wait for it. This delay will only affect users if all the following
   199  // are true:
   200  //   - the request body blocks
   201  //   - the content length is not set (or set to -1)
   202  //   - the method doesn't usually have a body (GET, HEAD, DELETE, ...)
   203  //   - there is no transfer-encoding=chunked already set.
   204  //
   205  // In other words, this delay will not normally affect anybody, and there
   206  // are workarounds if it does.
   207  func (t *transferWriter) probeRequestBody() {
   208  	t.ByteReadCh = make(chan readResult, 1)
   209  	go func(body io.Reader) {
   210  		var buf [1]byte
   211  		var rres readResult
   212  		rres.n, rres.err = body.Read(buf[:])
   213  		if rres.n == 1 {
   214  			rres.b = buf[0]
   215  		}
   216  		t.ByteReadCh <- rres
   217  		close(t.ByteReadCh)
   218  	}(t.Body)
   219  	timer := time.NewTimer(200 * time.Millisecond)
   220  	select {
   221  	case rres := <-t.ByteReadCh:
   222  		timer.Stop()
   223  		if rres.n == 0 && rres.err == io.EOF {
   224  			// It was empty.
   225  			t.Body = nil
   226  			t.ContentLength = 0
   227  		} else if rres.n == 1 {
   228  			if rres.err != nil {
   229  				t.Body = io.MultiReader(&byteReader{b: rres.b}, errorReader{rres.err})
   230  			} else {
   231  				t.Body = io.MultiReader(&byteReader{b: rres.b}, t.Body)
   232  			}
   233  		} else if rres.err != nil {
   234  			t.Body = errorReader{rres.err}
   235  		}
   236  	case <-timer.C:
   237  		// Too slow. Don't wait. Read it later, and keep
   238  		// assuming that this is ContentLength == -1
   239  		// (unknown), which means we'll send a
   240  		// "Transfer-Encoding: chunked" header.
   241  		t.Body = io.MultiReader(finishAsyncByteRead{t}, t.Body)
   242  		// Request that Request.Write flush the headers to the
   243  		// network before writing the body, since our body may not
   244  		// become readable until it's seen the response headers.
   245  		t.FlushHeaders = true
   246  	}
   247  }
   248  
   249  func noResponseBodyExpected(requestMethod string) bool {
   250  	return requestMethod == "HEAD"
   251  }
   252  
   253  func (t *transferWriter) shouldSendContentLength() bool {
   254  	if chunked(t.TransferEncoding) {
   255  		return false
   256  	}
   257  	if t.ContentLength > 0 {
   258  		return true
   259  	}
   260  	if t.ContentLength < 0 {
   261  		return false
   262  	}
   263  	// Many servers expect a Content-Length for these methods
   264  	if t.Method == "POST" || t.Method == "PUT" || t.Method == "PATCH" {
   265  		return true
   266  	}
   267  	if t.ContentLength == 0 && isIdentity(t.TransferEncoding) {
   268  		if t.Method == "GET" || t.Method == "HEAD" {
   269  			return false
   270  		}
   271  		return true
   272  	}
   273  
   274  	return false
   275  }
   276  
   277  func (t *transferWriter) writeHeader(w io.Writer, trace *httptrace.ClientTrace) error {
   278  	if t.Close && !hasToken(t.Header.get("Connection"), "close") {
   279  		if _, err := io.WriteString(w, "Connection: close\r\n"); err != nil {
   280  			return err
   281  		}
   282  		if trace != nil && trace.WroteHeaderField != nil {
   283  			trace.WroteHeaderField("Connection", []string{"close"})
   284  		}
   285  	}
   286  
   287  	// Write Content-Length and/or Transfer-Encoding whose values are a
   288  	// function of the sanitized field triple (Body, ContentLength,
   289  	// TransferEncoding)
   290  	if t.shouldSendContentLength() {
   291  		if _, err := io.WriteString(w, "Content-Length: "); err != nil {
   292  			return err
   293  		}
   294  		if _, err := io.WriteString(w, strconv.FormatInt(t.ContentLength, 10)+"\r\n"); err != nil {
   295  			return err
   296  		}
   297  		if trace != nil && trace.WroteHeaderField != nil {
   298  			trace.WroteHeaderField("Content-Length", []string{strconv.FormatInt(t.ContentLength, 10)})
   299  		}
   300  	} else if chunked(t.TransferEncoding) {
   301  		if _, err := io.WriteString(w, "Transfer-Encoding: chunked\r\n"); err != nil {
   302  			return err
   303  		}
   304  		if trace != nil && trace.WroteHeaderField != nil {
   305  			trace.WroteHeaderField("Transfer-Encoding", []string{"chunked"})
   306  		}
   307  	}
   308  
   309  	// Write Trailer header
   310  	if t.Trailer != nil {
   311  		keys := make([]string, 0, len(t.Trailer))
   312  		for k := range t.Trailer {
   313  			k = CanonicalHeaderKey(k)
   314  			switch k {
   315  			case "Transfer-Encoding", "Trailer", "Content-Length":
   316  				return badStringError("invalid Trailer key", k)
   317  			}
   318  			keys = append(keys, k)
   319  		}
   320  		if len(keys) > 0 {
   321  			sort.Strings(keys)
   322  			// TODO: could do better allocation-wise here, but trailers are rare,
   323  			// so being lazy for now.
   324  			if _, err := io.WriteString(w, "Trailer: "+strings.Join(keys, ",")+"\r\n"); err != nil {
   325  				return err
   326  			}
   327  			if trace != nil && trace.WroteHeaderField != nil {
   328  				trace.WroteHeaderField("Trailer", keys)
   329  			}
   330  		}
   331  	}
   332  
   333  	return nil
   334  }
   335  
   336  // always closes t.BodyCloser
   337  func (t *transferWriter) writeBody(w io.Writer) (err error) {
   338  	var ncopy int64
   339  	closed := false
   340  	defer func() {
   341  		if closed || t.BodyCloser == nil {
   342  			return
   343  		}
   344  		if closeErr := t.BodyCloser.Close(); closeErr != nil && err == nil {
   345  			err = closeErr
   346  		}
   347  	}()
   348  
   349  	// Write body. We "unwrap" the body first if it was wrapped in a
   350  	// nopCloser or readTrackingBody. This is to ensure that we can take advantage of
   351  	// OS-level optimizations in the event that the body is an
   352  	// *os.File.
   353  	if t.Body != nil {
   354  		var body = t.unwrapBody()
   355  		if chunked(t.TransferEncoding) {
   356  			if bw, ok := w.(*bufio.Writer); ok && !t.IsResponse {
   357  				w = &internal.FlushAfterChunkWriter{Writer: bw}
   358  			}
   359  			cw := internal.NewChunkedWriter(w)
   360  			_, err = t.doBodyCopy(cw, body)
   361  			if err == nil {
   362  				err = cw.Close()
   363  			}
   364  		} else if t.ContentLength == -1 {
   365  			dst := w
   366  			if t.Method == "CONNECT" {
   367  				dst = bufioFlushWriter{dst}
   368  			}
   369  			ncopy, err = t.doBodyCopy(dst, body)
   370  		} else {
   371  			ncopy, err = t.doBodyCopy(w, io.LimitReader(body, t.ContentLength))
   372  			if err != nil {
   373  				return err
   374  			}
   375  			var nextra int64
   376  			nextra, err = t.doBodyCopy(io.Discard, body)
   377  			ncopy += nextra
   378  		}
   379  		if err != nil {
   380  			return err
   381  		}
   382  	}
   383  	if t.BodyCloser != nil {
   384  		closed = true
   385  		if err := t.BodyCloser.Close(); err != nil {
   386  			return err
   387  		}
   388  	}
   389  
   390  	if !t.ResponseToHEAD && t.ContentLength != -1 && t.ContentLength != ncopy {
   391  		return fmt.Errorf("http: ContentLength=%d with Body length %d",
   392  			t.ContentLength, ncopy)
   393  	}
   394  
   395  	if chunked(t.TransferEncoding) {
   396  		// Write Trailer header
   397  		if t.Trailer != nil {
   398  			if err := t.Trailer.Write(w); err != nil {
   399  				return err
   400  			}
   401  		}
   402  		// Last chunk, empty trailer
   403  		_, err = io.WriteString(w, "\r\n")
   404  	}
   405  	return err
   406  }
   407  
   408  // doBodyCopy wraps a copy operation, with any resulting error also
   409  // being saved in bodyReadError.
   410  //
   411  // This function is only intended for use in writeBody.
   412  func (t *transferWriter) doBodyCopy(dst io.Writer, src io.Reader) (n int64, err error) {
   413  	buf := getCopyBuf()
   414  	defer putCopyBuf(buf)
   415  
   416  	n, err = io.CopyBuffer(dst, src, buf)
   417  	if err != nil && err != io.EOF {
   418  		t.bodyReadError = err
   419  	}
   420  	return
   421  }
   422  
   423  // unwrapBody unwraps the body's inner reader if it's a
   424  // nopCloser. This is to ensure that body writes sourced from local
   425  // files (*os.File types) are properly optimized.
   426  //
   427  // This function is only intended for use in writeBody.
   428  func (t *transferWriter) unwrapBody() io.Reader {
   429  	if r, ok := unwrapNopCloser(t.Body); ok {
   430  		return r
   431  	}
   432  	if r, ok := t.Body.(*readTrackingBody); ok {
   433  		r.didRead = true
   434  		return r.ReadCloser
   435  	}
   436  	return t.Body
   437  }
   438  
   439  type transferReader struct {
   440  	// Input
   441  	Header        Header
   442  	StatusCode    int
   443  	RequestMethod string
   444  	ProtoMajor    int
   445  	ProtoMinor    int
   446  	// Output
   447  	Body          io.ReadCloser
   448  	ContentLength int64
   449  	Chunked       bool
   450  	Close         bool
   451  	Trailer       Header
   452  }
   453  
   454  func (t *transferReader) protoAtLeast(m, n int) bool {
   455  	return t.ProtoMajor > m || (t.ProtoMajor == m && t.ProtoMinor >= n)
   456  }
   457  
   458  // bodyAllowedForStatus reports whether a given response status code
   459  // permits a body. See RFC 7230, section 3.3.
   460  func bodyAllowedForStatus(status int) bool {
   461  	switch {
   462  	case status >= 100 && status <= 199:
   463  		return false
   464  	case status == 204:
   465  		return false
   466  	case status == 304:
   467  		return false
   468  	}
   469  	return true
   470  }
   471  
   472  var (
   473  	suppressedHeaders304    = []string{"Content-Type", "Content-Length", "Transfer-Encoding"}
   474  	suppressedHeadersNoBody = []string{"Content-Length", "Transfer-Encoding"}
   475  	excludedHeadersNoBody   = map[string]bool{"Content-Length": true, "Transfer-Encoding": true}
   476  )
   477  
   478  func suppressedHeaders(status int) []string {
   479  	switch {
   480  	case status == 304:
   481  		// RFC 7232 section 4.1
   482  		return suppressedHeaders304
   483  	case !bodyAllowedForStatus(status):
   484  		return suppressedHeadersNoBody
   485  	}
   486  	return nil
   487  }
   488  
   489  // msg is *Request or *Response.
   490  func readTransfer(msg any, r *bufio.Reader) (err error) {
   491  	t := &transferReader{RequestMethod: "GET"}
   492  
   493  	// Unify input
   494  	isResponse := false
   495  	switch rr := msg.(type) {
   496  	case *Response:
   497  		t.Header = rr.Header
   498  		t.StatusCode = rr.StatusCode
   499  		t.ProtoMajor = rr.ProtoMajor
   500  		t.ProtoMinor = rr.ProtoMinor
   501  		t.Close = shouldClose(t.ProtoMajor, t.ProtoMinor, t.Header, true)
   502  		isResponse = true
   503  		if rr.Request != nil {
   504  			t.RequestMethod = rr.Request.Method
   505  		}
   506  	case *Request:
   507  		t.Header = rr.Header
   508  		t.RequestMethod = rr.Method
   509  		t.ProtoMajor = rr.ProtoMajor
   510  		t.ProtoMinor = rr.ProtoMinor
   511  		// Transfer semantics for Requests are exactly like those for
   512  		// Responses with status code 200, responding to a GET method
   513  		t.StatusCode = 200
   514  		t.Close = rr.Close
   515  	default:
   516  		panic("unexpected type")
   517  	}
   518  
   519  	// Default to HTTP/1.1
   520  	if t.ProtoMajor == 0 && t.ProtoMinor == 0 {
   521  		t.ProtoMajor, t.ProtoMinor = 1, 1
   522  	}
   523  
   524  	// Transfer-Encoding: chunked, and overriding Content-Length.
   525  	if err := t.parseTransferEncoding(); err != nil {
   526  		return err
   527  	}
   528  
   529  	realLength, err := fixLength(isResponse, t.StatusCode, t.RequestMethod, t.Header, t.Chunked)
   530  	if err != nil {
   531  		return err
   532  	}
   533  	if isResponse && t.RequestMethod == "HEAD" {
   534  		if n, err := parseContentLength(t.Header["Content-Length"]); err != nil {
   535  			return err
   536  		} else {
   537  			t.ContentLength = n
   538  		}
   539  	} else {
   540  		t.ContentLength = realLength
   541  	}
   542  
   543  	// Trailer
   544  	t.Trailer, err = fixTrailer(t.Header, t.Chunked)
   545  	if err != nil {
   546  		return err
   547  	}
   548  
   549  	// If there is no Content-Length or chunked Transfer-Encoding on a *Response
   550  	// and the status is not 1xx, 204 or 304, then the body is unbounded.
   551  	// See RFC 7230, section 3.3.
   552  	switch msg.(type) {
   553  	case *Response:
   554  		if realLength == -1 && !t.Chunked && bodyAllowedForStatus(t.StatusCode) {
   555  			// Unbounded body.
   556  			t.Close = true
   557  		}
   558  	}
   559  
   560  	// Prepare body reader. ContentLength < 0 means chunked encoding
   561  	// or close connection when finished, since multipart is not supported yet
   562  	switch {
   563  	case t.Chunked:
   564  		if isResponse && (noResponseBodyExpected(t.RequestMethod) || !bodyAllowedForStatus(t.StatusCode)) {
   565  			t.Body = NoBody
   566  		} else {
   567  			t.Body = &body{src: internal.NewChunkedReader(r), hdr: msg, r: r, closing: t.Close}
   568  		}
   569  	case realLength == 0:
   570  		t.Body = NoBody
   571  	case realLength > 0:
   572  		t.Body = &body{src: io.LimitReader(r, realLength), closing: t.Close}
   573  	default:
   574  		// realLength < 0, i.e. "Content-Length" not mentioned in header
   575  		if t.Close {
   576  			// Close semantics (i.e. HTTP/1.0)
   577  			t.Body = &body{src: r, closing: t.Close}
   578  		} else {
   579  			// Persistent connection (i.e. HTTP/1.1)
   580  			t.Body = NoBody
   581  		}
   582  	}
   583  
   584  	// Unify output
   585  	switch rr := msg.(type) {
   586  	case *Request:
   587  		rr.Body = t.Body
   588  		rr.ContentLength = t.ContentLength
   589  		if t.Chunked {
   590  			rr.TransferEncoding = []string{"chunked"}
   591  		}
   592  		rr.Close = t.Close
   593  		rr.Trailer = t.Trailer
   594  	case *Response:
   595  		rr.Body = t.Body
   596  		rr.ContentLength = t.ContentLength
   597  		if t.Chunked {
   598  			rr.TransferEncoding = []string{"chunked"}
   599  		}
   600  		rr.Close = t.Close
   601  		rr.Trailer = t.Trailer
   602  	}
   603  
   604  	return nil
   605  }
   606  
   607  // Checks whether chunked is part of the encodings stack.
   608  func chunked(te []string) bool { return len(te) > 0 && te[0] == "chunked" }
   609  
   610  // Checks whether the encoding is explicitly "identity".
   611  func isIdentity(te []string) bool { return len(te) == 1 && te[0] == "identity" }
   612  
   613  // unsupportedTEError reports unsupported transfer-encodings.
   614  type unsupportedTEError struct {
   615  	err string
   616  }
   617  
   618  func (uste *unsupportedTEError) Error() string {
   619  	return uste.err
   620  }
   621  
   622  // isUnsupportedTEError checks if the error is of type
   623  // unsupportedTEError. It is usually invoked with a non-nil err.
   624  func isUnsupportedTEError(err error) bool {
   625  	_, ok := err.(*unsupportedTEError)
   626  	return ok
   627  }
   628  
   629  // parseTransferEncoding sets t.Chunked based on the Transfer-Encoding header.
   630  func (t *transferReader) parseTransferEncoding() error {
   631  	raw, present := t.Header["Transfer-Encoding"]
   632  	if !present {
   633  		return nil
   634  	}
   635  	delete(t.Header, "Transfer-Encoding")
   636  
   637  	// Issue 12785; ignore Transfer-Encoding on HTTP/1.0 requests.
   638  	if !t.protoAtLeast(1, 1) {
   639  		return nil
   640  	}
   641  
   642  	// Like nginx, we only support a single Transfer-Encoding header field, and
   643  	// only if set to "chunked". This is one of the most security sensitive
   644  	// surfaces in HTTP/1.1 due to the risk of request smuggling, so we keep it
   645  	// strict and simple.
   646  	if len(raw) != 1 {
   647  		return &unsupportedTEError{fmt.Sprintf("too many transfer encodings: %q", raw)}
   648  	}
   649  	if !ascii.EqualFold(raw[0], "chunked") {
   650  		return &unsupportedTEError{fmt.Sprintf("unsupported transfer encoding: %q", raw[0])}
   651  	}
   652  
   653  	// RFC 7230 3.3.2 says "A sender MUST NOT send a Content-Length header field
   654  	// in any message that contains a Transfer-Encoding header field."
   655  	//
   656  	// but also: "If a message is received with both a Transfer-Encoding and a
   657  	// Content-Length header field, the Transfer-Encoding overrides the
   658  	// Content-Length. Such a message might indicate an attempt to perform
   659  	// request smuggling (Section 9.5) or response splitting (Section 9.4) and
   660  	// ought to be handled as an error. A sender MUST remove the received
   661  	// Content-Length field prior to forwarding such a message downstream."
   662  	//
   663  	// Reportedly, these appear in the wild.
   664  	delete(t.Header, "Content-Length")
   665  
   666  	t.Chunked = true
   667  	return nil
   668  }
   669  
   670  // Determine the expected body length, using RFC 7230 Section 3.3. This
   671  // function is not a method, because ultimately it should be shared by
   672  // ReadResponse and ReadRequest.
   673  func fixLength(isResponse bool, status int, requestMethod string, header Header, chunked bool) (int64, error) {
   674  	isRequest := !isResponse
   675  	contentLens := header["Content-Length"]
   676  
   677  	// Hardening against HTTP request smuggling
   678  	if len(contentLens) > 1 {
   679  		// Per RFC 7230 Section 3.3.2, prevent multiple
   680  		// Content-Length headers if they differ in value.
   681  		// If there are dups of the value, remove the dups.
   682  		// See Issue 16490.
   683  		first := textproto.TrimString(contentLens[0])
   684  		for _, ct := range contentLens[1:] {
   685  			if first != textproto.TrimString(ct) {
   686  				return 0, fmt.Errorf("http: message cannot contain multiple Content-Length headers; got %q", contentLens)
   687  			}
   688  		}
   689  
   690  		// deduplicate Content-Length
   691  		header.Del("Content-Length")
   692  		header.Add("Content-Length", first)
   693  
   694  		contentLens = header["Content-Length"]
   695  	}
   696  
   697  	// Logic based on response type or status
   698  	if isResponse && noResponseBodyExpected(requestMethod) {
   699  		return 0, nil
   700  	}
   701  	if status/100 == 1 {
   702  		return 0, nil
   703  	}
   704  	switch status {
   705  	case 204, 304:
   706  		return 0, nil
   707  	}
   708  
   709  	// Logic based on Transfer-Encoding
   710  	if chunked {
   711  		return -1, nil
   712  	}
   713  
   714  	if len(contentLens) > 0 {
   715  		// Logic based on Content-Length
   716  		n, err := parseContentLength(contentLens)
   717  		if err != nil {
   718  			return -1, err
   719  		}
   720  		return n, nil
   721  	}
   722  
   723  	header.Del("Content-Length")
   724  
   725  	if isRequest {
   726  		// RFC 7230 neither explicitly permits nor forbids an
   727  		// entity-body on a GET request so we permit one if
   728  		// declared, but we default to 0 here (not -1 below)
   729  		// if there's no mention of a body.
   730  		// Likewise, all other request methods are assumed to have
   731  		// no body if neither Transfer-Encoding chunked nor a
   732  		// Content-Length are set.
   733  		return 0, nil
   734  	}
   735  
   736  	// Body-EOF logic based on other methods (like closing, or chunked coding)
   737  	return -1, nil
   738  }
   739  
   740  // Determine whether to hang up after sending a request and body, or
   741  // receiving a response and body
   742  // 'header' is the request headers.
   743  func shouldClose(major, minor int, header Header, removeCloseHeader bool) bool {
   744  	if major < 1 {
   745  		return true
   746  	}
   747  
   748  	conv := header["Connection"]
   749  	hasClose := httpguts.HeaderValuesContainsToken(conv, "close")
   750  	if major == 1 && minor == 0 {
   751  		return hasClose || !httpguts.HeaderValuesContainsToken(conv, "keep-alive")
   752  	}
   753  
   754  	if hasClose && removeCloseHeader {
   755  		header.Del("Connection")
   756  	}
   757  
   758  	return hasClose
   759  }
   760  
   761  // Parse the trailer header.
   762  func fixTrailer(header Header, chunked bool) (Header, error) {
   763  	vv, ok := header["Trailer"]
   764  	if !ok {
   765  		return nil, nil
   766  	}
   767  	if !chunked {
   768  		// Trailer and no chunking:
   769  		// this is an invalid use case for trailer header.
   770  		// Nevertheless, no error will be returned and we
   771  		// let users decide if this is a valid HTTP message.
   772  		// The Trailer header will be kept in Response.Header
   773  		// but not populate Response.Trailer.
   774  		// See issue #27197.
   775  		return nil, nil
   776  	}
   777  	header.Del("Trailer")
   778  
   779  	trailer := make(Header)
   780  	var err error
   781  	for _, v := range vv {
   782  		foreachHeaderElement(v, func(key string) {
   783  			key = CanonicalHeaderKey(key)
   784  			switch key {
   785  			case "Transfer-Encoding", "Trailer", "Content-Length":
   786  				if err == nil {
   787  					err = badStringError("bad trailer key", key)
   788  					return
   789  				}
   790  			}
   791  			trailer[key] = nil
   792  		})
   793  	}
   794  	if err != nil {
   795  		return nil, err
   796  	}
   797  	if len(trailer) == 0 {
   798  		return nil, nil
   799  	}
   800  	return trailer, nil
   801  }
   802  
   803  // body turns a Reader into a ReadCloser.
   804  // Close ensures that the body has been fully read
   805  // and then reads the trailer if necessary.
   806  type body struct {
   807  	src          io.Reader
   808  	hdr          any           // non-nil (Response or Request) value means read trailer
   809  	r            *bufio.Reader // underlying wire-format reader for the trailer
   810  	closing      bool          // is the connection to be closed after reading body?
   811  	doEarlyClose bool          // whether Close should stop early
   812  
   813  	mu         sync.Mutex // guards following, and calls to Read and Close
   814  	sawEOF     bool
   815  	closed     bool
   816  	earlyClose bool   // Close called and we didn't read to the end of src
   817  	onHitEOF   func() // if non-nil, func to call when EOF is Read
   818  }
   819  
   820  // ErrBodyReadAfterClose is returned when reading a [Request] or [Response]
   821  // Body after the body has been closed. This typically happens when the body is
   822  // read after an HTTP [Handler] calls WriteHeader or Write on its
   823  // [ResponseWriter].
   824  var ErrBodyReadAfterClose = errors.New("http: invalid Read on closed Body")
   825  
   826  func (b *body) Read(p []byte) (n int, err error) {
   827  	b.mu.Lock()
   828  	defer b.mu.Unlock()
   829  	if b.closed {
   830  		return 0, ErrBodyReadAfterClose
   831  	}
   832  	return b.readLocked(p)
   833  }
   834  
   835  // Must hold b.mu.
   836  func (b *body) readLocked(p []byte) (n int, err error) {
   837  	if b.sawEOF {
   838  		return 0, io.EOF
   839  	}
   840  	n, err = b.src.Read(p)
   841  
   842  	if err == io.EOF {
   843  		b.sawEOF = true
   844  		// Chunked case. Read the trailer.
   845  		if b.hdr != nil {
   846  			if e := b.readTrailer(); e != nil {
   847  				err = e
   848  				// Something went wrong in the trailer, we must not allow any
   849  				// further reads of any kind to succeed from body, nor any
   850  				// subsequent requests on the server connection. See
   851  				// golang.org/issue/12027
   852  				b.sawEOF = false
   853  				b.closed = true
   854  			}
   855  			b.hdr = nil
   856  		} else {
   857  			// If the server declared the Content-Length, our body is a LimitedReader
   858  			// and we need to check whether this EOF arrived early.
   859  			if lr, ok := b.src.(*io.LimitedReader); ok && lr.N > 0 {
   860  				err = io.ErrUnexpectedEOF
   861  			}
   862  		}
   863  	}
   864  
   865  	// If we can return an EOF here along with the read data, do
   866  	// so. This is optional per the io.Reader contract, but doing
   867  	// so helps the HTTP transport code recycle its connection
   868  	// earlier (since it will see this EOF itself), even if the
   869  	// client doesn't do future reads or Close.
   870  	if err == nil && n > 0 {
   871  		if lr, ok := b.src.(*io.LimitedReader); ok && lr.N == 0 {
   872  			err = io.EOF
   873  			b.sawEOF = true
   874  		}
   875  	}
   876  
   877  	if b.sawEOF && b.onHitEOF != nil {
   878  		b.onHitEOF()
   879  	}
   880  
   881  	return n, err
   882  }
   883  
   884  var (
   885  	singleCRLF = []byte("\r\n")
   886  	doubleCRLF = []byte("\r\n\r\n")
   887  )
   888  
   889  func seeUpcomingDoubleCRLF(r *bufio.Reader) bool {
   890  	for peekSize := 4; ; peekSize++ {
   891  		// This loop stops when Peek returns an error,
   892  		// which it does when r's buffer has been filled.
   893  		buf, err := r.Peek(peekSize)
   894  		if bytes.HasSuffix(buf, doubleCRLF) {
   895  			return true
   896  		}
   897  		if err != nil {
   898  			break
   899  		}
   900  	}
   901  	return false
   902  }
   903  
   904  var errTrailerEOF = errors.New("http: unexpected EOF reading trailer")
   905  
   906  func (b *body) readTrailer() error {
   907  	// The common case, since nobody uses trailers.
   908  	buf, err := b.r.Peek(2)
   909  	if bytes.Equal(buf, singleCRLF) {
   910  		b.r.Discard(2)
   911  		return nil
   912  	}
   913  	if len(buf) < 2 {
   914  		return errTrailerEOF
   915  	}
   916  	if err != nil {
   917  		return err
   918  	}
   919  
   920  	// Make sure there's a header terminator coming up, to prevent
   921  	// a DoS with an unbounded size Trailer. It's not easy to
   922  	// slip in a LimitReader here, as textproto.NewReader requires
   923  	// a concrete *bufio.Reader. Also, we can't get all the way
   924  	// back up to our conn's LimitedReader that *might* be backing
   925  	// this bufio.Reader. Instead, a hack: we iteratively Peek up
   926  	// to the bufio.Reader's max size, looking for a double CRLF.
   927  	// This limits the trailer to the underlying buffer size, typically 4kB.
   928  	if !seeUpcomingDoubleCRLF(b.r) {
   929  		return errors.New("http: suspiciously long trailer after chunked body")
   930  	}
   931  
   932  	hdr, err := textproto.NewReader(b.r).ReadMIMEHeader()
   933  	if err != nil {
   934  		if err == io.EOF {
   935  			return errTrailerEOF
   936  		}
   937  		return err
   938  	}
   939  	switch rr := b.hdr.(type) {
   940  	case *Request:
   941  		mergeSetHeader(&rr.Trailer, Header(hdr))
   942  	case *Response:
   943  		mergeSetHeader(&rr.Trailer, Header(hdr))
   944  	}
   945  	return nil
   946  }
   947  
   948  func mergeSetHeader(dst *Header, src Header) {
   949  	if *dst == nil {
   950  		*dst = src
   951  		return
   952  	}
   953  	for k, vv := range src {
   954  		(*dst)[k] = vv
   955  	}
   956  }
   957  
   958  // unreadDataSizeLocked returns the number of bytes of unread input.
   959  // It returns -1 if unknown.
   960  // b.mu must be held.
   961  func (b *body) unreadDataSizeLocked() int64 {
   962  	if lr, ok := b.src.(*io.LimitedReader); ok {
   963  		return lr.N
   964  	}
   965  	return -1
   966  }
   967  
   968  func (b *body) Close() error {
   969  	b.mu.Lock()
   970  	defer b.mu.Unlock()
   971  	if b.closed {
   972  		return nil
   973  	}
   974  	var err error
   975  	switch {
   976  	case b.sawEOF:
   977  		// Already saw EOF, so no need going to look for it.
   978  	case b.hdr == nil && b.closing:
   979  		// no trailer and closing the connection next.
   980  		// no point in reading to EOF.
   981  	case b.doEarlyClose:
   982  		// Read up to maxPostHandlerReadBytes bytes of the body, looking
   983  		// for EOF (and trailers), so we can re-use this connection.
   984  		if lr, ok := b.src.(*io.LimitedReader); ok && lr.N > maxPostHandlerReadBytes {
   985  			// There was a declared Content-Length, and we have more bytes remaining
   986  			// than our maxPostHandlerReadBytes tolerance. So, give up.
   987  			b.earlyClose = true
   988  		} else {
   989  			var n int64
   990  			// Consume the body, or, which will also lead to us reading
   991  			// the trailer headers after the body, if present.
   992  			n, err = io.CopyN(io.Discard, bodyLocked{b}, maxPostHandlerReadBytes)
   993  			if err == io.EOF {
   994  				err = nil
   995  			}
   996  			if n == maxPostHandlerReadBytes {
   997  				b.earlyClose = true
   998  			}
   999  		}
  1000  	default:
  1001  		// Fully consume the body, which will also lead to us reading
  1002  		// the trailer headers after the body, if present.
  1003  		_, err = io.Copy(io.Discard, bodyLocked{b})
  1004  	}
  1005  	b.closed = true
  1006  	return err
  1007  }
  1008  
  1009  func (b *body) didEarlyClose() bool {
  1010  	b.mu.Lock()
  1011  	defer b.mu.Unlock()
  1012  	return b.earlyClose
  1013  }
  1014  
  1015  // bodyRemains reports whether future Read calls might
  1016  // yield data.
  1017  func (b *body) bodyRemains() bool {
  1018  	b.mu.Lock()
  1019  	defer b.mu.Unlock()
  1020  	return !b.sawEOF
  1021  }
  1022  
  1023  func (b *body) registerOnHitEOF(fn func()) {
  1024  	b.mu.Lock()
  1025  	defer b.mu.Unlock()
  1026  	b.onHitEOF = fn
  1027  }
  1028  
  1029  // bodyLocked is an io.Reader reading from a *body when its mutex is
  1030  // already held.
  1031  type bodyLocked struct {
  1032  	b *body
  1033  }
  1034  
  1035  func (bl bodyLocked) Read(p []byte) (n int, err error) {
  1036  	if bl.b.closed {
  1037  		return 0, ErrBodyReadAfterClose
  1038  	}
  1039  	return bl.b.readLocked(p)
  1040  }
  1041  
  1042  var laxContentLength = godebug.New("httplaxcontentlength")
  1043  
  1044  // parseContentLength checks that the header is valid and then trims
  1045  // whitespace. It returns -1 if no value is set otherwise the value
  1046  // if it's >= 0.
  1047  func parseContentLength(clHeaders []string) (int64, error) {
  1048  	if len(clHeaders) == 0 {
  1049  		return -1, nil
  1050  	}
  1051  	cl := textproto.TrimString(clHeaders[0])
  1052  
  1053  	// The Content-Length must be a valid numeric value.
  1054  	// See: https://datatracker.ietf.org/doc/html/rfc2616/#section-14.13
  1055  	if cl == "" {
  1056  		if laxContentLength.Value() == "1" {
  1057  			laxContentLength.IncNonDefault()
  1058  			return -1, nil
  1059  		}
  1060  		return 0, badStringError("invalid empty Content-Length", cl)
  1061  	}
  1062  	n, err := strconv.ParseUint(cl, 10, 63)
  1063  	if err != nil {
  1064  		return 0, badStringError("bad Content-Length", cl)
  1065  	}
  1066  	return int64(n), nil
  1067  }
  1068  
  1069  // finishAsyncByteRead finishes reading the 1-byte sniff
  1070  // from the ContentLength==0, Body!=nil case.
  1071  type finishAsyncByteRead struct {
  1072  	tw *transferWriter
  1073  }
  1074  
  1075  func (fr finishAsyncByteRead) Read(p []byte) (n int, err error) {
  1076  	if len(p) == 0 {
  1077  		return
  1078  	}
  1079  	rres := <-fr.tw.ByteReadCh
  1080  	n, err = rres.n, rres.err
  1081  	if n == 1 {
  1082  		p[0] = rres.b
  1083  	}
  1084  	if err == nil {
  1085  		err = io.EOF
  1086  	}
  1087  	return
  1088  }
  1089  
  1090  var nopCloserType = reflect.TypeOf(io.NopCloser(nil))
  1091  var nopCloserWriterToType = reflect.TypeOf(io.NopCloser(struct {
  1092  	io.Reader
  1093  	io.WriterTo
  1094  }{}))
  1095  
  1096  // unwrapNopCloser return the underlying reader and true if r is a NopCloser
  1097  // else it return false.
  1098  func unwrapNopCloser(r io.Reader) (underlyingReader io.Reader, isNopCloser bool) {
  1099  	switch reflect.TypeOf(r) {
  1100  	case nopCloserType, nopCloserWriterToType:
  1101  		return reflect.ValueOf(r).Field(0).Interface().(io.Reader), true
  1102  	default:
  1103  		return nil, false
  1104  	}
  1105  }
  1106  
  1107  // isKnownInMemoryReader reports whether r is a type known to not
  1108  // block on Read. Its caller uses this as an optional optimization to
  1109  // send fewer TCP packets.
  1110  func isKnownInMemoryReader(r io.Reader) bool {
  1111  	switch r.(type) {
  1112  	case *bytes.Reader, *bytes.Buffer, *strings.Reader:
  1113  		return true
  1114  	}
  1115  	if r, ok := unwrapNopCloser(r); ok {
  1116  		return isKnownInMemoryReader(r)
  1117  	}
  1118  	if r, ok := r.(*readTrackingBody); ok {
  1119  		return isKnownInMemoryReader(r.ReadCloser)
  1120  	}
  1121  	return false
  1122  }
  1123  
  1124  // bufioFlushWriter is an io.Writer wrapper that flushes all writes
  1125  // on its wrapped writer if it's a *bufio.Writer.
  1126  type bufioFlushWriter struct{ w io.Writer }
  1127  
  1128  func (fw bufioFlushWriter) Write(p []byte) (n int, err error) {
  1129  	n, err = fw.w.Write(p)
  1130  	if bw, ok := fw.w.(*bufio.Writer); n > 0 && ok {
  1131  		ferr := bw.Flush()
  1132  		if ferr != nil && err == nil {
  1133  			err = ferr
  1134  		}
  1135  	}
  1136  	return
  1137  }
  1138  

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