fix(dataflow): 'update' infinite loop and nil pointer dereference

[eraac]

There is currently a nil pointer dereference in a specific edge case that hides the real error and makes it impossible to debug.

If the Dataflow API is not enabled in the service account project, then jobsResponse.Jobs is nil, and the for loop panics. Checking for errors before the for loop allows us to catch the error and return it to the end user.

EDIT: After the initial fix, I also found in the non-happy path an infinite loop if the job name is not found with the -update flag set. I can fix it in another PR, but since it is the same code, it is probably not worth opening another one.

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[gemini-code-assist]

Summary of Changes

Hello @eraac, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request enhances the robustness of the Dataflow job retrieval logic by preventing a potential nil pointer dereference. By moving and adding error checks, the system now gracefully handles scenarios where the Dataflow API might not be accessible or returns an error, ensuring that real errors are surfaced to the user rather than hidden by a program crash, thus improving debuggability and overall stability.

Highlights

• Nil Pointer Dereference Fix: Addressed a nil pointer dereference issue that occurred when the Dataflow API was not enabled, causing jobsResponse.Jobs to be nil and leading to a panic during iteration.
• Improved Error Handling: Introduced immediate error checks after jobsListCall.Do() calls, both for the initial request and subsequent paginated requests, to properly return errors instead of panicking.

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[eraac]

I'm not sure about moving the if err != nil to the end of the for-loop. Because the condition for the loop can be false, and the err might not be nil after the last page, this will change the current behaviour.

I’ve run some cases locally, and (even if I rollback my changes), the for-loop never stops if the jobsResponse.Jobs returns at least one job and there is no matching job name. I guess this is due to the fact that an empty page token is a valid value (for the first page).

I'll check it more tomorrow, I can't do any more today, but I guess I can fix it easily tomorrow if it's true. I'm not sure how to add a unit test for this :/

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EDIT: I've update the title and the initial message according the new changes, to include fix of the infinite loop

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R: @jrmccluskey for label go.

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[jrmccluskey]

LGTM, thanks!