Implement IsSampled for OpenTelemetry bridgeSpanContext (#3570)

* Add IsSampled to OpenTracing bridge

* Add entry to CHANGELOG

* Add note to the README

* Update CHANGELOG.md

Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>

* Update bridge/opentracing/README.md

Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>

* Update bridge/opentracing/README.md

Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>

* Update bridge/opentracing/README.md

Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>

* Update bridge/opentracing/README.md

Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>

* Add PR ID to changelog note

---------

Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>

CHANGELOG.md

@@ -30,6 +30,7 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
     - `OtelLibraryName` -> `OTelLibraryName`
     - `OtelLibraryVersion` -> `OTelLibraryVersion`
     - `OtelStatusDescription` -> `OTelStatusDescription`
+- Add `bridgetSpanContext.IsSampled` to `go.opentelemetry.io/otel/bridget/opentracing` to expose whether span is sampled or not. (#3570)
 - The `WithInstrumentationAttributes` option to `go.opentelemetry.io/otel/metric`. (#3738)
 - The `WithInstrumentationAttributes` option to `go.opentelemetry.io/otel/trace`. (#3739)
 

bridge/opentracing/README.md

@@ -38,3 +38,22 @@ When you have started an OpenTracing Span, make sure the OpenTelemetry knows abo
 	// Propagate the otSpan to both OpenTracing and OpenTelemetry
 	// instrumentation by using the ctxWithOTAndOTelSpan context.
 ```
+
+## Extended Functionality
+
+The bridge functionality can be extended beyond the OpenTracing API.
+
+### `SpanContext.IsSampled`
+
+Return the underlying OpenTelemetry [`Span.IsSampled`](https://pkg.go.dev/go.opentelemetry.io/otel/trace#SpanContext.IsSampled) value by converting a `bridgeSpanContext`.
+
+```go
+type samplable interface {
+	IsSampled() bool
+}
+
+var sc opentracing.SpanContext = ...
+if s, ok := sc.(samplable); ok && s.IsSampled() {
+	// Do something with sc knowing it is sampled.
+}
+```

bridge/opentracing/bridge.go

@@ -72,6 +72,10 @@ func (c *bridgeSpanContext) ForeachBaggageItem(handler func(k, v string) bool) {
 	}
 }
 
+func (c *bridgeSpanContext) IsSampled() bool {
+	return c.otelSpanContext.IsSampled()
+}
+
 func (c *bridgeSpanContext) setBaggageItem(restrictedKey, value string) {
 	crk := http.CanonicalHeaderKey(restrictedKey)
 	m, err := baggage.NewMember(crk, value)

bridge/opentracing/bridge_test.go

@@ -257,6 +257,10 @@ func (t *testTextMapWriter) Set(key, val string) {
 	(*t.m)[key] = val
 }
 
+type samplable interface {
+	IsSampled() bool
+}
+
 func TestBridgeTracer_ExtractAndInject(t *testing.T) {
 	bridge := NewBridgeTracer()
 	bridge.SetTextMapPropagator(new(testTextMapPropagator))
@@ -510,3 +514,35 @@ func Test_otTagsToOTelAttributesKindAndError(t *testing.T) {
 		})
 	}
 }
+
+func TestBridge_SpanContext_IsSampled(t *testing.T) {
+	testCases := []struct {
+		name     string
+		flags    trace.TraceFlags
+		expected bool
+	}{
+		{
+			name:     "not sampled",
+			flags:    0,
+			expected: false,
+		},
+		{
+			name:     "sampled",
+			flags:    trace.FlagsSampled,
+			expected: true,
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			tracer := internal.NewMockTracer()
+			tracer.TraceFlags = tc.flags
+
+			b, _ := NewTracerPair(tracer)
+			s := b.StartSpan("abc")
+			sc := s.Context()
+
+			assert.Equal(t, tc.expected, sc.(samplable).IsSampled())
+		})
+	}
+}

bridge/opentracing/internal/mock.go

@@ -48,6 +48,7 @@ type MockTracer struct {
 	SpareTraceIDs         []trace.TraceID
 	SpareSpanIDs          []trace.SpanID
 	SpareContextKeyValues []MockContextKeyValue
+	TraceFlags            trace.TraceFlags
 
 	randLock sync.Mutex
 	rand     *rand.Rand
@@ -76,7 +77,7 @@ func (t *MockTracer) Start(ctx context.Context, name string, opts ...trace.SpanS
 	spanContext := trace.NewSpanContext(trace.SpanContextConfig{
 		TraceID:    t.getTraceID(ctx, &config),
 		SpanID:     t.getSpanID(),
-		TraceFlags: 0,
+		TraceFlags: t.TraceFlags,
 	})
 	span := &MockSpan{
 		mockTracer:     t,