From c1f21f2612f76a5c8f953a2a38b9ce9b6fa6316e Mon Sep 17 00:00:00 2001
From: vmarchaud <contact@vmarchaud.fr>
Date: Sun, 13 Sep 2020 15:57:53 +0200
Subject: [PATCH] feat(api): propagate spanContext only using API #1456

---
 .../src/metrics/NoopMeter.ts                  | 12 ++----
 .../opentelemetry-api/src/trace/NoopTracer.ts | 38 ++++++++++++++++--
 .../noop-implementations/noop-tracer.test.ts  | 40 ++++++++++++++++++-
 3 files changed, 77 insertions(+), 13 deletions(-)

diff --git a/packages/opentelemetry-api/src/metrics/NoopMeter.ts b/packages/opentelemetry-api/src/metrics/NoopMeter.ts
index 765a0fd8ae3..f3c8feeddd1 100644
--- a/packages/opentelemetry-api/src/metrics/NoopMeter.ts
+++ b/packages/opentelemetry-api/src/metrics/NoopMeter.ts
@@ -131,24 +131,21 @@ export class NoopMetric<T> implements UnboundMetric<T> {
   }
 }
 
-export class NoopCounterMetric
-  extends NoopMetric<BoundCounter>
+export class NoopCounterMetric extends NoopMetric<BoundCounter>
   implements Counter {
   add(value: number, labels: Labels) {
     this.bind(labels).add(value);
   }
 }
 
-export class NoopValueRecorderMetric
-  extends NoopMetric<BoundValueRecorder>
+export class NoopValueRecorderMetric extends NoopMetric<BoundValueRecorder>
   implements ValueRecorder {
   record(value: number, labels: Labels) {
     this.bind(labels).record(value);
   }
 }
 
-export class NoopBaseObserverMetric
-  extends NoopMetric<BoundBaseObserver>
+export class NoopBaseObserverMetric extends NoopMetric<BoundBaseObserver>
   implements BaseObserver {
   observation() {
     return {
@@ -158,8 +155,7 @@ export class NoopBaseObserverMetric
   }
 }
 
-export class NoopBatchObserverMetric
-  extends NoopMetric<void>
+export class NoopBatchObserverMetric extends NoopMetric<void>
   implements BatchObserver {}
 
 export class NoopBoundCounter implements BoundCounter {
diff --git a/packages/opentelemetry-api/src/trace/NoopTracer.ts b/packages/opentelemetry-api/src/trace/NoopTracer.ts
index 2fdc4dc3104..8c2d22defeb 100644
--- a/packages/opentelemetry-api/src/trace/NoopTracer.ts
+++ b/packages/opentelemetry-api/src/trace/NoopTracer.ts
@@ -14,8 +14,17 @@
  * limitations under the License.
  */
 
-import { Span, SpanOptions, Tracer } from '..';
-import { NOOP_SPAN } from './NoopSpan';
+import { Span, SpanOptions, Tracer, SpanContext } from '..';
+import { Context } from '@opentelemetry/context-base';
+import { NoopSpan, NOOP_SPAN } from './NoopSpan';
+import { isSpanContextValid } from './spancontext-utils';
+
+/**
+ * Internal key used by the core to store spanContext in the global context
+ */
+export const _EXTRACTED_SPAN_CONTEXT_KEY = Context.createKey(
+  'OpenTelemetry Context Key EXTRACTED_SPAN_CONTEXT'
+);
 
 /**
  * No-op implementations of {@link Tracer}.
@@ -26,8 +35,20 @@ export class NoopTracer implements Tracer {
   }
 
   // startSpan starts a noop span.
-  startSpan(name: string, options?: SpanOptions): Span {
-    return NOOP_SPAN;
+  startSpan(name: string, options?: SpanOptions, context?: Context): Span {
+    const parent = options?.parent;
+    const parentFromContext =
+      context && context.getValue(_EXTRACTED_SPAN_CONTEXT_KEY);
+    if (isSpanContext(parent) && isSpanContextValid(parent)) {
+      return new NoopSpan(parent);
+    } else if (
+      isSpanContext(parentFromContext) &&
+      isSpanContextValid(parentFromContext)
+    ) {
+      return new NoopSpan(parentFromContext);
+    } else {
+      return NOOP_SPAN;
+    }
   }
 
   withSpan<T extends (...args: unknown[]) => ReturnType<T>>(
@@ -42,4 +63,13 @@ export class NoopTracer implements Tracer {
   }
 }
 
+function isSpanContext(spanContext: any): spanContext is SpanContext {
+  return (
+    typeof spanContext === 'object' &&
+    typeof spanContext['spanId'] === 'string' &&
+    typeof spanContext['traceId'] === 'string' &&
+    typeof spanContext['traceFlags'] === 'number'
+  );
+}
+
 export const NOOP_TRACER = new NoopTracer();
diff --git a/packages/opentelemetry-api/test/noop-implementations/noop-tracer.test.ts b/packages/opentelemetry-api/test/noop-implementations/noop-tracer.test.ts
index 62ed24bb8ee..c6bbe7d0cd2 100644
--- a/packages/opentelemetry-api/test/noop-implementations/noop-tracer.test.ts
+++ b/packages/opentelemetry-api/test/noop-implementations/noop-tracer.test.ts
@@ -15,7 +15,15 @@
  */
 
 import * as assert from 'assert';
-import { NoopTracer, NOOP_SPAN, SpanKind } from '../../src';
+import {
+  NoopTracer,
+  NOOP_SPAN,
+  SpanContext,
+  SpanKind,
+  TraceFlags,
+  context,
+  _EXTRACTED_SPAN_CONTEXT_KEY,
+} from '../../src';
 
 describe('NoopTracer', () => {
   it('should not crash', () => {
@@ -51,4 +59,34 @@ describe('NoopTracer', () => {
     const patchedFn = tracer.bind(fn, NOOP_SPAN);
     return patchedFn();
   });
+
+  it('should propagate valid spanContext on the span (from parent)', () => {
+    const tracer = new NoopTracer();
+    const parent: SpanContext = {
+      traceId: 'd4cda95b652f4a1592b449d5929fda1b',
+      spanId: '6e0c63257de34c92',
+      traceFlags: TraceFlags.NONE,
+    };
+    const span = tracer.startSpan('test-1', { parent });
+    assert(span.context().traceId === parent.traceId);
+    assert(span.context().spanId === parent.spanId);
+    assert(span.context().traceFlags === parent.traceFlags);
+  });
+
+  it('should propagate valid spanContext on the span (from context)', () => {
+    const tracer = new NoopTracer();
+    const parent: SpanContext = {
+      traceId: 'd4cda95b652f4a1592b449dd92ffda3b',
+      spanId: '6e0c63ffe4e34c42',
+      traceFlags: TraceFlags.NONE,
+    };
+    const span = tracer.startSpan(
+      'test-1',
+      {},
+      context.active().setValue(_EXTRACTED_SPAN_CONTEXT_KEY, parent)
+    );
+    assert(span.context().traceId === parent.traceId);
+    assert(span.context().spanId === parent.spanId);
+    assert(span.context().traceFlags === parent.traceFlags);
+  });
 });