Thomas Eizinger e1c13d448a fix(connlib): retry sending packet on ENOBUFS (#10965) ...

In #9798, we added a check to map `ENOBUFS` to `WOUDLBLOCK` on MacOS.
More experimentation on that front revealed that this was actually
incorrect and the UDP sending task will hang as the OS does **not**
notify us once there are new buffers available.

This may explain some random connection hangs that some users have
recently complained about. I've already disabled the feature flag in
production, this PR therefore only removes code that is now inactive.

In order to make this as robust as possible, we implement a retry loop
with an exponential backoff, starting a 2ns. At most, we will be
retrying such a packet for 16ms. Local experiments on my Macbook have
shown that most of the time, new buffer space is available within 1ms.
The exponential backoff ensures we retry very quickly on faster machines
but still successfully send the packet on slower machines.

According to the linked mailing list, the link-speed of the attached
network has nothing to do with this which makes sense. UDP has no
congestion control so sending packets is merely a function of how fast
the CPU can process them.

Related:
https://lists.freebsd.org/pipermail/freebsd-hackers/2004-January/005369.html

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Signed-off-by: Thomas Eizinger <thomas@eizinger.io>
Co-authored-by: Jamil <jamilbk@users.noreply.github.com>

2025-11-26 04:36:36 +00:00

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