src/pkg/net/http/transfer.go - go - Git at Google

 // Copyright 2009 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.

 package http

 import (
 	"bufio"
 	"bytes"
 	"errors"
 	"fmt"
 	"io"
 	"io/ioutil"
 	"net/textproto"
 	"strconv"
 	"strings"
 )

 // transferWriter inspects the fields of a user-supplied Request or Response,
 // sanitizes them without changing the user object and provides methods for
 // writing the respective header, body and trailer in wire format.
 type transferWriter struct {
 	Method           string
 	Body             io.Reader
 	BodyCloser       io.Closer
 	ResponseToHEAD   bool
 	ContentLength    int64 // -1 means unknown, 0 means exactly none
 	Close            bool
 	TransferEncoding []string
 	Trailer          Header
 }

 func newTransferWriter(r interface{}) (t *transferWriter, err error) {
 	t = &transferWriter{}

 	// Extract relevant fields
 	atLeastHTTP11 := false
 	switch rr := r.(type) {
 	case *Request:
 		if rr.ContentLength != 0 && rr.Body == nil {
 			return nil, fmt.Errorf("http: Request.ContentLength=%d with nil Body", rr.ContentLength)
 		}
 		t.Method = rr.Method
 		t.Body = rr.Body
 		t.BodyCloser = rr.Body
 		t.ContentLength = rr.ContentLength
 		t.Close = rr.Close
 		t.TransferEncoding = rr.TransferEncoding
 		t.Trailer = rr.Trailer
 		atLeastHTTP11 = rr.ProtoAtLeast(1, 1)
 		if t.Body != nil && len(t.TransferEncoding) == 0 && atLeastHTTP11 {
 			if t.ContentLength == 0 {
 				// Test to see if it's actually zero or just unset.
 				var buf [1]byte
 				n, _ := io.ReadFull(t.Body, buf[:])
 				if n == 1 {
 					// Oh, guess there is data in this Body Reader after all.
 					// The ContentLength field just wasn't set.
 					// Stich the Body back together again, re-attaching our
 					// consumed byte.
 					t.ContentLength = -1
 					t.Body = io.MultiReader(bytes.NewBuffer(buf[:]), t.Body)
 				} else {
 					// Body is actually empty.
 					t.Body = nil
 					t.BodyCloser = nil
 				}
 			}
 			if t.ContentLength < 0 {
 				t.TransferEncoding = []string{"chunked"}
 			}
 		}
 	case *Response:
 		t.Method = rr.Request.Method
 		t.Body = rr.Body
 		t.BodyCloser = rr.Body
 		t.ContentLength = rr.ContentLength
 		t.Close = rr.Close
 		t.TransferEncoding = rr.TransferEncoding
 		t.Trailer = rr.Trailer
 		atLeastHTTP11 = rr.ProtoAtLeast(1, 1)
 		t.ResponseToHEAD = noBodyExpected(rr.Request.Method)
 	}

 	// Sanitize Body,ContentLength,TransferEncoding
 	if t.ResponseToHEAD {
 		t.Body = nil
 		t.TransferEncoding = nil
 		// ContentLength is expected to hold Content-Length
 		if t.ContentLength < 0 {
 			return nil, ErrMissingContentLength
 		}
 	} else {
 		if !atLeastHTTP11 || t.Body == nil {
 			t.TransferEncoding = nil
 		}
 		if chunked(t.TransferEncoding) {
 			t.ContentLength = -1
 		} else if t.Body == nil { // no chunking, no body
 			t.ContentLength = 0
 		}
 	}

 	// Sanitize Trailer
 	if !chunked(t.TransferEncoding) {
 		t.Trailer = nil
 	}

 	return t, nil
 }

 func noBodyExpected(requestMethod string) bool {
 	return requestMethod == "HEAD"
 }

 func (t *transferWriter) shouldSendContentLength() bool {
 	if chunked(t.TransferEncoding) {
 		return false
 	}
 	if t.ContentLength > 0 {
 		return true
 	}
 	if t.ResponseToHEAD {
 		return true
 	}
 	// Many servers expect a Content-Length for these methods
 	if t.Method == "POST" || t.Method == "PUT" {
 		return true
 	}
 	if t.ContentLength == 0 && isIdentity(t.TransferEncoding) {
 		return true
 	}

 	return false
 }

 func (t *transferWriter) WriteHeader(w io.Writer) (err error) {
 	if t.Close {
 		_, err = io.WriteString(w, "Connection: close\r\n")
 		if err != nil {
 			return
 		}
 	}

 	// Write Content-Length and/or Transfer-Encoding whose values are a
 	// function of the sanitized field triple (Body, ContentLength,
 	// TransferEncoding)
 	if t.shouldSendContentLength() {
 		io.WriteString(w, "Content-Length: ")
 		_, err = io.WriteString(w, strconv.FormatInt(t.ContentLength, 10)+"\r\n")
 		if err != nil {
 			return
 		}
 	} else if chunked(t.TransferEncoding) {
 		_, err = io.WriteString(w, "Transfer-Encoding: chunked\r\n")
 		if err != nil {
 			return
 		}
 	}

 	// Write Trailer header
 	if t.Trailer != nil {
 		// TODO: At some point, there should be a generic mechanism for
 		// writing long headers, using HTTP line splitting
 		io.WriteString(w, "Trailer: ")
 		needComma := false
 		for k := range t.Trailer {
 			k = CanonicalHeaderKey(k)
 			switch k {
 			case "Transfer-Encoding", "Trailer", "Content-Length":
 				return &badStringError{"invalid Trailer key", k}
 			}
 			if needComma {
 				io.WriteString(w, ",")
 			}
 			io.WriteString(w, k)
 			needComma = true
 		}
 		_, err = io.WriteString(w, "\r\n")
 	}

 	return
 }

 func (t *transferWriter) WriteBody(w io.Writer) (err error) {
 	var ncopy int64

 	// Write body
 	if t.Body != nil {
 		if chunked(t.TransferEncoding) {
 			cw := newChunkedWriter(w)
 			_, err = io.Copy(cw, t.Body)
 			if err == nil {
 				err = cw.Close()
 			}
 		} else if t.ContentLength == -1 {
 			ncopy, err = io.Copy(w, t.Body)
 		} else {
 			ncopy, err = io.Copy(w, io.LimitReader(t.Body, t.ContentLength))
 			nextra, err := io.Copy(ioutil.Discard, t.Body)
 			if err != nil {
 				return err
 			}
 			ncopy += nextra
 		}
 		if err != nil {
 			return err
 		}
 		if err = t.BodyCloser.Close(); err != nil {
 			return err
 		}
 	}

 	if t.ContentLength != -1 && t.ContentLength != ncopy {
 		return fmt.Errorf("http: Request.ContentLength=%d with Body length %d",
 			t.ContentLength, ncopy)
 	}

 	// TODO(petar): Place trailer writer code here.
 	if chunked(t.TransferEncoding) {
 		// Last chunk, empty trailer
 		_, err = io.WriteString(w, "\r\n")
 	}

 	return
 }

 type transferReader struct {
 	// Input
 	Header        Header
 	StatusCode    int
 	RequestMethod string
 	ProtoMajor    int
 	ProtoMinor    int
 	// Output
 	Body             io.ReadCloser
 	ContentLength    int64
 	TransferEncoding []string
 	Close            bool
 	Trailer          Header
 }

 // bodyAllowedForStatus returns whether a given response status code
 // permits a body.  See RFC2616, section 4.4.
 func bodyAllowedForStatus(status int) bool {
 	switch {
 	case status >= 100 && status <= 199:
 		return false
 	case status == 204:
 		return false
 	case status == 304:
 		return false
 	}
 	return true
 }

 // msg is *Request or *Response.
 func readTransfer(msg interface{}, r *bufio.Reader) (err error) {
 	t := &transferReader{}

 	// Unify input
 	isResponse := false
 	switch rr := msg.(type) {
 	case *Response:
 		t.Header = rr.Header
 		t.StatusCode = rr.StatusCode
 		t.RequestMethod = rr.Request.Method
 		t.ProtoMajor = rr.ProtoMajor
 		t.ProtoMinor = rr.ProtoMinor
 		t.Close = shouldClose(t.ProtoMajor, t.ProtoMinor, t.Header)
 		isResponse = true
 	case *Request:
 		t.Header = rr.Header
 		t.ProtoMajor = rr.ProtoMajor
 		t.ProtoMinor = rr.ProtoMinor
 		// Transfer semantics for Requests are exactly like those for
 		// Responses with status code 200, responding to a GET method
 		t.StatusCode = 200
 		t.RequestMethod = "GET"
 	default:
 		panic("unexpected type")
 	}

 	// Default to HTTP/1.1
 	if t.ProtoMajor == 0 && t.ProtoMinor == 0 {
 		t.ProtoMajor, t.ProtoMinor = 1, 1
 	}

 	// Transfer encoding, content length
 	t.TransferEncoding, err = fixTransferEncoding(t.RequestMethod, t.Header)
 	if err != nil {
 		return err
 	}

 	t.ContentLength, err = fixLength(isResponse, t.StatusCode, t.RequestMethod, t.Header, t.TransferEncoding)
 	if err != nil {
 		return err
 	}

 	// Trailer
 	t.Trailer, err = fixTrailer(t.Header, t.TransferEncoding)
 	if err != nil {
 		return err
 	}

 	// If there is no Content-Length or chunked Transfer-Encoding on a *Response
 	// and the status is not 1xx, 204 or 304, then the body is unbounded.
 	// See RFC2616, section 4.4.
 	switch msg.(type) {
 	case *Response:
 		if t.ContentLength == -1 &&
 			!chunked(t.TransferEncoding) &&
 			bodyAllowedForStatus(t.StatusCode) {
 			// Unbounded body.
 			t.Close = true
 		}
 	}

 	// Prepare body reader.  ContentLength < 0 means chunked encoding
 	// or close connection when finished, since multipart is not supported yet
 	switch {
 	case chunked(t.TransferEncoding):
 		t.Body = &body{Reader: newChunkedReader(r), hdr: msg, r: r, closing: t.Close}
 	case t.ContentLength >= 0:
 		// TODO: limit the Content-Length. This is an easy DoS vector.
 		t.Body = &body{Reader: io.LimitReader(r, t.ContentLength), closing: t.Close}
 	default:
 		// t.ContentLength < 0, i.e. "Content-Length" not mentioned in header
 		if t.Close {
 			// Close semantics (i.e. HTTP/1.0)
 			t.Body = &body{Reader: r, closing: t.Close}
 		} else {
 			// Persistent connection (i.e. HTTP/1.1)
 			t.Body = &body{Reader: io.LimitReader(r, 0), closing: t.Close}
 		}
 	}

 	// Unify output
 	switch rr := msg.(type) {
 	case *Request:
 		rr.Body = t.Body
 		rr.ContentLength = t.ContentLength
 		rr.TransferEncoding = t.TransferEncoding
 		rr.Close = t.Close
 		rr.Trailer = t.Trailer
 	case *Response:
 		rr.Body = t.Body
 		rr.ContentLength = t.ContentLength
 		rr.TransferEncoding = t.TransferEncoding
 		rr.Close = t.Close
 		rr.Trailer = t.Trailer
 	}

 	return nil
 }

 // Checks whether chunked is part of the encodings stack
 func chunked(te []string) bool { return len(te) > 0 && te[0] == "chunked" }

 // Checks whether the encoding is explicitly "identity".
 func isIdentity(te []string) bool { return len(te) == 1 && te[0] == "identity" }

 // Sanitize transfer encoding
 func fixTransferEncoding(requestMethod string, header Header) ([]string, error) {
 	raw, present := header["Transfer-Encoding"]
 	if !present {
 		return nil, nil
 	}

 	delete(header, "Transfer-Encoding")

 	// Head responses have no bodies, so the transfer encoding
 	// should be ignored.
 	if requestMethod == "HEAD" {
 		return nil, nil
 	}

 	encodings := strings.Split(raw[0], ",")
 	te := make([]string, 0, len(encodings))
 	// TODO: Even though we only support "identity" and "chunked"
 	// encodings, the loop below is designed with foresight. One
 	// invariant that must be maintained is that, if present,
 	// chunked encoding must always come first.
 	for _, encoding := range encodings {
 		encoding = strings.ToLower(strings.TrimSpace(encoding))
 		// "identity" encoding is not recored
 		if encoding == "identity" {
 			break
 		}
 		if encoding != "chunked" {
 			return nil, &badStringError{"unsupported transfer encoding", encoding}
 		}
 		te = te[0 : len(te)+1]
 		te[len(te)-1] = encoding
 	}
 	if len(te) > 1 {
 		return nil, &badStringError{"too many transfer encodings", strings.Join(te, ",")}
 	}
 	if len(te) > 0 {
 		// Chunked encoding trumps Content-Length. See RFC 2616
 		// Section 4.4. Currently len(te) > 0 implies chunked
 		// encoding.
 		delete(header, "Content-Length")
 		return te, nil
 	}

 	return nil, nil
 }

 // Determine the expected body length, using RFC 2616 Section 4.4. This
 // function is not a method, because ultimately it should be shared by
 // ReadResponse and ReadRequest.
 func fixLength(isResponse bool, status int, requestMethod string, header Header, te []string) (int64, error) {

 	// Logic based on response type or status
 	if noBodyExpected(requestMethod) {
 		return 0, nil
 	}
 	if status/100 == 1 {
 		return 0, nil
 	}
 	switch status {
 	case 204, 304:
 		return 0, nil
 	}

 	// Logic based on Transfer-Encoding
 	if chunked(te) {
 		return -1, nil
 	}

 	// Logic based on Content-Length
 	cl := strings.TrimSpace(header.Get("Content-Length"))
 	if cl != "" {
 		n, err := strconv.ParseInt(cl, 10, 64)
 		if err != nil || n < 0 {
 			return -1, &badStringError{"bad Content-Length", cl}
 		}
 		return n, nil
 	} else {
 		header.Del("Content-Length")
 	}

 	if !isResponse && requestMethod == "GET" {
 		// RFC 2616 doesn't explicitly permit nor forbid an
 		// entity-body on a GET request so we permit one if
 		// declared, but we default to 0 here (not -1 below)
 		// if there's no mention of a body.
 		return 0, nil
 	}

 	// Logic based on media type. The purpose of the following code is just
 	// to detect whether the unsupported "multipart/byteranges" is being
 	// used. A proper Content-Type parser is needed in the future.
 	if strings.Contains(strings.ToLower(header.Get("Content-Type")), "multipart/byteranges") {
 		return -1, ErrNotSupported
 	}

 	// Body-EOF logic based on other methods (like closing, or chunked coding)
 	return -1, nil
 }

 // Determine whether to hang up after sending a request and body, or
 // receiving a response and body
 // 'header' is the request headers
 func shouldClose(major, minor int, header Header) bool {
 	if major < 1 {
 		return true
 	} else if major == 1 && minor == 0 {
 		if !strings.Contains(strings.ToLower(header.Get("Connection")), "keep-alive") {
 			return true
 		}
 		return false
 	} else {
 		// TODO: Should split on commas, toss surrounding white space,
 		// and check each field.
 		if strings.ToLower(header.Get("Connection")) == "close" {
 			header.Del("Connection")
 			return true
 		}
 	}
 	return false
 }

 // Parse the trailer header
 func fixTrailer(header Header, te []string) (Header, error) {
 	raw := header.Get("Trailer")
 	if raw == "" {
 		return nil, nil
 	}

 	header.Del("Trailer")
 	trailer := make(Header)
 	keys := strings.Split(raw, ",")
 	for _, key := range keys {
 		key = CanonicalHeaderKey(strings.TrimSpace(key))
 		switch key {
 		case "Transfer-Encoding", "Trailer", "Content-Length":
 			return nil, &badStringError{"bad trailer key", key}
 		}
 		trailer.Del(key)
 	}
 	if len(trailer) == 0 {
 		return nil, nil
 	}
 	if !chunked(te) {
 		// Trailer and no chunking
 		return nil, ErrUnexpectedTrailer
 	}
 	return trailer, nil
 }

 // body turns a Reader into a ReadCloser.
 // Close ensures that the body has been fully read
 // and then reads the trailer if necessary.
 type body struct {
 	io.Reader
 	hdr     interface{}   // non-nil (Response or Request) value means read trailer
 	r       *bufio.Reader // underlying wire-format reader for the trailer
 	closing bool          // is the connection to be closed after reading body?
 	closed  bool

 	res *response // response writer for server requests, else nil
 }

 // ErrBodyReadAfterClose is returned when reading a Request Body after
 // the body has been closed. This typically happens when the body is
 // read after an HTTP Handler calls WriteHeader or Write on its
 // ResponseWriter.
 var ErrBodyReadAfterClose = errors.New("http: invalid Read on closed request Body")

 func (b *body) Read(p []byte) (n int, err error) {
 	if b.closed {
 		return 0, ErrBodyReadAfterClose
 	}
 	n, err = b.Reader.Read(p)

 	// Read the final trailer once we hit EOF.
 	if err == io.EOF && b.hdr != nil {
 		if e := b.readTrailer(); e != nil {
 			err = e
 		}
 		b.hdr = nil
 	}
 	return n, err
 }

 var (
 	singleCRLF = []byte("\r\n")
 	doubleCRLF = []byte("\r\n\r\n")
 )

 func seeUpcomingDoubleCRLF(r *bufio.Reader) bool {
 	for peekSize := 4; ; peekSize++ {
 		// This loop stops when Peek returns an error,
 		// which it does when r's buffer has been filled.
 		buf, err := r.Peek(peekSize)
 		if bytes.HasSuffix(buf, doubleCRLF) {
 			return true
 		}
 		if err != nil {
 			break
 		}
 	}
 	return false
 }

 func (b *body) readTrailer() error {
 	// The common case, since nobody uses trailers.
 	buf, _ := b.r.Peek(2)
 	if bytes.Equal(buf, singleCRLF) {
 		b.r.ReadByte()
 		b.r.ReadByte()
 		return nil
 	}

 	// Make sure there's a header terminator coming up, to prevent
 	// a DoS with an unbounded size Trailer.  It's not easy to
 	// slip in a LimitReader here, as textproto.NewReader requires
 	// a concrete *bufio.Reader.  Also, we can't get all the way
 	// back up to our conn's LimitedReader that *might* be backing
 	// this bufio.Reader.  Instead, a hack: we iteratively Peek up
 	// to the bufio.Reader's max size, looking for a double CRLF.
 	// This limits the trailer to the underlying buffer size, typically 4kB.
 	if !seeUpcomingDoubleCRLF(b.r) {
 		return errors.New("http: suspiciously long trailer after chunked body")
 	}

 	hdr, err := textproto.NewReader(b.r).ReadMIMEHeader()
 	if err != nil {
 		return err
 	}
 	switch rr := b.hdr.(type) {
 	case *Request:
 		rr.Trailer = Header(hdr)
 	case *Response:
 		rr.Trailer = Header(hdr)
 	}
 	return nil
 }

 func (b *body) Close() error {
 	if b.closed {
 		return nil
 	}
 	defer func() {
 		b.closed = true
 	}()
 	if b.hdr == nil && b.closing {
 		// no trailer and closing the connection next.
 		// no point in reading to EOF.
 		return nil
 	}

 	// In a server request, don't continue reading from the client
 	// if we've already hit the maximum body size set by the
 	// handler. If this is set, that also means the TCP connection
 	// is about to be closed, so getting to the next HTTP request
 	// in the stream is not necessary.
 	if b.res != nil && b.res.requestBodyLimitHit {
 		return nil
 	}

 	// Fully consume the body, which will also lead to us reading
 	// the trailer headers after the body, if present.
 	if _, err := io.Copy(ioutil.Discard, b); err != nil {
 		return err
 	}
 	return nil
 }
	// Copyright 2009 The Go Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style
	// license that can be found in the LICENSE file.

	package http

	import (
	"bufio"
	"bytes"
	"errors"
	"fmt"
	"io"
	"io/ioutil"
	"net/textproto"
	"strconv"
	"strings"
	)

	// transferWriter inspects the fields of a user-supplied Request or Response,
	// sanitizes them without changing the user object and provides methods for
	// writing the respective header, body and trailer in wire format.
	type transferWriter struct {
	Method string
	Body io.Reader
	BodyCloser io.Closer
	ResponseToHEAD bool
	ContentLength int64 // -1 means unknown, 0 means exactly none
	Close bool
	TransferEncoding []string
	Trailer Header
	}

	func newTransferWriter(r interface{}) (t *transferWriter, err error) {
	t = &transferWriter{}

	// Extract relevant fields
	atLeastHTTP11 := false
	switch rr := r.(type) {
	case *Request:
	if rr.ContentLength != 0 && rr.Body == nil {
	return nil, fmt.Errorf("http: Request.ContentLength=%d with nil Body", rr.ContentLength)
	}
	t.Method = rr.Method
	t.Body = rr.Body
	t.BodyCloser = rr.Body
	t.ContentLength = rr.ContentLength
	t.Close = rr.Close
	t.TransferEncoding = rr.TransferEncoding
	t.Trailer = rr.Trailer
	atLeastHTTP11 = rr.ProtoAtLeast(1, 1)
	if t.Body != nil && len(t.TransferEncoding) == 0 && atLeastHTTP11 {
	if t.ContentLength == 0 {
	// Test to see if it's actually zero or just unset.
	var buf [1]byte
	n, _ := io.ReadFull(t.Body, buf[:])
	if n == 1 {
	// Oh, guess there is data in this Body Reader after all.
	// The ContentLength field just wasn't set.
	// Stich the Body back together again, re-attaching our
	// consumed byte.
	t.ContentLength = -1
	t.Body = io.MultiReader(bytes.NewBuffer(buf[:]), t.Body)
	} else {
	// Body is actually empty.
	t.Body = nil
	t.BodyCloser = nil
	}
	}
	if t.ContentLength < 0 {
	t.TransferEncoding = []string{"chunked"}
	}
	}
	case *Response:
	t.Method = rr.Request.Method
	t.Body = rr.Body
	t.BodyCloser = rr.Body
	t.ContentLength = rr.ContentLength
	t.Close = rr.Close
	t.TransferEncoding = rr.TransferEncoding
	t.Trailer = rr.Trailer
	atLeastHTTP11 = rr.ProtoAtLeast(1, 1)
	t.ResponseToHEAD = noBodyExpected(rr.Request.Method)
	}

	// Sanitize Body,ContentLength,TransferEncoding
	if t.ResponseToHEAD {
	t.Body = nil
	t.TransferEncoding = nil
	// ContentLength is expected to hold Content-Length
	if t.ContentLength < 0 {
	return nil, ErrMissingContentLength
	}
	} else {
	if !atLeastHTTP11 \|\| t.Body == nil {
	t.TransferEncoding = nil
	}
	if chunked(t.TransferEncoding) {
	t.ContentLength = -1
	} else if t.Body == nil { // no chunking, no body
	t.ContentLength = 0
	}
	}

	// Sanitize Trailer
	if !chunked(t.TransferEncoding) {
	t.Trailer = nil
	}

	return t, nil
	}

	func noBodyExpected(requestMethod string) bool {
	return requestMethod == "HEAD"
	}

	func (t *transferWriter) shouldSendContentLength() bool {
	if chunked(t.TransferEncoding) {
	return false
	}
	if t.ContentLength > 0 {
	return true
	}
	if t.ResponseToHEAD {
	return true
	}
	// Many servers expect a Content-Length for these methods
	if t.Method == "POST" \|\| t.Method == "PUT" {
	return true
	}
	if t.ContentLength == 0 && isIdentity(t.TransferEncoding) {
	return true
	}

	return false
	}

	func (t *transferWriter) WriteHeader(w io.Writer) (err error) {
	if t.Close {
	_, err = io.WriteString(w, "Connection: close\r\n")
	if err != nil {
	return
	}
	}

	// Write Content-Length and/or Transfer-Encoding whose values are a
	// function of the sanitized field triple (Body, ContentLength,
	// TransferEncoding)
	if t.shouldSendContentLength() {
	io.WriteString(w, "Content-Length: ")
	_, err = io.WriteString(w, strconv.FormatInt(t.ContentLength, 10)+"\r\n")
	if err != nil {
	return
	}
	} else if chunked(t.TransferEncoding) {
	_, err = io.WriteString(w, "Transfer-Encoding: chunked\r\n")
	if err != nil {
	return
	}
	}

	// Write Trailer header
	if t.Trailer != nil {
	// TODO: At some point, there should be a generic mechanism for
	// writing long headers, using HTTP line splitting
	io.WriteString(w, "Trailer: ")
	needComma := false
	for k := range t.Trailer {
	k = CanonicalHeaderKey(k)
	switch k {
	case "Transfer-Encoding", "Trailer", "Content-Length":
	return &badStringError{"invalid Trailer key", k}
	}
	if needComma {
	io.WriteString(w, ",")
	}
	io.WriteString(w, k)
	needComma = true
	}
	_, err = io.WriteString(w, "\r\n")
	}

	return
	}

	func (t *transferWriter) WriteBody(w io.Writer) (err error) {
	var ncopy int64

	// Write body
	if t.Body != nil {
	if chunked(t.TransferEncoding) {
	cw := newChunkedWriter(w)
	_, err = io.Copy(cw, t.Body)
	if err == nil {
	err = cw.Close()
	}
	} else if t.ContentLength == -1 {
	ncopy, err = io.Copy(w, t.Body)
	} else {
	ncopy, err = io.Copy(w, io.LimitReader(t.Body, t.ContentLength))
	nextra, err := io.Copy(ioutil.Discard, t.Body)
	if err != nil {
	return err
	}
	ncopy += nextra
	}
	if err != nil {
	return err
	}
	if err = t.BodyCloser.Close(); err != nil {
	return err
	}
	}

	if t.ContentLength != -1 && t.ContentLength != ncopy {
	return fmt.Errorf("http: Request.ContentLength=%d with Body length %d",
	t.ContentLength, ncopy)
	}

	// TODO(petar): Place trailer writer code here.
	if chunked(t.TransferEncoding) {
	// Last chunk, empty trailer
	_, err = io.WriteString(w, "\r\n")
	}

	return
	}

	type transferReader struct {
	// Input
	Header Header
	StatusCode int
	RequestMethod string
	ProtoMajor int
	ProtoMinor int
	// Output
	Body io.ReadCloser
	ContentLength int64
	TransferEncoding []string
	Close bool
	Trailer Header
	}

	// bodyAllowedForStatus returns whether a given response status code
	// permits a body. See RFC2616, section 4.4.
	func bodyAllowedForStatus(status int) bool {
	switch {
	case status >= 100 && status <= 199:
	return false
	case status == 204:
	return false
	case status == 304:
	return false
	}
	return true
	}

	// msg is Request or Response.
	func readTransfer(msg interface{}, r *bufio.Reader) (err error) {
	t := &transferReader{}

	// Unify input
	isResponse := false
	switch rr := msg.(type) {
	case *Response:
	t.Header = rr.Header
	t.StatusCode = rr.StatusCode
	t.RequestMethod = rr.Request.Method
	t.ProtoMajor = rr.ProtoMajor
	t.ProtoMinor = rr.ProtoMinor
	t.Close = shouldClose(t.ProtoMajor, t.ProtoMinor, t.Header)
	isResponse = true
	case *Request:
	t.Header = rr.Header
	t.ProtoMajor = rr.ProtoMajor
	t.ProtoMinor = rr.ProtoMinor
	// Transfer semantics for Requests are exactly like those for
	// Responses with status code 200, responding to a GET method
	t.StatusCode = 200
	t.RequestMethod = "GET"
	default:
	panic("unexpected type")
	}

	// Default to HTTP/1.1
	if t.ProtoMajor == 0 && t.ProtoMinor == 0 {
	t.ProtoMajor, t.ProtoMinor = 1, 1
	}

	// Transfer encoding, content length
	t.TransferEncoding, err = fixTransferEncoding(t.RequestMethod, t.Header)
	if err != nil {
	return err
	}

	t.ContentLength, err = fixLength(isResponse, t.StatusCode, t.RequestMethod, t.Header, t.TransferEncoding)
	if err != nil {
	return err
	}

	// Trailer
	t.Trailer, err = fixTrailer(t.Header, t.TransferEncoding)
	if err != nil {
	return err
	}

	// If there is no Content-Length or chunked Transfer-Encoding on a *Response
	// and the status is not 1xx, 204 or 304, then the body is unbounded.
	// See RFC2616, section 4.4.
	switch msg.(type) {
	case *Response:
	if t.ContentLength == -1 &&
	!chunked(t.TransferEncoding) &&
	bodyAllowedForStatus(t.StatusCode) {
	// Unbounded body.
	t.Close = true
	}
	}

	// Prepare body reader. ContentLength < 0 means chunked encoding
	// or close connection when finished, since multipart is not supported yet
	switch {
	case chunked(t.TransferEncoding):
	t.Body = &body{Reader: newChunkedReader(r), hdr: msg, r: r, closing: t.Close}
	case t.ContentLength >= 0:
	// TODO: limit the Content-Length. This is an easy DoS vector.
	t.Body = &body{Reader: io.LimitReader(r, t.ContentLength), closing: t.Close}
	default:
	// t.ContentLength < 0, i.e. "Content-Length" not mentioned in header
	if t.Close {
	// Close semantics (i.e. HTTP/1.0)
	t.Body = &body{Reader: r, closing: t.Close}
	} else {
	// Persistent connection (i.e. HTTP/1.1)
	t.Body = &body{Reader: io.LimitReader(r, 0), closing: t.Close}
	}
	}

	// Unify output
	switch rr := msg.(type) {
	case *Request:
	rr.Body = t.Body
	rr.ContentLength = t.ContentLength
	rr.TransferEncoding = t.TransferEncoding
	rr.Close = t.Close
	rr.Trailer = t.Trailer
	case *Response:
	rr.Body = t.Body
	rr.ContentLength = t.ContentLength
	rr.TransferEncoding = t.TransferEncoding
	rr.Close = t.Close
	rr.Trailer = t.Trailer
	}

	return nil
	}

	// Checks whether chunked is part of the encodings stack
	func chunked(te []string) bool { return len(te) > 0 && te[0] == "chunked" }

	// Checks whether the encoding is explicitly "identity".
	func isIdentity(te []string) bool { return len(te) == 1 && te[0] == "identity" }

	// Sanitize transfer encoding
	func fixTransferEncoding(requestMethod string, header Header) ([]string, error) {
	raw, present := header["Transfer-Encoding"]
	if !present {
	return nil, nil
	}

	delete(header, "Transfer-Encoding")

	// Head responses have no bodies, so the transfer encoding
	// should be ignored.
	if requestMethod == "HEAD" {
	return nil, nil
	}

	encodings := strings.Split(raw[0], ",")
	te := make([]string, 0, len(encodings))
	// TODO: Even though we only support "identity" and "chunked"
	// encodings, the loop below is designed with foresight. One
	// invariant that must be maintained is that, if present,
	// chunked encoding must always come first.
	for _, encoding := range encodings {
	encoding = strings.ToLower(strings.TrimSpace(encoding))
	// "identity" encoding is not recored
	if encoding == "identity" {
	break
	}
	if encoding != "chunked" {
	return nil, &badStringError{"unsupported transfer encoding", encoding}
	}
	te = te[0 : len(te)+1]
	te[len(te)-1] = encoding
	}
	if len(te) > 1 {
	return nil, &badStringError{"too many transfer encodings", strings.Join(te, ",")}
	}
	if len(te) > 0 {
	// Chunked encoding trumps Content-Length. See RFC 2616
	// Section 4.4. Currently len(te) > 0 implies chunked
	// encoding.
	delete(header, "Content-Length")
	return te, nil
	}

	return nil, nil
	}

	// Determine the expected body length, using RFC 2616 Section 4.4. This
	// function is not a method, because ultimately it should be shared by
	// ReadResponse and ReadRequest.
	func fixLength(isResponse bool, status int, requestMethod string, header Header, te []string) (int64, error) {

	// Logic based on response type or status
	if noBodyExpected(requestMethod) {
	return 0, nil
	}
	if status/100 == 1 {
	return 0, nil
	}
	switch status {
	case 204, 304:
	return 0, nil
	}

	// Logic based on Transfer-Encoding
	if chunked(te) {
	return -1, nil
	}

	// Logic based on Content-Length
	cl := strings.TrimSpace(header.Get("Content-Length"))
	if cl != "" {
	n, err := strconv.ParseInt(cl, 10, 64)
	if err != nil \|\| n < 0 {
	return -1, &badStringError{"bad Content-Length", cl}
	}
	return n, nil
	} else {
	header.Del("Content-Length")
	}

	if !isResponse && requestMethod == "GET" {
	// RFC 2616 doesn't explicitly permit nor forbid an
	// entity-body on a GET request so we permit one if
	// declared, but we default to 0 here (not -1 below)
	// if there's no mention of a body.
	return 0, nil
	}

	// Logic based on media type. The purpose of the following code is just
	// to detect whether the unsupported "multipart/byteranges" is being
	// used. A proper Content-Type parser is needed in the future.
	if strings.Contains(strings.ToLower(header.Get("Content-Type")), "multipart/byteranges") {
	return -1, ErrNotSupported
	}

	// Body-EOF logic based on other methods (like closing, or chunked coding)
	return -1, nil
	}

	// Determine whether to hang up after sending a request and body, or
	// receiving a response and body
	// 'header' is the request headers
	func shouldClose(major, minor int, header Header) bool {
	if major < 1 {
	return true
	} else if major == 1 && minor == 0 {
	if !strings.Contains(strings.ToLower(header.Get("Connection")), "keep-alive") {
	return true
	}
	return false
	} else {
	// TODO: Should split on commas, toss surrounding white space,
	// and check each field.
	if strings.ToLower(header.Get("Connection")) == "close" {
	header.Del("Connection")
	return true
	}
	}
	return false
	}

	// Parse the trailer header
	func fixTrailer(header Header, te []string) (Header, error) {
	raw := header.Get("Trailer")
	if raw == "" {
	return nil, nil
	}

	header.Del("Trailer")
	trailer := make(Header)
	keys := strings.Split(raw, ",")
	for _, key := range keys {
	key = CanonicalHeaderKey(strings.TrimSpace(key))
	switch key {
	case "Transfer-Encoding", "Trailer", "Content-Length":
	return nil, &badStringError{"bad trailer key", key}
	}
	trailer.Del(key)
	}
	if len(trailer) == 0 {
	return nil, nil
	}
	if !chunked(te) {
	// Trailer and no chunking
	return nil, ErrUnexpectedTrailer
	}
	return trailer, nil
	}

	// body turns a Reader into a ReadCloser.
	// Close ensures that the body has been fully read
	// and then reads the trailer if necessary.
	type body struct {
	io.Reader
	hdr interface{} // non-nil (Response or Request) value means read trailer
	r *bufio.Reader // underlying wire-format reader for the trailer
	closing bool // is the connection to be closed after reading body?
	closed bool

	res *response // response writer for server requests, else nil
	}

	// ErrBodyReadAfterClose is returned when reading a Request Body after
	// the body has been closed. This typically happens when the body is
	// read after an HTTP Handler calls WriteHeader or Write on its
	// ResponseWriter.
	var ErrBodyReadAfterClose = errors.New("http: invalid Read on closed request Body")

	func (b *body) Read(p []byte) (n int, err error) {
	if b.closed {
	return 0, ErrBodyReadAfterClose
	}
	n, err = b.Reader.Read(p)

	// Read the final trailer once we hit EOF.
	if err == io.EOF && b.hdr != nil {
	if e := b.readTrailer(); e != nil {
	err = e
	}
	b.hdr = nil
	}
	return n, err
	}

	var (
	singleCRLF = []byte("\r\n")
	doubleCRLF = []byte("\r\n\r\n")
	)

	func seeUpcomingDoubleCRLF(r *bufio.Reader) bool {
	for peekSize := 4; ; peekSize++ {
	// This loop stops when Peek returns an error,
	// which it does when r's buffer has been filled.
	buf, err := r.Peek(peekSize)
	if bytes.HasSuffix(buf, doubleCRLF) {
	return true
	}
	if err != nil {
	break
	}
	}
	return false
	}

	func (b *body) readTrailer() error {
	// The common case, since nobody uses trailers.
	buf, _ := b.r.Peek(2)
	if bytes.Equal(buf, singleCRLF) {
	b.r.ReadByte()
	b.r.ReadByte()
	return nil
	}

	// Make sure there's a header terminator coming up, to prevent
	// a DoS with an unbounded size Trailer. It's not easy to
	// slip in a LimitReader here, as textproto.NewReader requires
	// a concrete *bufio.Reader. Also, we can't get all the way
	// back up to our conn's LimitedReader that might be backing
	// this bufio.Reader. Instead, a hack: we iteratively Peek up
	// to the bufio.Reader's max size, looking for a double CRLF.
	// This limits the trailer to the underlying buffer size, typically 4kB.
	if !seeUpcomingDoubleCRLF(b.r) {
	return errors.New("http: suspiciously long trailer after chunked body")
	}

	hdr, err := textproto.NewReader(b.r).ReadMIMEHeader()
	if err != nil {
	return err
	}
	switch rr := b.hdr.(type) {
	case *Request:
	rr.Trailer = Header(hdr)
	case *Response:
	rr.Trailer = Header(hdr)
	}
	return nil
	}

	func (b *body) Close() error {
	if b.closed {
	return nil
	}
	defer func() {
	b.closed = true
	}()
	if b.hdr == nil && b.closing {
	// no trailer and closing the connection next.
	// no point in reading to EOF.
	return nil
	}

	// In a server request, don't continue reading from the client
	// if we've already hit the maximum body size set by the
	// handler. If this is set, that also means the TCP connection
	// is about to be closed, so getting to the next HTTP request
	// in the stream is not necessary.
	if b.res != nil && b.res.requestBodyLimitHit {
	return nil
	}

	// Fully consume the body, which will also lead to us reading
	// the trailer headers after the body, if present.
	if _, err := io.Copy(ioutil.Discard, b); err != nil {
	return err
	}
	return nil
	}