From 9283ba29b23dd6dc7faaf138188fd02ab38b30e8 Mon Sep 17 00:00:00 2001
From: Till Kamppeter <till.kamppeter@gmail.com>
Date: Fri, 15 Dec 2017 10:16:28 -0200
Subject: [PATCH] Add support to advertise local services ("localhost") on the
 local machine only

This is the patch attached to Issue #125 (on Dec 6, 2017) and also
shown in the readme.md of ippusbxd
(https://github.com/OpenPrinting/ippusbxd).

It makes also services on the loopback ("lo") interface being
advertised and these records use "localhost" instead of the network
host name of the machine as server host name. This way clients, like
for example CUPS or cups-browsed will find these local services and be
able to work with them as they were network services.
---
 avahi-core/iface-linux.c     | 4 ++--
 avahi-core/iface-pfroute.c   | 8 ++++----
 avahi-core/resolve-service.c | 3 ++-
 3 files changed, 8 insertions(+), 7 deletions(-)

diff --git a/avahi-core/iface-linux.c b/avahi-core/iface-linux.c
index c6c5f77..e116c7b 100644
--- a/avahi-core/iface-linux.c
+++ b/avahi-core/iface-linux.c
@@ -104,8 +104,8 @@ static void netlink_callback(AvahiNetlink *nl, struct nlmsghdr *n, void* userdat
         hw->flags_ok =
             (ifinfomsg->ifi_flags & IFF_UP) &&
             (!m->server->config.use_iff_running || (ifinfomsg->ifi_flags & IFF_RUNNING)) &&
-            !(ifinfomsg->ifi_flags & IFF_LOOPBACK) &&
-            (ifinfomsg->ifi_flags & IFF_MULTICAST) &&
+            ((ifinfomsg->ifi_flags & IFF_LOOPBACK) ||
+             (ifinfomsg->ifi_flags & IFF_MULTICAST)) &&
             (m->server->config.allow_point_to_point || !(ifinfomsg->ifi_flags & IFF_POINTOPOINT));
 
         /* Handle interface attributes */
diff --git a/avahi-core/iface-pfroute.c b/avahi-core/iface-pfroute.c
index 9a2e953..27c3443 100644
--- a/avahi-core/iface-pfroute.c
+++ b/avahi-core/iface-pfroute.c
@@ -80,8 +80,8 @@ static void rtm_info(struct rt_msghdr *rtm, AvahiInterfaceMonitor *m)
   hw->flags_ok =
     (ifm->ifm_flags & IFF_UP) &&
     (!m->server->config.use_iff_running || (ifm->ifm_flags & IFF_RUNNING)) &&
-    !(ifm->ifm_flags & IFF_LOOPBACK) &&
-    (ifm->ifm_flags & IFF_MULTICAST) &&
+    ((ifm->ifm_flags & IFF_LOOPBACK) ||
+     (ifm->ifm_flags & IFF_MULTICAST)) &&
     (m->server->config.allow_point_to_point || !(ifm->ifm_flags & IFF_POINTOPOINT));
 
   avahi_free(hw->name);
@@ -427,8 +427,8 @@ static void if_add_interface(struct lifreq *lifreq, AvahiInterfaceMonitor *m, in
         hw->flags_ok =
             (flags & IFF_UP) &&
             (!m->server->config.use_iff_running || (flags & IFF_RUNNING)) &&
-            !(flags & IFF_LOOPBACK) &&
-            (flags & IFF_MULTICAST) &&
+            ((flags & IFF_LOOPBACK) ||
+             (flags & IFF_MULTICAST)) &&
             (m->server->config.allow_point_to_point || !(flags & IFF_POINTOPOINT));
         hw->name = avahi_strdup(lifreq->lifr_name);
         hw->mtu = mtu;
diff --git a/avahi-core/resolve-service.c b/avahi-core/resolve-service.c
index 3377a50..3311b6b 100644
--- a/avahi-core/resolve-service.c
+++ b/avahi-core/resolve-service.c
@@ -24,6 +24,7 @@
 #include <string.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include <net/if.h>
 
 #include <avahi-common/domain.h>
 #include <avahi-common/timeval.h>
@@ -129,7 +130,7 @@ static void finish(AvahiSServiceResolver *r, AvahiResolverEvent event) {
                 r->service_name,
                 r->service_type,
                 r->domain_name,
-                r->srv_record->data.srv.name,
+                (r->interface == if_nametoindex("lo")) ? "localhost" : r->srv_record->data.srv.name,
                 r->address_record ? &a : NULL,
                 r->srv_record->data.srv.port,
                 r->txt_record ? r->txt_record->data.txt.string_list : NULL,
-- 
2.17.2