External task client `setVariables` doesn't set variables correctly

[danielkelemen]

Environment (Required on creation)

All versions.

Description (Required on creation; please attach any relevant screenshots, stacktraces, log files, etc. to the ticket)

The Java external task client setVariables uses a wrong parameter and thus it doesn't set any variables.

Steps to reproduce (Required on creation)

• Call the setVariables method in the client.
  • client.setVariables(processInstanceId, variables);
• Check the process variables.

Observed Behavior (Required on creation)

Variables passed to the client are missing.

Expected behavior (Required on creation)

Variables passed to the client are set correctly.

Root Cause (Required on prioritization)

The client's request class implements the wrong variables property: SetVariablesRequestDto.java#L27 instead the correct modifications.

API: Process-Instance/operation/modifyProcessInstanceVariables Engine DTO: PatchVariablesDto

Furthermore, the ExternalTaskHandlerIT contains a bug as well. It doesn't fail because the we also call the complete with the same variables, which can set them correctly and this hides the aforementioned bug.

Solution Ideas

Hints

Links

Breakdown

### Pull Requests
- [ ] https://github.com/camunda/camunda-bpm-platform/pull/4236
- [ ] https://github.com/camunda/camunda-bpm-platform/pull/4281

Dev2QA handover

• [ ] Does this ticket need a QA test and the testing goals are not clear from the description? Add a Dev2QA handover comment

[danielkelemen]

@tasso94 a community user found this bug in the Java external client with the setVariables call. Should we backport this to older versions?

[tasso94]

@danielkelemen, let's wait for customer feedback if a backport is needed.

[hkupitz]

Just for info: a training participant and me stumbled upon this two weeks ago. https://camunda.slack.com/archives/C80C0EC79/p1710947683545529