Case insensitive header key retrieval for asgi instrumentation (#308)

Author: garnertan

CHANGELOG.md

@@ -10,6 +10,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Remove `component` span attribute in instrumentations. 
   `opentelemetry-instrumentation-aiopg`, `opentelemetry-instrumentation-dbapi` Remove unused `database_type` parameter from `trace_integration` function.
   ([#301](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/301))
+- `opentelemetry-instrumentation-asgi` Return header values using case insensitive keys
+  ([#308](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/308))
 
 ## [0.17b0](https://github.com/open-telemetry/opentelemetry-python-contrib/releases/tag/v0.17b0) - 2021-01-20
 

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

@@ -47,6 +47,11 @@ def get(
                 else None.
         """
         headers = carrier.get("headers")
+        if not headers:
+            return None
+
+        # asgi header keys are in lower case
+        key = key.lower()
         decoded = [
             _value.decode("utf8")
             for (_key, _value) in headers

instrumentation/opentelemetry-instrumentation-asgi/tests/test_getter.py

@@ -0,0 +1,50 @@
+# Copyright The OpenTelemetry Authors
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from unittest import TestCase
+
+from opentelemetry.instrumentation.asgi import CarrierGetter
+
+
+class TestCarrierGetter(TestCase):
+    def test_get_none(self):
+        getter = CarrierGetter()
+        carrier = {}
+        val = getter.get(carrier, "test")
+        self.assertIsNone(val)
+
+    def test_get_(self):
+        getter = CarrierGetter()
+        carrier = {"headers": [(b"test-key", b"val")]}
+        expected_val = ["val"]
+        self.assertEqual(
+            getter.get(carrier, "Test-Key"),
+            expected_val,
+            "Should be case insensitive",
+        )
+        self.assertEqual(
+            getter.get(carrier, "test-key"),
+            expected_val,
+            "Should be case insensitive",
+        )
+        self.assertEqual(
+            getter.get(carrier, "TEST-KEY"),
+            expected_val,
+            "Should be case insensitive",
+        )
+
+    def test_keys(self):
+        getter = CarrierGetter()
+        keys = getter.keys({})
+        self.assertEqual(keys, [])