Uncatchable exception thrown in MqttClientConnection.connect()

• I’ve searched for previous similar issues and didn’t find any solution

Known Issue

• I’m using ATS data type endpoint: the endpoint should look like <prefix>-ats.iot.<region>.amazonaws.com

Describe the bug If connect() fails an uncatchable exception is thrown.

I am using JITP for our devices, but when connecting using the AWS IoT SDK v2 for JavaScript, and the device gets disconnected after the first connect (which IS expected), the disconnect creates an uncatchable exception.

SDK version number 1.8.3

Platform/OS/Hardware/Device node.js v16.5.0

To Reproduce (observed behavior)

import { mqtt, io, iot } from 'aws-iot-device-sdk-v2'

io.enable_logging(io.LogLevel.DEBUG)
const clientBootstrap = new io.ClientBootstrap()

const mqttEndpoint = 'foo-ats.iot.eu-west-1.amazonaws.com'
const clientId = 'bar'
const cfg = iot.AwsIotMqttConnectionConfigBuilder.new_mtls_builder('foo', 'bar')
cfg.with_clean_session(true)
cfg.with_client_id(clientId)
cfg.with_endpoint(mqttEndpoint)
;(async () => {
	const client = new mqtt.MqttClient(clientBootstrap)
	const connection = client.new_connection(cfg.build())
	try {
		await connection.connect()
	} catch (err) {
		console.error('Caught', err)
	}
})()

Expected behavior It should be possible to handle this exception using try/catch

Logs/output

[INFO] [2021-07-20T15:09:41Z] [00007f42d3eae780] [dns] - id=0x562cd24d78f0: Initializing default host resolver with 64 max host entries.
[INFO] [2021-07-20T15:09:41Z] [00007f42d3eae780] [channel-bootstrap] - id=0x562cd219f4c0: Initializing client bootstrap with event-loop group 0x562cd24b5e20
[DEBUG] [2021-07-20T15:09:41Z] [00007f42d3eae780] [mqtt-client] - client=0x562cd24c9920: Initalizing MQTT client
[INFO] [2021-07-20T15:09:41Z] [00007f42d3eae780] [tls-handler] - ctx: cannot enable ocsp stapling: OCSP stapling was requested, but is not supported
[DEBUG] [2021-07-20T15:09:41Z] [00007f42d3eae780] [tls-handler] - ctx: Setting ALPN list x-amzn-mqtt-ca
[DEBUG] [2021-07-20T15:09:41Z] [00007f42d3eae780] [mqtt-client] - id=0x562cd260e3f0: Creating new connection
[DEBUG] [2021-07-20T15:09:41Z] [00007f42d3eae780] [mqtt-topic-tree] - tree=0x562cd260e658: Creating new topic tree
[DEBUG] [2021-07-20T15:09:41Z] [00007f42d3eae780] [mqtt-client] - id=0x562cd260e3f0: Begin connecting process, switch state to CONNECTING.
[INFO] [2021-07-20T15:09:41Z] [00007f42d3eae780] [mqtt-client] - id=0x562cd260e3f0: using ping timeout of 3000000000 ns
[DEBUG] [2021-07-20T15:09:41Z] [00007f42d3eae780] [dns] - id=0x562cd24d78f0: Host resolution requested for foo-ats.iot.eu-west-1.amazonaws.com
[DEBUG] [2021-07-20T15:09:41Z] [00007f42d3eae780] [dns] - id=0x562cd24d78f0: No cached entries found for foo-ats.iot.eu-west-1.amazonaws.com starting new resolver thread.
[DEBUG] [2021-07-20T15:09:41Z] [00007f42d0892640] [dns] - static: resolving host foo-ats.iot.eu-west-1.amazonaws.com
[ERROR] [2021-07-20T15:09:41Z] [00007f42d0892640] [dns] - static: getaddrinfo failed with error_code -2
[WARN] [2021-07-20T15:09:41Z] [00007f42d0892640] [dns] - static, resolving host foo-ats.iot.eu-west-1.amazonaws.com failed, ec 1059 (aws-c-io: AWS_IO_DNS_INVALID_NAME, Host name was invalid for dns resolution.)
[DEBUG] [2021-07-20T15:09:41Z] [00007f42d0892640] [dns] - static, invoking resolution callback for host foo-ats.iot.eu-west-1.amazonaws.com with failure
[ERROR] [2021-07-20T15:09:41Z] [00007f42d0892640] [channel-bootstrap] - id=0x562cd219f4c0: dns resolution failed, or all socket connections to the endpoint failed.
[DEBUG] [2021-07-20T15:09:41Z] [00007f42d0892640] [channel-bootstrap] - id=0x562cd219f4c0: releasing bootstrap reference
node:events:371
      throw er; // Unhandled 'error' event
      ^

CrtError: Failed to connect: aws-c-io: AWS_IO_DNS_INVALID_NAME, Host name was invalid for dns resolution.
    at /home/m/nrf-asset-tracker/aws/node_modules/aws-crt/dist/native/mqtt.js:333:36
    at processTicksAndRejections (node:internal/process/task_queues:78:11)
Emitted 'error' event on MqttClientConnection instance at:
    at MqttClientConnection.emit (/home/m/nrf-asset-tracker/aws/node_modules/aws-crt/dist/common/event.js:75:22)
    at /home/m/nrf-asset-tracker/aws/node_modules/aws-crt/dist/native/mqtt.js:333:22
    at processTicksAndRejections (node:internal/process/task_queues:78:11) {
  error: 'Failed to connect: aws-c-io: AWS_IO_DNS_INVALID_NAME, Host name was invalid for dns resolution.',
  error_code: undefined,
  error_name: undefined
}

[TingDaoK]

Turns out it’s not an actual bug. The connection is an EventEmitter, and once error happens, the error event will be invoked. And you need to handle that as well. But, to be honest, I am not a JS developer, that does seem a bit weird to me.

[coderbyheart]

Note that I intentionally set an invalid hostname in the example so it triggers this error. In my code I use the correct ATS hostname.