Propagators: specify case sensitivity of get_from_carrier

[mauriciovasquezbernal]

The w3c specification states that the implementation must ignore the case of the traceparent header name: https://www.w3.org/TR/trace-context/#header-name.

The current implementation just calls get_from_carrier without further info about the case:

opentelemetry-python/opentelemetry-api/src/opentelemetry/context/propagation/tracecontexthttptextformat.py

Line 66 in b0da53d

header = get_from_carrier(carrier, cls._TRACEPARENT_HEADER_NAME)

.

Probably we'll need to add a new parameter to get_from_carrier that specifies if the case must be considered or not.

Related: #197, #125

[Oberon00]

I think that get_from_carrier should be the one to decide if case is important, not the caller/propagator. EDIT: E.g. HTTP headers are case-insensitive but some messaging system properties might not be.

[Oberon00]

Will be resolved with open-telemetry/opentelemetry-specification#346

[mauriciovasquezbernal]

Closing as open-telemetry/opentelemetry-specification#346 was merged.