Activate ESM loader hook of the "import-in-the-middle" library for ES…

… (EcmaScript) based user handlers

nodejs/packages/layer/scripts/otel-handler

@@ -2,7 +2,7 @@
 
 set -ef -o pipefail
 
-export NODE_OPTIONS="${NODE_OPTIONS} --require /opt/wrapper.js"
+export NODE_OPTIONS="${NODE_OPTIONS} --import /opt/loader.mjs --require /opt/wrapper.js"
 
 if [[ $OTEL_RESOURCE_ATTRIBUTES != *"service.name="* ]]; then
   export OTEL_RESOURCE_ATTRIBUTES="service.name=${AWS_LAMBDA_FUNCTION_NAME},${OTEL_RESOURCE_ATTRIBUTES}"

nodejs/packages/layer/src/loader.mjs

@@ -0,0 +1,71 @@
+import { register } from 'module';
+import * as path from 'path';
+import * as fs from 'fs';
+
+function _hasFolderPackageJsonTypeModule(folder) {
+  if (folder.endsWith('/node_modules')) {
+    return false;
+  }
+  let pj = path.join(folder, '/package.json');
+  if (fs.existsSync(pj)) {
+    try {
+      let pkg = JSON.parse(fs.readFileSync(pj).toString());
+      if (pkg) {
+        if (pkg.type === 'module') {
+          return true;
+        } else {
+          return false;
+        }
+      }
+    } catch (e) {
+      console.warn(`${pj} cannot be read, it will be ignored for ES module detection purposes.`, e);
+      return false;
+    }
+  }
+  if (folder === '/') {
+    return false;
+  }
+  return _hasFolderPackageJsonTypeModule(path.resolve(folder, '..'));
+}
+
+function _hasPackageJsonTypeModule(file) {
+  let jsPath = file + '.js';
+  if (fs.existsSync(jsPath)) {
+    return _hasFolderPackageJsonTypeModule(path.resolve(path.dirname(jsPath)));
+  }
+  return false;
+}
+
+function _resolveHandlerFileName() {
+  const taskRoot = process.env.LAMBDA_TASK_ROOT;
+  const handlerDef = process.env._HANDLER;
+  const handler = path.basename(handlerDef);
+  const moduleRoot = handlerDef.substr(0, handlerDef.length - handler.length);
+  const [module, _] = handler.split('.', 2);
+  return path.resolve(taskRoot, moduleRoot, module);
+}
+
+function _isHandlerAnESModule() {
+  const handlerFileName = _resolveHandlerFileName();
+  if (fs.existsSync(handlerFileName + '.mjs')) {
+    return true;
+  } else if (fs.existsSync(handlerFileName + '.cjs')) {
+    return false;
+  } else {
+    return _hasPackageJsonTypeModule(handlerFileName);
+  }
+}
+
+if (_isHandlerAnESModule()) {
+  /*
+  We could activate ESM loader hook of the "import-in-the-middle" library,
+  - by "--loader=import-in-the-middle/hook.mjs" Node CLI option, but "--loader" option has been deprecated
+  - or by "--import=import-in-the-middle/hook.mjs" Node CLI option, but in this case,
+    there will always be "import-in-the-middle" hook initialization overhead even for non-ESM (CommonJS) modules
+
+  Hence, instead, we initialize "import-in-the-middle" hook only for ES (EcmaScript) based user handlers
+  to prevent redundant "import-in-the-middle" hook initialization overhead during coldstart
+  of the CommonJS based user handlers.
+   */
+  register('import-in-the-middle/hook.mjs', import.meta.url);
+}