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smtpconn: Treat wrapped dial errors as network errors - #874
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Since fd6d880, attemptConnect wraps dial errors as "dialer: %w". wrapClientErr matched *net.OpError with a type switch, so wrapped dial errors fell through to the default case and were reported as permanent "554 5.0.0 Internal server error" instead of "450 4.4.2 Network I/O error". For LMTP this made maddy reject RCPT permanently while the LMTP server was restarting, instead of asking the sender to retry. Look for *net.OpError with errors.As in the default case, so the wrapped error is classified as before while keeping the added context. Fixes foxcpp#872 Signed-off-by: Ahmed Laban <amlaban@outlook.com>
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Fixes #872
Problem
Since fd6d880,
attemptConnectwraps dial errors asfmt.Errorf("dialer: %w", err).wrapClientErrrecognizes network errors with a type switch on*net.OpError, so a wrapped dial error now falls through to thedefaultcase. It is no longer turned into450 4.4.2 Network I/O errorand ends up as a permanent554 5.0.0 Internal server error. With an LMTP target, maddy rejected RCPT permanently while the LMTP server was restarting, instead of asking the sender to retry.Change
defaultcase ofwrapClientErr, look for a*net.OpErrorwitherrors.As.*net.OpErrorhandling into a smallwrapNetErrhelper, used for both the direct and the wrapped case. The returnedSMTPErrorkeeps the full error (including thedialer:context) inErr. The codes and messages are unchanged.Testing
TestConnectRefusedininternal/smtpconn. It dials a closed local port with bothConnectandConnectLMTPand checks for a temporary450 4.4.2SMTPError. It fails ondevwithout the fix (the error comes back asexterrors.fieldsWrap: dialer: dial tcp ...: connection refused) and passes with it.go test ./internal/smtpconn/... ./internal/target/smtp/ ./internal/target/remote/passes.gofmtandgo vet ./internal/smtpconn/are clean.tests/. Locally I used Go 1.25.1 with a temporary modfile (go.mod asks for 1.26), so CI is the check on the real toolchain.