xP: allow setting a fixed WS URI

For reverse proxies.

xP/xP.go

@@ -22,6 +22,7 @@ import (
 var (
 	addressBind    string
 	addressConnect string
+	addressWS      string
 )
 
 func clientToRelay(
@@ -163,18 +164,24 @@ func handleDefault(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	wsURI := fmt.Sprintf("ws://%s/ws", r.Host)
+	wsURI := addressWS
+	if wsURI == "" {
+		wsURI = fmt.Sprintf("ws://%s/ws", r.Host)
+	}
 	if err := page.Execute(w, wsURI); err != nil {
 		log.Println("Template execution failed: " + err.Error())
 	}
 }
 
 func main() {
-	if len(os.Args) != 3 {
-		log.Fatalf("usage: %s BIND CONNECT\n", os.Args[0])
+	if len(os.Args) < 3 || len(os.Args) > 4 {
+		log.Fatalf("usage: %s BIND CONNECT [WSURI]\n", os.Args[0])
 	}
 
 	addressBind, addressConnect = os.Args[1], os.Args[2]
+	if len(os.Args) > 3 {
+		addressWS = os.Args[3]
+	}
 
 	http.Handle("/ws", websocket.Handler(handleWebSocket))
 	http.Handle("/", http.HandlerFunc(handleDefault))