Twisted Logic by Ashwini Oruganti

This talk will be a survey of my learning experience adding new endpoint APIs to Twisted, an event-driven networking engine (as a Google Summer of Code project), with a special focus on the analysis of some of the horror stories that surround Twisted. Right from the asynchronous I/O model to Deferreds: if it scares you, we’ll figure a way out and see what the makers of Twisted say when confronted.

Transcript

1. Twisted Logic - Ashwini Oruganti @_ashfall_ PyCon 2013
2. Twisted asynchronous event-driven networking framework
3. Twisted asynchronous event-driven networking framework aka... HARD
4. Google Summer of Code spend the summer working on an open source project with a mentoring organization
5. Endpoint an interface with a single method that takes an argument returns*: a listening port / a connected protocol
6. endpoint = TCP4ServerEndpoint(reactor, 8007) endpoint.listen(Factory()) endpoint = TCP4ClientEndpoint(reactor, "localhost", 8007) endpoint.connect(Factory()) Server Client
7. class TCP4ServerEndpoint(object): """ Implements TCP server endpoint with an IPv4 configuration """ ... def __init__(self, reactor, port, backlog=50, interface=''): ... def listen(self, protocolFactory): return defer.execute( self._reactor.listenTCP, ...)
8. class TCP6ServerEndpoint(object): """ Implements TCP server endpoint with an IPv6 configuration """ ... def __init__(self, reactor, port, backlog=50, interface='::'): ... def listen(self, protocolFactory): return defer.execute( self._reactor.listenTCP, ...)
10. It’s just code.
11. class StandardIOEndpoint(object): """ A Standard Input/Output endpoint """ implements(interfaces.IStreamServerEndpoint) def __init__(self, reactor): ... def listen(self, stdioProtocolFactory): return defer.execute(stdio.StandardIO, stdioProtocolFactory.buildProtocol( PipeAddress()))
12. Moral of the story: Do not get flustered. Do not overthink.. Forget it's Twisted
13. Read the code. Solve the problem (write code) Moral of the story:
14. There’s nothing more boring than the comfort zone
15. TCP Client Endpoint IPv6 addresses Hostname Resolution
16. class TCP6ClientEndpoint(object): def __init__(self, reactor, host, port, timeout=30, bindAddress=None): ... def connect(self, protocolFactory): """ Connect via TCP, once the hostname resolution is done. """ ...
17. def _nameResolution(self, host): """ Resolve the hostname string into a tuple containing the host IPv6 address. """ ... def _resolvedHostConnect(self, resolvedHost, protocolFactory): """ Connect to the server using the resolved hostname. """ ...
18. Deferred Callbacks and Errbacks Flow is not obvious Debugging is tricky
19. class SomeState(object): def __init__(self): self.values = [] def getValue(self): return self.values.pop(0) def addValue(self, value): self.values.append(value)
20. def foo(): return SomeState() def bar(): state = foo() print state.getValue()
21. Firing the Deferred def foo(): s = SomeState() s.addValue(2) return s
22. It’s just code.
23. It’s 'X', when it isn't really 'X'
24. It’s full of highly complex concepts!
25. “It was created by a couple of dudes who dropped out of school, and a 16-year-old. HOW HARD COULD IT BE?”
27. It’s foreign!
28. camelCase PEP8: July 5, 2001 Twisted’s coding standard: May 2, 2001
29. It’s huge!
30. “Core can fit into a floppy disk.”
31. Know what you're doing.
33. <conclusion />