fix(netwatch): ignore transient recv errors

[Frando]

Description

On Windows, UdpSocket::recv can return an error if the previous send operation on that socket failed with an ICMP error.

The error either surfaces as WSAECONNRESET, which the Rust standard library converts into a io::ErrorKind::ConnectionReset, or as a WSAENETRESET, which becomes ErrorKind::Uncategorized.

WSAECONNRESET is emitted if the previous send failed due to a ICMP port unreachable, and WSAENETRESET if the previous send got a TTL expired (I think, not sure exactly).

Both of these errors are transient, because they are issued max. once per sent datagram. The next recv on the socket then returns either a datagram, a different error, or WouldBlock.

This PR changes the behavior such that we ignore these errors.

It comes with a regression test (first commit). I confirmed that it fails on windows without the fix in the second commit.

Fixes n0-computer/iroh#4297
Fixes n0-computer/iroh-gossip#149
Also tested in n0-computer/iroh#4348

Breaking Changes

None

Notes & open questions

We can and likely should set the SIO_UDP_CONNRESET socket option on the underlying socket, which supresses at least the WSAECONNRESET error altogether. This would need to happen in noq_udp though. And even if we did it, it's still better to also ignore these errors here IMO.

Change checklist

• Self-review.
• Documentation updates following the style guide, if relevant.
• Tests if relevant.
• All breaking changes documented.

[github-actions]

Documentation for this PR has been generated and is available at: https://n0-computer.github.io/net-tools/pr/166/docs/net_tools/

Last updated: 2026-06-16T10:10:30Z

[flub]

very nice

We can and likely should set the SIO_UDP_CONNRESET socket option on the underlying socket, which supresses at least the WSAECONNRESET error altogether. This would need to happen in noq_udp though. And even if we did it, it's still better to also ignore these errors here IMO.

Yes to setting this socket option. There's no point in wasting the syscalls to read this.