fix(eio): close HTTP requests with invalid content type

Before this commit, after the initial handshake, an HTTP request with a "application/octet-stream"
content type would trigger a "invalid content" error at the Engine.IO level, but would not be
properly closed, which could possibly lead to resource exhaustion.

This behavior was introduced in [1] (engine.io@4.1.0, January 2021).

[1]: 663d326

Author: darrachequesne

packages/engine.io/lib/transports-uws/polling.ts

@@ -136,7 +136,8 @@ export class Polling extends Transport {
     const isBinary = "application/octet-stream" === req.headers["content-type"];
 
     if (isBinary && this.protocol === 4) {
-      return this.onError("invalid content");
+      this.onError("invalid content");
+      return res.writeStatus("400 Bad Request").end();
     }
 
     this.dataReq = req;

packages/engine.io/lib/transports/polling.ts

@@ -122,7 +122,8 @@ export class Polling extends Transport {
     const isBinary = "application/octet-stream" === req.headers["content-type"];
 
     if (isBinary && this.protocol === 4) {
-      return this.onError("invalid content");
+      this.onError("invalid content");
+      return res.writeHead(400).end();
     }
 
     this.dataReq = req;

packages/engine.io/test/common.js

@@ -60,6 +60,32 @@ exports.listen = (opts, fn) => {
   return e;
 };
 
+exports.listenAsync = function listenAsync(opts = {}) {
+  return new Promise((resolve) => {
+    const engine = exports.listen(opts, (port) => {
+      resolve({
+        port,
+        close: () => {
+          engine.close();
+          if (engine.httpServer) {
+            engine.httpServer.close();
+          }
+        },
+      });
+    });
+  });
+};
+
+exports.runHandshake = async function runHandshake(port) {
+  const res = await fetch(
+    `http://localhost:${port}/engine.io/?EIO=4&transport=polling`,
+  );
+  const data = await res.text();
+  return {
+    sid: JSON.parse(data.substring(1)).sid,
+  };
+};
+
 exports.ClientSocket = Socket;
 
 exports.createPartialDone = (done, count) => {

packages/engine.io/test/server.js

@@ -7,7 +7,13 @@ const path = require("path");
 const exec = require("child_process").exec;
 const zlib = require("zlib");
 const { Server, Socket, attach } = require("..");
-const { ClientSocket, listen, createPartialDone } = require("./common");
+const {
+  ClientSocket,
+  listen,
+  listenAsync,
+  runHandshake,
+  createPartialDone,
+} = require("./common");
 const expect = require("expect.js");
 const request = require("superagent");
 const cookieMod = require("cookie");
@@ -1458,6 +1464,26 @@ describe("server", () => {
       },
     );
 
+    it("should abort the polling data request if the content type is invalid", async () => {
+      const { port, close } = await listenAsync();
+      const { sid } = await runHandshake(port);
+
+      const res = await fetch(
+        `http://localhost:${port}/engine.io/?EIO=4&transport=polling&sid=${sid}`,
+        {
+          method: "POST",
+          headers: {
+            "content-type": "application/octet-stream",
+          },
+          body: Buffer.of(1, 2, 3),
+        },
+      );
+
+      expect(res.status).to.eql(400);
+
+      close();
+    });
+
     // tests https://github.com/LearnBoost/engine.io-client/issues/207
     // websocket test, transport error
     it("should trigger transport close before open for ws", (done) => {