gnu: Add AutoSSH service.

* gnu/services/ssh.scm (<autossh-configuration>): New record type.
(autossh-service-type): New variable.
(autossh-service-activation, autossh-file-name): New procedures.
* doc/guix.texi (Networking Services): Document this.

Signed-off-by: Oleg Pykhalov <go.wigust@gmail.com>

doc/guix.texi

@@ -79,6 +79,7 @@ Copyright @copyright{} 2020 Naga Malleswari@*
 Copyright @copyright{} 2020 Brice Waegeneire@*
 Copyright @copyright{} 2020 R Veera Kumar@*
 Copyright @copyright{} 2020 Pierre Langlois@*
+Copyright @copyright{} 2020 pinoaffe@*
 
 Permission is granted to copy, distribute and/or modify this document
 under the terms of the GNU Free Documentation License, Version 1.3 or
@@ -14390,6 +14391,80 @@ Whether to enable password-based authentication.
 @end table
 @end deftp
 
+@cindex AutoSSH
+@deffn {Scheme Variable} autossh-service-type
+This is the type for the @uref{https://www.harding.motd.ca/autossh,
+AutoSSH} program that runs a copy of @code{ssh} and monitors it,
+restarting it as necessary should it die or stop passing traffic.
+AutoSSH can be run manually from the commandline by passing arguments to
+the binary @code{autossh} from the package @code{autossh}, but it can
+also be run as a guix service. This latter usecase is documented here.
+
+AutoSSH can be used to forward local traffic to a remote machine using an SSH tunnel,
+and it respects the @file{~/.ssh/config} of the user it is run as.
+
+For example, to specify a service running autossh as the user @code{pino}
+and forwarding all local connections to port @code{8081} to @code{remote:8081}
+using an SSH tunnel, add this call to the operating system's @code{services} field:
+
+@lisp
+(service autossh-service-type
+         (autossh-configuration
+          (user "pino")
+          (ssh-options (list "-T" "-N" "-L" "8081:localhost:8081" "remote.net"))))
+@end lisp
+@end deffn
+
+@deftp {Data Type} autossh-configuration
+This data type represents the configuration of an AutoSSH service.
+
+@table @asis
+
+@item @code{user} (default @code{"autossh"})
+The user as which the AutoSSH service is to be run.
+This assumes that the specified user exists.
+
+@item @code{poll} (default @code{600})
+Specifies the connection poll time in seconds.
+
+@item @code{first-poll} (default @code{#f})
+Specifies how long autossh waits before the first connection test in seconds.
+After this first test, polling is resumed at the pace defined in @code{poll}.
+When set to @code{#f}, the first poll is not treated specially and
+will also use the connection poll specified in @code{poll}
+
+@item @code{gate-time} (default @code{30})
+Specifies (in seconds) how long an SSH connection must be active
+before it is considered successful.
+
+@item @code{log-level} (default @code{1})
+The log level, corresponding to the levels used by syslog
+(so @code{0} is the most silent while @code{7} is the chattiest.)
+
+@item @code{max-start} (default @code{#f})
+The maximum number of times SSH may be (re)started before AutoSSH exits.
+When set to @code{#f}, no maximum is configured and AutoSSH may restart indefinitely.
+
+@item @code{message} (default @code{""})
+The message to append to the echo message sent when testing connections.
+
+@item @code{port} (default @code{"0"})
+The ports used for monitoring the connection. When set to @code{"0"},
+monitoring is disabled. When set to @code{"n"} where @code{n} is a positive integer,
+ports @code{n} and @code{n+1} are used for monitoring the connection, such that
+port @code{n} is the base monitoring port and @code{n+1} is the echo port.
+When set to @code{"n:m"} where @code{n} and @code{m} are positive integers,
+the ports @code{n} and @code{n+1} are used for monitoring the connection, such
+that port @code{n} is the base monitoring port and @code{m} is the echo port.
+
+@item @code{ssh-options} (default @code{'()})
+The list of commandline arguments to pass to ssh when it is run.
+Options @code{-f} and @code{-M ....} are reserved for AutoSSH
+and may cause undefined behaviour.
+
+@end table
+@end deftp
+
 @defvr {Scheme Variable} %facebook-host-aliases
 This variable contains a string for use in @file{/etc/hosts}
 (@pxref{Host Names,,, libc, The GNU C Library Reference Manual}).  Each

gnu/services/ssh.scm

@@ -4,6 +4,7 @@
 ;;; Copyright © 2016 Julien Lepiller <julien@lepiller.eu>
 ;;; Copyright © 2017 Clément Lassieur <clement@lassieur.org>
 ;;; Copyright © 2019 Ricardo Wurmus <rekado@elephly.net>
+;;; Copyright © 2020 pinoaffe <pinoaffe@airmail.cc>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -45,7 +46,11 @@ (define-module (gnu services ssh)
             dropbear-configuration
             dropbear-configuration?
             dropbear-service-type
-            dropbear-service))
+            dropbear-service
+
+            autossh-configuration
+            autossh-configuration?
+            autossh-service-type))
 
 ;;; Commentary:
 ;;;
@@ -628,4 +633,103 @@ (define* (dropbear-service #:optional (config (dropbear-configuration)))
 object."
   (service dropbear-service-type config))
 
+
+;;;
+;;; AutoSSH.
+;;;
+
+
+(define-record-type* <autossh-configuration>
+  autossh-configuration make-autossh-configuration
+  autossh-configuration?
+  (user            autossh-configuration-user
+                   (default "autossh"))
+  (poll            autossh-configuration-poll
+                   (default 600))
+  (first-poll      autossh-configuration-first-poll
+                   (default #f))
+  (gate-time       autossh-configuration-gate-time
+                   (default 30))
+  (log-level       autossh-configuration-log-level
+                   (default 1))
+  (max-start       autossh-configuration-max-start
+                   (default #f))
+  (message         autossh-configuration-message
+                   (default ""))
+  (port            autossh-configuration-port
+                   (default "0"))
+  (ssh-options     autossh-configuration-ssh-options
+                   (default '())))
+
+(define (autossh-file-name config file)
+  "Return a path in /var/run/autossh/ that is writable
+   by @code{user} from @code{config}."
+  (string-append "/var/run/autossh/"
+                 (autossh-configuration-user config)
+                 "/" file))
+
+(define (autossh-shepherd-service config)
+  (shepherd-service
+   (documentation "Automatically set up ssh connections (and keep them alive).")
+   (provision '(autossh))
+   (start #~(make-forkexec-constructor
+             (list #$(file-append autossh "/bin/autossh")
+                   #$@(autossh-configuration-ssh-options config))
+             #:user #$(autossh-configuration-user config)
+             #:group (passwd:gid (getpw #$(autossh-configuration-user config)))
+             #:pid-file #$(autossh-file-name config "pid")
+             #:log-file #$(autossh-file-name config "log")
+             #:environment-variables
+             '(#$(string-append "AUTOSSH_PIDFILE="
+                                (autossh-file-name config "pid"))
+               #$(string-append "AUTOSSH_LOGFILE="
+                                (autossh-file-name config "log"))
+               #$(string-append "AUTOSSH_POLL="
+                                (number->string
+                                 (autossh-configuration-poll config)))
+               #$(string-append "AUTOSSH_FIRST_POLL="
+                                (number->string
+                                 (or
+                                  (autossh-configuration-first-poll config)
+                                  (autossh-configuration-poll config))))
+               #$(string-append "AUTOSSH_GATETIME="
+                                (number->string
+                                 (autossh-configuration-gate-time config)))
+               #$(string-append "AUTOSSH_LOGLEVEL="
+                                (number->string
+                                 (autossh-configuration-log-level config)))
+               #$(string-append "AUTOSSH_MAXSTART="
+                                (number->string
+                                 (or (autossh-configuration-max-start config)
+                                     -1)))
+               #$(string-append "AUTOSSH_MESSAGE="
+                                (autossh-configuration-message config))
+               #$(string-append "AUTOSSH_PORT="
+                                (autossh-configuration-port config)))))
+   (stop #~(make-kill-destructor))))
+
+(define (autossh-service-activation config)
+  (with-imported-modules '((guix build utils))
+    #~(begin
+        (use-modules (guix build utils))
+        (define %user
+          (getpw #$(autossh-configuration-user config)))
+        (let* ((directory #$(autossh-file-name config ""))
+               (log (string-append directory "/log")))
+          (mkdir-p directory)
+          (chown directory (passwd:uid %user) (passwd:gid %user))
+          (call-with-output-file log (const #t))
+          (chown log (passwd:uid %user) (passwd:gid %user))))))
+
+(define autossh-service-type
+  (service-type
+   (name 'autossh)
+   (description "Automatically set up ssh connections (and keep them alive).")
+   (extensions
+    (list (service-extension shepherd-root-service-type
+                             (compose list autossh-shepherd-service))
+          (service-extension activation-service-type
+                             autossh-service-activation)))
+   (default-value (autossh-configuration))))
+
 ;;; ssh.scm ends here