Make message and forward async to avoid contention and losing logs

[ncode]

This pull request introduces significant improvements to the audit server's asynchronous processing and error handling for notifications and forwarding, as well as new tests for these features. The main changes include refactoring notification and forwarding to be handled asynchronously via a side queue, adding configuration options and metrics for this queue, improving UDP forwarder timeout handling, and updating tests to reflect the new async behavior.

Asynchronous Processing and Queue Management:

• Introduced a sideQueue and background workers to handle notifications (messenger.Send) and forwarding (forwarder.Forward) asynchronously in AuditServer. This decouples these potentially slow operations from the main request processing path, improving throughput and reliability. ([[1]](https://github.com/ncode/vault-audit-filter/pull/22/files#diff-214cde7b7434e7b07bb1f44bb1792ef3255bd9fba5b33b7dc41aa306d990908eR1-R47), [[2]](https://github.com/ncode/vault-audit-filter/pull/22/files#diff-1367c9b0c20c80ea4c787543aa30a8f9e4524359e9f774a5ea08682da9fae5a7R135-R138), [[3]](https://github.com/ncode/vault-audit-filter/pull/22/files#diff-1367c9b0c20c80ea4c787543aa30a8f9e4524359e9f774a5ea08682da9fae5a7L148-R201))
• Added configuration options for async queue size and timeout (async.queue_size, async.timeout) with sensible defaults, and exposed a metric (sideDrops) to track dropped tasks when the queue is full. ([[1]](https://github.com/ncode/vault-audit-filter/pull/22/files#diff-1367c9b0c20c80ea4c787543aa30a8f9e4524359e9f774a5ea08682da9fae5a7R228-R241), [[2]](https://github.com/ncode/vault-audit-filter/pull/22/files#diff-1367c9b0c20c80ea4c787543aa30a8f9e4524359e9f774a5ea08682da9fae5a7R135-R138), [[3]](https://github.com/ncode/vault-audit-filter/pull/22/files#diff-1367c9b0c20c80ea4c787543aa30a8f9e4524359e9f774a5ea08682da9fae5a7R317-R327))

Error Handling and Default Behavior:

• Changed the server's behavior so that errors in notification or forwarding no longer cause the connection to close; only unmatched rules do. This is reflected in the tests and main logic. ([[1]](https://github.com/ncode/vault-audit-filter/pull/22/files#diff-1367c9b0c20c80ea4c787543aa30a8f9e4524359e9f774a5ea08682da9fae5a7L148-R201), [[2]](https://github.com/ncode/vault-audit-filter/pull/22/files#diff-b894c5214cd453e7d99616e679bc60172cd313bea6ceaa0446a704ea8d737500L163-R180), [[3]](https://github.com/ncode/vault-audit-filter/pull/22/files#diff-b894c5214cd453e7d99616e679bc60172cd313bea6ceaa0446a704ea8d737500L698-R809), [[4]](https://github.com/ncode/vault-audit-filter/pull/22/files#diff-b894c5214cd453e7d99616e679bc60172cd313bea6ceaa0446a704ea8d737500L889-R1018))
• Ensured that a default rule group is created if none are configured, improving robustness and simplifying configuration. ([[1]](https://github.com/ncode/vault-audit-filter/pull/22/files#diff-1367c9b0c20c80ea4c787543aa30a8f9e4524359e9f774a5ea08682da9fae5a7R250-R257), [[2]](https://github.com/ncode/vault-audit-filter/pull/22/files#diff-b894c5214cd453e7d99616e679bc60172cd313bea6ceaa0446a704ea8d737500R354-R447))

UDP Forwarder Improvements:

• Added a per-write timeout for the UDP forwarder, making it more robust to network issues and configurable via the async timeout setting. ([[1]](https://github.com/ncode/vault-audit-filter/pull/22/files#diff-a14c4239c1b85a957fd71e7038cf38822e97afc3d2edf4169414bc28d8b12248R18-R19), [[2]](https://github.com/ncode/vault-audit-filter/pull/22/files#diff-a14c4239c1b85a957fd71e7038cf38822e97afc3d2edf4169414bc28d8b12248R35-R49), [[3]](https://github.com/ncode/vault-audit-filter/pull/22/files#diff-1367c9b0c20c80ea4c787543aa30a8f9e4524359e9f774a5ea08682da9fae5a7L255-R287), [[4]](https://github.com/ncode/vault-audit-filter/pull/22/files#diff-1367c9b0c20c80ea4c787543aa30a8f9e4524359e9f774a5ea08682da9fae5a7R303-R305))

Testing Enhancements:

• Added new and updated existing tests to cover async queue behavior (including queue drops), async notification/forwarding, and default rule group creation. Introduced concurrency-safe test helpers. ([[1]](https://github.com/ncode/vault-audit-filter/pull/22/files#diff-b894c5214cd453e7d99616e679bc60172cd313bea6ceaa0446a704ea8d737500R354-R447), [[2]](https://github.com/ncode/vault-audit-filter/pull/22/files#diff-b894c5214cd453e7d99616e679bc60172cd313bea6ceaa0446a704ea8d737500L698-R809), [[3]](https://github.com/ncode/vault-audit-filter/pull/22/files#diff-b894c5214cd453e7d99616e679bc60172cd313bea6ceaa0446a704ea8d737500L727-R838), [[4]](https://github.com/ncode/vault-audit-filter/pull/22/files#diff-b894c5214cd453e7d99616e679bc60172cd313bea6ceaa0446a704ea8d737500R920-R955), [[5]](https://github.com/ncode/vault-audit-filter/pull/22/files#diff-b894c5214cd453e7d99616e679bc60172cd313bea6ceaa0446a704ea8d737500L889-R1018))
• Added benchmarks for React and rule evaluation to measure performance improvements from async processing. ([pkg/auditserver/bench_test.goR1-R43](https://github.com/ncode/vault-audit-filter/pull/22/files#diff-4928cc6308985a8649cab17eed8ed131a67a8eae2b52cc12ab89f89715d18318R1-R43))

Miscellaneous:

• Improved thread safety and test reliability with concurrency-safe buffers and counters in test helpers. ([[1]](https://github.com/ncode/vault-audit-filter/pull/22/files#diff-b894c5214cd453e7d99616e679bc60172cd313bea6ceaa0446a704ea8d737500R63-R79), [[2]](https://github.com/ncode/vault-audit-filter/pull/22/files#diff-b894c5214cd453e7d99616e679bc60172cd313bea6ceaa0446a704ea8d737500R920-R955))

References:

• [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25]

[codecov-commenter]

Codecov Report

❌ Patch coverage is 87.35632% with 11 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.01%. Comparing base (d5e6e1a) to head (3367f5f).

Files with missing lines	Patch %	Lines
pkg/auditserver/server.go	83.01%	5 Missing and 4 partials ⚠️
pkg/forwarder/forwarder.go	75.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #22      +/-   ##
==========================================
- Coverage   88.88%   88.01%   -0.88%     
==========================================
  Files           8        9       +1     
  Lines         279      342      +63     
==========================================
+ Hits          248      301      +53     
- Misses         24       29       +5     
- Partials        7       12       +5     

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