fix(lambda): fix lambda instr to work with a '.' in the handler module path

CHANGELOG.asciidoc

@@ -33,6 +33,24 @@ Notes:
 
 See the <<upgrade-to-v4>> guide.
 
+==== Unreleased
+
+[float]
+===== Breaking changes
+
+[float]
+===== Features
+
+[float]
+===== Bug fixes
+
+* Fix AWS Lambda instrumentation to work with a "handler" string that includes
+  a period (`.`) in the module path. E.g. the leading `.` in `Handler: ./src/functions/myfunc/handler.main`. ({issues}4293[#4293]).
+
+[float]
+===== Chores
+
+
 [[release-notes-4.8.0]]
 ==== 4.8.0 - 2024/10/08
 

lib/instrumentation/index.js

@@ -374,7 +374,7 @@ Instrumentation.prototype.clearPatches = function (modules) {
 
 // If in a Lambda environment, find its handler and add a patcher for it.
 Instrumentation.prototype._maybeLoadLambdaPatcher = function () {
-  let lambdaHandlerInfo = getLambdaHandlerInfo(process.env);
+  let lambdaHandlerInfo = getLambdaHandlerInfo(process.env, this._log);
 
   if (lambdaHandlerInfo && this._patcherReg.has(lambdaHandlerInfo.modName)) {
     this._log.warn(

lib/lambda.js

@@ -817,18 +817,34 @@ function isLambdaExecutionEnvironment() {
 // .mjs file extension (which indicates an ECMAScript/import module, which the
 // agent does not support.
 //
-// @param string taskRoot
-// @param string handlerModule
-// @return string
-function getFilePath(taskRoot, handlerModule) {
-  let filePath = path.resolve(taskRoot, `${handlerModule}.js`);
-  if (!fs.existsSync(filePath)) {
-    filePath = path.resolve(taskRoot, `${handlerModule}.cjs`);
+// TODO: support "extensionless"? per https://github.com/aws/aws-lambda-nodejs-runtime-interface-client/blob/v3.2.1/src/UserFunction.js#L149 Is this for a dir/index.js?
+// TODO: support ESM and .mjs
+//
+// @param {string} taskRoot
+// @param {string} moduleRoot - The subdir under `taskRoot` holding the module.
+// @param {string} module - The module name.
+// @return {string | null}
+function getFilePath(taskRoot, moduleRoot, module) {
+  const lambdaStylePath = path.resolve(taskRoot, moduleRoot, module);
+  if (fs.existsSync(lambdaStylePath + '.js')) {
+    return lambdaStylePath + '.js';
+  } else if (fs.existsSync(lambdaStylePath + '.cjs')) {
+    return lambdaStylePath + '.cjs';
+  } else {
+    return null;
   }
-  return filePath;
 }
 
-function getLambdaHandlerInfo(env) {
+/**
+ * Gather module and export info for the Lambda "handler" string.
+ *
+ * Compare to the Node.js Lambda runtime's equivalent processing here:
+ * https://github.com/aws/aws-lambda-nodejs-runtime-interface-client/blob/v3.2.1/src/UserFunction.js#L288
+ *
+ * @param {object} env - The process environment.
+ * @param {any} [logger] - Optional logger for trace/warn log output.
+ */
+function getLambdaHandlerInfo(env, logger) {
   if (
     !isLambdaExecutionEnvironment() ||
     !env._HANDLER ||
@@ -837,22 +853,48 @@ function getLambdaHandlerInfo(env) {
     return null;
   }
 
-  // extract module name and "path" from handler using the same regex as the runtime
-  // from https://github.com/aws/aws-lambda-nodejs-runtime-interface-client/blob/c31c41ffe5f2f03ae9e8589b96f3b005e2bb8a4a/src/utils/UserFunction.ts#L21
-  const functionExpression = /^([^.]*)\.(.*)$/;
-  const match = env._HANDLER.match(functionExpression);
+  // Dev Note: This intentionally uses some of the same var names at
+  // https://github.com/aws/aws-lambda-nodejs-runtime-interface-client/blob/v3.2.1/src/UserFunction.js#L288
+  const fullHandlerString = env._HANDLER;
+  const moduleAndHandler = path.basename(fullHandlerString);
+  const moduleRoot = fullHandlerString.substring(
+    0,
+    fullHandlerString.indexOf(moduleAndHandler),
+  );
+  const FUNCTION_EXPR = /^([^.]*)\.(.*)$/;
+  const match = moduleAndHandler.match(FUNCTION_EXPR);
   if (!match || match.length !== 3) {
+    if (logger) {
+      logger.warn(
+        { fullHandlerString, moduleAndHandler },
+        'Lambda handler string did not match FUNCTION_EXPR',
+      );
+    }
+    return null;
+  }
+  const module = match[1];
+  const handlerPath = match[2];
+
+  const moduleAbsPath = getFilePath(env.LAMBDA_TASK_ROOT, moduleRoot, module);
+  if (!moduleAbsPath) {
+    if (logger) {
+      logger.warn(
+        { fullHandlerString, moduleRoot, module },
+        'could not find Lambda handler module file (ESM not yet supported)',
+      );
+    }
     return null;
   }
-  const handlerModule = match[1].split('/').pop();
-  const handlerFunctionPath = match[2];
-  const handlerFilePath = getFilePath(env.LAMBDA_TASK_ROOT, match[1]);
 
-  return {
-    filePath: handlerFilePath,
-    modName: handlerModule,
-    propPath: handlerFunctionPath,
+  const lambdaHandlerInfo = {
+    filePath: moduleAbsPath,
+    modName: module,
+    propPath: handlerPath,
   };
+  if (logger) {
+    logger.trace({ fullHandlerString, lambdaHandlerInfo }, 'lambdaHandlerInfo');
+  }
+  return lambdaHandlerInfo;
 }
 
 function lowerCaseObjectKeys(obj) {

test/lambda/fixtures/foo.js

@@ -0,0 +1,13 @@
+/*
+ * Copyright Elasticsearch B.V. and other contributors where applicable.
+ * Licensed under the BSD 2-Clause License; you may not use this file except in
+ * compliance with the BSD 2-Clause License.
+ */
+
+'use strict';
+
+module.exports = {
+  bar: function (event, context) {
+    return 'fake handler';
+  },
+};

test/lambda/fixtures/handlermodule.cjs

@@ -0,0 +1,13 @@
+/*
+ * Copyright Elasticsearch B.V. and other contributors where applicable.
+ * Licensed under the BSD 2-Clause License; you may not use this file except in
+ * compliance with the BSD 2-Clause License.
+ */
+
+module.exports = {
+  lambda: {
+    foo: function myHandler(event, context) {
+      return 'hi';
+    },
+  },
+};

test/lambda/wrapper.test.js

@@ -37,6 +37,24 @@ tape.test('getLambdaHandlerInfo', function (suite) {
     t.end();
   });
 
+  suite.test('extracts info with leading "./" on _HANDLER path', function (t) {
+    process.env.AWS_LAMBDA_FUNCTION_NAME = 'foo';
+
+    const info = getLambdaHandlerInfo({
+      _HANDLER: './lambda.bar',
+      LAMBDA_TASK_ROOT: path.resolve(__dirname, 'fixtures'),
+    });
+
+    t.equals(
+      info.filePath,
+      path.resolve(__dirname, 'fixtures', 'lambda.js'),
+      'extracted handler file path',
+    );
+    t.equals(info.modName, 'lambda', 'extracted handler module');
+    t.equals(info.propPath, 'bar', 'extracted handler propPath');
+    t.end();
+  });
+
   suite.test('extracts info with extended path, cjs extension', function (t) {
     process.env.AWS_LAMBDA_FUNCTION_NAME = 'foo';
 
@@ -93,7 +111,7 @@ tape.test('getLambdaHandlerInfo', function (suite) {
   suite.test('malformed handler: too few', function (t) {
     process.env.AWS_LAMBDA_FUNCTION_NAME = 'foo';
     const handler = getLambdaHandlerInfo({
-      LAMBDA_TASK_ROOT: '/var/task',
+      LAMBDA_TASK_ROOT: path.resolve(__dirname, 'fixtures'),
       _HANDLER: 'foo',
     });
 
@@ -104,13 +122,13 @@ tape.test('getLambdaHandlerInfo', function (suite) {
   suite.test('longer handler', function (t) {
     process.env.AWS_LAMBDA_FUNCTION_NAME = 'foo';
     const handler = getLambdaHandlerInfo({
-      LAMBDA_TASK_ROOT: '/var/task',
+      LAMBDA_TASK_ROOT: path.resolve(__dirname, 'fixtures'),
       _HANDLER: 'foo.baz.bar',
     });
 
     t.equals(
       handler.filePath,
-      path.resolve('/var', 'task', 'foo.cjs'),
+      path.resolve(__dirname, 'fixtures', 'foo.js'),
       'extracted handler file path',
     );
     t.equals(handler.modName, 'foo', 'extracted handler module name');