[RFC PATCH] Support debuginfo and source file fetching via debuginfo server

[Frank Ch. Eigler]

Hi, Simon -

> [...]
> I think that providing a void pointer for context is pretty standard thing
> for C libraries that accept callbacks.  I would use __thread and the promise
> to call the function back in the same thread to "retro-fit" some thread-safety
> in an existing API that doesn't provide a context pointer, 

Remember that this is a batch file downloading tool.  We expect it to
be interrupted if a user gets impatient, in which case such a signal
would affect all downloads.  In the absence of a plausible user story
for the need for fine control over multiple different debuginfo
transfers in progress, I believe something simple is enough for now.


> Ok, well I think it would be a good reason to adopt an API of the
> style: [...]  Again, this is easy to add in the beginning, but hard
> to retro-fit later on.

Retro-fitting it later on is not that bad, when/if actual use cases
appear.  The default 'client context' can be the current global one.
A hypothetical future api can pass void* context parameters; we can
have two callback function types.  It being simple now does not
preclude necessary complexity later.  I appreciate the ideas, really,
but I am about as wary of overengineering as underengineering.

- FChE