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Kneel And Disconnect: Getting The Fastest Connection Out Of A Hostname

Kneel And Disconnect: Getting The Fastest Connection Out Of A Hostname

Did you know that when you resolve a hostname, you can get multiple addresses back, and pick any one to connect to? Some of these addresses will connect near instantly, while others might take a long time or time out. This talk is about a Twisted endpoint API I built that takes a hostname, and returns the connection that takes the least time to complete, from the list of resolved host addresses.

Ashwini Oruganti

April 11, 2014

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  1. Endpoint an interface with a single method that takes an

    argument returns*: a listening port / a connected protocol
  2. “There are probably people out there who are smart enough

    not to need [tests], we’re not one of those. ” - PyPy docs
  3. Step 2: Sort them from simplest to most complex. (the

    failure ones come before the success ones)
  4. def _nameResolution(self, host): try: d = self.deferToThread( self._getaddrinfo, host, 0)

    return d except socket.gaierror: defer.fail( error.DNSLookupError("...")) # WRONG
  5. def _nameResolution(self, host): return self._deferToThread( self._getaddrinfo, host, 0) def connect(self,

    protocolFactory): [...] def errbackForGai(obj): return fail(error.DNSLookupError("...")) d = self._nameResolution(self._host) d.addErrback(errbackForGai)
  6. If something is hard to test, it is usually a

    bad idea. Good code is generally easy to test.
  7. 0 seconds later is still "some amount of time" later,

    even if it's not a very big amount of time
  8. def connect(self, protocolFactory): [...] def _canceller(d): [...] def errbackForGai(failure) [...]

    def _endpoints(gaiResult): [...] def attemptConnection(endpoints): [...] def usedEndpointRemoval(connResult, connAttempt): [...] def afterConnectionAttempt(connResult): [...] def checkDone(): [...] def connectFailed(reason): [...] def iterateEndpoint(): [...]