[bug#73955] [PATCH v3 2/3] services: wireguard: Support lists of gexps for most fields.

[Richard Sent <richard@freakingpenguin.com>]

In order to support more flexibility in Wireguard configuration, ungexp the
configuration fields directly instead of ungexp-splicing a sexp
calculator. This allows for the fields to take arbitrary gexps instead of only
strings which is particularly helpful for the Pre/Post Up/Down commands.

For example, the wg-quick(8) manual has an example on how to use
password-store to retrieve a private key with a PreUp entry. This is now
possible.

* gnu/services/vpn.scm (wireguard-configuration-file): Ungexp configuration
lists instead of ungexp-splicing the code surrounding them.
* doc/guix.texi (VPN Services)[wireguard]: Document it.

Change-Id: If074cbb78473b6fd34e0e4e990d2ed268001d6c7
---
 doc/guix.texi        | 31 +++++++++++++++++++++++++------
 gnu/services/vpn.scm | 39 ++++++++++++++++++++-------------------
 2 files changed, 45 insertions(+), 25 deletions(-)

diff --git a/doc/guix.texi b/doc/guix.texi
index 5558bd7d44..0520b24c23 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -34430,13 +34430,15 @@ VPN Services
 The interface name for the VPN.
 
 @item @code{addresses} (default: @code{'("10.0.0.1/32")})
-The IP addresses to be assigned to the above interface.
+List of strings or G-expressions which represent the IP addresses to be
+assigned to the above interface.
 
 @item @code{port} (default: @code{51820})
 The port on which to listen for incoming connections.
 
 @item @code{dns} (default: @code{'())})
-The DNS server(s) to announce to VPN clients via DHCP.
+List of strings or G-expressions which represent the DNS server(s) to
+announce to VPN clients via DHCP.
 
 @item @code{monitor-ips?} (default: @code{#f})
 @cindex Dynamic IP, with Wireguard
@@ -34463,16 +34465,33 @@ VPN Services
 @var{wireguard-peer} records.
 
 @item @code{pre-up} (default: @code{'()})
-The script commands to be run before setting up the interface.
+List of strings or G-expressions.  These are script snippets which will
+be executed before setting up the interface.
+
+One example shown in the @code{wg-quick(8)} manual is retrieving a
+private key using @code{password-store}.  This can be achieved with the
+following code:
+
+@lisp
+(wireguard-configuration
+ ;; Retrieve the private key manually.
+ (private-key #f)
+ (pre-up (list #~(string-append "wg set %i private-key <("
+                                #$(file-append password-store "/bin/pass")
+                                " WireGuard/private-keys/%i)"))))
+@end lisp
 
 @item @code{post-up} (default: @code{'()})
-The script commands to be run after setting up the interface.
+List of strings or G-expressions.  These are script snippets which will
+be executed after setting up the interface.
 
 @item @code{pre-down} (default: @code{'()})
-The script commands to be run before tearing down the interface.
+List of strings or G-expressions.  These are script snippets which will
+be executed before tearing down the interface.
 
 @item @code{post-down} (default: @code{'()})
-The script commands to be run after tearing down the interface.
+List of strings or G-expressions.  These are script snippets which will
+be executed after tearing down the interface.
 
 @item @code{table} (default: @code{"auto"})
 The routing table to which routes are added, as a string.  There are two
diff --git a/gnu/services/vpn.scm b/gnu/services/vpn.scm
index b62e0ac838..c1daba5dc1 100644
--- a/gnu/services/vpn.scm
+++ b/gnu/services/vpn.scm
@@ -12,6 +12,7 @@
 ;;; Copyright © 2022 Cameron V Chaparro <cameron@cameronchaparro.com>
 ;;; Copyright © 2022 Timo Wilken <guix@twilken.net>
 ;;; Copyright © 2023 Maxim Cournoyer <maxim.cournoyer@gmail.com>
+;;; Copyright © 2024 Richard Sent <richard@freakingpenguin.com>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -797,33 +798,33 @@ (define (wireguard-configuration-file config)
                  (define lines
                    (list
                     "[Interface]"
-                    #$@(if (null? addresses)
-                           '()
-                           (list (format #f "Address = ~{~a~^, ~}"
-                                         addresses)))
+                    (if (null? '#$addresses)
+                        ""
+                        (format #f "Address = ~{~a~^, ~}"
+                                (list #$@addresses)))
                     (format #f "~@[Table = ~a~]" #$table)
-                    #$@(if (null? pre-up)
-                           '()
-                           (list (format #f "~{PreUp = ~a~%~}" pre-up)))
+                    (if (null? '#$pre-up)
+                        ""
+                        (format #f "~{PreUp = ~a~%~}" (list #$@pre-up)))
                     (if #$private-key
                         (format #f "PostUp = ~a set %i private-key ~a\
 ~{ peer ~a preshared-key ~a~}"
                                 #$(file-append wireguard "/bin/wg")
                                 #$private-key '#$peer-keys)
                         "")
-                    #$@(if (null? post-up)
-                           '()
-                           (list (format #f "~{PostUp = ~a~%~}" post-up)))
-                    #$@(if (null? pre-down)
-                           '()
-                           (list (format #f "~{PreDown = ~a~%~}" pre-down)))
-                    #$@(if (null? post-down)
-                           '()
-                           (list (format #f "~{PostDown = ~a~%~}" post-down)))
+                    (if (null? '#$post-up)
+                        ""
+                        (format #f "~{PostUp = ~a~%~}" (list #$@post-up)))
+                    (if (null? '#$pre-down)
+                        ""
+                        (format #f "~{PreDown = ~a~%~}" (list #$@pre-down)))
+                    (if (null? '#$post-down)
+                        ""
+                        (format #f "~{PostDown = ~a~%~}" (list #$@post-down)))
                     (format #f "~@[ListenPort = ~a~]" #$port)
-                    #$@(if (null? dns)
-                           '()
-                           (list (format #f "DNS = ~{~a~^, ~}" dns)))))
+                    (if (null? '#$dns)
+                        ""
+                        (format #f "DNS = ~{~a~^, ~}" (list #$@dns)))))
 
                  (mkdir #$output)
                  (chdir #$output)
-- 
2.46.0