src/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/http/internal"
 	"net/textproto"
 	"sort"
 	"strconv"
 	"strings"
 	"sync"
 )

 // ErrLineTooLong is returned when reading request or response bodies
 // with malformed chunked encoding.
 var ErrLineTooLong = internal.ErrLineTooLong

 type errorReader struct {
 	err error
 }

 func (r *errorReader) Read(p []byte) (n int, err error) {
 	return 0, r.err
 }

 // 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, rerr := io.ReadFull(t.Body, buf[:])
 				if rerr != nil && rerr != io.EOF {
 					t.ContentLength = -1
 					t.Body = &errorReader{rerr}
 				} else 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.NewReader(buf[:]), t.Body)
 				} else {
 					// Body is actually empty.
 					t.Body = nil
 					t.BodyCloser = nil
 				}
 			}
 			if t.ContentLength < 0 {
 				t.TransferEncoding = []string{"chunked"}
 			}
 		}
 	case *Response:
 		if rr.Request != nil {
 			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(t.Method)
 	}

 	// Sanitize Body,ContentLength,TransferEncoding
 	if t.ResponseToHEAD {
 		t.Body = nil
 		if chunked(t.TransferEncoding) {
 			t.ContentLength = -1
 		}
 	} 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
 	}
 	// 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) error {
 	if t.Close {
 		if _, err := io.WriteString(w, "Connection: close\r\n"); err != nil {
 			return err
 		}
 	}

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

 	// Write Trailer header
 	if t.Trailer != nil {
 		keys := make([]string, 0, len(t.Trailer))
 		for k := range t.Trailer {
 			k = CanonicalHeaderKey(k)
 			switch k {
 			case "Transfer-Encoding", "Trailer", "Content-Length":
 				return &badStringError{"invalid Trailer key", k}
 			}
 			keys = append(keys, k)
 		}
 		if len(keys) > 0 {
 			sort.Strings(keys)
 			// TODO: could do better allocation-wise here, but trailers are rare,
 			// so being lazy for now.
 			if _, err := io.WriteString(w, "Trailer: "+strings.Join(keys, ",")+"\r\n"); err != nil {
 				return err
 			}
 		}
 	}

 	return nil
 }

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

 	// Write body
 	if t.Body != nil {
 		if chunked(t.TransferEncoding) {
 			cw := internal.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))
 			if err != nil {
 				return err
 			}
 			var nextra int64
 			nextra, err = io.Copy(ioutil.Discard, t.Body)
 			ncopy += nextra
 		}
 		if err != nil {
 			return err
 		}
 		if err = t.BodyCloser.Close(); err != nil {
 			return err
 		}
 	}

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

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

 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 reports 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
 }

 var (
 	suppressedHeaders304    = []string{"Content-Type", "Content-Length", "Transfer-Encoding"}
 	suppressedHeadersNoBody = []string{"Content-Length", "Transfer-Encoding"}
 )

 func suppressedHeaders(status int) []string {
 	switch {
 	case status == 304:
 		// RFC 2616 section 10.3.5: "the response MUST NOT include other entity-headers"
 		return suppressedHeaders304
 	case !bodyAllowedForStatus(status):
 		return suppressedHeadersNoBody
 	}
 	return nil
 }

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

 	// Unify input
 	isResponse := false
 	switch rr := msg.(type) {
 	case *Response:
 		t.Header = rr.Header
 		t.StatusCode = rr.StatusCode
 		t.ProtoMajor = rr.ProtoMajor
 		t.ProtoMinor = rr.ProtoMinor
 		t.Close = shouldClose(t.ProtoMajor, t.ProtoMinor, t.Header, true)
 		isResponse = true
 		if rr.Request != nil {
 			t.RequestMethod = rr.Request.Method
 		}
 	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
 	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
 	}

 	realLength, err := fixLength(isResponse, t.StatusCode, t.RequestMethod, t.Header, t.TransferEncoding)
 	if err != nil {
 		return err
 	}
 	if isResponse && t.RequestMethod == "HEAD" {
 		if n, err := parseContentLength(t.Header.get("Content-Length")); err != nil {
 			return err
 		} else {
 			t.ContentLength = n
 		}
 	} else {
 		t.ContentLength = realLength
 	}

 	// 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 realLength == -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):
 		if noBodyExpected(t.RequestMethod) {
 			t.Body = eofReader
 		} else {
 			t.Body = &body{src: internal.NewChunkedReader(r), hdr: msg, r: r, closing: t.Close}
 		}
 	case realLength == 0:
 		t.Body = eofReader
 	case realLength > 0:
 		t.Body = &body{src: io.LimitReader(r, realLength), closing: t.Close}
 	default:
 		// realLength < 0, i.e. "Content-Length" not mentioned in header
 		if t.Close {
 			// Close semantics (i.e. HTTP/1.0)
 			t.Body = &body{src: r, closing: t.Close}
 		} else {
 			// Persistent connection (i.e. HTTP/1.1)
 			t.Body = eofReader
 		}
 	}

 	// 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")

 	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 recorded
 		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 := parseContentLength(cl)
 		if err != nil {
 			return -1, err
 		}
 		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
 	}

 	// 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, removeCloseHeader bool) 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" {
 			if removeCloseHeader {
 				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[key] = nil
 	}
 	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 {
 	src     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?

 	mu     sync.Mutex // guards closed, and calls to Read and Close
 	closed bool
 }

 // ErrBodyReadAfterClose is returned when reading a Request or Response
 // 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 Body")

 func (b *body) Read(p []byte) (n int, err error) {
 	b.mu.Lock()
 	defer b.mu.Unlock()
 	if b.closed {
 		return 0, ErrBodyReadAfterClose
 	}
 	return b.readLocked(p)
 }

 // Must hold b.mu.
 func (b *body) readLocked(p []byte) (n int, err error) {
 	n, err = b.src.Read(p)

 	if err == io.EOF {
 		// Chunked case. Read the trailer.
 		if b.hdr != nil {
 			if e := b.readTrailer(); e != nil {
 				err = e
 			}
 			b.hdr = nil
 		} else {
 			// If the server declared the Content-Length, our body is a LimitedReader
 			// and we need to check whether this EOF arrived early.
 			if lr, ok := b.src.(*io.LimitedReader); ok && lr.N > 0 {
 				err = io.ErrUnexpectedEOF
 			}
 		}
 	}

 	// If we can return an EOF here along with the read data, do
 	// so. This is optional per the io.Reader contract, but doing
 	// so helps the HTTP transport code recycle its connection
 	// earlier (since it will see this EOF itself), even if the
 	// client doesn't do future reads or Close.
 	if err == nil && n > 0 {
 		if lr, ok := b.src.(*io.LimitedReader); ok && lr.N == 0 {
 			err = io.EOF
 		}
 	}

 	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
 }

 var errTrailerEOF = errors.New("http: unexpected EOF reading trailer")

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

 	// 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 {
 		if err == io.EOF {
 			return errTrailerEOF
 		}
 		return err
 	}
 	switch rr := b.hdr.(type) {
 	case *Request:
 		mergeSetHeader(&rr.Trailer, Header(hdr))
 	case *Response:
 		mergeSetHeader(&rr.Trailer, Header(hdr))
 	}
 	return nil
 }

 func mergeSetHeader(dst *Header, src Header) {
 	if *dst == nil {
 		*dst = src
 		return
 	}
 	for k, vv := range src {
 		(*dst)[k] = vv
 	}
 }

 func (b *body) Close() error {
 	b.mu.Lock()
 	defer b.mu.Unlock()
 	if b.closed {
 		return nil
 	}
 	var err error
 	switch {
 	case b.hdr == nil && b.closing:
 		// no trailer and closing the connection next.
 		// no point in reading to EOF.
 	default:
 		// Fully consume the body, which will also lead to us reading
 		// the trailer headers after the body, if present.
 		_, err = io.Copy(ioutil.Discard, bodyLocked{b})
 	}
 	b.closed = true
 	return err
 }

 // bodyLocked is a io.Reader reading from a *body when its mutex is
 // already held.
 type bodyLocked struct {
 	b *body
 }

 func (bl bodyLocked) Read(p []byte) (n int, err error) {
 	if bl.b.closed {
 		return 0, ErrBodyReadAfterClose
 	}
 	return bl.b.readLocked(p)
 }

 // parseContentLength trims whitespace from s and returns -1 if no value
 // is set, or the value if it's >= 0.
 func parseContentLength(cl string) (int64, error) {
 	cl = strings.TrimSpace(cl)
 	if cl == "" {
 		return -1, nil
 	}
 	n, err := strconv.ParseInt(cl, 10, 64)
 	if err != nil || n < 0 {
 		return 0, &badStringError{"bad Content-Length", cl}
 	}
 	return n, 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/http/internal"
	"net/textproto"
	"sort"
	"strconv"
	"strings"
	"sync"
	)

	// ErrLineTooLong is returned when reading request or response bodies
	// with malformed chunked encoding.
	var ErrLineTooLong = internal.ErrLineTooLong

	type errorReader struct {
	err error
	}

	func (r *errorReader) Read(p []byte) (n int, err error) {
	return 0, r.err
	}

	// 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, rerr := io.ReadFull(t.Body, buf[:])
	if rerr != nil && rerr != io.EOF {
	t.ContentLength = -1
	t.Body = &errorReader{rerr}
	} else 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.NewReader(buf[:]), t.Body)
	} else {
	// Body is actually empty.
	t.Body = nil
	t.BodyCloser = nil
	}
	}
	if t.ContentLength < 0 {
	t.TransferEncoding = []string{"chunked"}
	}
	}
	case *Response:
	if rr.Request != nil {
	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(t.Method)
	}

	// Sanitize Body,ContentLength,TransferEncoding
	if t.ResponseToHEAD {
	t.Body = nil
	if chunked(t.TransferEncoding) {
	t.ContentLength = -1
	}
	} 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
	}
	// 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) error {
	if t.Close {
	if _, err := io.WriteString(w, "Connection: close\r\n"); err != nil {
	return err
	}
	}

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

	// Write Trailer header
	if t.Trailer != nil {
	keys := make([]string, 0, len(t.Trailer))
	for k := range t.Trailer {
	k = CanonicalHeaderKey(k)
	switch k {
	case "Transfer-Encoding", "Trailer", "Content-Length":
	return &badStringError{"invalid Trailer key", k}
	}
	keys = append(keys, k)
	}
	if len(keys) > 0 {
	sort.Strings(keys)
	// TODO: could do better allocation-wise here, but trailers are rare,
	// so being lazy for now.
	if _, err := io.WriteString(w, "Trailer: "+strings.Join(keys, ",")+"\r\n"); err != nil {
	return err
	}
	}
	}

	return nil
	}

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

	// Write body
	if t.Body != nil {
	if chunked(t.TransferEncoding) {
	cw := internal.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))
	if err != nil {
	return err
	}
	var nextra int64
	nextra, err = io.Copy(ioutil.Discard, t.Body)
	ncopy += nextra
	}
	if err != nil {
	return err
	}
	if err = t.BodyCloser.Close(); err != nil {
	return err
	}
	}

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

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

	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 reports 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
	}

	var (
	suppressedHeaders304 = []string{"Content-Type", "Content-Length", "Transfer-Encoding"}
	suppressedHeadersNoBody = []string{"Content-Length", "Transfer-Encoding"}
	)

	func suppressedHeaders(status int) []string {
	switch {
	case status == 304:
	// RFC 2616 section 10.3.5: "the response MUST NOT include other entity-headers"
	return suppressedHeaders304
	case !bodyAllowedForStatus(status):
	return suppressedHeadersNoBody
	}
	return nil
	}

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

	// Unify input
	isResponse := false
	switch rr := msg.(type) {
	case *Response:
	t.Header = rr.Header
	t.StatusCode = rr.StatusCode
	t.ProtoMajor = rr.ProtoMajor
	t.ProtoMinor = rr.ProtoMinor
	t.Close = shouldClose(t.ProtoMajor, t.ProtoMinor, t.Header, true)
	isResponse = true
	if rr.Request != nil {
	t.RequestMethod = rr.Request.Method
	}
	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
	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
	}

	realLength, err := fixLength(isResponse, t.StatusCode, t.RequestMethod, t.Header, t.TransferEncoding)
	if err != nil {
	return err
	}
	if isResponse && t.RequestMethod == "HEAD" {
	if n, err := parseContentLength(t.Header.get("Content-Length")); err != nil {
	return err
	} else {
	t.ContentLength = n
	}
	} else {
	t.ContentLength = realLength
	}

	// 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 realLength == -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):
	if noBodyExpected(t.RequestMethod) {
	t.Body = eofReader
	} else {
	t.Body = &body{src: internal.NewChunkedReader(r), hdr: msg, r: r, closing: t.Close}
	}
	case realLength == 0:
	t.Body = eofReader
	case realLength > 0:
	t.Body = &body{src: io.LimitReader(r, realLength), closing: t.Close}
	default:
	// realLength < 0, i.e. "Content-Length" not mentioned in header
	if t.Close {
	// Close semantics (i.e. HTTP/1.0)
	t.Body = &body{src: r, closing: t.Close}
	} else {
	// Persistent connection (i.e. HTTP/1.1)
	t.Body = eofReader
	}
	}

	// 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")

	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 recorded
	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 := parseContentLength(cl)
	if err != nil {
	return -1, err
	}
	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
	}

	// 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, removeCloseHeader bool) 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" {
	if removeCloseHeader {
	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[key] = nil
	}
	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 {
	src 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?

	mu sync.Mutex // guards closed, and calls to Read and Close
	closed bool
	}

	// ErrBodyReadAfterClose is returned when reading a Request or Response
	// 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 Body")

	func (b *body) Read(p []byte) (n int, err error) {
	b.mu.Lock()
	defer b.mu.Unlock()
	if b.closed {
	return 0, ErrBodyReadAfterClose
	}
	return b.readLocked(p)
	}

	// Must hold b.mu.
	func (b *body) readLocked(p []byte) (n int, err error) {
	n, err = b.src.Read(p)

	if err == io.EOF {
	// Chunked case. Read the trailer.
	if b.hdr != nil {
	if e := b.readTrailer(); e != nil {
	err = e
	}
	b.hdr = nil
	} else {
	// If the server declared the Content-Length, our body is a LimitedReader
	// and we need to check whether this EOF arrived early.
	if lr, ok := b.src.(*io.LimitedReader); ok && lr.N > 0 {
	err = io.ErrUnexpectedEOF
	}
	}
	}

	// If we can return an EOF here along with the read data, do
	// so. This is optional per the io.Reader contract, but doing
	// so helps the HTTP transport code recycle its connection
	// earlier (since it will see this EOF itself), even if the
	// client doesn't do future reads or Close.
	if err == nil && n > 0 {
	if lr, ok := b.src.(*io.LimitedReader); ok && lr.N == 0 {
	err = io.EOF
	}
	}

	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
	}

	var errTrailerEOF = errors.New("http: unexpected EOF reading trailer")

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

	// 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 {
	if err == io.EOF {
	return errTrailerEOF
	}
	return err
	}
	switch rr := b.hdr.(type) {
	case *Request:
	mergeSetHeader(&rr.Trailer, Header(hdr))
	case *Response:
	mergeSetHeader(&rr.Trailer, Header(hdr))
	}
	return nil
	}

	func mergeSetHeader(dst *Header, src Header) {
	if *dst == nil {
	*dst = src
	return
	}
	for k, vv := range src {
	(*dst)[k] = vv
	}
	}

	func (b *body) Close() error {
	b.mu.Lock()
	defer b.mu.Unlock()
	if b.closed {
	return nil
	}
	var err error
	switch {
	case b.hdr == nil && b.closing:
	// no trailer and closing the connection next.
	// no point in reading to EOF.
	default:
	// Fully consume the body, which will also lead to us reading
	// the trailer headers after the body, if present.
	_, err = io.Copy(ioutil.Discard, bodyLocked{b})
	}
	b.closed = true
	return err
	}

	// bodyLocked is a io.Reader reading from a *body when its mutex is
	// already held.
	type bodyLocked struct {
	b *body
	}

	func (bl bodyLocked) Read(p []byte) (n int, err error) {
	if bl.b.closed {
	return 0, ErrBodyReadAfterClose
	}
	return bl.b.readLocked(p)
	}

	// parseContentLength trims whitespace from s and returns -1 if no value
	// is set, or the value if it's >= 0.
	func parseContentLength(cl string) (int64, error) {
	cl = strings.TrimSpace(cl)
	if cl == "" {
	return -1, nil
	}
	n, err := strconv.ParseInt(cl, 10, 64)
	if err != nil \|\| n < 0 {
	return 0, &badStringError{"bad Content-Length", cl}
	}
	return n, nil

	}