MQTTClient fails to raise appropriate exception if URI is broken

[FabianElsmer]

A broken URI leads to the following exception when trying to connect to an MQTT broker:

Unhandled exception: 'NoneType' object has no attribute 'write'
paxexpress-api | Connection failed: AttributeError("'NoneType' object has no attribute 'write'")
paxexpress-api | Unhandled exception: 'NoneType' object has no attribute 'write'
paxexpress-api | Reconnection attempt failed: AttributeError("'NoneType' object has no attribute 'write'")
paxexpress-api | Unhandled exception: 'NoneType' object has no attribute 'write'
paxexpress-api | Reconnection attempt failed: AttributeError("'NoneType' object has no attribute 'write'")
paxexpress-api | Unhandled exception: 'NoneType' object has no attribute 'write'
paxexpress-api | Reconnection attempt failed: AttributeError("'NoneType' object has no attribute 'write'")
paxexpress-api | Maximum number of connection attempts reached. Reconnection aborted
paxexpress-api | ERROR:    Traceback (most recent call last):
paxexpress-api |   File "/opt/pysetup/.venv/lib/python3.8/site-packages/amqtt/client.py", line 165, in connect
paxexpress-api |     return await self._do_connect()
paxexpress-api |   File "/opt/pysetup/.venv/lib/python3.8/site-packages/amqtt/client.py", line 254, in _do_connect
paxexpress-api |     return_code = await self._connect_coro()
paxexpress-api |   File "/opt/pysetup/.venv/lib/python3.8/site-packages/amqtt/client.py", line 468, in _connect_coro
paxexpress-api |     return_code = await self._handler.mqtt_connect()
paxexpress-api |   File "/opt/pysetup/.venv/lib/python3.8/site-packages/amqtt/mqtt/protocol/client_handler.py", line 79, in mqtt_connect
paxexpress-api |     await self._send_packet(connect_packet)
paxexpress-api |   File "/opt/pysetup/.venv/lib/python3.8/site-packages/amqtt/mqtt/protocol/handler.py", line 543, in _send_packet
paxexpress-api |     await packet.to_stream(self.writer)
paxexpress-api |   File "/opt/pysetup/.venv/lib/python3.8/site-packages/amqtt/mqtt/packet.py", line 218, in to_stream
paxexpress-api |     writer.write(self.to_bytes())
paxexpress-api | AttributeError: 'NoneType' object has no attribute 'write'

Broken URI: mqtt://"user":"pass"@eu1.thethings.network"

Expectation: A descriptive exception should already be raised when creating the session and mention that no writer could be instantiated due to failing to properly parse the URI.

[HerrMuellerluedenscheid]

Hey, thanks for reporting. Unfortunately, I was not able to reproduce that. I added a test in test_client.py:

@pytest.mark.asyncio
async def test_connect_broken_uri():
    config = {"auto_reconnect": False}
    client = MQTTClient(config=config)
    await client.connect("mqtt://xxx:xxxx@eu1.thethings.network")

Which raises:

        except (ProtocolHandlerException, ConnectionError, OSError) as e:
            self.logger.warning("MQTT connection failed: %r" % e)
            self.session.transitions.disconnect()
>           raise ConnectException(e)
E           amqtt.client.ConnectException: [Errno 8] nodename nor servname provided, or not known

../amqtt/client.py:502: ConnectException

I also tried with await client.connect("mqtt://\"xxx\":xxxx@eu1.thethings.network"). Same effect. Can you provide a minimalistic example that reproduces the issue?

[FlorianLudwig]

I played around with quotes and ended up reproducing the exception with:

@pytest.mark.asyncio
async def test_connect_broken_uri():
    config = {"auto_reconnect": False}
    client = MQTTClient(config=config)
    await client.connect('"mqtt://someplace')