python-zeroconf · bdraco · Apr 14, 2025 · Apr 10, 2025 · Apr 10, 2025 · Apr 14, 2025
diff --git a/src/zeroconf/_utils/net.py b/src/zeroconf/_utils/net.py
@@ -168,8 +168,17 @@ def normalize_interface_choice(
     result: list[str | tuple[tuple[str, int, int], int]] = []
     if choice is InterfaceChoice.Default:
         if ip_version != IPVersion.V4Only:
-            # IPv6 multicast uses interface 0 to mean the default
-            result.append((("", 0, 0), 0))
+            # IPv6 multicast uses interface 0 to mean the default. However,
+            # the default interface can't be used for outgoing IPv6 multicast
+            # requests. In a way, interface choice default isn't really working
+            # with IPv6. Inform the user accordingly.
+            message = (
+                "IPv6 multicast requests can't be sent using default interface. "
+                "Use V4Only, InterfaceChoice.All or an explicit list of interfaces."
+            )
+            log.error(message)
+            warnings.warn(message, DeprecationWarning, stacklevel=2)
+                result.append((("::", 0, 0), 0))
         if ip_version != IPVersion.V6Only:
             result.append("0.0.0.0")
     elif choice is InterfaceChoice.All:
@@ -220,28 +229,33 @@ def set_so_reuseport_if_available(s: socket.socket) -> None:
             raise
 
 
-def set_mdns_port_socket_options_for_ip_version(
+def set_respond_socket_multicast_options(
     s: socket.socket,
-    bind_addr: tuple[str] | tuple[str, int, int],
     ip_version: IPVersion,
 ) -> None:
-    """Set ttl/hops and loop for mdns port."""
-    if ip_version != IPVersion.V6Only:
-        ttl = struct.pack(b"B", 255)
-        loop = struct.pack(b"B", 1)
+    """Set ttl/hops and loop for mDNS respond socket."""
+    if ip_version == IPVersion.V4Only:
         # OpenBSD needs the ttl and loop values for the IP_MULTICAST_TTL and
         # IP_MULTICAST_LOOP socket options as an unsigned char.
-        try:
-            s.setsockopt(socket.IPPROTO_IP, socket.IP_MULTICAST_TTL, ttl)
-            s.setsockopt(socket.IPPROTO_IP, socket.IP_MULTICAST_LOOP, loop)
-        except OSError as e:
-            if bind_addr[0] != "" or get_errno(e) != errno.EINVAL:  # Fails to set on MacOS
-                raise
-
-    if ip_version != IPVersion.V4Only:
+        ttl = struct.pack(b"B", 255)
+        loop = struct.pack(b"B", 1)
+        s.setsockopt(socket.IPPROTO_IP, socket.IP_MULTICAST_TTL, ttl)
+        s.setsockopt(socket.IPPROTO_IP, socket.IP_MULTICAST_LOOP, loop)
+    elif ip_version == IPVersion.V6Only:
         # However, char doesn't work here (at least on Linux)
         s.setsockopt(_IPPROTO_IPV6, socket.IPV6_MULTICAST_HOPS, 255)
         s.setsockopt(_IPPROTO_IPV6, socket.IPV6_MULTICAST_LOOP, True)
+    else:
+        # A shared sender socket is not really possible, especially with link-local
+        # multicast addresses (ff02::/16), the kernel needs to know which interface
+        # to use for routing.
+        #
+        # It seems that macOS even refuses to take IPv4 socket options if this is an
+        # AF_INET6 socket.
+        #
+        # In theory we could reconfigure the socket on each send, but that is not
+        # really practical for Python Zerconf.
+        raise RuntimeError("Dual-stack responder socket not supported")
 
 
 def new_socket(
@@ -266,14 +280,12 @@ def new_socket(
     s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
     set_so_reuseport_if_available(s)
 
-    if port == _MDNS_PORT:
-        set_mdns_port_socket_options_for_ip_version(s, bind_addr, ip_version)
-
     if apple_p2p:
         # SO_RECV_ANYIF = 0x1104
         # https://opensource.apple.com/source/xnu/xnu-4570.41.2/bsd/sys/socket.h
         s.setsockopt(socket.SOL_SOCKET, 0x1104, 1)
 
+    # Bind expects (address, port) for AF_INET and (address, port, flowinfo, scope_id) for AF_INET6
     bind_tup = (bind_addr[0], port, *bind_addr[1:])
     try:
         s.bind(bind_tup)
@@ -392,15 +404,27 @@ def add_multicast_member(
 def new_respond_socket(
     interface: str | tuple[tuple[str, int, int], int],
     apple_p2p: bool = False,
+    unicast: bool = False,
 ) -> socket.socket | None:
+    """Create interface specific socket for responding to multicast queries."""
     is_v6 = isinstance(interface, tuple)
+
+    # For response sockets:
+    # - Bind explicitly to the interface address
+    # - Use ephemeral ports if in unicast mode
+    # - Create socket according to the interface IP type (IPv4 or IPv6)
     respond_socket = new_socket(
+        bind_addr=cast(tuple[tuple[str, int, int], int], interface)[0] if is_v6 else (cast(str, interface),),
+        port=0 if unicast else _MDNS_PORT,
         ip_version=(IPVersion.V6Only if is_v6 else IPVersion.V4Only),
         apple_p2p=apple_p2p,
-        bind_addr=cast(tuple[tuple[str, int, int], int], interface)[0] if is_v6 else (cast(str, interface),),
     )
+    if unicast:
+        return respond_socket
+
     if not respond_socket:
         return None
+
     log.debug("Configuring socket %s with multicast interface %s", respond_socket, interface)
     if is_v6:
         iface_bin = struct.pack("@I", cast(int, interface[1]))
@@ -411,6 +435,7 @@ def new_respond_socket(
             socket.IP_MULTICAST_IF,
             socket.inet_aton(cast(str, interface)),
         )
+    set_respond_socket_multicast_options(respond_socket, IPVersion.V6Only if is_v6 else IPVersion.V4Only)
     return respond_socket
 
 
@@ -423,33 +448,27 @@ def create_sockets(
     if unicast:
         listen_socket = None
     else:
-        listen_socket = new_socket(ip_version=ip_version, apple_p2p=apple_p2p, bind_addr=("",))
+        listen_socket = new_socket(bind_addr=("",), ip_version=ip_version, apple_p2p=apple_p2p)
 
     normalized_interfaces = normalize_interface_choice(interfaces, ip_version)
 
-    # If we are using InterfaceChoice.Default we can use
+    # If we are using InterfaceChoice.Default with only IPv4 or only IPv6, we can use
     # a single socket to listen and respond.
-    if not unicast and interfaces is InterfaceChoice.Default:
-        for i in normalized_interfaces:
-            add_multicast_member(cast(socket.socket, listen_socket), i)
+    if not unicast and interfaces is InterfaceChoice.Default and ip_version != IPVersion.All:
+        for interface in normalized_interfaces:
+            add_multicast_member(cast(socket.socket, listen_socket), interface)
+        # Sent responder socket options to the dual-use listen socket
+        set_respond_socket_multicast_options(cast(socket.socket, listen_socket), ip_version)
         return listen_socket, [cast(socket.socket, listen_socket)]
 
     respond_sockets = []
 
-    for i in normalized_interfaces:
-        if not unicast:
-            if add_multicast_member(cast(socket.socket, listen_socket), i):
-                respond_socket = new_respond_socket(i, apple_p2p=apple_p2p)
-            else:
-                respond_socket = None
-        else:
-            is_v6 = isinstance(i, tuple)
-            respond_socket = new_socket(
-                port=0,
-                ip_version=IPVersion.V6Only if is_v6 else IPVersion.V4Only,
-                apple_p2p=apple_p2p,
-                bind_addr=cast(tuple[tuple[str, int, int], int], i)[0] if is_v6 else (cast(str, i),),
-            )
+    for interface in normalized_interfaces:
+        # Only create response socket if unicast or becoming multicast member was successful
+        if not unicast and not add_multicast_member(cast(socket.socket, listen_socket), interface):
+            continue
+
+        respond_socket = new_respond_socket(interface, apple_p2p=apple_p2p, unicast=unicast)
 
         if respond_socket is not None:
             respond_sockets.append(respond_socket)

diff --git a/tests/test_core.py b/tests/test_core.py
@@ -11,6 +11,7 @@
 import time
 import unittest
 import unittest.mock
+import warnings
 from typing import cast
 from unittest.mock import AsyncMock, Mock, patch
 
@@ -87,16 +88,26 @@ def test_close_multiple_times(self):
     def test_launch_and_close_v4_v6(self):
         rv = r.Zeroconf(interfaces=r.InterfaceChoice.All, ip_version=r.IPVersion.All)
         rv.close()
-        rv = r.Zeroconf(interfaces=r.InterfaceChoice.Default, ip_version=r.IPVersion.All)
-        rv.close()
+        with warnings.catch_warnings(record=True) as warned:
+            rv = r.Zeroconf(interfaces=r.InterfaceChoice.Default, ip_version=r.IPVersion.All)
+            rv.close()
+            first_warning = warned[0]
+            assert "IPv6 multicast requests can't be sent using default interface" in str(
+                first_warning.message
+            )
 
     @unittest.skipIf(not has_working_ipv6(), "Requires IPv6")
     @unittest.skipIf(os.environ.get("SKIP_IPV6"), "IPv6 tests disabled")
     def test_launch_and_close_v6_only(self):
         rv = r.Zeroconf(interfaces=r.InterfaceChoice.All, ip_version=r.IPVersion.V6Only)
         rv.close()
-        rv = r.Zeroconf(interfaces=r.InterfaceChoice.Default, ip_version=r.IPVersion.V6Only)
-        rv.close()
+        with warnings.catch_warnings(record=True) as warned:
+            rv = r.Zeroconf(interfaces=r.InterfaceChoice.Default, ip_version=r.IPVersion.V6Only)
+            rv.close()
+            first_warning = warned[0]
+            assert "IPv6 multicast requests can't be sent using default interface" in str(
+                first_warning.message
+            )
 
     @unittest.skipIf(sys.platform == "darwin", reason="apple_p2p failure path not testable on mac")
     def test_launch_and_close_apple_p2p_not_mac(self):

diff --git a/tests/utils/test_net.py b/tests/utils/test_net.py
@@ -7,7 +7,7 @@
 import sys
 import unittest
 import warnings
-from unittest.mock import MagicMock, Mock, patch
+from unittest.mock import MagicMock, Mock, call, patch
 
 import ifaddr
 import pytest
@@ -20,11 +20,11 @@
 def _generate_mock_adapters():
     mock_lo0 = Mock(spec=ifaddr.Adapter)
     mock_lo0.nice_name = "lo0"
-    mock_lo0.ips = [ifaddr.IP("127.0.0.1", 8, "lo0")]
+    mock_lo0.ips = [ifaddr.IP("127.0.0.1", 8, "lo0"), ifaddr.IP(("::1", 0, 0), 128, "lo")]
     mock_lo0.index = 0
     mock_eth0 = Mock(spec=ifaddr.Adapter)
     mock_eth0.nice_name = "eth0"
-    mock_eth0.ips = [ifaddr.IP(("2001:db8::", 1, 1), 8, "eth0")]
+    mock_eth0.ips = [ifaddr.IP(("2001:db8::", 1, 1), 8, "eth0"), ifaddr.IP(("fd00:db8::", 1, 1), 8, "eth0")]
     mock_eth0.index = 1
     mock_eth1 = Mock(spec=ifaddr.Adapter)
     mock_eth1.nice_name = "eth1"
@@ -65,7 +65,7 @@ def test_get_all_addresses_v6() -> None:
     ):
         addresses = get_all_addresses_v6()
         assert isinstance(addresses, list)
-        assert len(addresses) == 1
+        assert len(addresses) == 3
         assert len(warned) == 1
         first_warning = warned[0]
         assert "get_all_addresses_v6 is deprecated" in str(first_warning.message)
@@ -200,28 +200,20 @@ def test_set_so_reuseport_if_available_not_present():
         netutils.set_so_reuseport_if_available(sock)
 
 
-def test_set_mdns_port_socket_options_for_ip_version():
+def test_set_respond_socket_multicast_options():
     """Test OSError with errno with EINVAL and bind address ''.
 
     from setsockopt IP_MULTICAST_TTL does not raise."""
-    with socket.socket(socket.AF_INET, socket.SOCK_DGRAM) as sock:
-        # Should raise on EPERM always
-        with (
-            pytest.raises(OSError),
-            patch("socket.socket.setsockopt", side_effect=OSError(errno.EPERM, None)),
-        ):
-            netutils.set_mdns_port_socket_options_for_ip_version(sock, ("",), r.IPVersion.V4Only)
-
-        # Should raise on EINVAL always when bind address is not ''
-        with (
-            pytest.raises(OSError),
-            patch("socket.socket.setsockopt", side_effect=OSError(errno.EINVAL, None)),
-        ):
-            netutils.set_mdns_port_socket_options_for_ip_version(sock, ("127.0.0.1",), r.IPVersion.V4Only)
+    # Should raise on EINVAL always
+    with (
+        socket.socket(socket.AF_INET, socket.SOCK_DGRAM) as sock,
+        pytest.raises(OSError),
+        patch("socket.socket.setsockopt", side_effect=OSError(errno.EINVAL, None)),
+    ):
+        netutils.set_respond_socket_multicast_options(sock, r.IPVersion.V4Only)
 
-        # Should not raise on EINVAL when bind address is ''
-        with patch("socket.socket.setsockopt", side_effect=OSError(errno.EINVAL, None)):
-            netutils.set_mdns_port_socket_options_for_ip_version(sock, ("",), r.IPVersion.V4Only)
+    with pytest.raises(RuntimeError):
+        netutils.set_respond_socket_multicast_options(sock, r.IPVersion.All)
 
 
 def test_add_multicast_member(caplog: pytest.LogCaptureFixture) -> None:
@@ -352,8 +344,8 @@ def test_new_respond_socket_new_socket_returns_none():
         assert netutils.new_respond_socket(("0.0.0.0", 0)) is None  # type: ignore[arg-type]
 
 
-def test_create_sockets():
-    """Test create_sockets with unicast and IPv4."""
+def test_create_sockets_interfaces_all_unicast():
+    """Test create_sockets with unicast."""
 
     with (
         patch("zeroconf._utils.net.new_socket") as mock_new_socket,
@@ -382,3 +374,62 @@ def test_create_sockets():
             apple_p2p=False,
             bind_addr=("192.168.1.5",),
         )
+
+
+def test_create_sockets_interfaces_all() -> None:
+    """Test create_sockets with all interfaces.
+
+    Tests if a responder socket is created for every successful multicast
+    join.
+    """
+    adapters = _generate_mock_adapters()
+
+    # Additional IPv6 addresses usually fail to add membership
+    failure_interface = ("fd00:db8::", 1, 1)
+
+    expected_calls = []
+    for adapter in adapters:
+        for ip in adapter.ips:
+            if ip.ip == failure_interface:
+                continue
+
+            if ip.is_IPv4:
+                bind_addr = (ip.ip,)
+                ip_version = r.IPVersion.V4Only
+            else:
+                bind_addr = ip.ip
+                ip_version = r.IPVersion.V6Only
+
+            expected_calls.append(
+                call(
+                    port=5353,
+                    ip_version=ip_version,
+                    apple_p2p=False,
+                    bind_addr=bind_addr,
+                )
+            )
+
+    def _patched_add_multicast_member(sock, interface):
+        return interface[0] != failure_interface
+
+    with (
+        patch("zeroconf._utils.net.new_socket") as mock_new_socket,
+        patch(
+            "zeroconf._utils.net.ifaddr.get_adapters",
+            return_value=adapters,
+        ),
+        patch("zeroconf._utils.net.add_multicast_member", side_effect=_patched_add_multicast_member),
+    ):
+        mock_socket = Mock(spec=socket.socket)
+        mock_new_socket.return_value = mock_socket
+
+        r.create_sockets(interfaces=r.InterfaceChoice.All, ip_version=r.IPVersion.All)
+
+        def call_to_tuple(c):
+            return (c.args, tuple(sorted(c.kwargs.items())))
+
+        # Exclude first new_socket call as this is the listen socket
+        actual_calls_set = {call_to_tuple(c) for c in mock_new_socket.call_args_list[1:]}
+        expected_calls_set = {call_to_tuple(c) for c in expected_calls}
+
+        assert actual_calls_set == expected_calls_set