[Async-sig] Cancelling SSL connection

[Nathaniel Smith]

SSLObject.unwrap has the contract that if it finishes successfully, then
the SSL connection has been cleanly shut down and both sides remain in
sync, and can continue to use the socket in unencrypted mode. When asyncio
calls unwrap before the handshake has completed, then this contract is
impossible to fulfill, and raising an error is the right thing to do. So
imo the ssl module is correct here, and this is a (minor) bug in asyncio.

On Jun 21, 2017 12:49 PM, "Dima Tisnek" <dimaqq at gmail.com> wrote:

> Looks like a bug in the `ssl` module, not `asyncio`.
>
> Refer to https://github.com/openssl/openssl/issues/710
> IMO `ssl` module should be prepared for this.
>
> I'd say post a bug to cpython and see what core devs have to say about it
> :)
> Please note exact versions of python and openssl ofc.
>
> my 2c: openssl has been a moving target every so often, it's quite
> possible that this change in the API escaped the devs.
>
> On 21 June 2017 at 19:50, Mark E. Haase <mehaase at gmail.com> wrote:
> > (I'm not sure if this is a newbie question or a bug report or something
> in
> > between. I apologize in advance if its off-topic. Let me know if I should
> > post this somewhere else.)
> >
> > If a task is cancelled while SSL is being negotiated, then an SSLError is
> > raised, but there's no way (as far as I can tell) for the caller to catch
> > it. (The example below is pretty contrived, but in an application I'm
> > working on, the user can cancel downloads at any time.) Here's an
> example:
> >
> >     import asyncio, random, ssl
> >
> >     async def download(host):
> >         ssl_context = ssl.create_default_context()
> >         reader, writer = await asyncio.open_connection(host, 443,
> > ssl=ssl_context)
> >         request = f'HEAD / HTTP/1.1\r\nHost: {host}\r\n\r\n'
> >         writer.write(request.encode('ascii'))
> >         lines = list()
> >         while True:
> >             newdata = await reader.readline()
> >             if newdata == b'\r\n':
> >                 break
> >             else:
> >                 lines.append(newdata.decode('utf8').rstrip('\r\n'))
> >         return lines[0]
> >
> >     async def main():
> >         while True:
> >             task = asyncio.Task(download('www.python.org'))
> >             await asyncio.sleep(random.uniform(0.0, 0.5))
> >             task.cancel()
> >             try:
> >                 response = await task
> >                 print(response)
> >             except asyncio.CancelledError:
> >                 print('request cancelled!')
> >             except ssl.SSLError:
> >                 print('caught SSL error')
> >             await asyncio.sleep(1)
> >
> >     loop = asyncio.get_event_loop()
> >     loop.run_until_complete(main())
> >     loop.close()
> >
> > Running this script yields the following output:
> >
> >     HTTP/1.1 200 OK
> >     request cancelled!
> >     HTTP/1.1 200 OK
> >     HTTP/1.1 200 OK
> >     <asyncio.sslproto.SSLProtocol object at 0x7fe7c00e5a20>: SSL
> handshake
> > failed
> >     Traceback (most recent call last):
> >       File "/usr/lib/python3.6/asyncio/base_events.py", line 803, in
> > _create_connection_transport
> >         yield from waiter
> >       File "/usr/lib/python3.6/asyncio/tasks.py", line 304, in _wakeup
> >         future.result()
> >     concurrent.futures._base.CancelledError
> >
> >     During handling of the above exception, another exception occurred:
> >
> >     Traceback (most recent call last):
> >       File "/usr/lib/python3.6/asyncio/sslproto.py", line 577, in
> > _on_handshake_complete
> >         raise handshake_exc
> >       File "/usr/lib/python3.6/asyncio/sslproto.py", line 638, in
> > _process_write_backlog
> >         ssldata = self._sslpipe.shutdown(self._finalize)
> >       File "/usr/lib/python3.6/asyncio/sslproto.py", line 155, in
> shutdown
> >         ssldata, appdata = self.feed_ssldata(b'')
> >       File "/usr/lib/python3.6/asyncio/sslproto.py", line 219, in
> > feed_ssldata
> >         self._sslobj.unwrap()
> >       File "/usr/lib/python3.6/ssl.py", line 692, in unwrap
> >         return self._sslobj.shutdown()
> >     ssl.SSLError: [SSL] shutdown while in init (_ssl.c:2299)
> >
> > Is this a bug that I should file, or is there some reason that it's
> intended
> > to work this way? I can work around it with asyncio.shield(), but I
> think I
> > would prefer for the asyncio/sslproto.py to catch the SSLError and ignore
> > it. Maybe I'm being short sighted.
> >
> > Thanks,
> > Mark
> >
> > _______________________________________________
> > Async-sig mailing list
> > Async-sig at python.org
> > https://mail.python.org/mailman/listinfo/async-sig
> > Code of Conduct: https://www.python.org/psf/codeofconduct/
> >
> _______________________________________________
> Async-sig mailing list
> Async-sig at python.org
> https://mail.python.org/mailman/listinfo/async-sig
> Code of Conduct: https://www.python.org/psf/codeofconduct/
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.python.org/pipermail/async-sig/attachments/20170621/6c4a2bb8/attachment-0001.html>