[New-bugs-announce] [issue37226] Asyncio Fatal Error on SSL Transport - IndexError Deque Index Out Of Range

[Ben Brown]

New submission from Ben Brown <ben.brown at envisionvirginracing.com>:

I have been getting an intermittent errors when using asyncio with SSL. The error always occurs in the _process_write_backlog method in asyncio's sslproto.py file. I have looked at lots of possibilities as to what the cause is and found that for some reason when in _process_write_backlog's loop the deque seems to be empty, I added some quick terrible hacky code to confirm it fixed the issue and checking at each point it is used wether it is empty fixes the issue, I am unusure as to what causes it to become empty but still run through the loop. The most frequent time it happens is after we have a successful message the client sends a request to join a data stream this request mostly causes the error but sometimes it happens while the client is receiving data. I am currently using python 3.7.1 but have also tested my code on 3.7.3 with the same result. 

NOTE: I am currently working on a minimal sample to show the issue easier.

Fatal error on SSL transport
protocol: <asyncio.sslproto.SSLProtocol object at 0x7f267462e780>
transport: <_SelectorSocketTransport fd=38 read=polling write=<idle, bufsize=0>>
Traceback (most recent call last):
    File "/usr/local/lib/python3.7/asyncio/sslproto.py", line 689, in _process_write_backlog
    del self._write_backlog[0]
IndexError: deque index out of range

Fatal error on SSL transport
protocol: <asyncio.sslproto.SSLProtocol object at 0x7f45f802ec88>
transport: <_SelectorSocketTransport fd=29 read=polling write=<idle, bufsize=0>>
Traceback (most recent call last):
    File "/usr/local/lib/python3.7/asyncio/sslproto.py", line 664, in _process_write_backlog
    data, offset = self._write_backlog[0]
IndexError: deque index out of range

----------
assignee: christian.heimes
components: SSL
messages: 345201
nosy: ben.brown, christian.heimes
priority: normal
severity: normal
status: open
title: Asyncio Fatal Error on SSL Transport - IndexError Deque Index Out Of Range
type: behavior
versions: Python 3.7

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue37226>
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