fix(websocket): handle IPv6 4-tuple in listener getsockname()

libp2p/transport/websocket/listener.py

@@ -31,6 +31,26 @@
 logger = logging.getLogger(__name__)
 
 
+def _extract_host_port_from_sockname(
+    sock_name: object,
+) -> tuple[str, int] | None:
+    """
+    Return ``(host, port)`` from a ``socket.getsockname()`` return value, or
+    ``None`` if the value is not recognised.
+
+    ``socket.getsockname()`` yields a 2-tuple ``(host, port)`` for IPv4 and a
+    4-tuple ``(host, port, flowinfo, scopeid)`` for IPv6. Only the first two
+    fields are meaningful for multiaddr reconstruction, so we accept any
+    tuple of length ≥ 2 where the first two elements are a string and an int.
+    """
+    if not isinstance(sock_name, tuple) or len(sock_name) < 2:
+        return None
+    host, port = sock_name[0], sock_name[1]
+    if not isinstance(host, str) or not isinstance(port, int):
+        return None
+    return host, port
+
+
 @dataclass
 class WebsocketListenerConfig:
     """Configuration for WebSocket listener."""
@@ -297,9 +317,19 @@ async def _run_server() -> None:
                 if hasattr(server_info, "socket"):
                     sock = server_info.socket
                     if hasattr(sock, "getsockname"):
-                        sock_addr, sock_port = sock.getsockname()
-                        actual_host = sock_addr
-                        actual_port = sock_port
+                        sock_name = sock.getsockname()
+                        host_port = _extract_host_port_from_sockname(sock_name)
+                        if host_port is not None:
+                            actual_host, actual_port = host_port
+                        else:
+                            # Explicitly restore the requested host/port so the
+                            # fallback mentioned in the warning is self-contained.
+                            actual_host, actual_port = host, port
+                            logger.warning(
+                                "Unexpected getsockname() result %r; "
+                                "falling back to requested host/port",
+                                sock_name,
+                            )
                 elif hasattr(server_info, "port"):
                     # If we can't get socket, at least get the port
                     actual_port = server_info.port

newsfragments/1316.bugfix.rst

@@ -0,0 +1,6 @@
+Fix ``WebsocketListener.listen()`` binding IPv6 addresses. ``socket.getsockname()``
+returns a 4-tuple ``(host, port, flowinfo, scopeid)`` for IPv6 sockets, which
+previously failed to unpack into ``(sock_addr, sock_port)`` and surfaced as
+``OpenConnectionError("Failed to listen on ...")``. The listener now accepts
+any 2-or-more-tuple with ``(host: str, port: int)`` in the first two slots and
+falls back to the requested host/port on unknown shapes.

tests/core/transport/websocket/test_extract_host_port.py

@@ -0,0 +1,43 @@
+"""
+Unit tests for ``_extract_host_port_from_sockname``.
+
+Historically ``WebsocketListener.listen`` unpacked ``sock.getsockname()``
+as a 2-tuple, which worked for IPv4 sockets but failed with
+``ValueError: too many values to unpack`` for IPv6 sockets (whose
+``getsockname()`` returns a 4-tuple ``(host, port, flowinfo, scopeid)``).
+This regression test pins the supported shapes for the extractor so the
+IPv6 path doesn't re-break.
+"""
+
+from __future__ import annotations
+
+from libp2p.transport.websocket.listener import _extract_host_port_from_sockname
+
+
+def test_ipv4_two_tuple() -> None:
+    assert _extract_host_port_from_sockname(("127.0.0.1", 12345)) == (
+        "127.0.0.1",
+        12345,
+    )
+
+
+def test_ipv6_four_tuple() -> None:
+    # (host, port, flowinfo, scopeid)
+    assert _extract_host_port_from_sockname(("::1", 23456, 0, 0)) == ("::1", 23456)
+
+
+def test_ipv6_four_tuple_with_nonzero_scopeid() -> None:
+    assert _extract_host_port_from_sockname(("fe80::1", 34567, 0, 3)) == (
+        "fe80::1",
+        34567,
+    )
+
+
+def test_unexpected_shape_returns_none() -> None:
+    # Not a tuple, single element, wrong element types — all graceful.
+    assert _extract_host_port_from_sockname(None) is None
+    assert _extract_host_port_from_sockname(("127.0.0.1",)) is None
+    assert _extract_host_port_from_sockname((12345, "127.0.0.1")) is None
+    # A raw string (e.g. what an AF_UNIX socket's getsockname returns) is
+    # not a tuple and must be rejected.
+    assert _extract_host_port_from_sockname("socket-path") is None