code review 5303096: websocket: manage subprotocol negotiation in the websoc...

src/pkg/websocket/websocket.go

Index: src/pkg/websocket/websocket.go 
=================================================================== 
--- a/src/pkg/websocket/websocket.go 
+++ b/src/pkg/websocket/websocket.go 
@@ -89,11 +89,39 @@ 
	handshakeData map[string]string 
 } 
 
+// A ProtocolChooser returns the preferred subprotocol from the list supplied 
+// by the client. 
+// If none of the subprotocols are suitable to the server, 
+// the string returned should be "". 
+// If there is some fatal error (including the lack of a suitable subprotocol, 
+// though this is not required), the error value should be 
+// websocket.ErrUnsupportedSubProtocol. 
+// If the error value is non-nil, an HTTP 400 Bad Request will be 
+// generated with the string value of the error. It is an error to 
+// return a string other than "" or one of the provided protocols. 
+type ProtocolChooser func([]string) (string, error) 
+ 
+// Returnss the first protocol in the argument list that matches 
+// a protocol requested by the client. If there is no match, returns "" 
+func SimpleChooser(preferences []string) ProtocolChooser { 
+	return func(clientPrefs []string) (string, error) { 
+	for _, pref := range preferences { 
+	for _, clientPref := range clientPrefs { 
+	if pref == clientPref { 
+	return pref, nil 
+	} 
+	} 
+	} 
+	return "", nil 
+	} 
+} 
+ 
 // serverHandshaker is an interface to handle WebSocket server side handshake. 
 type serverHandshaker interface { 
	// ReadHandshake reads handshake request message from client. 
	// Returns http response code and error if any. 
-	ReadHandshake(buf *bufio.Reader, req *http.Request) (code int, err error) 
+	ReadHandshake(buf *bufio.Reader, req *http.Request, 
+	protocolChooser ProtocolChooser) (code int, err error) 
 
	// AcceptHandshake accepts the client handshake request and sends 
	// handshake response back to client.