Silencing unexpected errors from std.posix syscalls in debug builds

tsdtas · November 15, 2024, 1:06pm

I’m working with nonblocking datagram file sockets on an embedded yocto Linux platform. In this configuration, calling sendto on a socket file that doesn’t exist can sometimes set errno to 2 (file not found), and sometimes 111 (connection refused).

error.ConnectionRefused, is not in the error set for std.posix.sendto, so when sendto triggers that error, I get an unexpected error and a stack trace printout from Zig.

I can handle the error just fine.

Is there anything I can do to silence the printing from my debug builds, besides patching the standard library?

dimdin · November 15, 2024, 1:43pm

It is in the error set:

github.com

ziglang/zig/blob/bfcf18c5a7d13d990c6bbda04d6a2cd37038a9ea/lib/std/posix.zig#L6010-L6015


      
          pub const SendToError = SendMsgError || error{
              /// The destination address is not reachable by the bound address.
              UnreachableAddress,
              /// The destination address is not listening.
              ConnectionRefused,
          };

squeek502 · November 15, 2024, 4:47pm

error.Unexpected is always indicative of a bug in the standard library; system error codes that trigger error.Unexpected should be handled once they are known to be possible.

github.com

ziglang/zig/blob/bfcf18c5a7d13d990c6bbda04d6a2cd37038a9ea/lib/std/posix.zig#L7395-L7400


      
          /// Whether or not `error.Unexpected` will print its value and a stack trace.
          ///
          /// If this happens the fix is to add the error code to the corresponding
          /// switch expression, possibly introduce a new error in the error set, and
          /// send a patch to Zig.
          pub const unexpected_error_tracing = builtin.zig_backend == .stage2_llvm and builtin.mode == .Debug;

(note also that the debug printing only happens in Debug mode)

squeek502 · November 15, 2024, 4:50pm

I am confused about your reproduction, though. std.posix.sendto handles ENOENT and ECONNREFUSED. Could you provide exactly the error.Unexpected debug printing you’re hitting / the full reproduction?

EDIT: Actually, it looks like ECONNREFUSED was added as a possible error two days after 0.13.0 released: Add ECONNREFUSED to sendto by onlined · Pull Request #20223 · ziglang/zig · GitHub

tsdtas · November 18, 2024, 7:44am

Can confirm, present on 13.0 and fixed on 14.0.
I’ve upgraded my toolchain to the current release.

Do people generally follow the master branch?

Edit: Noted that error.Unexpected should always be considered a bug.
Good to know in case I hit on something like it in the future.