Initial commit for Correlation Context API

This change removes Distributed Context and replaces it with the Correlations Context API. Things to do:
- add more tests
- implement correlation context propagation and add it to the default propagator

Signed-off-by: Alex Boten <[email protected]>

opentelemetry-api/src/opentelemetry/correlationcontext/__init__.py

@@ -0,0 +1,124 @@
+# Copyright 2020, 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 abc
+import itertools
+import string
+import typing
+from contextlib import contextmanager
+
+from opentelemetry.context import attach, get_value, set_value
+from opentelemetry.context.context import Context
+
+CORRELATION_CONTEXT_KEY = "correlation-context"
+
+
+class CorrelationContext(abc.ABC):
+    """A container for correlation context"""
+
+    @abc.abstractmethod
+    def get_correlations(self, context: typing.Optional[Context] = None):
+        """ Returns the name/value pairs in the CorrelationContext
+        
+        Args:
+            context: the Context to use. If not set, uses current Context
+
+        Returns:
+            name/value pairs in the CorrelationContext
+        """
+
+    @abc.abstractmethod
+    def get_correlation(
+        self, name, context: typing.Optional[Context] = None
+    ) -> typing.Optional[object]:
+        """ Provides access to the value for a name/value pair by a prior event
+        
+        Args:
+            name: the name of the value to retrieve
+            context: the Context to use. If not set, uses current Context
+
+        Returns:
+            the value associated with the given name, or null if the given name is
+            not present.
+        """
+
+    @abc.abstractmethod
+    def set_correlation(
+        self, name, value, context: typing.Optional[Context] = None
+    ) -> Context:
+        """
+
+        Args:
+            name: the name of the value to set
+            value: the value to set
+            context: the Context to use. If not set, uses current Context
+
+        Returns:
+            a Context with the value updated
+        """
+
+    @abc.abstractmethod
+    def remove_correlation(
+        self, name, context: typing.Optional[Context] = None
+    ) -> Context:
+        """
+
+        Args:
+            name: the name of the value to remove
+            context: the Context to use. If not set, uses current Context
+
+        Returns:
+            a Context with the name/value removed
+        """
+
+    @abc.abstractmethod
+    def clear_correlations(
+        self, context: typing.Optional[Context] = None
+    ) -> Context:
+        """
+        Args:
+            context: the Context to use. If not set, uses current Context
+
+        Returns:
+            a Context with all correlations removed
+        """
+
+
+class DefaultCorrelationContext(CorrelationContext):
+    """ Default no-op implementation of CorrelationContext """
+
+    def get_correlations(
+        self, context: typing.Optional[Context] = None
+    ) -> typing.Dict:
+        return {}
+
+    def get_correlation(
+        self, name, context: typing.Optional[Context] = None
+    ) -> typing.Optional[object]:
+        return None
+
+    def set_correlation(
+        self, name, value, context: typing.Optional[Context] = None
+    ) -> Context:
+        return context
+
+    def remove_correlation(
+        self, name, context: typing.Optional[Context] = None
+    ) -> Context:
+        return context
+
+    def clear_correlations(
+        self, context: typing.Optional[Context] = None
+    ) -> Context:
+        return context

opentelemetry-api/tests/correlationcontext/test_correlation_context.py

@@ -0,0 +1,23 @@
+# Copyright 2020, 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 import correlationcontext
+
+
+class TestCorrelationContext(unittest.TestCase):
+    def test_correlation_context(self):
+        default_context = correlationcontext.DefaultCorrelationContext()
+        self.assertEqual(default_context.get_correlations(), {})