Adding a linkifier can cause sending messages to timeout.

[davidtwco]

I've found that when creating two linkifiers, one of which is a subset of the other, then sending a message with the "more restrictive" linkifier will cause Zulip to timeout when rendering the message.

For example, given this linkifier that matches any JIRA ticket - (?P<id>[A-Z]+-[0-9]+) (URL isn't important) - and this linkifier which matches a specific JIRA project (which could be on a different instance and thus isn't handled correctly by the first linkifier) - FOO-(?P<id>[0-9]+) - then when sending a message like FOO-3, Zulip will timeout when rendering the message.

Logger root, from module zerver.lib.bugdown line 2211:
Error generated by Anonymous user (not logged in) on chat deployment

Traceback (most recent call last):
  File "/home/zulip/deployments/2019-05-04-17-26-36/zerver/lib/bugdown/__init__.py", line 2195, in do_convert
    rendered_content = timeout(5, _md_engine.convert, content)
  File "/home/zulip/deployments/2019-05-04-17-26-36/zerver/lib/timeout.py", line 83, in timeout
    raise TimeoutExpired
zerver.lib.timeout.TimeoutExpired: Function call timed out.


Deployed code:
- ZULIP_VERSION: 2.0.3
- version: 2.0.3


Request info: none

[timabbott]

Yes, overlapping patterns are not supported. My guess is you're causing an infinite loop in the markdown processor, which is being caught by our timeout for detecting that. I'm not sure there's an easy way for us to handle this generically, but generally the advice is to use mutually exclusive patterns (e.g. require a # before the ID in the first pattern or whatever).