Subject: Re: [PATCH 11/17] services: mpd: Warn when the MPD user is not in the "audio" group.

From: Liliana Marie Prikler <[email-masked]>
Date: Sat, 29 Apr 2023 08:29:53 +0200

Am Freitag, dem 28.04.2023 um 10:27 -0400 schrieb Maxim Cournoyer:
> Relates to <https://issues.guix.gnu.org>.
> 
> * gnu/services/audio.scm (%mpd-user) [group]: Add comment.
> (mpd-user-sanitizer): Warn if the MPD user is not in the audio group.
> ---
>  gnu/services/audio.scm | 16 +++++++++++++---
>  1 file changed, 13 insertions(+), 3 deletions(-)
> 
> diff --git a/gnu/services/audio.scm b/gnu/services/audio.scm
> index 550ccc542c..9579432ea3 100644
> --- a/gnu/services/audio.scm
> +++ b/gnu/services/audio.scm
> @@ -30,6 +30,7 @@ (define-module (gnu services audio)
>    #:use-module (gnu services configuration)
>    #:use-module (gnu services shepherd)
>    #:use-module (gnu services admin)
> +  #:use-module (gnu system accounts)
>    #:use-module (gnu system shadow)
>    #:use-module (gnu packages admin)
>    #:use-module (gnu packages mpd)
> @@ -172,6 +173,8 @@ (define-maybe boolean (prefix mpd-))
>  (define %mpd-user
>    (user-account
>     (name "mpd")
> +   ;; Being in the audio group ensures that PulseAudio can access
> sound
> +   ;; devices.
>     (group "audio")
>     (system? #t)
>     (comment "Music Player Daemon (MPD) user")
> @@ -208,10 +211,17 @@ (define (mpd-serialize-port field-name value)
>  
>  (define-maybe port (prefix mpd-))
>  
> -;;; Procedures for unsupported value types, to be removed.
> -
> +;;; Sanitizer procedures.
>  (define (mpd-user-sanitizer value)
> -  (cond ((user-account? value) value)
> +  (cond ((user-account? value)
> +         (match-record value <user-account>
> +           (group supplementary-groups)
> +           (unless (or (string=? "audio" group)
> +                       (member "audio" supplementary-groups))
> +             ;; Being in the "audio" group is necessary for access
> to the
> +             ;; sound devices.
> +             (warning (G_ "mpd user not member of \"audio\"
> group~%"))))
> +         value)
>          ((string? value)
>           (warning (G_ "string value for 'user' is deprecated, use \
>  user-account instead~%"))
I think this check is "only" required when using alsa/pulseaudio for
outputs and should be a hard error then.  When configured to write to
httpd or null outputs, other checks are needed.

Cheers