vendor/github.com/gorilla/websocket/server.go - voltha-go - Gitiles

 // Copyright 2013 The Gorilla WebSocket 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 websocket

 import (
 	"bufio"
 	"errors"
 	"io"
 	"net/http"
 	"net/url"
 	"strings"
 	"time"
 )

 // HandshakeError describes an error with the handshake from the peer.
 type HandshakeError struct {
 	message string
 }

 func (e HandshakeError) Error() string { return e.message }

 // Upgrader specifies parameters for upgrading an HTTP connection to a
 // WebSocket connection.
 type Upgrader struct {
 	// HandshakeTimeout specifies the duration for the handshake to complete.
 	HandshakeTimeout time.Duration

 	// ReadBufferSize and WriteBufferSize specify I/O buffer sizes in bytes. If a buffer
 	// size is zero, then buffers allocated by the HTTP server are used. The
 	// I/O buffer sizes do not limit the size of the messages that can be sent
 	// or received.
 	ReadBufferSize, WriteBufferSize int

 	// WriteBufferPool is a pool of buffers for write operations. If the value
 	// is not set, then write buffers are allocated to the connection for the
 	// lifetime of the connection.
 	//
 	// A pool is most useful when the application has a modest volume of writes
 	// across a large number of connections.
 	//
 	// Applications should use a single pool for each unique value of
 	// WriteBufferSize.
 	WriteBufferPool BufferPool

 	// Subprotocols specifies the server's supported protocols in order of
 	// preference. If this field is not nil, then the Upgrade method negotiates a
 	// subprotocol by selecting the first match in this list with a protocol
 	// requested by the client. If there's no match, then no protocol is
 	// negotiated (the Sec-Websocket-Protocol header is not included in the
 	// handshake response).
 	Subprotocols []string

 	// Error specifies the function for generating HTTP error responses. If Error
 	// is nil, then http.Error is used to generate the HTTP response.
 	Error func(w http.ResponseWriter, r *http.Request, status int, reason error)

 	// CheckOrigin returns true if the request Origin header is acceptable. If
 	// CheckOrigin is nil, then a safe default is used: return false if the
 	// Origin request header is present and the origin host is not equal to
 	// request Host header.
 	//
 	// A CheckOrigin function should carefully validate the request origin to
 	// prevent cross-site request forgery.
 	CheckOrigin func(r *http.Request) bool

 	// EnableCompression specify if the server should attempt to negotiate per
 	// message compression (RFC 7692). Setting this value to true does not
 	// guarantee that compression will be supported. Currently only "no context
 	// takeover" modes are supported.
 	EnableCompression bool
 }

 func (u *Upgrader) returnError(w http.ResponseWriter, r *http.Request, status int, reason string) (*Conn, error) {
 	err := HandshakeError{reason}
 	if u.Error != nil {
 		u.Error(w, r, status, err)
 	} else {
 		w.Header().Set("Sec-Websocket-Version", "13")
 		http.Error(w, http.StatusText(status), status)
 	}
 	return nil, err
 }

 // checkSameOrigin returns true if the origin is not set or is equal to the request host.
 func checkSameOrigin(r *http.Request) bool {
 	origin := r.Header["Origin"]
 	if len(origin) == 0 {
 		return true
 	}
 	u, err := url.Parse(origin[0])
 	if err != nil {
 		return false
 	}
 	return equalASCIIFold(u.Host, r.Host)
 }

 func (u *Upgrader) selectSubprotocol(r *http.Request, responseHeader http.Header) string {
 	if u.Subprotocols != nil {
 		clientProtocols := Subprotocols(r)
 		for _, serverProtocol := range u.Subprotocols {
 			for _, clientProtocol := range clientProtocols {
 				if clientProtocol == serverProtocol {
 					return clientProtocol
 				}
 			}
 		}
 	} else if responseHeader != nil {
 		return responseHeader.Get("Sec-Websocket-Protocol")
 	}
 	return ""
 }

 // Upgrade upgrades the HTTP server connection to the WebSocket protocol.
 //
 // The responseHeader is included in the response to the client's upgrade
 // request. Use the responseHeader to specify cookies (Set-Cookie) and the
 // application negotiated subprotocol (Sec-WebSocket-Protocol).
 //
 // If the upgrade fails, then Upgrade replies to the client with an HTTP error
 // response.
 func (u *Upgrader) Upgrade(w http.ResponseWriter, r *http.Request, responseHeader http.Header) (*Conn, error) {
 	const badHandshake = "websocket: the client is not using the websocket protocol: "

 	if !tokenListContainsValue(r.Header, "Connection", "upgrade") {
 		return u.returnError(w, r, http.StatusBadRequest, badHandshake+"'upgrade' token not found in 'Connection' header")
 	}

 	if !tokenListContainsValue(r.Header, "Upgrade", "websocket") {
 		return u.returnError(w, r, http.StatusBadRequest, badHandshake+"'websocket' token not found in 'Upgrade' header")
 	}

 	if r.Method != "GET" {
 		return u.returnError(w, r, http.StatusMethodNotAllowed, badHandshake+"request method is not GET")
 	}

 	if !tokenListContainsValue(r.Header, "Sec-Websocket-Version", "13") {
 		return u.returnError(w, r, http.StatusBadRequest, "websocket: unsupported version: 13 not found in 'Sec-Websocket-Version' header")
 	}

 	if _, ok := responseHeader["Sec-Websocket-Extensions"]; ok {
 		return u.returnError(w, r, http.StatusInternalServerError, "websocket: application specific 'Sec-WebSocket-Extensions' headers are unsupported")
 	}

 	checkOrigin := u.CheckOrigin
 	if checkOrigin == nil {
 		checkOrigin = checkSameOrigin
 	}
 	if !checkOrigin(r) {
 		return u.returnError(w, r, http.StatusForbidden, "websocket: request origin not allowed by Upgrader.CheckOrigin")
 	}

 	challengeKey := r.Header.Get("Sec-Websocket-Key")
 	if challengeKey == "" {
 		return u.returnError(w, r, http.StatusBadRequest, "websocket: not a websocket handshake: 'Sec-WebSocket-Key' header is missing or blank")
 	}

 	subprotocol := u.selectSubprotocol(r, responseHeader)

 	// Negotiate PMCE
 	var compress bool
 	if u.EnableCompression {
 		for _, ext := range parseExtensions(r.Header) {
 			if ext[""] != "permessage-deflate" {
 				continue
 			}
 			compress = true
 			break
 		}
 	}

 	h, ok := w.(http.Hijacker)
 	if !ok {
 		return u.returnError(w, r, http.StatusInternalServerError, "websocket: response does not implement http.Hijacker")
 	}
 	var brw *bufio.ReadWriter
 	netConn, brw, err := h.Hijack()
 	if err != nil {
 		return u.returnError(w, r, http.StatusInternalServerError, err.Error())
 	}

 	if brw.Reader.Buffered() > 0 {
 		netConn.Close()
 		return nil, errors.New("websocket: client sent data before handshake is complete")
 	}

 	var br *bufio.Reader
 	if u.ReadBufferSize == 0 && bufioReaderSize(netConn, brw.Reader) > 256 {
 		// Reuse hijacked buffered reader as connection reader.
 		br = brw.Reader
 	}

 	buf := bufioWriterBuffer(netConn, brw.Writer)

 	var writeBuf []byte
 	if u.WriteBufferPool == nil && u.WriteBufferSize == 0 && len(buf) >= maxFrameHeaderSize+256 {
 		// Reuse hijacked write buffer as connection buffer.
 		writeBuf = buf
 	}

 	c := newConn(netConn, true, u.ReadBufferSize, u.WriteBufferSize, u.WriteBufferPool, br, writeBuf)
 	c.subprotocol = subprotocol

 	if compress {
 		c.newCompressionWriter = compressNoContextTakeover
 		c.newDecompressionReader = decompressNoContextTakeover
 	}

 	// Use larger of hijacked buffer and connection write buffer for header.
 	p := buf
 	if len(c.writeBuf) > len(p) {
 		p = c.writeBuf
 	}
 	p = p[:0]

 	p = append(p, "HTTP/1.1 101 Switching Protocols\r\nUpgrade: websocket\r\nConnection: Upgrade\r\nSec-WebSocket-Accept: "...)
 	p = append(p, computeAcceptKey(challengeKey)...)
 	p = append(p, "\r\n"...)
 	if c.subprotocol != "" {
 		p = append(p, "Sec-WebSocket-Protocol: "...)
 		p = append(p, c.subprotocol...)
 		p = append(p, "\r\n"...)
 	}
 	if compress {
 		p = append(p, "Sec-WebSocket-Extensions: permessage-deflate; server_no_context_takeover; client_no_context_takeover\r\n"...)
 	}
 	for k, vs := range responseHeader {
 		if k == "Sec-Websocket-Protocol" {
 			continue
 		}
 		for _, v := range vs {
 			p = append(p, k...)
 			p = append(p, ": "...)
 			for i := 0; i < len(v); i++ {
 				b := v[i]
 				if b <= 31 {
 					// prevent response splitting.
 					b = ' '
 				}
 				p = append(p, b)
 			}
 			p = append(p, "\r\n"...)
 		}
 	}
 	p = append(p, "\r\n"...)

 	// Clear deadlines set by HTTP server.
 	netConn.SetDeadline(time.Time{})

 	if u.HandshakeTimeout > 0 {
 		netConn.SetWriteDeadline(time.Now().Add(u.HandshakeTimeout))
 	}
 	if _, err = netConn.Write(p); err != nil {
 		netConn.Close()
 		return nil, err
 	}
 	if u.HandshakeTimeout > 0 {
 		netConn.SetWriteDeadline(time.Time{})
 	}

 	return c, nil
 }

 // Upgrade upgrades the HTTP server connection to the WebSocket protocol.
 //
 // Deprecated: Use websocket.Upgrader instead.
 //
 // Upgrade does not perform origin checking. The application is responsible for
 // checking the Origin header before calling Upgrade. An example implementation
 // of the same origin policy check is:
 //
 //	if req.Header.Get("Origin") != "http://"+req.Host {
 //		http.Error(w, "Origin not allowed", http.StatusForbidden)
 //		return
 //	}
 //
 // If the endpoint supports subprotocols, then the application is responsible
 // for negotiating the protocol used on the connection. Use the Subprotocols()
 // function to get the subprotocols requested by the client. Use the
 // Sec-Websocket-Protocol response header to specify the subprotocol selected
 // by the application.
 //
 // The responseHeader is included in the response to the client's upgrade
 // request. Use the responseHeader to specify cookies (Set-Cookie) and the
 // negotiated subprotocol (Sec-Websocket-Protocol).
 //
 // The connection buffers IO to the underlying network connection. The
 // readBufSize and writeBufSize parameters specify the size of the buffers to
 // use. Messages can be larger than the buffers.
 //
 // If the request is not a valid WebSocket handshake, then Upgrade returns an
 // error of type HandshakeError. Applications should handle this error by
 // replying to the client with an HTTP error response.
 func Upgrade(w http.ResponseWriter, r *http.Request, responseHeader http.Header, readBufSize, writeBufSize int) (*Conn, error) {
 	u := Upgrader{ReadBufferSize: readBufSize, WriteBufferSize: writeBufSize}
 	u.Error = func(w http.ResponseWriter, r *http.Request, status int, reason error) {
 		// don't return errors to maintain backwards compatibility
 	}
 	u.CheckOrigin = func(r *http.Request) bool {
 		// allow all connections by default
 		return true
 	}
 	return u.Upgrade(w, r, responseHeader)
 }

 // Subprotocols returns the subprotocols requested by the client in the
 // Sec-Websocket-Protocol header.
 func Subprotocols(r *http.Request) []string {
 	h := strings.TrimSpace(r.Header.Get("Sec-Websocket-Protocol"))
 	if h == "" {
 		return nil
 	}
 	protocols := strings.Split(h, ",")
 	for i := range protocols {
 		protocols[i] = strings.TrimSpace(protocols[i])
 	}
 	return protocols
 }

 // IsWebSocketUpgrade returns true if the client requested upgrade to the
 // WebSocket protocol.
 func IsWebSocketUpgrade(r *http.Request) bool {
 	return tokenListContainsValue(r.Header, "Connection", "upgrade") &&
 		tokenListContainsValue(r.Header, "Upgrade", "websocket")
 }

 // bufioReaderSize size returns the size of a bufio.Reader.
 func bufioReaderSize(originalReader io.Reader, br *bufio.Reader) int {
 	// This code assumes that peek on a reset reader returns
 	// bufio.Reader.buf[:0].
 	// TODO: Use bufio.Reader.Size() after Go 1.10
 	br.Reset(originalReader)
 	if p, err := br.Peek(0); err == nil {
 		return cap(p)
 	}
 	return 0
 }

 // writeHook is an io.Writer that records the last slice passed to it vio
 // io.Writer.Write.
 type writeHook struct {
 	p []byte
 }

 func (wh *writeHook) Write(p []byte) (int, error) {
 	wh.p = p
 	return len(p), nil
 }

 // bufioWriterBuffer grabs the buffer from a bufio.Writer.
 func bufioWriterBuffer(originalWriter io.Writer, bw *bufio.Writer) []byte {
 	// This code assumes that bufio.Writer.buf[:1] is passed to the
 	// bufio.Writer's underlying writer.
 	var wh writeHook
 	bw.Reset(&wh)
 	bw.WriteByte(0)
 	bw.Flush()

 	bw.Reset(originalWriter)

 	return wh.p[:cap(wh.p)]
 }
	// Copyright 2013 The Gorilla WebSocket 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 websocket

	import (
	"bufio"
	"errors"
	"io"
	"net/http"
	"net/url"
	"strings"
	"time"
	)

	// HandshakeError describes an error with the handshake from the peer.
	type HandshakeError struct {
	message string
	}

	func (e HandshakeError) Error() string { return e.message }

	// Upgrader specifies parameters for upgrading an HTTP connection to a
	// WebSocket connection.
	type Upgrader struct {
	// HandshakeTimeout specifies the duration for the handshake to complete.
	HandshakeTimeout time.Duration

	// ReadBufferSize and WriteBufferSize specify I/O buffer sizes in bytes. If a buffer
	// size is zero, then buffers allocated by the HTTP server are used. The
	// I/O buffer sizes do not limit the size of the messages that can be sent
	// or received.
	ReadBufferSize, WriteBufferSize int

	// WriteBufferPool is a pool of buffers for write operations. If the value
	// is not set, then write buffers are allocated to the connection for the
	// lifetime of the connection.
	//
	// A pool is most useful when the application has a modest volume of writes
	// across a large number of connections.
	//
	// Applications should use a single pool for each unique value of
	// WriteBufferSize.
	WriteBufferPool BufferPool

	// Subprotocols specifies the server's supported protocols in order of
	// preference. If this field is not nil, then the Upgrade method negotiates a
	// subprotocol by selecting the first match in this list with a protocol
	// requested by the client. If there's no match, then no protocol is
	// negotiated (the Sec-Websocket-Protocol header is not included in the
	// handshake response).
	Subprotocols []string

	// Error specifies the function for generating HTTP error responses. If Error
	// is nil, then http.Error is used to generate the HTTP response.
	Error func(w http.ResponseWriter, r *http.Request, status int, reason error)

	// CheckOrigin returns true if the request Origin header is acceptable. If
	// CheckOrigin is nil, then a safe default is used: return false if the
	// Origin request header is present and the origin host is not equal to
	// request Host header.
	//
	// A CheckOrigin function should carefully validate the request origin to
	// prevent cross-site request forgery.
	CheckOrigin func(r *http.Request) bool

	// EnableCompression specify if the server should attempt to negotiate per
	// message compression (RFC 7692). Setting this value to true does not
	// guarantee that compression will be supported. Currently only "no context
	// takeover" modes are supported.
	EnableCompression bool
	}

	func (u Upgrader) returnError(w http.ResponseWriter, r http.Request, status int, reason string) (*Conn, error) {
	err := HandshakeError{reason}
	if u.Error != nil {
	u.Error(w, r, status, err)
	} else {
	w.Header().Set("Sec-Websocket-Version", "13")
	http.Error(w, http.StatusText(status), status)
	}
	return nil, err
	}

	// checkSameOrigin returns true if the origin is not set or is equal to the request host.
	func checkSameOrigin(r *http.Request) bool {
	origin := r.Header["Origin"]
	if len(origin) == 0 {
	return true
	}
	u, err := url.Parse(origin[0])
	if err != nil {
	return false
	}
	return equalASCIIFold(u.Host, r.Host)
	}

	func (u Upgrader) selectSubprotocol(r http.Request, responseHeader http.Header) string {
	if u.Subprotocols != nil {
	clientProtocols := Subprotocols(r)
	for _, serverProtocol := range u.Subprotocols {
	for _, clientProtocol := range clientProtocols {
	if clientProtocol == serverProtocol {
	return clientProtocol
	}
	}
	}
	} else if responseHeader != nil {
	return responseHeader.Get("Sec-Websocket-Protocol")
	}
	return ""
	}

	// Upgrade upgrades the HTTP server connection to the WebSocket protocol.
	//
	// The responseHeader is included in the response to the client's upgrade
	// request. Use the responseHeader to specify cookies (Set-Cookie) and the
	// application negotiated subprotocol (Sec-WebSocket-Protocol).
	//
	// If the upgrade fails, then Upgrade replies to the client with an HTTP error
	// response.
	func (u Upgrader) Upgrade(w http.ResponseWriter, r http.Request, responseHeader http.Header) (*Conn, error) {
	const badHandshake = "websocket: the client is not using the websocket protocol: "

	if !tokenListContainsValue(r.Header, "Connection", "upgrade") {
	return u.returnError(w, r, http.StatusBadRequest, badHandshake+"'upgrade' token not found in 'Connection' header")
	}

	if !tokenListContainsValue(r.Header, "Upgrade", "websocket") {
	return u.returnError(w, r, http.StatusBadRequest, badHandshake+"'websocket' token not found in 'Upgrade' header")
	}

	if r.Method != "GET" {
	return u.returnError(w, r, http.StatusMethodNotAllowed, badHandshake+"request method is not GET")
	}

	if !tokenListContainsValue(r.Header, "Sec-Websocket-Version", "13") {
	return u.returnError(w, r, http.StatusBadRequest, "websocket: unsupported version: 13 not found in 'Sec-Websocket-Version' header")
	}

	if _, ok := responseHeader["Sec-Websocket-Extensions"]; ok {
	return u.returnError(w, r, http.StatusInternalServerError, "websocket: application specific 'Sec-WebSocket-Extensions' headers are unsupported")
	}

	checkOrigin := u.CheckOrigin
	if checkOrigin == nil {
	checkOrigin = checkSameOrigin
	}
	if !checkOrigin(r) {
	return u.returnError(w, r, http.StatusForbidden, "websocket: request origin not allowed by Upgrader.CheckOrigin")
	}

	challengeKey := r.Header.Get("Sec-Websocket-Key")
	if challengeKey == "" {
	return u.returnError(w, r, http.StatusBadRequest, "websocket: not a websocket handshake: 'Sec-WebSocket-Key' header is missing or blank")
	}

	subprotocol := u.selectSubprotocol(r, responseHeader)

	// Negotiate PMCE
	var compress bool
	if u.EnableCompression {
	for _, ext := range parseExtensions(r.Header) {
	if ext[""] != "permessage-deflate" {
	continue
	}
	compress = true
	break
	}
	}

	h, ok := w.(http.Hijacker)
	if !ok {
	return u.returnError(w, r, http.StatusInternalServerError, "websocket: response does not implement http.Hijacker")
	}
	var brw *bufio.ReadWriter
	netConn, brw, err := h.Hijack()
	if err != nil {
	return u.returnError(w, r, http.StatusInternalServerError, err.Error())
	}

	if brw.Reader.Buffered() > 0 {
	netConn.Close()
	return nil, errors.New("websocket: client sent data before handshake is complete")
	}

	var br *bufio.Reader
	if u.ReadBufferSize == 0 && bufioReaderSize(netConn, brw.Reader) > 256 {
	// Reuse hijacked buffered reader as connection reader.
	br = brw.Reader
	}

	buf := bufioWriterBuffer(netConn, brw.Writer)

	var writeBuf []byte
	if u.WriteBufferPool == nil && u.WriteBufferSize == 0 && len(buf) >= maxFrameHeaderSize+256 {
	// Reuse hijacked write buffer as connection buffer.
	writeBuf = buf
	}

	c := newConn(netConn, true, u.ReadBufferSize, u.WriteBufferSize, u.WriteBufferPool, br, writeBuf)
	c.subprotocol = subprotocol

	if compress {
	c.newCompressionWriter = compressNoContextTakeover
	c.newDecompressionReader = decompressNoContextTakeover
	}

	// Use larger of hijacked buffer and connection write buffer for header.
	p := buf
	if len(c.writeBuf) > len(p) {
	p = c.writeBuf
	}
	p = p[:0]

	p = append(p, "HTTP/1.1 101 Switching Protocols\r\nUpgrade: websocket\r\nConnection: Upgrade\r\nSec-WebSocket-Accept: "...)
	p = append(p, computeAcceptKey(challengeKey)...)
	p = append(p, "\r\n"...)
	if c.subprotocol != "" {
	p = append(p, "Sec-WebSocket-Protocol: "...)
	p = append(p, c.subprotocol...)
	p = append(p, "\r\n"...)
	}
	if compress {
	p = append(p, "Sec-WebSocket-Extensions: permessage-deflate; server_no_context_takeover; client_no_context_takeover\r\n"...)
	}
	for k, vs := range responseHeader {
	if k == "Sec-Websocket-Protocol" {
	continue
	}
	for _, v := range vs {
	p = append(p, k...)
	p = append(p, ": "...)
	for i := 0; i < len(v); i++ {
	b := v[i]
	if b <= 31 {
	// prevent response splitting.
	b = ' '
	}
	p = append(p, b)
	}
	p = append(p, "\r\n"...)
	}
	}
	p = append(p, "\r\n"...)

	// Clear deadlines set by HTTP server.
	netConn.SetDeadline(time.Time{})

	if u.HandshakeTimeout > 0 {
	netConn.SetWriteDeadline(time.Now().Add(u.HandshakeTimeout))
	}
	if _, err = netConn.Write(p); err != nil {
	netConn.Close()
	return nil, err
	}
	if u.HandshakeTimeout > 0 {
	netConn.SetWriteDeadline(time.Time{})
	}

	return c, nil
	}

	// Upgrade upgrades the HTTP server connection to the WebSocket protocol.
	//
	// Deprecated: Use websocket.Upgrader instead.
	//
	// Upgrade does not perform origin checking. The application is responsible for
	// checking the Origin header before calling Upgrade. An example implementation
	// of the same origin policy check is:
	//
	// if req.Header.Get("Origin") != "http://"+req.Host {
	// http.Error(w, "Origin not allowed", http.StatusForbidden)
	// return
	// }
	//
	// If the endpoint supports subprotocols, then the application is responsible
	// for negotiating the protocol used on the connection. Use the Subprotocols()
	// function to get the subprotocols requested by the client. Use the
	// Sec-Websocket-Protocol response header to specify the subprotocol selected
	// by the application.
	//
	// The responseHeader is included in the response to the client's upgrade
	// request. Use the responseHeader to specify cookies (Set-Cookie) and the
	// negotiated subprotocol (Sec-Websocket-Protocol).
	//
	// The connection buffers IO to the underlying network connection. The
	// readBufSize and writeBufSize parameters specify the size of the buffers to
	// use. Messages can be larger than the buffers.
	//
	// If the request is not a valid WebSocket handshake, then Upgrade returns an
	// error of type HandshakeError. Applications should handle this error by
	// replying to the client with an HTTP error response.
	func Upgrade(w http.ResponseWriter, r http.Request, responseHeader http.Header, readBufSize, writeBufSize int) (Conn, error) {
	u := Upgrader{ReadBufferSize: readBufSize, WriteBufferSize: writeBufSize}
	u.Error = func(w http.ResponseWriter, r *http.Request, status int, reason error) {
	// don't return errors to maintain backwards compatibility
	}
	u.CheckOrigin = func(r *http.Request) bool {
	// allow all connections by default
	return true
	}
	return u.Upgrade(w, r, responseHeader)
	}

	// Subprotocols returns the subprotocols requested by the client in the
	// Sec-Websocket-Protocol header.
	func Subprotocols(r *http.Request) []string {
	h := strings.TrimSpace(r.Header.Get("Sec-Websocket-Protocol"))
	if h == "" {
	return nil
	}
	protocols := strings.Split(h, ",")
	for i := range protocols {
	protocols[i] = strings.TrimSpace(protocols[i])
	}
	return protocols
	}

	// IsWebSocketUpgrade returns true if the client requested upgrade to the
	// WebSocket protocol.
	func IsWebSocketUpgrade(r *http.Request) bool {
	return tokenListContainsValue(r.Header, "Connection", "upgrade") &&
	tokenListContainsValue(r.Header, "Upgrade", "websocket")
	}

	// bufioReaderSize size returns the size of a bufio.Reader.
	func bufioReaderSize(originalReader io.Reader, br *bufio.Reader) int {
	// This code assumes that peek on a reset reader returns
	// bufio.Reader.buf[:0].
	// TODO: Use bufio.Reader.Size() after Go 1.10
	br.Reset(originalReader)
	if p, err := br.Peek(0); err == nil {
	return cap(p)
	}
	return 0
	}

	// writeHook is an io.Writer that records the last slice passed to it vio
	// io.Writer.Write.
	type writeHook struct {
	p []byte
	}

	func (wh *writeHook) Write(p []byte) (int, error) {
	wh.p = p
	return len(p), nil
	}

	// bufioWriterBuffer grabs the buffer from a bufio.Writer.
	func bufioWriterBuffer(originalWriter io.Writer, bw *bufio.Writer) []byte {
	// This code assumes that bufio.Writer.buf[:1] is passed to the
	// bufio.Writer's underlying writer.
	var wh writeHook
	bw.Reset(&wh)
	bw.WriteByte(0)
	bw.Flush()

	bw.Reset(originalWriter)

	return wh.p[:cap(wh.p)]
	}