Provide more specific error for failures during MQTT WS handshake

[NickDarvey]

Describe the feature

mqtt5_client_builder.websockets_with_default_aws_signing(...) raises a AWS_ERROR_HTTP_CALLBACK_FAILURE for both network errors and misconfiguration.

Use Case

For example, if I have a misconfigured client (like I connect with invalid client TLS details, or with a client identifier which I'm not authorized), I'd like to know about it so I can terminate the process because it's never going to connect. If it's a network issue, I'd like to let the MQTT client continue retrying to connect.

Proposed Solution

aws-crt-python/source/mqtt5_client.c

Lines 720 to 721 in c11a554

	/* TODO: Translate Python exception to aws error. In the meantime here's a catch-all. */
	error_code = AWS_ERROR_HTTP_CALLBACK_FAILURE;

:)

Using AwsCredentialProvider.get_credentials(...) I get AWS_IO_TLS_ERROR_NEGOTIATION_FAILURE and AWS_AUTH_CREDENTIALS_PROVIDER_HTTP_STATUS_FAILURE for the misconfigurations mentioned above, and AWS_IO_DNS_QUERY_FAILED and AWS_IO_DNS_INVALID_NAME for network issues.

Other Information

No response

Acknowledgements

• I may be able to implement this feature request
• This feature might incur a breaking change

[NickDarvey]

@bretambrose, I've updated to awscrt==0.20.10; awsiotsdk==1.21.5.

Unfortunately, I still get just one kind of error, though it's a different one now!

AWS_AUTH_SIGNING_NO_CREDENTIALS: Attempt to sign an http request without credentials

I get this error if I have no internet, but I also get the same error if I use an invalid client_id with mqtt_builder.websockets_with_default_aws_signing (that is a client_id for which I don't have the right IAM permissions).

Should I open a new issue for this?

[bretambrose]

That is the expected error that will be returned with any failure to source credentials for websocket handshake signing. I dont think it should be returned on a IAM policy failure though; I'll look into that when I can.

[bretambrose]

I am not able to repro:

If I remove connect permissions from my IAM policy, the connection attempt fails with AWS_ERROR_MQTT5_CONNACK_CONNECTION_REFUSED: Remote endpoint rejected the CONNECT attempt by returning an unsuccessful CONNACK

If I use good credentials but target the wrong account, the connection attempt fails with AWS_ERROR_HTTP_WEBSOCKET_UPGRADE_FAILURE: Failed to upgrade HTTP connection to Websocket

Both of these are accurate/expected.