Wednesday, May 4, 2011

Internet Protocols

Since starting off my GSoC assignment to get offline mode to work on the Lightning extension, there are a couple of things, that are needed to be studied in more careful details. One of them is the protocols that calendar providers use, in order to update calendars.
WebDAV is the base protocol over which a large number of other protocols such as CalDAV and CardDAV are based. HTTP itself does not collaboration among the authors of a document, it also does not say that it is impossible to do so.
As such a working group of the IETF drafted the WebDAV specs and they are being widely in the world right now in creation of newer methods of communication. It is being proposed that WebDAV become the standard of shared documents/resources on the web, thereby replacing FTP and other resource access protocols.
I was going through the specifications this week and found that WebDAV collaborators did not have any WebDAV enabled applications at that time, as such most of their work was based in using e-mails as a form of communicating changes in the document to a central author who then changed the document and mailed the document to the rest. Imagine, how painful it would be to mail everytime, and if the central author is not merging the changes (maybe he takes a break), the mechanism would certainly fail, causing trouble for many.
WebDAV Distributed Authoring Protocol defines a set of extensions to the base Hypertext Transfer Protocol for the capabilities like overwrite prevention, namespace management and properties.
I describe some details below:

  • under overwrite prevention, WebDAV uses shared and exclusive locking mechanism, in order to prevent conflicts
  • by properties, WebDAV protocol allows metadata to be stored and retrieved.
  • namespace management, allows copying, moving and listing of shared resources, also known as collections.
Phew! that was simple. My next target is looking up at the specs of CalDAV and look up its implementation inside Lightning =)


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