Add alternative hostname and service name helpers

[devgianlu]

No description provided.

[devgianlu]

@alexpevzner Any chance for this to get merged? These helpers are quite important for implementing service name conflict resolution.

[alexpevzner]

Any chance for this to get merged?

Yes — sorry for not spotting this earlier.

To get this merged, we'll need proper function comments that explain what each function does, not just what it calls.

One of the core values of this project is providing clear, usable documentation for Avahi's API, since the native documentation is often opaque and incomplete. So simply stating that AlternativeHostname calls avahi_alternative_host_name won't be enough — we need to explain the semantics: what the function actually does, why you'd use it, and what the expected behavior is.

Could you add that? Happy to review once it's in.

[devgianlu]

Done ;)

[alexpevzner]

Hi!

I have reviewed avahi_alternative_host_name source. It can return NULL in a case of error, but doesn't indicate the error reason, so we have to guess.

But this is very unlikely that it will fail due to insufficient memory, so ErrNoMemory doesn't look to be the best guess. This function works by adding numerical suffix to the first label of DNS domain name, and to do it, it parses the hostname. So if this function fails, must likely this is due to the syntax error in the hostname. So ErrInvalidHostName looks to be the best guess if it happens.

Similarly, ErrInvalidServiceName is the best guess for AlternativeServiceName

And also please add to the functions explanations a couple of words that these functions are helper functions to resolve possible name collisions.

Everything else looks good for me.

[alexpevzner]

I have merged and updated by myself...