Skip interfaces without IPv4 addresses for mDNS

Instead of blindly try to use every interface for IPv4, add a patch
which filters interfaces without IPv4 addresses. IPv4 addresses are
required for any multicast operation, so an interface without IPv4
address will never be able to use mDNS.

Author: agners

0008-MinMDNS-skip-interfaces-without-IPv4-addresses.patch

@@ -0,0 +1,96 @@
+From 72e9a1c20118b6c41c750a8bcaca578ff85488e2 Mon Sep 17 00:00:00 2001
+From: Stefan Agner <stefan@agner.ch>
+Date: Wed, 28 Feb 2024 10:38:37 +0100
+Subject: [PATCH] MinMDNS skip interfaces without IPv4 addresses
+
+IPv4 multicast require an IPv4 address to be present on a particular
+interface. Skip interfaces without IPv4 addresses in the default
+address policy. This avoids errors when trying to join the multicast
+group later on:
+MDNS failed to join multicast group on veth3cdf62f for address type IPv4: src/inet/UDPEndPointImplSockets.cpp:777: Inet Error 0x00000110: Address not found
+---
+ .../minimal_mdns/AddressPolicy_LibNlImpl.cpp  | 42 +++++++++++++++++--
+ 1 file changed, 38 insertions(+), 4 deletions(-)
+
+diff --git a/src/lib/dnssd/minimal_mdns/AddressPolicy_LibNlImpl.cpp b/src/lib/dnssd/minimal_mdns/AddressPolicy_LibNlImpl.cpp
+index e73627f423..b1802c8d25 100644
+--- a/src/lib/dnssd/minimal_mdns/AddressPolicy_LibNlImpl.cpp
++++ b/src/lib/dnssd/minimal_mdns/AddressPolicy_LibNlImpl.cpp
+@@ -48,6 +48,7 @@ private:
+ 
+     nl_sock * mNlSocket            = nullptr;
+     nl_cache * mNlCache            = nullptr;
++    nl_cache * mNlAddrCache        = nullptr;
+     nl_object * mCurrentLink       = nullptr;
+     IPAddressType mCurrentLinkType = IPAddressType::kUnknown;
+ 
+@@ -94,6 +95,12 @@ AllListenIterator::~AllListenIterator()
+         mNlCache = nullptr;
+     }
+ 
++    if (mNlAddrCache != nullptr)
++    {
++        nl_cache_free(mNlAddrCache);
++        mNlAddrCache = nullptr;
++    }
++
+     if (mNlSocket != nullptr)
+     {
+         nl_socket_free(mNlSocket);
+@@ -151,7 +158,6 @@ bool AllListenIterator::Next(InterfaceId * id, IPAddressType * type)
+     while (true)
+     {
+ #if INET_CONFIG_ENABLE_IPV4
+-        // FOR IPv4, report all interfaces as 'try IPv4 here as well'
+         if (mCurrentLinkType == IPAddressType::kIPv6)
+         {
+             mCurrentLinkType = IPAddressType::kIPv4;
+@@ -176,14 +182,42 @@ bool AllListenIterator::Next(InterfaceId * id, IPAddressType * type)
+             continue;
+         }
+ 
+-        int idx = rtnl_link_get_ifindex(CurrentLink());
+-        if (idx == 0)
++        int ifindex = rtnl_link_get_ifindex(CurrentLink());
++        if (ifindex == 0)
+         {
+             // Invalid index, move to the next interface
+             continue;
+         }
+ 
+-        *id   = InterfaceId(idx);
++        // For IPv4, report only interfaces which have an IPv4 address
++        if (mCurrentLinkType == IPAddressType::kIPv4)
++        {
++            if (mNlAddrCache == nullptr)
++            {
++                int result = rtnl_addr_alloc_cache(mNlSocket, &mNlAddrCache);
++                if (result != 0)
++                {
++                    ChipLogError(Inet, "Failed to cache addresses");
++                    return false;
++                }
++            }
++
++            // Find IPv4 address for this interface
++            struct rtnl_addr * filter = rtnl_addr_alloc();
++            rtnl_addr_set_family(filter, AF_INET);
++            rtnl_addr_set_ifindex(filter, ifindex);
++
++            struct nl_object * addr = nl_cache_find(mNlAddrCache, OBJ_CAST(filter));
++            nl_object_put(OBJ_CAST(filter));
++
++            // No IPv4 address, skip this interface for IPv4.
++            if (addr == nullptr)
++                continue;
++
++            nl_object_put(addr);
++        }
++
++        *id   = InterfaceId(ifindex);
+         *type = mCurrentLinkType; // advancing should have set this
+         return true;
+     }
+-- 
+2.44.0
+