From a16d6225ee519cb7031d1610784daefe99b570e8 Mon Sep 17 00:00:00 2001
From: Sergey Trofimov <sarg@sarg.org.ru>
Date: Mon, 6 Oct 2025 16:57:06 +0200
Subject: nss: Allow selecting IP protocol for mDNS lookups.
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* gnu/system/nss.scm (mdns-host-lookup-nss): New procedure.
* doc/guix.texi (Name Service Switch): Document it.

Change-Id: Ie4ff4aab6bf41eb2cec69b78a8427594b20bc954
Signed-off-by: Ludovic Courtès <ludo@gnu.org>
---
 gnu/system/nss.scm | 41 +++++++++++++++++++++++++----------------
 1 file changed, 25 insertions(+), 16 deletions(-)

(limited to 'gnu/system')

diff --git a/gnu/system/nss.scm b/gnu/system/nss.scm
index 673b96c7132..e46840713fe 100644
--- a/gnu/system/nss.scm
+++ b/gnu/system/nss.scm
@@ -27,6 +27,7 @@
             name-service
 
             lookup-specification
+            mdns-host-lookup-nss
 
             %default-nss
             %mdns-host-lookup-nss
@@ -152,26 +153,34 @@
   ;; Default NSS configuration.
   (name-service-switch))
 
-(define %mdns-host-lookup-nss
-  (name-service-switch
-    (hosts (list %files                           ;first, check /etc/hosts
+(define* (mdns-host-lookup-nss #:key (ipv6? #t) (ipv4? #t))
+  (let ((flavour (cond
+                  ((and ipv6? ipv4?) "mdns")
+                  (ipv6? "mdns6")
+                  (ipv4? "mdns4")
+                  (#t (error "No protocols enabled for mDNS lookups.")))))
+    (name-service-switch
+      (hosts (list %files               ;first, check /etc/hosts
 
-                 ;; If the above did not succeed, try with 'mdns_minimal'.
-                 (name-service
-                   (name "mdns_minimal")
+                   ;; If the above did not succeed, try with 'mdns_minimal'.
+                   (name-service
+                     (name (string-append flavour "_minimal"))
 
-                   ;; 'mdns_minimal' is authoritative for '.local'.  When it
-                   ;; returns "not found", no need to try the next methods.
-                   (reaction (lookup-specification
-                              (not-found => return))))
+                     ;; 'mdns_minimal' is authoritative for '.local'.  When it
+                     ;; returns "not found", no need to try the next methods.
+                     (reaction (lookup-specification
+                                (not-found => return))))
 
-                 ;; Then fall back to DNS.
-                 (name-service
-                   (name "dns"))
+                   ;; Then fall back to DNS.
+                   (name-service
+                     (name "dns"))
 
-                 ;; Finally, try with the "full" 'mdns'.
-                 (name-service
-                   (name "mdns"))))))
+                   ;; Finally, try with the "full" 'mdns'.
+                   (name-service
+                     (name flavour)))))))
+
+
+(define %mdns-host-lookup-nss (mdns-host-lookup-nss))
 
 
 ;;;
-- 
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