The eXtensible REST Services Protocol allows clients to consume services and extend hosts through plug-ins. Hosts are RESTful applications with an extension registry to register plug-ins. Plug-ins receive callbacks from hosts and can decorate host responses. The protocol uses asynchronous callbacks for concurrent execution and synchronous callbacks to allow response decoration in a failure-flexible manner.

1. eXtensible REST Services Protocol
Plug-in Architectural Style for the Cloud
http://xrest.googlecode.com

2. Protocol Objectives
• Running the Web as Platform
• Unify the Experience and Implementation of
Programmable Web Services
Pub/Sub
Browser Blog Plug-in
Social Twitter
Desktop Network Plug-in
... Mail Your Tool

3. Protocol Model
Clients:
• Consume services on the host
• Add plug-in references (extensions) to the host
extension registry
Browser Plug-in A
Desktop Host Plug-in B
... Plug-in C

4. Protocol Model
Hosts:
• Restful application (HTTP: RFC2616)
• Extension registry (AtomPub: RFC5023)
• Callback to plug-ins (Web Hooks: http://webhooks.org)
Browser Plug-in A
Desktop Host Plug-in B
... Plug-in C

5. Protocol Model
Plug-ins:
• Receive callback parameters from the host
• Can decorate the host response to the client.
Browser Plug-in A
Desktop Host Plug-in B
... Plug-in C

6. Protocol Runtime
POST Plug-in A
extension
Browser Plug-in A
Desktop Host Plug-in B
... Plug-in C

7. Protocol Runtime
GET Plug-in A
acknowledgement
Browser Plug-in A
Desktop Host Plug-in B
... Plug-in C

8. Protocol Runtime
OK
Browser Plug-in A
Desktop Host Plug-in B
... Plug-in C

9. Protocol Runtime
OK
Browser Plug-in A
Desktop Host Plug-in B
... Plug-in C

10. Protocol Runtime
Browser Plug-in A
Desktop Host Plug-in B
... Plug-in C
The service has
been extended

11. Protocol Runtime
REST call
Browser Plug-in A
Desktop Host Plug-in B
... Plug-in C

12. Protocol Runtime
Compute
response
Browser Plug-in A
Desktop Host Plug-in B
... Plug-in C

13. Protocol Runtime
POST
response body +
extension header
Browser Plug-in A
Desktop Host Plug-in B
... Plug-in C

14. Protocol Runtime
Decorated
response body
Browser Plug-in A
Desktop Host Plug-in B
... Plug-in C

15. Protocol Runtime
Decorated
response body
Browser Plug-in A
Desktop Host Plug-in B
... Plug-in C

16. Scheduling
Asynchronous Callbacks:
• May be executed concurrently
• Cannot decorate the host response
Synchronous Callbacks:
• Sequential execution
• Can decorate the host response
• Flexible to failures

17. Resources
Specification: http://tiny.cc/xrest
Questions and feedbacks:
xrest@googlegroups.com
More infos:
http://xrest.googlecode.com