rmw_zenohd crashes on IPv4-only systems

[gavanderhoorn]

As per title.

On systems that have no IPv6 support at all, starting rmw_zenohd results in:

2025-02-05T17:23:30.329605Z  WARN ThreadId(03) zenoh::net::runtime::orchestrator: Unable to open listener tcp/[::]:7447: Can not create a new TCP listener bound to tcp/[::]:7447: [Os { code: 97, kind: Uncategorized, message: "Address family not supported by protocol" }] at /home/buildfarm/.cargo/git/checkouts/zenoh-cc237f2570fab813/9640d22/io/zenoh-links/zenoh-link-tcp/src/unicast.rs:326.
2025-02-05T17:23:30.329864Z ERROR ThreadId(03) zenohc::session: Error opening session: Can not create a new TCP listener bound to tcp/[::]:7447: [Os { code: 97, kind: Uncategorized, message: "Address family not supported by protocol" }] at /home/buildfarm/.cargo/git/checkouts/zenoh-cc237f2570fab813/9640d22/io/zenoh-links/zenoh-link-tcp/src/unicast.rs:326.
Error opening Session!\n[ros2run]: Process exited with failure 1

Note the tcp/[::]:7447 in the error message, which indicates it's trying to bind to ANY but IPv6.

This seems to be due to eclipse-zenoh/zenoh#366, which was also discussed in eclipse-zenoh/zenoh-plugin-ros2dds#84.

So technically not a bug, but at least surprising.

Perhaps the error message could be improved? Anyone not into networking (which I guess would be at least part of the audience of rmw_zenoh) would likely not immediately understand the error.

[gavanderhoorn]

Thought to report this to give some visibility to it.

Note also: the only way to work around this seems to be creating a custom .json5 config file which adds "tcp/0.0.0.0:7447" (back?) to the endpoints to listen on.

That's not that user friendly I feel, but I understand why that works the way it does.

[Yadunund]

@gavanderhoorn thanks for reporting the issue. I would imagine a more descriptive error message would be something to add to upstream Zenoh.
What we could do in rmw_zenoh for now is add an entry for this under the Known issues section of the README to inform users of the issue and possible workarounds.

Please open a PR and i'll be happy to review it!

[gavanderhoorn]

I would imagine a more descriptive error message would be something to add to upstream Zenoh.

could be. I'm a user of rmw_zenoh though, hence I report it here.

Please open a PR and i'll be happy to review it!

this may take a while, but I'll put it on the TODO list.