[Issue #12486][Python Client]JsonSchema encoding is not idempotent

[tsturzl]

Fixes #12486

Motivation

JsonSchemas delete part of the Record which makes it impossible to reuse a Record. Resulting in a KeyError anytime you encode the message more than once.

Modifications

Copy on encoding the Record so modifications don't change the root object. Check keys before deleting so you don't get a KeyError.

Verifying this change

• Make sure that the change passes the CI checks.

(Please pick either of the following options)

This change is a trivial rework / code cleanup without any test coverage.

(or)

This change is already covered by existing tests, such as (please describe tests).

(or)

This change added tests and can be verified as follows:

(example:)

• Added integration tests for end-to-end deployment with large payloads (10MB)
• Extended integration test for recovery after broker failure

Does this pull request potentially affect one of the following parts:

If yes was chosen, please highlight the changes

• Dependencies (does it add or upgrade a dependency): (yes / no)
• The public API: (yes / no)
• The schema: (yes / no / don't know)
• The default values of configurations: (yes / no)
• The wire protocol: (yes / no)
• The rest endpoints: (yes / no)
• The admin cli options: (yes / no)
• Anything that affects deployment: (yes / no / don't know)

Documentation

Check the box below and label this PR (if you have committer privilege).

Need to update docs?

• doc-required

  (If you need help on updating docs, create a doc issue)

• no-need-doc

  (Please explain why)

• doc

  (If this PR contains doc changes)

[merlimat]

It might also a good idea to add a test to repro the issue, so that we're not going to break it in the future.

[tsturzl]

@merlimat That's a good point. I actually had completely overlooked the unit tests. If you'd like I can add that to this PR. I may not have time until next week however.

[tsturzl]

I cannot get the cpp client to build, and therefore I'm not able to run the test I wrote. I couldn't build via the readme, nor could I get the docker build to succeed. I don't really have the free time currently to delve into CMake to figure out what's going on. If I had to guess based on the error message, the docker build fails probably because the docker system dependencies hasn't been kept up with the CMake dependencies for Boost Python. As for why it's failing on my machine I'm running Ubuntu 20.04 and the guide states 16.04, so maybe there's a breaking change in the version of cmake or some other tool or dependency required?