Bug #16277: UNIXServer#listen fails with Errno::EADDRINUSE error under Windows 10 / WSL Ubuntu 18.04

• Status: Closed
• Assignee: -
• Target version: -
• ruby -v: ruby 2.6.5p114 (2019-10-01 revision 67812) [x86_64-linux-gnu]
• Backport: 2.5: UNKNOWN, 2.6: UNKNOWN
• Tags: win, maybenotbug, ext

[bradland (Brad Landers)]

When running the following script under Windows 10 / WSL Ubuntu 18.04, an Errno::EADDRINUSE error is thrown. Expected result is that the script would run and simply exit.

#!/usr/bin/env ruby

# This script establishes a UNIX server socket.
# 
# Expected result: Script should run and immediately exit.
# 
# Actual result: Script fails with Errno::EADDRINUSE error.
# 
# Environment: Windows 10 Pro, WSL, Ubuntu 18.04.2, ruby 2.6.5p114 (2019-10-01 revision 67812) [x86_64-linux-gnu]
# 
# To reproduce: Create a tmp folder, copy this script there, and execute.

require 'socket'

path = File.expand_path('listen.sock')
backlog = 5

s = UNIXServer.new(path)
if backlog
  s.listen backlog
else
  s.listen
end

File.delete(path) if File.exists?(path)

The bug was discoverd as part of Puma (gem) issue #1521: https://github.com/puma/puma/issues/1521.

[shyouhei (Shyouhei Urabe)]

This is very nuanced. I'm not sure who is in charge of the exception.

UNIXServer.new's return value socket is already listened inside of the method. Calling listen again on a socket that is already listening, might or might not error depending on OS. That's why you see exceptions on WSL and not on Linux.

The problem I see is why at the beginning you want to listen again a socket returned from UNIXServer.new. I guess you want to change (maybe increase) the backlog? Then there seems to be no way for UNIXServer.new to change backlog than listening again. Is it possible for a WSL-hosted application to dynamically change the backlog per-socket? If not (== there is no way but to specify enough backlog at the birth), I guess this is a misfeature of UNIXServer.

[MSP-Greg (Greg L)]

Would something like the following yield an equivalent object?

require 'socket'
sock = Socket.new :UNIX, :STREAM
sock.bind Addrinfo.unix('tmp.sock', :STREAM)
sock.listen 1024
puts sock.local_address.unix?

[mame (Yusuke Endoh)]

• Status changed from Open to Closed

I tried the script on Windows 11 / WSL2 Ubuntu 22.04, but couldn't repro the issue. I guess WSL2 solved the issue. Please ping me if it still occurs.