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tranport.get_extra_info('peername') occasionally returns None

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
35/100
Issue type
Bug
Clarity
Needs clarification
Activity status
Stale
Tech stack
python
Domain
networking

Research direction

Start by reproducing the uvloop 0.17.0, Python 3.11.4 case on Linux and tracing the accept/getpeername behavior shown in the report. Then review the linked libuv issue #3339; done means the cause is confirmed and peername behavior is verified after an actionable fix or dependency resolution.

Written by the indexing model from the issue text.

Description

uvloop version: 0.17.0
Python version: 3.11.4
Platform: Linux

I believe the root cause of this issue is that:

  • libuv doesn't retrieve peer address while calling accept()
  • getpeername() fails if the client disconnected already (which is unlikely, but possible)

Here's strace log:

561904 setsockopt(19, SOL_TCP, TCP_NODELAY, [1], 4) = 0
561904 accept4(18, NULL, NULL, SOCK_CLOEXEC|SOCK_NONBLOCK) = -1 EAGAIN (Resource temporarily unavailable)
561904 getsockname(19, {sa_family=AF_INET, sin_port=htons(32111), sin_addr=inet_addr("127.0.0.1")}, [128 => 16]) = 0
561904 getpeername(19, {sa_family=AF_INET, sin_port=htons(39898), sin_addr=inet_addr("127.0.0.1")}, [128 => 16]) = 0
561904 getpid()                         = 561904

Please note, that standard asyncio loop uses accept4() call to get the peer address:

564955 accept4(13, {sa_family=AF_INET, sin_port=htons(35516), sin_addr=inet_addr("127.0.0.1")}, [16], SOCK_CLOEXEC) = 16
564955 getsockname(16, {sa_family=AF_INET, sin_port=htons(32111), sin_addr=inet_addr("127.0.0.1")}, [128 => 16]) = 0
564955 ioctl(16, FIONBIO, [1])          = 0

Said that, there's an issue raised in libuv repo which should be addressed first, I suppose: https://github.com/libuv/libuv/issues/3339

Dominant language
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