A TextMap Propagator is a Propagator that performs injection and extraction with ASCII keys and values.

An example of configuring the TextMap Propagator to inject and extract Baggage and TraceContext:

  {text_map_propagators, [trace_context, baggage]},

The propagators are then used at the points that cross service communication is performed. By default inject and extract work on a generic list of 2-tuple's with binary string keys and values. A user defined function for setting a key/value in the carrier and for getting the value of a key from a carrier can be passed as an argument. For example, injecting and extracting to and from Hackney headers could be done with Hackney specific functions:

  set_header(Key, Value, Headers) ->
    hackney_headers:store(Key, Value, Headers).
 
  some_fun_calling_hackney() ->
    Headers = otel_propagator_text_map:inject(opentelemetry:get_text_map_injector(), hackney_headers:new(), fun set_header/2),
    ...

An example of extraction in an Elli request handler:

  get_header(Req, Key) ->
    elli_request:get_header(Key, Req, Default).
 
  handle(Req, _Args) ->
    otel_propagator_text_map:extract(Req, fun get_header/2),
    ...
    {ok, [], <<"hello world">>}.