Converted TextMap propagator getter to a class and added keys method (#1196)

Co-authored-by: alrex <aboten@lightstep.com>

instrumentation/opentelemetry-instrumentation-celery/src/opentelemetry/instrumentation/celery/__init__.py

@@ -67,7 +67,7 @@ from opentelemetry import propagators, trace
 from opentelemetry.instrumentation.celery import utils
 from opentelemetry.instrumentation.celery.version import __version__
 from opentelemetry.instrumentation.instrumentor import BaseInstrumentor
-from opentelemetry.trace.propagation import get_current_span
+from opentelemetry.trace.propagation.textmap import DictGetter
 from opentelemetry.trace.status import Status, StatusCode
 
 logger = logging.getLogger(__name__)
@@ -84,6 +84,20 @@ _TASK_NAME_KEY = "celery.task_name"
 _MESSAGE_ID_ATTRIBUTE_NAME = "messaging.message_id"
 
 
+class CarrierGetter(DictGetter):
+    def get(self, carrier, key):
+        value = getattr(carrier, key, [])
+        if isinstance(value, str) or not isinstance(value, Iterable):
+            value = (value,)
+        return value
+
+    def keys(self, carrier):
+        return []
+
+
+carrier_getter = CarrierGetter()
+
+
 class CeleryInstrumentor(BaseInstrumentor):
     def _instrument(self, **kwargs):
         tracer_provider = kwargs.get("tracer_provider")
@@ -118,7 +132,7 @@ class CeleryInstrumentor(BaseInstrumentor):
             return
 
         request = task.request
-        tracectx = propagators.extract(carrier_extractor, request) or None
+        tracectx = propagators.extract(carrier_getter, request) or None
 
         logger.debug("prerun signal start task_id=%s", task_id)
 
@@ -246,10 +260,3 @@ class CeleryInstrumentor(BaseInstrumentor):
         # Use `str(reason)` instead of `reason.message` in case we get
         # something that isn't an `Exception`
         span.set_attribute(_TASK_RETRY_REASON_KEY, str(reason))
-
-
-def carrier_extractor(carrier, key):
-    value = getattr(carrier, key, [])
-    if isinstance(value, str) or not isinstance(value, Iterable):
-        value = (value,)
-    return value