fix: .cjs extension support for lambda functions (open-telemetry#1442)

plugins/node/opentelemetry-instrumentation-aws-lambda/src/instrumentation.ts

@@ -15,6 +15,7 @@
  */
 
 import * as path from 'path';
+import * as fs from 'fs';
 
 import {
   InstrumentationBase,
@@ -99,8 +100,15 @@ export class AwsLambdaInstrumentation extends InstrumentationBase {
     // Lambda loads user function using an absolute path.
     let filename = path.resolve(taskRoot, moduleRoot, module);
     if (!filename.endsWith('.js')) {
-      // Patching infrastructure currently requires a filename when requiring with an absolute path.
-      filename += '.js';
+      // its impossible to know in advance if the user has a cjs or js file.
+      // check that the .js file exists otherwise fallback to next known possibility
+      try {
+        fs.statSync(`${filename}.js`);
+        filename += '.js';
+      } catch (e) {
+        // fallback to .cjs
+        filename += '.cjs';
+      }
     }
 
     return [

plugins/node/opentelemetry-instrumentation-aws-lambda/test/integrations/lambda-handler.test.ts

@@ -861,5 +861,21 @@ describe('lambda handler', () => {
         assert.strictEqual(span.attributes[ERR_ATTR], error!.message);
       });
     });
+
+    describe('.cjs lambda bundle', () => {
+      it('should export a valid span', async () => {
+        initializeHandler('lambda-test/commonjs.handler');
+        const result = await lambdaRequire('lambda-test/commonjs.cjs').handler(
+          'arg',
+          ctx
+        );
+        assert.strictEqual(result, 'ok');
+        const spans = memoryExporter.getFinishedSpans();
+        const [span] = spans;
+        assert.strictEqual(spans.length, 1);
+        assertSpanSuccess(span);
+        assert.strictEqual(span.parentSpanId, undefined);
+      });
+    });
   });
 });

plugins/node/opentelemetry-instrumentation-aws-lambda/test/lambda-test/commonjs.cjs

@@ -0,0 +1,3 @@
+exports.handler = async function (event, context) {
+	return "ok";
+};