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|
;;; GNU Guix --- Functional package management for GNU
;;; Copyright © 2020 Mathieu Othacehe <othacehe@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 (guix scripts discover)
#:use-module (guix avahi)
#:use-module (guix config)
#:use-module (guix scripts)
#:use-module (guix ui)
#:use-module (guix build syscalls)
#:use-module (guix build utils)
#:use-module (guix scripts publish)
#:use-module (ice-9 rdelim)
#:use-module (srfi srfi-37)
#:export (read-substitute-urls
guix-discover))
(define (show-help)
(format #t (G_ "Usage: guix discover [OPTION]...
Discover Guix related services using Avahi.\n"))
(display (G_ "
-c, --cache=DIRECTORY cache discovery results in DIRECTORY"))
(display (G_ "
-h, --help display this help and exit"))
(display (G_ "
-V, --version display version information and exit"))
(newline)
(show-bug-report-information))
(define %options
(list (option '(#\c "cache") #t #f
(lambda (opt name arg result)
(alist-cons 'cache arg result)))
(option '(#\h "help") #f #f
(lambda _
(show-help)
(exit 0)))
(option '(#\V "version") #f #f
(lambda _
(show-version-and-exit "guix discover")))))
(define %default-options
`((cache . ,%state-directory)))
;;;
;;; Publish servers.
;;;
(define %publish-services
;; Set of discovered publish services.
(make-hash-table))
(define (publish-file cache-directory)
"Return the name of the file storing the discovered publish services inside
CACHE-DIRECTORY."
(let ((directory (string-append cache-directory "/discover")))
(string-append directory "/publish")))
(define %publish-file
(make-parameter (publish-file %state-directory)))
(define* (write-publish-file #:key (file (%publish-file)))
"Dump the content of %PUBLISH-SERVICES hash table into FILE. Use a write
lock on FILE to synchronize with any potential readers."
(with-file-lock file
(call-with-output-file file
(lambda (port)
(hash-for-each
(lambda (name service)
(format port "http://~a:~a~%"
(avahi-service-address service)
(avahi-service-port service)))
%publish-services)))
(chmod file #o644)))
(define (call-with-read-file-lock file thunk)
"Call THUNK with a read lock on FILE."
(let ((port #f))
(dynamic-wind
(lambda ()
(set! port
(let ((port (open-file file "r0")))
(fcntl-flock port 'read-lock)
port)))
thunk
(lambda ()
(when port
(unlock-file port))))))
(define-syntax-rule (with-read-file-lock file exp ...)
"Wait to acquire a read lock on FILE and evaluate EXP in that context."
(call-with-read-file-lock file (lambda () exp ...)))
(define* (read-substitute-urls #:key (file (%publish-file)))
"Read substitute urls list from FILE and return it. Use a read lock on FILE
to synchronize with the writer."
(if (file-exists? file)
(with-read-file-lock file
(call-with-input-file file
(lambda (port)
(let loop ((url (read-line port))
(urls '()))
(if (eof-object? url)
urls
(loop (read-line port) (cons url urls)))))))
'()))
;;;
;;; Entry point.
;;;
(define %services
;; List of services we want to discover.
(list publish-service-type))
(define (service-proc action service)
(let ((name (avahi-service-name service))
(type (avahi-service-type service)))
(when (string=? type publish-service-type)
(case action
((new-service)
(hash-set! %publish-services name service))
((remove-service)
(hash-remove! %publish-services name)))
(write-publish-file))))
(define-command (guix-discover . args)
(category internal)
(synopsis "discover Guix related services using Avahi")
(with-error-handling
(let* ((opts (args-fold* args %options
(lambda (opt name arg result)
(leave (G_ "~A: unrecognized option~%") name))
(lambda (arg result)
(leave (G_ "~A: extraneous argument~%") arg))
%default-options))
(cache (assoc-ref opts 'cache))
(publish-file (publish-file cache)))
(parameterize ((%publish-file publish-file))
(mkdir-p (dirname publish-file))
(avahi-browse-service-thread service-proc
#:types %services)))))
;;; Local Variables:
;;; eval: (put 'with-read-file-lock 'scheme-indent-function 1)
;;; End:
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