示例#1
0
async def _unittest_redundant_transport_reconfiguration() -> None:
    from pyuavcan.transport import OutputSessionSpecifier, MessageDataSpecifier, PayloadMetadata

    tr = RedundantTransport()
    tr.attach_inferior(LoopbackTransport(1234))
    ses = tr.get_output_session(
        OutputSessionSpecifier(MessageDataSpecifier(5555), None),
        PayloadMetadata(0))
    assert ses
    tr.detach_inferior(tr.inferiors[0])
    tr.attach_inferior(LoopbackTransport(1235))  # Different node-ID
    tr.detach_inferior(tr.inferiors[0])
    tr.attach_inferior(LoopbackTransport(
        None, allow_anonymous_transfers=True))  # Anonymous
    with pytest.raises(
            pyuavcan.transport.OperationNotDefinedForAnonymousNodeError):
        tr.attach_inferior(
            LoopbackTransport(None, allow_anonymous_transfers=False))
    assert len(tr.inferiors) == 1

    tr.close()
    await asyncio.sleep(2.0)
示例#2
0
async def _unittest_redundant_transport(caplog: typing.Any) -> None:
    from pyuavcan.transport import MessageDataSpecifier, PayloadMetadata, Transfer
    from pyuavcan.transport import Priority, Timestamp, InputSessionSpecifier, OutputSessionSpecifier
    from pyuavcan.transport import ProtocolParameters

    loop = asyncio.get_event_loop()
    loop.slow_callback_duration = 1.0

    tr_a = RedundantTransport()
    tr_b = RedundantTransport(loop)
    assert tr_a.sample_statistics() == RedundantTransportStatistics([])
    assert tr_a.inferiors == []
    assert tr_a.local_node_id is None
    assert tr_a.loop is asyncio.get_event_loop()
    assert tr_a.local_node_id is None
    assert tr_a.protocol_parameters == ProtocolParameters(
        transfer_id_modulo=0,
        max_nodes=0,
        mtu=0,
    )
    assert tr_a.descriptor == '<redundant></redundant>'  # Empty, no inferiors.
    assert tr_a.input_sessions == []
    assert tr_a.output_sessions == []

    assert tr_a.loop == tr_b.loop

    #
    # Instantiate session objects.
    #
    meta = PayloadMetadata(10_240)

    pub_a = tr_a.get_output_session(
        OutputSessionSpecifier(MessageDataSpecifier(2345), None), meta)
    sub_any_a = tr_a.get_input_session(
        InputSessionSpecifier(MessageDataSpecifier(2345), None), meta)
    assert pub_a is tr_a.get_output_session(
        OutputSessionSpecifier(MessageDataSpecifier(2345), None), meta)
    assert set(tr_a.input_sessions) == {sub_any_a}
    assert set(tr_a.output_sessions) == {pub_a}
    assert tr_a.sample_statistics() == RedundantTransportStatistics()

    pub_b = tr_b.get_output_session(
        OutputSessionSpecifier(MessageDataSpecifier(2345), None), meta)
    sub_any_b = tr_b.get_input_session(
        InputSessionSpecifier(MessageDataSpecifier(2345), None), meta)
    sub_sel_b = tr_b.get_input_session(
        InputSessionSpecifier(MessageDataSpecifier(2345), 3210), meta)
    assert sub_sel_b is tr_b.get_input_session(
        InputSessionSpecifier(MessageDataSpecifier(2345), 3210), meta)
    assert set(tr_b.input_sessions) == {sub_any_b, sub_sel_b}
    assert set(tr_b.output_sessions) == {pub_b}
    assert tr_b.sample_statistics() == RedundantTransportStatistics()

    #
    # Exchange test with no inferiors, expected to fail.
    #
    assert len(pub_a.inferiors) == 0
    assert len(sub_any_a.inferiors) == 0
    assert not await pub_a.send_until(Transfer(
        timestamp=Timestamp.now(),
        priority=Priority.LOW,
        transfer_id=1,
        fragmented_payload=[memoryview(b'abc')]),
                                      monotonic_deadline=loop.time() + 1.0)
    assert not await sub_any_a.receive_until(loop.time() + 0.1)
    assert not await sub_any_b.receive_until(loop.time() + 0.1)
    assert tr_a.sample_statistics() == RedundantTransportStatistics()
    assert tr_b.sample_statistics() == RedundantTransportStatistics()

    #
    # Adding inferiors - loopback, transport A only.
    #
    with pytest.raises(InconsistentInferiorConfigurationError,
                       match='(?i).*loop.*'):
        tr_a.attach_inferior(
            LoopbackTransport(
                111, loop=asyncio.new_event_loop()))  # Wrong event loop.
    assert len(pub_a.inferiors) == 0
    assert len(sub_any_a.inferiors) == 0

    lo_mono_0 = LoopbackTransport(111)
    lo_mono_1 = LoopbackTransport(111)

    tr_a.attach_inferior(lo_mono_0)
    assert len(pub_a.inferiors) == 1
    assert len(sub_any_a.inferiors) == 1

    with pytest.raises(ValueError):
        tr_a.detach_inferior(lo_mono_1)  # Not a registered inferior (yet).

    tr_a.attach_inferior(lo_mono_1)
    assert len(pub_a.inferiors) == 2
    assert len(sub_any_a.inferiors) == 2

    with pytest.raises(ValueError):
        tr_a.attach_inferior(lo_mono_0)  # Double-add not allowed.

    with pytest.raises(InconsistentInferiorConfigurationError,
                       match='(?i).*node-id.*'):
        tr_a.attach_inferior(LoopbackTransport(None))  # Wrong node-ID.

    with pytest.raises(InconsistentInferiorConfigurationError,
                       match='(?i).*node-id.*'):
        tr_a.attach_inferior(LoopbackTransport(1230))  # Wrong node-ID.

    assert tr_a.inferiors == [lo_mono_0, lo_mono_1]
    assert len(pub_a.inferiors) == 2
    assert len(sub_any_a.inferiors) == 2

    assert tr_a.sample_statistics() == RedundantTransportStatistics(inferiors=[
        lo_mono_0.sample_statistics(),
        lo_mono_1.sample_statistics(),
    ])
    assert tr_a.local_node_id == 111
    assert tr_a.descriptor == '<redundant><loopback/><loopback/></redundant>'

    assert await pub_a.send_until(Transfer(
        timestamp=Timestamp.now(),
        priority=Priority.LOW,
        transfer_id=2,
        fragmented_payload=[memoryview(b'def')]),
                                  monotonic_deadline=loop.time() + 1.0)
    rx = await sub_any_a.receive_until(loop.time() + 1.0)
    assert rx is not None
    assert rx.fragmented_payload == [memoryview(b'def')]
    assert rx.transfer_id == 2
    assert not await sub_any_b.receive_until(loop.time() + 0.1)

    #
    # Incapacitate one inferior, ensure things are still OK.
    #
    with caplog.at_level(logging.CRITICAL,
                         logger=pyuavcan.transport.redundant.__name__):
        for s in lo_mono_0.output_sessions:
            s.exception = RuntimeError('INTENDED EXCEPTION')

        assert await pub_a.send_until(Transfer(
            timestamp=Timestamp.now(),
            priority=Priority.LOW,
            transfer_id=3,
            fragmented_payload=[memoryview(b'qwe')]),
                                      monotonic_deadline=loop.time() + 1.0)
        rx = await sub_any_a.receive_until(loop.time() + 1.0)
        assert rx is not None
        assert rx.fragmented_payload == [memoryview(b'qwe')]
        assert rx.transfer_id == 3

    #
    # Remove old loopback transports. Configure new ones with cyclic TID.
    #
    lo_cyc_0 = LoopbackTransport(111)
    lo_cyc_1 = LoopbackTransport(111)
    cyc_proto_params = ProtocolParameters(
        transfer_id_modulo=32,  # Like CAN
        max_nodes=128,  # Like CAN
        mtu=63,  # Like CAN
    )
    lo_cyc_0.protocol_parameters = cyc_proto_params
    lo_cyc_1.protocol_parameters = cyc_proto_params
    assert lo_cyc_0.protocol_parameters == lo_cyc_1.protocol_parameters == cyc_proto_params

    assert tr_a.protocol_parameters.transfer_id_modulo >= 2**56
    with pytest.raises(InconsistentInferiorConfigurationError,
                       match='(?i).*transfer-id.*'):
        tr_a.attach_inferior(lo_cyc_0)  # Transfer-ID modulo mismatch

    tr_a.detach_inferior(lo_mono_0)
    tr_a.detach_inferior(lo_mono_1)
    del lo_mono_0  # Prevent accidental reuse.
    del lo_mono_1
    assert tr_a.inferiors == []  # All removed, okay.
    assert pub_a.inferiors == []
    assert sub_any_a.inferiors == []
    assert tr_a.local_node_id is None  # Back to the roots
    assert tr_a.descriptor == '<redundant></redundant>'  # Yes yes

    # Now we can add our cyclic transports safely.
    tr_a.attach_inferior(lo_cyc_0)
    assert tr_a.protocol_parameters.transfer_id_modulo == 32
    tr_a.attach_inferior(lo_cyc_1)
    assert tr_a.protocol_parameters == cyc_proto_params, 'Protocol parameter mismatch'
    assert tr_a.local_node_id == 111
    assert tr_a.descriptor == '<redundant><loopback/><loopback/></redundant>'

    # Exchange test.
    assert await pub_a.send_until(Transfer(
        timestamp=Timestamp.now(),
        priority=Priority.LOW,
        transfer_id=4,
        fragmented_payload=[memoryview(b'rty')]),
                                  monotonic_deadline=loop.time() + 1.0)
    rx = await sub_any_a.receive_until(loop.time() + 1.0)
    assert rx is not None
    assert rx.fragmented_payload == [memoryview(b'rty')]
    assert rx.transfer_id == 4

    #
    # Real heterogeneous transport test.
    #
    tr_a.detach_inferior(lo_cyc_0)
    tr_a.detach_inferior(lo_cyc_1)
    del lo_cyc_0  # Prevent accidental reuse.
    del lo_cyc_1

    udp_a = UDPTransport('127.0.0.111/8')
    udp_b = UDPTransport('127.0.0.222/8')

    serial_a = SerialTransport(SERIAL_URI, 111)
    serial_b = SerialTransport(SERIAL_URI, 222, mtu=2048)  # Heterogeneous.

    tr_a.attach_inferior(udp_a)
    tr_a.attach_inferior(serial_a)

    tr_b.attach_inferior(udp_b)
    tr_b.attach_inferior(serial_b)

    print('tr_a.descriptor', tr_a.descriptor)
    print('tr_b.descriptor', tr_b.descriptor)

    assert tr_a.protocol_parameters == ProtocolParameters(
        transfer_id_modulo=2**64,
        max_nodes=4096,
        mtu=1024,
    )
    assert tr_a.local_node_id == 111
    assert tr_a.descriptor == f'<redundant>{udp_a.descriptor}{serial_a.descriptor}</redundant>'

    assert tr_b.protocol_parameters == ProtocolParameters(
        transfer_id_modulo=2**64,
        max_nodes=4096,
        mtu=1024,
    )
    assert tr_b.local_node_id == 222
    assert tr_b.descriptor == f'<redundant>{udp_b.descriptor}{serial_b.descriptor}</redundant>'

    assert await pub_a.send_until(Transfer(
        timestamp=Timestamp.now(),
        priority=Priority.LOW,
        transfer_id=5,
        fragmented_payload=[memoryview(b'uio')]),
                                  monotonic_deadline=loop.time() + 1.0)
    rx = await sub_any_b.receive_until(loop.time() + 1.0)
    assert rx is not None
    assert rx.fragmented_payload == [memoryview(b'uio')]
    assert rx.transfer_id == 5
    assert not await sub_any_a.receive_until(loop.time() + 0.1)
    assert not await sub_any_b.receive_until(loop.time() + 0.1)
    assert not await sub_sel_b.receive_until(loop.time() + 0.1)

    #
    # Construct new session with the transports configured.
    #
    pub_a_new = tr_a.get_output_session(
        OutputSessionSpecifier(MessageDataSpecifier(2345), 222), meta)
    assert pub_a_new is tr_a.get_output_session(
        OutputSessionSpecifier(MessageDataSpecifier(2345), 222), meta)
    assert set(tr_a.output_sessions) == {pub_a, pub_a_new}

    assert await pub_a_new.send_until(Transfer(
        timestamp=Timestamp.now(),
        priority=Priority.LOW,
        transfer_id=6,
        fragmented_payload=[memoryview(b'asd')]),
                                      monotonic_deadline=loop.time() + 1.0)
    rx = await sub_any_b.receive_until(loop.time() + 1.0)
    assert rx is not None
    assert rx.fragmented_payload == [memoryview(b'asd')]
    assert rx.transfer_id == 6

    #
    # Termination.
    #
    tr_a.close()
    tr_a.close()  # Idempotency
    tr_b.close()
    tr_b.close()  # Idempotency

    with pytest.raises(pyuavcan.transport.ResourceClosedError
                       ):  # Make sure the inferiors are closed.
        udp_a.get_output_session(
            OutputSessionSpecifier(MessageDataSpecifier(2345), None), meta)

    with pytest.raises(pyuavcan.transport.ResourceClosedError
                       ):  # Make sure the inferiors are closed.
        serial_b.get_output_session(
            OutputSessionSpecifier(MessageDataSpecifier(2345), None), meta)

    with pytest.raises(pyuavcan.transport.ResourceClosedError
                       ):  # Make sure the sessions are closed.
        await pub_a.send_until(Transfer(timestamp=Timestamp.now(),
                                        priority=Priority.LOW,
                                        transfer_id=100,
                                        fragmented_payload=[]),
                               monotonic_deadline=loop.time() + 1.0)

    await asyncio.sleep(
        1
    )  # Let all pending tasks finalize properly to avoid stack traces in the output.
示例#3
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async def _unittest_redundant_transport_capture() -> None:
    from threading import Lock
    from pyuavcan.transport import Capture, Trace, TransferTrace, Priority, ServiceDataSpecifier
    from pyuavcan.transport import AlienTransfer, AlienTransferMetadata, AlienSessionSpecifier
    from pyuavcan.transport.redundant import RedundantDuplicateTransferTrace, RedundantCapture
    from tests.transport.can.media.mock import MockMedia as CANMockMedia

    asyncio.get_event_loop().slow_callback_duration = 5.0

    tracer = RedundantTransport.make_tracer()
    traces: typing.List[typing.Optional[Trace]] = []
    lock = Lock()

    def handle_capture(cap: Capture) -> None:
        with lock:
            # Drop TX frames, they are not interesting for this test.
            assert isinstance(cap, RedundantCapture)
            if isinstance(cap.inferior, pyuavcan.transport.serial.SerialCapture
                          ) and cap.inferior.own:
                return
            if isinstance(
                    cap.inferior,
                    pyuavcan.transport.can.CANCapture) and cap.inferior.own:
                return
            print("CAPTURE:", cap)
            traces.append(tracer.update(cap))

    async def wait(how_many: int) -> None:
        for _ in range(10):
            await asyncio.sleep(0.1)
            with lock:
                if len(traces) >= how_many:
                    return
        assert False, "No traces received"

    # Setup capture -- one is added before capture started, the other is added later.
    # Make sure they are treated identically.
    tr = RedundantTransport()
    inf_a: pyuavcan.transport.Transport = SerialTransport(SERIAL_URI, 1234)
    inf_b: pyuavcan.transport.Transport = SerialTransport(SERIAL_URI, 1234)
    tr.attach_inferior(inf_a)
    assert not tr.capture_active
    assert not inf_a.capture_active
    assert not inf_b.capture_active
    tr.begin_capture(handle_capture)
    assert tr.capture_active
    assert inf_a.capture_active
    assert not inf_b.capture_active
    tr.attach_inferior(inf_b)
    assert tr.capture_active
    assert inf_a.capture_active
    assert inf_b.capture_active

    # Send a transfer and make sure it is handled and deduplicated correctly.
    transfer = AlienTransfer(
        AlienTransferMetadata(
            priority=Priority.IMMEDIATE,
            transfer_id=1234,
            session_specifier=AlienSessionSpecifier(
                source_node_id=321,
                destination_node_id=222,
                data_specifier=ServiceDataSpecifier(
                    77, ServiceDataSpecifier.Role.REQUEST),
            ),
        ),
        [memoryview(b"hello")],
    )
    assert await tr.spoof(transfer,
                          monotonic_deadline=asyncio.get_event_loop().time() +
                          1.0)
    await wait(2)
    with lock:
        # Check the status of the deduplication process. We should get two: one transfer, one duplicate.
        assert len(traces) == 2
        trace = traces.pop(0)
        assert isinstance(trace, TransferTrace)
        assert trace.transfer == transfer
        # This is the duplicate.
        assert isinstance(traces.pop(0), RedundantDuplicateTransferTrace)
        assert not traces

    # Spoof the same thing again, get nothing out: transfers discarded by the inferior's own reassemblers.
    # WARNING: this will fail if too much time has passed since the previous transfer due to TID timeout.
    assert await tr.spoof(transfer,
                          monotonic_deadline=asyncio.get_event_loop().time() +
                          1.0)
    await wait(2)
    with lock:
        assert None is traces.pop(0)
        assert None is traces.pop(0)
        assert not traces

    # But if we change ONLY destination, deduplication will not take place.
    transfer = AlienTransfer(
        AlienTransferMetadata(
            priority=Priority.IMMEDIATE,
            transfer_id=1234,
            session_specifier=AlienSessionSpecifier(
                source_node_id=321,
                destination_node_id=333,
                data_specifier=ServiceDataSpecifier(
                    77, ServiceDataSpecifier.Role.REQUEST),
            ),
        ),
        [memoryview(b"hello")],
    )
    assert await tr.spoof(transfer,
                          monotonic_deadline=asyncio.get_event_loop().time() +
                          1.0)
    await wait(2)
    with lock:
        # Check the status of the deduplication process. We should get two: one transfer, one duplicate.
        assert len(traces) == 2
        trace = traces.pop(0)
        assert isinstance(trace, TransferTrace)
        assert trace.transfer == transfer
        # This is the duplicate.
        assert isinstance(traces.pop(0), RedundantDuplicateTransferTrace)
        assert not traces

    # Change the inferior configuration and make sure it is handled properly.
    tr.detach_inferior(inf_a)
    tr.detach_inferior(inf_b)
    inf_a.close()
    inf_b.close()
    # The new inferiors use cyclic transfer-ID; the tracer should reconfigure itself automatically!
    can_peers: typing.Set[CANMockMedia] = set()
    inf_a = CANTransport(CANMockMedia(can_peers, 64, 2), 111)
    inf_b = CANTransport(CANMockMedia(can_peers, 64, 2), 111)
    tr.attach_inferior(inf_a)
    tr.attach_inferior(inf_b)
    # Capture should have been launched automatically.
    assert inf_a.capture_active
    assert inf_b.capture_active

    # Send transfer over CAN and observe that it is handled well.
    transfer = AlienTransfer(
        AlienTransferMetadata(
            priority=Priority.IMMEDIATE,
            transfer_id=19,
            session_specifier=AlienSessionSpecifier(
                source_node_id=111,
                destination_node_id=22,
                data_specifier=ServiceDataSpecifier(
                    77, ServiceDataSpecifier.Role.REQUEST),
            ),
        ),
        [memoryview(b"hello")],
    )
    assert await tr.spoof(transfer,
                          monotonic_deadline=asyncio.get_event_loop().time() +
                          1.0)
    await wait(2)
    with lock:
        # Check the status of the deduplication process. We should get two: one transfer, one duplicate.
        assert len(traces) == 2
        trace = traces.pop(0)
        assert isinstance(trace, TransferTrace)
        assert trace.transfer == transfer
        # This is the duplicate.
        assert isinstance(traces.pop(0), RedundantDuplicateTransferTrace)
        assert not traces

    # Dispose of everything.
    tr.close()
    await asyncio.sleep(1.0)
示例#4
0
async def _unittest_slow_node(
        compiled: typing.List[pyuavcan.dsdl.GeneratedPackageInfo]) -> None:
    from pyuavcan.application import make_node, make_registry
    import uavcan.primitive
    from uavcan.node import Version_1_0, Heartbeat_1_0, GetInfo_1_0, Mode_1_0, Health_1_0

    asyncio.get_running_loop().slow_callback_duration = 3.0

    assert compiled
    remote_pres = Presentation(UDPTransport("127.1.1.1"))
    remote_hb_sub = remote_pres.make_subscriber_with_fixed_subject_id(
        Heartbeat_1_0)
    remote_info_cln = remote_pres.make_client_with_fixed_service_id(
        GetInfo_1_0, 258)

    trans = RedundantTransport()
    try:
        info = GetInfo_1_0.Response(
            protocol_version=Version_1_0(
                *pyuavcan.UAVCAN_SPECIFICATION_VERSION),
            software_version=Version_1_0(*pyuavcan.__version_info__[:2]),
            name="org.uavcan.pyuavcan.test.node",
        )
        node = make_node(info,
                         make_registry(None, typing.cast(Dict[str, bytes],
                                                         {})),
                         transport=trans)
        print("node:", node)
        assert node.presentation.transport is trans
        node.start()
        node.start()  # Idempotency

        # Check port instantiation API for non-fixed-port-ID types.
        assert "uavcan.pub.optional.id" not in node.registry  # Nothing yet.
        with pytest.raises(KeyError, match=r".*uavcan\.pub\.optional\.id.*"):
            node.make_publisher(uavcan.primitive.Empty_1_0, "optional")
        assert 0xFFFF == int(
            node.registry["uavcan.pub.optional.id"])  # Created automatically!
        with pytest.raises(TypeError):
            node.make_publisher(uavcan.primitive.Empty_1_0)

        # Same but for fixed port-ID types.
        assert "uavcan.pub.atypical_heartbeat.id" not in node.registry  # Nothing yet.
        port = node.make_publisher(uavcan.node.Heartbeat_1_0,
                                   "atypical_heartbeat")
        assert port.port_id == pyuavcan.dsdl.get_model(
            uavcan.node.Heartbeat_1_0).fixed_port_id
        port.close()
        assert 0xFFFF == int(node.registry["uavcan.pub.atypical_heartbeat.id"]
                             )  # Created automatically!
        node.registry[
            "uavcan.pub.atypical_heartbeat.id"] = 111  # Override the default.
        port = node.make_publisher(uavcan.node.Heartbeat_1_0,
                                   "atypical_heartbeat")
        assert port.port_id == 111
        port.close()

        node.heartbeat_publisher.priority = pyuavcan.transport.Priority.FAST
        node.heartbeat_publisher.period = 0.5
        node.heartbeat_publisher.mode = Mode_1_0.MAINTENANCE  # type: ignore
        node.heartbeat_publisher.health = Health_1_0.ADVISORY  # type: ignore
        node.heartbeat_publisher.vendor_specific_status_code = 93
        with pytest.raises(ValueError):
            node.heartbeat_publisher.period = 99.0
        with pytest.raises(ValueError):
            node.heartbeat_publisher.vendor_specific_status_code = -299

        assert node.heartbeat_publisher.priority == pyuavcan.transport.Priority.FAST
        assert node.heartbeat_publisher.period == pytest.approx(0.5)
        assert node.heartbeat_publisher.mode == Mode_1_0.MAINTENANCE
        assert node.heartbeat_publisher.health == Health_1_0.ADVISORY
        assert node.heartbeat_publisher.vendor_specific_status_code == 93

        assert None is await remote_hb_sub.receive_for(2.0)

        assert trans.local_node_id is None
        trans.attach_inferior(UDPTransport("127.1.1.2"))
        assert trans.local_node_id == 258

        for _ in range(2):
            hb_transfer = await remote_hb_sub.receive_for(2.0)
            assert hb_transfer is not None
            hb, transfer = hb_transfer
            assert transfer.source_node_id == 258
            assert transfer.priority == pyuavcan.transport.Priority.FAST
            assert 1 <= hb.uptime <= 9
            assert hb.mode.value == Mode_1_0.MAINTENANCE
            assert hb.health.value == Health_1_0.ADVISORY
            assert hb.vendor_specific_status_code == 93

        info_transfer = await remote_info_cln.call(GetInfo_1_0.Request())
        assert info_transfer is not None
        resp, transfer = info_transfer
        assert transfer.source_node_id == 258
        assert isinstance(resp, GetInfo_1_0.Response)
        assert resp.name.tobytes().decode() == "org.uavcan.pyuavcan.test.node"
        assert resp.protocol_version.major == pyuavcan.UAVCAN_SPECIFICATION_VERSION[
            0]
        assert resp.software_version.major == pyuavcan.__version_info__[0]

        trans.detach_inferior(trans.inferiors[0])
        assert trans.local_node_id is None

        assert None is await remote_hb_sub.receive_for(2.0)

        node.close()
        node.close()  # Idempotency
    finally:
        trans.close()
        remote_pres.close()
        await asyncio.sleep(1.0)  # Let the background tasks terminate.