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webapps/examples/WEB-INF/classes/websocket/drawboard/Client.java
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webapps/examples/WEB-INF/classes/websocket/drawboard/Client.java
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/*
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* Licensed to the Apache Software Foundation (ASF) under one or more
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* contributor license agreements. See the NOTICE file distributed with
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* this work for additional information regarding copyright ownership.
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* The ASF licenses this file to You under the Apache License, Version 2.0
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* (the "License"); you may not use this file except in compliance with
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* the License. You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package websocket.drawboard;
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import java.io.IOException;
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import java.util.LinkedList;
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import javax.websocket.CloseReason;
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import javax.websocket.CloseReason.CloseCodes;
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import javax.websocket.RemoteEndpoint.Async;
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import javax.websocket.SendHandler;
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import javax.websocket.SendResult;
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import javax.websocket.Session;
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import websocket.drawboard.wsmessages.AbstractWebsocketMessage;
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import websocket.drawboard.wsmessages.BinaryWebsocketMessage;
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import websocket.drawboard.wsmessages.CloseWebsocketMessage;
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import websocket.drawboard.wsmessages.StringWebsocketMessage;
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/**
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* Represents a client with methods to send messages asynchronously.
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*/
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public class Client {
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private final Session session;
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private final Async async;
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/**
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* Contains the messages which are buffered until the previous
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* send operation has finished.
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*/
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private final LinkedList<AbstractWebsocketMessage> messagesToSend =
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new LinkedList<>();
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/**
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* If this client is currently sending a messages asynchronously.
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*/
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private volatile boolean isSendingMessage = false;
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/**
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* If this client is closing. If <code>true</code>, new messages to
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* send will be ignored.
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*/
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private volatile boolean isClosing = false;
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/**
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* The length of all current buffered messages, to avoid iterating
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* over a linked list.
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*/
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private volatile long messagesToSendLength = 0;
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public Client(Session session) {
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this.session = session;
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this.async = session.getAsyncRemote();
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}
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/**
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* Asynchronously closes the Websocket session. This will wait until all
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* remaining messages have been sent to the Client and then close
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* the Websocket session.
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*/
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public void close() {
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sendMessage(new CloseWebsocketMessage());
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}
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/**
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* Sends the given message asynchronously to the client.
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* If there is already a async sending in progress, then the message
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* will be buffered and sent when possible.<br><br>
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*
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* This method can be called from multiple threads.
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*
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* @param msg The message to send
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*/
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public void sendMessage(AbstractWebsocketMessage msg) {
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synchronized (messagesToSend) {
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if (!isClosing) {
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// Check if we have a Close message
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if (msg instanceof CloseWebsocketMessage) {
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isClosing = true;
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}
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if (isSendingMessage) {
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// Check if the buffered messages exceed
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// a specific amount - in that case, disconnect the client
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// to prevent DoS.
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// In this case we check if there are >= 1000 messages
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// or length(of all messages) >= 1000000 bytes.
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if (messagesToSend.size() >= 1000
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|| messagesToSendLength >= 1000000) {
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isClosing = true;
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// Discard the new message and close the session immediately.
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CloseReason cr = new CloseReason(
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CloseCodes.VIOLATED_POLICY,
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"Send Buffer exceeded");
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try {
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// TODO: close() may block if the remote endpoint doesn't read the data
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// (eventually there will be a TimeoutException). However, this method
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// (sendMessage) is intended to run asynchronous code and shouldn't
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// block. Otherwise it would temporarily stop processing of messages
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// from other clients.
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// Maybe call this method on another thread.
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// Note that when this method is called, the RemoteEndpoint.Async
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// is still in the process of sending data, so there probably should
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// be another way to abort the Websocket connection.
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// Ideally, there should be some abort() method that cancels the
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// connection immediately...
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session.close(cr);
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} catch (IOException e) {
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// Ignore
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}
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} else {
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// Check if the last message and the new message are
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// String messages - in that case we concatenate them
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// to reduce TCP overhead (using ";" as separator).
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if (msg instanceof StringWebsocketMessage
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&& !messagesToSend.isEmpty()
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&& messagesToSend.getLast()
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instanceof StringWebsocketMessage) {
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StringWebsocketMessage ms =
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(StringWebsocketMessage) messagesToSend.removeLast();
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messagesToSendLength -= calculateMessageLength(ms);
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String concatenated = ms.getString() + ";" +
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((StringWebsocketMessage) msg).getString();
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msg = new StringWebsocketMessage(concatenated);
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}
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messagesToSend.add(msg);
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messagesToSendLength += calculateMessageLength(msg);
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}
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} else {
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isSendingMessage = true;
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internalSendMessageAsync(msg);
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}
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}
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}
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}
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private long calculateMessageLength(AbstractWebsocketMessage msg) {
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if (msg instanceof BinaryWebsocketMessage) {
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return ((BinaryWebsocketMessage) msg).getBytes().capacity();
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} else if (msg instanceof StringWebsocketMessage) {
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return ((StringWebsocketMessage) msg).getString().length() * 2;
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}
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return 0;
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}
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/**
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* Internally sends the messages asynchronously.
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* @param msg
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*/
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private void internalSendMessageAsync(AbstractWebsocketMessage msg) {
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try {
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if (msg instanceof StringWebsocketMessage) {
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StringWebsocketMessage sMsg = (StringWebsocketMessage) msg;
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async.sendText(sMsg.getString(), sendHandler);
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} else if (msg instanceof BinaryWebsocketMessage) {
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BinaryWebsocketMessage bMsg = (BinaryWebsocketMessage) msg;
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async.sendBinary(bMsg.getBytes(), sendHandler);
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} else if (msg instanceof CloseWebsocketMessage) {
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// Close the session.
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session.close();
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}
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} catch (IllegalStateException|IOException ex) {
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// Trying to write to the client when the session has
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// already been closed.
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// Ignore
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}
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}
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/**
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* SendHandler that will continue to send buffered messages.
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*/
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private final SendHandler sendHandler = new SendHandler() {
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@Override
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public void onResult(SendResult result) {
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if (!result.isOK()) {
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// Message could not be sent. In this case, we don't
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// set isSendingMessage to false because we must assume the connection
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// broke (and onClose will be called), so we don't try to send
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// other messages.
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// As a precaution, we close the session (e.g. if a send timeout occurred).
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// TODO: session.close() blocks, while this handler shouldn't block.
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// Ideally, there should be some abort() method that cancels the
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// connection immediately...
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try {
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session.close();
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} catch (IOException ex) {
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// Ignore
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}
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}
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synchronized (messagesToSend) {
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if (!messagesToSend.isEmpty()) {
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AbstractWebsocketMessage msg = messagesToSend.remove();
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messagesToSendLength -= calculateMessageLength(msg);
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internalSendMessageAsync(msg);
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} else {
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isSendingMessage = false;
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}
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}
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}
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};
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}
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