@Override
    public WebSocket doWebSocketConnect(HttpServletRequest request, String protocol) {

        final TunnelRequest tunnelRequest = new HTTPTunnelRequest(request);

        // Return new WebSocket which communicates through tunnel
        return new WebSocket.OnTextMessage() {

            /**
             * The GuacamoleTunnel associated with the connected WebSocket. If
             * the WebSocket has not yet been connected, this will be null.
             */
            private GuacamoleTunnel tunnel = null;

            /**
             * The active WebSocket connection. This value will always be
             * non-null if tunnel is non-null.
             */
            private Connection connection = null;

            /**
             * Sends a Guacamole instruction along the outbound WebSocket
             * connection to the connected Guacamole client. If an instruction
             * is already in the process of being sent by another thread, this
             * function will block until in-progress instructions are complete.
             *
             * @param instruction
             *     The instruction to send.
             *
             * @throws IOException
             *     If an I/O error occurs preventing the given instruction from
             *     being sent.
             */
            private void sendInstruction(String instruction)
                    throws IOException {

                // NOTE: Synchronization on the non-final remote field here is
                // intentional. The outbound websocket connection is only
                // sensitive to simultaneous attempts to send messages with
                // respect to itself. If the connection changes, then
                // synchronization need only be performed in context of the new
                // connection
                synchronized (connection) {
                    connection.sendMessage(instruction);
                }

            }

            /**
             * Sends a Guacamole instruction along the outbound WebSocket
             * connection to the connected Guacamole client. If an instruction
             * is already in the process of being sent by another thread, this
             * function will block until in-progress instructions are complete.
             *
             * @param instruction
             *     The instruction to send.
             *
             * @throws IOException
             *     If an I/O error occurs preventing the given instruction from being
             *     sent.
             */
            private void sendInstruction(GuacamoleInstruction instruction)
                    throws IOException {
                sendInstruction(instruction.toString());
            }

            @Override
            public void onMessage(String string) {

                // Ignore inbound messages if there is no associated tunnel
                if (tunnel == null)
                    return;

                // Filter received instructions, handling tunnel-internal
                // instructions without passing through to guacd
                GuacamoleWriter writer = new FilteredGuacamoleWriter(tunnel.acquireWriter(), new GuacamoleFilter() {

                    @Override
                    public GuacamoleInstruction filter(GuacamoleInstruction instruction)
                            throws GuacamoleException {

                        // Filter out all tunnel-internal instructions
                        if (instruction.getOpcode().equals(GuacamoleTunnel.INTERNAL_DATA_OPCODE)) {

                            // Respond to ping requests
                            List<String> args = instruction.getArgs();
                            if (args.size() >= 2 && args.get(0).equals(PING_OPCODE)) {

                                try {
                                    sendInstruction(new GuacamoleInstruction(
                                        GuacamoleTunnel.INTERNAL_DATA_OPCODE,
                                        PING_OPCODE, args.get(1)
                                    ));
                                }
                                catch (IOException e) {
                                    logger.debug("Unable to send \"ping\" response for WebSocket tunnel.", e);
                                }

                            }

                            return null;

                        }

                        // Pass through all non-internal instructions untouched
                        return instruction;

                    }

                });

                // Write message received
                try {
                    writer.write(string.toCharArray());
                }
                catch (GuacamoleConnectionClosedException e) {
                    logger.debug("Connection to guacd closed.", e);
                }
                catch (GuacamoleException e) {
                    logger.debug("WebSocket tunnel write failed.", e);
                }

                tunnel.releaseWriter();

            }

            @Override
            public void onOpen(final Connection connection) {

                // Store websocket connection for future use via sendInstruction()
                this.connection = connection;

                try {
                    tunnel = doConnect(tunnelRequest);
                }
                catch (GuacamoleException e) {
                    logger.error("Creation of WebSocket tunnel to guacd failed: {}", e.getMessage());
                    logger.debug("Error connecting WebSocket tunnel.", e);
                    closeConnection(connection, e.getStatus().getGuacamoleStatusCode(),
                            e.getWebSocketCode());
                    return;
                }

                // Do not start connection if tunnel does not exist
                if (tunnel == null) {
                    closeConnection(connection, GuacamoleStatus.RESOURCE_NOT_FOUND);
                    return;
                }

                Thread readThread = new Thread() {

                    @Override
                    public void run() {

                        StringBuilder buffer = new StringBuilder(BUFFER_SIZE);
                        GuacamoleReader reader = tunnel.acquireReader();
                        char[] readMessage;

                        try {

                            // Send tunnel UUID
                            sendInstruction(new GuacamoleInstruction(
                                GuacamoleTunnel.INTERNAL_DATA_OPCODE,
                                tunnel.getUUID().toString()
                            ));

                            try {

                                // Attempt to read
                                while ((readMessage = reader.read()) != null) {

                                    // Buffer message
                                    buffer.append(readMessage);

                                    // Flush if we expect to wait or buffer is getting full
                                    if (!reader.available() || buffer.length() >= BUFFER_SIZE) {
                                        sendInstruction(buffer.toString());
                                        buffer.setLength(0);
                                    }

                                }

                                // No more data
                                closeConnection(connection, GuacamoleStatus.SUCCESS);
                                
                            }

                            // Catch any thrown guacamole exception and attempt
                            // to pass within the WebSocket connection, logging
                            // each error appropriately.
                            catch (GuacamoleClientException e) {
                                logger.info("WebSocket connection terminated: {}", e.getMessage());
                                logger.debug("WebSocket connection terminated due to client error.", e);
                                closeConnection(connection, e.getStatus().getGuacamoleStatusCode(),
                                        e.getWebSocketCode());
                            }
                            catch (GuacamoleConnectionClosedException e) {
                                logger.debug("Connection to guacd closed.", e);
                                closeConnection(connection, GuacamoleStatus.SUCCESS);
                            }
                            catch (GuacamoleException e) {
                                logger.error("Connection to guacd terminated abnormally: {}", e.getMessage());
                                logger.debug("Internal error during connection to guacd.", e);
                                closeConnection(connection, e.getStatus().getGuacamoleStatusCode(),
                                        e.getWebSocketCode());
                            }

                        }
                        catch (IOException e) {
                            logger.debug("WebSocket tunnel read failed due to I/O error.", e);
                            closeConnection(connection, GuacamoleStatus.SERVER_ERROR);
                        }

                    }

                };

                readThread.start();

            }

            @Override
            public void onClose(int i, String string) {
                try {
                    if (tunnel != null)
                        tunnel.close();
                }
                catch (GuacamoleException e) {
                    logger.debug("Unable to close connection to guacd.", e);
                }
            }

        };

    }
Sends the given status on the given WebSocket connection
and closes the connection.

@param connection
    The WebSocket connection to close.

@param guacStatus
    The status to send.
guacamole/src/main/java/org/apache/guacamole/tunnel/websocket/jetty8/GuacamoleWebSocketTunnelServlet.java