http: unified body transfer (read & write) logic in http.Request/Response.

Compliance issue addressed here: POST requests carrying form data are required
to use "identity" transfer encoding by common nginx and apache server configurations,
e.g. wordpress.com (and many others). So, Request needed to be able to send
non-chunked encodings.

Thus, Request is extended to support identity and chunked encodings, like
Response.  Since the Read() and Write() logic are shared by both (and are
quite long), it is exported in a separate file transfer.go.

R=rsc
CC=golang-dev
https://golang.org/cl/217048

6 files changed, 482 insertions, 348 deletions

diff --git a/src/pkg/http/Makefile b/src/pkg/http/Makefile
index d7149d70b1..235ff0279e 100644
--- a/src/pkg/http/Makefile
+++ b/src/pkg/http/Makefile
@@ -16,6 +16,7 @@ GOFILES=\
 	response.go\
 	server.go\
 	status.go\
+	transfer.go\
 	url.go\
 
 include ../../Make.pkg
diff --git a/src/pkg/http/readrequest_test.go b/src/pkg/http/readrequest_test.go
index 5438ba1735..ed2ebe97bb 100644
--- a/src/pkg/http/readrequest_test.go
+++ b/src/pkg/http/readrequest_test.go
@@ -60,6 +60,7 @@ var reqTests = []reqTest{
 				"Content-Length": "7",
 			},
 			Close: false,
+			ContentLength: 7,
 			Host: "www.techcrunch.com",
 			Referer: "",
 			UserAgent: "Fake",
diff --git a/src/pkg/http/request.go b/src/pkg/http/request.go
index bd8f00d552..d077224026 100644
--- a/src/pkg/http/request.go
+++ b/src/pkg/http/request.go
@@ -49,7 +49,14 @@ type badStringError struct {
 
 func (e *badStringError) String() string { return fmt.Sprintf("%s %q", e.what, e.str) }
 
-var reqExcludeHeader = map[string]int{"Host": 0, "User-Agent": 0, "Referer": 0}
+var reqExcludeHeader = map[string]int{
+	"Host": 0,
+	"User-Agent": 0,
+	"Referer": 0,
+	"Content-Length": 0,
+	"Transfer-Encoding": 0,
+	"Trailer": 0,
+}
 
 // A Request represents a parsed HTTP request header.
 type Request struct {
@@ -84,6 +91,15 @@ type Request struct {
 	// The message body.
 	Body io.ReadCloser
 
+	// ContentLength records the length of the associated content.
+	// The value -1 indicates that the length is unknown.
+	// Values >= 0 indicate that the given number of bytes may be read from Body.
+	ContentLength int64
+
+	// TransferEncoding lists the transfer encodings from outermost to innermost.
+	// An empty list denotes the "identity" encoding.
+	TransferEncoding []string
+
 	// Whether to close the connection after replying to this request.
 	Close bool
 
@@ -109,6 +125,11 @@ type Request struct {
 
 	// The parsed form. Only available after ParseForm is called.
 	Form map[string][]string
+
+	// Trailer maps trailer keys to values.  Like for Header, if the
+	// response has multiple trailer lines with the same key, they will be
+	// concatenated, delimited by commas.
+	Trailer map[string]string
 }
 
 // ProtoAtLeast returns whether the HTTP protocol used
@@ -152,16 +173,22 @@ func (req *Request) Write(w io.Writer) os.Error {
 	}
 
 	fmt.Fprintf(w, "%s %s HTTP/1.1\r\n", valueOrDefault(req.Method, "GET"), uri)
+
+	// Header lines
 	fmt.Fprintf(w, "Host: %s\r\n", host)
 	fmt.Fprintf(w, "User-Agent: %s\r\n", valueOrDefault(req.UserAgent, defaultUserAgent))
-
 	if req.Referer != "" {
 		fmt.Fprintf(w, "Referer: %s\r\n", req.Referer)
 	}
 
-	if req.Body != nil {
-		// Force chunked encoding
-		req.Header["Transfer-Encoding"] = "chunked"
+	// Process Body,ContentLength,Close,Trailer
+	tw, err := newTransferWriter(req)
+	if err != nil {
+		return err
+	}
+	err = tw.WriteHeader(w)
+	if err != nil {
+		return err
 	}
 
 	// TODO: split long values?  (If so, should share code with Conn.Write)
@@ -171,29 +198,17 @@ func (req *Request) Write(w io.Writer) os.Error {
 	// from Request, and introduce Request methods along the lines of
 	// Response.{GetHeader,AddHeader} and string constants for "Host",
 	// "User-Agent" and "Referer".
-	err := writeSortedKeyValue(w, req.Header, reqExcludeHeader)
+	err = writeSortedKeyValue(w, req.Header, reqExcludeHeader)
 	if err != nil {
 		return err
 	}
 
 	io.WriteString(w, "\r\n")
 
-	if req.Body != nil {
-		cw := NewChunkedWriter(w)
-		if _, err := io.Copy(cw, req.Body); err != nil {
-			return err
-		}
-		if err := cw.Close(); err != nil {
-			return err
-		}
-		// TODO(petar): Write trailer here and append \r\n. For now, we
-		// simply send the final \r\n:
-		if _, err := fmt.Fprint(w, "\r\n"); err != nil {
-			return err
-		}
-		if err := req.Body.Close(); err != nil {
-			return err
-		}
+	// Write body and trailer
+	err = tw.WriteBody(w)
+	if err != nil {
+		return err
 	}
 
 	return nil
@@ -507,26 +522,7 @@ func ReadRequest(b *bufio.Reader) (req *Request, err os.Error) {
 		req.Header["Host"] = "", false
 	}
 
-	// RFC2616: Should treat
-	//	Pragma: no-cache
-	// like
-	//	Cache-Control: no-cache
-	if v, present := req.Header["Pragma"]; present && v == "no-cache" {
-		if _, presentcc := req.Header["Cache-Control"]; !presentcc {
-			req.Header["Cache-Control"] = "no-cache"
-		}
-	}
-
-	// Determine whether to hang up after sending the reply.
-	if req.ProtoMajor < 1 || (req.ProtoMajor == 1 && req.ProtoMinor < 1) {
-		req.Close = true
-	} else if v, present := req.Header["Connection"]; present {
-		// TODO: Should split on commas, toss surrounding white space,
-		// and check each field.
-		if v == "close" {
-			req.Close = true
-		}
-	}
+	fixPragmaCacheControl(req.Header)
 
 	// Pull out useful fields as a convenience to clients.
 	if v, present := req.Header["Referer"]; present {
@@ -564,17 +560,9 @@ func ReadRequest(b *bufio.Reader) (req *Request, err os.Error) {
 	//	Via
 	//	Warning
 
-	// A message body exists when either Content-Length or Transfer-Encoding
-	// headers are present. Transfer-Encoding trumps Content-Length.
-	if v, present := req.Header["Transfer-Encoding"]; present && v == "chunked" {
-		req.Body = &body{Reader: newChunkedReader(b), hdr: req, r: b, closing: req.Close}
-	} else if v, present := req.Header["Content-Length"]; present {
-		length, err := strconv.Btoi64(v, 10)
-		if err != nil {
-			return nil, &badStringError{"invalid Content-Length", v}
-		}
-		// TODO: limit the Content-Length. This is an easy DoS vector.
-		req.Body = &body{Reader: io.LimitReader(b, length), closing: req.Close}
+	err = readTransfer(req, b)
+	if err != nil {
+		return nil, err
 	}
 
 	return req, nil
diff --git a/src/pkg/http/requestwrite_test.go b/src/pkg/http/requestwrite_test.go
index da2d5e375b..b04e0babae 100644
--- a/src/pkg/http/requestwrite_test.go
+++ b/src/pkg/http/requestwrite_test.go
@@ -70,9 +70,10 @@ var reqWriteTests = []reqWriteTest{
 				Path: "/search",
 			},
 			ProtoMajor: 1,
-			ProtoMinor: 0,
+			ProtoMinor: 1,
 			Header: map[string]string{},
 			Body: nopCloser{bytes.NewBufferString("abcdef")},
+			TransferEncoding: []string{"chunked"},
 		},
 
 		"GET /search HTTP/1.1\r\n" +
@@ -83,9 +84,6 @@ var reqWriteTests = []reqWriteTest{
 	},
 }
 
-// FIXME(petar): The write order of keys in Request.Header depends on the
-// map[string]string iterator. Since this isn't defined in Go's semantics, we
-// should eventually fix Request.Write()
 func TestRequestWrite(t *testing.T) {
 	for i := range reqWriteTests {
 		tt := &reqWriteTests[i]
diff --git a/src/pkg/http/response.go b/src/pkg/http/response.go
index ffdcaa2386..87ca7f1cd1 100644
--- a/src/pkg/http/response.go
+++ b/src/pkg/http/response.go
@@ -16,7 +16,11 @@ import (
 	"strings"
 )
 
-var respExcludeHeader = map[string]int{}
+var respExcludeHeader = map[string]int{
+	"Content-Length": 0,
+	"Transfer-Encoding": 0,
+	"Trailer": 0,
+}
 
 // Response represents the response from an HTTP request.
 //
@@ -116,78 +120,14 @@ func ReadResponse(r *bufio.Reader, requestMethod string) (resp *Response, err os
 
 	fixPragmaCacheControl(resp.Header)
 
-	// Transfer encoding, content length
-	resp.TransferEncoding, err = fixTransferEncoding(resp.Header)
-	if err != nil {
-		return nil, err
-	}
-
-	resp.ContentLength, err = fixLength(resp.StatusCode, resp.RequestMethod,
-		resp.Header, resp.TransferEncoding)
-	if err != nil {
-		return nil, err
-	}
-
-	// Closing
-	resp.Close = shouldClose(resp.ProtoMajor, resp.ProtoMinor, resp.Header)
-
-	// Trailer
-	resp.Trailer, err = fixTrailer(resp.Header, resp.TransferEncoding)
+	err = readTransfer(resp, r)
 	if err != nil {
 		return nil, err
 	}
 
-	// Prepare body reader.  ContentLength < 0 means chunked encoding
-	// or close connection when finished, since multipart is not supported yet
-	switch {
-	case chunked(resp.TransferEncoding):
-		resp.Body = &body{Reader: newChunkedReader(r), hdr: resp, r: r, closing: resp.Close}
-	case resp.ContentLength >= 0:
-		resp.Body = &body{Reader: io.LimitReader(r, resp.ContentLength), closing: resp.Close}
-	default:
-		resp.Body = &body{Reader: r, closing: resp.Close}
-	}
-
 	return resp, 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?
-}
-
-func (b *body) Close() os.Error {
-	if b.hdr == nil && b.closing {
-		// no trailer and closing the connection next.
-		// no point in reading to EOF.
-		return nil
-	}
-
-	trashBuf := make([]byte, 1024) // local for thread safety
-	for {
-		_, err := b.Read(trashBuf)
-		if err == nil {
-			continue
-		}
-		if err == os.EOF {
-			break
-		}
-		return err
-	}
-	if b.hdr == nil { // not reading trailer
-		return nil
-	}
-
-	// TODO(petar): Put trailer reader code here
-
-	return nil
-}
-
 // RFC2616: Should treat
 //	Pragma: no-cache
 // like
@@ -200,147 +140,6 @@ func fixPragmaCacheControl(header map[string]string) {
 	}
 }
 
-// Parse the trailer header
-func fixTrailer(header map[string]string, te []string) (map[string]string, os.Error) {
-	raw, present := header["Trailer"]
-	if !present {
-		return nil, nil
-	}
-
-	header["Trailer"] = "", false
-	trailer := make(map[string]string)
-	keys := strings.Split(raw, ",", 0)
-	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] = ""
-	}
-	if len(trailer) == 0 {
-		return nil, nil
-	}
-	if !chunked(te) {
-		// Trailer and no chunking
-		return nil, ErrUnexpectedTrailer
-	}
-	return trailer, nil
-}
-
-// Sanitize transfer encoding
-func fixTransferEncoding(header map[string]string) ([]string, os.Error) {
-	raw, present := header["Transfer-Encoding"]
-	if !present {
-		return nil, nil
-	}
-
-	header["Transfer-Encoding"] = "", false
-	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.
-		header["Content-Length"] = "", false
-		return te, nil
-	}
-
-	return nil, nil
-}
-
-func noBodyExpected(requestMethod string) bool {
-	return requestMethod == "HEAD"
-}
-
-// 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(status int, requestMethod string, header map[string]string, te []string) (int64, os.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
-	if cl, present := header["Content-Length"]; present {
-		cl = strings.TrimSpace(cl)
-		if cl != "" {
-			n, err := strconv.Atoi64(cl)
-			if err != nil || n < 0 {
-				return -1, &badStringError{"bad Content-Length", cl}
-			}
-			return n, nil
-		} else {
-			header["Content-Length"] = "", false
-		}
-	}
-
-	// 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 ct, present := header["Content-Type"]; present {
-		ct = strings.ToLower(ct)
-		if strings.Index(ct, "multipart/byteranges") >= 0 {
-			return -1, ErrNotSupported
-		}
-	}
-
-
-	// Logic based on close
-	return -1, nil
-}
-
-// Determine whether to hang up after sending a request and body, or
-// receiving a response and body
-func shouldClose(major, minor int, header map[string]string) bool {
-	if major < 1 || (major == 1 && minor < 1) {
-		return true
-	} else if v, present := header["Connection"]; present {
-		// TODO: Should split on commas, toss surrounding white space,
-		// and check each field.
-		if v == "close" {
-			return true
-		}
-	}
-	return false
-}
-
-// Checks whether chunked is part of the encodings stack
-func chunked(te []string) bool { return len(te) > 0 && te[0] == "chunked" }
-
 // AddHeader adds a value under the given key.  Keys are not case sensitive.
 func (r *Response) AddHeader(key, value string) {
 	key = CanonicalHeaderKey(key)
@@ -397,70 +196,18 @@ func (resp *Response) Write(w io.Writer) os.Error {
 	io.WriteString(w, strconv.Itoa(resp.ProtoMinor)+" ")
 	io.WriteString(w, strconv.Itoa(resp.StatusCode)+" "+text+"\r\n")
 
-	// Sanitize the field triple (Body, ContentLength, TransferEncoding)
-	contentLength := resp.ContentLength
-	if noBodyExpected(resp.RequestMethod) {
-		resp.Body = nil
-		resp.TransferEncoding = nil
-		// resp.ContentLength is expected to hold Content-Length
-		if contentLength < 0 {
-			return ErrMissingContentLength
-		}
-	} else {
-		if !resp.ProtoAtLeast(1, 1) || resp.Body == nil {
-			resp.TransferEncoding = nil
-		}
-		if chunked(resp.TransferEncoding) {
-			contentLength = -1
-		} else if resp.Body == nil { // no chunking, no body
-			contentLength = 0
-		}
-	}
-
-	// Write Content-Length and/or Transfer-Encoding whose values are a
-	// function of the sanitized field triple (Body, ContentLength,
-	// TransferEncoding)
-	if chunked(resp.TransferEncoding) {
-		io.WriteString(w, "Transfer-Encoding: chunked\r\n")
-	} else {
-		if contentLength > 0 || resp.RequestMethod == "HEAD" {
-			io.WriteString(w, "Content-Length: ")
-			io.WriteString(w, strconv.Itoa64(contentLength)+"\r\n")
-		}
-	}
-	if resp.Header != nil {
-		resp.Header["Content-Length"] = "", false
-		resp.Header["Transfer-Encoding"] = "", false
-	}
-
-	// Sanitize Trailer
-	if !chunked(resp.TransferEncoding) {
-		resp.Trailer = nil
-	} else if resp.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 resp.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
-		}
-		io.WriteString(w, "\r\n")
+	// Process Body,ContentLength,Close,Trailer
+	tw, err := newTransferWriter(resp)
+	if err != nil {
+		return err
 	}
-	if resp.Header != nil {
-		resp.Header["Trailer"] = "", false
+	err = tw.WriteHeader(w)
+	if err != nil {
+		return err
 	}
 
 	// Rest of header
-	err := writeSortedKeyValue(w, resp.Header, respExcludeHeader)
+	err = writeSortedKeyValue(w, resp.Header, respExcludeHeader)
 	if err != nil {
 		return err
 	}
@@ -468,30 +215,10 @@ func (resp *Response) Write(w io.Writer) os.Error {
 	// End-of-header
 	io.WriteString(w, "\r\n")
 
-	// Write body
-	if resp.Body != nil {
-		var err os.Error
-		if chunked(resp.TransferEncoding) {
-			cw := NewChunkedWriter(w)
-			_, err = io.Copy(cw, resp.Body)
-			if err == nil {
-				err = cw.Close()
-			}
-		} else {
-			_, err = io.Copy(w, io.LimitReader(resp.Body, contentLength))
-		}
-		if err != nil {
-			return err
-		}
-		if err = resp.Body.Close(); err != nil {
-			return err
-		}
-	}
-
-	// TODO(petar): Place trailer writer code here.
-	if chunked(resp.TransferEncoding) {
-		// Last chunk, empty trailer
-		io.WriteString(w, "\r\n")
+	// Write body and trailer
+	err = tw.WriteBody(w)
+	if err != nil {
+		return err
 	}
 
 	// Success
diff --git a/src/pkg/http/transfer.go b/src/pkg/http/transfer.go
new file mode 100644
index 0000000000..a6d9a21a8d
--- /dev/null
+++ b/src/pkg/http/transfer.go
@@ -0,0 +1,419 @@
+// 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"
+	"io"
+	"os"
+	"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 {
+	Body             io.ReadCloser
+	ResponseToHEAD   bool
+	ContentLength    int64
+	Close            bool
+	TransferEncoding []string
+	Trailer          map[string]string
+}
+
+func newTransferWriter(r interface{}) (t *transferWriter, err os.Error) {
+	t = &transferWriter{}
+
+	// Extract relevant fields
+	atLeastHTTP11 := false
+	switch rr := r.(type) {
+	case *Request:
+		t.Body = rr.Body
+		t.ContentLength = rr.ContentLength
+		t.Close = rr.Close
+		t.TransferEncoding = rr.TransferEncoding
+		t.Trailer = rr.Trailer
+		atLeastHTTP11 = rr.ProtoAtLeast(1, 1)
+	case *Response:
+		t.Body = 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.RequestMethod)
+	}
+
+	// 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) WriteHeader(w io.Writer) (err os.Error) {
+	// Write Content-Length and/or Transfer-Encoding whose values are a
+	// function of the sanitized field triple (Body, ContentLength,
+	// TransferEncoding)
+	if chunked(t.TransferEncoding) {
+		_, err = io.WriteString(w, "Transfer-Encoding: chunked\r\n")
+	} else {
+		if t.ContentLength > 0 || t.ResponseToHEAD {
+			io.WriteString(w, "Content-Length: ")
+			_, err = io.WriteString(w, strconv.Itoa64(t.ContentLength)+"\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 os.Error) {
+	// 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 {
+			_, err = io.Copy(w, io.LimitReader(t.Body, t.ContentLength))
+		}
+		if err != nil {
+			return err
+		}
+		if err = t.Body.Close(); err != nil {
+			return err
+		}
+	}
+
+	// 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        map[string]string
+	StatusCode    int
+	RequestMethod string
+	ProtoMajor    int
+	ProtoMinor    int
+	// Output
+	Body             io.ReadCloser
+	ContentLength    int64
+	TransferEncoding []string
+	Close            bool
+	Trailer          map[string]string
+}
+
+// msg is *Request or *Response.
+func readTransfer(msg interface{}, r *bufio.Reader) (err os.Error) {
+	t := &transferReader{}
+
+	// Unify input
+	switch rr := msg.(type) {
+	case *Response:
+		t.Header = rr.Header
+		t.StatusCode = rr.StatusCode
+		t.RequestMethod = rr.RequestMethod
+		t.ProtoMajor = rr.ProtoMajor
+		t.ProtoMinor = rr.ProtoMinor
+	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"
+	}
+
+	// Transfer encoding, content length
+	t.TransferEncoding, err = fixTransferEncoding(t.Header)
+	if err != nil {
+		return err
+	}
+
+	t.ContentLength, err = fixLength(t.StatusCode, t.RequestMethod, t.Header, t.TransferEncoding)
+	if err != nil {
+		return err
+	}
+
+	// Closing
+	t.Close = shouldClose(t.ProtoMajor, t.ProtoMinor, t.Header)
+
+	// Trailer
+	t.Trailer, err = fixTrailer(t.Header, t.TransferEncoding)
+	if err != nil {
+		return err
+	}
+
+	// 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}
+		}
+		// TODO(petar): It may be a good idea, for extra robustness, to
+		// assume ContentLength=0 for GET requests (and other special
+		// cases?). This logic should be in fixLength().
+	}
+
+	// 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" }
+
+// Sanitize transfer encoding
+func fixTransferEncoding(header map[string]string) ([]string, os.Error) {
+	raw, present := header["Transfer-Encoding"]
+	if !present {
+		return nil, nil
+	}
+
+	header["Transfer-Encoding"] = "", false
+	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.
+		header["Content-Length"] = "", false
+		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(status int, requestMethod string, header map[string]string, te []string) (int64, os.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
+	if cl, present := header["Content-Length"]; present {
+		cl = strings.TrimSpace(cl)
+		if cl != "" {
+			n, err := strconv.Atoi64(cl)
+			if err != nil || n < 0 {
+				return -1, &badStringError{"bad Content-Length", cl}
+			}
+			return n, nil
+		} else {
+			header["Content-Length"] = "", false
+		}
+	}
+
+	// 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 ct, present := header["Content-Type"]; present {
+		ct = strings.ToLower(ct)
+		if strings.Index(ct, "multipart/byteranges") >= 0 {
+			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
+func shouldClose(major, minor int, header map[string]string) bool {
+	if major < 1 || (major == 1 && minor < 1) {
+		return true
+	} else if v, present := header["Connection"]; present {
+		// TODO: Should split on commas, toss surrounding white space,
+		// and check each field.
+		if v == "close" {
+			return true
+		}
+	}
+	return false
+}
+
+// Parse the trailer header
+func fixTrailer(header map[string]string, te []string) (map[string]string, os.Error) {
+	raw, present := header["Trailer"]
+	if !present {
+		return nil, nil
+	}
+
+	header["Trailer"] = "", false
+	trailer := make(map[string]string)
+	keys := strings.Split(raw, ",", 0)
+	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] = ""
+	}
+	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?
+}
+
+func (b *body) Close() os.Error {
+	if b.hdr == nil && b.closing {
+		// no trailer and closing the connection next.
+		// no point in reading to EOF.
+		return nil
+	}
+
+	trashBuf := make([]byte, 1024) // local for thread safety
+	for {
+		_, err := b.Read(trashBuf)
+		if err == nil {
+			continue
+		}
+		if err == os.EOF {
+			break
+		}
+		return err
+	}
+	if b.hdr == nil { // not reading trailer
+		return nil
+	}
+
+	// TODO(petar): Put trailer reader code here
+
+	return nil
+}