From 2be701b03cc7408ff8aa8dba4c372571954cdc45 Mon Sep 17 00:00:00 2001
From: Lukas Stracke <lukas.stracke@sentry.io>
Date: Fri, 26 Jul 2024 11:39:14 +0200
Subject: [PATCH] add new cls file, oops

---
 packages/browser-utils/src/metrics/cls.ts | 114 ++++++++++++++++++++++
 1 file changed, 114 insertions(+)
 create mode 100644 packages/browser-utils/src/metrics/cls.ts

diff --git a/packages/browser-utils/src/metrics/cls.ts b/packages/browser-utils/src/metrics/cls.ts
new file mode 100644
index 000000000000..c93705c86b1f
--- /dev/null
+++ b/packages/browser-utils/src/metrics/cls.ts
@@ -0,0 +1,114 @@
+import {
+  SEMANTIC_ATTRIBUTE_EXCLUSIVE_TIME,
+  SEMANTIC_ATTRIBUTE_SENTRY_MEASUREMENT_UNIT,
+  SEMANTIC_ATTRIBUTE_SENTRY_MEASUREMENT_VALUE,
+  SEMANTIC_ATTRIBUTE_SENTRY_OP,
+  SEMANTIC_ATTRIBUTE_SENTRY_ORIGIN,
+  getClient,
+  getCurrentScope,
+} from '@sentry/core';
+import type { SpanAttributes } from '@sentry/types';
+import { browserPerformanceTimeOrigin, dropUndefinedKeys, htmlTreeAsString, logger } from '@sentry/utils';
+import { DEBUG_BUILD } from '../debug-build';
+import { addClsInstrumentationHandler } from './instrument';
+import { msToSec, startStandaloneWebVitalSpan } from './utils';
+import { onHidden } from './web-vitals/lib/onHidden';
+
+/**
+ * Starts tracking the Cumulative Layout Shift on the current page and collects the value once
+ *
+ * - the page visibility is hidden
+ * - a navigation span is started (to stop CLS measurement for SPA soft navigations)
+ *
+ * Once either of these events triggers, the CLS value is sent as a standalone span and we stop
+ * measuring CLS.
+ */
+export function trackClsAsStandaloneSpan(): () => void {
+  let standaloneCLsValue = 0;
+  let standaloneClsEntry: LayoutShift | undefined;
+
+  // Cleanup for standalone span mode is handled in this function.
+  // Returning a no-op for API compatibility with `_trackCLS` measurement mode (saves some bytes)
+  const cleanupNoop = () => undefined;
+
+  if (!supportsLayoutShift()) {
+    return cleanupNoop;
+  }
+
+  let sentSpan = false;
+  function _collectClsOnce() {
+    if (sentSpan) {
+      return;
+    }
+    sendStandaloneClsSpan(standaloneCLsValue, standaloneClsEntry);
+    cleanupClsHandler();
+    sentSpan = true;
+  }
+
+  const cleanupClsHandler = addClsInstrumentationHandler(({ metric }) => {
+    const entry = metric.entries[metric.entries.length - 1] as LayoutShift | undefined;
+    if (!entry) {
+      return;
+    }
+    standaloneCLsValue = metric.value;
+    standaloneClsEntry = entry;
+  }, true);
+
+  // use pagehide event from web-vitals
+  onHidden(() => {
+    _collectClsOnce();
+  });
+
+  // Since the call chain of this function is synchronous and evaluates before the SDK client is created,
+  // we need to wait with subscribing to a client hook until the client is created. Therefore, we defer
+  // to the next tick after the SDK setup.
+  setTimeout(() => {
+    const unsubscribe = getClient()?.on('startNavigationSpan', () => {
+      _collectClsOnce();
+      typeof unsubscribe === 'function' && unsubscribe();
+    });
+  }, 0);
+
+  return cleanupNoop;
+}
+
+function sendStandaloneClsSpan(clsValue: number, entry: LayoutShift | undefined) {
+  DEBUG_BUILD && logger.log(`Sending CLS span (${clsValue})`);
+
+  const startTime = msToSec(browserPerformanceTimeOrigin as number) + (entry?.startTime || 0);
+  const duration = msToSec(entry?.duration || 0);
+  const routeName = getCurrentScope().getScopeData().transactionName;
+
+  // TODO: Is this fine / does it provide any value? Alternatively, we can
+  // - send the CLS source node as an attribute
+  // - do nothing at all and ignore the source node
+  const name = entry ? htmlTreeAsString(entry.sources[0]?.node) : 'Layout shift';
+
+  const attributes: SpanAttributes = dropUndefinedKeys({
+    [SEMANTIC_ATTRIBUTE_SENTRY_ORIGIN]: 'auto.http.browser.cls',
+    [SEMANTIC_ATTRIBUTE_SENTRY_OP]: 'ui.webvital.cls',
+    [SEMANTIC_ATTRIBUTE_EXCLUSIVE_TIME]: entry?.duration || 0,
+  });
+
+  const span = startStandaloneWebVitalSpan({
+    name,
+    transaction: routeName,
+    attributes,
+    startTime,
+  });
+
+  span?.addEvent('cls', {
+    [SEMANTIC_ATTRIBUTE_SENTRY_MEASUREMENT_UNIT]: '',
+    [SEMANTIC_ATTRIBUTE_SENTRY_MEASUREMENT_VALUE]: clsValue,
+  });
+
+  span?.end(startTime + duration);
+}
+
+function supportsLayoutShift(): boolean {
+  try {
+    return PerformanceObserver.supportedEntryTypes?.includes('layout-shift');
+  } catch {
+    return false;
+  }
+}