services: Add exim-service-type.

* gnu/services/mail.scm (<exim-configuration>): New record type.
(exim-computed-config-file, exim-shepherd-service, exim-activation, exim-etc,
exim-profile): New procedures.
(exim-service-type, %exim-accounts): New variables.
* doc/guix.text (Mail Services): Document it.

Signed-off-by: Ludovic Courtès <ludo@gnu.org>

doc/guix.texi

@@ -32,7 +32,8 @@ Copyright @copyright{} 2016 Julien Lepiller@*
 Copyright @copyright{} 2016 Alex ter Weele@*
 Copyright @copyright{} 2017 Clément Lassieur@*
 Copyright @copyright{} 2017 Mathieu Othacehe@*
-Copyright @copyright{} 2017 Federico Beffa
+Copyright @copyright{} 2017 Federico Beffa@*
+Copyright @copyright{} 2017 Carlo Zancanaro
 
 Permission is granted to copy, distribute and/or modify this document
 under the terms of the GNU Free Documentation License, Version 1.3 or
@@ -12206,6 +12207,45 @@ remote servers.  Run @command{man smtpd.conf} for more information.
 @end table
 @end deftp
 
+@subsubheading Exim Service
+
+@deffn {Scheme Variable} exim-service-type
+This is the type of the @uref{https://exim.org, Exim} service, whose value
+should be an @code{exim-configuration} object as in this example:
+
+@example
+(service exim-service-type
+         (exim-configuration
+           (config-file (local-file "./my-exim.conf"))
+           (aliases '(("postmaster" "bob")
+                      ("bob" "bob@@example.com" "bob@@example2.com")))))
+@end example
+@end deffn
+
+@deftp {Data Type} exim-configuration
+Data type representing the configuration of exim.
+
+@table @asis
+@item @code{package} (default: @var{exim})
+Package object of the Exim server.
+
+@item @code{config-file} (default: @code{#f})
+File-like object of the Exim configuration file to use. If its value is
+@code{#f} then use the default configuration file from the package
+provided in @code{package}. The resulting configuration file is loaded
+after setting the @code{exim_user} and @code{exim_group} configuration
+variables.
+
+@item @code{aliases} (default: @code{'()})
+List of aliases to use when delivering mail on this system. The
+@code{car} of each list is used to match incoming mail, with the
+@code{cdr} of each list designating how to deliver it. There may be many
+delivery methods provided, in which case the mail is delivered to them
+all.
+
+@end table
+@end deftp
+
 @node Messaging Services
 @subsubsection Messaging Services
 

gnu/services/mail.scm

@@ -1,6 +1,7 @@
 ;;; GNU Guix --- Functional package management for GNU
 ;;; Copyright © 2015 Andy Wingo <wingo@igalia.com>
 ;;; Copyright © 2017 Clément Lassieur <clement@lassieur.org>
+;;; Copyright © 2017 Carlo Zancanaro <carlo@zancanaro.id.au>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -33,6 +34,7 @@
   #:use-module (guix packages)
   #:use-module (guix gexp)
   #:use-module (ice-9 match)
+  #:use-module (ice-9 format)
   #:export (dovecot-service
             dovecot-service-type
             dovecot-configuration
@@ -53,7 +55,12 @@
             opensmtpd-configuration
             opensmtpd-configuration?
             opensmtpd-service-type
-            %default-opensmtpd-config-file))
+            %default-opensmtpd-config-file
+
+            exim-configuration
+            exim-configuration?
+            exim-service-type
+            %default-exim-config-file))
 
 ;;; Commentary:
 ;;;
@@ -1620,3 +1627,96 @@ accept from local for any relay
                              (compose list opensmtpd-configuration-package))
           (service-extension shepherd-root-service-type
                              opensmtpd-shepherd-service)))))
+
+
+;;;
+;;; Exim.
+;;;
+
+(define-record-type* <exim-configuration> exim-configuration
+  make-exim-configuration
+  exim-configuration?
+  (package       exim-configuration-package ;<package>
+                 (default exim))
+  (config-file   exim-configuration-config-file ;file-like
+                 (default #f))
+  (aliases       exim-configuration-aliases ;; list of lists
+                 (default '())))
+
+(define %exim-accounts
+  (list (user-group
+         (name "exim")
+         (system? #t))
+        (user-account
+         (name "exim")
+         (group "exim")
+         (system? #t)
+         (comment "Exim Daemon")
+         (home-directory "/var/empty")
+         (shell (file-append shadow "/sbin/nologin")))))
+
+(define (exim-computed-config-file package config-file)
+  (computed-file "exim.conf"
+                 #~(call-with-output-file #$output
+                     (lambda (port)
+                       (format port "
+exim_user = exim
+exim_group = exim
+.include ~a"
+                               #$(or config-file
+                                     (file-append package "/etc/exim.conf")))))))
+
+(define exim-shepherd-service
+  (match-lambda
+    (($ <exim-configuration> package config-file aliases)
+     (list (shepherd-service
+            (provision '(exim mta))
+            (documentation "Run the exim daemon.")
+            (requirement '(networking))
+            (start #~(make-forkexec-constructor
+                      '(#$(file-append package "/bin/exim")
+                        "-bd" "-v" "-C"
+                        #$(exim-computed-config-file package config-file))))
+            (stop #~(make-kill-destructor)))))))
+
+(define exim-activation
+  (match-lambda
+    (($ <exim-configuration> package config-file aliases)
+     (with-imported-modules '((guix build utils))
+       #~(begin
+           (use-modules (guix build utils))
+
+           (let ((uid (passwd:uid (getpw "exim")))
+                 (gid (group:gid (getgr "exim"))))
+             (mkdir-p "/var/spool/exim")
+             (chown "/var/spool/exim" uid gid))
+
+           (zero? (system* #$(file-append package "/bin/exim")
+                           "-bV" "-C" #$(exim-computed-config-file package config-file))))))))
+
+(define exim-etc
+  (match-lambda
+    (($ <exim-configuration> package config-file aliases)
+     `(("aliases" ,(plain-file "aliases"
+                               ;; Ideally we'd use a format string like
+                               ;; "~:{~a: ~{~a~^,~}\n~}", but it gives a
+                               ;; warning that I can't figure out how to fix,
+                               ;; so we'll just use string-join below instead.
+                               (format #f "~:{~a: ~a\n~}"
+                                       (map (lambda (entry)
+                                              (list (car entry)
+                                                    (string-join (cdr entry) ",")))
+                                            aliases))))))))
+
+(define exim-profile
+  (compose list exim-configuration-package))
+
+(define exim-service-type
+  (service-type
+   (name 'exim)
+   (extensions
+    (list (service-extension shepherd-root-service-type exim-shepherd-service)
+          (service-extension account-service-type (const %exim-accounts))
+          (service-extension activation-service-type exim-activation)
+          (service-extension profile-service-type exim-profile)
+          (service-extension etc-service-type exim-etc)))))