93 lines
3.3 KiB
Python
93 lines
3.3 KiB
Python
import abc
|
|
import logging
|
|
import six
|
|
|
|
|
|
logger = logging.getLogger(__name__)
|
|
|
|
|
|
@six.add_metaclass(abc.ABCMeta)
|
|
class PipelineHandlerBase(object):
|
|
"""Base class for Pipeline handlers.
|
|
|
|
Pipeline handlers perform the actual processing on a set of events
|
|
captured by a stream. The handlers are chained together, each handler
|
|
in a pipeline is called in order, and receives the output of the previous
|
|
handler.
|
|
|
|
Once all of the handlers in a pipeline have successfully processed the
|
|
events (with .handle_events() ), each handler's .commit() method will be
|
|
called. If any handler in the chain raises an exception, processing of
|
|
events will stop, and each handler's .rollback() method will be called."""
|
|
|
|
def __init__(self, **kw):
|
|
"""Setup the pipeline handler.
|
|
|
|
A new instance of each handler for a pipeline is used for each
|
|
stream (set of events) processed.
|
|
|
|
:param kw: The parameters listed in the pipeline config file for
|
|
this handler (if any).
|
|
"""
|
|
|
|
@abc.abstractmethod
|
|
def handle_events(self, events, env):
|
|
""" This method handles the actual event processing.
|
|
|
|
This method receives a list of events and should return a list of
|
|
events as well. The return value of this method will be passed to
|
|
the next handler's .handle_events() method. Handlers can add new
|
|
events simply by adding them to the list they return. New events
|
|
(those with unrecognized message_id's), will be saved to the
|
|
database if all handlers in this pipeline complete successfully.
|
|
Likewise, handlers can omit events from the list they return to
|
|
act as a filter for downstream handlers.
|
|
|
|
Care should be taken to avoid any operation with side-effects in
|
|
this method. Pipelines can be re-tried if a handler throws an
|
|
error. If you need to perform such operations, such as interacting
|
|
with an external system, save the needed information in an instance
|
|
variable, and perform the operation in the .commit() method.
|
|
|
|
:param events: A list of events.
|
|
:param env: Just a dictionary, it's passed to each handler, and
|
|
can act as a shared scratchpad.
|
|
|
|
:returns: A list of events.
|
|
"""
|
|
|
|
@abc.abstractmethod
|
|
def commit(self):
|
|
""" Called when each handler in this pipeline has successfully
|
|
completed.
|
|
|
|
If you have operations with side effects, preform them here.
|
|
Exceptions raised here will be logged, but otherwise ignored.
|
|
"""
|
|
|
|
@abc.abstractmethod
|
|
def rollback(self):
|
|
""" Called if there is an error for any handler while processing a list
|
|
of events.
|
|
|
|
If you need to perform some kind of cleanup, do it here.
|
|
Exceptions raised here will be logged, but otherwise ignored.
|
|
"""
|
|
|
|
|
|
class LoggingHandler(PipelineHandlerBase):
|
|
|
|
def handle_events(self, events, env):
|
|
emsg = ', '.join("%s: %s" % (event['event_type'], event['message_id'])
|
|
for event in events)
|
|
logger.info("Received %s events: \n%s" % (len(events)), emsg)
|
|
return events
|
|
|
|
def commit(self):
|
|
pass
|
|
|
|
def rollback(self):
|
|
pass
|
|
|
|
|