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GSoC Week 8: Reworking

The 8th. week of GSoC is there. The second evaluation phase has begun.

This week I was not as productive as the weeks before. This is due to me having my last (hopefully :D ) bachelors exam. But that is now done, so I can finally give 100% to coding :) .

I made some more progress on my Jingle code rework. Most of the transports code is now finished. I started to rework the descriptions code which includes the base classes as well as the JingleFileTransfer code. I’m very happy with the new design, since it is way more modular and less interlocked than the last iteration. Below you can find an UML-like diagram of the current structure.

UML diagram of the jingle code

UML-like diagram of the current jingle implementation

During the rework I stumbled across a slight ambiguity in the Jingle XEP(s), which made me wonder: There are multiple jingle actions, which denote the purpose of a Jingle stanza (eg. transport-replace to replace the used transport message, session-initiate to initiate a session (duh) and so forth). Now there is the session-info Jingle action, which is used to announce session specific events. This is used for example in RTP sessions to let the peers client ring during a call, or to send the checksum of a file in a file transfer session. My problem with this is, that such use-cases are in my opinion highly description related and instead the description-info action should be used. The description part of a Jingle session is the part that represents the actual purpose of the session (eg. file transfer, video calls etc.).

The session itself is description agnostic, since it only bundles together a set of contents. One content is composed of one description, one transport and optionally one security element. In a content you should be able to combine different description, transport and security components in an arbitrary way. Thats the whole purpose of the Jingle protocol. In my opinion it does no make much sense to denote description related informational stanzas with the session-info action.

My proposal to make more use of the description-info element is also consistent with other uses of *-info actions. The transport-info action for example is used to denote transport related stanzas, while the security-info action is used for security related information.

But why do I even care?

Lets get back to my implementation for that :) . As you can see in the diagram above, I split the different Jingle components into different classes like JingleTransport, JingleSecurity, JingleDescription and so on. Now I’d like to pass component-related jingles down to the respective classes (a transport-info usually only contains information valuable to the transport-component). I’d like to do the same for the JingleDescription. At the moment I have no real “recipient” for the session-info action. It might contain session related infos, but might also be interesting for the description. As a consequence I have to make exceptions for those actions, which make the code more bloated and less logical.

Another point is, that such session-info elements (due to the fact that they target a single content in most cases) often contain a “name” attribute that matches the name of the targeted content. I’d propose to not only replace session-info with description-info, but also specify, that the description-info MUST have one or more content child elements that denote the targeted contents. That would make parsing much easier, since the parser always can expect content elements.

That’s all for now :)

Happy Hacking!

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