OpenTracing bridge: BridgeTracer.Inject errors with ErrInvalidCarrier

[yvrhdn]

Description

We are migrating our OpenTracing app to OpenTelemetry using the OpenTracing bridge. Unfortunately tracer.Inject is failing with ErrInvalidCarrier despite providing a valid HTTPHeaders carrier.

The code:

• we are injecting a carrier with format HTTPHeaders here
• our carrier HttpgrpcHeadersCarrier implements TextMapWriter as documented on HTTPHeaders
• BridgeTracer tries to cast this carrier into a HTTPHeadersCarrier which is not possible

Is this a known limitation of the OpenTracing bridge?

I'd guess to solve this we'd need some kind of adapter from the OpenTracing TextMapWriter into OTel's TextMapCarrier.
I see Inject only calls Set so maybe we can get away with only implementing that function?

Environment

• opentelemetry-go version: v1.0.0-RC2
• github.com/opentracing/opentracing-go: v1.2.0

Steps To Reproduce

1. Use BridgeTracer from the OpenTracing bridge
2. Inject a carrier with format HTTPHeaders that implements TextMapWriter but is not of type HTTPHeadersCarrier

Expected behavior

The BridgeTracer.Inject should accept a carrier of type TextMapWriter.

[bboreham]

I started working on this.