Fix fingerprint processor failures during concurrent bulk request

[tanyabti]

Description

The fingerprint ingest processor failed under concurrent bulk ingestion, throwing ArrayIndexOutOfBoundsException from the native crypto provider and, once triggered, breaking all fingerprint hashing on the affected node until it was replaced.

Cause: TheHashMethod enum cached a single MessageDigest instance per algorithm and reused the same one for every request. MessageDigest is not thread-safe, so when multiple ingest threads used that shared instance at once, they corrupt its internal state.

Fix: Store a supplier per algorithm and resolve a fresh per-call (ThreadLocal-backed) digest on each execute(). Now each call gets its own fresh (thread-local) MessageDigest, so threads no longer share one. Added a test that runs the processor from many threads at once and checks the output stays correct with no errors.

Related Issues

Resolves #[Issue number to be closed when this PR is merged]

Check List

• Functionality includes testing.
• API changes companion pull request created, if applicable.
• Public documentation issue/PR created, if applicable.

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[github-actions]

PR Reviewer Guide 🔍

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🧪 PR contains tests

🔒 No security concerns identified

✅ No TODO sections

🔀 No multiple PR themes

⚡ No major issues detected

[github-actions]

PR Code Suggestions ✨

Explore these optional code suggestions:

Category	Suggestion	Impact
General	Preserve stack traces from worker failures If a thread throws (e.g. ArrayIndexOutOfBoundsException from a corrupted digest), the loop aborts but the test still passes as long as mismatches is empty and failures gets populated — however, the assertion on failures uses equalTo(List.of()) which will surface it. Still, consider also asserting non-empty progress (e.g. that the loop actually ran) and rethrowing the first Throwable with its cause preserved so the stack trace is visible in test output rather than just its toString(). modules/ingest-common/src/test/java/org/opensearch/ingest/common/FingerprintProcessorTests.java [203-213] for (int i = 0; i < iterationsPerThread; i++) { IngestDocument doc = new IngestDocument( new java.util.HashMap<>(Map.of(fieldName, fieldValue)), new java.util.HashMap<>() ); processor.execute(doc); String actual = doc.getFieldValue(targetField, String.class); if (expectedFingerprint.equals(actual) == false) { mismatches.add(actual); } } +if (failures.isEmpty() == false) { + throw new AssertionError("thread failed", failures.get(0)); +} Suggestion importance[1-10]: 3 __ Why: Minor test-diagnostic improvement; the existing assertThat on failures will still surface the failure via toString(), so the added rethrow only marginally improves debugging output.	Low

[github-actions]

✅ Gradle check result for 9d09030: SUCCESS

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 71.76%. Comparing base (0249cde) to head (9d09030).
⚠️ Report is 7 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main   #23027      +/-   ##
============================================
+ Coverage     71.67%   71.76%   +0.09%     
- Complexity    77559    77640      +81     
============================================
  Files          6168     6168              
  Lines        360105   360105              
  Branches      52380    52380              
============================================
+ Hits         258095   258421     +326     
+ Misses        81495    81181     -314     
+ Partials      20515    20503      -12     

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