From e10e0500c4f247910db278a092f9e09aaf7a572c Mon Sep 17 00:00:00 2001
From: Stuart Longland <me@vk4msl.com>
Date: Sat, 4 May 2024 19:40:40 +1000
Subject: [PATCH 1/9] kiss: Define a "FAILED" state for the device.

---
 aioax25/kiss.py | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/aioax25/kiss.py b/aioax25/kiss.py
index f943976..2c4d7b9 100644
--- a/aioax25/kiss.py
+++ b/aioax25/kiss.py
@@ -45,12 +45,15 @@ class KISSDeviceState(Enum):
     - OPEN: Serial port is open, TNC in KISS mode.
     - CLOSING: Close instruction just received.  Putting TNC back into
       TNC2-mode if requested then closing the port.
+    - FAILED: A critical error has occurred and the port is now no longer
+      functional.
     """
 
     CLOSED = 0
     OPENING = 1
     OPEN = 2
     CLOSING = 3
+    FAILED = -1
 
 
 # Command classes

From f7fbc9a70b25d23b47705423cee8691a23934c05 Mon Sep 17 00:00:00 2001
From: Stuart Longland <me@vk4msl.com>
Date: Sat, 4 May 2024 20:23:09 +1000
Subject: [PATCH 2/9] kiss: Add handling around open/close/send failures

---
 aioax25/kiss.py              |  56 +++++++++++--
 tests/test_kiss/test_base.py | 152 +++++++++++++++++++++++++++++++++++
 2 files changed, 202 insertions(+), 6 deletions(-)

diff --git a/aioax25/kiss.py b/aioax25/kiss.py
index 2c4d7b9..e9bd978 100644
--- a/aioax25/kiss.py
+++ b/aioax25/kiss.py
@@ -13,6 +13,7 @@
 from binascii import b2a_hex
 import time
 import logging
+from sys import exc_info
 
 
 # Constants
@@ -260,6 +261,13 @@ def __init__(
         self._send_block_size = send_block_size
         self._send_block_delay = send_block_delay
 
+        # Signal fired when the device enters the FAILED state
+        # Keyword arguments:
+        # - action: the action being performed at the time of failure
+        #           ('open', 'send', 'close')
+        # - exc_info: the exception trace information for debugging
+        self.failed = Signal()
+
     def _receive(self, data):
         """
         Handle incoming data by appending to our receive buffer.  The
@@ -384,13 +392,13 @@ def _send_data(self):
         if self._log.isEnabledFor(logging.DEBUG):
             self._log.debug("XMIT RAW %r", b2a_hex(data).decode())
 
-        self._send_raw_data(data)
+        self._try_send_raw_data(data)
 
         # If we are closing, wait for this to be sent
         if (self._state == KISSDeviceState.CLOSING) and (
             len(self._tx_buffer) == 0
         ):
-            self._close()
+            self._try_close()
             return
 
         if self._tx_buffer:
@@ -416,9 +424,9 @@ def _send_kiss_cmd(self):
         command = command.encode("US-ASCII")
         self._rx_buffer = bytearray()
         for bv in command:
-            self._send_raw_data(bytes([bv]))
+            self._try_send_raw_data(bytes([bv]))
             time.sleep(0.1)
-        self._send_raw_data(b"\r")
+        self._try_send_raw_data(b"\r")
         self._loop.call_later(0.5, self._check_open)
 
     def _check_open(self):
@@ -427,6 +435,35 @@ def _check_open(self):
         """
         self._loop.call_soon(self._send_kiss_cmd)
 
+    def _try_open(self):
+        try:
+            self._open()
+        except:
+            self._on_fail("open", exc_info())
+            raise
+
+    def _try_send_raw_data(self, data):
+        try:
+            self._send_raw_data(data)
+        except:
+            self._on_fail("send", exc_info())
+            raise
+
+    def _try_close(self):
+        try:
+            self._close()
+        except:
+            self._on_fail("close", exc_info())
+            raise
+
+    def _on_fail(self, action, exc_info):
+        (ex_t, ex_v, _) = exc_info
+        self._log.warning(
+            "KISS device has failed: %s: %s", ex_t.__name__, ex_v
+        )
+        self._state = KISSDeviceState.FAILED
+        self.failed.emit(action=action, exc_info=exc_info)
+
     def __getitem__(self, port):
         """
         Retrieve an instance of a specified port.
@@ -449,7 +486,7 @@ def open(self):
         assert self.state == KISSDeviceState.CLOSED, "Device is not closed"
         self._log.debug("Opening device")
         self._state = KISSDeviceState.OPENING
-        self._open()
+        self._try_open()
 
     def close(self):
         assert self.state == KISSDeviceState.OPEN, "Device is not open"
@@ -458,7 +495,12 @@ def close(self):
         if self._reset_on_close:
             self._send(KISSCmdReturn())
         else:
-            self._close()
+            self._try_close()
+
+    def reset(self):
+        assert self.state == KISSDeviceState.FAILED, "Device has not failed"
+        self._log.warning("Resetting device")
+        self._state = KISSDeviceState.CLOSED
 
 
 class BaseTransportDevice(BaseKISSDevice):
@@ -695,6 +737,8 @@ def __init__(self, device, port, log):
         self._log = log
 
         # Signal for receiving packets
+        # Keyword arguments:
+        # - frame: the raw KISS frame as a `bytes()` object
         self.received = Signal()
 
     @property
diff --git a/tests/test_kiss/test_base.py b/tests/test_kiss/test_base.py
index 15ad7ff..6159302 100644
--- a/tests/test_kiss/test_base.py
+++ b/tests/test_kiss/test_base.py
@@ -32,6 +32,31 @@ def _send_raw_data(self, data):
         self.transmitted += data
 
 
+class DummyKISSDeviceError(IOError):
+    pass
+
+
+class FailingKISSDevice(BaseKISSDevice):
+    def __init__(self, **kwargs):
+        super(FailingKISSDevice, self).__init__(**kwargs)
+
+        self.transmitted = bytearray()
+        self.open_calls = 0
+        self.close_calls = 0
+
+    def _open(self):
+        self.open_calls += 1
+        raise DummyKISSDeviceError("Open fails")
+
+    def _close(self):
+        self.close_calls += 1
+        raise DummyKISSDeviceError("Close fails")
+
+    def _send_raw_data(self, data):
+        self.transmitted += data
+        raise DummyKISSDeviceError("Send fails")
+
+
 def test_constructor_own_loop():
     """
     Test constructor uses its own IOLoop if not given one
@@ -47,11 +72,49 @@ def test_open():
     loop = DummyLoop()
     kissdev = DummyKISSDevice(loop=loop)
 
+    failures = []
+    def _on_fail(**kwargs):
+        failures.append(kwargs)
+    kissdev.failed.connect(_on_fail)
+
     assert kissdev.open_calls == 0
     kissdev.open()
 
     assert kissdev.open_calls == 1
 
+    assert failures == []
+
+
+def test_open_fail():
+    """
+    Test an open call that fails triggers the failed signal
+    """
+    loop = DummyLoop()
+    kissdev = FailingKISSDevice(loop=loop)
+
+    failures = []
+    def _on_fail(**kwargs):
+        failures.append(kwargs)
+    kissdev.failed.connect(_on_fail)
+
+    assert kissdev.open_calls == 0
+    try:
+        kissdev.open()
+        open_ex = None
+    except DummyKISSDeviceError as e:
+        assert str(e) == "Open fails"
+        open_ex = e
+
+    assert kissdev.open_calls == 1
+    assert kissdev.state == KISSDeviceState.FAILED
+    assert len(failures) == 1
+    failure = failures.pop(0)
+
+    assert failure.pop("action") == "open"
+    (ex_c, ex_v, _) = failure.pop("exc_info")
+    assert ex_c is DummyKISSDeviceError
+    assert ex_v is open_ex
+
 
 def test_close():
     """
@@ -60,6 +123,11 @@ def test_close():
     loop = DummyLoop()
     kissdev = DummyKISSDevice(loop=loop, reset_on_close=False)
 
+    failures = []
+    def _on_fail(**kwargs):
+        failures.append(kwargs)
+    kissdev.failed.connect(_on_fail)
+
     # Force the port open
     kissdev._state = KISSDeviceState.OPEN
 
@@ -69,6 +137,44 @@ def test_close():
     kissdev.close()
     assert kissdev.close_calls == 1
 
+    assert failures == []
+
+
+def test_close_fail():
+    """
+    Test a close call that fails triggers the failed signal
+    """
+    loop = DummyLoop()
+    kissdev = FailingKISSDevice(loop=loop, reset_on_close=False)
+
+    failures = []
+    def _on_fail(**kwargs):
+        failures.append(kwargs)
+    kissdev.failed.connect(_on_fail)
+
+    # Force the port open
+    kissdev._state = KISSDeviceState.OPEN
+
+    assert kissdev.close_calls == 0
+
+    # Now try closing the port
+    try:
+        kissdev.close()
+        close_ex = None
+    except DummyKISSDeviceError as e:
+        assert str(e) == "Close fails"
+        close_ex = e
+
+    assert kissdev.close_calls == 1
+    assert kissdev.state == KISSDeviceState.FAILED
+    assert len(failures) == 1
+    failure = failures.pop(0)
+
+    assert failure.pop("action") == "close"
+    (ex_c, ex_v, _) = failure.pop("exc_info")
+    assert ex_c is DummyKISSDeviceError
+    assert ex_v is close_ex
+
 
 def test_close_reset():
     """
@@ -288,6 +394,11 @@ def test_send_data():
     kissdev = DummyKISSDevice(loop=loop)
     kissdev._tx_buffer += b"test output data"
 
+    failures = []
+    def _on_fail(**kwargs):
+        failures.append(kwargs)
+    kissdev.failed.connect(_on_fail)
+
     # Send the data out.
     kissdev._send_data()
 
@@ -297,6 +408,47 @@ def test_send_data():
     # That should be the lot
     assert len(loop.calls) == 0
 
+    # There should be no failures
+    assert failures == []
+
+
+def test_send_data_fail():
+    """
+    Test that _send_data puts device in failed state if send fails.
+    """
+    loop = DummyLoop()
+    kissdev = FailingKISSDevice(loop=loop)
+    kissdev._tx_buffer += b"test output data"
+
+    failures = []
+    def _on_fail(**kwargs):
+        failures.append(kwargs)
+    kissdev.failed.connect(_on_fail)
+
+    # Send the data out.
+    try:
+        kissdev._send_data()
+        send_ex = None
+    except DummyKISSDeviceError as e:
+        assert str(e) == "Send fails"
+        send_ex = e
+
+    # We should now see this was "sent" and now in 'transmitted'
+    assert bytes(kissdev.transmitted) == b"test output data"
+
+    # That should be the lot
+    assert len(loop.calls) == 0
+
+    # We should be in the failed state
+    assert kissdev.state == KISSDeviceState.FAILED
+    assert len(failures) == 1
+    failure = failures.pop(0)
+
+    assert failure.pop("action") == "send"
+    (ex_c, ex_v, _) = failure.pop("exc_info")
+    assert ex_c is DummyKISSDeviceError
+    assert ex_v is send_ex
+
 
 def test_send_data_block_size_exceed_reschedule():
     """

From 0eb8e05beed01e69d243f6d277e922a0da012710 Mon Sep 17 00:00:00 2001
From: Stuart Longland <me@vk4msl.com>
Date: Sat, 4 May 2024 20:24:20 +1000
Subject: [PATCH 3/9] kiss tests: code formatting clean-up

---
 tests/test_kiss/test_base.py | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/tests/test_kiss/test_base.py b/tests/test_kiss/test_base.py
index 6159302..72f2cb4 100644
--- a/tests/test_kiss/test_base.py
+++ b/tests/test_kiss/test_base.py
@@ -73,8 +73,10 @@ def test_open():
     kissdev = DummyKISSDevice(loop=loop)
 
     failures = []
+
     def _on_fail(**kwargs):
         failures.append(kwargs)
+
     kissdev.failed.connect(_on_fail)
 
     assert kissdev.open_calls == 0
@@ -93,8 +95,10 @@ def test_open_fail():
     kissdev = FailingKISSDevice(loop=loop)
 
     failures = []
+
     def _on_fail(**kwargs):
         failures.append(kwargs)
+
     kissdev.failed.connect(_on_fail)
 
     assert kissdev.open_calls == 0
@@ -124,8 +128,10 @@ def test_close():
     kissdev = DummyKISSDevice(loop=loop, reset_on_close=False)
 
     failures = []
+
     def _on_fail(**kwargs):
         failures.append(kwargs)
+
     kissdev.failed.connect(_on_fail)
 
     # Force the port open
@@ -148,8 +154,10 @@ def test_close_fail():
     kissdev = FailingKISSDevice(loop=loop, reset_on_close=False)
 
     failures = []
+
     def _on_fail(**kwargs):
         failures.append(kwargs)
+
     kissdev.failed.connect(_on_fail)
 
     # Force the port open
@@ -395,8 +403,10 @@ def test_send_data():
     kissdev._tx_buffer += b"test output data"
 
     failures = []
+
     def _on_fail(**kwargs):
         failures.append(kwargs)
+
     kissdev.failed.connect(_on_fail)
 
     # Send the data out.
@@ -421,8 +431,10 @@ def test_send_data_fail():
     kissdev._tx_buffer += b"test output data"
 
     failures = []
+
     def _on_fail(**kwargs):
         failures.append(kwargs)
+
     kissdev.failed.connect(_on_fail)
 
     # Send the data out.

From cd2d39721db7bb8cff68d7e5857b56f88b11f74c Mon Sep 17 00:00:00 2001
From: Stuart Longland <me@vk4msl.com>
Date: Sat, 4 May 2024 20:28:15 +1000
Subject: [PATCH 4/9] kiss: Test resetting the base device

---
 tests/test_kiss/test_base.py | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/tests/test_kiss/test_base.py b/tests/test_kiss/test_base.py
index 72f2cb4..6bca1e0 100644
--- a/tests/test_kiss/test_base.py
+++ b/tests/test_kiss/test_base.py
@@ -208,6 +208,22 @@ def test_close_reset():
     assert func == kissdev._send_data
 
 
+def test_reset():
+    """
+    Test a reset call resets a failed device
+    """
+    loop = DummyLoop()
+    kissdev = DummyKISSDevice(loop=loop, reset_on_close=False)
+
+    # Force the port failed
+    kissdev._state = KISSDeviceState.FAILED
+
+    # Reset the device
+    kissdev.reset()
+
+    assert kissdev._state == KISSDeviceState.CLOSED
+
+
 def test_receive():
     """
     Test that a call to _receive stashes the data then schedules _receive_frame.

From f3fb34b6e0408c1fc1cc27d57964b03ad0917794 Mon Sep 17 00:00:00 2001
From: Stuart Longland <me@vk4msl.com>
Date: Sat, 4 May 2024 20:35:31 +1000
Subject: [PATCH 5/9] kiss: Test transport shutdown

---
 aioax25/kiss.py                | 13 ++++++
 tests/test_kiss/test_serial.py | 82 ++++++++++++++++++++++++++++++++++
 2 files changed, 95 insertions(+)

diff --git a/aioax25/kiss.py b/aioax25/kiss.py
index e9bd978..e2fe5c1 100644
--- a/aioax25/kiss.py
+++ b/aioax25/kiss.py
@@ -555,6 +555,19 @@ def _on_close(self, exc=None):
     def _send_raw_data(self, data):
         self._transport.write(data)
 
+    def reset(self):
+        super(BaseTransportDevice, self).reset()
+
+        try:
+            if self._transport:
+                self._transport.close()
+        except:
+            self._log.warning(
+                "Failed to close transport, ignoring!", exc_info=1
+            )
+
+        self._transport = None
+
 
 class SerialKISSDevice(BaseTransportDevice):
     """
diff --git a/tests/test_kiss/test_serial.py b/tests/test_kiss/test_serial.py
index 952c5ee..4cf0d3e 100644
--- a/tests/test_kiss/test_serial.py
+++ b/tests/test_kiss/test_serial.py
@@ -299,3 +299,85 @@ async def test_send_raw_data():
 
     kissdev._send_raw_data(b"a test frame")
     assert bytes(connection.port.tx_buffer) == b"a test frame"
+
+
+def test_reset_no_transport():
+    """
+    Test reset handles the "no transport" case
+    """
+    loop = get_event_loop()
+    kissdev = TestDevice(device="/dev/ttyS0", baudrate=9600, loop=loop)
+    assert kissdev._transport is None
+
+    # Inject state
+    kissdev._state = kiss.KISSDeviceState.FAILED
+
+    # Reset
+    kissdev.reset()
+
+    assert kissdev.state == kiss.KISSDeviceState.CLOSED
+
+
+def test_reset_with_transport():
+    """
+    Test reset closes the transport if it exists
+    """
+    loop = get_event_loop()
+    kissdev = TestDevice(device="/dev/ttyS0", baudrate=9600, loop=loop)
+
+    assert kissdev._transport is None
+
+    class MyTransport(object):
+        def __init__(self):
+            self.closed = False
+
+        def close(self):
+            assert not self.closed
+            self.closed = True
+
+    # Inject transport
+    transport = MyTransport()
+    kissdev._transport = transport
+
+    # Inject state
+    kissdev._state = kiss.KISSDeviceState.FAILED
+
+    # Reset
+    kissdev.reset()
+
+    assert kissdev.state == kiss.KISSDeviceState.CLOSED
+    assert kissdev._transport is None
+    assert transport.closed
+
+
+def test_reset_with_transport_err():
+    """
+    Test reset swallows close errors from the transport
+    """
+    loop = get_event_loop()
+    kissdev = TestDevice(device="/dev/ttyS0", baudrate=9600, loop=loop)
+
+    assert kissdev._transport is None
+
+    class MyTransport(object):
+        def __init__(self):
+            self.closed = False
+
+        def close(self):
+            assert not self.closed
+            self.closed = True
+            raise IOError("Whoopsie!")
+
+    # Inject transport
+    transport = MyTransport()
+    kissdev._transport = transport
+
+    # Inject state
+    kissdev._state = kiss.KISSDeviceState.FAILED
+
+    # Reset
+    kissdev.reset()
+
+    assert kissdev.state == kiss.KISSDeviceState.CLOSED
+    assert kissdev._transport is None
+    assert transport.closed

From 071a27eaaf63408cdca976fdfc209d40f9b4353b Mon Sep 17 00:00:00 2001
From: Stuart Longland <me@vk4msl.com>
Date: Sat, 4 May 2024 20:39:59 +1000
Subject: [PATCH 6/9] README.md: Document failure handling

---
 README.md | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/README.md b/README.md
index ff0eb52..866026b 100644
--- a/README.md
+++ b/README.md
@@ -111,6 +111,21 @@ their `received` signals and accept raw AX.25 frames via the `send` method.
 Any object passed to `send` is wrapped in a `bytes` call -- this will
 implicitly call the `__bytes__` method on the object you pass in.
 
+#### Exception handling on the KISS device
+
+There are a couple of exception cases that are emitted via a signal, so that
+any consumer of the KISS device can react to issues, such as the port failing
+to open, transmission failures, or failures to shut down.
+
+```python
+def _on_fail(action, exc_info, **kwargs):
+    # Put your error handling code here
+    # action is a string: "open", "send" or "close"
+    # exc_info is the output of sys.exc_info() at the time of the error
+    pass
+kissdev.failed.connect(_on_fail)
+```
+
 ### Setting up an AX.25 Interface
 
 The AX.25 interface is a logical routing and queueing layer which decodes the

From 00e584a3fefe3f07b7fde5b5e1a5735392e40bc5 Mon Sep 17 00:00:00 2001
From: Stuart Longland <me@vk4msl.com>
Date: Sat, 4 May 2024 20:55:24 +1000
Subject: [PATCH 7/9] kiss: Catch async open errors on serial devices

---
 aioax25/kiss.py                | 68 +++++++++++++++++-----------
 tests/test_kiss/test_serial.py | 82 ++++++++++++++++++++++++++--------
 2 files changed, 104 insertions(+), 46 deletions(-)

diff --git a/aioax25/kiss.py b/aioax25/kiss.py
index e2fe5c1..b48f345 100644
--- a/aioax25/kiss.py
+++ b/aioax25/kiss.py
@@ -594,22 +594,28 @@ def __init__(self, device, baudrate, *args, **kwargs):
         self._baudrate = baudrate
 
     async def _open_connection(self):
-        self._log.debug("Delegating to KISS serial device %r", self._device)
-        await create_serial_connection(
-            self._loop,
-            self._make_protocol,
-            self._device,
-            baudrate=self._baudrate,
-            bytesize=EIGHTBITS,
-            parity=PARITY_NONE,
-            stopbits=STOPBITS_ONE,
-            timeout=None,
-            xonxoff=False,
-            rtscts=False,
-            write_timeout=None,
-            dsrdtr=False,
-            inter_byte_timeout=None,
-        )
+        try:
+            self._log.debug(
+                "Delegating to KISS serial device %r", self._device
+            )
+            await create_serial_connection(
+                self._loop,
+                self._make_protocol,
+                self._device,
+                baudrate=self._baudrate,
+                bytesize=EIGHTBITS,
+                parity=PARITY_NONE,
+                stopbits=STOPBITS_ONE,
+                timeout=None,
+                xonxoff=False,
+                rtscts=False,
+                write_timeout=None,
+                dsrdtr=False,
+                inter_byte_timeout=None,
+            )
+        except:
+            self._log.warning("Failed to open serial connection", exc_info=1)
+            self._on_fail("open", exc_info())
 
 
 class TCPKISSDevice(BaseTransportDevice):
@@ -679,9 +685,13 @@ def __init__(
         )
 
     async def _open_connection(self):
-        await self._loop.create_connection(
-            self._make_protocol, **self._conn_args
-        )
+        try:
+            await self._loop.create_connection(
+                self._make_protocol, **self._conn_args
+            )
+        except:
+            self._log.warning("Failed to open TCP connection", exc_info=1)
+            self._on_fail("open", exc_info())
 
 
 class SubprocKISSDevice(BaseTransportDevice):
@@ -719,14 +729,18 @@ def _make_protocol(self):
         )
 
     async def _open_connection(self):
-        if self._shell:
-            await self._loop.subprocess_shell(
-                self._make_protocol, " ".join(self._command)
-            )
-        else:
-            await self._loop.subprocess_exec(
-                self._make_protocol, *self._command
-            )
+        try:
+            if self._shell:
+                await self._loop.subprocess_shell(
+                    self._make_protocol, " ".join(self._command)
+                )
+            else:
+                await self._loop.subprocess_exec(
+                    self._make_protocol, *self._command
+                )
+        except:
+            self._log.warning("Failed to call subprocess", exc_info=1)
+            self._on_fail("open", exc_info())
 
     def _send_raw_data(self, data):
         self._transport.get_pipe_transport(0).write(data)
diff --git a/tests/test_kiss/test_serial.py b/tests/test_kiss/test_serial.py
index 4cf0d3e..0de3ed2 100644
--- a/tests/test_kiss/test_serial.py
+++ b/tests/test_kiss/test_serial.py
@@ -27,7 +27,8 @@ def __init__(
         dsrdtr,
         inter_byte_timeout,
     ):
-        assert port == "/dev/ttyS0"
+
+        assert port in ("/dev/ttyS0", "/dev/ttyS1")
         assert baudrate == 9600
         assert bytesize == EIGHTBITS
         assert parity == PARITY_NONE
@@ -95,37 +96,45 @@ def write(self, *args, **kwargs):
 
 # Stub the serial port connection factory
 async def dummy_create_serial_connection(
-    loop, proto_factory, *args, **kwargs
+    loop, proto_factory, device, *args, **kwargs
 ):
     future = loop.create_future()
     create_serial_conn_log.debug(
         "Creating new serial connection: "
-        "loop=%r proto=%r args=%r kwargs=%r",
+        "loop=%r proto=%r device=%r args=%r kwargs=%r",
         loop,
         proto_factory,
+        device,
         args,
         kwargs,
     )
 
     def _open():
-        create_serial_conn_log.debug("Creating objects")
-        # Create the objects
-        protocol = proto_factory()
-        port = DummySerial(*args, **kwargs)
-        transport = DummyTransport(loop, port)
-
-        # Record the created object references
-        connections.append(
-            PortConnection(port=port, protocol=protocol, transport=transport)
-        )
+        if device == "/dev/ttyS0":
+            create_serial_conn_log.debug("Creating objects")
+            # Create the objects
+            protocol = proto_factory()
+            port = DummySerial(device, *args, **kwargs)
+            transport = DummyTransport(loop, port)
+
+            # Record the created object references
+            connections.append(
+                PortConnection(
+                    port=port, protocol=protocol, transport=transport
+                )
+            )
 
-        # Pass the protocol the transport object
-        create_serial_conn_log.debug("Passing transport to protocol")
-        protocol.connection_made(transport)
+            # Pass the protocol the transport object
+            create_serial_conn_log.debug("Passing transport to protocol")
+            protocol.connection_made(transport)
 
-        # Finish up the future
-        create_serial_conn_log.debug("Finishing up")
-        future.set_result((protocol, transport))
+            # Finish up the future
+            create_serial_conn_log.debug("Finishing up")
+            future.set_result((protocol, transport))
+        else:
+            # Abort with an error
+            create_serial_conn_log.debug("Failing")
+            future.set_exception(IOError("Open device failed"))
 
     create_serial_conn_log.debug("Scheduled in IOLoop")
     loop.call_soon(_open)
@@ -169,6 +178,41 @@ async def test_open():
     assert kissdev.init_called
 
 
+@asynctest
+async def test_open_fail():
+    """
+    Test open failures are handled.
+    """
+    loop = get_event_loop()
+    kissdev = TestDevice(device="/dev/ttyS1", baudrate=9600, loop=loop)
+    assert kissdev._transport is None
+
+    failures = []
+
+    def _on_fail(**kwargs):
+        failures.append(kwargs)
+
+    kissdev.failed.connect(_on_fail)
+
+    kissdev.open()
+    await sleep(0.01)
+
+    # We should NOT have created a new port
+    assert len(connections) == 0
+
+    # Connection should be in the failed state
+    assert kissdev.state == kiss.KISSDeviceState.FAILED
+
+    # Failure should have been reported
+    assert failures
+    failure = failures.pop(0)
+
+    assert failure.pop("action") == "open"
+    (ex_c, ex_v, _) = failure.pop("exc_info")
+    assert ex_c is IOError
+    assert str(ex_v) == "Open device failed"
+
+
 @asynctest
 async def test_close():
     """

From a85d19ec32d489efac8a57be93c2c4c970bf14ea Mon Sep 17 00:00:00 2001
From: Stuart Longland <me@vk4msl.com>
Date: Sat, 4 May 2024 20:59:20 +1000
Subject: [PATCH 8/9] kiss tests: Test TCP connection failure handling

---
 tests/test_kiss/test_tcp.py | 66 +++++++++++++++++++++++++++++++++++++
 1 file changed, 66 insertions(+)

diff --git a/tests/test_kiss/test_tcp.py b/tests/test_kiss/test_tcp.py
index fbd9074..507ceee 100644
--- a/tests/test_kiss/test_tcp.py
+++ b/tests/test_kiss/test_tcp.py
@@ -58,3 +58,69 @@ async def _create_connection(proto_factory, **kwargs):
     finally:
         # Restore mock
         loop.create_connection = orig_create_connection
+
+
+@asynctest
+async def test_open_connection_fail():
+    # This will receive the arguments passed to create_connection
+    connection_args = {}
+
+    loop = get_event_loop()
+
+    # Stub the create_connection method
+    orig_create_connection = loop.create_connection
+
+    async def _create_connection(proto_factory, **kwargs):
+        # proto_factory should give us a KISSProtocol object
+        protocol = proto_factory()
+        assert isinstance(protocol, kiss.KISSProtocol)
+
+        connection_args.update(kwargs)
+        raise IOError("Connection failed")
+
+    loop.create_connection = _create_connection
+
+    try:
+        device = kiss.TCPKISSDevice(
+            host="localhost",
+            port=5432,
+            loop=loop,
+            log=logging.getLogger(__name__),
+        )
+
+        failures = []
+
+        def _on_fail(**kwargs):
+            failures.append(kwargs)
+
+        device.failed.connect(_on_fail)
+
+        await device._open_connection()
+
+        # Expect a connection attempt to have been made
+        assert connection_args == dict(
+            host="localhost",
+            port=5432,
+            ssl=None,
+            family=0,
+            proto=0,
+            flags=0,
+            sock=None,
+            local_addr=None,
+            server_hostname=None,
+        )
+
+        # Connection should be in the failed state
+        assert device.state == kiss.KISSDeviceState.FAILED
+
+        # Failure should have been reported
+        assert failures
+        failure = failures.pop(0)
+
+        assert failure.pop("action") == "open"
+        (ex_c, ex_v, _) = failure.pop("exc_info")
+        assert ex_c is IOError
+        assert str(ex_v) == "Connection failed"
+    finally:
+        # Restore mock
+        loop.create_connection = orig_create_connection

From 1d2c2d35de90330afcd8cc8b5c9c092cea52b174 Mon Sep 17 00:00:00 2001
From: Stuart Longland <me@vk4msl.com>
Date: Sat, 4 May 2024 21:02:00 +1000
Subject: [PATCH 9/9] kiss: Test subproc handling

---
 tests/test_kiss/test_subproc.py | 59 +++++++++++++++++++++++++++++++++
 1 file changed, 59 insertions(+)

diff --git a/tests/test_kiss/test_subproc.py b/tests/test_kiss/test_subproc.py
index 25c90a2..d586c6d 100644
--- a/tests/test_kiss/test_subproc.py
+++ b/tests/test_kiss/test_subproc.py
@@ -91,6 +91,65 @@ async def _subprocess_shell(proto_factory, *args):
         loop.subprocess_shell = orig_subprocess_shell
 
 
+@asynctest
+async def test_open_connection_failure():
+    """
+    Test subprocess failure is detected and handled.
+    """
+    # This will receive the arguments passed to subprocess_shell
+    connection_args = []
+
+    loop = get_event_loop()
+
+    # Stub the subprocess_shell method
+    orig_subprocess_shell = loop.subprocess_shell
+
+    async def _subprocess_shell(proto_factory, *args):
+        # proto_factory should give us a KISSSubprocessProtocol object
+        protocol = proto_factory()
+        assert isinstance(protocol, kiss.KISSSubprocessProtocol)
+
+        connection_args.extend(args)
+        raise IOError("Exec failed")
+
+    loop.subprocess_shell = _subprocess_shell
+
+    try:
+        device = kiss.SubprocKISSDevice(
+            command=["kisspipecmd", "arg1", "arg2"],
+            shell=True,
+            loop=loop,
+            log=logging.getLogger(__name__),
+        )
+
+        failures = []
+
+        def _on_fail(**kwargs):
+            failures.append(kwargs)
+
+        device.failed.connect(_on_fail)
+
+        await device._open_connection()
+
+        # Expect a connection attempt to have been made
+        assert connection_args == ["kisspipecmd arg1 arg2"]
+
+        # Connection should be in the failed state
+        assert device.state == kiss.KISSDeviceState.FAILED
+
+        # Failure should have been reported
+        assert failures
+        failure = failures.pop(0)
+
+        assert failure.pop("action") == "open"
+        (ex_c, ex_v, _) = failure.pop("exc_info")
+        assert ex_c is IOError
+        assert str(ex_v) == "Exec failed"
+    finally:
+        # Restore mock
+        loop.subprocess_shell = orig_subprocess_shell
+
+
 def test_send_raw_data():
     """
     Test data written to the device gets written to the subprocess ``stdin``.