Re: Caching calls to download-to-store?

[Ludovic Courtès]

Hi,

Ricardo Wurmus <rekado@elephly.net> skribis:

> the CRAN updater downloads every upstream archive three times.  The
> importer memoizes calls to the download procedure, but one download that
> is out of reach is the very first.
>
> It is triggered by package-update/url-fetch in (guix upstream).  It uses
> download-to-store, which will unconditionally fetch whatever URL it is
> given.

Why three times (and not two)?

> I would very much like to parameterize download-to-store, so that we can
> optionally cache the results of its invocation.

I’m not sure exactly how to do that, but why not.

Another option would be to register GC roots (or mere symlinks) in
~/.cache for things that are downloaded, and then to use
‘If-Modified-Since’ plus some default TTL to determine whether to
re-download things.

HTH,
Ludo’.