Return none for Getter if key does not exist

opentelemetry-api/CHANGELOG.md

@@ -4,6 +4,8 @@
 
 - Add `fields` to propagators
   ([#1374](https://github.com/open-telemetry/opentelemetry-python/pull/1374))
+- Return `None` for `DictGetter` if key not found
+  ([#1449](https://github.com/open-telemetry/opentelemetry-python/pull/1449))
 
 ## Version 0.16b0
 

opentelemetry-api/src/opentelemetry/baggage/propagation/__init__.py

@@ -101,7 +101,7 @@ def _format_baggage(baggage_entries: typing.Mapping[str, object]) -> str:
 
 
 def _extract_first_element(
-    items: typing.Iterable[textmap.TextMapPropagatorT],
+    items: typing.Optional[typing.Iterable[textmap.TextMapPropagatorT]],
 ) -> typing.Optional[textmap.TextMapPropagatorT]:
     if items is None:
         return None

opentelemetry-api/src/opentelemetry/trace/propagation/textmap.py

@@ -29,7 +29,9 @@ class Getter(typing.Generic[TextMapPropagatorT]):
 
     """
 
-    def get(self, carrier: TextMapPropagatorT, key: str) -> typing.List[str]:
+    def get(
+        self, carrier: TextMapPropagatorT, key: str
+    ) -> typing.Optional[typing.List[str]]:
         """Function that can retrieve zero
         or more values from the carrier. In the case that
         the value does not exist, returns an empty list.
@@ -38,8 +40,8 @@ def get(self, carrier: TextMapPropagatorT, key: str) -> typing.List[str]:
             carrier: An object which contains values that are used to
                     construct a Context.
             key: key of a field in carrier.
-        Returns: first value of the propagation key or an empty list if the
-                key doesn't exist.
+        Returns: first value of the propagation key or None if the key doesn't
+                exist.
         """
         raise NotImplementedError()
 
@@ -58,8 +60,10 @@ def keys(self, carrier: TextMapPropagatorT) -> typing.List[str]:
 class DictGetter(Getter[typing.Dict[str, CarrierValT]]):
     def get(
         self, carrier: typing.Dict[str, CarrierValT], key: str
-    ) -> typing.List[str]:
-        val = carrier.get(key, [])
+    ) -> typing.Optional[typing.List[str]]:
+        val = carrier.get(key, None)
+        if val is None:
+            return None
         if isinstance(val, typing.Iterable) and not isinstance(val, str):
             return list(val)
         return [val]

opentelemetry-api/src/opentelemetry/trace/propagation/tracecontext.py

@@ -91,7 +91,10 @@ def extract(
             return trace.set_span_in_context(trace.INVALID_SPAN, context)
 
         tracestate_headers = getter.get(carrier, self._TRACESTATE_HEADER_NAME)
-        tracestate = _parse_tracestate(tracestate_headers)
+        if tracestate_headers is None:
+            tracestate = None
+        else:
+            tracestate = _parse_tracestate(tracestate_headers)
 
         span_context = trace.SpanContext(
             trace_id=int(trace_id, 16),

opentelemetry-api/src/opentelemetry/trace/span.py

@@ -175,8 +175,8 @@ def __new__(
         trace_id: int,
         span_id: int,
         is_remote: bool,
-        trace_flags: "TraceFlags" = DEFAULT_TRACE_OPTIONS,
-        trace_state: "TraceState" = DEFAULT_TRACE_STATE,
+        trace_flags: typing.Optional["TraceFlags"] = DEFAULT_TRACE_OPTIONS,
+        trace_state: typing.Optional["TraceState"] = DEFAULT_TRACE_STATE,
     ) -> "SpanContext":
         if trace_flags is None:
             trace_flags = DEFAULT_TRACE_OPTIONS

opentelemetry-api/tests/trace/propagation/test_textmap.py

@@ -0,0 +1,42 @@
+# 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.
+
+import unittest
+
+from opentelemetry.trace.propagation.textmap import DictGetter
+
+
+class TestDictGetter(unittest.TestCase):
+    def test_get_none(self):
+        getter = DictGetter()
+        carrier = {}
+        val = getter.get(carrier, "test")
+        self.assertIsNone(val)
+
+    def test_get_str(self):
+        getter = DictGetter()
+        carrier = {"test": "val"}
+        val = getter.get(carrier, "test")
+        self.assertEqual(val, ["val"])
+
+    def test_get_iter(self):
+        getter = DictGetter()
+        carrier = {"test": ["val"]}
+        val = getter.get(carrier, "test")
+        self.assertEqual(val, ["val"])
+
+    def test_keys(self):
+        getter = DictGetter()
+        keys = getter.keys({"test": "val"})
+        self.assertEqual(keys, ["test"])