fix(propagator-ot-trace): read sampled flag correctly from span context

The way the sampled flag is currently read from the span context will
break when more flags are introduced. This is mentioned explicitly in
the [specification](https://www.w3.org/TR/trace-context/#trace-flags).

propagators/opentelemetry-propagator-ot-trace/src/OTTracePropagator.ts

@@ -72,7 +72,9 @@ export class OTTracePropagator implements TextMapPropagator {
     setter.set(
       carrier,
       OT_SAMPLED_HEADER,
-      spanContext.traceFlags === TraceFlags.SAMPLED ? 'true' : 'false'
+      (spanContext.traceFlags & TraceFlags.SAMPLED) === TraceFlags.SAMPLED
+        ? 'true'
+        : 'false'
     );
 
     const baggage = propagation.getBaggage(context);

propagators/opentelemetry-propagator-ot-trace/test/OTTracePropagator.test.ts

@@ -78,6 +78,25 @@ describe('OTTracePropagator', () => {
       assert.strictEqual(carrier[OT_SAMPLED_HEADER], 'true');
     });
 
+    it('correctly reads the sampled flag even if other flags are set', () => {
+      const spanContext: SpanContext = {
+        traceId: '80f198ee56343ba864fe8b2a57d3eff7',
+        spanId: 'e457b5a2e4d86bd1',
+        // 81 = 1000 0001, so this sets the sampled flag (rightmost bit) and one other flag (leftmost bit, semantics unspecified at the time of writing)
+        traceFlags: 81,
+      };
+
+      propagator.inject(
+        trace.setSpan(ROOT_CONTEXT, trace.wrapSpanContext(spanContext)),
+        carrier,
+        defaultTextMapSetter
+      );
+
+      assert.strictEqual(carrier[OT_TRACE_ID_HEADER], '64fe8b2a57d3eff7');
+      assert.strictEqual(carrier[OT_SPAN_ID_HEADER], 'e457b5a2e4d86bd1');
+      assert.strictEqual(carrier[OT_SAMPLED_HEADER], 'true');
+    });
+
     it('injects context with unspecified trace flags', () => {
       const spanContext: SpanContext = {
         traceId: '80f198ee56343ba864fe8b2a57d3eff7',