Throws timeout if header value is not given in list

[prat0318]

In [22]: fido.fetch("http://google.com", headers={'Accept-Charset': 'utf-8'}).result(timeout=4)
---------------------------------------------------------------------------
TimeoutError                              Traceback (most recent call last)

/nail/home/agarwal/srv/swagger-py/<ipython console> in <module>()

/nail/home/agarwal/mypy/lib/python2.6/site-packages/concurrent/futures/_base.pyc in result(self, timeout)
    407                 return self.__get_result()
    408             else:
--> 409                 raise TimeoutError()
    410
    411     def exception_info(self, timeout=None):

TimeoutError:

[prat0318]

On removing the .result() call from above, i found that even though Twisted raises a correct exception, no exception is raised eventually.

In [2]: fido.fetch("http://google.com", headers={'Accept-Charset': 'utf-8'})
Out[2]: <Future at 0x255ed50 state=running>

On adding a debug point and watching the trace, it turns out that Twisted throws back a correct exception Header entry 'Accept-Charset' should be list but found instance of <type 'str'> instead. But it is caught and a future object is always returned back. I could not find out from the trace calls where the exception is caught among this:

  /usr/lib64/python2.6/threading.py(532)__bootstrap_inner()
-> self.run()
  /usr/lib64/python2.6/threading.py(484)run()
-> self.__target(*self.__args, **self.__kwargs)
  /nail/home/agarwal/mypy/lib/python2.6/site-packages/crochet/_eventloop.py(382)<lambda>()
-> target=lambda: self._reactor.run(installSignalHandlers=False),
  /nail/home/agarwal/mypy/lib/python2.6/site-packages/twisted/internet/base.py(1192)run()
-> self.mainLoop()
  /nail/home/agarwal/mypy/lib/python2.6/site-packages/twisted/internet/base.py(1201)mainLoop()
-> self.runUntilCurrent()
  /nail/home/agarwal/mypy/lib/python2.6/site-packages/twisted/internet/base.py(797)runUntilCurrent()
-> f(*a, **kw)
  /nail/home/agarwal/mypy/lib/python2.6/site-packages/crochet/_eventloop.py(416)runs_in_reactor()
-> d = maybeDeferred(function, *args, **kwargs)
  /nail/home/agarwal/mypy/lib/python2.6/site-packages/twisted/internet/defer.py(140)maybeDeferred()
-> result = f(*args, **kw)
  /nail/home/agarwal/srv/fido/fido/fido.py(85)fetch_inner()
-> headers=listify_headers(headers),
  /nail/home/agarwal/srv/fido/common.py(10)listify_headers()
-> return Headers(headers)

But, addding this in fido.py correctly print outs the error:

    try:
        a = Headers(headers)
    except Exception as e:
        print e

Header entry 'Accept-Charset' should be list but found instance of <type 'str'> instead

So, IMO the PR still holds good. It is the creation of the future object which is eating up the exception.

[dnephin]

I think that is the correct behaviour. A future should compose an exception, and it should get raised when we try to resolve the future. But I would not except a TimeoutError, it should be the TypeError about the header.

So there is still another bug here somewhere, masking the original exception.