connectd: set IPV6_V6ONLY=1 on IPv6 sockets for consistent dual-stack behaviour

.github/workflows/macos.yaml

@@ -52,23 +52,15 @@ jobs:
           uv run ./configure --disable-valgrind --disable-compat
           uv run gmake
           uv run gmake check-gen-updated
+          sudo gmake install
 
-      - name: Start bitcoind in regtest mode
+      - name: Run pytest
+        env:
+          SLOW_MACHINE: 1
+          PYTEST_OPTS: "-vvv --timeout=1800 --durations=10"
+          PYTEST_TESTS: |
+            tests/test_misc.py::test_ipv4_and_ipv6
+            tests/test_connection.py::test_websocket
+            tests/test_connection.py::test_wss_proxy
         run: |
-          bitcoind -regtest -daemon
-          sleep 5
-
-      - name: Generate initial block
-        run: |
-          bitcoin-cli -regtest createwallet default_wallet
-          bitcoin-cli -regtest generatetoaddress 1 $(bitcoin-cli -regtest getnewaddress)
-          sleep 2
-
-      - name: Start CLN in regtest mode
-        run: |
-          lightningd/lightningd --network=regtest --log-file=/tmp/l1.log --daemon
-          sleep 5
-
-      - name: Verify CLN is running
-        run: |
-          cli/lightning-cli --regtest getinfo
+          VALGRIND=0 uv run pytest $PYTEST_TESTS -n $(sysctl -n hw.ncpu) ${PYTEST_OPTS}

connectd/connectd.c

@@ -1301,6 +1301,21 @@ static struct listen_fd *make_listen_fd(const tal_t *ctx,
 		status_unusual("Failed setting socket reuse: %s",
 			       strerror(errno));
 
+#ifdef IPV6_V6ONLY
+	/* Most Linux distros (Debian, Ubuntu) ship net.ipv6.bindv6only=1 in
+	 * sysctl, making IPv6 sockets IPv6-only by default, so a separate IPv4
+	 * wildcard socket can also bind.  macOS, Fedora, Arch and vanilla
+	 * kernels default to 0 (dual-stack): binding '::' also covers
+	 * '0.0.0.0', and the subsequent IPv4 bind fails with EADDRINUSE.
+	 * Explicitly set IPV6_V6ONLY=1 so both sockets always bind
+	 * independently, regardless of the system sysctl. */
+	if (domain == AF_INET6) {
+		if (setsockopt(fd, IPPROTO_IPV6, IPV6_V6ONLY, &on, sizeof(on)))
+			status_unusual("Failed setting IPV6_V6ONLY: %s",
+				       strerror(errno));
+	}
+#endif
+
 	if (bind(fd, addr, len) != 0) {
 		const char *es = strerror(errno);
 		*errstr = tal_fmt(ctx, "Failed to bind socket for %s%s: %s",
@@ -1535,6 +1550,9 @@ setup_listeners(const tal_t *ctx,
 			} else if (!ipv6_ok) {
 				/* Both failed, return now, errstr set. */
 				return NULL;
+			} else {
+				/* IPv4 failed, but IPv6 (dual-stack) succeeded: discard errstr. */
+				*errstr = tal_free(*errstr);
 			}
 			continue;
 		}

tests/test_misc.py

@@ -1842,10 +1842,10 @@ def test_ipv4_and_ipv6(node_factory):
         assert bind[1]['address'] == '0.0.0.0'
         assert int(bind[1]['port']) == port
     else:
-        # Assume we're IPv4 only...
+        # Either IPv4-only, or IPv6 dual-stack (covers IPv4 too, so no separate IPv4 socket)
         assert len(bind) == 1
-        assert bind[0]['type'] == 'ipv4'
-        assert bind[0]['address'] == '0.0.0.0'
+        assert bind[0]['type'] in ('ipv4', 'ipv6')
+        assert bind[0]['address'] in ('0.0.0.0', '::')
         assert int(bind[0]['port']) == port