[Bug 1741913] Re: [master] Twisted seems to not handle disconnect from client correctly

[Eric Desrochers]

With this test package I want to see if the 'traceback' will disapear
and if this will also solve the MAAS UI telling "X rack controllers are
not yet connected to the region. Visit the rack controllers page for
more information" despite that everything else look good (network,
firewall rules, nc test, ...)

With that test package we will be able to see if it's 2 separate
situations or if they have this bug in common as the culprit.

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Title:
  [master] Twisted seems to not handle disconnect from client correctly

Status in MAAS:
  New
Status in twisted package in Ubuntu:
  Confirmed

Bug description:
  [Impact]

  Web http/wsgi doesn't fail gracefully when the client closes the
  connection, causing 'Traceback' in MAAS /var/log/maas/rackd.log as
  follows:

  ....
     File "/usr/lib/python3/dist-packages/twisted/python/failure.py", line 385, in raiseException
       raise self.value.with_traceback(self.tb)
   builtins.AttributeError: 'NoneType' object has no attribute 'writeHeaders'
  ....
     File "/usr/lib/python3/dist-packages/twisted/web/http.py", line 1474, in loseConnection
       self.channel.loseConnection()
   builtins.AttributeError: 'NoneType' object has no attribute 'loseConnection'
  ....

  [Test Case]

  [Regression Potential]

  [Other Information]

  * Upstream bug:
  https://twistedmatrix.com/trac/ticket/9410

  * Upstream fix:
  https://github.com/twisted/twisted/commit/169fd1d93b7af06bf0f6893b193ce19970881868

  # git describe --contains 169fd1d93b
  twisted-19.7.0~20^2~13

  # rmadison
   => python3-twisted | 17.9.0-2ubuntu0.1 | bionic-updates | all
   => python3-twisted | 18.9.0-11 | focal | all
   => python3-twisted | 18.9.0-11 | groovy | all

  [Original Description]

  When latest master just moving around the UI caused a wierd
  stacktrace. It didn't seem to affect the experience of using MAAS, but
  needs to be looked into.

  2018-01-08 15:33:45 -: [critical] WSGI application error
   Traceback (most recent call last):
     File "/usr/lib/python3/dist-packages/twisted/python/context.py", line 122, in callWithContext
       return self.currentContext().callWithContext(ctx, func, *args, **kw)
     File "/usr/lib/python3/dist-packages/twisted/python/context.py", line 87, in callWithContext
       self.contexts.pop()
     File "/usr/lib/python3/dist-packages/provisioningserver/utils/twisted.py", line 875, in callInContext
       return func(*args, **kwargs)
     File "/usr/lib/python3/dist-packages/twisted/web/wsgi.py", line 522, in run
       self.started = True
   --- <exception caught here> ---
     File "/usr/lib/python3/dist-packages/twisted/web/wsgi.py", line 500, in run
       self.write(elem)
     File "/usr/lib/python3/dist-packages/twisted/web/wsgi.py", line 455, in write
       self.reactor, wsgiWrite, self.started)
     File "/usr/lib/python3/dist-packages/twisted/internet/threads.py", line 122, in blockingCallFromThread
       result.raiseException()
     File "/usr/lib/python3/dist-packages/twisted/python/failure.py", line 385, in raiseException
       raise self.value.with_traceback(self.tb)
   builtins.AttributeError: 'NoneType' object has no attribute 'writeHeaders'

  2018-01-08 15:33:45 -: [critical] WSGI application error
   Traceback (most recent call last):
     File "/usr/lib/python3/dist-packages/twisted/python/context.py", line 122, in callWithContext
       return self.currentContext().callWithContext(ctx, func, *args, **kw)
     File "/usr/lib/python3/dist-packages/twisted/python/context.py", line 87, in callWithContext
       self.contexts.pop()
     File "/usr/lib/python3/dist-packages/provisioningserver/utils/twisted.py", line 875, in callInContext
       return func(*args, **kwargs)
     File "/usr/lib/python3/dist-packages/twisted/web/wsgi.py", line 522, in run
       self.started = True
   --- <exception caught here> ---
     File "/usr/lib/python3/dist-packages/twisted/web/wsgi.py", line 500, in run
       self.write(elem)
     File "/usr/lib/python3/dist-packages/twisted/web/wsgi.py", line 455, in write
       self.reactor, wsgiWrite, self.started)
     File "/usr/lib/python3/dist-packages/twisted/internet/threads.py", line 122, in blockingCallFromThread
       result.raiseException()
     File "/usr/lib/python3/dist-packages/twisted/python/failure.py", line 385, in raiseException
       raise self.value.with_traceback(self.tb)
   builtins.AttributeError: 'NoneType' object has no attribute 'writeHeaders'

  2018-01-08 15:33:45 -: [critical] Unhandled Error
   Traceback (most recent call last):
     File "/usr/lib/python3/dist-packages/twisted/application/app.py", line 396, in startReactor
       self.config, oldstdout, oldstderr, self.profiler, reactor)
     File "/usr/lib/python3/dist-packages/twisted/application/app.py", line 311, in runReactorWithLogging
       reactor.run()
     File "/usr/lib/python3/dist-packages/twisted/internet/base.py", line 1243, in run
       self.mainLoop()
     File "/usr/lib/python3/dist-packages/twisted/internet/base.py", line 1252, in mainLoop
       self.runUntilCurrent()
   --- <exception caught here> ---
     File "/usr/lib/python3/dist-packages/twisted/internet/base.py", line 851, in runUntilCurrent
       f(*a, **kw)
     File "/usr/lib/python3/dist-packages/twisted/web/wsgi.py", line 510, in wsgiError
       self.request.loseConnection()
     File "/usr/lib/python3/dist-packages/twisted/web/http.py", line 1474, in loseConnection
       self.channel.loseConnection()
   builtins.AttributeError: 'NoneType' object has no attribute 'loseConnection'

  2018-01-08 15:33:45 -: [critical] Unhandled Error
   Traceback (most recent call last):
     File "/usr/lib/python3/dist-packages/twisted/application/app.py", line 396, in startReactor
       self.config, oldstdout, oldstderr, self.profiler, reactor)
     File "/usr/lib/python3/dist-packages/twisted/application/app.py", line 311, in runReactorWithLogging
       reactor.run()
     File "/usr/lib/python3/dist-packages/twisted/internet/base.py", line 1243, in run
       self.mainLoop()
     File "/usr/lib/python3/dist-packages/twisted/internet/base.py", line 1252, in mainLoop
       self.runUntilCurrent()
   --- <exception caught here> ---
     File "/usr/lib/python3/dist-packages/twisted/internet/base.py", line 851, in runUntilCurrent
       f(*a, **kw)
     File "/usr/lib/python3/dist-packages/twisted/web/wsgi.py", line 510, in wsgiError
       self.request.loseConnection()
     File "/usr/lib/python3/dist-packages/twisted/web/http.py", line 1474, in loseConnection
       self.channel.loseConnection()
   builtins.AttributeError: 'NoneType' object has no attribute 'loseConnection'

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