feat(propagator): add extractor for xds router metadata

tracing/propagator.go

@@ -18,6 +18,7 @@ import (
 	"context"
 
 	"github.com/bytedance/gopkg/cloud/metainfo"
+	"go.opentelemetry.io/otel"
 	"go.opentelemetry.io/otel/baggage"
 	"go.opentelemetry.io/otel/propagation"
 	"go.opentelemetry.io/otel/trace"
@@ -71,3 +72,13 @@ func CGIVariableToHTTPHeaderMetadata(metadata map[string]string) map[string]stri
 	}
 	return res
 }
+
+// ExtractFromPropagator get metadata from propagator
+func ExtractFromPropagator(ctx context.Context) map[string]string {
+	metadata := metainfo.GetAllValues(ctx)
+	if metadata == nil {
+		metadata = make(map[string]string)
+	}
+	otel.GetTextMapPropagator().Inject(ctx, &metadataProvider{metadata: metadata})
+	return metadata
+}

tracing/propagator_test.go

@@ -23,6 +23,7 @@ import (
 	"github.com/stretchr/testify/assert"
 	"go.opentelemetry.io/contrib/propagators/b3"
 	"go.opentelemetry.io/contrib/propagators/ot"
+	"go.opentelemetry.io/otel"
 	"go.opentelemetry.io/otel/baggage"
 	"go.opentelemetry.io/otel/propagation"
 	"go.opentelemetry.io/otel/trace"
@@ -161,3 +162,42 @@ func TestCGIVariableToHTTPHeaderMetadata(t *testing.T) {
 		})
 	}
 }
+
+func TestExtractFromPropagator(t *testing.T) {
+	otel.SetTextMapPropagator(propagation.Baggage{})
+
+	type args struct {
+		ctx context.Context
+	}
+	tests := []struct {
+		name string
+		args args
+		want map[string]string
+	}{
+		{
+			name: "valid",
+			args: args{
+				ctx: metainfo.WithValue(context.Background(), "baggage", "foo=bar"),
+			},
+			want: map[string]string{
+				"baggage": "foo=bar",
+			},
+		},
+		{
+			name: "not valid",
+			args: args{
+				ctx: metainfo.WithValue(context.Background(), "other", "foo=bar"),
+			},
+			want: nil,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			ctx := otel.GetTextMapPropagator().Extract(
+				tt.args.ctx,
+				&metadataProvider{metadata: ExtractFromPropagator(tt.args.ctx)},
+			)
+			assert.Equal(t, baggage.FromContext(ctx).String(), tt.want["baggage"])
+		})
+	}
+}