improve express regex middleware path parsing (#3203)

Co-authored-by: Dominik Krejcik <dominik.krejcik@gmail.com>

packages/datadog-plugin-express/test/index.spec.js

@@ -705,6 +705,80 @@ describe('Plugin', () => {
           })
         })
 
+        it('long regex should not steal path', done => {
+          const app = express()
+
+          try {
+            app.use(/\/foo\/(bar|baz|bez)/, (req, res, next) => {
+              next()
+            })
+          } catch (err) {
+            // eslint-disable-next-line no-console
+            console.log('This version of Express (>4.0 <4.6) has broken support for regex routing. Skipping this test.')
+            this.skip && this.skip() // mocha allows dynamic skipping, tap does not
+            return done()
+          }
+
+          app.get('/foo/bar', (req, res) => {
+            res.status(200).send('')
+          })
+
+          getPort().then(port => {
+            agent
+              .use(traces => {
+                const spans = sort(traces[0])
+
+                expect(spans[0]).to.have.property('resource', 'GET /foo/bar')
+              })
+              .then(done)
+              .catch(done)
+
+            appListener = app.listen(port, 'localhost', () => {
+              axios
+                .get(`http://localhost:${port}/foo/bar`)
+                .catch(done)
+            })
+          })
+        })
+
+        it('long regex child of string router should not steal path', done => {
+          const app = express()
+          const router = express.Router()
+
+          try {
+            router.use(/\/(bar|baz|bez)/, (req, res, next) => {
+              next()
+            })
+            app.use('/foo', router)
+          } catch (err) {
+            // eslint-disable-next-line no-console
+            console.log('This version of Express (>4.0 <4.6) has broken support for regex routing. Skipping this test.')
+            this.skip && this.skip() // mocha allows dynamic skipping, tap does not
+            return done()
+          }
+
+          app.get('/foo/bar', (req, res) => {
+            res.status(200).send('')
+          })
+
+          getPort().then(port => {
+            agent
+              .use(traces => {
+                const spans = sort(traces[0])
+
+                expect(spans[0]).to.have.property('resource', 'GET /foo/bar')
+              })
+              .then(done)
+              .catch(done)
+
+            appListener = app.listen(port, 'localhost', () => {
+              axios
+                .get(`http://localhost:${port}/foo/bar`)
+                .catch(done)
+            })
+          })
+        })
+
         it('should not lose the current path on next', done => {
           const app = express()
           const Router = express.Router

packages/datadog-plugin-router/src/index.js

@@ -130,7 +130,7 @@ class RouterPlugin extends WebPlugin {
       route = context.stack.join('')
 
       // Longer route is more likely to be the actual route handler route.
-      if (route.length > context.route.length) {
+      if (isMoreSpecificThan(route, context.route)) {
         context.route = route
       }
     } else {
@@ -148,4 +148,15 @@ class RouterPlugin extends WebPlugin {
   }
 }
 
+function isMoreSpecificThan (routeA, routeB) {
+  if (!routeIsRegex(routeA) && routeIsRegex(routeB)) {
+    return true
+  }
+  return routeA.length > routeB.length
+}
+
+function routeIsRegex (route) {
+  return route.includes('(/') && route.includes('/)')
+}
+
 module.exports = RouterPlugin