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/*
* Copyright 2009 Richard Zschech.
*
* 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 net.zschech.gwt.comet.client.impl;
import java.io.Serializable;
import java.util.ArrayList;
import java.util.List;
import com.google.gwt.core.client.JavaScriptException;
import com.google.gwt.dom.client.NativeEvent;
import com.google.gwt.event.dom.client.KeyCodes;
import com.google.gwt.event.dom.client.KeyDownEvent;
import com.google.gwt.http.client.RequestException;
import com.google.gwt.http.client.Response;
import com.google.gwt.regexp.shared.RegExp;
import com.google.gwt.regexp.shared.SplitResult;
import com.google.gwt.user.client.Event;
import com.google.gwt.user.client.Event.NativePreviewEvent;
import com.google.gwt.user.client.Event.NativePreviewHandler;
import com.google.gwt.user.client.rpc.StatusCodeException;
import com.google.gwt.xhr.client.ReadyStateChangeHandler;
import com.google.gwt.xhr.client.XMLHttpRequest;
/**
* This class uses a XmlHttpRequest and onreadystatechange events to process stream events.
*
* The main issue with this implementation is that GWT does not generate RECEIVING events from its XMLHTTPRequest. The
* implementation of XMLHTTPRequest included in this package overrides that behaviour.
*
* Another issues is that the memory required for the XMLHTTPRequest's responseText constantly grows so the server
* occasionally disconnects the client who then reestablishes the connection.
*
* The protocol for this transport is a '\n' separated transport messages. The different types of transport message are
* identified by the first character in the line as follows:
*
* ! A connection message followed by the heartbeat duration as an integer
*
* ? A clean server disconnection message
*
* # A heartbeat message
*
* * A padding message to cause the browser to start processing the stream
*
* ] A string message that needs unescaping
*
* | A string message that does not need unescaping
*
* [ A GWT serialized object
*
* R, r or f A GWT deRPC object
*
* string messages are escaped for '\\' and '\n' characters as '\n' is the message separator.
*
* GWT serialized object messages are escaped by GWT so do not need to be escaped by the transport
*
* @author Richard Zschech
*/
public class HTTPRequestCometTransport extends RawDataCometTransport {
private static final String SEPARATOR = "\n";
private static RegExp separator;
static {
Event.addNativePreviewHandler(new NativePreviewHandler() {
@Override
public void onPreviewNativeEvent(NativePreviewEvent e) {
if (e.getTypeInt() == Event.getTypeInt(KeyDownEvent.getType().getName())) {
NativeEvent nativeEvent = e.getNativeEvent();
if (nativeEvent.getKeyCode() == KeyCodes.KEY_ESCAPE) {
nativeEvent.preventDefault();
}
}
}
});
separator = RegExp.compile(SEPARATOR);
}
private XMLHttpRequest xmlHttpRequest;
private int read;
@Override
public void connect(int connectionCount) {
super.connect(connectionCount);
read = 0;
xmlHttpRequest = XMLHttpRequest.create();
try {
xmlHttpRequest.open("GET", getUrl(connectionCount));
xmlHttpRequest.setRequestHeader("Accept", "application/comet");
xmlHttpRequest.setOnReadyStateChange(new ReadyStateChangeHandler() {
@Override
public void onReadyStateChange(XMLHttpRequest request) {
if (!disconnecting) {
switch (request.getReadyState()) {
case XMLHttpRequest.LOADING:
onReceiving(request.getStatus(), request.getResponseText());
break;
case XMLHttpRequest.DONE:
onLoaded(request.getStatus(), request.getResponseText());
break;
}
}
}
});
xmlHttpRequest.send();
}
catch (JavaScriptException e) {
xmlHttpRequest = null;
listener.onError(new RequestException(e.getMessage()), false);
}
}
@Override
public void disconnect() {
super.disconnect();
if (xmlHttpRequest != null) {
xmlHttpRequest.clearOnReadyStateChange();
xmlHttpRequest.abort();
xmlHttpRequest = null;
}
}
private void onLoaded(int statusCode, String responseText) {
xmlHttpRequest.clearOnReadyStateChange();
xmlHttpRequest = null;
onReceiving(statusCode, responseText, false);
}
private void onReceiving(int statusCode, String responseText) {
onReceiving(statusCode, responseText, true);
}
private void onReceiving(int statusCode, String responseText, boolean connected) {
if (statusCode != Response.SC_OK) {
if (!connected) {
super.disconnect();
listener.onError(new StatusCodeException(statusCode, responseText), connected);
}
}
else {
int index = responseText.lastIndexOf(SEPARATOR);
if (index > read) {
List<Serializable> messages = new ArrayList<Serializable>();
SplitResult data = separator.split(responseText.substring(read, index), index);
int length = data.length();
for (int i = 0; i < length; i++) {
if (disconnecting) {
return;
}
String message = data.get(i);
if (!message.isEmpty()) {
parse(message, messages);
}
}
read = index + 1;
if (!messages.isEmpty()) {
listener.onMessage(messages);
}
}
if (!connected) {
super.disconnected();
}
}
}
}
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