org.eclipse.leshan.server.demo.utils.EventSourceServlet Maven / Gradle / Ivy
/*
* Copyright (c) 2011 the original author or authors.
*
* Licensed 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 org.eclipse.leshan.server.demo.utils;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.StringReader;
import java.io.UnsupportedEncodingException;
import java.nio.charset.Charset;
import java.util.Enumeration;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.eclipse.jetty.continuation.Continuation;
import org.eclipse.jetty.continuation.ContinuationSupport;
/**
*
* A servlet that implements the event source protocol, also known as
* "server sent events".
*
*
* This servlet must be subclassed to implement abstract method {@link #newEventSource(HttpServletRequest)} to return an
* instance of {@link EventSource} that allows application to listen for event source events and to emit event source
* events.
*
*
* This servlet supports the following configuration parameters:
*
*
* heartBeatPeriod, that specifies the heartbeat period, in seconds, used to check whether the
* connection has been closed by the client; defaults to 10 seconds.
*
*
* NOTE: there is currently no support for last-event-id.
*
*/
@SuppressWarnings("serial")
public abstract class EventSourceServlet extends HttpServlet {
private static final Charset UTF_8 = Charset.forName("UTF-8");
private static final byte[] CRLF = new byte[] { '\r', '\n' };
private static final byte[] EVENT_FIELD;
private static final byte[] DATA_FIELD;
private static final byte[] COMMENT_FIELD;
static {
try {
EVENT_FIELD = "event: ".getBytes(UTF_8.name());
DATA_FIELD = "data: ".getBytes(UTF_8.name());
COMMENT_FIELD = ": ".getBytes(UTF_8.name());
} catch (UnsupportedEncodingException x) {
throw new RuntimeException(x);
}
}
private ScheduledExecutorService scheduler;
private int heartBeatPeriod = 10;
@Override
public void init() throws ServletException {
String heartBeatPeriodParam = getServletConfig().getInitParameter("heartBeatPeriod");
if (heartBeatPeriodParam != null)
heartBeatPeriod = Integer.parseInt(heartBeatPeriodParam);
scheduler = Executors.newSingleThreadScheduledExecutor();
}
@Override
public void destroy() {
if (scheduler != null)
scheduler.shutdown();
}
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
Enumeration acceptValues = request.getHeaders("Accept");
while (acceptValues.hasMoreElements()) {
String accept = acceptValues.nextElement();
if (accept.equals("text/event-stream")) {
EventSource eventSource = newEventSource(request);
if (eventSource == null) {
response.sendError(HttpServletResponse.SC_SERVICE_UNAVAILABLE);
} else {
respond(request, response);
Continuation continuation = ContinuationSupport.getContinuation(request);
// Infinite timeout because the continuation is never resumed,
// but only completed on close
continuation.setTimeout(0L);
continuation.suspend(response);
EventSourceEmitter emitter = new EventSourceEmitter(eventSource, continuation);
emitter.scheduleHeartBeat();
open(eventSource, emitter);
}
return;
}
}
super.doGet(request, response);
}
protected abstract EventSource newEventSource(HttpServletRequest request);
protected void respond(HttpServletRequest request, HttpServletResponse response) throws IOException {
response.setStatus(HttpServletResponse.SC_OK);
response.setCharacterEncoding(UTF_8.name());
response.setContentType("text/event-stream");
// By adding this header, and not closing the connection,
// we disable HTTP chunking, and we can use write()+flush()
// to send data in the text/event-stream protocol
response.addHeader("Connection", "close");
response.flushBuffer();
}
protected void open(EventSource eventSource, EventSource.Emitter emitter) throws IOException {
eventSource.onOpen(emitter);
}
protected class EventSourceEmitter implements EventSource.Emitter, Runnable {
private final EventSource eventSource;
private final Continuation continuation;
private final ServletOutputStream output;
private Future heartBeat;
private boolean closed;
public EventSourceEmitter(EventSource eventSource, Continuation continuation) throws IOException {
this.eventSource = eventSource;
this.continuation = continuation;
this.output = continuation.getServletResponse().getOutputStream();
}
public void event(String name, String data) throws IOException {
synchronized (this) {
output.write(EVENT_FIELD);
output.write(name.getBytes(UTF_8.name()));
output.write(CRLF);
data(data);
}
}
public void data(String data) throws IOException {
synchronized (this) {
BufferedReader reader = new BufferedReader(new StringReader(data));
String line;
while ((line = reader.readLine()) != null) {
output.write(DATA_FIELD);
output.write(line.getBytes(UTF_8.name()));
output.write(CRLF);
}
output.write(CRLF);
flush();
}
}
public void comment(String comment) throws IOException {
synchronized (this) {
output.write(COMMENT_FIELD);
output.write(comment.getBytes(UTF_8.name()));
output.write(CRLF);
output.write(CRLF);
flush();
}
}
public void run() {
// If the other peer closes the connection, the first
// flush() should generate a TCP reset that is detected
// on the second flush()
try {
synchronized (this) {
output.write('\r');
flush();
output.write('\n');
flush();
}
// We could write, reschedule heartbeat
scheduleHeartBeat();
} catch (IOException x) {
// The other peer closed the connection
close();
eventSource.onClose();
}
}
protected void flush() throws IOException {
continuation.getServletResponse().flushBuffer();
}
public void close() {
synchronized (this) {
closed = true;
heartBeat.cancel(false);
}
continuation.complete();
}
private void scheduleHeartBeat() {
synchronized (this) {
if (!closed)
heartBeat = scheduler.schedule(this, heartBeatPeriod, TimeUnit.SECONDS);
}
}
}
}