fix: crash in Lambda handler with ELB or API Gateway event with no 'h…

…eaders' (#3289)

If the lambda handler object for an ELB- or API Gateway-triggered Lambda
invocation did not have a 'headers' field, then the Lambda
instrumentation would crash. I'm not sure how to get an event with no
'headers' field, but we should still be defensive here.

Fixes: #3286

lib/lambda.js

@@ -144,7 +144,7 @@ function setApiGatewayData (agent, trans, event, context, faasId, isColdStart) {
         : undefined),
       method: requestContext.http.method,
       url: event.rawPath + (event.rawQueryString ? '?' + event.rawQueryString : ''),
-      headers: event.normedHeaders,
+      headers: event.normedHeaders || {},
       socket: { remoteAddress: requestContext.http.sourceIp },
       body: event.body
     }
@@ -162,7 +162,7 @@ function setApiGatewayData (agent, trans, event, context, faasId, isColdStart) {
       url: requestContext.path + (event.queryStringParameters
         ? '?' + querystring.encode(event.queryStringParameters)
         : ''),
-      headers: event.normedHeaders,
+      headers: event.normedHeaders || {},
       socket: { remoteAddress: requestContext.identity && requestContext.identity.sourceIp },
       // Limitation: Note that `getContextFromRequest` does *not* use this body,
       // because API Gateway payload format 1.0 does not include the
@@ -264,7 +264,7 @@ function setElbData (agent, trans, event, context, faasId, isColdStart) {
       event.queryStringParameters && Object.keys(event.queryStringParameters) > 0
         ? '?' + querystring.encode(event.queryStringParameters)
         : ''),
-    headers: event.normedHeaders,
+    headers: event.normedHeaders || {},
     body: event.body,
     bodyIsBase64Encoded: event.isBase64Encoded
   }

lib/parsers.js

@@ -28,6 +28,7 @@ const {
  *    However, some cases (e.g. Lambda and Azure Functions instrumentation)
  *    create a pseudo-req object that matches well enough for this function.
  *    Some relevant fields: (TODO: document all used fields)
+ *    - `headers` - Required. An object.
  *    - `body` - The incoming request body, if available. The `json` and
  *      `payload` fields are also checked to accomodate some web frameworks.
  *    - `bodyIsBase64Encoded` - An optional boolean. If `true`, then the `body`
@@ -109,9 +110,21 @@ function getContextFromResponse (res, conf, isError) {
   return context
 }
 
+/**
+ * Extract appropriate `{transaction,error}.context.user` from an HTTP
+ * request object.
+ *
+ * @param {Object} req - Typically `req` is a Node.js `http.IncomingMessage`.
+ *    However, some cases (e.g. Lambda and Azure Functions instrumentation)
+ *    create a pseudo-req object that matches well enough for this function.
+ *    Some relevant fields: (TODO: document all used fields)
+ *    - `headers` - Required. An object.
+ */
 function getUserContextFromRequest (req) {
   var user = req.user || basicAuth(req) || req.session
-  if (!user) return
+  if (!user) {
+    return
+  }
 
   var context = {}
 

test/lambda/transaction2.test.js

@@ -12,6 +12,9 @@
 // "AgentMock". The mock doesn't fully test the "transaction" intake event
 // object creation path.)
 
+const fs = require('fs')
+const path = require('path')
+
 const lambdaLocal = require('lambda-local')
 const tape = require('tape')
 
@@ -35,7 +38,7 @@ process.env.AWS_LAMBDA_LOG_STREAM_NAME = '2021/11/01/[1.0]lambda/e7b05091b39b4aa
 process.env.AWS_PROFILE = 'fake'
 
 function loadFixture (file) {
-  return require('./fixtures/' + file)
+  return JSON.parse(fs.readFileSync(path.join(__dirname, 'fixtures', file)))
 }
 
 tape.test('lambda transactions', function (suite) {
@@ -215,8 +218,41 @@ tape.test('lambda transactions', function (suite) {
         t.equal(trans.context.request.method, 'POST', 'transaction.context.request.method')
         t.deepEqual(trans.context.response, { status_code: 502, headers: {} }, 'transaction.context.response')
       }
+    },
+    {
+      name: 'API Gateway event, but without ".headers" field: APM agent should not crash',
+      event: (function () {
+        const ev = loadFixture('aws_api_http_test_data.json')
+        delete ev.headers
+        return ev
+      })(),
+      handler: (_event, _context, cb) => {
+        cb(null, { statusCode: 200, body: 'hi' })
+      },
+      checkApmEvents: (t, events) => {
+        const trans = events[1].transaction
+        t.equal(trans.name, 'POST /default/the-function-name', 'transaction.name')
+        t.equal(trans.outcome, 'success', 'transaction.outcome')
+      }
+    },
+    {
+      name: 'ELB event, but without ".headers" field: APM agent should not crash',
+      event: (function () {
+        const ev = loadFixture('aws_elb_test_data.json')
+        delete ev.headers
+        return ev
+      })(),
+      handler: (_event, _context, cb) => {
+        cb(null, { statusCode: 200, body: 'hi' })
+      },
+      checkApmEvents: (t, events) => {
+        const trans = events[1].transaction
+        t.equal(trans.faas.name, 'fixture-function-name', 'transaction.faas.name')
+        t.equal(trans.outcome, 'success', 'transaction.outcome')
+      }
     }
   ]
+
   testCases.forEach(c => {
     suite.test(c.name, { skip: c.skip || false }, function (t) {
       const handler = c.handler || (