fix: catch discard error and return

[ningmingxiao]

to fix containerd/containerd#12669 @fuweid @dmcgowan

[kzys]

Sorry for the late reply. I've updated GitHub Actions. Can you rebase this PR against main?

[ningmingxiao]

done thanks @kzys

[ningmingxiao]

can you review this pr @kzys @dmcgowan

[dmcgowan]

Did you confirm this fixed the issue? Looking through the bufio implementation of Discard, it is already doing something similar on the existing buffer. I don't see the allocation in that implementation either, it seems to just iterate filling up the existing buffer (defaulted to 4k).

[ningmingxiao]

you are right I create new pr will fix. @dmcgowan

[dmcgowan]

Catching any error on discard makes sense and exiting. If the discard did not succeed then the connection must be ended as it is no longer in a processable state.

[ningmingxiao]

done thanks @dmcgowan

[Retr0-XD]

LGTM. The discard failure should be terminal so the recv loop exits. Once this merges, containerd/containerd#13085 can vendor the fix cleanly.

[thaJeztah]

left some comments on the implementation and formatting of the error

[thaJeztah]

Looks like this error-type is only intended to be asserted internally, and not by users of this module; if that's the case, we should un-export it.

This can also be simplified by embedding error, then no constructor is needed, and no Error() method;

type discardError struct {
	error
}

Probably not necessary (because of how it's used), but optionally;

func (e *discardError) Unwrap() error {	return e.error }

Then used as;

return mh, nil, &discardError{fmt.Errorf("failed to discard after receiving oversized message: %w; message length %v, maximum message size %v", err, mh.Length, messageLengthMax)}

[ningmingxiao]

ci failed because other reason

--- FAIL: TestServerRequestTimeout (0.00s)
    server_test.go:435: expected deadline 2026-09-17 12:18:10.1187749 +0000 UTC m=+601.070806401, actual: 2026-09-17 12:18:10.1187748 +0000 UTC

[ningmingxiao]

ping @thaJeztah

[ningmingxiao]

@thaJeztah done ci already passed

[ningmingxiao]

ping @thaJeztah can you take a look? thanks