Make subprotocol negotiation more flexible.

server.go

@@ -34,9 +34,10 @@ type Upgrader struct {
 	// default values will be used.
 	ReadBufferSize, WriteBufferSize int
 
-	// Subprotocols specifies the server's supported protocols. If Subprotocols
-	// is nil, then Upgrade does not negotiate a subprotocol.
-	Subprotocols []string
+	// NegotiateSubprotocol specifies the function to negotiate a subprotocol
+	// based on a request. If NegotiateSubprotocol is nil, then no subprotocol
+	// will be used.
+	NegotiateSubprotocol func(r *http.Request) (string, error)
 
 	// Error specifies the function for generating HTTP error responses. If Error
 	// is nil, then http.Error is used to generate the HTTP response.
@@ -59,21 +60,6 @@ func (u *Upgrader) returnError(w http.ResponseWriter, r *http.Request, status in
 	return nil, err
 }
 
-// Check if the passed subprotocol is supported by the server
-func (u *Upgrader) hasSubprotocol(subprotocol string) bool {
-	if u.Subprotocols == nil {
-		return false
-	}
-
-	for _, s := range u.Subprotocols {
-		if s == subprotocol {
-			return true
-		}
-	}
-
-	return false
-}
-
 // Check if host in Origin header matches host of request
 func (u *Upgrader) checkSameOrigin(r *http.Request) bool {
 	origin := r.Header.Get("Origin")
@@ -155,12 +141,11 @@ func (u *Upgrader) Upgrade(w http.ResponseWriter, r *http.Request, responseHeade
 	}
 	c := newConn(netConn, true, readBufSize, writeBufSize)
 
-	if u.Subprotocols != nil {
-		for _, proto := range Subprotocols(r) {
-			if u.hasSubprotocol(proto) {
-				c.subprotocol = proto
-				break
-			}
+	if u.NegotiateSubprotocol != nil {
+		c.subprotocol, err = u.NegotiateSubprotocol(r)
+		if err != nil {
+			netConn.Close()
+			return nil, err
 		}
 	} else if responseHeader != nil {
 		c.subprotocol = responseHeader.Get("Sec-Websocket-Protocol")