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