feat(nitro-utils): Add patchEventHandler helper for nitro (#14614)

E2E tests and usage in nuxt in:
#14612

---------

Co-authored-by: Sigrid Huemer <32902192+s1gr1d@users.noreply.github.com>

Author: andreiborza

packages/nitro-utils/src/index.ts

@@ -1,3 +1,5 @@
+export { patchEventHandler } from './nitro/patchEventHandler';
+
 export {
   wrapServerEntryWithDynamicImport,
   type WrapServerEntryPluginOptions,

packages/nitro-utils/src/nitro/patchEventHandler.ts

@@ -0,0 +1,39 @@
+import { getDefaultIsolationScope, getIsolationScope, logger, withIsolationScope } from '@sentry/core';
+import type { EventHandler } from 'h3';
+import { flushIfServerless } from '../util/flush';
+
+/**
+ * A helper to patch a given `h3` event handler, ensuring that
+ * requests are properly isolated and data is flushed to Sentry.
+ */
+export function patchEventHandler(handler: EventHandler): EventHandler {
+  return new Proxy(handler, {
+    async apply(handlerTarget, handlerThisArg, handlerArgs: Parameters<EventHandler>) {
+      // In environments where we cannot make use of the OTel
+      // http instrumentation (e.g. when using top level import
+      // of the server instrumentation file instead of
+      // `--import` or dynamic import, like on vercel)
+      // we still need to ensure requests are properly isolated
+      // by comparing the current isolation scope to the default
+      // one.
+      // Requests are properly isolated if they differ.
+      // If that's not the case, we fork the isolation scope here.
+      const isolationScope = getIsolationScope();
+      const newIsolationScope = isolationScope === getDefaultIsolationScope() ? isolationScope.clone() : isolationScope;
+
+      logger.log(
+        `Patched h3 event handler. ${
+          isolationScope === newIsolationScope ? 'Using existing' : 'Created new'
+        } isolation scope.`,
+      );
+
+      return withIsolationScope(newIsolationScope, async () => {
+        try {
+          return await handlerTarget.apply(handlerThisArg, handlerArgs);
+        } finally {
+          await flushIfServerless();
+        }
+      });
+    },
+  });
+}

packages/nitro-utils/src/util/flush.ts

@@ -0,0 +1,30 @@
+import { GLOBAL_OBJ, flush, getClient, logger, vercelWaitUntil } from '@sentry/core';
+
+/**
+ * Flushes Sentry for serverless environments.
+ */
+export async function flushIfServerless(): Promise<void> {
+  const isServerless = !!process.env.LAMBDA_TASK_ROOT || !!process.env.VERCEL || !!process.env.NETLIFY;
+
+  // @ts-expect-error - this is not typed
+  if (GLOBAL_OBJ[Symbol.for('@vercel/request-context')]) {
+    vercelWaitUntil(flushWithTimeout());
+  } else if (isServerless) {
+    await flushWithTimeout();
+  }
+}
+
+/**
+ * Flushes Sentry.
+ */
+export async function flushWithTimeout(): Promise<void> {
+  const isDebug = getClient()?.getOptions()?.debug;
+
+  try {
+    isDebug && logger.log('Flushing events...');
+    await flush(2000);
+    isDebug && logger.log('Done flushing events');
+  } catch (e) {
+    isDebug && logger.log('Error while flushing events:\n', e);
+  }
+}