[bug#65119,8/8] home: services: Add Syncthing.

diff --git a/doc/guix.texi b/doc/guix.texi
index dd272636a3..a4993b7ae7 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -446,6 +446,7 @@  Top
 * Mail: Mail Home Services.     Services for managing mail.
 * Messaging: Messaging Home Services.  Services for managing messaging.
 * Media: Media Home Services.   Services for managing media.
+* Networking: Networking Home Services.  Networking services.
 * Miscellaneous: Miscellaneous Home Services.  More services.
 
 Platforms
@@ -21226,6 +21227,8 @@  Networking Services
 @end table
 @end deftp
 
+@cindex Syncthing, file synchronization service
+@cindex backup service, Syncthing
 The @code{(gnu services syncthing)} module provides the following services:
 @cindex syncthing
 
@@ -21243,7 +21246,14 @@  Networking Services
          (syncthing-configuration (user "alice")))
 @end lisp
 
+@quotation Note
+This service is also available for Guix Home, where it runs directly
+with your user privileges (@pxref{Networking Home Services,
+@code{home-syncthing-service-type}}).
+@end quotation
+
 See below for details about @code{syncthing-configuration}.
+@end defvar
 
 @deftp {Data Type} syncthing-configuration
 Data type representing the configuration for @code{syncthing-service-type}.
@@ -21273,7 +21283,6 @@  Networking Services
 
 @end table
 @end deftp
-@end defvar
 
 Furthermore, @code{(gnu services ssh)} provides the following services.
 @cindex SSH
@@ -42620,6 +42629,7 @@  Home Services
 * Mail: Mail Home Services.     Services for managing mail.
 * Messaging: Messaging Home Services.  Services for managing messaging.
 * Media: Media Home Services.   Services for managing media.
+* Networking: Networking Home Services.  Networking services.
 * Miscellaneous: Miscellaneous Home Services.  More services.
 @end menu
 @c In addition to that Home Services can provide
@@ -44210,6 +44220,45 @@  Media Home Services
 @end table
 @end deftp
 
+@node Networking Home Services
+@subsection Networking Home Services
+
+This section lists services somewhat networking-related that you may use
+with Guix Home.
+
+@cindex Syncthing, file synchronization service
+@cindex backup service, Syncthing
+The @code{(gnu home services syncthing)} module provides a service to
+set up the @uref{Syncthing, https://syncthing.net} continuous file
+backup service.
+
+@defvar home-syncthing-service-type
+This is the service type for the @command{syncthing} daemon; it is the
+Home counterpart of the @code{syncthing-service-type} system service
+(@pxref{Networking Services, @code{syncthing-service-type}}).  The value
+for this service type is a @command{syncthing-configuration}.
+
+Here is how you would set it up with the default configuration:
+
+@lisp
+(service home-syncthing-service-type)
+@end lisp
+
+For a custom configuration, wrap you @code{syncthing-configuration} in
+@code{for-home}, as in this example:
+
+@lisp
+(service home-syncthing-service-type
+         (for-home
+          (syncthing-configuration (logflags 5))))
+@end lisp
+
+For details about @code{syncthing-configuration}, check out the
+documentation of the system service (@pxref{Networking Services,
+@code{syncthing-service-type}}).
+@end defvar
+
+
 @node Miscellaneous Home Services
 @subsection Miscellaneous Home Services
 
diff --git a/gnu/home/services/syncthing.scm b/gnu/home/services/syncthing.scm
new file mode 100644
index 0000000000..9c9eb94ea1
--- /dev/null
+++ b/gnu/home/services/syncthing.scm
@@ -0,0 +1,30 @@ 
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2023 Ludovic Courtès <ludo@gnu.org>
+;;;
+;;; 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 home services syncthing)
+  #:use-module (gnu services)
+  #:use-module (gnu home services)
+  #:use-module (gnu services syncthing)
+  #:export (home-syncthing-service-type)
+  #:re-export (syncthing-configuration
+               syncthing-configuration?))
+
+(define home-syncthing-service-type
+  (service-type
+   (inherit (system->home-service-type syncthing-service-type))
+   (default-value (for-home (syncthing-configuration)))))
diff --git a/gnu/local.mk b/gnu/local.mk
index b496b53a97..d98ecfb7b4 100644
--- a/gnu/local.mk
+++ b/gnu/local.mk
@@ -104,6 +104,7 @@  GNU_SYSTEM_MODULES =				\
   %D%/home/services/shepherd.scm		\
   %D%/home/services/sound.scm			\
   %D%/home/services/ssh.scm			\
+  %D%/home/services/syncthing.scm		\
   %D%/home/services/mcron.scm			\
   %D%/home/services/utils.scm			\
   %D%/home/services/xdg.scm			\
diff --git a/gnu/services/syncthing.scm b/gnu/services/syncthing.scm
index 8f94aef088..f97a1a2ff4 100644
--- a/gnu/services/syncthing.scm
+++ b/gnu/services/syncthing.scm
@@ -48,32 +48,38 @@  (define-record-type* <syncthing-configuration>
   (group     syncthing-configuration-group     ;string
              (default "users"))
   (home      syncthing-configuration-home      ;string
-             (default #f)))
+             (default #f))
+  (home-service? syncthing-configuration-home-service?
+                 (default for-home?) (innate)))
 
 (define syncthing-shepherd-service
   (match-record-lambda <syncthing-configuration>
-      (syncthing arguments logflags user group home)
+      (syncthing arguments logflags user group home home-service?)
     (list
      (shepherd-service
-      (provision (list (string->symbol (string-append "syncthing-" user))))
+      (provision (if home-service?
+                     '(syncthing)
+                     (list (string->symbol
+                            (string-append "syncthing-" user)))))
       (documentation "Run syncthing.")
-      (requirement '(loopback))
+      (requirement (if home-service? '() '(loopback)))
       (start #~(make-forkexec-constructor
                 (append (list (string-append #$syncthing "/bin/syncthing")
                               "-no-browser"
                               "-no-restart"
                               (string-append "-logflags=" (number->string #$logflags)))
                         '#$arguments)
-                #:user #$user
-                #:group #$group
+                #:user #$(and (not home-service?) user)
+                #:group #$(and (not home-service?) group)
                 #:environment-variables
                 (append (list (string-append "HOME=" (or #$home (passwd:dir (getpw #$user))))
                               "SSL_CERT_DIR=/etc/ssl/certs"
                               "SSL_CERT_FILE=/etc/ssl/certs/ca-certificates.crt")
-                        (remove (lambda (str)
-                                  (or (string-prefix? "HOME=" str)
-                                      (string-prefix? "SSL_CERT_DIR=" str)
-                                      (string-prefix? "SSL_CERT_FILE=" str)))
+                        (filter (negate       ;XXX: 'remove' is not in (guile)
+                                 (lambda (str)
+                                   (or (string-prefix? "HOME=" str)
+                                       (string-prefix? "SSL_CERT_DIR=" str)
+                                       (string-prefix? "SSL_CERT_FILE=" str))))
                                 (environ)))))
       (respawn? #f)
       (stop #~(make-kill-destructor))))))