per message compression; only no context modes

client.go

@@ -23,6 +23,8 @@ import (
 // invalid.
 var ErrBadHandshake = errors.New("websocket: bad handshake")
 
+var errInvalidCompression = errors.New("websocket: invalid compression negotiation")
+
 // NewClient creates a new client connection using the given net connection.
 // The URL u specifies the host and request URI. Use requestHeader to specify
 // the origin (Origin), subprotocols (Sec-WebSocket-Protocol) and cookies
@@ -70,6 +72,12 @@ type Dialer struct {
 
 	// Subprotocols specifies the client's requested subprotocols.
 	Subprotocols []string
+
+	// CompressionSupported specifies if the client 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.
+	CompressionSupported bool
 }
 
 var errMalformedURL = errors.New("malformed ws or wss URL")
@@ -214,6 +222,7 @@ func (d *Dialer) Dial(urlStr string, requestHeader http.Header) (*Conn, *http.Re
 			k == "Connection" ||
 			k == "Sec-Websocket-Key" ||
 			k == "Sec-Websocket-Version" ||
+			k == "Sec-Websocket-Extensions" ||
 			(k == "Sec-Websocket-Protocol" && len(d.Subprotocols) > 0):
 			return nil, nil, errors.New("websocket: duplicate header not allowed: " + k)
 		default:
@@ -221,6 +230,10 @@ func (d *Dialer) Dial(urlStr string, requestHeader http.Header) (*Conn, *http.Re
 		}
 	}
 
+	if d.CompressionSupported {
+		req.Header.Set("Sec-Websocket-Extensions", "permessage-deflate; server_no_context_takeover; client_no_context_takeover")
+	}
+
 	hostPort, hostNoPort := hostPortNoPort(u)
 
 	var proxyURL *url.URL
@@ -337,6 +350,20 @@ func (d *Dialer) Dial(urlStr string, requestHeader http.Header) (*Conn, *http.Re
 		return nil, resp, ErrBadHandshake
 	}
 
+	for _, ext := range parseExtensions(req.Header) {
+		if ext[""] != "permessage-deflate" {
+			continue
+		}
+		_, snct := ext["server_no_context_takeover"]
+		_, cnct := ext["client_no_context_takeover"]
+		if !snct || !cnct {
+			return nil, resp, errInvalidCompression
+		}
+		conn.newCompressionWriter = compressNoContextTakeover
+		conn.newDecompressionReader = decompressNoContextTakeover
+		break
+	}
+
 	resp.Body = ioutil.NopCloser(bytes.NewReader([]byte{}))
 	conn.subprotocol = resp.Header.Get("Sec-Websocket-Protocol")
 

conn.go

@@ -985,6 +985,13 @@ func (c *Conn) UnderlyingConn() net.Conn {
 	return c.conn
 }
 
+// EnableWriteCompression enables and disables write compression of
+// subsequent text and binary messages. This function is a noop if
+// compression was not negotiated with the peer.
+func (c *Conn) EnableWriteCompression(enable bool) {
+	c.enableWriteCompression = enable
+}
+
 // FormatCloseMessage formats closeCode and text as a WebSocket close message.
 func FormatCloseMessage(closeCode int, text string) []byte {
 	buf := make([]byte, 2+len(text))

doc.go

@@ -149,4 +149,25 @@
 // The deprecated Upgrade function does not enforce an origin policy. It's the
 // application's responsibility to check the Origin header before calling
 // Upgrade.
+//
+// Compression [Experimental]
+//
+// Per message compression extensions (RFC 7692) are experimentally supported
+// by this package in a limited capacity. Enabling the CompressionSupported
+// option in Dialer or Upgrader will attempt to negotiate per message deflate
+// support. If compression was successfully negotiated with the connection's
+// peer, any message received in compressed form will be automatically
+// decompressed. All Read methods will return uncompressed bytes.
+//
+// Per message compression of messages written to a connection can be enabled
+// or disabled by calling the corresponding Conn method:
+//
+// conn.EnableWriteCompression(true)
+//
+// Currently this package does not support compression with "context takeover".
+// This means that messages must be compressed and decompressed in isolation,
+// without retaining sliding window or dictionary state across messages. For
+// more details refer to RFC 7692.
+//
+// Use of compression is experimental and may result in decreased performance.
 package websocket

server.go

@@ -46,6 +46,12 @@ type Upgrader struct {
 	// CheckOrigin is nil, the host in the Origin header must not be set or
 	// must match the host of the request.
 	CheckOrigin func(r *http.Request) bool
+
+	// CompressionSupported 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.
+	CompressionSupported bool
 }
 
 func (u *Upgrader) returnError(w http.ResponseWriter, r *http.Request, status int, reason string) (*Conn, error) {
@@ -100,6 +106,11 @@ func (u *Upgrader) Upgrade(w http.ResponseWriter, r *http.Request, responseHeade
 	if r.Method != "GET" {
 		return u.returnError(w, r, http.StatusMethodNotAllowed, "websocket: method not GET")
 	}
+
+	if _, ok := responseHeader["Sec-Websocket-Extensions"]; ok {
+		return u.returnError(w, r, http.StatusInternalServerError, "websocket: application specific Sec-Websocket-Extensions headers are unsupported")
+	}
+
 	if !tokenListContainsValue(r.Header, "Sec-Websocket-Version", "13") {
 		return u.returnError(w, r, http.StatusBadRequest, "websocket: version != 13")
 	}
@@ -127,6 +138,18 @@ func (u *Upgrader) Upgrade(w http.ResponseWriter, r *http.Request, responseHeade
 
 	subprotocol := u.selectSubprotocol(r, responseHeader)
 
+	// Negotiate PMCE
+	var compress bool
+	if u.CompressionSupported {
+		for _, ext := range parseExtensions(r.Header) {
+			if ext[""] != "permessage-deflate" {
+				continue
+			}
+			compress = true
+			break
+		}
+	}
+
 	var (
 		netConn net.Conn
 		br      *bufio.Reader
@@ -152,6 +175,11 @@ func (u *Upgrader) Upgrade(w http.ResponseWriter, r *http.Request, responseHeade
 	c := newConn(netConn, true, u.ReadBufferSize, u.WriteBufferSize)
 	c.subprotocol = subprotocol
 
+	if compress {
+		c.newCompressionWriter = compressNoContextTakeover
+		c.newDecompressionReader = decompressNoContextTakeover
+	}
+
 	p := c.writeBuf[: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)...)
@@ -161,6 +189,9 @@ func (u *Upgrader) Upgrade(w http.ResponseWriter, r *http.Request, responseHeade
 		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