Configuration option to allow IP fragmentation on outbound UDP sockets in ssserver

[tom-ryan]

Hello! I have a use case where outbound UDP traffic from ssserver sometimes needs to traverse a network with a smaller MTU. Unfortunately I don't have control over the network or the application sending the traffic.

I saw that per previous issues on this project, IP fragmentation was disabled to improve performance. For my use case, it's preferable to allow IP fragmentation / accept the performance overhead.

I tested that by commenting out the following lines, UDP traffic was fragmented as expected:

shadowsocks-rust/crates/shadowsocks/src/net/sys/unix/linux/mod.rs

Lines 313 to 315 in e791f23

	if let Err(err) = set_disable_ip_fragmentation(af, &socket) {
	warn!("failed to disable IP fragmentation, error: {}", err);
	}

What do you think about adding a new configuration option in ssserver like allow_outbound_udp_fragmentation ? The default will be false, keeping the current behavior. When allow_outbound_udp_fragmentation = true, set_disable_ip_fragmentation will be skipped. If that sounds OK, I'll be happy to submit a patch.

[zonyitoo]

It is Ok. I would prefer outbound_udp_allow_fragmentation. Just put it in ConnectOpts and supported it both globally and per-servers.

[tom-ryan]

Sounds good, thanks. I should be able to submit something end of this week / start of next week.

[Venkatesh1505]

Hey @zonyitoo !
When is the related PR planned to be released? I see here that it was planned in early december. Any tentative dates planned for the same? TIA

[zonyitoo]

Waiting for hickory-dns' new release. They said it could be released in early December, but obviously no..

[venkateshravichandran01]

Thanks @zonyitoo ! I could see that there is a release by hickory-dns recently - https://crates.io/crates/hickory-resolver
v0.24.2. Am I looking at the wrong place?
Asking since we are waiting for next release of shadowsocks-rust incorporating the changes to allow IP fragmentation.

[zonyitoo]

We are waiting for its v0.25 release.