feat service: introduce labels for logs/recorder (#104)

ctx/value.go

@@ -100,3 +100,17 @@ func ClientIDFromContext(ctx context.Context) ClientID {
 	v, _ := ctx.Value(clientIDKey{}).(ClientID)
 	return v
 }
+
+// labelsKey saves the static service labels.
+type labelsKey struct{}
+
+// ContextWithLabels returns a new context carrying the given service labels.
+func ContextWithLabels(ctx context.Context, labels map[string]string) context.Context {
+	return context.WithValue(ctx, labelsKey{}, labels)
+}
+
+// LabelsFromContext returns the service labels stored in the context, or nil.
+func LabelsFromContext(ctx context.Context) map[string]string {
+	v, _ := ctx.Value(labelsKey{}).(map[string]string)
+	return v
+}

ctx/value_test.go

@@ -3,6 +3,7 @@ package ctx
 import (
 	"context"
 	"net"
+	"reflect"
 	"testing"
 )
 
@@ -149,6 +150,29 @@ func TestClientIDFromContext_WrongType(t *testing.T) {
 	}
 }
 
+func TestContextWithLabels(t *testing.T) {
+	labels := map[string]string{"tenant": "acme", "region": "eu"}
+	ctx := ContextWithLabels(context.Background(), labels)
+
+	got := LabelsFromContext(ctx)
+	if !reflect.DeepEqual(got, labels) {
+		t.Errorf("LabelsFromContext() = %v, want %v", got, labels)
+	}
+}
+
+func TestLabelsFromContext_Empty(t *testing.T) {
+	if got := LabelsFromContext(context.Background()); got != nil {
+		t.Errorf("LabelsFromContext(empty) = %v, want nil", got)
+	}
+}
+
+func TestLabelsFromContext_WrongType(t *testing.T) {
+	ctx := context.WithValue(context.Background(), labelsKey{}, "not-a-map")
+	if got := LabelsFromContext(ctx); got != nil {
+		t.Errorf("LabelsFromContext(wrong type) = %v, want nil", got)
+	}
+}
+
 func TestMultipleValuesInContext(t *testing.T) {
 	ctx := context.Background()
 	ctx = ContextWithSrcAddr(ctx, &net.TCPAddr{IP: net.ParseIP("10.0.0.1"), Port: 8080})