Fix documented default value for community

[PierreF]

The documentation (README) say that the default value for the SNMP community is "public_v2". But I believe this is wrong:

• snmp_exporter/snmp.yml

  Line 4 in 9c42d6c

  community: public

• snmp_exporter/config/config.go

  Line 52 in 9c42d6c

  Community: "public",

[SuperQ]

The default is actually implemented in main.go. The struct default is ignored since it's actually part of the URL parm parsing.

If you curl the exporter with no auth params, you can see it in the debug log.

$ curl 'http://localhost:9116/snmp?target=192.168.1.1'

Result:

ts=2024-01-11T11:33:33.332Z caller=collector.go:464 level=debug auth=public_v2 target=192.168.1.1 module=if_mib msg="Finished scrape" duration_seconds=5.002192868

If you don't mind, please update the DefaultAuth value in config/config.go to match the new default.

[PierreF]

In main.go I see the default for the auth which default to "public_v2" which I'm fine with that.

In this PR I'm talking about the SNMP community send in the SNMP network query which currently had default to "public" but it's documented as "public_v2". And hopefully the default is "public" or I think it would break collection on most SNMP device which respond to "public" community.

So I'm not sure what you want:

• I don't want to change the default SNMP community from "public" to "public_v2" to match current documentation (due to risk breaking collection)
• I'm not sure changing the default auth from "public_v2" to "public" is a good idea, as it could cause breaking change on API

[SuperQ]

Oh, right, I'm confusing which strings mean which things.

[SuperQ]

Thanks!