support dynamic severity levels

[snqk]

I was expecting log messages through this handler would respect/translate slog.Level(s) to syslog severity level, but it looks like that's not dynamic today.

All messages are currently written as a static severity level, irrespective of the logging level of that slog.Record.

I think, using a syslog.Writer instead of an io.Writer would enable logging specific slog.Level to a specific syslog severity level. Due to the simplicity of slog.Level I don't think the translation will be complicated to do, but the change in syslog.Writer would be a breaking change.

I'm not sure if the current behaviour was intended or a bug.

[snqk]

If you are happy with the following translations, I'm happy to send a PR!

slog.Level	slog.Severity	syslog.Severity
-4	DEBUG	DEBUG
-3	DEBUG	DEBUG
-2	DEBUG	DEBUG
-1	DEBUG	DEBUG
0	INFO	INFO
1	INFO	INFO
2	INFO	NOTICE
3	INFO	NOTICE
4	WARNING	WARNING
5	WARNING	WARNING
6	WARNING	WARNING
7	WARNING	WARNING
8	ERROR	ERROR
9	ERROR	ERROR
10	ERROR	CRITICAL
11	ERROR	CRITICAL
12	ERROR	ALERT
13	ERROR	ALERT
14	ERROR	EMERGENCY
15	ERROR	EMERGENCY

[samber]

Hi @snqk and thanks for your proposal,

Can you confirm that moving to syslog package would also break the output format ?

Because the log level translation could be done without the syslog library.

[snqk]

Because the log level translation could be done without the syslog library.

Perhaps I'm missing something but I don't see how it can. You'll need to use *syslog.Writer which exposes the specific logging functions with different severities. See: https://pkg.go.dev/log/syslog

The output format isn't affected, as it's defined by whatever payload you write.

[samber]

Currently, we use the @cee prefix, followed by a json message.

Can you confirm that switching to syslog.Writer will break that format?

[snqk]

Can you confirm that switching to syslog.Writer will break that format?

No, it won't.

[samber]

Ok, nice. Would you like to prepare the PR ?

I have no more rsyslog available in my infrastructure.