fix: Updated express instrumentation to properly instrument an array of middleware defined on a route (#3473)

Author: bizob2828

lib/subscribers/express/route.js

@@ -33,6 +33,16 @@ class ExpressRouteSubscriber extends MiddlewareSubscriber {
         // express could have multiple routers, wrap them all
         for (let i = 0; i < routeArgs.length; i++) {
           const routeHandler = routeArgs[i]
+          // express supports an array of middlewares as well when defining route
+          // wrap each handler and reassign to args
+          if (Array.isArray(routeHandler)) {
+            for (let j = 0; j < routeHandler.length; j++) {
+              const handler = routeHandler[j]
+              routeArgs[i][j] = self.wrapper.wrap({ handler })
+            }
+            continue
+          }
+
           let segmentName = null
           let route = null
           if (routeHandler.stack) {

test/versioned/express/segments.test.js

@@ -784,6 +784,59 @@ test('when using a regular expression in path', function (t, end) {
   })
 })
 
+test('route defines middlewares as a series of arrays', function (t, end) {
+  const { app } = t.nr
+
+  function mw1(req, res, next) {
+    next()
+  }
+
+  function mw2(req, res, next) {
+    next()
+  }
+
+  function mw3(req, res, next) {
+    next()
+  }
+
+  function mw4(req, res, next) {
+    next()
+  }
+
+  function handler(req, res) {
+    res.end()
+  }
+
+  app.get('/test', [mw1, mw2], [mw3, mw4], handler)
+
+  runTest(t, '/test', function (root, transaction) {
+    assertSegments(
+      transaction.trace,
+      root,
+      ['Expressjs/Route Path: /test',
+        [
+        `${NAMES.EXPRESS.MIDDLEWARE}mw1`,
+        `${NAMES.EXPRESS.MIDDLEWARE}mw2`,
+        `${NAMES.EXPRESS.MIDDLEWARE}mw3`,
+        `${NAMES.EXPRESS.MIDDLEWARE}mw4`,
+        `${NAMES.EXPRESS.MIDDLEWARE}handler`
+        ]
+      ],
+      assertSegmentsOptions
+    )
+
+    checkMetrics(transaction.metrics, [
+      `${NAMES.EXPRESS.MIDDLEWARE}mw1//test`,
+      `${NAMES.EXPRESS.MIDDLEWARE}mw2//test`,
+      `${NAMES.EXPRESS.MIDDLEWARE}mw3//test`,
+      `${NAMES.EXPRESS.MIDDLEWARE}mw4//test`,
+      `${NAMES.EXPRESS.MIDDLEWARE}handler//test`
+    ], '/test')
+
+    end()
+  })
+})
+
 const codeLevelMetrics = [true, false]
 for (const enabled of codeLevelMetrics) {
   test(`Code Level Metrics ${enabled}`, function (t, end) {