RUMM-2619 Manual otel b3 headers injection

[maciejburda]

What and why?

Adds OpenTelemetryHTTPHeadersWriter and OpenTelemetryHTTPHeadersReader. That allow manual injection of the Open Telemetry b3 header (both single and multiple).

Currently we only support 64-bit version of the tracing header due to backward compatibility issues. Main issue is related to setup of current Open Tracing headers in RUM which rely on decimal instead of hex and no out of the box solution for 128-bit.

I plan to reiterate on this while implementing automatic injection.

How?

This implementation follows specification from https://github.com/openzipkin/b3-propagation while navigating around internal implementation details. This PR is initial take on the problem that will be expanded in the automatic injection PR.

Review checklist

• Feature or bugfix MUST have appropriate tests (unit, integration)
• Make sure each commit and the PR mention the Issue number or JIRA reference
• Add CHANGELOG entry for user facing changes

Custom CI job configuration (optional)

• Run unit tests
• Run integration tests
• Run smoke tests

[maxep]

Very nice, the documentation and tests looks great 👌

I wonder if we shouldn't reuse naming from OpenTelemetry, cf: https://www.npmjs.com/package/@opentelemetry/propagator-b3

e.g.: B3PropagatorWriter/B3PropagatorReader

[maciejburda]

@maxep Thanks for a great review! I addressed all the suggestions. Ready for the second pass 🙌

[maciejburda]

Note: I talked to @ncreated and for now we won't support 128-bit encoding. Values of tracing headers were hidden from the consumer, so we decided to keep it this way. Difficult part for automatic switch was hex/decimal encoding.

I incorporated code related to it in this PR - it will ease the work on the automatic Open Telemetry support (from DD configuration).

[datadog-datadog-prod-us1]

Datadog Report

Branch report: maciey/RUMM-2619-manual-otel-b3-headers-injection
Commit report: fe915ad

✅ dd-sdk-ios 0 Failed, 0 New Flaky, 116 Passed, 0 Skipped, 4m 28.21s Wall Time

[maxep]

Awesome, well done @maciejburda 👏

[ncreated]

Excellent work! 💪 Everything seems to be on the right place and having a pair of (public) writer + (internal) reader is a good choice - it should make it much easier for automatic injection (where both are in use).

I few feedbacks - none is blocking, but I would like to hear your opinion.

[maciejburda]

@ncreated Great feedback! I will incorporate all the comments in a separate PR if you don't mind. I want to leverage the fact that this one is already approved on CI.