services: Add syncthing service.

* gnu/services/syncthing.scm: New file.
* gnu/local.mk: Add this.
* doc/guix.texi: Document this.

doc/guix.texi

@@ -16507,6 +16507,55 @@ Group name or group ID that will be used when accessing the module.
 @end table
 @end deftp
 
+The @code{(gnu services syncthing)} module provides the following services:
+@cindex syncthing
+
+You might want a syncthing daemon if you have files between two or more
+computers and want to sync them in real time, safely protected from
+prying eyes.
+
+@deffn {Scheme Variable} syncthing-service-type
+This is the service type for the @uref{https://syncthing.net/,
+syncthing} daemon, The value for this service type is a
+@command{syncthing-configuration} record as in this example:
+
+@lisp
+(service syncthing-service-type
+         (syncthing-configuration (user "alice")))
+@end lisp
+
+See below for details about @code{syncthing-configuration}.
+
+@deftp {Data Type} syncthing-configuration
+Data type representing the configuration for @code{syncthing-service-type}.
+
+@table @asis
+@item @code{syncthing} (default: @var{syncthing})
+@code{syncthing} package to use.
+
+@item @code{arguments} (default: @var{'()})
+List of command-line arguments passing to @code{syncthing} binary.
+
+@item @code{logflags} (default: @var{0})
+Sum of loging flags, see
+@uref{https://docs.syncthing.net/users/syncthing.html#cmdoption-logflags, Syncthing documentation logflags}.
+
+@item @code{user} (default: @var{#f})
+The user as which the Syncthing service is to be run.
+This assumes that the specified user exists.
+
+@item @code{group} (default: @var{"users"})
+The group as which the Syncthing service is to be run.
+This assumes that the specified group exists.
+
+@item @code{home} (default: @var{#f})
+Common configuration and data directory.  The default configuration
+directory is @file{$HOME} of the specified Syncthing @code{user}.
+
+@end table
+@end deftp
+@end deffn
+
 Furthermore, @code{(gnu services ssh)} provides the following services.
 @cindex SSH
 @cindex SSH server

gnu/local.mk

@@ -17,7 +17,7 @@
 # Copyright © 2017, 2020 Mathieu Othacehe <m.othacehe@gmail.com>
 # Copyright © 2017, 2018, 2019 Gábor Boskovits <boskovits@gmail.com>
 # Copyright © 2018 Amirouche Boubekki <amirouche@hypermove.net>
-# Copyright © 2018, 2019, 2020 Oleg Pykhalov <go.wigust@gmail.com>
+# Copyright © 2018, 2019, 2020, 2021 Oleg Pykhalov <go.wigust@gmail.com>
 # Copyright © 2018 Stefan Stefanović <stefanx2ovic@gmail.com>
 # Copyright © 2018, 2020 Maxim Cournoyer <maxim.cournoyer@gmail.com>
 # Copyright © 2019, 2020 Guillaume Le Vaillant <glv@posteo.net>
@@ -630,6 +630,7 @@ GNU_SYSTEM_MODULES =				\
   %D%/services/sddm.scm				\
   %D%/services/spice.scm				\
   %D%/services/ssh.scm				\
+  %D%/services/syncthing.scm			\
   %D%/services/sysctl.scm			\
   %D%/services/telephony.scm			\
   %D%/services/version-control.scm              \

gnu/services/syncthing.scm

@@ -0,0 +1,89 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2021 Oleg Pykhalov <go.wigust@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 syncthing)
+  #:use-module (gnu packages syncthing)
+  #:use-module (gnu services)
+  #:use-module (gnu services shepherd)
+  #:use-module (guix gexp)
+  #:use-module (guix records)
+  #:use-module (ice-9 match)
+  #:use-module (srfi srfi-1)
+  #:export (syncthing-configuration
+            syncthing-configuration?
+            syncthing-service-type))
+
+;;; Commentary:
+;;;
+;;; This module provides a service definition for the syncthing service.
+;;;
+;;; Code:
+
+(define-record-type* <syncthing-configuration>
+  syncthing-configuration make-syncthing-configuration
+  syncthing-configuration?
+  (syncthing syncthing-configuration-syncthing ;<package>
+             (default syncthing))
+  (arguments syncthing-configuration-arguments ;list of strings
+             (default '()))
+  (logflags  syncthing-configuration-logflags  ;number
+             (default 0))
+  (user      syncthing-configuration-user      ;string
+             (default #f))
+  (group     syncthing-configuration-group     ;string
+             (default "users"))
+  (home      syncthing-configuration-home      ;string
+             (default #f)))
+
+(define syncthing-shepherd-service
+  (match-lambda
+    (($ <syncthing-configuration> syncthing arguments logflags user group home)
+     (list
+      (shepherd-service
+       (provision (list (string->symbol (string-append "syncthing-" user))))
+       (documentation "Run syncthing.")
+       (requirement '(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 #$group
+                 #:environment-variables
+                 (append (list (string-append "HOME=" (or #$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)))
+                                 (environ)))))
+       (respawn? #f)
+       (stop #~(make-kill-destructor)))))))
+
+(define syncthing-service-type
+  (service-type (name 'syncthing)
+                (extensions (list (service-extension shepherd-root-service-type
+                                                     syncthing-shepherd-service)))
+                (description
+                 "Run @uref{https://github.com/syncthing/syncthing, Syncthing}
+decentralized continuous file system synchronization.")))
+
+;;; syncthing.scm ends here