✨Add NoopSpan: no-op implementation of Span (open-telemetry#45)

* Add DefaultSpan: no-op implementation of Span

* Implement setAttributes method based on pull/44

* Remove protected methods

* Rename DefaultSpan -> BaseSpan, return non-null SpanContext, Add TODOs

* Rename BaseSpan -> NoopSpan

* NoopSpan: return a real SpanContext for propagation

packages/opentelemetry-core/src/index.ts

@@ -15,3 +15,4 @@
  */
 
 export * from './resources/Resource';
+export * from './trace/NoopSpan';

packages/opentelemetry-core/src/trace/NoopSpan.ts

@@ -0,0 +1,70 @@
+/**
+ * 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
+ *
+ *      https://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 * as types from '@opentelemetry/types';
+import { SpanContext } from '@opentelemetry/types';
+
+/**
+ * The NoopSpan is the default {@link Span} that is used when no Span
+ * implementation is available. All operations are no-op except context
+ * propagation.
+ */
+export class NoopSpan implements types.Span {
+  constructor(private readonly _spanContext: SpanContext) {}
+
+  // Returns a SpanContext.
+  context(): types.SpanContext {
+    return this._spanContext;
+  }
+
+  // By default does nothing
+  setAttribute(key: string, value: unknown): this {
+    return this;
+  }
+
+  // By default does nothing
+  setAttributes(attributes: types.Attributes): this {
+    return this;
+  }
+
+  // By default does nothing
+  addEvent(name: string, attributes?: types.Attributes): this {
+    return this;
+  }
+
+  // By default does nothing
+  addLink(spanContext: types.SpanContext, attributes?: types.Attributes): this {
+    return this;
+  }
+
+  // By default does nothing
+  setStatus(status: types.Status): this {
+    return this;
+  }
+
+  // By default does nothing
+  updateName(name: string): this {
+    return this;
+  }
+
+  // By default does nothing
+  end(endTime?: number): void {}
+
+  // isRecordingEvents always returns false for noopSpan.
+  isRecordingEvents(): boolean {
+    return false;
+  }
+}

packages/opentelemetry-core/test/trace/NoopSpan.test.ts

@@ -0,0 +1,63 @@
+/**
+ * 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
+ *
+ *      https://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 * as assert from 'assert';
+import { NoopSpan } from '../../src/trace/NoopSpan';
+import { CanonicalCode, TraceOptions } from '@opentelemetry/types';
+
+describe('NoopSpan', () => {
+  it('do not crash', () => {
+    const spanContext = {
+      traceId: 'd4cda95b652f4a1592b449d5929fda1b',
+      spanId: '6e0c63257de34c92',
+      traceOptions: TraceOptions.UNSAMPLED,
+    };
+
+    const span = new NoopSpan(spanContext);
+    span.setAttribute('my_string_attribute', 'foo');
+    span.setAttribute('my_number_attribute', 123);
+    span.setAttribute('my_boolean_attribute', false);
+    span.setAttribute('my_obj_attribute', { a: true });
+    span.setAttribute('my_sym_attribute', Symbol('a'));
+    span.setAttributes({
+      my_string_attribute: 'foo',
+      my_number_attribute: 123,
+    });
+
+    span.addEvent('sent');
+    span.addEvent('sent', { id: '42', key: 'value' });
+
+    span.addLink({
+      traceId: 'd4cda95b652f4a1592b449d5929fda1b',
+      spanId: '6e0c63257de34c92',
+    });
+    span.addLink(
+      {
+        traceId: 'd4cda95b652f4a1592b449d5929fda1b',
+        spanId: '6e0c63257de34c92',
+      },
+      { id: '42', key: 'value' }
+    );
+
+    span.setStatus({ code: CanonicalCode.CANCELLED });
+
+    span.updateName('my-span');
+
+    assert.ok(!span.isRecordingEvents());
+    assert.deepStrictEqual(span.context(), spanContext);
+    span.end();
+  });
+});