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From: Andrew Schulman <schulman.andrew@epa.gov>
Subject: Re: socat UDP-LISTEN,fork misbehaves
Date: Tue, 26 Oct 2021 21:48:07 -0400
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> I have socat 1.7.4.1-1 and the same version on Linux.
> When I try to create a forking UDP server, only the first client is served, unlike in Linux where subsequent clients are served properly.
> 
> Test case. Terminal 1:
> 
>     socat -v UDP-LISTEN:12345,reuseaddr,fork SYSTEM:"stdbuf -i0 -o0 -e0 sed s/././g"
> 
> Terminal 2
> 
>     ( ( date; sleep 10 ) | socat UDP:127.0.0.1:12345 - & sleep 1; date | socat UDP:127.0.0.1:12345 - )
> 
> Expected output in Terminal 2:
> 
>     ...............................
>     ...............................
> 
> Actual:
> 
>     ...............................
> 
> Reproducible: amd64, x86, Windows 10, Windows 7

Thanks for reporting. Unfortunately, I have no insight into what might
cause that fault in Cygwin. socat in Cygwin is compiled OOTB, with no
patches. Any debugging or patches would be welcome. Andrew