Friday, May 05, 2006

GData module for Drupal

Introduction :

GData is a (new) protocol from Google which is based on RSS and Atom and combines both of them. Infact underlying GData are actually RSS and Atom protocols. GData makes available :
request (syndication), query (for search), insert, update and delete.

All these together make *remote* usage of a CMS much more a reality and since Google is behind this, there is a good chance of this becoming the de-facto standard in future.

A little deeper :

GData allows for content to be syndicated as well as inserted, updated and deleted. Most importantly a seperate specification for query. Nice! GData uses XML as described in existing Atom and RSS specs for all these. Different features, btw, are supposed to use different HTTP request methods as outlines below:

Feature HTTP method
Request / QueryGET
Insert POST

Note: There are alternatives to HTTP PUT and HTTP DELETE : clients can use headers 'X-HTTP-Method-Override: PUT' and 'X-HTTP-Method-Override: DELETE' for PUT and DELETE respectively.

There is also the authentication part in GData which as Moshe pointed out in, is Google specific, and moreover work on it is still in progress. So for now I have not much concentrated there. I hope that area will get better soon.

Inside Drupal :

As far as I have studied, some problems which exist in relation to GData are:
  • Handling HTTP PUT and DELETE. PUT and DELETE do not seem to work well on all servers and clients across platforms. The headers ( X-HTTP-Method-Override: PUT and X-HTTP-Method-Override: DELETE ) ofcourse come to the rescue and to me the headers seem to be the best solution.
  • Queries have to use the URL format: q=query-string Here, as again Moshe pointed out on we, can not use the q part. In discussion with praseodym on #drupal-soc, the best solution seems to create a seperate file named say gfeed.php which handles user requests and passes them onto drupal after doing modifications as necessary. So for all GData related stuff there will exist clients will use URL gfeed.php is also used for non-query purposes like normal requests, insert, etc. gfeed.php ofcourse sends the request to drupal after modifications to the incoming request as necessary. Other solutions like using .htaccess also exist.

What is needed in GData module and how it is done:

The GData module needs to define an API through which any module can register itself to expose data.
Since GData allows for Insert or Updates, modules need to specify the access permissions too.
There will be a file (say gfeed.php) which will take in actual user requests since in query we need "q=something" format in URL and "q" has special meaning inside Drupal. Thus normal bootstrap will not work, which brings in the need for gfeed.php. Users/clients access Drupal GData in URL format : When they need to query they do gfeed.php then turns the request to Drupal after doing required changes.
Inside actual module the response is built and sent back to the user as XML.

Links :

GData overview
GData protocol
Drupal page on GData module
Roadmap for GData module
Me in a Drupal project

Related Links Elsewhere on the GData buzz :
GData - Google's new syndication protocol : From
Google's GData, MySQL, and the Future of on-line Databases : Jeremy Zawodny's blog
Why Google is extending RSS : From
Google Data APIs Protocol : Joe Gregorio
Google and RSS: GData : By Vincent
Google syndication : By Jeff Jarvis
GData - Google BCM protocol : By Deeje Cooley
GData: The end of Google's walled garden : By Maurice Codik
GData is a new protocol based on Atom 1.0 and RSS 2.0 : By Karl Martino
GData is about more than Google Calendar integration : By Mark McLaren
GData: Google's Extensible API : By Reto Meier
Google introduces GData: Google Calendar API : By Amit Agarwal

Also ASF has an application titled "Implement a Google Data API (GData) server using Lucene" for SoC 2006.

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