fix(uws): prevent crash when using with middlewares

The class used to accumulate the response headers did not expose the
exact same API as its wrapped type, which could lead to the following
error in some rare cases:

> TypeError: Cannot read properties of undefined (reading 'end')
>    at Polling.onDataRequest (build/transports-uws/polling.js:109:53)
>    at Polling.onRequest (build/transports-uws/polling.js:47:18)
>    at callback (build/userver.js:94:56)
>    at uServer.verify (build/server.js:152:9)

Related: socketio/socket.io#4643

lib/userver.ts

@@ -294,6 +294,7 @@ class ResponseWrapper {
     this.res.writeStatus(status);
     this.statusWritten = true;
     this.writeBufferedHeaders();
+    return this;
   }
 
   public writeHeader(key: string, value: string) {

test/middlewares.js

@@ -4,6 +4,7 @@ const request = require("superagent");
 const { WebSocket } = require("ws");
 const helmet = require("helmet");
 const session = require("express-session");
+const { ClientSocket } = require("./common");
 
 describe("middlewares", () => {
   it("should apply middleware (polling)", (done) => {
@@ -291,4 +292,30 @@ describe("middlewares", () => {
       });
     });
   });
+
+  it("should not be receiving data when getting a message longer than maxHttpBufferSize when polling (with a middleware)", (done) => {
+    const opts = {
+      allowUpgrades: false,
+      transports: ["polling"],
+      maxHttpBufferSize: 5,
+    };
+    const engine = listen(opts, (port) => {
+      engine.use((req, res, next) => {
+        next();
+      });
+
+      const socket = new ClientSocket(`ws://localhost:${port}`);
+      engine.on("connection", (conn) => {
+        conn.on("message", () => {
+          done(new Error("Test invalidation (message is longer than allowed)"));
+        });
+      });
+      socket.on("open", () => {
+        socket.send("aasdasdakjhasdkjhasdkjhasdkjhasdkjhasdkjhasdkjha");
+      });
+      socket.on("close", (reason) => {
+        done();
+      });
+    });
+  });
 });