[bug#46800] [PATCH] Allow defining multiple substituters

[Ludovic Courtès]

Hi Maxime,

Maxime Devos <maximedevos@telenet.be> skribis:

> This patch series is my suggestion for allowing
> multiple "substitution methods" or "substituters"
> as I call them.  Currently, only a method for HTTP/S
> is defined, though I hope it will be a good basis
> for a common framework for substitutes over GNUnet
> and IPFS.

Thanks for working on this!

As discussed on IRC, the daemon used to have support for multiple
substituters, but as a built-in C++ interface, which I removed in
f6919ebdc6b0ce0286814cc6ab0564b1a4c67f5f.

The Scheme interface you propose is of course nicer :-), but I’m still
not sure it’s necessary.  For example, in the IPFS prototype at
<https://issues.guix.gnu.org/33899>, IPFS support goes hand in hand with
HTTP support: narinfos are retrieved over HTTP and nars can be retrieved
over IPFS, or HTTP.  Likewise with “digests”:
<https://lists.gnu.org/archive/html/guix-devel/2021-01/msg00080.html>.

Another issue is that it may be that, instead of letting users choose
one method and stick to it, we’d rather let them choose a policy that
can automatically pick the “best” method, dynamically adjusting choices.

All in all, I would prefer to wait until there’s a clear need for this
abstraction.

WDYT?

Thanks,
Ludo’.