feat(views): add FilteringAttributesProcessor (#2733)

experimental/packages/opentelemetry-sdk-metrics-base/src/view/AttributesProcessor.ts

@@ -43,4 +43,22 @@ export class NoopAttributesProcessor extends AttributesProcessor {
   }
 }
 
+/**
+ * {@link AttributesProcessor} that filters by allowed attribute names and drops any names that are not in the
+ * allow list.
+ */
+export class FilteringAttributesProcessor extends AttributesProcessor {
+  constructor(private _allowedAttributeNames: string[]) {
+    super();
+  }
+
+  process(incoming: Attributes, _context: Context): Attributes {
+    const filteredAttributes: Attributes = {};
+    Object.keys(incoming)
+      .filter(attributeName => this._allowedAttributeNames.includes(attributeName))
+      .forEach(attributeName => filteredAttributes[attributeName] = incoming[attributeName]);
+    return filteredAttributes;
+  }
+}
+
 const NOOP = new NoopAttributesProcessor;

experimental/packages/opentelemetry-sdk-metrics-base/test/view/AttributesProcessor.test.ts

@@ -17,6 +17,7 @@
 import * as assert from 'assert';
 import { context } from '@opentelemetry/api';
 import { NoopAttributesProcessor } from '../../src/view/AttributesProcessor';
+import { FilteringAttributesProcessor } from '../../src/view/AttributesProcessor';
 
 describe('NoopAttributesProcessor', () => {
   const processor = new NoopAttributesProcessor();
@@ -30,3 +31,25 @@ describe('NoopAttributesProcessor', () => {
     );
   });
 });
+
+describe('FilteringAttributesProcessor', () => {
+  it('should not add keys when attributes do not exist', () => {
+    const processor = new FilteringAttributesProcessor(['foo', 'bar']);
+    assert.deepStrictEqual(
+      processor.process({}, context.active()), {});
+  });
+
+  it('should only keep allowed attributes', () => {
+    const processor = new FilteringAttributesProcessor(['foo', 'bar']);
+    assert.deepStrictEqual(
+      processor.process({
+        foo: 'fooValue',
+        bar: 'barValue',
+        baz: 'bazValue'
+      }, context.active()),
+      {
+        foo: 'fooValue',
+        bar: 'barValue'
+      });
+  });
+});