Lambda Extension returns invalid OTLP response payload causing protobuf decoding failures in OpenTelemetry SDKs

[jlabedo]

Summary

When sending OTLP trace data to the Datadog Lambda Extension, the extension returns a JSON payload that is not compliant with the OpenTelemetry OTLP protocol. This breaks any language SDK that attempts to deserialize the response as a standard ExportTraceServiceResponse protobuf message.

The problematic response comes from the following code:

datadog-lambda-extension/bottlecap/src/otlp/agent.rs

Line 210 in 5377d6f

json!({"rate_by_service":{"service:,env:":1}}).to_string(),

Opentelemetry Specification: https://opentelemetry.io/docs/specs/otlp/#otlpgrpc-response

Affected versions

v88 at least is affected.
I had to rollback to v68 of the extension that is not affected.

Tested with latest PHP opentelemetry SDK

Suggestion

Return an empty response for otlp agent.

Thank You

Happy to test a patch, PR, or experimental build.
Let me know if you need reproduction code.

[jchrostek-dd]

Team is starting to investigate.

[beubeu13220]

Thank you for identifying this issue, we are facing the same problem as well.