question: private void writeHandshake ( WebSocketOutputStream output , String key ) throws WebSocketException { mHandshakeBuilder . setKey ( key ) ; String requestLine = mHandshakeBuilder . buildRequestLine ( ) ; List < String [ ] > headers = mHandshakeBuilder . buildHeaders ( ) ; String handshake = HandshakeBuilder . build ( requestLine , headers ) ; mListenerManager . callOnSendingHandshake ( requestLine , headers ) ; try { output . write ( handshake ) ; output . flush ( ) ; } catch ( IOException e ) { throw new WebSocketException ( WebSocketError . OPENING_HAHDSHAKE_REQUEST_FAILURE , "Failed to send an opening handshake request to the server: " + e . getMessage ( ) , e ) ; } }
target:  Send an opening handshake request to the WebSocket server.