I think this library should not handle this normalization for users. It's easy enough that any caller that wants normalization can do strings.ToLower on their own. I do however think types.HostInfo could more explicitly document that the value is passed-through without any normalization.

go-sysinfo has avoided any global state thus far because this was a problem we observed with similar libraries. If two usages in the same process have different needs then they end up stepping on each other when configuring the global SetLowerHostname. We should avoid this.

I have mentioned this in other places, but haven't opened an issue (will do). The providers/ packages should be treated as internal, and I would like to make this official by moving it to internal/providers in a "v2" at some point. This way the only API surface is the top-level API. This will give us a little more flexibility in refactoring and force users to go through the front door as it was designed. This would mean that the lowercase behavior must be configurable as a ProviderOption, but I don't think this is a necessary configuration option.