fix(instr-express): normalize paths with double slashes (#1995)

* fix(instr-express): normalize paths with double slashes

* remove unnecessary listener count from test

---------

Co-authored-by: Marc Pichler <marc.pichler@dynatrace.com>

plugins/node/opentelemetry-instrumentation-express/src/instrumentation.ts

@@ -197,7 +197,9 @@ export class ExpressInstrumentation extends InstrumentationBase<
         storeLayerPath(req, layerPath);
         const route = (req[_LAYERS_STORE_PROPERTY] as string[])
           .filter(path => path !== '/' && path !== '/*')
-          .join('');
+          .join('')
+          // remove duplicate slashes to normalize route
+          .replace(/\/{2,}/g, '/');
 
         const attributes: Attributes = {
           [SemanticAttributes.HTTP_ROUTE]: route.length > 0 ? route : '/',

plugins/node/opentelemetry-instrumentation-express/test/express.test.ts

@@ -455,6 +455,39 @@ describe('ExpressInstrumentation', () => {
         }
       );
     });
+
+    it('should ignore double slashes in routes', async () => {
+      const rootSpan = tracer.startSpan('rootSpan');
+      let rpcMetadata: RPCMetadata | undefined;
+      const httpServer = await serverWithMiddleware(tracer, rootSpan, app => {
+        app.use(express.json());
+        app.use((req, res, next) => {
+          rpcMetadata = getRPCMetadata(context.active());
+          next();
+        });
+      });
+      server = httpServer.server;
+      port = httpServer.port;
+      assert.strictEqual(memoryExporter.getFinishedSpans().length, 0);
+      await context.with(
+        trace.setSpan(context.active(), rootSpan),
+        async () => {
+          const response = await httpRequest.get(
+            `http://localhost:${port}/double-slashes/foo`
+          );
+          assert.strictEqual(response, 'foo');
+          rootSpan.end();
+          const requestHandlerSpan = memoryExporter
+            .getFinishedSpans()
+            .find(span => span.name.includes('request handler'));
+          assert.strictEqual(
+            requestHandlerSpan?.attributes[SemanticAttributes.HTTP_ROUTE],
+            '/double-slashes/:id'
+          );
+          assert.strictEqual(rpcMetadata?.route, '/double-slashes/:id');
+        }
+      );
+    });
   });
 
   describe('Disabling plugin', () => {

plugins/node/opentelemetry-instrumentation-express/test/utils.ts

@@ -66,6 +66,7 @@ export async function serverWithMiddleware(
 
   const router = express.Router();
   app.use('/toto', router);
+  app.use('/double-slashes/', router);
   router.get('/:id', (req, res) => {
     setImmediate(() => {
       res.status(200).end(req.params.id);