Simpler is better – a single event type for StreamResult

23Feb13

StreamResult, covered in my last few blog posts, has panned out pretty well.

Until that is, that I sat down to do a serialised version of it. It became fairly clear that the wire protocol can be very simple – just one event type that has a bunch of optional fields – test ids, routing code, file data, mime-type etc. It is up to the recipient at the far end of a stream to derive semantic meaning, which means that encoding a lot of rules (such as a data packet can have either a test status or file data) into the wire protocol isn’t called for.

If the wire protocol doesn’t have those rules, Python parsers that convert a bytestream into StreamResult API calls will have to manually split packets that have both status() and file() data in them… this means it would be impossible to create many legitimate bytestreams via the normal StreamResult API.

That seems to be an unnecessary restriction, and thinking about it, having a very simple ‘here is an event about a test run’ API that carries any information we have and maps down a very simple wire protocol should be about as easy to work with as the current file or status API.

Most combinations of file+status parameters is trivially interpretable, but there is one that had no prior definition – a test_status with no test id specified. Files with no testid are easily considered as ‘global scope’ for their source, so perhaps test_status should be treated the same way? [Feedback in comments or email please]. For now I’m going to leave the meaning undefined and unconstrained.

So I’m preparing a change to my patchset for StreamResult to:

  • Drop the file() method altogether.
  • Add file_bytes, mime_type and eof parameters to status().
  • Make the test_id and test_status parameters to status() optional.

This will make the API trivially serialisable (both to JSON or protobufs or whatever, or to the custom binary format I’m considering for subunit), and equally trivially parsable, which I think is a good thing.

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