Added utls to websocket (#1256)

* Added utls to websocket

* Slightly better code

One less allocation

transport/internet/tls/tls.go

@@ -66,6 +66,33 @@ func (c *UConn) HandshakeAddress() net.Address {
 	return net.ParseAddress(state.ServerName)
 }
 
+// WebsocketHandshake basically calls UConn.Handshake inside it but it will only send
+// http/1.1 in its ALPN.
+func (c *UConn) WebsocketHandshake() error {
+	// Build the handshake state. This will apply every variable of the TLS of the
+	// fingerprint in the UConn
+	if err := c.BuildHandshakeState(); err != nil {
+		return err
+	}
+	// Iterate over extensions and check for utls.ALPNExtension
+	hasALPNExtension := false
+	for _, extension := range c.Extensions {
+		if alpn, ok := extension.(*utls.ALPNExtension); ok {
+			hasALPNExtension = true
+			alpn.AlpnProtocols = []string{"http/1.1"}
+			break
+		}
+	}
+	if !hasALPNExtension { // Append extension if doesn't exists
+		c.Extensions = append(c.Extensions, &utls.ALPNExtension{AlpnProtocols: []string{"http/1.1"}})
+	}
+	// Rebuild the client hello and do the handshake
+	if err := c.BuildHandshakeState(); err != nil {
+		return err
+	}
+	return c.Handshake()
+}
+
 func (c *UConn) NegotiatedProtocol() (name string, mutual bool) {
 	state := c.ConnectionState()
 	return state.NegotiatedProtocol, state.NegotiatedProtocolIsMutual