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+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2016 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 services herd)
+ #:use-module (guix ui)
+ #:use-module (guix utils)
+ #:use-module (srfi srfi-1)
+ #:use-module (srfi srfi-11)
+ #:use-module (ice-9 match)
+ #:export (current-services
+ unload-services
+ unload-service
+ load-services
+ start-service))
+
+;;; Commentary:
+;;;
+;;; This module provides an interface to the GNU Shepherd, similar to the
+;;; 'herd' command. Essentially it implements a subset of the (shepherd comm)
+;;; module, but focusing only on the parts relevant to 'guix system
+;;; reconfigure'.
+;;;
+;;; Code:
+
+(define %shepherd-socket-file
+ "/var/run/shepherd/socket")
+
+(define* (open-connection #:optional (file %shepherd-socket-file))
+ "Open a connection to the daemon, using the Unix-domain socket at FILE, and
+return the socket."
+ ;; The protocol is sexp-based and UTF-8-encoded.
+ (with-fluids ((%default-port-encoding "UTF-8"))
+ (let ((sock (socket PF_UNIX SOCK_STREAM 0))
+ (address (make-socket-address PF_UNIX file)))
+ (catch 'system-error
+ (lambda ()
+ (connect sock address)
+ (setvbuf sock _IOFBF 1024)
+ sock)
+ (lambda (key proc format-string format-args errno . rest)
+ (warning (_ "cannot connect to ~a: ~a~%") file
+ (apply format #f format-string format-args))
+ #f)))))
+
+(define-syntax-rule (with-shepherd connection body ...)
+ "Evaluate BODY... with CONNECTION bound to an open socket to PID 1."
+ (let ((connection (open-connection)))
+ (and connection
+ (dynamic-wind
+ (const #t)
+ (lambda ()
+ body ...)
+ (const #t)))))
+
+(define (report-action-error error)
+ "Report ERROR, an sexp received by a shepherd client in reply to COMMAND, a
+command object."
+ (match error
+ (('error ('version 0 x ...) 'service-not-found service)
+ (report-error (_ "service '~a' could not be found")
+ service))
+ (('error ('version 0 x ...) 'action-not-found action service)
+ (report-error (_ "service '~a' does not have an action '~a'")
+ service action))
+ (('error ('version 0 x ...) 'action-exception action service
+ key (args ...))
+ (report-error (_ "exception caught while executing '~a' \
+on service '~a':")
+ action service)
+ (print-exception (current-error-port) #f key args))
+ (('error . _)
+ (report-error (_ "something went wrong: ~s")
+ error))
+ (#f ;not an error
+ #t)))
+
+(define (display-message message)
+ ;; TRANSLATORS: Nothing to translate here.
+ (info (_ "shepherd: ~a~%") message))
+
+(define* (invoke-action service action arguments cont)
+ "Invoke ACTION on SERVICE with ARGUMENTS. On success, call CONT with the
+result. Otherwise return #f."
+ (with-shepherd sock
+ (write `(shepherd-command (version 0)
+ (action ,action)
+ (service ,service)
+ (arguments ,arguments)
+ (directory ,(getcwd)))
+ sock)
+ (force-output sock)
+
+ (match (read sock)
+ (('reply ('version 0 _ ...) ('result (result)) ('error #f)
+ ('messages messages))
+ (for-each display-message messages)
+ (cont result))
+ (('reply ('version 0 x ...) ('result y) ('error error)
+ ('messages messages))
+ (for-each display-message messages)
+ (report-action-error error)
+ #f)
+ (x
+ (warning (_ "invalid shepherd reply~%"))
+ #f))))
+
+(define-syntax-rule (with-shepherd-action service (action args ...)
+ result body ...)
+ (invoke-action service action (list args ...)
+ (lambda (result) body ...)))
+
+(define-syntax alist-let*
+ (syntax-rules ()
+ "Bind the given KEYs in EXP to the corresponding items in ALIST. ALIST
+is assumed to be a list of two-element tuples rather than a traditional list
+of pairs."
+ ((_ alist (key ...) exp ...)
+ (let ((key (and=> (assoc-ref alist 'key) car)) ...)
+ exp ...))))
+
+(define (current-services)
+ "Return two lists: the list of currently running services, and the list of
+currently stopped services."
+ (with-shepherd-action 'root ('status) services
+ (match services
+ ((('service ('version 0 _ ...) _ ...) ...)
+ (fold2 (lambda (service running-services stopped-services)
+ (alist-let* service (provides running)
+ (if running
+ (values (cons (first provides) running-services)
+ stopped-services)
+ (values running-services
+ (cons (first provides) stopped-services)))))
+ '()
+ '()
+ services))
+ (x
+ (warning (_ "failed to obtain list of shepherd services~%"))
+ (values #f #f)))))
+
+(define (unload-service service)
+ "Unload SERVICE, a symbol name; return #t on success."
+ (with-shepherd-action 'root ('unload (symbol->string service)) result
+ result))
+
+(define (%load-file file)
+ "Load FILE in the Shepherd."
+ (with-shepherd-action 'root ('load file) result
+ result))
+
+(define (eval-there exp)
+ "Eval EXP in the Shepherd."
+ (with-shepherd-action 'root ('eval (object->string exp)) result
+ result))
+
+(define (load-services files)
+ "Load and register the services from FILES, where FILES contain code that
+returns a shepherd <service> object."
+ (eval-there `(register-services
+ ,@(map (lambda (file)
+ `(primitive-load ,file))
+ files))))
+
+(define (start-service name)
+ (with-shepherd-action name ('start) result
+ result))
+
+;; Local Variables:
+;; eval: (put 'alist-let* 'scheme-indent-function 2)
+;; eval: (put 'with-shepherd 'scheme-indent-function 1)
+;; eval: (put 'with-shepherd-action 'scheme-indent-function 3)
+;; End:
+
+;;; herd.scm ends here