[otlp] Expand array buffer / add tests to existing base buffer

[rajkumar-rangaraj]

Fixes Part of #5730
Design discussion issue #

Changes

Please provide a brief description of the changes here.

• Expanded the array buffer when a limit is reached.
• Set the upper limit for the array buffer to 2 MB. If a single tag with an array value exceeds 2 MB, it will be dropped, and the value will be updated to "TRUNCATED." While dropping the entire array value tag would be simpler, it would make it harder for customers to identify the issue.
• Added additional test for base buffer increase
• Identified a bug where ArgumentException could be thrown when using these calls
  • Buffer.BlockCopy(value.Buffer, 0, state.Buffer, state.WritePosition, value.WritePosition);
  • var bytesWritten = Utf8Encoding.GetBytes(value, buffer.AsSpan().Slice(writePosition));
• Identified another bug where the buffer needs to be passed by reference, as it is being doubled in a different method.

Merge requirement checklist

• CONTRIBUTING guidelines followed (license requirements, nullable enabled, static analysis, etc.)
• Unit tests added/updated
• Appropriate CHANGELOG.md files updated for non-trivial changes
• Changes in public API reviewed (if applicable)

[codecov]

Codecov Report

Attention: Patch coverage is 89.28571% with 3 lines in your changes missing coverage. Please review.

Project coverage is 86.45%. Comparing base (145e7ad) to head (0218bd2).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...Implementation/Serializer/ProtobufOtlpTagWriter.cs	75.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6013      +/-   ##
==========================================
+ Coverage   86.29%   86.45%   +0.15%     
==========================================
  Files         257      257              
  Lines       11685    11699      +14     
==========================================
+ Hits        10084    10114      +30     
+ Misses       1601     1585      -16     

Flag	Coverage Δ
unittests-Project-Experimental	86.29% <89.28%> (+0.13%)	⬆️
unittests-Project-Stable	86.38% <89.28%> (+0.22%)	⬆️
unittests-Solution	86.08% <89.28%> (-0.16%)	⬇️
unittests-UnstableCoreLibraries-Experimental	85.78% <ø> (ø)

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

Files with missing lines	Coverage Δ
...tation/OpenTelemetryProtocolExporterEventSource.cs	84.00% <100.00%> (-3.68%)	⬇️
...ementation/Serializer/ProtobufOtlpLogSerializer.cs	98.47% <100.00%> (+3.05%)	⬆️
...ntation/Serializer/ProtobufOtlpMetricSerializer.cs	98.77% <100.00%> (+1.63%)	⬆️
...entation/Serializer/ProtobufOtlpTraceSerializer.cs	94.98% <100.00%> (+1.54%)	⬆️
...ol/Implementation/Serializer/ProtobufSerializer.cs	93.18% <100.00%> (+5.48%)	⬆️
....Exporter.OpenTelemetryProtocol/OtlpLogExporter.cs	100.00% <100.00%> (ø)
...porter.OpenTelemetryProtocol/OtlpMetricExporter.cs	80.76% <100.00%> (ø)
...xporter.OpenTelemetryProtocol/OtlpTraceExporter.cs	89.28% <100.00%> (ø)
...Implementation/Serializer/ProtobufOtlpTagWriter.cs	95.45% <75.00%> (-4.55%)	⬇️

... and 4 files with indirect coverage changes

[rajkumar-rangaraj]

@CodeBlanch Should we change this to readonly? With the current implementation, even if customers want to use a reflection hack to increase the size, const makes it impossible.

[CodeBlanch]

🤷

We do have this: https://github.com/open-telemetry/opentelemetry-dotnet/blob/main/src/OpenTelemetry.Exporter.OpenTelemetryProtocol/Implementation/ExperimentalOptions.cs

You could define some experimental options to control the two buffer sizes. Users will be able to bind them to IConfiguration/envvars if needed. Better mechanism than reflection if you want to make it configurable.

[rajkumar-rangaraj]

We could consider post RC release.

[CodeBlanch]

LGTM