Make Message Object Instantiable By Users

[ojasvajain]

Overview

1. Fixes issue feature request: make Message type user-instantiable #1535 by allowing Message objects to be instantiable by users.
2. Modify type hints of topic(), partition() and offset() getters to make them consistent with their implementations (ref)

Problem

Users were unable to create synthetic Message objects in their unit tests and had to resort to reading Message objects from a live Kafka cluster.

>>> import confluent_kafka
>>> confluent_kafka.Message()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: cannot create 'cimpl.Message' instances

Solution

A constructor has been defined in the Message class. All params have been intentionally kept optional to support easy instantiation without providing any params. This way of creating new messages is expected to be used only while writing unit tests. Producers and consumers will continue to use the internal factory method (Message_new0) for creating message objects.

>>> import confluent_kafka
>>> confluent_kafka.Message()
<cimpl.Message object at 0x101301640>
>>> 

Checklist

• Contains customer facing changes? Including API/behavior changes
• Did you add sufficient unit test and/or integration test coverage for this PR?

References

#1535

[confluent-cla-assistant]

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[MSeal]

Thanks for adding tests covering various init behaviors

[sonarqube-confluent]

Quality Gate failed

Failed conditions
0.0% Coverage on New Code (required ≥ 80%)

See analysis details on SonarQube