Il protocollo WebSocket è ormai diventato un protocollo standard (RFC 6455), e ormai quasi tutti i browsers lo supportano. A differenza di HTTP permette una vera comunicazione bidirezionale tra client e server, permettendo di realizzare applicazioni molto scalabili. In questa sessione daremo uno sguardo al protocollo WebSocket e esamineremo come scrivere una applicazione web utilizzando WebSocket.

1. Simone Bordet
1
sbordet@intalio.com

2. How to Build
WebSocket
Web Applications
Simone Bordet
2
sbordet@intalio.com

3. Simone Bordet
Senior Engineer/Architect at Intalio/Webtide
 Support for Jetty and CometD open source projects
Open Source Contributor
 Jetty, CometD, MX4J, Foxtrot, LiveTribe, JBoss, Larex
JVM tuning expert
Working on Web Network Protocols
 HTTP, WebSocket, SPDY, etc.
Simone Bordet
3
sbordet@intalio.com

4. Agenda
What is WebSocket
WebSocket Browser API
WebSocket Server API
Demo
Q&A
Simone Bordet
4
sbordet@intalio.com

5. What is WebSocket ?
Simone Bordet
5
sbordet@intalio.com

6. WebSocket
WebSocket is the HTML 5 standard protocol for
bidirectional web communication
 HTTP is always client-initiated
 Finally, standard server-push
Work began in 2009, ended in 2012
 Excruciatingly painful
 But at the end, a good standard protocol
Simone Bordet
6
sbordet@intalio.com

7. WebSocket Protocol
The WebSocket protocol is made of 2 parts
 WebSocket upgrade
 WebSocket data exchange
WebSocket upgrade
 It's plain old HTTP with an “Upgrade” header
 WebSocket runs on port 80
 Could be a trouble for inspecting HTTP proxies that
do not support WebSocket
Simone Bordet
7
sbordet@intalio.com

8. WebSocket Upgrade
REQUEST
GET / HTTP/1.1
Host: localhost:8080
Origin: http://localhost:8080
Connection: Upgrade
Upgrade: websocket
Sec-WebSocket-Key: SbdIETLKHQ1TNBLeZFZS0g==
Sec-WebSocket-Version: 13
RESPONSE
HTTP/1.1 101 Switching Protocols
Connection: Upgrade
Upgrade: websocket
Sec-WebSocket-Accept: y4yXRUolfnFfo3Jc5HFqRHNgx2A=
Simone Bordet
8
sbordet@intalio.com

9. WebSocket Protocol
WebSocket data exchange
 Sequence of WebSocket “frames”
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-------+-+-------------+-------------------------------+
|F|R|R|R| opcode|M| Payload len | Extended payload length |
|I|S|S|S| (4) |A| (7) | (16/64) |
|N|V|V|V| |S| | (if payload len==126/127) |
| |1|2|3| |K| | |
+-+-+-+-+-------+-+-------------+ - - - - - - - - - - - - - - - +
| Extended payload length continued, if payload len == 127 |
+ - - - - - - - - - - - - - - - +-------------------------------+
| |Masking-key, if MASK set to 1 |
+-------------------------------+-------------------------------+
| Masking-key (continued) | Payload Data |
+-------------------------------- - - - - - - - - - - - - - - - +
: Payload Data continued ... :
+ - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - +
| Payload Data continued |
+---------------------------------------------------------------+
Simone Bordet
9
sbordet@intalio.com

10. WebSocket Protocol
Very compact
 Smallest data frame has only 2 bytes overhead
Typical first byte is 0x81 for a text frame
 0x82 for a binary frame
 0x88 for a close frame
WebSocket “close” frame
 Sent by the application to signal end of data
 Must be replied before closing TCP connection
Prevents loss of data
Browsers MUST mask frames
 But servers are not required to
Simone Bordet
10
sbordet@intalio.com

11. WebSocket Performance
Simone Bordet
11
sbordet@intalio.com

12. WebSocket Performance
Simone Bordet
12
sbordet@intalio.com

13. WebSocket
Browser API
Simone Bordet
13
sbordet@intalio.com

14. WebSocket Browser API
interface WebSocket {
WebSocket(DOMString url, optional (DOMString or DOMString[]) protocols)]
attribute Function? onopen;
attribute Function? onerror;
attribute Function? onclose;
attribute Function? onmessage;
void send(DOMString data);
void close(optional unsigned short code, optional DOMString reason);
attribute DOMString binaryType; // “blob” or “arraybuffer”
void send(ArrayBuffer data);
void send(Blob data);
};
Simone Bordet
14
sbordet@intalio.com

15. WebSocket Browser API Usage
var ws = new window.WebSocket(“ws://localhost:8080/ws”);
ws.send(“Hello, World”);
ws.onopen = function() {
ws.send(“Hello, World”);
};
ws.onclose = function(event) {
// Server closed
}
ws.onmessage = function(event) {
var data = event.data;
window.console.info(“Server says: ” + data);
};
Simone Bordet
15
sbordet@intalio.com

16. WebSocket
Server API
Simone Bordet
16
sbordet@intalio.com

17. WebSocket Server API
No standard API for WebSocket webapps yet
Servlet 3.0 addressed asynchronous HTTP
Servlet 3.1 (JSR 340) to address this
 Expected Q1 2013
For now, rely on Jetty API
 Java API for both client and server
Simone Bordet
17
sbordet@intalio.com

18. WebSocket Jetty API
public class MyWebSocketServlet extends WebSocketServlet {
public WebSocket doWebSocketConnect(HttpServletRequest r, String p) {
return new MyWebSocket();
}
}
public class MyWebSocket implements WebSocket.OnTextMessage {
public void onOpen(Connection connection) {
}
public void onMessage(String data) {
}
public void onClose(int closeCode, String message) {
}
}
Simone Bordet
18
sbordet@intalio.com

19. Simone Bordet
19
sbordet@intalio.com

20. Conclusions
WebSocket programming is easy !
However, may not be widely deployed
 Old browsers
 Old internet proxies
WebSocket is low-level
 A framework on top gives much more productivity
 CometD
Simone Bordet
20
sbordet@intalio.com

21. References
WebSocket Protocol
 http://www.ietf.org/rfc/rfc6455.txt
JSR 340 (Servlet 3.1)
 http://jcp.org/en/jsr/detail?id=340
WebSocket API
 http://dev.w3.org/html5/websockets/
Jetty
 http://eclipse.org/jetty
CometD
 http://cometd.org
Simone Bordet
21
sbordet@intalio.com

22. Questions
&
Answers
Simone Bordet
22
sbordet@intalio.com