[bridge/ot] Fall-back to TextMap carrier when it's not ot.HttpHeaders

[yurishkuro]

Resolves #3678

[codecov]

Codecov Report

Merging #3679 (e6c2d53) into main (f3b4813) will increase coverage by 0.0%.
The diff coverage is 100.0%.

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #3679   +/-   ##
=====================================
  Coverage   79.6%   79.6%           
=====================================
  Files        171     171           
  Lines      12657   12661    +4     
=====================================
+ Hits       10085   10089    +4     
  Misses      2359    2359           
  Partials     213     213           

Impacted Files	Coverage Δ
bridge/opentracing/bridge.go	63.7% <100.0%> (+0.2%)	⬆️
sdk/trace/batch_span_processor.go	80.2% <0.0%> (-1.8%)	⬇️
exporters/jaeger/jaeger.go	91.1% <0.0%> (+0.8%)	⬆️
sdk/metric/periodic_reader.go	91.3% <0.0%> (+1.2%)	⬆️

[MadVikingGod]

It looks like this assumes that if the format is HTTPHeaders and we fall back to the TextMapCarrier, the backing type will do the appropriate URL encoding. I would suggest we document this edge case.

[yurishkuro]

It looks like this assumes that if the format is HTTPHeaders and we fall back to the TextMapCarrier, the backing type will do the appropriate URL encoding. I would suggest we document this edge case.

@MadVikingGod it's a good question. I don't see how OTEL handles this in general since it does not have a dedicated HTTP propagator. In OT it was the responsibility of the Tracer to encode values for http before passing them to the carrier. While it could be made a responsibility of the carrier in OTEL, I don't see it being done in OTEL. This is how net/http instrumentation does injection:

        r = r.WithContext(ctx)
        span.SetAttributes(semconv.HTTPClientAttributesFromHTTPRequest(r)...)
        t.propagators.Inject(ctx, propagation.HeaderCarrier(r.Header))

Here propagation.HeaderCarrier is a type alias for the http.Header and does not do any special encoding of the values (and neither does http.Header afaik). So at least in this respect my PR does not give a different behavior vs. what already happens.

Where does the encoding of values happen in OTEL?

[MadVikingGod]

http.Header.Set() does canonicalize keys, but it does look like it leaves values alone.

[yurishkuro]

can this be merged?