feat: implement FromStr and Display for Protocol

[davidhewitt]

Changes

Implements Display and FromStr for Protocol, using the values documented in https://opentelemetry.io/docs/languages/sdk-configuration/otlp-exporter/#otel_exporter_otlp_protocol

Merge requirement checklist

• CONTRIBUTING guidelines followed
• Unit tests added/updated (if applicable)
• Appropriate CHANGELOG.md files updated for non-trivial, user-facing changes
• Changes in public API reviewed (if applicable)

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: lalitb / name: Lalit Kumar Bhasin (82a6d3d)
• ✅ login: davidhewitt / name: David Hewitt (e23f7c9, e6711a2)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79.6%. Comparing base (b33f0cc) to head (e23f7c9).

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #2758   +/-   ##
=====================================
  Coverage   79.6%   79.6%           
=====================================
  Files        123     123           
  Lines      23034   23061   +27     
=====================================
+ Hits       18356   18379   +23     
- Misses      4678    4682    +4     

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[davidhewitt]

Possibly interesting to note that the Serialize and Deserialize values are automatically derived and will not match these.

(Perhaps the serde implementations should be changed to use these constants? They seem to be universal across all OTEL SDKs. I am happy to do that as a follow-up.)

[gruebel]

nice work 🍻 can you also add a short changelog entry for it? Regarding the serde part, it would be great to be consistent with other SDKs.

[utpilla]

Is this necessary? Why would a user have this awkward construct:

.with_protocol("grpc".parse::<Protocol>().unwrap())

when they could simply do this:

.with_protocol(Protocol::Grpc)

[davidhewitt]

Completely agree if hard coded then users should use the enum variant.

I am working on a downstream SDK which uses opentelemetry, tracing and log. We configure an otel exporter and are working to support setting the protocol via environment, which is not yet supported by this library (although in future perhaps I can also contribute a solution to that issue).

Other downstream packages to set up an exporter, like init-tracing-opentelemetry, also have similar code doing this conversion.

It feels most correct to have the FromStr implementation here in the library for all downstream implementations to re-use. This is also how the Compression type is already parsed from env within this library.

[utpilla]

What's the motivation behind adding a Display implementation for Protocol?

[davidhewitt]

After seeing the Compression implementation within this library had both FromStr and Display, I felt it was most correct to add Display to match the FromStr here too.

If you have concerns, I am happy to remove it - the FromStr is the functionality I need at present (as per above comment).

[davidhewitt]

nice work 🍻 can you also add a short changelog entry for it?

Done, please let me know if you want it adjusted.

[davidhewitt]

Sorry, fat finger error led to closing PR by mistake 🤦

[davidhewitt]

Regarding the serde part, it would be great to be consistent with other SDKs.

I opened #2765 for this as a separate PR, because it's potentially breaking and deserves its own visibility / changelog note.