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

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

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

@@ -29,21 +29,31 @@ from asgiref.compatibility import guarantee_single_callable
 from opentelemetry import context, propagators, trace
 from opentelemetry.instrumentation.asgi.version import __version__  # noqa
 from opentelemetry.instrumentation.utils import http_status_to_status_code
+from opentelemetry.trace.propagation.textmap import DictGetter
 from opentelemetry.trace.status import Status, StatusCode
 
 
-def get_header_from_scope(scope: dict, header_name: str) -> typing.List[str]:
-    """Retrieve a HTTP header value from the ASGI scope.
+class CarrierGetter(DictGetter):
+    def get(self, carrier: dict, key: str) -> typing.List[str]:
+        """Getter implementation to retrieve a HTTP header value from the ASGI
+        scope.
 
-    Returns:
-        A list with a single string with the header value if it exists, else an empty list.
-    """
-    headers = scope.get("headers")
-    return [
-        value.decode("utf8")
-        for (key, value) in headers
-        if key.decode("utf8") == header_name
-    ]
+        Args:
+            carrier: ASGI scope object
+            key: header name in scope
+        Returns:
+            A list with a single string with the header value if it exists,
+             else an empty list.
+        """
+        headers = carrier.get("headers")
+        return [
+            _value.decode("utf8")
+            for (_key, _value) in headers
+            if _key.decode("utf8") == key
+        ]
+
+
+carrier_getter = CarrierGetter()
 
 
 def collect_request_attributes(scope):
@@ -72,10 +82,10 @@ def collect_request_attributes(scope):
     http_method = scope.get("method")
     if http_method:
         result["http.method"] = http_method
-    http_host_value = ",".join(get_header_from_scope(scope, "host"))
+    http_host_value = ",".join(carrier_getter.get(scope, "host"))
     if http_host_value:
         result["http.server_name"] = http_host_value
-    http_user_agent = get_header_from_scope(scope, "user-agent")
+    http_user_agent = carrier_getter.get(scope, "user-agent")
     if len(http_user_agent) > 0:
         result["http.user_agent"] = http_user_agent[0]
 
@@ -154,9 +164,7 @@ class OpenTelemetryMiddleware:
         if scope["type"] not in ("http", "websocket"):
             return await self.app(scope, receive, send)
 
-        token = context.attach(
-            propagators.extract(get_header_from_scope, scope)
-        )
+        token = context.attach(propagators.extract(carrier_getter, scope))
         span_name, additional_attributes = self.span_details_callback(scope)
 
         try: