fix: add nil checks to prevent panics in leaderelection

[haitwang-cloud]

What type of PR is this?

/kind flake

What this PR does / why we need it:

This PR adds defensive nil checks throughout the pkg/util/leaderelection/leaderelection.go file to prevent potential runtime panics. The changes improve code robustness by handling cases where callback functions or lease object fields may be nil.

The original code had several potential panic scenarios:

1. Nil callback functions: When LeaderCallbacks are created without providing OnStartedLeading or OnStoppedLeading functions, calling them directly would cause a panic. This is a real scenario as seen in test code: NewLeaderManager("dev", "kube-system", "hami-scheduler", LeaderCallbacks{})

2. Nil lease pointer: The isHolderOf() method could receive a nil lease pointer without proper validation

3. Nil lease fields: The isLeaseValid() method could access nil observedLease or LeaseDurationSeconds fields causing nil pointer dereference

Changes made:

• Added nil checks for OnStartedLeading and OnStoppedLeading callbacks in onAdd(), onUpdate(), and onDelete() methods
• Added nil check for lease pointer in isHolderOf() method
• Added nil checks for observedLease and LeaseDurationSeconds in isLeaseValid() method

Which issue(s) this PR fixes:

Fixes potential runtime panics in leader election mechanism

Special notes for your reviewer:

• These changes are purely defensive programming improvements with no functional changes to the business logic
• The callback nil checks are necessary because the API design allows empty LeaderCallbacks{} to be passed (as seen in test code)
• All changes have minimal performance overhead (single pointer comparisons)
• Existing tests continue to pass and now safely handle edge cases

Does this PR introduce a user-facing change?:

Fix potential panics in leader election by adding nil checks for callbacks and lease fields

[hami-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: haitwang-cloud
Once this PR has been reviewed and has the lgtm label, please assign wawa0210 for approval. For more information see the Kubernetes Code Review Process.

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[gemini-code-assist]

Summary of Changes

Hello @haitwang-cloud, 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 significantly enhances the robustness of the leader election mechanism by introducing several defensive nil checks across key functions. These changes proactively address potential runtime panics that could arise from uninitialized callback functions or nil lease object fields, thereby improving the system's stability and reliability without altering its core functional behavior.

Highlights

• Callback Nil Checks: Implemented nil checks for OnStartedLeading and OnStoppedLeading callback functions within onAdd, onUpdate, and onDelete methods to prevent panics when callbacks are not provided, as seen in test scenarios.
• Lease Pointer Validation: Added a nil check for the lease pointer in the isHolderOf method to ensure safe access to its fields, addressing a potential nil pointer dereference.
• Lease Field Validation: Introduced nil checks for observedLease and LeaseDurationSeconds within the isLeaseValid method to prevent nil pointer dereferences when these fields might be uninitialized.

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[gemini-code-assist]

Code Review

This pull request effectively addresses potential nil pointer panics in the leader election logic by adding necessary checks for callbacks and lease objects. The changes are defensive and improve the robustness of the code. I have one suggestion to improve consistency in how the nil checks for callbacks are implemented.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

Flag	Coverage Δ
unittests	51.18% <100.00%> (+0.03%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
pkg/util/leaderelection/leaderelection.go	88.60% <100.00%> (+1.10%)	⬆️

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[archlitchi]

have you encountered an issue related to it?

[haitwang-cloud]

Hey@archlitchi, not yet. I recently noticed the new feature release that introduces leader election, reviewed the relevant code, and inserted a safeguard to prevent the panic.