[issue26278] BaseTransport.close() does not trigger connection_lost()

[STINNER Victor]

STINNER Victor  added the comment:

If a bug cannot be reproduced, it cannot be fixed. So I close the issue ;-)

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resolution:  -> out of date
stage:  -> resolved
status: open -> closed

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[issue26278] BaseTransport.close() does not trigger connection_lost()

[Sümer Cip]

Sümer Cip  added the comment:

Closing the issue seems like a good idea: as it seems nobody seems to have 
spotted similar issue and I have only been able to reproduce it in Python 3.4. 

Just for future ref.: The uncommon thing is that the server I was using is a 
TCP game server holding long-running connections as opposed to short-lived HTTP 
connections, maybe there is a very random issue at the core but as it is 
happening very randomly.

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[issue26278] BaseTransport.close() does not trigger connection_lost()

[Sümer Cip]

Sümer Cip  added the comment:

I do not know I still have the issue since I have circumvented the problem. I 
have been using Python3.4, I think it was one of the earliest asyncio 
implementations. The way it can be reproduced is as following: 
1) There are lots of active TCP connections connected to asyncio server 
(300-400 of them)
2) One of the clients close connection ungracefully(without sending a FIN)
3) We have a PING/PONG mechanism in the server (similar to http keep-alive), we 
call transport.close() on the socket if pong is not received within an interval.
connection_lost() event is never gets called for the socket. This is not 
happening all the time, this is a random issue, the key here is to disconnect 
client without sending a FIN and there is outgoing buffer for client.

Above is all I got.

Thanks!

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[issue26278] BaseTransport.close() does not trigger connection_lost()

[anthony shaw]

anthony shaw  added the comment:

This issue was never responded to, are you still having this issue? Which 
version of CPython are you using and can you please provide steps to reproduce 
the problem.

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nosy: +anthonypjshaw

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[issue26278] BaseTransport.close() does not trigger connection_lost()

[Sümer Cip]

New submission from Sümer Cip:

Hi all,

We have implemented a TCP server based on asyncio. And while doing some 
regression tests we randomly see following error:

1) Client connects to the server.
2) Client is closed ungracefully(without sending a FIN, deplug cable)
3) We have a custom PING handler that sends a PING and waits for PONG message.
4) After a while, we see that we timeout for the PING and we call close() on 
the Transport object. 

Now, most of the time, above just works fine, but at some point, somehow 
connection_lost() is NEVER gets called even though we call close() on the 
socket. As this issue is happening very randomly I don't have any asyncio logs 
for it. But can you think about any scenario that might lead to this somehow? 

Somehow, it seems we have an outgoing data in the TCP buffer when this happens 
and that is why the close() does not call the connection_lost immediately, but 
why it is never calling it is a mystery to me. Can that be following:

1) we call close() and is_closing is set to true we have outgoing data so we 
return.
2) Then a subsequent write occurs and connection ConnectionResetError() is 
raised and this calls _force_close(), but as we have previously set is_closing 
to True, connection_lost() does not get called.

Above is just a very trivial idea which is probably is not the case, I do not 
spend too much time on the code. 

Thanks,

--
components: asyncio
messages: 259487
nosy: Sümer.Cip, gvanrossum, haypo, yselivanov
priority: normal
severity: normal
status: open
title: BaseTransport.close() does not trigger connection_lost()
type: behavior
versions: Python 3.4

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