[GH-ISSUE #10] Errors returned by smtpd.Server.ListenAndServe() are ignored #4

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opened 2026-02-26 18:32:55 +03:00 by kerem · 1 comment

kerem commented

2026-02-26 18:32:55 +03:00

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Originally created by @JonathonReinhart on GitHub (Feb 15, 2021).
Original GitHub issue: https://github.com/decke/smtprelay/issues/10

Problem

Any errors returned by ListenAndServe() are ignored.

For example, trying to run as an unprivileged user:

$ ./smtprelay -logfile smtprelay.log
2021/02/15 01:03:28 Listen on 127.0.0.1:25 ...
2021/02/15 01:03:28 Listen on [::1]:25 ...

The server runs and looks like it is listening, but it is is not (because binding to port 25 is a privileged operation). This is confirmed by looking at lsof -p $(pidof smtprelay) or ss -tnlp.

Cause

The cause is simple: ListenAndServe() is invoked as a goroutine and the return value is lost.

Originally created by @JonathonReinhart on GitHub (Feb 15, 2021). Original GitHub issue: https://github.com/decke/smtprelay/issues/10 # Problem Any errors returned by `ListenAndServe()` are ignored. For example, trying to run as an unprivileged user: ``` $ ./smtprelay -logfile smtprelay.log 2021/02/15 01:03:28 Listen on 127.0.0.1:25 ... 2021/02/15 01:03:28 Listen on [::1]:25 ... ``` The server runs and looks like it is listening, but it is is not (because binding to port 25 is a privileged operation). This is confirmed by looking at `lsof -p $(pidof smtprelay)` or `ss -tnlp`. # Cause The cause is simple: [`ListenAndServe()` is invoked as a goroutine](https://github.com/decke/smtprelay/blob/0e8986ca79f94792343d93027ff28352bd1c212c/main.go#L259) and the return value is lost.