multicast example panic (Mac)

[dabat]

hi @lemunozm ! excellent work on this crate, very exciting!

just wanted to share that while i was reviewing and running some of the examples, i found this issue where the second client to attempt running the multicast example panics after connecting, with an Address already in use error.

[lemunozm]

Hi @dabat, thanks for the comment, I'm glad you like it 😃

It's really weird since on my computer this is working and this functionality is the base of termchat and anybody complains about it...

I checked the code and the reuse address is set to true correctly in multicast to avoid these issues.

Could you tell me the OS version are you using? Thanks!

[lemunozm]

Hi, what's the state of this issue? Did it work?

[dabat]

hi @lemunozm my apologies for not getting back to you, the emails were buried in my inbox.
i am still seeing this error in the multicast example.

i'm running on macOS 11.4 and i pulled latest on master branch.
as you can see in the error message,
thread 'main' panicked at 'called Result::unwrap()on anErr value: Os { code: 48, kind: AddrInUse, message: "Address already in use" }', examples/multicast/main.rs:23:70
this is the line that is panicing

message-io/examples/multicast/main.rs

Line 23 in 7e27a03

handler.network().listen(Transport::Udp, multicast_addr).unwrap();

[lemunozm]

Hi @dabat , thanks so much for your answer.

I made a integration test to run this use-case in CI: #94

As you noticed, multicast is not working in newer versions of Mac. Mac requires to add also the SO_REUSEPORT option in addition to SO_REUSEADDR.

Two interesting resources about it:

• https://stackoverflow.com/questions/32661091/behavior-of-so-reuseaddr-and-so-reuseport-changed
• https://stackoverflow.com/questions/14388706/how-do-so-reuseaddr-and-so-reuseport-differ
• https://stackoverflow.com/questions/67541705/ios-socket-with-so-reuseport-does-not-receive-all-multicast-packets (possible future problem?)

Solution overview:

net2 (used currently to enable SO_REUSEADDR) do not support SO_REUSE_PORT. Use socket2 instead that support it

[lemunozm]

Fixed in version 0.14.2

Since the test is already working in Mac I close the issue. If you continue having problems, feel free to reopen it.

Thanks for notifying the error!