[bug#44800] [PATCH v2 2/3] publish: Add avahi support.

[Mathieu Othacehe <othacehe@gnu.org>]

* guix/scripts/publish.scm (%options): Add "--enable-avahi" option.
(show-help): Document it.
(service-name): New procedure,
(publish-service-type): new variable.
(run-publish-server): Add "avahi?" and "port" parameters. Use them to publish
the server using Avahi.
(guix-publish): Pass the "avahi?" option to "run-publish-server".
* gnu/services/base.scm (<guix-publish-configuration>): Add "enable-avahi?"
field.
(guix-publish-shepherd-service): Honor it.
---
 doc/guix.texi            |  4 ++++
 gnu/services/base.scm    |  8 +++++++-
 guix/scripts/publish.scm | 24 ++++++++++++++++++++++++
 3 files changed, 35 insertions(+), 1 deletion(-)

diff --git a/doc/guix.texi b/doc/guix.texi
index e9cf25fc90..f8efc34310 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -12170,6 +12170,10 @@ The signing key pair must be generated before @command{guix publish} is
 launched, using @command{guix archive --generate-key} (@pxref{Invoking
 guix archive}).
 
+When the @option{--enable-avahi} option is passed, the publish server is
+advertised on the local network as an Avahi service, using Guile-Avahi
+bindings.
+
 The general syntax is:
 
 @example
diff --git a/gnu/services/base.scm b/gnu/services/base.scm
index 029df5ac16..87c247bdf1 100644
--- a/gnu/services/base.scm
+++ b/gnu/services/base.scm
@@ -1743,6 +1743,8 @@ proxy of 'guix-daemon'...~%")
            (default 80))
   (host    guix-publish-configuration-host        ;string
            (default "localhost"))
+  (enable-avahi? guix-publish-enable-avahi?       ;boolean
+                 (default #f))
   (compression       guix-publish-configuration-compression
                      (thunked)
                      (default (default-compression this-record
@@ -1789,7 +1791,8 @@ raise a deprecation warning if the 'compression-level' field was used."
                    lst))))
 
   (match-record config <guix-publish-configuration>
-    (guix port host nar-path cache workers ttl cache-bypass-threshold)
+    (guix port host nar-path cache workers ttl cache-bypass-threshold
+          enable-avahi?)
     (list (shepherd-service
            (provision '(guix-publish))
            (requirement '(guix-daemon))
@@ -1800,6 +1803,9 @@ raise a deprecation warning if the 'compression-level' field was used."
                            #$@(config->compression-options config)
                            (string-append "--nar-path=" #$nar-path)
                            (string-append "--listen=" #$host)
+                           #$@(if enable-avahi?
+                                  #~("--enable-avahi")
+                                  #~())
                            #$@(if workers
                                   #~((string-append "--workers="
                                                     #$(number->string
diff --git a/guix/scripts/publish.scm b/guix/scripts/publish.scm
index 2a2185e2b9..d2bb7ae982 100644
--- a/guix/scripts/publish.scm
+++ b/guix/scripts/publish.scm
@@ -42,6 +42,7 @@
   #:use-module (web server)
   #:use-module (web uri)
   #:autoload   (sxml simple) (sxml->xml)
+  #:use-module (guix avahi)
   #:use-module (guix base32)
   #:use-module (guix base64)
   #:use-module (guix config)
@@ -70,6 +71,7 @@
             signed-string
 
             open-server-socket
+            publish-service-type
             run-publish-server
             guix-publish))
 
@@ -83,6 +85,8 @@ Publish ~a over HTTP.\n") %store-directory)
   (display (G_ "
   -u, --user=USER        change privileges to USER as soon as possible"))
   (display (G_ "
+  -a, --enable-avahi     enable Avahi based discovery"))
+  (display (G_ "
   -C, --compression[=METHOD:LEVEL]
                          compress archives with METHOD at LEVEL"))
   (display (G_ "
@@ -157,6 +161,9 @@ usage."
         (option '(#\V "version") #f #f
                 (lambda _
                   (show-version-and-exit "guix publish")))
+        (option '(#\a "enable-avahi") #f #f
+                (lambda (opt name arg result)
+                  (alist-cons 'enable-avahi? #t result)))
         (option '(#\u "user") #t #f
                 (lambda (opt name arg result)
                   (alist-cons 'user arg result)))
@@ -1069,11 +1076,25 @@ methods, return the applicable compression."
           (x (not-found request)))
         (not-found request))))
 
+(define (service-name)
+  "Return the Avahi service name of the server."
+  (string-append "guix-publish-" (gethostname)))
+
+(define publish-service-type
+  ;; Return the Avahi service type of the server.
+  "_guix_publish._tcp")
+
 (define* (run-publish-server socket store
                              #:key
+                             avahi? port
                              (compressions (list %no-compression))
                              (nar-path "nar") narinfo-ttl
                              cache pool)
+  (when avahi?
+    (avahi-publish-service-thread (service-name)
+                                  #:type publish-service-type
+                                  #:port port))
+
   (run-server (make-request-handler store
                                     #:cache cache
                                     #:pool pool
@@ -1119,6 +1140,7 @@ methods, return the applicable compression."
                                 (lambda (arg result)
                                   (leave (G_ "~A: extraneous argument~%") arg))
                                 %default-options))
+           (avahi?  (assoc-ref opts 'enable-avahi?))
            (user    (assoc-ref opts 'user))
            (port    (assoc-ref opts 'port))
            (ttl     (assoc-ref opts 'narinfo-ttl))
@@ -1179,6 +1201,8 @@ consider using the '--user' option!~%")))
 
         (with-store store
           (run-publish-server socket store
+                              #:avahi? avahi?
+                              #:port port
                               #:cache cache
                               #:pool (and cache (make-pool workers
                                                            #:thread-name
-- 
2.29.2