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[bug#42048] [PATCH 6/6] services: provenance: Save channel introductions

From: zimoun
Subject: [bug#42048] [PATCH 6/6] services: provenance: Save channel introductions.
Date: Wed, 01 Jul 2020 10:51:14 +0200


On Tue, 30 Jun 2020 at 22:28, Ludovic Courtès <> wrote:

>> One thing that I worry about is authentication of channels that are
>> added as dependencies of user-selected channels.  Let’s say my channel
>> “guix-bimsb” depends on “guix-past”.  How will users of “guix-bimsb”
>> authenticate the commits of “guix-past” when they don’t know about
>> “guix-past” (they only care about “guix-bimsb”), and don’t explicitly
>> add introduction information to their channels file?
>> Is there something that the authors of “guix-bimsb” can do to not only
>> indicate the dependency on “guix-past”, but also to attach introduction
>> information?  Will the format of the “.guix-channel” need to be
>> adjusted?
> That’s a very good question and I had completely overlooked it.

Héhé, yet I had the same question one month ago. :-)

--8<---------------cut here---------------start------------->8---
> The question about recursive still applies. ;-)
> Currently, if the local channel file points to a channel A which
> contains the file '.guix-channel' which points to another channel B,
> then when one runs "guix pull" well the channel A will be pulled and
> then the channel B, even if this channel B is not explicit in the
> initial local channel.  (Even, there is bug about recursive implicit
> pulls, see; well another
> story.)
>What happens for such situation?

Nothing special, I guess: each channel would be authenticated (or not,if
it’s an unsigned channel).  I think it’s completely orthogonal.
--8<---------------cut here---------------end--------------->8---

> With this patch set, someone pulling guix-bimsb would just end up
> pulling guix-past unauthenticated; there’s not even a warning.
> (There’s currently a warning in (guix channels), but only when pulling
> an unauthenticated 'guix channel.  It’s perhaps too early to have that
> warning enabled for all channels.  WDYT?)

Enable the warning appears to me a good idea because this dependency is
like "doing something I am not necessary aware in my back".

For example, the first time I pulled the channel "guix-bimsb-non-free" which
depends on "guix-bimsb", it took me some time to understand why
"guix-bimsb" was pulled twice and once with a name I do not have in my
local channels.scm file.  Anyway.

> So yes, I suppose we would need to extend the ‘.guix-channel’ format for
> dependencies.  Luckily it should be quite simply because that format is
> extensible; older Guix versions would ignore the ‘introduction’ field.
> It would look something like this:
>      (channel
>       (version 0)
>       (dependencies
>        (channel
>         (name some-collection)
>         (url "";)
>         (introduction (channel-introduction
>                         (version 0)
>                         (commit "…")
>                         (signer "…"))))
>        (channel
>         (name some-other-collection)
>         (url "";)
>         (branch "testing"))))   ;not an authenticated channel
> It does mean that a channel can indirectly trick you into turning off
> authentication for a dependent channel.  But I think that’s within the
> expectations for channels: when you choose a channel, you trust it
> enough to run its code.

Sound good to me.

When I choose a channel, I trust the people enough to run their code.
But I do not trust the URL which serves it.  I mean, it is the point of
all this new authentication mechanism, isn't it?

However, I agree.  Channel should stay easy to fork and add something
(then maybe send a pull-request) without going in all the GPG signature
dance and/or running the options --allow-downgrades or
--disable-authentication (I do not remember the exact name).


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