This document discusses HTML5 communication and messaging APIs, including cross-document messaging, CORS, server-sent events, and web sockets. Cross-document messaging allows sending messages between windows using postMessage. CORS enables cross-domain requests if responses include access control headers. Server-sent events allow push data from servers to clients. Web sockets provide bidirectional communications over a single TCP connection. The session explored examples of these APIs and their browser support.

1. Using Communication and
Messaging API in The HTML5
World
Gil Fink
CEO, sparXys
@gilfink, http://www.gilfink.net

2. Agenda
• HTML5: Recap
• HTML5 Messaging APIs
• HTML5 Communication APIs
• Q&A
• Summary

3. HTML5: Recap
• HTML5 ~= HTML + CSS3 + new JavaScript API
• The present and future of the web
• W3C Recommendation!

4. What’s Under the HTML5
Umbrella?

5. Communication and Messaging

6. Cross-Document Messaging
• Simple API to send and receive in-window
messages
• Send messages using the postMessage function
• Wire handlers to the message event
6
window.postMessage(message, domain);
window.addEventListener("message", function () {
// do something
}, false);

7. DEMO
Cross-Document Messaging
Web Worker

8. Web Application APIs Support
– Cross-Document Messaging
http://caniuse.com

9. Cross-Origin Resource Sharing
(CORS)
• Browsers prevent cross-domain JavaScript requests
• CORS enables cross-domain requests as long as:
o Response includes Access-Control-Allow-Origin header
o XMLHttpRequest supports CORS
• XDomainRequest in IE8 and IE9

10. CORS – Client Side
var xhr = new XMLHttpRequest();
xhr.open(“get”, url, true);
xhr.onload = function () {
// instead of using onreadystatechange
}
xhr.send();

11. CORS – Client Side API
• Functions:
o abort() – stops a request that is already in progress
o send() – sends a request to the server
• Event handlers:
o onerror – handles request errors
o onload – handles request success

12. CORS – Access Control Flow
• Client sends ‘Access-Control’ headers during
request preflight
o Using the OPTIONS HTTP request
• Server checks whether the requested resource is
allowed
• Client checks the preflight response and decides
whether to allow the request

13. CORS – Server Side
• Use Access-Control headers to allow
o Origin – Specific request URI
o Method – request method (GET, POST and etc.)
o Headers – optional custom headers
o Credentials – request credentials

14. DEMO
CORS

15. Web Application APIs Support
– CORS
http://caniuse.com

16. Server-Sent Events
• Enables servers to push data over HTTP using push
protocols
• Use the EventSource JavaScript API
var source = new EventSource(url);
source.onmessage = function (e) {
console.log(e.data);
}

17. Server-Sent Events - Server
• Strict server protocol:
data: This is a message.
event: add
data: 73857293
• Response content type should be text/event-stream
• Keeps the connection open

18. DEMO
Server-Sent Events

19. Web Application APIs Support
– Server-Sent Events
http://caniuse.com

20. Real Time Web?

21. Existing Solutions

22. Web Sockets
• Bidirectional communications channels, over a
single TCP socket
• Don’t allow raw access to the underlying network
• Can replace old techniques such as:
o Forever frames
o Long-polling/comet

23. Web Sockets – Client Request
• The client sends a WebSocket handshake request
GET /chat HTTP/1.1
Host: server.example.com
Upgrade: websocket
Connection: Upgrade
Sec-WebSocket-Key: dGhlIHNhbXBsZSBub25jZQ==
Sec-WebSocket-Origin: http://example.com
Sec-WebSocket-Protocol: chat, superchat

24. Web Sockets – Server Response
• The server responses with a WebSocket handshake
response
HTTP/1.1 101 Switching Protocols
Upgrade: websocket
Connection: Upgrade
Sec-WebSocket-Accept: s3pPLMBiTxaQ9kYGzzhZRbK+xOo=
Sec-WebSocket-Protocol: chat

25. Web Sockets – API
• Create a WebSocket object using a URL
• Use the WebSocket object’s built-in events:
o onopen – fired when a web socket has opened
o onmessage – fired when a message has been received
o onclose – fired when a web socket has been closed

26. DEMO
Web Sockets

27. Web Application APIs Support
– Web Sockets
http://caniuse.com

28. Questions?

29. Summary
• HTML5 is a W3C recommendation
• In this session we explored communication and
messaging APIs
• You have a lot more to cover

30. Resources
• APIs specs –
http://www.w3.org/TR/html5/comms.html
http://www.w3.org/TR/cors/
http://www.w3.org/TR/eventsource/
http://www.w3.org/TR/websockets/
• My Blog – http://www.gilfink.net
• Follow me on Twitter – @gilfink

31. Thank You!