Implement compression extension negotiation

Author: nhooyr

conn.go

@@ -42,6 +42,7 @@ type Conn struct {
 	writeBuf []byte
 	closer   io.Closer
 	client   bool
+	copts    *CompressionOptions
 
 	closeOnce     sync.Once
 	closeErrOnce  sync.Once

doc.go

@@ -31,6 +31,7 @@
 //  - Accept and AcceptOptions
 //  - Conn.Ping
 //  - HTTPClient and HTTPHeader fields in DialOptions
+//  - CompressionOptions
 //
 // The *http.Response returned by Dial will always either be nil or &http.Response{} as
 // we do not have access to the handshake response in the browser.

handshake.go

@@ -59,13 +59,13 @@ func verifyClientRequest(w http.ResponseWriter, r *http.Request) error {
 		return err
 	}
 
-	if !headerValuesContainsToken(r.Header, "Connection", "Upgrade") {
+	if !headerContainsToken(r.Header, "Connection", "Upgrade") {
 		err := fmt.Errorf("websocket protocol violation: Connection header %q does not contain Upgrade", r.Header.Get("Connection"))
 		http.Error(w, err.Error(), http.StatusBadRequest)
 		return err
 	}
 
-	if !headerValuesContainsToken(r.Header, "Upgrade", "WebSocket") {
+	if !headerContainsToken(r.Header, "Upgrade", "WebSocket") {
 		err := fmt.Errorf("websocket protocol violation: Upgrade header %q does not contain websocket", r.Header.Get("Upgrade"))
 		http.Error(w, err.Error(), http.StatusBadRequest)
 		return err
@@ -144,6 +144,18 @@ func accept(w http.ResponseWriter, r *http.Request, opts *AcceptOptions) (*Conn,
 		w.Header().Set("Sec-WebSocket-Protocol", subproto)
 	}
 
+	var copts *CompressionOptions
+	if opts.Compression != nil {
+		copts, err = negotiateCompression(r.Header, opts.Compression)
+		if err != nil {
+			http.Error(w, err.Error(), http.StatusBadRequest)
+			return nil, err
+		}
+		if copts != nil {
+			copts.setHeader(w.Header())
+		}
+	}
+
 	w.WriteHeader(http.StatusSwitchingProtocols)
 
 	netConn, brw, err := hj.Hijack()
@@ -162,40 +174,65 @@ func accept(w http.ResponseWriter, r *http.Request, opts *AcceptOptions) (*Conn,
 		br:          brw.Reader,
 		bw:          brw.Writer,
 		closer:      netConn,
+		copts:       copts,
 	}
 	c.init()
 
 	return c, nil
 }
 
-func headerValuesContainsToken(h http.Header, key, token string) bool {
+func headerContainsToken(h http.Header, key, token string) bool {
 	key = textproto.CanonicalMIMEHeaderKey(key)
 
-	for _, val2 := range h[key] {
-		if headerValueContainsToken(val2, token) {
+	token = strings.ToLower(token)
+	match := func(t string) bool {
+		return t == token
+	}
+
+	for _, v := range h[key] {
+		if searchHeaderTokens(v, match) != "" {
 			return true
 		}
 	}
 
 	return false
 }
 
-func headerValueContainsToken(val2, token string) bool {
-	val2 = strings.TrimSpace(val2)
+func headerTokenHasPrefix(h http.Header, key, prefix string) string {
+	key = textproto.CanonicalMIMEHeaderKey(key)
 
-	for _, val2 := range strings.Split(val2, ",") {
-		val2 = strings.TrimSpace(val2)
-		if strings.EqualFold(val2, token) {
-			return true
+	prefix = strings.ToLower(prefix)
+	match := func(t string) bool {
+		return strings.HasPrefix(t, prefix)
+	}
+
+	for _, v := range h[key] {
+		found := searchHeaderTokens(v, match)
+		if found != "" {
+			return found
 		}
 	}
 
-	return false
+	return ""
+}
+
+func searchHeaderTokens(v string, match func(val string) bool) string {
+	v = strings.TrimSpace(v)
+
+	for _, v2 := range strings.Split(v, ",") {
+		v2 = strings.TrimSpace(v2)
+		v2 = strings.ToLower(v2)
+		if match(v2) {
+			return v2
+		}
+	}
+
+	return ""
 }
 
 func selectSubprotocol(r *http.Request, subprotocols []string) string {
 	for _, sp := range subprotocols {
-		if headerValuesContainsToken(r.Header, "Sec-WebSocket-Protocol", sp) {
+		if headerContainsToken(r.Header, "Sec-WebSocket-Protocol", sp) {
 			return sp
 		}
 	}
@@ -268,36 +305,32 @@ type DialOptions struct {
 //
 // See https://www.igvita.com/2013/11/27/configuring-and-optimizing-websocket-compression.
 //
-// Enabling compression will increase memory and CPU usage.
-// Thus it is not ideal for every use case and disabled by default.
+// Enabling compression will increase memory and CPU usage and should
+// be profiled before enabling in production.
 // See https://github.com/gorilla/websocket/issues/203
-// Profile before enabling in production.
 //
 // This API is experimental and subject to change.
 type CompressionOptions struct {
-	// ServerNoContextTakeover controls whether the server should use context takeover.
-	// See docs on CompressionOptions for discussion regarding context takeover.
-	//
-	// If set by the client, will guarantee that the server does not use context takeover.
-	ServerNoContextTakeover bool
-
 	// ClientNoContextTakeover controls whether the client should use context takeover.
 	// See docs on CompressionOptions for discussion regarding context takeover.
 	//
 	// If set by the server, will guarantee that the client does not use context takeover.
 	ClientNoContextTakeover bool
 
+	// ServerNoContextTakeover controls whether the server should use context takeover.
+	// See docs on CompressionOptions for discussion regarding context takeover.
+	//
+	// If set by the client, will guarantee that the server does not use context takeover.
+	ServerNoContextTakeover bool
+
 	// Level controls the compression level used.
 	// Defaults to flate.BestSpeed.
 	Level int
 
 	// Threshold controls the minimum message size in bytes before compression is used.
-	// In the case of ContextTakeover == false, a flate.Writer will not be grabbed
-	// from the pool until the message exceeds this threshold.
-	//
 	// Must not be greater than 4096 as that is the write buffer's size.
 	//
-	// Defaults to 512.
+	// Defaults to 256.
 	Threshold int
 }
 
@@ -319,25 +352,32 @@ func Dial(ctx context.Context, u string, opts *DialOptions) (*Conn, *http.Respon
 	return c, r, nil
 }
 
-func dial(ctx context.Context, u string, opts *DialOptions) (_ *Conn, _ *http.Response, err error) {
+func (opts *DialOptions) ensure() (*DialOptions, error) {
 	if opts == nil {
 		opts = &DialOptions{}
+	} else {
+		opts = &*opts
 	}
 
-	// Shallow copy to ensure defaults do not affect user passed options.
-	opts2 := *opts
-	opts = &opts2
-
 	if opts.HTTPClient == nil {
 		opts.HTTPClient = http.DefaultClient
 	}
 	if opts.HTTPClient.Timeout > 0 {
-		return nil, nil, fmt.Errorf("use context for cancellation instead of http.Client.Timeout; see https://github.com/nhooyr/websocket/issues/67")
+		return nil, fmt.Errorf("use context for cancellation instead of http.Client.Timeout; see https://github.com/nhooyr/websocket/issues/67")
 	}
 	if opts.HTTPHeader == nil {
 		opts.HTTPHeader = http.Header{}
 	}
 
+	return opts, nil
+}
+
+func dial(ctx context.Context, u string, opts *DialOptions) (_ *Conn, _ *http.Response, err error) {
+	opts, err = opts.ensure()
+	if err != nil {
+		return nil, nil, err
+	}
+
 	parsedURL, err := url.Parse(u)
 	if err != nil {
 		return nil, nil, fmt.Errorf("failed to parse url: %w", err)
@@ -367,7 +407,7 @@ func dial(ctx context.Context, u string, opts *DialOptions) (_ *Conn, _ *http.Re
 		req.Header.Set("Sec-WebSocket-Protocol", strings.Join(opts.Subprotocols, ","))
 	}
 	if opts.Compression != nil {
-		req.Header.Set("Sec-WebSocket-Extensions", "permessage-deflate; server_no_context_takeover; client_no_context_takeover")
+		opts.Compression.setHeader(req.Header)
 	}
 
 	resp, err := opts.HTTPClient.Do(req)
@@ -384,7 +424,7 @@ func dial(ctx context.Context, u string, opts *DialOptions) (_ *Conn, _ *http.Re
 		}
 	}()
 
-	err = verifyServerResponse(req, resp)
+	copts, err := verifyServerResponse(req, resp, opts)
 	if err != nil {
 		return nil, resp, err
 	}
@@ -400,38 +440,48 @@ func dial(ctx context.Context, u string, opts *DialOptions) (_ *Conn, _ *http.Re
 		bw:          getBufioWriter(rwc),
 		closer:      rwc,
 		client:      true,
+		copts:       copts,
 	}
 	c.extractBufioWriterBuf(rwc)
 	c.init()
 
 	return c, resp, nil
 }
 
-func verifyServerResponse(r *http.Request, resp *http.Response) error {
+func verifyServerResponse(r *http.Request, resp *http.Response, opts *DialOptions) (*CompressionOptions, error) {
 	if resp.StatusCode != http.StatusSwitchingProtocols {
-		return fmt.Errorf("expected handshake response status code %v but got %v", http.StatusSwitchingProtocols, resp.StatusCode)
+		return nil, fmt.Errorf("expected handshake response status code %v but got %v", http.StatusSwitchingProtocols, resp.StatusCode)
 	}
 
-	if !headerValuesContainsToken(resp.Header, "Connection", "Upgrade") {
-		return fmt.Errorf("websocket protocol violation: Connection header %q does not contain Upgrade", resp.Header.Get("Connection"))
+	if !headerContainsToken(resp.Header, "Connection", "Upgrade") {
+		return nil, fmt.Errorf("websocket protocol violation: Connection header %q does not contain Upgrade", resp.Header.Get("Connection"))
 	}
 
-	if !headerValuesContainsToken(resp.Header, "Upgrade", "WebSocket") {
-		return fmt.Errorf("websocket protocol violation: Upgrade header %q does not contain websocket", resp.Header.Get("Upgrade"))
+	if !headerContainsToken(resp.Header, "Upgrade", "WebSocket") {
+		return nil, fmt.Errorf("websocket protocol violation: Upgrade header %q does not contain websocket", resp.Header.Get("Upgrade"))
 	}
 
 	if resp.Header.Get("Sec-WebSocket-Accept") != secWebSocketAccept(r.Header.Get("Sec-WebSocket-Key")) {
-		return fmt.Errorf("websocket protocol violation: invalid Sec-WebSocket-Accept %q, key %q",
+		return nil, fmt.Errorf("websocket protocol violation: invalid Sec-WebSocket-Accept %q, key %q",
 			resp.Header.Get("Sec-WebSocket-Accept"),
 			r.Header.Get("Sec-WebSocket-Key"),
 		)
 	}
 
-	if proto := resp.Header.Get("Sec-WebSocket-Protocol"); proto != "" && !headerValuesContainsToken(r.Header, "Sec-WebSocket-Protocol", proto) {
-		return fmt.Errorf("websocket protocol violation: unexpected Sec-WebSocket-Protocol from server: %q", proto)
+	if proto := resp.Header.Get("Sec-WebSocket-Protocol"); proto != "" && !headerContainsToken(r.Header, "Sec-WebSocket-Protocol", proto) {
+		return nil, fmt.Errorf("websocket protocol violation: unexpected Sec-WebSocket-Protocol from server: %q", proto)
 	}
 
-	return nil
+	var copts *CompressionOptions
+	if opts.Compression != nil {
+		var err error
+		copts, err = negotiateCompression(resp.Header, opts.Compression)
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	return copts, nil
 }
 
 // The below pools can only be used by the client because http.Hijacker will always
@@ -477,3 +527,55 @@ func makeSecWebSocketKey() (string, error) {
 	}
 	return base64.StdEncoding.EncodeToString(b), nil
 }
+
+func negotiateCompression(h http.Header, copts *CompressionOptions) (*CompressionOptions, error) {
+	deflate := headerTokenHasPrefix(h, "Sec-WebSocket-Extensions", "permessage-deflate")
+	if deflate == "" {
+		return nil, nil
+	}
+
+	// Ensures our changes do not modify the real compression options.
+	copts = &*copts
+
+	params := strings.Split(deflate, ";")
+	for i := range params {
+		params[i] = strings.TrimSpace(params[i])
+	}
+
+	if params[0] != "permessage-deflate" {
+		return nil, fmt.Errorf("unexpected header format for permessage-deflate extension: %q", deflate)
+	}
+
+	for _, p := range params[1:] {
+		switch p {
+		case "client_no_context_takeover":
+			copts.ClientNoContextTakeover = true
+			continue
+		case "server_no_context_takeover":
+			copts.ServerNoContextTakeover = true
+			continue
+		case "client_max_window_bits", "server-max-window-bits":
+			server := h.Get("Sec-WebSocket-Key") != ""
+			if server {
+				// If we are the server, we are allowed to ignore these parameters.
+				// However, if we are the client, we must obey them but because of
+				// https://github.com/golang/go/issues/3155 we cannot.
+				continue
+			}
+		}
+		return nil, fmt.Errorf("unsupported permessage-deflate parameter %q in header: %q", p, deflate)
+	}
+
+	return copts, nil
+}
+
+func (copts *CompressionOptions) setHeader(h http.Header) {
+	s := "permessage-deflate"
+	if copts.ClientNoContextTakeover {
+		s += "; client_no_context_takeover"
+	}
+	if copts.ServerNoContextTakeover {
+		s += "; server_no_context_takeover"
+	}
+	h.Set("Sec-WebSocket-Extensions", s)
+}

handshake_test.go

@@ -377,7 +377,7 @@ func Test_verifyServerHandshake(t *testing.T) {
 				resp.Header.Set("Sec-WebSocket-Accept", secWebSocketAccept(key))
 			}
 
-			err = verifyServerResponse(r, resp)
+			_, err = verifyServerResponse(r, resp, &DialOptions{})
 			if (err == nil) != tc.success {
 				t.Fatalf("unexpected error: %+v", err)
 			}