bug#28059: [PATCH] gnu: Add mpd service.

[Christopher Baines <mail@cbaines.net>]

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On Sun, 13 Aug 2017 00:04:04 +0200
Peter Mikkelsen <petermikkelsen10@gmail.com> wrote:

> Christopher Baines <mail@cbaines.net> writes:
> 
> > On Sat, 12 Aug 2017 19:10:08 +0200
> > Peter Mikkelsen <petermikkelsen10@gmail.com> wrote:
> >  
> >> Hi, thanks for the quick review!
> >>
> >> Christopher Baines <mail@cbaines.net> writes:
> >>  
> >> > Hey,
> >> >
> >> > This looks great Peter, awesome job :) I've made some notes about
> >> > potential improvements inline below.
> >> >
> >> > I've succeeded in running the system test locally, but there was
> >> > some suspicious output in the log:
> >> >
> >> > exception: bind to '0.0.0.0:6600' failed (continuing anyway,
> >> > because binding to '[::]:6600' succeeded): Failed to bind
> >> > socket: Address already in use exception: Failed to
> >> > access /root/.mpd/playlists: No such file or directory
> >> >  
> >>
> >> This is pretty normal for mpd, and I believe happens because it
> >> first binds on IPv6 and then fails for IPv4. The error about the
> >> playlist dir happens because it does not exist, but AFAIK it is no
> >> problem unless you want to save playlists. The user can just
> >> create the dir.  
> >
> > Ok, good to know :)
> >  
> >> > On Sat, 12 Aug 2017 03:52:11 +0200
> >> > Peter Mikkelsen <petermikkelsen10@gmail.com> wrote:  
> >> >> * doc/guix.text: Add documentation.  
> >> >
> >> > Typo above, text rather than texi.
> >> >  
> >>
> >> Ups, my mistake.
> >>  
> >> >> * gnu/services/music.scm (<mpd-configuration>): New record type.
> >> >>   (mpd-service): New service extension.
> >> >>   (mpd-service-type): New service type.
> >> >> * gnu/tests/music.scm: New file.
> >> >> * gnu/local.mk: Add new files.
> >> >>
> >> >> ---
> >> >>  doc/guix.texi          | 53 +++++++++++++++++++++++++++++++
> >> >>  gnu/local.mk           |  2 ++
> >> >>  gnu/services/music.scm | 84
> >> >> ++++++++++++++++++++++++++++++++++++++++++++++++++
> >> >> gnu/tests/music.scm    | 83
> >> >> +++++++++++++++++++++++++++++++++++++++++++++++++ 4 files
> >> >> changed, 222 insertions(+) create mode 100644
> >> >> gnu/services/music.scm create mode 100644 gnu/tests/music.scm
> >> >>
> >> >> diff --git a/doc/guix.texi b/doc/guix.texi
> >> >> index 8f14ddd50..e565dfdc9 100644
> >> >> --- a/doc/guix.texi
> >> >> +++ b/doc/guix.texi
> >> >> @@ -227,6 +227,7 @@ Services
> >> >>  * Network File System::         NFS related services.
> >> >>  * Continuous Integration::      The Cuirass service.
> >> >>  * Power management Services::   The TLP tool.
> >> >> +* Music Services::              The MPD.
> >> >>  * Miscellaneous Services::      Other services.
> >> >>
> >> >>  Defining Services
> >> >> @@ -9035,6 +9036,7 @@ declaration.
> >> >>  * Network File System::         NFS related services.
> >> >>  * Continuous Integration::      The Cuirass service.
> >> >>  * Power management Services::   The TLP tool.
> >> >> +* Music Services::              The MPD.
> >> >>  * Miscellaneous Services::      Other services.
> >> >>  @end menu
> >> >>
> >> >> @@ -15635,6 +15637,57 @@ Package object of thermald.
> >> >>  @end table
> >> >>  @end deftp
> >> >>
> >> >> +@node Music Services
> >> >> +@subsubsection Music Services  
> >> >
> >> > I'm wondering if Audio services, rather than Music services
> >> > might be better? Maybe this would fit in other services related
> >> > to audio, e.g. Jack, MIDI stuff, etc...
> >> >  
> >>
> >> That sounds like a good idea.
> >>  
> >> >> +@cindex mpd
> >> >> +@subsubheading Music Player Daemon
> >> >> +
> >> >> +The @code{(gnu services music)} provides a service to start MPD
> >> >> (the Music +Player Daemon). It uses pulseaudio for output.
> >> >> +
> >> >> +@defvr {Scheme Variable} mpd-service-type
> >> >> +The service type for @command{mpd}
> >> >> +@end defvr
> >> >> +
> >> >> +@deftp {Data Type} mpd-configuration
> >> >> +Data type representing the configuration of @command{mpd}.
> >> >> +
> >> >> +@table @asis
> >> >> +@item @code{user} (default: @code{"mpd"})
> >> >> +The user to run mpd as.
> >> >> +
> >> >> +@item @code{music-dir} (default: @code{"~/Music"})
> >> >> +The directory to scan for music files.
> >> >> +
> >> >> +@item @code{playlist-dir} (default: @code{"~/.mpd/playlists"})
> >> >> +The directory to store playlists.
> >> >> +
> >> >> +@item @code{pid-file} (default: @code{"~/.mpd-pid"})
> >> >> +The file mpd wil store its PID.
> >> >> +
> >> >> +@item @code{port} (default: @code{"6600"})
> >> >> +The port to run mpd on.
> >> >> +
> >> >> +@item @code{address} (default: @code{"any"})
> >> >> +The address that mpd will bind to. To use a Unix domain socket,
> >> >> +an absolute path can be specified here.  
> >> >
> >> > The style for Guix is to use two spaces between sentences, I
> >> > always forget about this too.
> >> >  
> >>
> >> Oh yes, me too.
> >>  
> >> >> +
> >> >> +@end table
> >> >> +@end deftp
> >> >> +
> >> >> +@deffn {Scheme Procedure} mpd-service [#:config
> >> >> (mpd-configuration)] +Return a service that runs @code{mpd}
> >> >> using @var{configuration}, +a @code{<mpd-configuration>} object.
> >> >> +
> >> >> +The following example shows how one might run @code{mpd} as
> >> >> user +@code{"bob"} on port @code{6666}.
> >> >> +@example
> >> >> +(mpd-service (mpd-configuration
> >> >> +              (user "bob")
> >> >> +              (port "6666")))
> >> >> +@end example
> >> >> +@end deffn
> >> >>
> >> >>  @node Miscellaneous Services
> >> >>  @subsubsection Miscellaneous Services
> >> >> diff --git a/gnu/local.mk b/gnu/local.mk
> >> >> index b1ff72d6a..cad0ba38d 100644
> >> >> --- a/gnu/local.mk
> >> >> +++ b/gnu/local.mk
> >> >> @@ -441,6 +441,7 @@ GNU_SYSTEM_MODULES
> >> >> =				\
> >> >> %D%/services/mail.scm				\
> >> >> %D%/services/mcron.scm			\
> >> >> %D%/services/messaging.scm			\
> >> >> +  %D%/services/music.scm                        \
> >> >>    %D%/services/networking.scm			\
> >> >>    %D%/services/nfs.scm			\
> >> >>    %D%/services/shepherd.scm			\
> >> >> @@ -488,6 +489,7 @@ GNU_SYSTEM_MODULES
> >> >> =				\
> >> >> %D%/tests/install.scm				\
> >> >> %D%/tests/mail.scm				\
> >> >> %D%/tests/messaging.scm			\
> >> >> +  %D%/tests/music.scm				\
> >> >>    %D%/tests/networking.scm			\
> >> >>    %D%/tests/ssh.scm				\
> >> >>    %D%/tests/web.scm
> >> >> diff --git a/gnu/services/music.scm b/gnu/services/music.scm
> >> >> new file mode 100644
> >> >> index 000000000..77912d5c6
> >> >> --- /dev/null
> >> >> +++ b/gnu/services/music.scm
> >> >> @@ -0,0 +1,84 @@
> >> >> +;;; GNU Guix --- Functional package management for GNU
> >> >> +;;; Copyright © 2017 Peter Mikkelsen
> >> >> <petermikkelsen10@gmail.com> +;;;
> >> >> +;;; This file is part of GNU Guix.
> >> >> +;;;
> >> >> +;;; GNU Guix is free software; you can redistribute it and/or
> >> >> modify it +;;; under the terms of the GNU General Public
> >> >> License as published by +;;; the Free Software Foundation;
> >> >> either version 3 of the License, or (at +;;; your option) any
> >> >> later version. +;;;
> >> >> +;;; GNU Guix is distributed in the hope that it will be useful,
> >> >> but +;;; WITHOUT ANY WARRANTY; without even the implied
> >> >> warranty of +;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR
> >> >> PURPOSE.  See the +;;; GNU General Public License for more
> >> >> details. +;;;
> >> >> +;;; You should have received a copy of the GNU General Public
> >> >> License +;;; along with GNU Guix.  If not, see
> >> >> <http://www.gnu.org/licenses/>. +
> >> >> +(define-module (gnu services music)
> >> >> +  #:use-module (guix gexp)
> >> >> +  #:use-module (gnu services)
> >> >> +  #:use-module (gnu services shepherd)
> >> >> +  #:use-module (gnu packages mpd)
> >> >> +  #:use-module (guix records)
> >> >> +  #:export (mpd-configuration
> >> >> +            mpd-configuration?
> >> >> +            mpd-service
> >> >> +            mpd-service-type))
> >> >> +
> >> >> +;;; Commentary:
> >> >> +;;;
> >> >> +;;; Music related services
> >> >> +;;;
> >> >> +;;; Code:
> >> >> +
> >> >> +(define-record-type* <mpd-configuration>
> >> >> +  mpd-configuration make-mpd-configuration
> >> >> +  mpd-configuration?
> >> >> +  (user         mpd-configuration-user
> >> >> +                (default "mpd"))
> >> >> +  (music-dir    mpd-configuration-music-dir
> >> >> +                (default "~/Music"))
> >> >> +  (playlist-dir mpd-configuration-playlist-dir
> >> >> +                (default "~/.mpd/playlists"))
> >> >> +  (port         mpd-configuration-port
> >> >> +                (default "6600"))
> >> >> +  (address      mpd-configuration-address
> >> >> +                (default "any"))
> >> >> +  (pid-file     mpd-configuration-pid-file
> >> >> +                (default "~/.mpd-pid")))
> >> >> +
> >> >> +(define (mpd-config->file config)
> >> >> +  (apply
> >> >> +   mixed-text-file "mpd.conf"
> >> >> +   "audio_output {\n"
> >> >> +   "  type \"pulse\"\n"
> >> >> +   "  name \"MPD\"\n"
> >> >> +   "}\n"
> >> >> +   (map (lambda (config-line)
> >> >> +          (let ((config-name (car config-line))
> >> >> +                (config-val (cadr config-line)))
> >> >> +            (string-append config-name " \"" (config-val
> >> >> config) "\"\n")))
> >> >> +        `(("user" ,mpd-configuration-user)
> >> >> +          ("music_directory" ,mpd-configuration-music-dir)
> >> >> +
> >> >> ("playlist_directory" ,mpd-configuration-playlist-dir)
> >> >> +          ("port" ,mpd-configuration-port)
> >> >> +          ("bind_to_address" ,mpd-configuration-address)
> >> >> +          ("pid_file" ,mpd-configuration-pid-file)))))
> >> >> +
> >> >> +(define mpd-service-type
> >> >> +  (shepherd-service-type
> >> >> +   'mpd
> >> >> +   (lambda (config)
> >> >> +     (shepherd-service
> >> >> +      (documentation "Run the MPD (Music Player Daemon)")
> >> >> +      (provision '(mpd))
> >> >> +      (start #~(make-forkexec-constructor
> >> >> +                (list #$(file-append mpd "/bin/mpd")
> >> >> +                      "--no-daemon"
> >> >> +                      #$(mpd-config->file config))))
> >> >> +      (stop  #~(make-kill-destructor))))))
> >> >> +
> >> >> +(define* (mpd-service #:optional (config (mpd-configuration)))
> >> >> +  (service mpd-service-type config))  
> >> >
> >> > I've been trying a slightly different style for this recently. At
> >> > the moment, if you had a configuration file for MPD, you couldn't
> >> > use this with the service here. One way of addressing this is to
> >> > do something like the Tailon service, and define a gexp compiler
> >> > for the configuration file (e.g. [1]). For the Tailon service,
> >> > this means that you should be able to pass your own
> >> > configuration file to the service.  
> >>
> >> I am not sure I get how this works, and I would probs just make a
> >> big mess. What about we take my approach first, and then I can
> >> come back to it when I learn some more about guix?  
> >
> > No problem. Looking at it again, I think it might be a bit trickier
> > than I initially assumed, as the pid-file value is used.
> >  
> Oh i see.
> >> > Also, now that a <service-type> can have a default-value, I think
> >> > its easier to just have the mpd-service-type, without the
> >> > mpd-service procedure. If you add a default value, you should be
> >> > able to do (service mpd-service-type).
> >> >  
> >> Ok with me.
> >>  
> >> > 1:
> >> > https://git.savannah.gnu.org/cgit/guix.git/tree/gnu/services/admin.scm#n255
> >> >  
> >> >> diff --git a/gnu/tests/music.scm b/gnu/tests/music.scm
> >> >> new file mode 100644
> >> >> index 000000000..158513098
> >> >> --- /dev/null
> >> >> +++ b/gnu/tests/music.scm
> >> >> @@ -0,0 +1,83 @@
> >> >> +;;; GNU Guix --- Functional package management for GNU
> >> >> +;;; Copyright © 2017 Peter Mikkelsen
> >> >> <petermikkelsen10@gmail.com> +;;;
> >> >> +;;; This file is part of GNU Guix.
> >> >> +;;;
> >> >> +;;; GNU Guix is free software; you can redistribute it and/or
> >> >> modify it +;;; under the terms of the GNU General Public
> >> >> License as published by +;;; the Free Software Foundation;
> >> >> either version 3 of the License, or (at +;;; your option) any
> >> >> later version. +;;;
> >> >> +;;; GNU Guix is distributed in the hope that it will be useful,
> >> >> but +;;; WITHOUT ANY WARRANTY; without even the implied
> >> >> warranty of +;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR
> >> >> PURPOSE.  See the +;;; GNU General Public License for more
> >> >> details. +;;;
> >> >> +;;; You should have received a copy of the GNU General Public
> >> >> License +;;; along with GNU Guix.  If not, see
> >> >> <http://www.gnu.org/licenses/>. +
> >> >> +(define-module (gnu tests music)
> >> >> +  #:use-module (gnu tests)
> >> >> +  #:use-module (gnu system)
> >> >> +  #:use-module (gnu system vm)
> >> >> +  #:use-module (gnu services)
> >> >> +  #:use-module (gnu services music)
> >> >> +  #:use-module (gnu packages mpd)
> >> >> +  #:use-module (guix gexp)
> >> >> +  #:export (%test-mpd))
> >> >> +
> >> >> +(define %mpd-os
> >> >> +  (simple-operating-system
> >> >> +   (mpd-service (mpd-configuration
> >> >> +                 (user "root")))))
> >> >> +
> >> >> +(define (run-mpd-test)
> >> >> +  "Run tests in %mpd-os, which has mpd running."
> >> >> +  (define os
> >> >> +    (marionette-operating-system
> >> >> +     %mpd-os
> >> >> +     #:imported-modules '((gnu services herd))))
> >> >> +
> >> >> +  (define vm
> >> >> +    (virtual-machine os))
> >> >> +
> >> >> +  (define test
> >> >> +    (with-imported-modules '((gnu build marionette))
> >> >> +      #~(begin
> >> >> +          (use-modules (srfi srfi-64)
> >> >> +                       (gnu build marionette))
> >> >> +          (define marionette
> >> >> +            (make-marionette (list #$vm)))
> >> >> +
> >> >> +          (mkdir #$output)
> >> >> +          (chdir #$output)
> >> >> +
> >> >> +          (test-begin "mpd")
> >> >> +
> >> >> +          (test-eq "service is running"
> >> >> +            'running!
> >> >> +            (marionette-eval
> >> >> +             '(begin
> >> >> +                (use-modules (gnu services herd))
> >> >> +                (start-service 'mpd)
> >> >> +                'running!)
> >> >> +             marionette))  
> >> >
> >> > Recently, the start-service procedure was changed to return the
> >> > information from the shepherd, and this can be used to make this
> >> > check a bit more rigorous.
> >> >
> >> > I've got an patch for the Memcached service which demonstrates
> >> > this here [2], as with the test above, it will not always fail,
> >> > even if the service fails to create the PID file.
> >> >
> >> > 2: https://debbugs.gnu.org/cgi/bugreport.cgi?bug=28021
> >> >  
> >> >> +          (test-assert "pid file"
> >> >> +            (wait-for-file "/root/.mpd-pid"
> >> >> +             marionette))  
> >> >
> >> > If this is useful when using MPD, then I think it would be
> >> > valuable to get the shepherd to wait for the PID file. I think
> >> > you can do this by adding #:pid-file to the
> >> > make-forkexec-constructor call.
> >> >
> >> > If you do this, them I'm not sure this test adds anything, as I
> >> > think the start-service call would only return successfully when
> >> > the service has started, and created the PID file.
> >> >  
> >>
> >> Right, I have removed this test.  
> >
> > Great. Just to check I wasn't wrong, I've just tested what happens
> > if you break the service by getting mpd to create the PID file, and
> > shepherd to look for it in different places, and the previous test
> > about starting the service does indeed fail, which is what we
> > want :D 
> 
> Great!
> >> >> +          (test-assert "mpc connect"
> >> >> +            (marionette-eval
> >> >> +             '(zero? (system #$(file-append mpd-mpc
> >> >> "/bin/mpc")))
> >> >> +             marionette))
> >> >> +
> >> >> +          (test-end)
> >> >> +          (exit (= (test-runner-fail-count
> >> >> (test-runner-current)) 0)))))
> >> >> +  (gexp->derivation "mpd-test" test))
> >> >> +
> >> >> +(define %test-mpd
> >> >> +  (system-test
> >> >> +   (name "mpd")
> >> >> +   (description "Test that the mpd can run and be connected
> >> >> to.")
> >> >> +   (value (run-mpd-test))))  
> >>
> >> I think I have fixed all of your suggestions (apart from the
> >> gexp-compiler one). Please see my new patch.  
> >
> > Awesome, I've put a couple more suggestions below, but just on the
> > docs and a bit of code style. Regardless of these, I think this is
> > good to go.
> >
> >  
> >> From 419a8df59bc958ee87ece5519393b32cfbef609c Mon Sep 17 00:00:00
> >> 2001 From: Peter Mikkelsen <petermikkelsen10@gmail.com>
> >> Date: Sat, 12 Aug 2017 03:40:25 +0200
> >> Subject: [PATCH] gnu: Add mpd service.
> >>
> >> * doc/guix.texi: Add documentation.
> >> * gnu/services/audio.scm (<mpd-configuration>): New record type.
> >>   (mpd-service-type): New service type.
> >> * gnu/tests/audio.scm: New file.
> >> * gnu/local.mk: Add new files.
> >> ---
> >>  doc/guix.texi          | 49 ++++++++++++++++++++++++++++
> >>  gnu/local.mk           |  2 ++
> >>  gnu/services/audio.scm | 86
> >> ++++++++++++++++++++++++++++++++++++++++++++++++++
> >> gnu/tests/audio.scm    | 78
> >> +++++++++++++++++++++++++++++++++++++++++++++ 4 files changed, 215
> >> insertions(+) create mode 100644 gnu/services/audio.scm create mode
> >> 100644 gnu/tests/audio.scm
> >>
> >> diff --git a/doc/guix.texi b/doc/guix.texi
> >> index 8f14ddd50..754408ade 100644
> >> --- a/doc/guix.texi
> >> +++ b/doc/guix.texi
> >> @@ -227,6 +227,7 @@ Services
> >>  * Network File System::         NFS related services.
> >>  * Continuous Integration::      The Cuirass service.
> >>  * Power management Services::   The TLP tool.
> >> +* Audio Services::              The MPD.
> >>  * Miscellaneous Services::      Other services.
> >>
> >>  Defining Services
> >> @@ -9035,6 +9036,7 @@ declaration.
> >>  * Network File System::         NFS related services.
> >>  * Continuous Integration::      The Cuirass service.
> >>  * Power management Services::   The TLP tool.
> >> +* Audio Services::              The MPD.
> >>  * Miscellaneous Services::      Other services.
> >>  @end menu
> >>
> >> @@ -15635,6 +15637,53 @@ Package object of thermald.
> >>  @end table
> >>  @end deftp
> >>
> >> +@node Audio Services
> >> +@subsubsection Audio Services
> >> +
> >> +@cindex mpd
> >> +@subsubheading Music Player Daemon
> >> +
> >> +The @code{(gnu services audio)} provides a service to start MPD
> >> (the Music +Player Daemon).  It uses pulseaudio for output.
> >> +
> >> +@defvr {Scheme Variable} mpd-service-type
> >> +The service type for @command{mpd}
> >> +@end defvr
> >> +
> >> +@deftp {Data Type} mpd-configuration
> >> +Data type representing the configuration of @command{mpd}.
> >> +
> >> +@table @asis
> >> +@item @code{user} (default: @code{"mpd"})
> >> +The user to run mpd as.
> >> +
> >> +@item @code{music-dir} (default: @code{"~/Music"})
> >> +The directory to scan for music files.
> >> +
> >> +@item @code{playlist-dir} (default: @code{"~/.mpd/playlists"})
> >> +The directory to store playlists.
> >> +
> >> +@item @code{pid-file} (default: @code{"/var/run/mpd.pid"})
> >> +The file mpd wil store its PID.  This must be an absolute path.
> >> +
> >> +@item @code{port} (default: @code{"6600"})
> >> +The port to run mpd on.
> >> +
> >> +@item @code{address} (default: @code{"any"})
> >> +The address that mpd will bind to.  To use a Unix domain socket,
> >> +an absolute path can be specified here.
> >> +
> >> +@end table
> >> +@end deftp
> >> +
> >> +The following example shows how one might run @code{mpd} as user
> >> +@code{"bob"} on port @code{6666}.
> >> +@example
> >> +(service mpd-service-type
> >> +         (mpd-configuration
> >> +          (user "bob")
> >> +          (port "6666")))
> >> +@end example  
> >
> > I've got a few suggestions for the docs. Nothing too important, and
> > I'm fine if you still prefer docs without the suggestions below,
> > but feel free to pick and choose any changes that you think are
> > good, I've put my reasoning inline in round brackets.
> >
> >
> > @node Audio Services
> > @subsubsection Audio Services
> >
> > The @code{(gnu services audio)} module provides a service to
> > start MPD (the Music Player Daemon).
> >
> >   (
> >   Having the introduction to the module above the Music Player
> > Daemon subsubheading seems neater. Also, I think adding "module"
> > after @code{(gnu services audio)} helps with readability.
> >   )
> >
> > @cindex mpd
> > @subsubheading Music Player Daemon
> >
> > The Music Player Daemon (MPD) is a service that can play music while
> > being controlled from the local machine or over the network by a
> > variety of clients.
> >
> >   (
> >   An introductory paragraph about what the service does might be
> >   useful, so I've written one above.
> >   )
> >
> > The following example shows how one might run @code{mpd} as user
> > @code{"bob"} on port @code{6666}.  It uses pulseaudio for output.
> >
> > @example
> > (service mpd-service-type
> >          (mpd-configuration
> >           (user "bob")
> >           (port "6666")))
> > @end example
> >
> >   (
> >   Moving the example here might be more visible, rather than below
> > the reference documentation.
> >   )
> >
> > @defvr {Scheme Variable} mpd-service-type
> > The service type for @command{mpd}
> > @end defvr
> >
> > @deftp {Data Type} mpd-configuration
> > Data type representing the configuration of @command{mpd}.
> >
> > ...
> >
> > @end table
> > @end deftp
> >
> >  
> I like all your suggestions and they are all part of the new patch,
> thanks!
> >>  @node Miscellaneous Services
> >>  @subsubsection Miscellaneous Services
> >> diff --git a/gnu/local.mk b/gnu/local.mk
> >> index cffb18d3a..c12fd8559 100644
> >> --- a/gnu/local.mk
> >> +++ b/gnu/local.mk
> >> @@ -426,6 +426,7 @@ GNU_SYSTEM_MODULES
> >> =				\ \
> >>    %D%/services.scm				\
> >>    %D%/services/admin.scm			\
> >> +  %D%/services/audio.scm                        \
> >>    %D%/services/avahi.scm			\
> >>    %D%/services/base.scm				\
> >>    %D%/services/configuration.scm		\
> >> @@ -481,6 +482,7 @@ GNU_SYSTEM_MODULES
> >> =				\ \
> >>    %D%/tests.scm					\
> >>    %D%/tests/admin.scm				\
> >> +  %D%/tests/audio.scm				\
> >>    %D%/tests/base.scm				\
> >>    %D%/tests/databases.scm			\
> >>    %D%/tests/dict.scm				\
> >> diff --git a/gnu/services/audio.scm b/gnu/services/audio.scm
> >> new file mode 100644
> >> index 000000000..f5c465341
> >> --- /dev/null
> >> +++ b/gnu/services/audio.scm
> >> @@ -0,0 +1,86 @@
> >> +;;; GNU Guix --- Functional package management for GNU
> >> +;;; Copyright © 2017 Peter Mikkelsen <petermikkelsen10@gmail.com>
> >> +;;;
> >> +;;; This file is part of GNU Guix.
> >> +;;;
> >> +;;; GNU Guix is free software; you can redistribute it and/or
> >> modify it +;;; under the terms of the GNU General Public License as
> >> published by +;;; the Free Software Foundation; either version 3 of
> >> the License, or (at +;;; your option) any later version.
> >> +;;;
> >> +;;; GNU Guix is distributed in the hope that it will be useful,
> >> but +;;; WITHOUT ANY WARRANTY; without even the implied warranty of
> >> +;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> >> +;;; GNU General Public License for more details.
> >> +;;;
> >> +;;; You should have received a copy of the GNU General Public
> >> License +;;; along with GNU Guix.  If not, see
> >> <http://www.gnu.org/licenses/>. +
> >> +(define-module (gnu services audio)
> >> +  #:use-module (guix gexp)
> >> +  #:use-module (gnu services)
> >> +  #:use-module (gnu services shepherd)
> >> +  #:use-module (gnu packages mpd)
> >> +  #:use-module (guix records)
> >> +  #:export (mpd-configuration
> >> +            mpd-configuration?
> >> +            mpd-service-type))
> >> +
> >> +;;; Commentary:
> >> +;;;
> >> +;;; Audio related services
> >> +;;;
> >> +;;; Code:
> >> +
> >> +(define-record-type* <mpd-configuration>
> >> +  mpd-configuration make-mpd-configuration
> >> +  mpd-configuration?
> >> +  (user         mpd-configuration-user
> >> +                (default "mpd"))
> >> +  (music-dir    mpd-configuration-music-dir
> >> +                (default "~/Music"))
> >> +  (playlist-dir mpd-configuration-playlist-dir
> >> +                (default "~/.mpd/playlists"))
> >> +  (port         mpd-configuration-port
> >> +                (default "6600"))
> >> +  (address      mpd-configuration-address
> >> +                (default "any"))
> >> +  (pid-file     mpd-configuration-pid-file
> >> +                (default "/var/run/mpd.pid")))
> >> +
> >> +(define (mpd-config->file config)
> >> +  (apply
> >> +   mixed-text-file "mpd.conf"
> >> +   "audio_output {\n"
> >> +   "  type \"pulse\"\n"
> >> +   "  name \"MPD\"\n"
> >> +   "}\n"
> >> +   (map (lambda (config-line)
> >> +          (let ((config-name (car config-line))
> >> +                (config-val (cadr config-line)))
> >> +            (string-append config-name " \"" (config-val config)
> >> "\"\n")))  
> >
> > One way of making this a bit more concise and remove the need for
> > car and cadr is to use the match module (ice-9 match).
> >
> >    (map (match-lambda
> >          ((config-name config-val)
> >           (string-append config-name " \"" (config-val config)
> > "\"\n"))) ...
> >
> >  
> 
> I didn't know about match-lambda, but it seems pretty neat, so I used
> your example here, thanks.
> 
> >> +        `(("user" ,mpd-configuration-user)
> >> +          ("music_directory" ,mpd-configuration-music-dir)
> >> +          ("playlist_directory" ,mpd-configuration-playlist-dir)
> >> +          ("port" ,mpd-configuration-port)
> >> +          ("bind_to_address" ,mpd-configuration-address)
> >> +          ("pid_file" ,mpd-configuration-pid-file)))))
> >> +  
> >
> > ...  

Awesome, I've now pushed this to master :)

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