[Buildbot-devel] writing custom sources?

Timothee Besset ttimo at idsoftware.com
Mon Jul 28 09:56:58 UTC 2003

The logfile source starts to work. It's quite ugly. I compare dates
between a log file of checkins and a log file of builds. That's cause I
don't use CVSToys and use something else.

With the polling strategy I also need to be careful not sending further
changes until the checkins log evolves again (i.e. store last change

I can send you that code but it's not very interesting really. A proper
example in the source might be good though.


On Sun, 27 Jul 2003 11:54:31 -0700 (PDT)
Brian Warner <warner-buildbot at lothar.com> wrote:

> > What's the easiest way to write a custom source? For instance I need to
> > trigger a build when a logfile gets a new entry..
> The best way is probably to copy the FreshCVSSource class from
> buildbot/changes/freshcvs.py . I really need to get a better handle on the
> way Twisted uses "Interfaces" and create an IChangeSource to define what
> those classes are required to do, but basically it should be an object that
> defines the following methods:
>  def start(self):
>    """Called when the buildmaster starts up. Can be used to establish a
>    connection to a source control daemon, or start a timer to poll
>    something."""
>  def stop(self):
>    """Called when the buildmaster shuts down. Connections should be torn
>    down, timers should be canceled."""
>  def describe(self):
>    """Should return a string which describes this source and a brief summary
>    of its status (like [OFFLINE]). Will be used in an HTML status page."""
> Then, once the source is up and running, it should create Change objects
> (buildbot/changes/changes.py) and feed them to:
>   self.changemaster.addChange(c)
> Each Change object represents one person making changes to one or more files
> or directories, all with the same checkin comments.
> I can think of two ways to watch a logfile for new entries. One involves
> opening the file for reading, consuming everything that is available, then
> waking up when the file becomes readable again (meaning someone else has
> appended data to it): the "tail -f" approach. To do this you'd want to
> create a class derived from twisted.internet.abstract.FileDescriptor, call
> the startReading() method, and have a doRead() method that pulls off a line
> and submits a Change.
> The other way is a hack but might be easier: the "poll it" approach. In your
> change source class, have start() create a timer with reactor.callLater.
> When the timer fires, stat the logfile and remember its size. When the size
> changes, read data from it and construct/submit the Change object. Make sure
> to .cancel() the timer in the stop() method. It might also be useful
> (eventually) to have the describe() text indicate how long until the next
> poll takes place ("%d" % (self.timer.getTime() - time.time())).
> In either case, feel free to create "fake" Change objects. They were
> designed to accomodate CVS-style change notification, but if your build
> process doesn't care about which files are being modified, and you aren't
> trying to associate people with those changes, then you could just do:
>  c = Change("logfile", [], "the logfile was changed", 0)
>  self.changemaster.addChange(c)
> to trigger the build timer. The waterfall page would indicate "logfile" as
> the user in the Changes column, and no files would be listed.
> Or, of course, if your logfile contains information resembling source code
> control system change messages, you can parse them and create a more
> accurate Change object.
> Hope that helps.. please let me know how it goes, I am very hungry for
> feedback about the internal interfaces, as I want to make sure they're
> organized in such a way that it is easy to customize to do what you want.
> The only use cases I've had so far are the ones I've come up with myself,
> and that won't let me refactor it in the best way possible.
> thanks,
>  -Brian
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