DNS cleanup

[Eric S. Raymond]

Hal Murray <hmurray at megapathdsl.net>:
> esr at thyrsus.com said:
> > Be aware that at some point I would still be interested in replacing our
> > internal async-lookup code with calls to c_ares or equivalent, on the
> > general principle that it's better when specialty code unrelated to our
> > business logic is somebody else's maintainance problem. 
> 
> One possible reason to use something else is to get the TTL from the 
> response.  There is no way to get that with the normal API.

Pardon my ignorance, but what would we use the TTL for?

> Other than that, I'll be real surprised if you want to drag in another 
> dependency.

Don't think of it as a dependency, think of it as making specialized code
that we don't want to maintain into somebody else's problem. :-)

> I think you said that c_ares uses a callback.  To fit that into the 
> current/new structure, all we have to do is have the called-back routine save 
> or copy the data, then send a signal to the main thread.  The main thread 
> will then call in to do the real callbacks in the right context.

Noted.
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