fix: fix potential nil dereference error

[derekbit]

Which issue(s) this PR fixes:

Issue longhorn/longhorn#9244

What this PR does / why we need it:

Special notes for your reviewer:

Additional documentation or context

[coderabbitai]

Walkthrough

The changes in this pull request focus on enhancing the error handling logic within the ReplicaRebuildingSrcStart method of the SPDKClient struct in pkg/client/client.go. The method now includes a conditional check for errors after invoking the RPC call, ensuring that errors are properly captured and reported. If an error occurs, an empty string is returned along with a descriptive error message. If there is no error, the method returns the resp.ExposedSnapshotLvolAddress and a nil error.

Changes

File	Change Summary
pkg/client/client.go	Modified error handling in ReplicaRebuildingSrcStart method to check for errors post RPC call.

Assessment against linked issues

Objective	Addressed	Explanation
Consolidate the replica related maps such as bdev map, mode map and address map in SPDK engine (#9244)	❌	This PR does not address the consolidation request.

Possibly related PRs

• fix: spdk replica lists its own lvols so that everyone won't be affected by others #229: This PR modifies the Replica struct and its methods in pkg/spdk/replica.go, enhancing error handling and introducing filtering logic for logical volumes, which is relevant to the error handling improvements made in the ReplicaRebuildingSrcStart method of the main PR.
• refactor: refactor replica head and snap chain related implementation #234: This PR also involves significant changes to the Replica struct in pkg/spdk/replica.go, focusing on error handling and management of the Head field, which aligns with the error handling enhancements introduced in the main PR.

Suggested reviewers

• innobead
• c3y1huang
• shuo-wu
• DamiaSan

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📜 Recent review details

Configuration used: .coderabbit.yaml
Review profile: CHILL

📥 Commits

Reviewing files that changed from the base of the PR and between 114edff and 5cf64bb.

📒 Files selected for processing (1)

• pkg/client/client.go (1 hunks)

🔇 Additional comments (2)

pkg/client/client.go (2)

232-235: LGTM! Error handling improvement prevents nil dereference.

The changes correctly handle potential errors from the RPC call by checking the error before accessing the response. This prevents a possible nil pointer dereference that could occur if the response was nil due to an error.

---

232-235: Verify similar patterns in other RPC methods.

Let's check if there are other RPC methods that might need similar error handling improvements.

✅ Verification successful

All RPC methods properly check for errors before accessing response fields

Based on the search results, I can confirm that all RPC client method calls in the codebase follow proper error handling patterns. The search shows that:

1. Every RPC call follows the pattern resp, err := client.Method() followed by an error check
2. The specific case of ExposedSnapshotLvolAddress in ReplicaRebuildingSrcStart also has proper error handling before accessing the response field
3. No instances were found where response fields are accessed without prior error checking

🏁 Scripts executed

The following scripts were executed for the analysis:

Script:

#!/bin/bash
# Search for potential similar patterns where response fields are accessed without error checking
# Look for lines that access response fields immediately after RPC calls

# Pattern 1: Methods that return response fields directly
rg -U 'client\.[A-Za-z]+\(.*\).*\n.*return resp\.' 

# Pattern 2: Methods that access response fields without visible error checking
rg -U 'resp,\s*err\s*:=\s*client\.[A-Za-z]+\(.*\).*\n.*return resp\.'

Length of output: 124

---

Script:

#!/bin/bash
# Let's try a different approach to find similar patterns
# Look for RPC client calls followed by response field access

# Search for client method calls with response and error handling
rg -U "resp.*err.*:=.*client\." -A 3

# Search specifically for exposed snapshot patterns
rg -U "ExposedSnapshot.*Address" -A 2 -B 2

Length of output: 5090

---

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[codecov]

Codecov Report

Attention: Patch coverage is 25.00000% with 3 lines in your changes missing coverage. Please review.

Project coverage is 8.38%. Comparing base (114edff) to head (5cf64bb).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/client/client.go	25.00%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##            main    #248      +/-   ##
========================================
- Coverage   8.39%   8.38%   -0.01%     
========================================
  Files         21      21              
  Lines       7150    7153       +3     
========================================
  Hits         600     600              
- Misses      6470    6472       +2     
- Partials      80      81       +1     

Flag	Coverage Δ
unittests	8.38% <25.00%> (-0.01%)	⬇️

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