Register custom k6 metrics on module init

This is a fix for a breaking change introduced in k6 v0.38.0[1].

[1]: grafana/k6#2442

common/context.go

@@ -33,6 +33,7 @@ const (
 	ctxKeyPid
 	ctxKeyHooks
 	ctxKeyVU
+	ctxKeyCustomK6Metrics
 )
 
 func WithHooks(ctx context.Context, hooks *Hooks) context.Context {
@@ -87,6 +88,20 @@ func GetVU(ctx context.Context) k6modules.VU {
 	return nil
 }
 
+// WithCustomK6Metrics attaches the CustomK6Metrics object to the context.
+func WithCustomK6Metrics(ctx context.Context, k6m *CustomK6Metrics) context.Context {
+	return context.WithValue(ctx, ctxKeyCustomK6Metrics, k6m)
+}
+
+// GetCustomK6Metrics returns the CustomK6Metrics object attached to the context.
+func GetCustomK6Metrics(ctx context.Context) *CustomK6Metrics {
+	v := ctx.Value(ctxKeyCustomK6Metrics)
+	if k6m, ok := v.(*CustomK6Metrics); ok {
+		return k6m
+	}
+	return nil
+}
+
 // contextWithDoneChan returns a new context that is canceled either
 // when the done channel is closed or ctx is canceled.
 func contextWithDoneChan(ctx context.Context, done chan struct{}) context.Context {

common/frame_session.go

@@ -62,6 +62,7 @@ type FrameSession struct {
 	parent         *FrameSession
 	manager        *FrameManager
 	networkManager *NetworkManager
+	k6Metrics      *CustomK6Metrics
 
 	targetID target.ID
 	windowID browser.WindowID
@@ -103,6 +104,7 @@ func NewFrameSession(
 		eventCh:              make(chan Event),
 		childSessions:        make(map[cdp.FrameID]*FrameSession),
 		vu:                   GetVU(ctx),
+		k6Metrics:            GetCustomK6Metrics(ctx),
 		logger:               l,
 		serializer: &logrus.Logger{
 			Out:       l.log.Out,
@@ -714,12 +716,12 @@ func (fs *FrameSession) onPageLifecycle(event *cdppage.EventLifecycleEvent) {
 		fs.manager.frameLifecycleEvent(event.FrameID, LifecycleEventDOMContentLoad)
 	}
 
-	eventToMetric := map[string]*k6stats.Metric{
-		"load":                 BrowserLoaded,
-		"DOMContentLoaded":     BrowserDOMContentLoaded,
-		"firstPaint":           BrowserFirstPaint,
-		"firstContentfulPaint": BrowserFirstContentfulPaint,
-		"firstMeaningfulPaint": BrowserFirstMeaningfulPaint,
+	eventToMetric := map[string]*k6metrics.Metric{
+		"load":                 fs.k6Metrics.BrowserLoaded,
+		"DOMContentLoaded":     fs.k6Metrics.BrowserDOMContentLoaded,
+		"firstPaint":           fs.k6Metrics.BrowserFirstPaint,
+		"firstContentfulPaint": fs.k6Metrics.BrowserFirstContentfulPaint,
+		"firstMeaningfulPaint": fs.k6Metrics.BrowserFirstMeaningfulPaint,
 	}
 
 	if m, ok := eventToMetric[event.Name]; ok {

common/metrics.go

@@ -20,12 +20,30 @@
 
 package common
 
-import k6stats "go.k6.io/k6/stats"
+import k6metrics "go.k6.io/k6/metrics"
 
-var (
-	BrowserDOMContentLoaded     = k6stats.New("browser_dom_content_loaded", k6stats.Trend, k6stats.Time)
-	BrowserFirstPaint           = k6stats.New("browser_first_paint", k6stats.Trend, k6stats.Time)
-	BrowserFirstContentfulPaint = k6stats.New("browser_first_contentful_paint", k6stats.Trend, k6stats.Time)
-	BrowserFirstMeaningfulPaint = k6stats.New("browser_first_meaningful_paint", k6stats.Trend, k6stats.Time)
-	BrowserLoaded               = k6stats.New("browser_loaded", k6stats.Trend, k6stats.Time)
-)
+// CustomK6Metrics are the custom k6 metrics used by xk6-browser.
+type CustomK6Metrics struct {
+	BrowserDOMContentLoaded     *k6metrics.Metric
+	BrowserFirstPaint           *k6metrics.Metric
+	BrowserFirstContentfulPaint *k6metrics.Metric
+	BrowserFirstMeaningfulPaint *k6metrics.Metric
+	BrowserLoaded               *k6metrics.Metric
+}
+
+// RegisterCustomK6Metrics creates and registers our custom metrics with the k6
+// VU Registry and returns our internal struct pointer.
+func RegisterCustomK6Metrics(registry *k6metrics.Registry) *CustomK6Metrics {
+	return &CustomK6Metrics{
+		BrowserDOMContentLoaded: registry.MustNewMetric(
+			"browser_dom_content_loaded", k6metrics.Trend, k6metrics.Time),
+		BrowserFirstPaint: registry.MustNewMetric(
+			"browser_first_paint", k6metrics.Trend, k6metrics.Time),
+		BrowserFirstContentfulPaint: registry.MustNewMetric(
+			"browser_first_contentful_paint", k6metrics.Trend, k6metrics.Time),
+		BrowserFirstMeaningfulPaint: registry.MustNewMetric(
+			"browser_first_meaningful_paint", k6metrics.Trend, k6metrics.Time),
+		BrowserLoaded: registry.MustNewMetric(
+			"browser_loaded", k6metrics.Trend, k6metrics.Time),
+	}
+}

main.go

@@ -41,9 +41,10 @@ type (
 
 	// JSModule is the entrypoint into the browser JS module.
 	JSModule struct {
-		vu      k6modules.VU
-		Devices map[string]common.Device
-		Version string
+		vu        k6modules.VU
+		k6Metrics *common.CustomK6Metrics
+		Devices   map[string]common.Device
+		Version   string
 	}
 
 	// ModuleInstance represents an instance of the JS module.
@@ -65,11 +66,13 @@ func New() *RootModule {
 // NewModuleInstance implements the k6modules.Module interface to return
 // a new instance for each VU.
 func (*RootModule) NewModuleInstance(vu k6modules.VU) k6modules.Instance {
+	k6m := common.RegisterCustomK6Metrics(vu.InitEnv().Registry)
 	return &ModuleInstance{
 		mod: &JSModule{
-			vu:      vu,
-			Devices: common.GetDevices(),
-			Version: version,
+			vu:        vu,
+			k6Metrics: k6m,
+			Devices:   common.GetDevices(),
+			Version:   version,
 		},
 	}
 }
@@ -92,6 +95,7 @@ func (m *JSModule) Launch(browserName string, opts goja.Value) api.Browser {
 	}()*/
 
 	ctx := common.WithVU(m.vu.Context(), m.vu)
+	ctx = common.WithCustomK6Metrics(ctx, m.k6Metrics)
 
 	if browserName == "chromium" {
 		bt := chromium.NewBrowserType(ctx)

tests/test_browser.go

@@ -102,6 +102,10 @@ func newTestBrowser(tb testing.TB, opts ...interface{}) *testBrowser {
 		mockVU.CtxField = ctx
 	}
 
+	registry := k6metrics.NewRegistry()
+	k6m := common.RegisterCustomK6Metrics(registry)
+	mockVU.CtxField = common.WithCustomK6Metrics(mockVU.CtxField, k6m)
+
 	var (
 		state = mockVU.StateField
 		rt    = mockVU.RuntimeField