ddtrace/tracer/textmap: Added none as a supported propagator for trac…

…e context extraction and injection (#1610)

ddtrace/tracer/textmap.go

@@ -177,6 +177,9 @@ func getPropagators(cfg *PropagatorConfig, env string) []Propagator {
 	if ps == "" {
 		return defaultPs
 	}
+	if ps == "none" {
+		return nil
+	}
 	var list []Propagator
 	if cfg.B3 {
 		list = append(list, &propagatorB3{})
@@ -190,6 +193,9 @@ func getPropagators(cfg *PropagatorConfig, env string) []Propagator {
 				// propagatorB3 hasn't already been added, add a new one.
 				list = append(list, &propagatorB3{})
 			}
+		case "none":
+			log.Warn("Propagator \"none\" has no effect when combined with other propagators. "+
+				"To disable the propagator, set `%s=none`", env)
 		default:
 			log.Warn("unrecognized propagator: %s\n", v)
 		}

ddtrace/tracer/textmap_test.go

@@ -501,6 +501,7 @@ func testB3(t *testing.T, b3Header string) {
 func TestB3(t *testing.T) {
 	testB3(t, "b3")
 	testB3(t, "b3multi")
+	testB3(t, "none,b3multi")
 
 	t.Run("config", func(t *testing.T) {
 		os.Setenv("DD_PROPAGATION_STYLE_INJECT", "datadog")
@@ -555,6 +556,87 @@ func TestB3(t *testing.T) {
 	})
 }
 
+func TestNonePropagator(t *testing.T) {
+	t.Run("inject/none", func(t *testing.T) {
+		t.Setenv("DD_PROPAGATION_STYLE_INJECT", "none")
+		tracer := newTracer()
+		root := tracer.StartSpan("web.request").(*span)
+		root.SetTag(ext.SamplingPriority, -1)
+		root.SetBaggageItem("item", "x")
+		ctx, ok := root.Context().(*spanContext)
+		ctx.traceID = 1
+		ctx.spanID = 1
+		headers := TextMapCarrier(map[string]string{})
+		err := tracer.Inject(ctx, headers)
+
+		assert := assert.New(t)
+		assert.True(ok)
+		assert.Nil(err)
+		assert.Len(headers, 0)
+	})
+
+	t.Run("inject/none,b3", func(t *testing.T) {
+		t.Setenv("DD_PROPAGATION_STYLE_INJECT", "none,b3")
+		tp := new(testLogger)
+		tracer := newTracer(WithLogger(tp))
+		// reinitializing to capture log output, since propagators are parsed before logger is set
+		tracer.config.propagator = NewPropagator(&PropagatorConfig{})
+		root := tracer.StartSpan("web.request").(*span)
+		root.SetTag(ext.SamplingPriority, -1)
+		root.SetBaggageItem("item", "x")
+		ctx, ok := root.Context().(*spanContext)
+		ctx.traceID = 1
+		ctx.spanID = 1
+		headers := TextMapCarrier(map[string]string{})
+		err := tracer.Inject(ctx, headers)
+
+		assert := assert.New(t)
+		assert.True(ok)
+		assert.Nil(err)
+		assert.Equal("0000000000000001", headers[b3TraceIDHeader])
+		assert.Equal("0000000000000001", headers[b3SpanIDHeader])
+		assert.Contains(tp.lines[0], "Propagator \"none\" has no effect when combined with other propagators. "+
+			"To disable the propagator, set `DD_PROPAGATION_STYLE_INJECT=none`")
+	})
+
+	t.Run("extract/none", func(t *testing.T) {
+		t.Setenv("DD_PROPAGATION_STYLE_EXTRACT", "none")
+		assert := assert.New(t)
+		tracer := newTracer()
+		root := tracer.StartSpan("web.request").(*span)
+		root.SetTag(ext.SamplingPriority, -1)
+		root.SetBaggageItem("item", "x")
+		headers := TextMapCarrier(map[string]string{})
+
+		_, err := tracer.Extract(headers)
+
+		assert.Equal(err, ErrSpanContextNotFound)
+		assert.Len(headers, 0)
+	})
+
+	t.Run("inject,extract/none", func(t *testing.T) {
+		t.Setenv("DD_PROPAGATION_STYLE_INJECT", "none")
+		t.Setenv("DD_PROPAGATION_STYLE_EXTRACT", "none")
+		tracer := newTracer()
+		root := tracer.StartSpan("web.request").(*span)
+		root.SetTag(ext.SamplingPriority, -1)
+		root.SetBaggageItem("item", "x")
+		ctx, ok := root.Context().(*spanContext)
+		ctx.traceID = 1
+		ctx.spanID = 1
+		headers := TextMapCarrier(map[string]string{})
+		err := tracer.Inject(ctx, headers)
+
+		assert := assert.New(t)
+		assert.True(ok)
+		assert.Nil(err)
+		assert.Len(headers, 0)
+
+		_, err = tracer.Extract(headers)
+		assert.Equal(err, ErrSpanContextNotFound)
+	})
+}
+
 func assertTraceTags(t *testing.T, expected, actual string) {
 	assert.ElementsMatch(t, strings.Split(expected, ","), strings.Split(actual, ","))
 }