src/pkg/http/request.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.

 // HTTP Request reading and parsing.

 // The http package implements parsing of HTTP requests, replies,
 // and URLs and provides an extensible HTTP server and a basic
 // HTTP client.
 package http

 import (
 	"bufio"
 	"bytes"
 	"container/vector"
 	"fmt"
 	"io"
 	"io/ioutil"
 	"mime"
 	"mime/multipart"
 	"os"
 	"strconv"
 	"strings"
 )

 const (
 	maxLineLength  = 4096 // assumed <= bufio.defaultBufSize
 	maxValueLength = 4096
 	maxHeaderLines = 1024
 	chunkSize      = 4 << 10 // 4 KB chunks
 )

 // HTTP request parsing errors.
 type ProtocolError struct {
 	os.ErrorString
 }

 var (
 	ErrLineTooLong          = &ProtocolError{"header line too long"}
 	ErrHeaderTooLong        = &ProtocolError{"header too long"}
 	ErrShortBody            = &ProtocolError{"entity body too short"}
 	ErrNotSupported         = &ProtocolError{"feature not supported"}
 	ErrUnexpectedTrailer    = &ProtocolError{"trailer header without chunked transfer encoding"}
 	ErrMissingContentLength = &ProtocolError{"missing ContentLength in HEAD response"}
 	ErrNotMultipart         = &ProtocolError{"request Content-Type isn't multipart/form-data"}
 	ErrMissingBoundary      = &ProtocolError{"no multipart boundary param Content-Type"}
 )

 type badStringError struct {
 	what string
 	str  string
 }

 func (e *badStringError) String() string { return fmt.Sprintf("%s %q", e.what, e.str) }

 var reqExcludeHeader = map[string]bool{
 	"Host":              true,
 	"User-Agent":        true,
 	"Referer":           true,
 	"Content-Length":    true,
 	"Transfer-Encoding": true,
 	"Trailer":           true,
 }

 // A Request represents a parsed HTTP request header.
 type Request struct {
 	Method     string // GET, POST, PUT, etc.
 	RawURL     string // The raw URL given in the request.
 	URL        *URL   // Parsed URL.
 	Proto      string // "HTTP/1.0"
 	ProtoMajor int    // 1
 	ProtoMinor int    // 0

 	// A header maps request lines to their values.
 	// If the header says
 	//
 	//	accept-encoding: gzip, deflate
 	//	Accept-Language: en-us
 	//	Connection: keep-alive
 	//
 	// then
 	//
 	//	Header = map[string]string{
 	//		"Accept-Encoding": "gzip, deflate",
 	//		"Accept-Language": "en-us",
 	//		"Connection": "keep-alive",
 	//	}
 	//
 	// HTTP defines that header names are case-insensitive.
 	// The request parser implements this by canonicalizing the
 	// name, making the first character and any characters
 	// following a hyphen uppercase and the rest lowercase.
 	Header map[string]string

 	// 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

 	// The host on which the URL is sought.
 	// Per RFC 2616, this is either the value of the Host: header
 	// or the host name given in the URL itself.
 	Host string

 	// The referring URL, if sent in the request.
 	//
 	// Referer is misspelled as in the request itself,
 	// a mistake from the earliest days of HTTP.
 	// This value can also be fetched from the Header map
 	// as Header["Referer"]; the benefit of making it
 	// available as a structure field is that the compiler
 	// can diagnose programs that use the alternate
 	// (correct English) spelling req.Referrer but cannot
 	// diagnose programs that use Header["Referrer"].
 	Referer string

 	// The User-Agent: header string, if sent in the request.
 	UserAgent string

 	// 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
 // in the request is at least major.minor.
 func (r *Request) ProtoAtLeast(major, minor int) bool {
 	return r.ProtoMajor > major ||
 		r.ProtoMajor == major && r.ProtoMinor >= minor
 }

 // MultipartReader returns a MIME multipart reader if this is a
 // multipart/form-data POST request, else returns nil and an error.
 func (r *Request) MultipartReader() (multipart.Reader, os.Error) {
 	v, ok := r.Header["Content-Type"]
 	if !ok {
 		return nil, ErrNotMultipart
 	}
 	d, params := mime.ParseMediaType(v)
 	if d != "multipart/form-data" {
 		return nil, ErrNotMultipart
 	}
 	boundary, ok := params["boundary"]
 	if !ok {
 		return nil, ErrMissingBoundary
 	}
 	return multipart.NewReader(r.Body, boundary), nil
 }

 // Return value if nonempty, def otherwise.
 func valueOrDefault(value, def string) string {
 	if value != "" {
 		return value
 	}
 	return def
 }

 const defaultUserAgent = "Go http package"

 // Write writes an HTTP/1.1 request -- header and body -- in wire format.
 // This method consults the following fields of req:
 //	Host
 //	RawURL, if non-empty, or else URL
 //	Method (defaults to "GET")
 //	UserAgent (defaults to defaultUserAgent)
 //	Referer
 //	Header
 //	Body
 //
 // If Body is present, Write forces "Transfer-Encoding: chunked" as a header
 // and then closes Body when finished sending it.
 func (req *Request) Write(w io.Writer) os.Error {
 	host := req.Host
 	if host == "" {
 		host = req.URL.Host
 	}

 	uri := req.RawURL
 	if uri == "" {
 		uri = valueOrDefault(urlEscape(req.URL.Path, encodePath), "/")
 		if req.URL.RawQuery != "" {
 			uri += "?" + req.URL.RawQuery
 		}
 	}

 	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)
 	}

 	// 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)
 	// TODO: if Header includes values for Host, User-Agent, or Referer, this
 	// may conflict with the User-Agent or Referer headers we add manually.
 	// One solution would be to remove the Host, UserAgent, and Referer fields
 	// 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)
 	if err != nil {
 		return err
 	}

 	io.WriteString(w, "\r\n")

 	// Write body and trailer
 	err = tw.WriteBody(w)
 	if err != nil {
 		return err
 	}

 	return nil
 }

 // Read a line of bytes (up to \n) from b.
 // Give up if the line exceeds maxLineLength.
 // The returned bytes are a pointer into storage in
 // the bufio, so they are only valid until the next bufio read.
 func readLineBytes(b *bufio.Reader) (p []byte, err os.Error) {
 	if p, err = b.ReadSlice('\n'); err != nil {
 		// We always know when EOF is coming.
 		// If the caller asked for a line, there should be a line.
 		if err == os.EOF {
 			err = io.ErrUnexpectedEOF
 		} else if err == bufio.ErrBufferFull {
 			err = ErrLineTooLong
 		}
 		return nil, err
 	}
 	if len(p) >= maxLineLength {
 		return nil, ErrLineTooLong
 	}

 	// Chop off trailing white space.
 	var i int
 	for i = len(p); i > 0; i-- {
 		if c := p[i-1]; c != ' ' && c != '\r' && c != '\t' && c != '\n' {
 			break
 		}
 	}
 	return p[0:i], nil
 }

 // readLineBytes, but convert the bytes into a string.
 func readLine(b *bufio.Reader) (s string, err os.Error) {
 	p, e := readLineBytes(b)
 	if e != nil {
 		return "", e
 	}
 	return string(p), nil
 }

 var colon = []byte{':'}

 // Read a key/value pair from b.
 // A key/value has the form Key: Value\r\n
 // and the Value can continue on multiple lines if each continuation line
 // starts with a space.
 func readKeyValue(b *bufio.Reader) (key, value string, err os.Error) {
 	line, e := readLineBytes(b)
 	if e != nil {
 		return "", "", e
 	}
 	if len(line) == 0 {
 		return "", "", nil
 	}

 	// Scan first line for colon.
 	i := bytes.Index(line, colon)
 	if i < 0 {
 		goto Malformed
 	}

 	key = string(line[0:i])
 	if strings.Contains(key, " ") {
 		// Key field has space - no good.
 		goto Malformed
 	}

 	// Skip initial space before value.
 	for i++; i < len(line); i++ {
 		if line[i] != ' ' {
 			break
 		}
 	}
 	value = string(line[i:])

 	// Look for extension lines, which must begin with space.
 	for {
 		c, e := b.ReadByte()
 		if c != ' ' {
 			if e != os.EOF {
 				b.UnreadByte()
 			}
 			break
 		}

 		// Eat leading space.
 		for c == ' ' {
 			if c, e = b.ReadByte(); e != nil {
 				if e == os.EOF {
 					e = io.ErrUnexpectedEOF
 				}
 				return "", "", e
 			}
 		}
 		b.UnreadByte()

 		// Read the rest of the line and add to value.
 		if line, e = readLineBytes(b); e != nil {
 			return "", "", e
 		}
 		value += " " + string(line)

 		if len(value) >= maxValueLength {
 			return "", "", &badStringError{"value too long for key", key}
 		}
 	}
 	return key, value, nil

 Malformed:
 	return "", "", &badStringError{"malformed header line", string(line)}
 }

 // Convert decimal at s[i:len(s)] to integer,
 // returning value, string position where the digits stopped,
 // and whether there was a valid number (digits, not too big).
 func atoi(s string, i int) (n, i1 int, ok bool) {
 	const Big = 1000000
 	if i >= len(s) || s[i] < '0' || s[i] > '9' {
 		return 0, 0, false
 	}
 	n = 0
 	for ; i < len(s) && '0' <= s[i] && s[i] <= '9'; i++ {
 		n = n*10 + int(s[i]-'0')
 		if n > Big {
 			return 0, 0, false
 		}
 	}
 	return n, i, true
 }

 // Parse HTTP version: "HTTP/1.2" -> (1, 2, true).
 func parseHTTPVersion(vers string) (int, int, bool) {
 	if len(vers) < 5 || vers[0:5] != "HTTP/" {
 		return 0, 0, false
 	}
 	major, i, ok := atoi(vers, 5)
 	if !ok || i >= len(vers) || vers[i] != '.' {
 		return 0, 0, false
 	}
 	var minor int
 	minor, i, ok = atoi(vers, i+1)
 	if !ok || i != len(vers) {
 		return 0, 0, false
 	}
 	return major, minor, true
 }

 // CanonicalHeaderKey returns the canonical format of the
 // HTTP header key s.  The canonicalization converts the first
 // letter and any letter following a hyphen to upper case;
 // the rest are converted to lowercase.  For example, the
 // canonical key for "accept-encoding" is "Accept-Encoding".
 func CanonicalHeaderKey(s string) string {
 	// canonicalize: first letter upper case
 	// and upper case after each dash.
 	// (Host, User-Agent, If-Modified-Since).
 	// HTTP headers are ASCII only, so no Unicode issues.
 	var a []byte
 	upper := true
 	for i := 0; i < len(s); i++ {
 		v := s[i]
 		if upper && 'a' <= v && v <= 'z' {
 			if a == nil {
 				a = []byte(s)
 			}
 			a[i] = v + 'A' - 'a'
 		}
 		if !upper && 'A' <= v && v <= 'Z' {
 			if a == nil {
 				a = []byte(s)
 			}
 			a[i] = v + 'a' - 'A'
 		}
 		upper = false
 		if v == '-' {
 			upper = true
 		}
 	}
 	if a != nil {
 		return string(a)
 	}
 	return s
 }

 type chunkedReader struct {
 	r   *bufio.Reader
 	n   uint64 // unread bytes in chunk
 	err os.Error
 }

 func newChunkedReader(r *bufio.Reader) *chunkedReader {
 	return &chunkedReader{r: r}
 }

 func (cr *chunkedReader) beginChunk() {
 	// chunk-size CRLF
 	var line string
 	line, cr.err = readLine(cr.r)
 	if cr.err != nil {
 		return
 	}
 	cr.n, cr.err = strconv.Btoui64(line, 16)
 	if cr.err != nil {
 		return
 	}
 	if cr.n == 0 {
 		// trailer CRLF
 		for {
 			line, cr.err = readLine(cr.r)
 			if cr.err != nil {
 				return
 			}
 			if line == "" {
 				break
 			}
 		}
 		cr.err = os.EOF
 	}
 }

 func (cr *chunkedReader) Read(b []uint8) (n int, err os.Error) {
 	if cr.err != nil {
 		return 0, cr.err
 	}
 	if cr.n == 0 {
 		cr.beginChunk()
 		if cr.err != nil {
 			return 0, cr.err
 		}
 	}
 	if uint64(len(b)) > cr.n {
 		b = b[0:cr.n]
 	}
 	n, cr.err = cr.r.Read(b)
 	cr.n -= uint64(n)
 	if cr.n == 0 && cr.err == nil {
 		// end of chunk (CRLF)
 		b := make([]byte, 2)
 		if _, cr.err = io.ReadFull(cr.r, b); cr.err == nil {
 			if b[0] != '\r' || b[1] != '\n' {
 				cr.err = os.NewError("malformed chunked encoding")
 			}
 		}
 	}
 	return n, cr.err
 }

 // ReadRequest reads and parses a request from b.
 func ReadRequest(b *bufio.Reader) (req *Request, err os.Error) {
 	req = new(Request)

 	// First line: GET /index.html HTTP/1.0
 	var s string
 	if s, err = readLine(b); err != nil {
 		return nil, err
 	}

 	var f []string
 	if f = strings.Split(s, " ", 3); len(f) < 3 {
 		return nil, &badStringError{"malformed HTTP request", s}
 	}
 	req.Method, req.RawURL, req.Proto = f[0], f[1], f[2]
 	var ok bool
 	if req.ProtoMajor, req.ProtoMinor, ok = parseHTTPVersion(req.Proto); !ok {
 		return nil, &badStringError{"malformed HTTP version", req.Proto}
 	}

 	if req.URL, err = ParseURL(req.RawURL); err != nil {
 		return nil, err
 	}

 	// Subsequent lines: Key: value.
 	nheader := 0
 	req.Header = make(map[string]string)
 	for {
 		var key, value string
 		if key, value, err = readKeyValue(b); err != nil {
 			return nil, err
 		}
 		if key == "" {
 			break
 		}
 		if nheader++; nheader >= maxHeaderLines {
 			return nil, ErrHeaderTooLong
 		}

 		key = CanonicalHeaderKey(key)

 		// RFC 2616 says that if you send the same header key
 		// multiple times, it has to be semantically equivalent
 		// to concatenating the values separated by commas.
 		oldvalue, present := req.Header[key]
 		if present {
 			req.Header[key] = oldvalue + "," + value
 		} else {
 			req.Header[key] = value
 		}
 	}

 	// RFC2616: Must treat
 	//	GET /index.html HTTP/1.1
 	//	Host: www.google.com
 	// and
 	//	GET http://www.google.com/index.html HTTP/1.1
 	//	Host: doesntmatter
 	// the same.  In the second case, any Host line is ignored.
 	req.Host = req.URL.Host
 	if req.Host == "" {
 		req.Host = req.Header["Host"]
 	}
 	req.Header["Host"] = "", false

 	fixPragmaCacheControl(req.Header)

 	// Pull out useful fields as a convenience to clients.
 	req.Referer = req.Header["Referer"]
 	req.Header["Referer"] = "", false

 	req.UserAgent = req.Header["User-Agent"]
 	req.Header["User-Agent"] = "", false

 	// TODO: Parse specific header values:
 	//	Accept
 	//	Accept-Encoding
 	//	Accept-Language
 	//	Authorization
 	//	Cache-Control
 	//	Connection
 	//	Date
 	//	Expect
 	//	From
 	//	If-Match
 	//	If-Modified-Since
 	//	If-None-Match
 	//	If-Range
 	//	If-Unmodified-Since
 	//	Max-Forwards
 	//	Proxy-Authorization
 	//	Referer [sic]
 	//	TE (transfer-codings)
 	//	Trailer
 	//	Transfer-Encoding
 	//	Upgrade
 	//	User-Agent
 	//	Via
 	//	Warning

 	err = readTransfer(req, b)
 	if err != nil {
 		return nil, err
 	}

 	return req, nil
 }

 // ParseQuery parses the URL-encoded query string and returns
 // a map listing the values specified for each key.
 // ParseQuery always returns a non-nil map containing all the
 // valid query parameters found; err describes the first decoding error
 // encountered, if any.
 func ParseQuery(query string) (m map[string][]string, err os.Error) {
 	m = make(map[string][]string)
 	err = parseQuery(m, query)
 	return
 }

 func parseQuery(m map[string][]string, query string) (err os.Error) {
 	for _, kv := range strings.Split(query, "&", -1) {
 		if len(kv) == 0 {
 			continue
 		}
 		kvPair := strings.Split(kv, "=", 2)

 		var key, value string
 		var e os.Error
 		key, e = URLUnescape(kvPair[0])
 		if e == nil && len(kvPair) > 1 {
 			value, e = URLUnescape(kvPair[1])
 		}
 		if e != nil {
 			err = e
 			continue
 		}
 		vec := vector.StringVector(m[key])
 		vec.Push(value)
 		m[key] = vec
 	}
 	return err
 }

 // ParseForm parses the request body as a form for POST requests, or the raw query for GET requests.
 // It is idempotent.
 func (r *Request) ParseForm() (err os.Error) {
 	if r.Form != nil {
 		return
 	}

 	r.Form = make(map[string][]string)
 	if r.URL != nil {
 		err = parseQuery(r.Form, r.URL.RawQuery)
 	}
 	if r.Method == "POST" {
 		if r.Body == nil {
 			return os.ErrorString("missing form body")
 		}
 		ct := r.Header["Content-Type"]
 		switch strings.Split(ct, ";", 2)[0] {
 		case "text/plain", "application/x-www-form-urlencoded", "":
 			b, e := ioutil.ReadAll(r.Body)
 			if e != nil {
 				if err == nil {
 					err = e
 				}
 				break
 			}
 			e = parseQuery(r.Form, string(b))
 			if err == nil {
 				err = e
 			}
 		// TODO(dsymonds): Handle multipart/form-data
 		default:
 			return &badStringError{"unknown Content-Type", ct}
 		}
 	}
 	return err
 }

 // FormValue returns the first value for the named component of the query.
 // FormValue calls ParseForm if necessary.
 func (r *Request) FormValue(key string) string {
 	if r.Form == nil {
 		r.ParseForm()
 	}
 	if vs := r.Form[key]; len(vs) > 0 {
 		return vs[0]
 	}
 	return ""
 }

 func (r *Request) expectsContinue() bool {
 	expectation, ok := r.Header["Expect"]
 	return ok && strings.ToLower(expectation) == "100-continue"
 }

 func (r *Request) wantsHttp10KeepAlive() bool {
 	if r.ProtoMajor != 1 || r.ProtoMinor != 0 {
 		return false
 	}
 	value, exists := r.Header["Connection"]
 	if !exists {
 		return false
 	}
 	return strings.Contains(strings.ToLower(value), "keep-alive")
 }
	// 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.

	// HTTP Request reading and parsing.

	// The http package implements parsing of HTTP requests, replies,
	// and URLs and provides an extensible HTTP server and a basic
	// HTTP client.
	package http

	import (
	"bufio"
	"bytes"
	"container/vector"
	"fmt"
	"io"
	"io/ioutil"
	"mime"
	"mime/multipart"
	"os"
	"strconv"
	"strings"
	)

	const (
	maxLineLength = 4096 // assumed <= bufio.defaultBufSize
	maxValueLength = 4096
	maxHeaderLines = 1024
	chunkSize = 4 << 10 // 4 KB chunks
	)

	// HTTP request parsing errors.
	type ProtocolError struct {
	os.ErrorString
	}

	var (
	ErrLineTooLong = &ProtocolError{"header line too long"}
	ErrHeaderTooLong = &ProtocolError{"header too long"}
	ErrShortBody = &ProtocolError{"entity body too short"}
	ErrNotSupported = &ProtocolError{"feature not supported"}
	ErrUnexpectedTrailer = &ProtocolError{"trailer header without chunked transfer encoding"}
	ErrMissingContentLength = &ProtocolError{"missing ContentLength in HEAD response"}
	ErrNotMultipart = &ProtocolError{"request Content-Type isn't multipart/form-data"}
	ErrMissingBoundary = &ProtocolError{"no multipart boundary param Content-Type"}
	)

	type badStringError struct {
	what string
	str string
	}

	func (e *badStringError) String() string { return fmt.Sprintf("%s %q", e.what, e.str) }

	var reqExcludeHeader = map[string]bool{
	"Host": true,
	"User-Agent": true,
	"Referer": true,
	"Content-Length": true,
	"Transfer-Encoding": true,
	"Trailer": true,
	}

	// A Request represents a parsed HTTP request header.
	type Request struct {
	Method string // GET, POST, PUT, etc.
	RawURL string // The raw URL given in the request.
	URL *URL // Parsed URL.
	Proto string // "HTTP/1.0"
	ProtoMajor int // 1
	ProtoMinor int // 0

	// A header maps request lines to their values.
	// If the header says
	//
	// accept-encoding: gzip, deflate
	// Accept-Language: en-us
	// Connection: keep-alive
	//
	// then
	//
	// Header = map[string]string{
	// "Accept-Encoding": "gzip, deflate",
	// "Accept-Language": "en-us",
	// "Connection": "keep-alive",
	// }
	//
	// HTTP defines that header names are case-insensitive.
	// The request parser implements this by canonicalizing the
	// name, making the first character and any characters
	// following a hyphen uppercase and the rest lowercase.
	Header map[string]string

	// 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

	// The host on which the URL is sought.
	// Per RFC 2616, this is either the value of the Host: header
	// or the host name given in the URL itself.
	Host string

	// The referring URL, if sent in the request.
	//
	// Referer is misspelled as in the request itself,
	// a mistake from the earliest days of HTTP.
	// This value can also be fetched from the Header map
	// as Header["Referer"]; the benefit of making it
	// available as a structure field is that the compiler
	// can diagnose programs that use the alternate
	// (correct English) spelling req.Referrer but cannot
	// diagnose programs that use Header["Referrer"].
	Referer string

	// The User-Agent: header string, if sent in the request.
	UserAgent string

	// 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
	// in the request is at least major.minor.
	func (r *Request) ProtoAtLeast(major, minor int) bool {
	return r.ProtoMajor > major \|\|
	r.ProtoMajor == major && r.ProtoMinor >= minor
	}

	// MultipartReader returns a MIME multipart reader if this is a
	// multipart/form-data POST request, else returns nil and an error.
	func (r *Request) MultipartReader() (multipart.Reader, os.Error) {
	v, ok := r.Header["Content-Type"]
	if !ok {
	return nil, ErrNotMultipart
	}
	d, params := mime.ParseMediaType(v)
	if d != "multipart/form-data" {
	return nil, ErrNotMultipart
	}
	boundary, ok := params["boundary"]
	if !ok {
	return nil, ErrMissingBoundary
	}
	return multipart.NewReader(r.Body, boundary), nil
	}

	// Return value if nonempty, def otherwise.
	func valueOrDefault(value, def string) string {
	if value != "" {
	return value
	}
	return def
	}

	const defaultUserAgent = "Go http package"

	// Write writes an HTTP/1.1 request -- header and body -- in wire format.
	// This method consults the following fields of req:
	// Host
	// RawURL, if non-empty, or else URL
	// Method (defaults to "GET")
	// UserAgent (defaults to defaultUserAgent)
	// Referer
	// Header
	// Body
	//
	// If Body is present, Write forces "Transfer-Encoding: chunked" as a header
	// and then closes Body when finished sending it.
	func (req *Request) Write(w io.Writer) os.Error {
	host := req.Host
	if host == "" {
	host = req.URL.Host
	}

	uri := req.RawURL
	if uri == "" {
	uri = valueOrDefault(urlEscape(req.URL.Path, encodePath), "/")
	if req.URL.RawQuery != "" {
	uri += "?" + req.URL.RawQuery
	}
	}

	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)
	}

	// 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)
	// TODO: if Header includes values for Host, User-Agent, or Referer, this
	// may conflict with the User-Agent or Referer headers we add manually.
	// One solution would be to remove the Host, UserAgent, and Referer fields
	// 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)
	if err != nil {
	return err
	}

	io.WriteString(w, "\r\n")

	// Write body and trailer
	err = tw.WriteBody(w)
	if err != nil {
	return err
	}

	return nil
	}

	// Read a line of bytes (up to \n) from b.
	// Give up if the line exceeds maxLineLength.
	// The returned bytes are a pointer into storage in
	// the bufio, so they are only valid until the next bufio read.
	func readLineBytes(b *bufio.Reader) (p []byte, err os.Error) {
	if p, err = b.ReadSlice('\n'); err != nil {
	// We always know when EOF is coming.
	// If the caller asked for a line, there should be a line.
	if err == os.EOF {
	err = io.ErrUnexpectedEOF
	} else if err == bufio.ErrBufferFull {
	err = ErrLineTooLong
	}
	return nil, err
	}
	if len(p) >= maxLineLength {
	return nil, ErrLineTooLong
	}

	// Chop off trailing white space.
	var i int
	for i = len(p); i > 0; i-- {
	if c := p[i-1]; c != ' ' && c != '\r' && c != '\t' && c != '\n' {
	break
	}
	}
	return p[0:i], nil
	}

	// readLineBytes, but convert the bytes into a string.
	func readLine(b *bufio.Reader) (s string, err os.Error) {
	p, e := readLineBytes(b)
	if e != nil {
	return "", e
	}
	return string(p), nil
	}

	var colon = []byte{':'}

	// Read a key/value pair from b.
	// A key/value has the form Key: Value\r\n
	// and the Value can continue on multiple lines if each continuation line
	// starts with a space.
	func readKeyValue(b *bufio.Reader) (key, value string, err os.Error) {
	line, e := readLineBytes(b)
	if e != nil {
	return "", "", e
	}
	if len(line) == 0 {
	return "", "", nil
	}

	// Scan first line for colon.
	i := bytes.Index(line, colon)
	if i < 0 {
	goto Malformed
	}

	key = string(line[0:i])
	if strings.Contains(key, " ") {
	// Key field has space - no good.
	goto Malformed
	}

	// Skip initial space before value.
	for i++; i < len(line); i++ {
	if line[i] != ' ' {
	break
	}
	}
	value = string(line[i:])

	// Look for extension lines, which must begin with space.
	for {
	c, e := b.ReadByte()
	if c != ' ' {
	if e != os.EOF {
	b.UnreadByte()
	}
	break
	}

	// Eat leading space.
	for c == ' ' {
	if c, e = b.ReadByte(); e != nil {
	if e == os.EOF {
	e = io.ErrUnexpectedEOF
	}
	return "", "", e
	}
	}
	b.UnreadByte()

	// Read the rest of the line and add to value.
	if line, e = readLineBytes(b); e != nil {
	return "", "", e
	}
	value += " " + string(line)

	if len(value) >= maxValueLength {
	return "", "", &badStringError{"value too long for key", key}
	}
	}
	return key, value, nil

	Malformed:
	return "", "", &badStringError{"malformed header line", string(line)}
	}

	// Convert decimal at s[i:len(s)] to integer,
	// returning value, string position where the digits stopped,
	// and whether there was a valid number (digits, not too big).
	func atoi(s string, i int) (n, i1 int, ok bool) {
	const Big = 1000000
	if i >= len(s) \|\| s[i] < '0' \|\| s[i] > '9' {
	return 0, 0, false
	}
	n = 0
	for ; i < len(s) && '0' <= s[i] && s[i] <= '9'; i++ {
	n = n*10 + int(s[i]-'0')
	if n > Big {
	return 0, 0, false
	}
	}
	return n, i, true
	}

	// Parse HTTP version: "HTTP/1.2" -> (1, 2, true).
	func parseHTTPVersion(vers string) (int, int, bool) {
	if len(vers) < 5 \|\| vers[0:5] != "HTTP/" {
	return 0, 0, false
	}
	major, i, ok := atoi(vers, 5)
	if !ok \|\| i >= len(vers) \|\| vers[i] != '.' {
	return 0, 0, false
	}
	var minor int
	minor, i, ok = atoi(vers, i+1)
	if !ok \|\| i != len(vers) {
	return 0, 0, false
	}
	return major, minor, true
	}

	// CanonicalHeaderKey returns the canonical format of the
	// HTTP header key s. The canonicalization converts the first
	// letter and any letter following a hyphen to upper case;
	// the rest are converted to lowercase. For example, the
	// canonical key for "accept-encoding" is "Accept-Encoding".
	func CanonicalHeaderKey(s string) string {
	// canonicalize: first letter upper case
	// and upper case after each dash.
	// (Host, User-Agent, If-Modified-Since).
	// HTTP headers are ASCII only, so no Unicode issues.
	var a []byte
	upper := true
	for i := 0; i < len(s); i++ {
	v := s[i]
	if upper && 'a' <= v && v <= 'z' {
	if a == nil {
	a = []byte(s)
	}
	a[i] = v + 'A' - 'a'
	}
	if !upper && 'A' <= v && v <= 'Z' {
	if a == nil {
	a = []byte(s)
	}
	a[i] = v + 'a' - 'A'
	}
	upper = false
	if v == '-' {
	upper = true
	}
	}
	if a != nil {
	return string(a)
	}
	return s
	}

	type chunkedReader struct {
	r *bufio.Reader
	n uint64 // unread bytes in chunk
	err os.Error
	}

	func newChunkedReader(r bufio.Reader) chunkedReader {
	return &chunkedReader{r: r}
	}

	func (cr *chunkedReader) beginChunk() {
	// chunk-size CRLF
	var line string
	line, cr.err = readLine(cr.r)
	if cr.err != nil {
	return
	}
	cr.n, cr.err = strconv.Btoui64(line, 16)
	if cr.err != nil {
	return
	}
	if cr.n == 0 {
	// trailer CRLF
	for {
	line, cr.err = readLine(cr.r)
	if cr.err != nil {
	return
	}
	if line == "" {
	break
	}
	}
	cr.err = os.EOF
	}
	}

	func (cr *chunkedReader) Read(b []uint8) (n int, err os.Error) {
	if cr.err != nil {
	return 0, cr.err
	}
	if cr.n == 0 {
	cr.beginChunk()
	if cr.err != nil {
	return 0, cr.err
	}
	}
	if uint64(len(b)) > cr.n {
	b = b[0:cr.n]
	}
	n, cr.err = cr.r.Read(b)
	cr.n -= uint64(n)
	if cr.n == 0 && cr.err == nil {
	// end of chunk (CRLF)
	b := make([]byte, 2)
	if _, cr.err = io.ReadFull(cr.r, b); cr.err == nil {
	if b[0] != '\r' \|\| b[1] != '\n' {
	cr.err = os.NewError("malformed chunked encoding")
	}
	}
	}
	return n, cr.err
	}

	// ReadRequest reads and parses a request from b.
	func ReadRequest(b bufio.Reader) (req Request, err os.Error) {
	req = new(Request)

	// First line: GET /index.html HTTP/1.0
	var s string
	if s, err = readLine(b); err != nil {
	return nil, err
	}

	var f []string
	if f = strings.Split(s, " ", 3); len(f) < 3 {
	return nil, &badStringError{"malformed HTTP request", s}
	}
	req.Method, req.RawURL, req.Proto = f[0], f[1], f[2]
	var ok bool
	if req.ProtoMajor, req.ProtoMinor, ok = parseHTTPVersion(req.Proto); !ok {
	return nil, &badStringError{"malformed HTTP version", req.Proto}
	}

	if req.URL, err = ParseURL(req.RawURL); err != nil {
	return nil, err
	}

	// Subsequent lines: Key: value.
	nheader := 0
	req.Header = make(map[string]string)
	for {
	var key, value string
	if key, value, err = readKeyValue(b); err != nil {
	return nil, err
	}
	if key == "" {
	break
	}
	if nheader++; nheader >= maxHeaderLines {
	return nil, ErrHeaderTooLong
	}

	key = CanonicalHeaderKey(key)

	// RFC 2616 says that if you send the same header key
	// multiple times, it has to be semantically equivalent
	// to concatenating the values separated by commas.
	oldvalue, present := req.Header[key]
	if present {
	req.Header[key] = oldvalue + "," + value
	} else {
	req.Header[key] = value
	}
	}

	// RFC2616: Must treat
	// GET /index.html HTTP/1.1
	// Host: www.google.com
	// and
	// GET http://www.google.com/index.html HTTP/1.1
	// Host: doesntmatter
	// the same. In the second case, any Host line is ignored.
	req.Host = req.URL.Host
	if req.Host == "" {
	req.Host = req.Header["Host"]
	}
	req.Header["Host"] = "", false

	fixPragmaCacheControl(req.Header)

	// Pull out useful fields as a convenience to clients.
	req.Referer = req.Header["Referer"]
	req.Header["Referer"] = "", false

	req.UserAgent = req.Header["User-Agent"]
	req.Header["User-Agent"] = "", false

	// TODO: Parse specific header values:
	// Accept
	// Accept-Encoding
	// Accept-Language
	// Authorization
	// Cache-Control
	// Connection
	// Date
	// Expect
	// From
	// If-Match
	// If-Modified-Since
	// If-None-Match
	// If-Range
	// If-Unmodified-Since
	// Max-Forwards
	// Proxy-Authorization
	// Referer [sic]
	// TE (transfer-codings)
	// Trailer
	// Transfer-Encoding
	// Upgrade
	// User-Agent
	// Via
	// Warning

	err = readTransfer(req, b)
	if err != nil {
	return nil, err
	}

	return req, nil
	}

	// ParseQuery parses the URL-encoded query string and returns
	// a map listing the values specified for each key.
	// ParseQuery always returns a non-nil map containing all the
	// valid query parameters found; err describes the first decoding error
	// encountered, if any.
	func ParseQuery(query string) (m map[string][]string, err os.Error) {
	m = make(map[string][]string)
	err = parseQuery(m, query)
	return
	}

	func parseQuery(m map[string][]string, query string) (err os.Error) {
	for _, kv := range strings.Split(query, "&", -1) {
	if len(kv) == 0 {
	continue
	}
	kvPair := strings.Split(kv, "=", 2)

	var key, value string
	var e os.Error
	key, e = URLUnescape(kvPair[0])
	if e == nil && len(kvPair) > 1 {
	value, e = URLUnescape(kvPair[1])
	}
	if e != nil {
	err = e
	continue
	}
	vec := vector.StringVector(m[key])
	vec.Push(value)
	m[key] = vec
	}
	return err
	}

	// ParseForm parses the request body as a form for POST requests, or the raw query for GET requests.
	// It is idempotent.
	func (r *Request) ParseForm() (err os.Error) {
	if r.Form != nil {
	return
	}

	r.Form = make(map[string][]string)
	if r.URL != nil {
	err = parseQuery(r.Form, r.URL.RawQuery)
	}
	if r.Method == "POST" {
	if r.Body == nil {
	return os.ErrorString("missing form body")
	}
	ct := r.Header["Content-Type"]
	switch strings.Split(ct, ";", 2)[0] {
	case "text/plain", "application/x-www-form-urlencoded", "":
	b, e := ioutil.ReadAll(r.Body)
	if e != nil {
	if err == nil {
	err = e
	}
	break
	}
	e = parseQuery(r.Form, string(b))
	if err == nil {
	err = e
	}
	// TODO(dsymonds): Handle multipart/form-data
	default:
	return &badStringError{"unknown Content-Type", ct}
	}
	}
	return err
	}

	// FormValue returns the first value for the named component of the query.
	// FormValue calls ParseForm if necessary.
	func (r *Request) FormValue(key string) string {
	if r.Form == nil {
	r.ParseForm()
	}
	if vs := r.Form[key]; len(vs) > 0 {
	return vs[0]
	}
	return ""
	}

	func (r *Request) expectsContinue() bool {
	expectation, ok := r.Header["Expect"]
	return ok && strings.ToLower(expectation) == "100-continue"
	}

	func (r *Request) wantsHttp10KeepAlive() bool {
	if r.ProtoMajor != 1 \|\| r.ProtoMinor != 0 {
	return false
	}
	value, exists := r.Header["Connection"]
	if !exists {
	return false
	}
	return strings.Contains(strings.ToLower(value), "keep-alive")
	}