Adding the Resource API

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

@@ -11,3 +11,45 @@
 # 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 abc import ABC, abstractmethod
+from typing import Dict, Union
+
+
+class Resource(ABC):
+    """This the interface that resources must implement"""
+    def __init__(self, labels: Dict[str, str]):
+        """Construct a resource.
+
+        Direct calling of the constructor is discouraged, as it cannot
+        take advantage of caching and restricts to the type of object
+        that can be returned.
+        """
+        self._labels = labels
+
+    @staticmethod
+    def create(labels: Dict[str, str]) -> "Resource":
+        """create a new resource.
+
+        Args:
+            labels: the labels that define the resource
+
+        Returns:
+            The resource with the labels in question
+        """
+    @property
+    @abstractmethod
+    def labels(self) -> Dict[str, str]:
+        """Return the label dictionary associated with this resource.
+
+        Returns:
+            A dictionary with the labels of the resource
+        """
+    def merge(self, other: Union["Resource", None]) -> "Resource":
+        """Return a resource with the union of labels for both resources.
+
+        Labels that exist in the main Resource take
+        precedence unless the label value is the empty string.
+
+        Args:
+            other: the resource to merge in
+        """

opentelemetry-sdk/src/opentelemetry/sdk/resources/__init__.py

@@ -0,0 +1,44 @@
+# Copyright 2019, 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 typing import Any, Dict, Union
+from opentelemetry.resources import Resource
+
+
+class DefaultResource(Resource):
+    def __init__(self, labels):
+        self._labels = labels
+
+    @property
+    def labels(self):
+        return self._labels
+
+    @staticmethod
+    def create(labels):
+        return DefaultResource(labels)
+
+    def merge(self, other):
+        if other is None:
+            return self
+        if not self._labels:
+            return other
+        merged_labels = self.labels.copy()
+        for key, value in other.labels.items():
+            if key not in merged_labels or merged_labels[key] == "":
+                merged_labels[key] = value
+        return DefaultResource(merged_labels)
+
+    def __eq__(self, other: object) -> bool:
+        if not isinstance(other, DefaultResource):
+            return False
+        return self.labels == other.labels

opentelemetry-sdk/tests/resources/test_init.py

@@ -0,0 +1,28 @@
+import unittest
+from opentelemetry.sdk.resources import DefaultResource
+
+
+class TestResources(unittest.TestCase):
+    def test_resource_merge(self):
+        left = DefaultResource({"service": "ui"})
+        right = DefaultResource({"host": "service-host"})
+        self.assertEqual(
+            left.merge(right),
+            DefaultResource({
+                "service": "ui",
+                "host": "service-host"
+            }))
+
+    def test_resource_merge_empty_string(self):
+        """
+        labels from the source Resource take
+        precedence, with the exception of the empty string.
+        """
+        left = DefaultResource({"service": "ui", "host": ""})
+        right = DefaultResource({"host": "service-host", "service": "not-ui"})
+        self.assertEqual(
+            left.merge(right),
+            DefaultResource({
+                "service": "ui",
+                "host": "service-host"
+            }))