Add `MsgpackTIPCStream`, the `AF_TIPC` `MsgTransport`

Wire `.connect_to()` (dial by service name), `.connected()`
and `.get_stream_addrs()` on top of `MsgpackTransport` so
`trio.SocketStream` + the existing `<I`-prefix framing carry
`msgpack` msgs over TIPC unchanged.

XXX both ends of a connected TIPC sock answer `TIPC_ADDR_ID`
port-ids and a port-id carries NO service name, so,
- the *dialling* side re-asserts the name it actually dialled
  over `._raddr` (same move as `MsgpackUDSStream`s peer-pid
  re-assign),
- the *accepting* side keeps a `TIPC_NAME_UNKNOWN` sentinel
  plus the observed `(node, ref)`. It doesn't need more — the
  `Aid` from `._do_handshake()` already carries the peer's
  logical identity.

Also normalize dial failures: TIPC answers an unpublished-name
lookup with `EHOSTUNREACH`, which python maps to a **bare**
`OSError` and NOT a `ConnectionError` subtype the way
`ECONNREFUSED` maps to `ConnectionRefusedError`. The
discovery-ping path needs the `ConnectionError` shape, so the
`_reraise_as_connerr()` wrap is load-bearing, not polish.

XXX ALSO tolerate a dead peer in `.get_stream_addrs()`!
Unlike tcp/uds — where the kernel keeps answering the peer
addr until *we* close — TIPC answers `ENOTCONN` once the peer
is gone. Since `MsgpackTransport.__init__()` calls
`.get_stream_addrs()` (via `Channel.from_stream()`) BEFORE the
handshake, an unguarded `OSError` there escapes
`handle_stream_from_peer()`s handshake tolerance (contract §4)
and tears down the WHOLE actor. Any connect-then-drop peer — a
port scan, a liveness probe, a cancelled dial — was a remote
actor-kill. A dead peer must cost us an addr, not the runtime.

Deats,
- `TIPC_IMPORTANCE` exposed as a `.connect_to()` kwarg — TIPC
  can rank a conn's traffic under congestion, which no other
  backend can do. Defaulted to the kernel default for now;
  wiring the parent<->child chan to `HIGH` is a follow-up.
- `TIPC_DEST_DROPPABLE = 0` so undeliverable msgs surface as
  errors instead of being silently dropped.

(this patch was generated in some part by `claude-code` using `claude-opus-5` (`anthropic`))

tests/ipc/test_tipc.py

@@ -0,0 +1,629 @@
+'''
+Unit tests for the `AF_TIPC` transport backend, `tractor.ipc._tipc`.
+
+The kernel-touching cases are gated on `is_tipc_available()` since
+the `tipc` module is NOT loaded by default (`sudo modprobe tipc`);
+the pure address-algebra cases run everywhere.
+
+'''
+from __future__ import annotations
+import errno
+from socket import (
+    SOCK_STREAM,
+    SOL_SOCKET,
+    SO_ACCEPTCONN,
+    SOL_TIPC,
+)
+
+import pytest
+import trio
+
+from tractor.msg.types import Aid
+from tractor.discovery import _addr
+from tractor.discovery._addr import wrap_address
+from tractor.discovery._multiaddr import (
+    mk_maddr,
+    parse_maddr,
+)
+from tractor.ipc import _tipc
+from tractor.ipc._tipc import (
+    AF_TIPC,
+    TIPC_ADDR_ID,
+    TIPC_ADDR_NAME,
+    TIPC_CLUSTER_SCOPE,
+    TIPC_DEST_DROPPABLE,
+    TIPC_HIGH_IMPORTANCE,
+    TIPC_IMPORTANCE,
+    TIPC_NAME_UNKNOWN,
+    TIPC_NODE_SCOPE,
+    TIPC_ZONE_SCOPE,
+    TRACTOR_STYPE,
+    MsgpackTIPCStream,
+    TIPCAddress,
+    instance_from_seed,
+    is_tipc_available,
+    start_listener,
+)
+
+
+pytestmark = pytest.mark.tipc
+
+requires_tipc = pytest.mark.skipif(
+    not is_tipc_available(),
+    reason=(
+        '`tipc` kernel module not loaded (`sudo modprobe tipc`)'
+    ),
+)
+
+
+# ------------------------------------------------------------------
+# address algebra (no kernel needed)
+# ------------------------------------------------------------------
+
+@pytest.mark.parametrize(
+    'addr',
+    [
+        TIPCAddress.get_root(),
+        TIPCAddress(
+            _stype=TRACTOR_STYPE,
+            _instance=42,
+            _scope=TIPC_NODE_SCOPE,
+        ),
+    ],
+    ids=['root', 'node-scoped'],
+)
+def test_addr_unwrap_roundtrip(addr: TIPCAddress):
+    '''
+    `.unwrap()` is proto-keyed and `.from_addr()` inverts it — for
+    both the `tuple` form and the `list` form msgpack decodes to.
+
+    '''
+    unwrapped: tuple = addr.unwrap()
+    assert unwrapped[0] == 'tipc' == TIPCAddress.proto_key
+    assert len(unwrapped) == 4
+
+    assert TIPCAddress.from_addr(unwrapped) == addr
+    assert TIPCAddress.from_addr(list(unwrapped)) == addr
+
+
+def test_addr_scope_defaults_when_omitted():
+    '''
+    A 3-elem `('tipc', stype, inst)` form defaults to the
+    cluster-scope bindspace.
+
+    '''
+    addr: TIPCAddress = TIPCAddress.from_addr(
+        ('tipc', TRACTOR_STYPE, 99),
+    )
+    assert addr._scope == TIPC_CLUSTER_SCOPE
+    assert addr.bindspace == TIPCAddress.def_bindspace
+
+
+def test_zone_scope_normalized_to_cluster():
+    '''
+    `TIPC_ZONE_SCOPE` is deprecated/aliased in modern kernels;
+    accept it on input, fold it to cluster.
+
+    '''
+    addr: TIPCAddress = TIPCAddress.from_addr(
+        ('tipc', TRACTOR_STYPE, 7, TIPC_ZONE_SCOPE),
+    )
+    assert addr._scope == TIPC_CLUSTER_SCOPE
+    assert addr.is_valid
+
+
+def test_addr_from_bare_port_id_raises():
+    '''
+    A `TIPC_ADDR_ID` 5-tuple carries no service-name so it can
+    NEVER be wrapped; it must fail loudly rather than silently
+    fabricate an un-dialable addr.
+
+    This is the invariant that lets
+    `TIPCAddress.rebind_from_sockname` be `False`.
+
+    '''
+    with pytest.raises(ValueError) as excinfo:
+        TIPCAddress.from_addr((TIPC_ADDR_ID, 0, 12345, 0, 0))
+
+    assert 'port-id' in str(excinfo.value)
+
+
+def test_addr_is_valid_predicate():
+    assert TIPCAddress.get_root().is_valid
+
+    # instance 0 is not a bindable name
+    assert not TIPCAddress(
+        _stype=TRACTOR_STYPE,
+        _instance=0,
+    ).is_valid
+
+    # service-types 0..63 are TIPC-internal (`TIPC_CFG_SRV`,
+    # `TIPC_TOP_SRV`, ..)
+    assert not TIPCAddress(
+        _stype=1,
+        _instance=1616,
+    ).is_valid
+
+
+def test_port_id_is_annotation_only():
+    '''
+    `.maybe_node`/`.maybe_ref` are *observed* metadata, excluded
+    from `.unwrap()` exactly like `UDSAddress.maybe_pid`.
+
+    '''
+    addr: TIPCAddress = TIPCAddress.get_root()
+    annotated: TIPCAddress = addr.with_port_id(
+        node=0xdead,
+        ref=1234,
+    )
+    assert annotated.unwrap() == addr.unwrap()
+    assert annotated.maybe_ref == 1234
+    assert '1234' in repr(annotated)
+
+
+def test_instance_from_seed_is_pure():
+    '''
+    Same seed -> same instance (what the follow-up registrar-less
+    discovery fast-path will lean on), and always clear of the
+    reserved low range.
+
+    '''
+    for seed in ('doggy@123', 'kitty@456', ''):
+        inst: int = instance_from_seed(seed)
+        assert inst == instance_from_seed(seed)
+        assert 64 <= inst < 2**32
+
+
+def test_get_random_collision_resistance():
+    '''
+    A `.get_random()` clash does NOT raise `EADDRINUSE` — TIPC
+    accepts multiple publishers of one name and round-robins
+    connects between them, so a collision is *silent crosstalk*.
+
+    Assert the 4-byte digest spreads well enough for that to stay
+    improbable.
+
+    NOTE the bound is birthday-statistical, not absolute:
+    P(collision) ~= 1 - exp(-n**2 / 2**33) ~= 1.2e-2 for n=10k, so
+    a strict `== n` assert would be ~1-in-86 flaky. P(>2
+    collisions) is ~1e-7, hence the slack. See plan 01 §9 for the
+    escalation path if this ever trips.
+
+    '''
+    n: int = 10_000
+    addrs: list[TIPCAddress] = [
+        TIPCAddress.get_random()
+        for _ in range(n)
+    ]
+    instances: set[int] = {
+        addr._instance
+        for addr in addrs
+    }
+    assert len(instances) >= n - 2
+
+    # every one is a legal, bindable name
+    assert all(addr.is_valid for addr in addrs)
+
+
+def test_get_random_honors_bindspace():
+    addr: TIPCAddress = TIPCAddress.get_random(
+        bindspace=TIPC_NODE_SCOPE,
+    )
+    assert addr.bindspace == TIPC_NODE_SCOPE == addr._scope
+
+
+def test_wrap_address_dispatches_on_the_proto_key():
+    '''
+    The proto-keyed unwrapped form must round-trip through the
+    *global* `wrap_address()` — and NOT get stolen by `tcp`s
+    `(str(), int())` case nor `uds`s `(_, str())` one.
+
+    '''
+    addr: TIPCAddress = TIPCAddress.get_random()
+    assert wrap_address(addr.unwrap()) == addr
+    # ..and via the `list` form `msgpack` decodes to
+    assert wrap_address(list(addr.unwrap())) == addr
+
+    assert _addr._address_types['tipc'] is TIPCAddress
+    assert _addr.get_address_cls('tipc') is TIPCAddress
+
+    # the host-singleton registrar default is import-time cheap
+    # (no kernel module, no I/O) and mirrors the `1616` idiom
+    assert _addr._default_lo_addrs['tipc'] == (
+        'tipc', TRACTOR_STYPE, 1616, TIPC_CLUSTER_SCOPE,
+    )
+
+
+def test_maddr_roundtrip():
+    '''
+    Interim `str`-only `/tipc/` maddr grammar (there's no
+    registered `/tipc` multiaddr proto yet, gh #483), which
+    `parse_maddr()` special-cases before `Multiaddr()` ever sees
+    the string.
+
+    '''
+    addr: TIPCAddress = TIPCAddress.get_random()
+    maddr: str = mk_maddr(addr)
+
+    assert isinstance(maddr, str)
+    assert maddr == (
+        f'/tipc/{addr._stype}/{addr._instance}/{addr._scope}'
+    )
+    assert parse_maddr(maddr) == addr
+    # ..and through the generic entrypoint
+    assert wrap_address(maddr) == addr
+
+
+def test_eafnosupport_is_actionable_connerr(
+    monkeypatch: pytest.MonkeyPatch,
+):
+    '''
+    With no `tipc` module the kernel answers `EAFNOSUPPORT`; that
+    MUST surface as a `ConnectionError` naming the fix rather than
+    a bare `OSError`.
+
+    '''
+    class _NoTIPCKernel:
+        @staticmethod
+        def socket(*args, **kwargs):
+            raise OSError(
+                errno.EAFNOSUPPORT,
+                'Address family not supported by protocol',
+            )
+
+    monkeypatch.setattr(_tipc, 'trio_socket', _NoTIPCKernel)
+
+    async def main():
+        await start_listener(addr=TIPCAddress.get_root())
+
+    with pytest.raises(ConnectionError) as excinfo:
+        trio.run(main)
+
+    report: str = str(excinfo.value)
+    assert 'modprobe tipc' in report
+    assert type(excinfo.value.__cause__) is OSError
+
+
+# ------------------------------------------------------------------
+# kernel-touching
+# ------------------------------------------------------------------
+
+@requires_tipc
+def test_listener_tolerates_so_acceptconn():
+    '''
+    `trio.SocketListener.__init__` asserts
+    `getsockopt(SOL_SOCKET, SO_ACCEPTCONN)` is truthy, suppressing
+    `OSError` for exotic families.
+
+    Pin which of the two branches `AF_TIPC` actually takes (plan 01
+    §3.1 left it as an assumption) so a kernel-side regression is
+    caught here rather than as a mystery bind failure.
+
+    '''
+    async def main():
+        addr: TIPCAddress = TIPCAddress.get_random()
+        lstnr = await start_listener(addr=addr)
+        try:
+            assert lstnr.socket.getsockopt(
+                SOL_SOCKET,
+                SO_ACCEPTCONN,
+            )
+        finally:
+            lstnr.socket.close()
+
+    trio.run(main)
+
+
+@requires_tipc
+def test_bind_publishes_a_dialable_service_name():
+    '''
+    "Publishing a bind IS registration": `.bind()` a singleton
+    name-seq and a second task resolves it by *name* — with NO
+    `tractor` registrar in the loop.
+
+    This is the core #378 property.
+
+    '''
+    async def main():
+        addr: TIPCAddress = TIPCAddress.get_random()
+        lstnr = await start_listener(addr=addr)
+
+        accepted: list = []
+
+        async def _accept():
+            stream = await lstnr.accept()
+            accepted.append(stream)
+            await stream.send_all(b'woof')
+            await stream.aclose()
+
+        async with trio.open_nursery() as tn:
+            tn.start_soon(_accept)
+            await trio.sleep(0.05)
+
+            sock = _tipc.trio_socket.socket(
+                AF_TIPC,
+                SOCK_STREAM,
+            )
+            # NOTE, connect by *name* -> the kernel does the
+            # lookup, i.e. this call IS the discovery query.
+            await sock.connect((
+                TIPC_ADDR_NAME,
+                addr._stype,
+                addr._instance,
+                0,  # domain: 0 == "anywhere in scope"
+                addr._scope,
+            ))
+            stream = trio.SocketStream(sock)
+            assert await stream.receive_some(16) == b'woof'
+            await stream.aclose()
+
+        assert len(accepted) == 1
+        lstnr.socket.close()
+
+    trio.run(main)
+
+
+@requires_tipc
+def test_getsockname_is_a_port_id_not_the_bound_name():
+    '''
+    The reason `TIPCAddress.rebind_from_sockname` is `False`.
+
+    A NAMESEQ-bound listener's `getsockname()` answers a
+    `TIPC_ADDR_ID` port-id, which never equals `.unwrap()` and
+    cannot be wrapped back into a service name.
+
+    '''
+    async def main():
+        addr: TIPCAddress = TIPCAddress.get_random()
+        lstnr = await start_listener(addr=addr)
+        try:
+            sockname: tuple = lstnr.socket.getsockname()
+            assert sockname[0] == TIPC_ADDR_ID
+            assert sockname != addr.unwrap()
+            with pytest.raises(ValueError):
+                TIPCAddress.from_addr(sockname)
+        finally:
+            lstnr.socket.close()
+
+    trio.run(main)
+
+
+@requires_tipc
+def test_msgpack_roundtrip_over_service_name():
+    '''
+    Two `trio` tasks in ONE proc exchange `msgpack`-framed msgs
+    over a TIPC service name — no `tractor` runtime involved.
+
+    Also pins the `(laddr, raddr)` story of plan 01 §3.4a: the
+    dialling side knows the name it dialled, the accepting side
+    only ever learns a port-id.
+
+    '''
+    async def main():
+        addr: TIPCAddress = TIPCAddress.get_random()
+        lstnr = await start_listener(addr=addr)
+
+        ping = Aid(name='doggy', uuid='abc123', pid=1)
+        pong = Aid(name='kitty', uuid='def456', pid=2)
+        srv_got: list = []
+
+        async def _serve():
+            stream = await lstnr.accept()
+            tpt = MsgpackTIPCStream(stream)
+
+            # accepting side can NOT know the peer's service name
+            assert not tpt.raddr.is_valid
+            assert tpt.raddr._instance == TIPC_NAME_UNKNOWN
+            assert tpt.raddr.maybe_ref is not None
+
+            srv_got.append(await tpt.recv())
+            await tpt.send(pong)
+            await stream.aclose()
+
+        async with trio.open_nursery() as tn:
+            tn.start_soon(_serve)
+            await trio.sleep(0.05)
+
+            cli: MsgpackTIPCStream = await MsgpackTIPCStream.connect_to(
+                destaddr=addr,
+            )
+            assert cli.connected()
+
+            # dialling side DOES know the name, and it round-trips
+            assert cli.raddr.is_valid
+            assert cli.raddr.unwrap() == addr.unwrap()
+            assert cli.raddr.maybe_ref is not None
+
+            await cli.send(ping)
+            assert await cli.recv() == pong
+            await cli.stream.aclose()
+
+        assert srv_got == [ping]
+        lstnr.socket.close()
+
+    trio.run(main)
+
+
+@requires_tipc
+def test_dial_unpublished_name_is_connerr():
+    '''
+    Contract §4: a dead/absent peer must normalize to
+    `ConnectionError` — the discovery-ping path depends on it.
+
+    XXX TIPC answers an unpublished-name lookup with
+    `EHOSTUNREACH`, which python maps to a **bare** `OSError` (NOT
+    a `ConnectionError` subtype the way `ECONNREFUSED` maps to
+    `ConnectionRefusedError`), so the normalization is load-bearing
+    rather than cosmetic.
+
+    '''
+    async def main():
+        # nothing has ever `.bind()`ed this one
+        nowhere = TIPCAddress(
+            _stype=TRACTOR_STYPE,
+            _instance=0xDEADBEEF,
+        )
+        with trio.fail_after(5):
+            await MsgpackTIPCStream.connect_to(destaddr=nowhere)
+
+    with pytest.raises(ConnectionError) as excinfo:
+        trio.run(main)
+
+    src_exc = excinfo.value.__cause__
+    assert src_exc.errno == errno.EHOSTUNREACH
+    assert 'No TIPC publisher' in str(excinfo.value)
+
+
+@requires_tipc
+def test_importance_sockopt_roundtrips():
+    '''
+    The `TIPC_IMPORTANCE` QoS knob (plan 01 §3.3) is settable and
+    readable back — TIPC can rank a conn's traffic under
+    congestion, which no other backend can do.
+
+    '''
+    async def main():
+        addr: TIPCAddress = TIPCAddress.get_random()
+        lstnr = await start_listener(addr=addr)
+
+        # XXX hold the accepted conn open for the duration; a
+        # peer that closes first makes `getpeername()` (called
+        # from `MsgpackTransport.__init__`) raise `ENOTCONN`.
+        done = trio.Event()
+
+        async def _accept():
+            stream = await lstnr.accept()
+            await done.wait()
+            await stream.aclose()
+
+        async with trio.open_nursery() as tn:
+            tn.start_soon(_accept)
+            await trio.sleep(0.05)
+            cli = await MsgpackTIPCStream.connect_to(
+                destaddr=addr,
+                importance=TIPC_HIGH_IMPORTANCE,
+            )
+            sock = cli.stream.socket
+            assert sock.getsockopt(
+                SOL_TIPC,
+                TIPC_IMPORTANCE,
+            ) == TIPC_HIGH_IMPORTANCE
+            assert sock.getsockopt(
+                SOL_TIPC,
+                TIPC_DEST_DROPPABLE,
+            ) == 0
+            await cli.stream.aclose()
+            done.set()
+
+        lstnr.socket.close()
+
+    trio.run(main)
+
+
+@requires_tipc
+def test_dropped_peer_does_not_kill_the_listener():
+    '''
+    A peer that connects then drops BEFORE we read must cost us
+    an addr, not the runtime.
+
+    XXX unlike tcp/uds — where the kernel keeps answering the
+    peer addr until *we* close — TIPC answers `ENOTCONN` on
+    `getpeername()` once the peer is gone. Since
+    `MsgpackTransport.__init__()` calls `.get_stream_addrs()`
+    (via `Channel.from_stream()`) BEFORE the handshake, an
+    unguarded `OSError` there escapes
+    `handle_stream_from_peer()`s handshake tolerance (contract
+    §4) and tears down the whole actor.
+
+    Real-world triggers: a port scan, a liveness probe (our own
+    `tests/discovery/conftest.py::daemon` readiness poll does
+    exactly this!), or a cancelled dial.
+
+    '''
+    async def main():
+        addr: TIPCAddress = TIPCAddress.get_random()
+        lstnr = await start_listener(addr=addr)
+
+        tpts: list = []
+
+        async def _accept():
+            stream = await lstnr.accept()
+            # MUST NOT raise even though the peer is already gone
+            tpts.append(MsgpackTIPCStream(stream))
+
+        async with trio.open_nursery() as tn:
+            tn.start_soon(_accept)
+            await trio.sleep(0.05)
+
+            # connect-then-immediately-drop
+            sock = _tipc.trio_socket.socket(AF_TIPC, SOCK_STREAM)
+            await sock.connect((
+                TIPC_ADDR_NAME,
+                addr._stype,
+                addr._instance,
+                0,
+                addr._scope,
+            ))
+            sock.close()
+            await trio.sleep(0.2)
+
+        # NOTE the assertion that matters is simply that
+        # `MsgpackTIPCStream()` above did NOT raise; whether
+        # `getpeername()` still answers is a kernel-side race on
+        # the disconnect indication, so don't pin `.maybe_ref`.
+        assert len(tpts) == 1
+        raddr: TIPCAddress = tpts[0].raddr
+        assert not raddr.is_valid
+        # ..and it still reprs cleanly for the con-status logs
+        assert 'unknown-service' in repr(raddr)
+
+        lstnr.socket.close()
+
+    trio.run(main)
+
+
+def test_observed_addr_tolerates_a_dead_peer():
+    '''
+    The deterministic half of the above: `_maybe_sockaddr()`
+    swallows the `ENOTCONN` and `_observed_addr()` still yields
+    a usable (name-less, port-id-less) addr.
+
+    '''
+    def _enotconn():
+        raise OSError(
+            errno.ENOTCONN,
+            'Transport endpoint is not connected',
+        )
+
+    assert _tipc._maybe_sockaddr(_enotconn) is None
+
+    addr: TIPCAddress = _tipc._observed_addr(None)
+    assert not addr.is_valid
+    assert addr.maybe_node is None
+    assert addr.maybe_ref is None
+    assert 'unknown-service' in repr(addr)
+
+
+@requires_tipc
+def test_duplicate_name_bind_does_not_raise():
+    '''
+    Unlike every other backend, TIPC permits *two* publishers of
+    one service name and round-robins connects between them.
+
+    Pin that observed behaviour — it's the whole reason
+    `.get_random()` bothers with a well-spread digest, and a
+    future kernel that starts raising `EADDRINUSE` here would be
+    very good news worth noticing.
+
+    '''
+    async def main():
+        addr: TIPCAddress = TIPCAddress.get_random()
+        first = await start_listener(addr=addr)
+        second = await start_listener(addr=addr)
+        try:
+            assert first.socket.getsockname() != second.socket.getsockname()
+        finally:
+            first.socket.close()
+            second.socket.close()
+
+    trio.run(main)

tractor/_testing/pytest.py

@@ -501,6 +501,12 @@ def pytest_configure(
         'trio: legacy mark for tests meant to run under the `trio` '
         'spawn backend (e.g. `test_local.py`).'
     )
+    config.addinivalue_line(
+        'markers',
+        'tipc: test targets the `AF_TIPC` tpt backend; the kernel- '
+        'touching cases self-skip unless the `tipc` module is loaded '
+        '(`sudo modprobe tipc`).'
+    )
 
     # `--enable-stackscope`: install SIGUSR1 → trio task-tree
     # dump in pytest itself + propagate to every subactor via
@@ -797,6 +803,27 @@ def tpt_protos(
         addr_type = _addr._address_types[proto_key]
         assert addr_type.proto_key == proto_key
 
+        # XXX, generic capability gate: an env-dependent tpt
+        # whose backing kernel-mod/lib/netns isn't present here
+        # must fail LOUDLY and EARLY rather than as a few hundred
+        # confusing connect-timeouts downstream.
+        #
+        # Any `Address` type MAY expose `.is_available()`
+        # returning `(ok, why_not)`; absence means "always
+        # available" (i.e. tcp/uds).
+        is_avail = getattr(
+            addr_type,
+            'is_available',
+            None,
+        )
+        if is_avail:
+            avail, why_not = is_avail()
+            if not avail:
+                pytest.fail(
+                    f'--tpt-proto={proto_key!r} is NOT usable here!\n'
+                    f'{why_not}\n'
+                )
+
     yield proto_keys
 
 

tractor/discovery/_addr.py

@@ -33,6 +33,7 @@ from ..runtime._state import (
 )
 from ..ipc._tcp import TCPAddress
 from ..ipc._uds import UDSAddress
+from ..ipc._tipc import TIPCAddress
 
 if TYPE_CHECKING:
     from ..runtime._runtime import Actor
@@ -65,9 +66,22 @@ log = get_logger()
 #
 UnwrappedAddress = (
     # tcp/udp/uds
+    #   ('127.0.0.1', 1616)
+    #   ('/run/user/1000/tractor', 'registry@1616.sock')
+    #
+    # ..and the explicitly proto-keyed (`multiaddr`-spelled)
+    # form, which is where ALL backends should eventually land
+    # per the note below,
+    #   ('tipc', 1953628160, 1616, 2)
+    #
+    # XXX VARIADIC bc `msgspec` refuses a union of >1 array-like
+    # type, so the two shapes can't be spelled as a union. Keep
+    # in sync with `.msg.types.UnwrappedAddress` which
+    # re-declares this to dodge a circular import AND is what
+    # actually validates the `SpawnSpec` wire msg!
     tuple[
-        str,  # host/domain(tcp), filesys-dir(uds)
+        str|int,
-        int|str,  # port/path(uds)
+        ...,
     ]
     # ?TODO? should we also include another 2 fields from
     # our `Aid` msg such that we include the runtime `Actor.uid`
@@ -83,6 +97,17 @@ class Address(Protocol):
     proto_key: ClassVar[str]
     unwrapped_type: ClassVar[UnwrappedAddress]
 
+    # whether `.ipc._server.Endpoint.start_listener()` should
+    # reconcile a bound `.addr` against its listener's
+    # `socket.getsockname()`.
+    #
+    # XXX NOTE, that reconciliation exists ONLY to learn the
+    # kernel-*assigned* port from a `port=0` tcp bind; a backend
+    # whose `getsockname()` reports a categorically different thing
+    # than what was `.bind()`ed must opt out with `False`, else the
+    # ep's addr gets clobbered by an un-dialable one.
+    rebind_from_sockname: ClassVar[bool]
+
     # TODO, i feel like an `.is_bound()` is a better thing to
     # support?
     # Lke, what use does this have besides a noop and if it's not
@@ -172,7 +197,8 @@ class Address(Protocol):
 
 _address_types: bidict[str, Type[Address]] = {
     'tcp': TCPAddress,
-    'uds': UDSAddress
+    'uds': UDSAddress,
+    'tipc': TIPCAddress,
 }
 
 
@@ -184,6 +210,9 @@ _default_lo_addrs: dict[
 ] = {
     'tcp': TCPAddress.get_root().unwrap(),
     'uds': UDSAddress.get_root().unwrap(),
+    # NOTE, pure/cheap: a service-name pair, no kernel module
+    # nor I/O required at import time.
+    'tipc': TIPCAddress.get_root().unwrap(),
 }
 
 
@@ -229,6 +258,16 @@ def wrap_address(
     #     import pdbp; pdbp.set_trace()
     match addr:
 
+        # XXX, the explicitly proto-keyed form (spelled with the
+        # `multiaddr` proto name) which is where ALL backends
+        # should eventually land per the `UnwrappedAddress`
+        # migration note above.
+        #
+        # NOTE, a bare seq-pattern matches `list` too, which is
+        # what `msgpack` decodes our tuples back to.
+        case ('tipc', *_):
+            cls = TIPCAddress
+
         # classic network socket-address as tuple/list
         case (
             (str(), int())

tractor/ipc/_server.py

@@ -661,7 +661,16 @@ class Endpoint(Struct):
 
         # NOTE, for handling the resolved non-0 port for
         # TCP/UDP network sockets.
+        #
+        # XXX, gated on the addr-type's opt-in since for some
+        # backends `getsockname()` does NOT answer "the addr you
+        # bound"; `tipc` reports a `TIPC_ADDR_ID` port-id instead
+        # of the published name-seq, so rebinding from it would
+        # replace a dialable service-name with an un-dialable
+        # (and un-reconstructable) port-id.
         if (
+            self.addr.rebind_from_sockname
+            and
             (unwrapped := lstnr.socket.getsockname())
             !=
             self.addr.unwrap()

tractor/ipc/_tcp.py

@@ -65,6 +65,10 @@ class TCPAddress(
     unwrapped_type: ClassVar[type] = tuple[str, int]
     def_bindspace: ClassVar[str] = '127.0.0.1'
 
+    # XXX, REQUIRED here since a `port=0` bind means the kernel
+    # picks and `getsockname()` is the only way we learn it.
+    rebind_from_sockname: ClassVar[bool] = True
+
     # ?TODO, actually validate ipv4/6 with stdlib's `ipaddress`
     @property
     def is_valid(self) -> bool:

tractor/ipc/_tipc.py

@@ -0,0 +1,777 @@
+# tractor: distributed structured concurrency.
+# Copyright 2018-eternity Tyler Goodlet.
+
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <https://www.gnu.org/licenses/>.
+'''
+`AF_TIPC` (Transparent Inter-Process Communication) implementation of
+the `tractor.ipc._transport.MsgTransport` protocol.
+
+TIPC is a linux-kernel cluster IPC protocol whose *service names* are
+published in a cluster-wide name-table by the kernel itself. That
+makes a `.bind()` literally a service **registration** and
+a `.connect()` literally a service **lookup**, i.e. the discovery
+machinery `tractor.discovery` normally implements with a registrar
+actor comes for free, in-kernel.
+
+An actor's TIPC address is therefore a *service name* pair,
+`(stype, instance)`,
+
+- a listener `.bind()`s the singleton published range
+  `(stype, instance, instance)` as a `TIPC_ADDR_NAMESEQ`,
+- a peer `.connect()`s that name as a `TIPC_ADDR_NAME` and the kernel
+  resolves it,
+- `TIPC_ADDR_ID` (a `(node, ref)` port-id) is only ever an *observed*
+  address, never a user-facing one.
+
+NOTE, the `tipc` kernel module is NOT loaded by default; see
+`is_tipc_available()` and the `sudo modprobe tipc` hint carried in
+this module's `ConnectionError` messages.
+
+Normative refs are the kernel sources (the tipc.io docs are stale),
+- `include/uapi/linux/tipc.h`
+- `net/tipc/socket.c`
+
+'''
+from __future__ import annotations
+from contextlib import (
+    contextmanager as cm,
+)
+import errno
+from hashlib import blake2b
+import os
+import socket
+from socket import SOCK_STREAM
+from typing import (
+    Callable,
+    ClassVar,
+    Type,
+    TYPE_CHECKING,
+)
+from uuid import uuid4
+
+import msgspec
+import trio
+from trio import (
+    socket as trio_socket,
+    SocketListener,
+)
+
+from multiaddr import Multiaddr
+from tractor.msg import MsgCodec
+from tractor.log import get_logger
+from tractor.discovery._multiaddr import mk_maddr
+from tractor.ipc._transport import (
+    MsgpackTransport,
+)
+from tractor.runtime._state import (
+    current_actor,
+    is_root_process,
+)
+
+if TYPE_CHECKING:
+    from tractor.runtime._runtime import Actor
+
+
+log = get_logger()
+
+
+# XXX, `AF_TIPC` and every `TIPC_*` constant are linux-ONLY in
+# CPython's `socketmodule.c`. Mirror the `_uds.py` `SO_PASSCRED`
+# precedent and fall back to the uapi values so this module stays
+# **importable everywhere** — `.discovery._addr` builds its
+# registration tables at import time (contract §2.3) — while
+# `is_tipc_available()` remains the single *runtime* gate.
+#
+# values verified against `include/uapi/linux/tipc.h`
+try:
+    from socket import (
+        AF_TIPC,
+        SOL_TIPC,
+        TIPC_ADDR_ID,
+        TIPC_ADDR_NAME,
+        TIPC_ADDR_NAMESEQ,
+        TIPC_CLUSTER_SCOPE,
+        TIPC_DEST_DROPPABLE,
+        TIPC_HIGH_IMPORTANCE,
+        TIPC_IMPORTANCE,
+        TIPC_LOW_IMPORTANCE,
+        TIPC_NODE_SCOPE,
+        TIPC_ZONE_SCOPE,
+    )
+except ImportError:
+    AF_TIPC: int = 30
+    SOL_TIPC: int = 271
+    TIPC_ADDR_NAMESEQ: int = 1
+    TIPC_ADDR_NAME: int = 2
+    TIPC_ADDR_ID: int = 3
+    TIPC_ZONE_SCOPE: int = 1
+    TIPC_CLUSTER_SCOPE: int = 2
+    TIPC_NODE_SCOPE: int = 3
+    TIPC_LOW_IMPORTANCE: int = 0
+    TIPC_HIGH_IMPORTANCE: int = 2
+    TIPC_IMPORTANCE: int = 127
+    TIPC_DEST_DROPPABLE: int = 129
+
+
+# `tractor`'s reserved TIPC service-class ("type"), spelling out
+# ascii 'tr' in the high half and leaving the low 16b free for
+# app-side partitioning via an explicit `TIPCAddress._stype`.
+#
+# NOTE, two `tractor` trees sharing BOTH a cluster and an `_stype`
+# share a service-name space; see `.get_random()` on why that's
+# only a *probabilistic* hazard.
+TRACTOR_STYPE: int = 0x74_72_00_00
+
+# TIPC reserves service-*types* 0..63 for its own internal services
+# (`TIPC_CFG_SRV == 0`, `TIPC_TOP_SRV == 1`); see
+# `include/uapi/linux/tipc.h`.
+_tipc_reserved_stypes: range = range(0, 64)
+
+# sentinel for "this addr was *observed* off a `TIPC_ADDR_ID`, so
+# the peer's service-name is unknowable from the socket alone".
+# See `MsgpackTIPCStream.get_stream_addrs()` and plan 01 §3.4.
+TIPC_NAME_UNKNOWN: int = -1
+
+# XXX, the kernel default (`TIPC_LOW_IMPORTANCE`), i.e. today this
+# is a no-op knob preserving stock behaviour.
+#
+# ?TODO, TIPC can rank a connection's traffic under congestion —
+# something no other backend can do — so the parent<->child
+# *supervision* chan deserves `TIPC_HIGH_IMPORTANCE` while bulk app
+# streams stay low. Wiring `_runtime.py`'s parent-chan path to pass
+# it is deliberately a follow-up; see plan 01 §3.3 + §10.
+TRACTOR_DEF_IMPORTANCE: int = TIPC_LOW_IMPORTANCE
+
+_scope_names: dict[int, str] = {
+    TIPC_ZONE_SCOPE: 'zone',
+    TIPC_CLUSTER_SCOPE: 'cluster',
+    TIPC_NODE_SCOPE: 'node',
+}
+
+# see `is_tipc_available()`
+_tipc_avail: bool|None = None
+
+
+def is_tipc_available() -> bool:
+    '''
+    `True` iff this kernel can create an `AF_TIPC` socket, i.e. the
+    `tipc` module is loaded (`sudo modprobe tipc`).
+
+    Pure predicate; no side effects, no logging. The answer can't
+    change without a `modprobe` so it's memoized after the first
+    (one syscall) probe.
+
+    '''
+    global _tipc_avail
+    if _tipc_avail is None:
+        try:
+            socket.socket(
+                AF_TIPC,
+                SOCK_STREAM,
+            ).close()
+            _tipc_avail = True
+        except OSError:
+            _tipc_avail = False
+
+    return _tipc_avail
+
+
+class TIPCAddress(
+    msgspec.Struct,
+    frozen=True,
+):
+    '''
+    A TIPC *service name* as an address, i.e. the
+    `(type, instance)` pair a listener publishes and a peer
+    resolves, plus the optionally-*observed* `TIPC_ADDR_ID`
+    port-id of a live connection.
+
+    '''
+    _stype: int
+    _instance: int
+    _scope: int = TIPC_CLUSTER_SCOPE
+
+    # observed-only, from a `TIPC_ADDR_ID` `getsockname()`/
+    # `getpeername()`; excluded from `.unwrap()` exactly like
+    # `UDSAddress.maybe_pid`.
+    maybe_node: int|None = None
+    maybe_ref: int|None = None
+
+    proto_key: ClassVar[str] = 'tipc'
+    unwrapped_type: ClassVar[type] = tuple[str, int, int, int]
+    def_bindspace: ClassVar[int] = TIPC_CLUSTER_SCOPE
+
+    # XXX, TIPC's `getsockname()` answers a `TIPC_ADDR_ID` port-id
+    # and NEVER the name-seq we bound, so the `Endpoint`-level
+    # reconciliation would clobber a dialable service-name with an
+    # un-dialable port-id. There's also nothing to learn: unlike
+    # tcp's `port=0` there is no kernel-assigned-name analogue.
+    rebind_from_sockname: ClassVar[bool] = False
+
+    @property
+    def bindspace(self) -> int:
+        '''
+        The TIPC *scope*, i.e. literally "the set of hosts from
+        which this published name is reachable": `TIPC_NODE_SCOPE`
+        for same-host-only (the UDS analogue),
+        `TIPC_CLUSTER_SCOPE` for cluster-visible.
+
+        '''
+        return self._scope
+
+    @property
+    def is_valid(self) -> bool:
+        '''
+        Is this a *publishable/dialable* service name?
+
+        NOTE the `> 0` (rather than `!= 0`) guards double-duty as
+        the `TIPC_NAME_UNKNOWN` reject, i.e. an addr merely
+        *observed* off a peer's port-id is never dialable.
+
+        '''
+        return (
+            self._instance > 0
+            and
+            self._stype > 0
+            and
+            self._stype not in _tipc_reserved_stypes
+            and
+            self._scope in (
+                TIPC_NODE_SCOPE,
+                TIPC_CLUSTER_SCOPE,
+            )
+        )
+
+    @classmethod
+    def from_addr(
+        cls,
+        addr: tuple[str, int, int, int],
+    ) -> TIPCAddress:
+        match addr:
+            # our proto-keyed unwrapped form, w/ scope optional
+            case (
+                ('tipc', int() as stype, int() as inst, int() as scope)
+                |
+                ['tipc', int() as stype, int() as inst, int() as scope]
+            ):
+                return TIPCAddress(
+                    _stype=stype,
+                    _instance=inst,
+                    _scope=_norm_scope(scope),
+                )
+
+            case (
+                ('tipc', int() as stype, int() as inst)
+                |
+                ['tipc', int() as stype, int() as inst]
+            ):
+                return TIPCAddress(
+                    _stype=stype,
+                    _instance=inst,
+                )
+
+            # a kernel-observed `TIPC_ADDR_ID` 5-tuple.
+            #
+            # XXX, a port-id carries NO service-name info, so we
+            # cannot reconstruct `(stype, instance)` from it. This
+            # is exactly why `.rebind_from_sockname` is `False`;
+            # if you land here something re-enabled that path.
+            case (int() as atype, *_) if atype == TIPC_ADDR_ID:
+                raise ValueError(
+                    f'Can not wrap a bare TIPC_ADDR_ID port-id !\n'
+                    f'addr: {addr!r}\n'
+                    f'\n'
+                    f'A port-id carries no service-name, so the\n'
+                    f'`(stype, instance)` identity is unrecoverable.\n'
+                    f'Use `.with_port_id()` to *annotate* a known\n'
+                    f'{cls.__name__} instead.\n'
+                )
+
+            case _:
+                raise TypeError(
+                    f'Bad unwrapped-address for {cls} !\n'
+                    f'{addr!r}\n'
+                )
+
+    def unwrap(self) -> tuple[str, int, int, int]:
+        # NOTE, proto-keyed (w/ the `multiaddr` proto spelling) so
+        # `wrap_address()` can dispatch unambiguously against the
+        # other backends' 2-tuple forms; see contract §1.1.
+        return (
+            'tipc',
+            self._stype,
+            self._instance,
+            self._scope,
+        )
+
+    def with_port_id(
+        self,
+        node: int,
+        ref: int,
+    ) -> TIPCAddress:
+        '''
+        A copy annotated with an *observed* `TIPC_ADDR_ID`
+        port-id, purely for logging/`__repr__`.
+
+        '''
+        return msgspec.structs.replace(
+            self,
+            maybe_node=node,
+            maybe_ref=ref,
+        )
+
+    @classmethod
+    def get_random(
+        cls,
+        bindspace: int|None = None,
+    ) -> TIPCAddress:
+        '''
+        A per-subactor ephemeral service-name.
+
+        XXX, TIPC has NO kernel-assigned-instance analogue of tcp's
+        `port=0`, so we must choose the instance ourselves — and a
+        clash does **not** raise `EADDRINUSE`: TIPC happily accepts
+        multiple publishers of one name and round-robins connects
+        between them (verified). I.e. a collision manifests as
+        *silent crosstalk*, not an error.
+
+        So the instance is a `blake2b` digest of a per-call-unique
+        seed, giving a well-spread 32b value. Being a pure fn of the
+        seed it is also *reproducible*, which the (follow-up)
+        registrar-less discovery fast-path wants.
+
+        NOTE the residual risk is birthday-bounded: ~1.2e-2 for 10k
+        names sharing one `_stype`. See plan 01 §9 for the
+        escalation (post-bind verification) if that ever bites.
+
+        '''
+        pid: int = os.getpid()
+        actor: Actor|None = current_actor(
+            err_on_no_runtime=False,
+        )
+        if actor:
+            seed: str = f'{actor.aid.name}@{pid}'
+        else:
+            if is_root_process():
+                prefix: str = 'no_runtime_root'
+            else:
+                prefix: str = 'no_runtime_actor'
+
+            # XXX, no live actor -> no `Aid` to key off, so mix
+            # a per-CALL token in; w/o it the seed degenerates to
+            # a pure fn of `(prefix, pid)` and two calls in one
+            # proc alias to the SAME service name — the `_uds.py`
+            # `.get_random()` hazard, but silent here.
+            seed: str = f'{prefix}.{uuid4().hex[:8]}@{pid}'
+
+        return TIPCAddress(
+            _stype=TRACTOR_STYPE,
+            _instance=instance_from_seed(seed),
+            _scope=(
+                bindspace
+                if bindspace is not None
+                else cls.def_bindspace
+            ),
+        )
+
+    @classmethod
+    def is_available(cls) -> tuple[bool, str]:
+        '''
+        Generic tpt-capability hook: `(ok, why_not)`.
+
+        Consumed by the `tpt_protos` test fixture so a
+        `--tpt-proto tipc` run on a box with no `tipc` module
+        fails loudly and early rather than as a few hundred
+        confusing connect timeouts. Apps can use it too.
+
+        NOTE, deliberately spelled generically (NOT `is_tipc_*`)
+        so the sibling env-dependent backends — `quic`/`iroh`
+        (gh #353) and the `wg` netns bindspace (gh #482) — get
+        the same gate for free.
+
+        '''
+        if is_tipc_available():
+            return (True, '')
+
+        return (
+            False,
+            'the `tipc` kernel module is not loaded'
+            ' |_try: `sudo modprobe tipc`',
+        )
+
+    @classmethod
+    def get_root(cls) -> TIPCAddress:
+        # NOTE, `1616` mirrors `TCPAddress.get_root()`s port and
+        # the UDS `registry@1616.sock` filename so the "1616 is
+        # tractor's registrar" idiom holds across all backends.
+        return TIPCAddress(
+            _stype=TRACTOR_STYPE,
+            _instance=1616,
+            _scope=TIPC_CLUSTER_SCOPE,
+        )
+
+    def __repr__(self) -> str:
+        if self._instance == TIPC_NAME_UNKNOWN:
+            name: str = '<unknown-service>'
+        else:
+            name: str = f'0x{self._stype:08x}:{self._instance}'
+
+        body: str = (
+            f'{name}, {_scope_names.get(self._scope, self._scope)}'
+        )
+        if (node := self.maybe_node) is not None:
+            body += f', @0x{node:08x}:{self.maybe_ref}'
+
+        return (
+            f'{type(self).__name__}'
+            f'['
+            f'{body}'
+            f']'
+        )
+
+
+def instance_from_seed(seed: str) -> int:
+    '''
+    Derive a TIPC service *instance* from an actor-identity `seed`.
+
+    A `blake2b` digest folded into `[64, 2**32)`; the low values are
+    skipped to stay clear of TIPC's own reserved numbering
+    conventions.
+
+    '''
+    inst: int = int.from_bytes(
+        blake2b(
+            seed.encode(),
+            digest_size=4,
+        ).digest(),
+        'big',
+    )
+    return 64 + (inst % (2**32 - 64))
+
+
+def _norm_scope(scope: int) -> int:
+    '''
+    Normalize a `TIPC_*_SCOPE` value.
+
+    `TIPC_ZONE_SCOPE` is deprecated and aliased to cluster-scope by
+    modern kernels; accept it on input and fold it.
+
+    '''
+    if scope == TIPC_ZONE_SCOPE:
+        log.transport(
+            f'Normalizing deprecated TIPC_ZONE_SCOPE -> cluster\n'
+            f'scope: {scope!r}\n'
+        )
+        return TIPC_CLUSTER_SCOPE
+
+    return scope
+
+
+@cm
+def _reraise_as_connerr(
+    src_excs: tuple[Type[Exception]],
+    addr: TIPCAddress,
+):
+    '''
+    Normalize TIPC's `OSError`s into `ConnectionError`s.
+
+    XXX REQUIRED, not polish: TIPC answers a lookup for an
+    unpublished name with `EHOSTUNREACH` which python maps to a
+    **bare** `OSError`, NOT a `ConnectionError` subtype (unlike
+    `ECONNREFUSED` -> `ConnectionRefusedError`). Contract §4's
+    discovery-ping path requires the `ConnectionError` shape.
+
+    '''
+    try:
+        yield
+    except src_excs as src_exc:
+        match src_exc.errno:
+            case errno.EAFNOSUPPORT:
+                why: str = (
+                    'TIPC unavailable — is the kernel module loaded?\n'
+                    ' |_try: `sudo modprobe tipc`\n'
+                )
+            case errno.EHOSTUNREACH:
+                why: str = (
+                    'No TIPC publisher for this service name\n'
+                    ' |_nothing has `.bind()`ed it in-scope\n'
+                )
+            case _:
+                why: str = 'Bad TIPC service-name-as-address ??\n'
+
+        raise ConnectionError(
+            f'{why}'
+            f'{addr}\n'
+            f'\n'
+            f'from src: {src_exc!r}\n'
+        ) from src_exc
+
+
+async def start_listener(
+    addr: TIPCAddress,
+    backlog: int = 128,
+    **kwargs,
+) -> SocketListener:
+    '''
+    Publish `addr` as a TIPC service name and listen on it.
+
+    The `.bind()` of a singleton `TIPC_ADDR_NAMESEQ` range
+    `(stype, instance, instance)` **is** the service registration —
+    it's what shows up in `tipc nametable show` and what a peer's
+    `.connect()`-by-name resolves against.
+
+    NOTE, unlike every other backend a duplicate bind does NOT
+    raise: TIPC permits multiple publishers of one name and
+    round-robins connects between them. See
+    `TIPCAddress.get_random()`.
+
+    '''
+    log.info(
+        f'Attempting to publish TIPC service name\n'
+        f'>[\n'
+        f'|_{addr}\n'
+    )
+    with _reraise_as_connerr(
+        src_excs=(OSError,),
+        addr=addr,
+    ):
+        sock = trio_socket.socket(
+            AF_TIPC,
+            SOCK_STREAM,
+        )
+        await sock.bind((
+            TIPC_ADDR_NAMESEQ,
+            addr._stype,
+            addr._instance,  # lower
+            addr._instance,  # upper
+            addr._scope,
+        ))
+
+    # NOTE, backlog matches `_uds.start_listener()`'s hard-won
+    # value; a backlog of 1 overflows during concurrent
+    # deregistration storms at actor-tree teardown.
+    sock.listen(backlog)
+    log.info(
+        f'Published TIPC service name\n'
+        f'[>\n'
+        f' |_{addr}\n'
+    )
+    return SocketListener(sock)
+
+
+# NOTE, deliberately NO `close_listener()`: there's no filesys
+# entry to unlink and the kernel withdraws the published name on
+# socket close. Per contract §1.2 absence means "closing is
+# implicit".
+
+
+@cm
+def _close_on_error(sock):
+    '''
+    Close `sock` if the wrapped block raises.
+
+    Equivalent to `trio._highlevel_open_unix_stream.close_on_error`
+    but inlined so this (linux-cluster) backend doesn't import a
+    *unix-domain* private module.
+
+    '''
+    try:
+        yield sock
+    except BaseException:
+        sock.close()
+        raise
+
+
+class MsgpackTIPCStream(MsgpackTransport):
+    '''
+    A `trio.SocketStream` around an `AF_TIPC` service-name
+    connection delivering `msgpack` encoded msgs via the `msgspec`
+    codec lib.
+
+    '''
+    address_type = TIPCAddress
+    layer_key: int = 4
+
+    @property
+    def maddr(self) -> Multiaddr|str:
+        if not self.raddr:
+            return '<unknown-peer>'
+
+        return mk_maddr(self.raddr)
+
+    def connected(self) -> bool:
+        return self.stream.socket.fileno() != -1
+
+    @classmethod
+    async def connect_to(
+        cls,
+        destaddr: TIPCAddress,
+        prefix_size: int = 4,
+        codec: MsgCodec|None = None,
+        importance: int = TRACTOR_DEF_IMPORTANCE,
+        **kwargs,
+    ) -> MsgpackTIPCStream:
+        '''
+        Dial `destaddr` **by service name**.
+
+        NOTE, the `.connect()` here *is* the discovery lookup — the
+        kernel resolves the published name-table entry for us, so
+        there's no registrar hop on this path.
+
+        '''
+        sock = trio_socket.socket(
+            AF_TIPC,
+            SOCK_STREAM,
+        )
+        with _close_on_error(sock):
+            sock.setsockopt(
+                SOL_TIPC,
+                TIPC_IMPORTANCE,
+                importance,
+            )
+            # NOTE, surface undeliverable msgs as errors rather
+            # than let the kernel silently drop them.
+            sock.setsockopt(
+                SOL_TIPC,
+                TIPC_DEST_DROPPABLE,
+                0,
+            )
+            with _reraise_as_connerr(
+                src_excs=(OSError,),
+                addr=destaddr,
+            ):
+                await sock.connect((
+                    TIPC_ADDR_NAME,
+                    destaddr._stype,
+                    destaddr._instance,
+                    0,  # domain: 0 == "anywhere in scope"
+                    destaddr._scope,
+                ))
+
+        tpt_stream = MsgpackTIPCStream(
+            trio.SocketStream(sock),
+            prefix_size=prefix_size,
+            codec=codec,
+        )
+        # XXX, the dialling side is the ONLY side that knows the
+        # peer's *service name* (a port-id can't be reversed into
+        # one), so re-assert it over the observed-only `._raddr`
+        # that `.get_stream_addrs()` just derived.
+        #
+        # Same move as `MsgpackUDSStream.connect_to()`s peer-pid
+        # re-assign.
+        tpt_stream._raddr = destaddr.with_port_id(
+            *_port_id(sock.getpeername()),
+        )
+        return tpt_stream
+
+    @classmethod
+    def get_stream_addrs(
+        cls,
+        stream: trio.SocketStream,
+    ) -> tuple[
+        TIPCAddress,
+        TIPCAddress,
+    ]:
+        '''
+        Derive `(laddr, raddr)` from a connected TIPC socket.
+
+        XXX, BOTH ends answer `TIPC_ADDR_ID` port-ids and a port-id
+        carries NO service-name, so neither addr is dialable here;
+        they're name-`TIPC_NAME_UNKNOWN` and carry only the
+        observed `(node, ref)`.
+
+        That's fine and deliberate (plan 01 §3.4a):
+
+        - the *dialling* side overrides `._raddr` with the name it
+          actually dialled (see `.connect_to()`),
+        - the *accepting* side genuinely cannot know the peer's
+          name from the socket — but it doesn't need to, since the
+          `Aid` from `Channel._do_handshake()` already carries the
+          peer's logical identity.
+
+        '''
+        sock = stream.socket
+        return (
+            _observed_addr(_maybe_sockaddr(sock.getsockname)),
+            _observed_addr(_maybe_sockaddr(sock.getpeername)),
+        )
+
+
+def _maybe_sockaddr(
+    getter: Callable[[], tuple],
+) -> tuple|None:
+    '''
+    Call a `sock.getsockname`/`.getpeername` tolerantly.
+
+    XXX REQUIRED for TIPC: unlike tcp/uds — where the kernel keeps
+    answering the peer addr until *we* close — a TIPC socket whose
+    peer has already gone answers `ENOTCONN`. That happens for any
+    connect-then-immediately-drop peer: a port scan, a liveness
+    probe, a cancelled dial.
+
+    Since `MsgpackTransport.__init__()` calls `.get_stream_addrs()`
+    (via `Channel.from_stream()`) BEFORE the handshake, letting the
+    `OSError` fly would escape `handle_stream_from_peer()`s
+    handshake tolerance (contract §4) and tear down the whole
+    actor. A dead peer must cost us an addr, not the runtime.
+
+    '''
+    try:
+        return getter()
+    except OSError as oserr:
+        log.transport(
+            f'TIPC peer already gone, no port-id available\n'
+            f'from src: {oserr!r}\n'
+        )
+        return None
+
+
+def _port_id(
+    sockaddr: tuple[int, int, int, int, int],
+) -> tuple[int, int]:
+    '''
+    Unpack the `(node, ref)` of a `TIPC_ADDR_ID` 5-tuple as
+    delivered by `getsockname()`/`getpeername()`.
+
+    Layout is `(addrtype, node, ref, 0, scope)`; see
+    `makesockaddr()`s `AF_TIPC` case in CPython's `socketmodule.c`.
+
+    '''
+    _, node, ref, *_ = sockaddr
+    return (node, ref)
+
+
+def _observed_addr(
+    sockaddr: tuple[int, int, int, int, int]|None,
+) -> TIPCAddress:
+    '''
+    Wrap a `TIPC_ADDR_ID` port-id as a name-less `TIPCAddress`
+    usable for logging/`repr` only.
+
+    A `None` `sockaddr` (peer already gone, see
+    `_maybe_sockaddr()`) yields the same addr sans port-id.
+
+    '''
+    node: int|None = None
+    ref: int|None = None
+    if sockaddr is not None:
+        node, ref = _port_id(sockaddr)
+
+    return TIPCAddress(
+        _stype=TIPC_NAME_UNKNOWN,
+        _instance=TIPC_NAME_UNKNOWN,
+        maybe_node=node,
+        maybe_ref=ref,
+    )

tractor/ipc/_uds.py

@@ -117,6 +117,12 @@ class UDSAddress(
     unwrapped_type: ClassVar[type] = tuple[str, int]
     def_bindspace: ClassVar[Path] = get_rt_dir()
 
+    # NOTE, `getsockname()` answers the sock-file path as a `str`
+    # which never `==` our 2-tuple `.unwrap()`, so the round-trip
+    # always fires; it's a no-op modulo `.maybe_pid` and is kept
+    # `True` to preserve pre-existing behaviour exactly.
+    rebind_from_sockname: ClassVar[bool] = True
+
     @property
     def bindspace(self) -> Path:
         '''