STORM-3164: Fix usage of traceback.format_exc in multilang

[mal]

Misuse of traceback.format_exc was causing exceptions thrown in python bolts to throw TypeErrors during attempts to handle them. Fixing the calls results in expect behaviour.

Examples of the change can be seen below where the Storm side messages have been mocked so as to directly inspect the python side response. Lines prefixed with # are the prompt, > are stdin (manually entered) and > denotes stdout. Unprefixed lines are stderr.

https://issues.apache.org/jira/browse/STORM-3164

Test Code

from storm import Bolt


class TestBolt(Bolt):
    def process(self, tup):
        raise Exception('harakiri!')


if __name__ == '__main__':
    TestBolt().run()

while true; do
  printf '> ' > /dev/tty
  read line
  echo "$line"
  sleep 0.1
  printf '\n' # trigger sigpipe if python is dead
done | python3 multilang/resources/bolt.py | sed 's/^/< /'

Before

# sh ./bolttest
> {"conf": {}, "context": {}, "pidDir": "/tmp"}
> end
< {"pid": 10643}
< end
> {"id":1, "comp": 2, "stream": 3, "task": 4, "tuple": ["foo", "bar"]}
> end
Traceback (most recent call last):
  File "/usr/src/test/storm.py", line 198, in run
    self.process(tup)
  File "bolt.py", line 6, in process
    raise Exception('harakiri!')
Exception: harakiri!

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "bolt.py", line 10, in <module>
    TestBolt().run()
  File "/usr/src/test/storm.py", line 200, in run
    reportError(traceback.format_exc(e))
  File "/usr/lib/python3.4/traceback.py", line 256, in format_exc
    return "".join(format_exception(*sys.exc_info(), limit=limit, chain=chain))
  File "/usr/lib/python3.4/traceback.py", line 181, in format_exception
    return list(_format_exception_iter(etype, value, tb, limit, chain))
  File "/usr/lib/python3.4/traceback.py", line 153, in _format_exception_iter
    yield from _format_list_iter(_extract_tb_iter(tb, limit=limit))
  File "/usr/lib/python3.4/traceback.py", line 18, in _format_list_iter
    for filename, lineno, name, line in extracted_list:
  File "/usr/lib/python3.4/traceback.py", line 58, in _extract_tb_or_stack_iter
    while curr is not None and (limit is None or n < limit):
TypeError: unorderable types: int() < Exception()

After

# sh ./bolttest
> {"conf": {}, "context": {}, "pidDir": "/tmp"}
> end
< {"pid": 10644}
< end
> {"id":1, "comp": 2, "stream": 3, "task": 4, "tuple": ["foo", "bar"]}
> end
< {"command": "error", "msg": "Traceback (most recent call last):\n  File \"/usr/src/test/storm.py\", line 198, in run\n    self.process(tup)\n  File \"bolt.py\", line 6, in process\n    raise Exception('harakiri!')\nException: harakiri!\n"}
< end

[HeartSaVioR]

+1 Wondering why we miss this so long. Nice catch!

[revans2]

+1