What is REST

REST is an alternative to RPC based web services such as JSONRPC, XMLRPC and SOAP. Instead of simply using HTTP POST for all of its requests (with JSONRPC’s proposed GET implementation excepted) like RPC services do, it uses all the HTTP methods. It usually includes GET, POST, DELETE, PUT and other methods to achieve different results and thereby uses relatively few URIs.

Some people think any web service that makes various services available at URIs is REST. It isn’t. Some people make a service at one URI for getting an object, another for saving the object, another for getting a list of ojects, another for a list of objects matching a certain criteria. This is just RPC outisde of the realm of a specific protocol (like XMLRPC). If people are going to use simple HTTP RPC requests to get all their data but not follow any specific pattern, they’d be better off with a real RPC implementation.

How is it Better (or Worse)

REST has a lot going for it. Because it is a little more “native” to the HTTP protocol, caching can work very efficiently. Depending on language support, it may be be easier to work with a REST interface than working with a more complex RPC specific protocol. Its simplicity can be very beautiful. The RESTful idea of making your data available as a “resource” that links via hypertext to more resources can make REST very powerful.

Instead of

GET http://example.com/testcase/56

<testcase>
<results>
<result>1</result>
<result>2</result>
</results>
</testcase>

You have

GET http://example.com/testcase/56

<testcase>
<results>
<result>http://example.com/result/1</result>
<result>http://example.com/result/2</result>
</results>
</testcase>

In the 2nd method a full test case object can be generated by off of a request to the testcase object and later requests for the result objects. The client would not need to know anything special about testcases or the specific domain as it would in the first example.

RPC also has a lot going for it and there are some cases where I would pick it over REST. Caching is not always very important and when it isn’t, the benefits REST are not as apparent. Most RPC protocols already have the capability out of the box to construct objects (for SOAP — very complex objects) from web service calls. They also usually have introspection methods or WSDL to figure out what services are available. These would need to be built by a crafty REST service developer. RPC, however, doesn’t take much advantage of the HTTP protocol in that most requests are just POST requests with an RPC payload. At the same time, every HTTP implementation supports POST and not all of them support PUT or DELETE.

Next Steps

Django has a few libraries to help with REST interfaces, but nothing I’ve seen is that great. I am going to look into creating one or contributing to an existing project. Here are some things I’d like to see in a REST API:

• In the Django 1.1 development version, PUT, DELETE, OPTIONS and HEAD are available in django.test.client.Client. A REST interface should use them by default and have another mechanism for clients that do not support these lesser used HTTP methods.
• caching and ETags
• different output formats (eg. XML and JSON)
• service/resource discovery or introspection (similar to WSDL or system.listMethods)
• a client library than can generate complex native python objects given a URI
• models and other sources of data as REST resources
• integration at some point with the Django trunk!

What’s Already Out There

There’s a few Django projects for making data available via REST. These efforts seem to have stalled or be in infant stages.

• Django model views — A GSoC project to make Django model data available via REST.This project never seemed to get far off of the ground. I don’t think it has been updated much since 2007.
• Django REST interface — Another GSoC project to create RESTful interfaces.There seem to be some active users of this one and it seems to be more fully featured than the above model views project. However, it has stalled and there hasn’t been much work on it in the past few years.
• Django RESTAPI — Another project to make models available via REST.This project seems to have been more recently updated and it seems ok, but it still isn’t ready for prime time or in Pypi.
• RESTinPy — A sourceforge project that makes data available in REST.
  This project seems somewhat advanced but it hasn’t been updated since the first cut was put onto sourceforge and Pypi.
• DAPI — Another model to REST mapping module

Reading

• HTTP protocol
• Fielding’s dissertation on REST — the inspiration of REST
• REST Worst Practices — by Jacob Kaplan-Moss of Django fame
• Creating a REST protocol
• Common REST mistakes
• A counterpoint on why Django may not need a REST API

Edit (July 15, 2010): I wrote an update involving Piston, a popular REST framework for Django.
Update (September 7, 2011): There were some updates on what folks in the community were using at Djangocon.