JSON parsing produces invalid trace and span IDs

[craigandrews]

I am using RegisterTraceServiceHandlerFromEndpoint from go.opentelemetry.io/proto/otlp/collector/trace/v1 to allow forwarding of traces sent via HTTP to the gRPC endpoint. This works perfectly for Protobuf records, but produces invalid records when JSON is sent.

Expected behavior

Telemetry sent as JSON is parsed and converted to valid models.

Observed behaviour

Models produced by JSON input have trace and span IDs that are 50% longer than expected.

This appears to be because the code uses the default Protobuf JSON handler via the runtime.MarshalerForRequest function. This uses base64 to encode and decode binary arrays. This differs from the OTLP spec that states that trace and span IDs must be hex encoded.

The result is that the hex encoded IDs are being decoded as if they were base64.

[craigandrews]

My workaround is to base64 encode the invalid IDs, then hex decode the result. This inverts the incorrect decoding and produces valid IDs.