Malformed XPath filters fail silently at client side.

[timstaley]

I can start Comet with an XPath filter, like so:

 twistd -n comet --remote localhost \
    --filter='not(starts-with(@ivorn,"ivo://voevent.phys.soton.ac.uk/FOO"))'

which works fine. But, if the XPath is broken, e.g.

--filter='not(starts-with(@ivorn,"ivo://voevent.phys.soton.ac.uk/FOO"'

(note missing close brackets), then Comet will start up quietly and the filter will silently fail. Currently, the only way to check if the XPath translates to a successfully installed filter is to monitor the logs at the server end.

[jdswinbank]

This is addressed by b1e83bd. In the event of an XPath syntax error, Comet will refuse to start as follows:

$ twistd-2.7 -n comet --remote=localhost --filter='not(starts-with(@ivorn,"ivo://voevent.phys.soton.ac.uk/FOO"'
[...]
/opt/local/bin/twistd-2.7: Invalid XPath expression: not(starts-with(@ivorn,"ivo://voevent.phys.soton.ac.uk/FOO"

Note that this is just checking the XPath for syntax correctness. There's no mechanism for the broker to report back to the subscriber that the filter has been accepted and installed successfully; indeed, brokers which are not Comet should simply silently ignore the filter and you'll get no feedback that that's what they're doing.

Does this solve your problem?

[timstaley]

Sounds sensible, this should at least catch the stupidest errors, that's all you can do without case-by-case unit / integration testing, I think. Thanks!

[jdswinbank]

Ok, thanks for the feedback.

I don't think it's worth doing a 1.1.2 release just for this, but when I get around to fixing #31 I'll roll them both into a point release.