refactor: improve types

2026-01-08 22:48:20 -05:00 · 2024-06-21 13:13:36 +02:00
parent 362bc78191
commit c310b7b6b6
11 changed files with 198 additions and 190 deletions
--- a/lib/engine.io.ts
+++ b/lib/engine.io.ts
@@ -17,7 +17,6 @@ export const protocol = parser.protocol;
 * @param {Function} callback
 * @param {Object} options
 * @return {Server} websocket.io server
- * @api public
 */

 function listen(port, options: AttachOptions & ServerOptions, fn) {
@@ -46,7 +45,6 @@ function listen(port, options: AttachOptions & ServerOptions, fn) {
 * @param {http.Server} server
 * @param {Object} options
 * @return {Server} engine server
- * @api public
 */

 function attach(server, options: AttachOptions & ServerOptions) {
--- a/lib/server.ts
+++ b/lib/server.ts
@@ -17,12 +17,13 @@ import type { CorsOptions, CorsOptionsDelegate } from "cors";
 import type { Duplex } from "stream";
 import { WebTransport } from "./transports/webtransport";
 import { createPacketDecoderStream } from "engine.io-parser";
+import type { EngineRequest } from "./transport";

 const debug = debugModule("engine");

 const kResponseHeaders = Symbol("responseHeaders");

-type Transport = "polling" | "websocket";
+type Transport = "polling" | "websocket" | "webtransport";

 export interface AttachOptions {
  /**
@@ -169,7 +170,6 @@ export abstract class BaseServer extends EventEmitter {
   * Server constructor.
   *
   * @param {Object} opts - options
-   * @api public
   */
  constructor(opts: ServerOptions = {}) {
    super();
@@ -246,9 +246,8 @@ export abstract class BaseServer extends EventEmitter {
   * Returns a list of available transports for upgrade given a certain transport.
   *
   * @return {Array}
-   * @api public
   */
-  public upgrades(transport) {
+  public upgrades(transport: string) {
    if (!this.opts.allowUpgrades) return [];
    return transports[transport].upgradesTo || [];
  }
@@ -256,11 +255,16 @@ export abstract class BaseServer extends EventEmitter {
  /**
   * Verifies a request.
   *
-   * @param {http.IncomingMessage}
-   * @return {Boolean} whether the request is valid
-   * @api private
+   * @param {EngineRequest} req
+   * @param upgrade - whether it's an upgrade request
+   * @param fn
+   * @protected
   */
-  protected verify(req, upgrade, fn) {
+  protected verify(
+    req: any,
+    upgrade: boolean,
+    fn: (errorCode?: number, errorContext?: any) => void
+  ) {
    // transport check
    const transport = req._query.transport;
    // WebTransport does not go through the verify() method, see the onWebTransportSession() method
@@ -384,8 +388,6 @@ export abstract class BaseServer extends EventEmitter {

  /**
   * Closes all clients.
-   *
-   * @api public
   */
  public close() {
    debug("closing all open clients");
@@ -404,23 +406,26 @@ export abstract class BaseServer extends EventEmitter {
   * generate a socket id.
   * Overwrite this method to generate your custom socket id
   *
-   * @param {Object} request object
-   * @api public
+   * @param {IncomingMessage} req - the request object
   */
-  public generateId(req) {
+  public generateId(req: IncomingMessage) {
    return base64id.generateId();
  }

  /**
   * Handshakes a new client.
   *
-   * @param {String} transport name
-   * @param {Object} request object
+   * @param {String} transportName
+   * @param {Object} req - the request object
   * @param {Function} closeConnection
   *
-   * @api protected
+   * @protected
   */
-  protected async handshake(transportName, req, closeConnection) {
+  protected async handshake(
+    transportName: string,
+    req: any,
+    closeConnection: (errorCode?: number, errorContext?: any) => void
+  ) {
    const protocol = req._query.EIO === "4" ? 4 : 3; // 3rd revision by default
    if (protocol === 3 && !this.opts.allowEIO3) {
      debug("unsupported protocol version");
@@ -661,7 +666,7 @@ export class Server extends BaseServer {
  /**
   * Initialize websocket server
   *
-   * @api protected
+   * @protected
   */
  protected init() {
    if (!~this.opts.transports.indexOf("websocket")) return;
@@ -708,30 +713,30 @@ export class Server extends BaseServer {
  /**
   * Prepares a request by processing the query string.
   *
-   * @api private
+   * @private
   */
-  private prepare(req) {
+  private prepare(req: EngineRequest) {
    // try to leverage pre-existing `req._query` (e.g: from connect)
    if (!req._query) {
-      req._query = ~req.url.indexOf("?") ? qs.parse(parse(req.url).query) : {};
+      req._query = (
+        ~req.url.indexOf("?") ? qs.parse(parse(req.url).query) : {}
+      ) as Record<string, string>;
    }
  }

-  protected createTransport(transportName, req) {
+  protected createTransport(transportName: string, req: IncomingMessage) {
    return new transports[transportName](req);
  }

  /**
   * Handles an Engine.IO HTTP request.
   *
-   * @param {IncomingMessage} req
+   * @param {EngineRequest} req
   * @param {ServerResponse} res
-   * @api public
   */
-  public handleRequest(req: IncomingMessage, res: ServerResponse) {
+  public handleRequest(req: EngineRequest, res: ServerResponse) {
    debug('handling "%s" http request "%s"', req.method, req.url);
    this.prepare(req);
-    // @ts-ignore
    req.res = res;

    const callback = (errorCode, errorContext) => {
@@ -746,15 +751,12 @@ export class Server extends BaseServer {
        return;
      }

-      // @ts-ignore
      if (req._query.sid) {
        debug("setting new request for existing client");
-        // @ts-ignore
        this.clients[req._query.sid].transport.onRequest(req);
      } else {
        const closeConnection = (errorCode, errorContext) =>
          abortRequest(res, errorCode, errorContext);
-        // @ts-ignore
        this.handshake(req._query.transport, req, closeConnection);
      }
    };
@@ -770,11 +772,9 @@ export class Server extends BaseServer {

  /**
   * Handles an Engine.IO HTTP Upgrade.
-   *
-   * @api public
   */
  public handleUpgrade(
-    req: IncomingMessage,
+    req: EngineRequest,
    socket: Duplex,
    upgradeHead: Buffer
  ) {
@@ -819,7 +819,7 @@ export class Server extends BaseServer {
   * Called upon a ws.io connection.
   *
   * @param {ws.Socket} websocket
-   * @api private
+   * @private
   */
  private onWebSocket(req, socket, websocket) {
    websocket.on("error", onUpgradeError);
@@ -877,7 +877,6 @@ export class Server extends BaseServer {
   *
   * @param {http.Server} server
   * @param {Object} options
-   * @api public
   */
  public attach(server: HttpServer, options: AttachOptions = {}) {
    const path = this._computePath(options);
@@ -898,7 +897,7 @@ export class Server extends BaseServer {
    server.on("request", (req, res) => {
      if (check(req)) {
        debug('intercepting request for path "%s"', path);
-        this.handleRequest(req, res);
+        this.handleRequest(req as EngineRequest, res);
      } else {
        let i = 0;
        const l = listeners.length;
@@ -911,7 +910,7 @@ export class Server extends BaseServer {
    if (~this.opts.transports.indexOf("websocket")) {
      server.on("upgrade", (req, socket, head) => {
        if (check(req)) {
-          this.handleUpgrade(req, socket, head);
+          this.handleUpgrade(req as EngineRequest, socket, head);
        } else if (false !== options.destroyUpgrade) {
          // default node behavior is to disconnect when no handlers
          // but by adding a handler, we prevent that
@@ -939,7 +938,7 @@ export class Server extends BaseServer {
 * @param errorCode - the error code
 * @param errorContext - additional error context
 *
- * @api private
+ * @private
 */

 function abortRequest(res, errorCode, errorContext) {
@@ -964,8 +963,6 @@ function abortRequest(res, errorCode, errorContext) {
 * @param {net.Socket} socket
 * @param {string} errorCode - the error code
 * @param {object} errorContext - additional error context
- *
- * @api private
 */

 function abortUpgrade(
--- a/lib/socket.ts
+++ b/lib/socket.ts
@@ -1,10 +1,10 @@
 import { EventEmitter } from "events";
 import debugModule from "debug";
-import { IncomingMessage } from "http";
-import { Transport } from "./transport";
-import { Server } from "./server";
+import type { IncomingMessage } from "http";
+import type { EngineRequest, Transport } from "./transport";
+import type { BaseServer } from "./server";
 import { setTimeout, clearTimeout } from "timers";
-import { Packet, PacketType, RawData } from "engine.io-parser";
+import type { Packet, PacketType, RawData } from "engine.io-parser";

 const debug = debugModule("engine:socket");

@@ -17,15 +17,38 @@ type ReadyState = "opening" | "open" | "closing" | "closed";
 type SendCallback = (transport: Transport) => void;

 export class Socket extends EventEmitter {
+  /**
+   * The revision of the protocol:
+   *
+   * - 3rd is used in Engine.IO v3 / Socket.IO v2
+   * - 4th is used in Engine.IO v4 and above / Socket.IO v3 and above
+   *
+   * It is found in the `EIO` query parameters of the HTTP requests.
+   *
+   * @see https://github.com/socketio/engine.io-protocol
+   */
  public readonly protocol: number;
-  // TODO for the next major release: do not keep the reference to the first HTTP request, as it stays in memory
+  /**
+   * A reference to the first HTTP request of the session
+   *
+   * TODO for the next major release: remove it
+   */
  public request: IncomingMessage;
+  /**
+   * The IP address of the client.
+   */
  public readonly remoteAddress: string;

+  /**
+   * The current state of the socket.
+   */
  public _readyState: ReadyState = "opening";
+  /**
+   * The current low-level transport.
+   */
  public transport: Transport;

-  private server: Server;
+  private server: BaseServer;
  /* private */ upgrading = false;
  /* private */ upgraded = false;
  private writeBuffer: Packet[] = [];
@@ -52,12 +75,13 @@ export class Socket extends EventEmitter {
    this._readyState = state;
  }

-  /**
-   * Client class (abstract).
-   *
-   * @api private
-   */
-  constructor(id, server, transport, req, protocol) {
+  constructor(
+    id: string,
+    server: BaseServer,
+    transport: Transport,
+    req: EngineRequest,
+    protocol: number
+  ) {
    super();
    this.id = id;
    this.server = server;
@@ -86,7 +110,7 @@ export class Socket extends EventEmitter {
  /**
   * Called upon transport considered open.
   *
-   * @api private
+   * @private
   */
  private onOpen() {
    this.readyState = "open";
@@ -123,7 +147,7 @@ export class Socket extends EventEmitter {
   * Called upon transport packet.
   *
   * @param {Object} packet
-   * @api private
+   * @private
   */
  private onPacket(packet: Packet) {
    if ("open" !== this.readyState) {
@@ -136,7 +160,7 @@ export class Socket extends EventEmitter {
    switch (packet.type) {
      case "ping":
        if (this.transport.protocol !== 3) {
-          this.onError("invalid heartbeat direction");
+          this.onError(new Error("invalid heartbeat direction"));
          return;
        }
        debug("got ping");
@@ -147,7 +171,7 @@ export class Socket extends EventEmitter {

      case "pong":
        if (this.transport.protocol === 3) {
-          this.onError("invalid heartbeat direction");
+          this.onError(new Error("invalid heartbeat direction"));
          return;
        }
        debug("got pong");
@@ -171,9 +195,9 @@ export class Socket extends EventEmitter {
   * Called upon transport error.
   *
   * @param {Error} err - error object
-   * @api private
+   * @private
   */
-  private onError(err) {
+  private onError(err: Error) {
    debug("transport error");
    this.onClose("transport error", err);
  }
@@ -182,7 +206,7 @@ export class Socket extends EventEmitter {
   * Pings client every `this.pingInterval` and expects response
   * within `this.pingTimeout` or closes connection.
   *
-   * @api private
+   * @private
   */
  private schedulePing() {
    this.pingIntervalTimer = setTimeout(() => {
@@ -198,7 +222,7 @@ export class Socket extends EventEmitter {
  /**
   * Resets ping timeout.
   *
-   * @api private
+   * @private
   */
  private resetPingTimeout() {
    clearTimeout(this.pingTimeoutTimer);
@@ -217,9 +241,9 @@ export class Socket extends EventEmitter {
   * Attaches handlers for the given transport.
   *
   * @param {Transport} transport
-   * @api private
+   * @private
   */
-  private setTransport(transport) {
+  private setTransport(transport: Transport) {
    const onError = this.onError.bind(this);
    const onReady = () => this.flush();
    const onPacket = this.onPacket.bind(this);
@@ -263,7 +287,7 @@ export class Socket extends EventEmitter {
   * Upgrades socket to the given transport
   *
   * @param {Transport} transport
-   * @api private
+   * @private
   */
  /* private */ _maybeUpgrade(transport: Transport) {
    debug(
@@ -357,7 +381,7 @@ export class Socket extends EventEmitter {
  /**
   * Clears listeners and timers associated with current transport.
   *
-   * @api private
+   * @private
   */
  private clearTransport() {
    let cleanup;
@@ -412,7 +436,6 @@ export class Socket extends EventEmitter {
   * @param {Object} options
   * @param {Function} callback
   * @return {Socket} for chaining
-   * @api public
   */
  public send(data: RawData, options?: SendOptions, callback?: SendCallback) {
    this.sendPacket("message", data, options, callback);
@@ -439,7 +462,7 @@ export class Socket extends EventEmitter {
   * @param {Object} options
   * @param {Function} callback
   *
-   * @api private
+   * @private
   */
  private sendPacket(
    type: PacketType,
@@ -480,7 +503,7 @@ export class Socket extends EventEmitter {
  /**
   * Attempts to flush the packets buffer.
   *
-   * @api private
+   * @private
   */
  private flush() {
    if (
@@ -510,14 +533,12 @@ export class Socket extends EventEmitter {
  /**
   * Get available upgrades for this socket.
   *
-   * @api private
+   * @private
   */
  private getAvailableUpgrades() {
    const availableUpgrades = [];
    const allUpgrades = this.server.upgrades(this.transport.name);
-    let i = 0;
-    const l = allUpgrades.length;
-    for (; i < l; ++i) {
+    for (let i = 0; i < allUpgrades.length; ++i) {
      const upg = allUpgrades[i];
      if (this.server.opts.transports.indexOf(upg) !== -1) {
        availableUpgrades.push(upg);
@@ -531,7 +552,6 @@ export class Socket extends EventEmitter {
   *
   * @param {Boolean} discard - optional, discard the transport
   * @return {Socket} for chaining
-   * @api public
   */
  public close(discard?: boolean) {
    if ("open" !== this.readyState) return;
@@ -558,9 +578,9 @@ export class Socket extends EventEmitter {
   * Closes the underlying transport.
   *
   * @param {Boolean} discard
-   * @api private
+   * @private
   */
-  private closeTransport(discard) {
+  private closeTransport(discard: boolean) {
    debug("closing the transport (discard? %s)", discard);
    if (discard) this.transport.discard();
    this.transport.close(this.onClose.bind(this, "forced close"));
--- a/lib/transport.ts
+++ b/lib/transport.ts
@@ -2,30 +2,63 @@ import { EventEmitter } from "events";
 import * as parser_v4 from "engine.io-parser";
 import * as parser_v3 from "./parser-v3/index";
 import debugModule from "debug";
-import { IncomingMessage } from "http";
-import { Packet } from "engine.io-parser";
+import type { IncomingMessage, ServerResponse } from "http";
+import { Packet, RawData } from "engine.io-parser";

 const debug = debugModule("engine:transport");

-/**
- * Noop function.
- *
- * @api private
- */
-
 function noop() {}

 type ReadyState = "open" | "closing" | "closed";

+export type EngineRequest = IncomingMessage & {
+  _query: Record<string, string>;
+  res?: ServerResponse;
+  cleanup?: Function;
+  websocket?: any;
+};
+
 export abstract class Transport extends EventEmitter {
+  /**
+   * The session ID.
+   */
  public sid: string;
+  /**
+   * Whether the transport is currently ready to send packets.
+   */
  public writable = false;
+  /**
+   * The revision of the protocol:
+   *
+   * - 3 is used in Engine.IO v3 / Socket.IO v2
+   * - 4 is used in Engine.IO v4 and above / Socket.IO v3 and above
+   *
+   * It is found in the `EIO` query parameters of the HTTP requests.
+   *
+   * @see https://github.com/socketio/engine.io-protocol
+   */
  public protocol: number;

+  /**
+   * The current state of the transport.
+   * @protected
+   */
  protected _readyState: ReadyState = "open";
+  /**
+   * Whether the transport is discarded and can be safely closed (used during upgrade).
+   * @protected
+   */
  protected discarded = false;
+  /**
+   * The parser to use (depends on the revision of the {@link Transport#protocol}.
+   * @protected
+   */
  protected parser: any;
-  protected req: IncomingMessage & { cleanup: Function };
+  protected req: EngineRequest;
+  /**
+   * Whether the transport supports binary payloads (else it will be base64-encoded)
+   * @protected
+   */
  protected supportsBinary: boolean;

  get readyState() {
@@ -45,10 +78,9 @@ export abstract class Transport extends EventEmitter {
  /**
   * Transport constructor.
   *
-   * @param {http.IncomingMessage} req
-   * @api public
+   * @param {EngineRequest} req
   */
-  constructor(req) {
+  constructor(req: { _query: Record<string, string> }) {
    super();
    this.protocol = req._query.EIO === "4" ? 4 : 3; // 3rd revision by default
    this.parser = this.protocol === 4 ? parser_v4 : parser_v3;
@@ -58,7 +90,7 @@ export abstract class Transport extends EventEmitter {
  /**
   * Flags the transport as discarded.
   *
-   * @api private
+   * @package
   */
  discard() {
    this.discarded = true;
@@ -68,9 +100,9 @@ export abstract class Transport extends EventEmitter {
   * Called with an incoming HTTP request.
   *
   * @param {http.IncomingMessage} req
-   * @api protected
+   * @package
   */
-  protected onRequest(req) {
+  onRequest(req) {
    debug("setting request");
    this.req = req;
  }
@@ -78,9 +110,9 @@ export abstract class Transport extends EventEmitter {
  /**
   * Closes the transport.
   *
-   * @api private
+   * @package
   */
-  close(fn?) {
+  close(fn?: () => void) {
    if ("closed" === this.readyState || "closing" === this.readyState) return;

    this.readyState = "closing";
@@ -92,7 +124,7 @@ export abstract class Transport extends EventEmitter {
   *
   * @param {String} msg - message error
   * @param {Object} desc - error description
-   * @api protected
+   * @protected
   */
  protected onError(msg: string, desc?) {
    if (this.listeners("error").length) {
@@ -111,7 +143,7 @@ export abstract class Transport extends EventEmitter {
   * Called with parsed out a packets from the data stream.
   *
   * @param {Object} packet
-   * @api protected
+   * @protected
   */
  protected onPacket(packet: Packet) {
    this.emit("packet", packet);
@@ -121,16 +153,16 @@ export abstract class Transport extends EventEmitter {
   * Called with the encoded packet data.
   *
   * @param {String} data
-   * @api protected
+   * @protected
   */
-  protected onData(data) {
+  protected onData(data: RawData) {
    this.onPacket(this.parser.decodePacket(data));
  }

  /**
   * Called upon transport close.
   *
-   * @api protected
+   * @protected
   */
  protected onClose() {
    this.readyState = "closed";
@@ -140,7 +172,7 @@ export abstract class Transport extends EventEmitter {
  /**
   * The name of the transport.
   */
-  abstract get name();
+  abstract get name(): string;

  /**
   * Sends an array of packets.
@@ -148,10 +180,10 @@ export abstract class Transport extends EventEmitter {
   * @param {Array} packets
   * @package
   */
-  abstract send(packets);
+  abstract send(packets: Packet[]): void;

  /**
   * Closes the transport.
   */
-  abstract doClose(fn?);
+  abstract doClose(fn?: () => void): void;
 }
--- a/lib/transports-uws/polling.ts
+++ b/lib/transports-uws/polling.ts
@@ -24,8 +24,6 @@ export class Polling extends Transport {

  /**
   * HTTP polling constructor.
-   *
-   * @api public.
   */
  constructor(req) {
    super(req);
@@ -35,8 +33,6 @@ export class Polling extends Transport {

  /**
   * Transport name
-   *
-   * @api public
   */
  get name() {
    return "polling";
@@ -47,7 +43,7 @@ export class Polling extends Transport {
   *
   * @param req
   *
-   * @api private
+   * @private
   */
  onRequest(req) {
    const res = req.res;
@@ -67,7 +63,7 @@ export class Polling extends Transport {
  /**
   * The client sends a request awaiting for us to send data.
   *
-   * @api private
+   * @private
   */
  onPollRequest(req, res) {
    if (this.req) {
@@ -109,7 +105,7 @@ export class Polling extends Transport {
  /**
   * The client sends a request with data.
   *
-   * @api private
+   * @private
   */
  onDataRequest(req, res) {
    if (this.dataReq) {
@@ -206,7 +202,7 @@ export class Polling extends Transport {
  /**
   * Cleanup request.
   *
-   * @api private
+   * @private
   */
  private onDataRequestCleanup() {
    this.dataReq = this.dataRes = null;
@@ -216,7 +212,7 @@ export class Polling extends Transport {
   * Processes the incoming data payload.
   *
   * @param {String} encoded payload
-   * @api private
+   * @private
   */
  onData(data) {
    debug('received "%s"', data);
@@ -240,7 +236,7 @@ export class Polling extends Transport {
  /**
   * Overrides onClose.
   *
-   * @api private
+   * @private
   */
  onClose() {
    if (this.writable) {
@@ -254,7 +250,7 @@ export class Polling extends Transport {
   * Writes a packet payload.
   *
   * @param {Object} packet
-   * @api private
+   * @private
   */
  send(packets) {
    this.writable = false;
@@ -285,7 +281,7 @@ export class Polling extends Transport {
   *
   * @param {String} data
   * @param {Object} options
-   * @api private
+   * @private
   */
  write(data, options) {
    debug('writing "%s"', data);
@@ -298,7 +294,7 @@ export class Polling extends Transport {
  /**
   * Performs the write.
   *
-   * @api private
+   * @private
   */
  doWrite(data, options, callback) {
    // explicit UTF-8 is required for pages not served under utf
@@ -355,7 +351,7 @@ export class Polling extends Transport {
  /**
   * Compresses data.
   *
-   * @api private
+   * @private
   */
  compress(data, encoding, callback) {
    debug("compressing");
@@ -378,7 +374,7 @@ export class Polling extends Transport {
  /**
   * Closes the transport.
   *
-   * @api private
+   * @private
   */
  doClose(fn) {
    debug("closing");
@@ -410,7 +406,7 @@ export class Polling extends Transport {
   *
   * @param req - request
   * @param {Object} extra headers
-   * @api private
+   * @private
   */
  headers(req, headers) {
    headers = headers || {};
--- a/lib/transports-uws/websocket.ts
+++ b/lib/transports-uws/websocket.ts
@@ -11,7 +11,6 @@ export class WebSocket extends Transport {
   * WebSocket transport
   *
   * @param req
-   * @api public
   */
  constructor(req) {
    super(req);
@@ -21,8 +20,6 @@ export class WebSocket extends Transport {

  /**
   * Transport name
-   *
-   * @api public
   */
  get name() {
    return "websocket";
@@ -30,8 +27,6 @@ export class WebSocket extends Transport {

  /**
   * Advertise upgrade support.
-   *
-   * @api public
   */
  get handlesUpgrades() {
    return true;
@@ -41,7 +36,7 @@ export class WebSocket extends Transport {
   * Writes a packet payload.
   *
   * @param {Array} packets
-   * @api private
+   * @private
   */
  send(packets) {
    this.writable = false;
@@ -77,7 +72,7 @@ export class WebSocket extends Transport {
  /**
   * Closes the transport.
   *
-   * @api private
+   * @private
   */
  doClose(fn) {
    debug("closing");
--- a/lib/transports/index.ts
+++ b/lib/transports/index.ts
@@ -11,8 +11,6 @@ export default {

 /**
 * Polling polymorphic constructor.
- *
- * @api private
 */

 function polling(req) {
--- a/lib/transports/polling-jsonp.ts
+++ b/lib/transports/polling-jsonp.ts
@@ -1,5 +1,6 @@
 import { Polling } from "./polling";
 import * as qs from "querystring";
+import type { RawData } from "engine.io-parser";

 const rDoubleSlashes = /\\\\n/g;
 const rSlashes = /(\\)?\\n/g;
@@ -10,8 +11,6 @@ export class JSONP extends Polling {

  /**
   * JSON-P polling transport.
-   *
-   * @api public
   */
  constructor(req) {
    super(req);
@@ -20,16 +19,10 @@ export class JSONP extends Polling {
    this.foot = ");";
  }

-  /**
-   * Handles incoming data.
-   * Due to a bug in \n handling by browsers, we expect a escaped string.
-   *
-   * @api private
-   */
-  onData(data) {
+  override onData(data: RawData) {
    // we leverage the qs module so that we get built-in DoS protection
    // and the fast alternative to decodeURIComponent
-    data = qs.parse(data).d;
+    data = qs.parse(data).d as string;
    if ("string" === typeof data) {
      // client will send already escaped newlines as \\\\n and newlines as \\n
      // \\n must be replaced with \n and \\\\n with \\n
@@ -40,12 +33,7 @@ export class JSONP extends Polling {
    }
  }

-  /**
-   * Performs the write.
-   *
-   * @api private
-   */
-  doWrite(data, options, callback) {
+  override doWrite(data, options, callback) {
    // we must output valid javascript, not valid json
    // see: http://timelessrepo.com/json-isnt-a-javascript-subset
    const js = JSON.stringify(data)
--- a/lib/transports/polling.ts
+++ b/lib/transports/polling.ts
@@ -1,8 +1,9 @@
-import { Transport } from "../transport";
+import { EngineRequest, Transport } from "../transport";
 import { createGzip, createDeflate } from "zlib";
 import * as accepts from "accepts";
 import debugModule from "debug";
-import { IncomingMessage, ServerResponse } from "http";
+import type { IncomingMessage, ServerResponse } from "http";
+import type { Packet, RawData } from "engine.io-parser";

 const debug = debugModule("engine:polling");

@@ -18,14 +19,12 @@ export class Polling extends Transport {
  private res: ServerResponse;
  private dataReq: IncomingMessage;
  private dataRes: ServerResponse;
-  private shouldClose: Function;
+  private shouldClose: () => void;

  private readonly closeTimeout: number;

  /**
   * HTTP polling constructor.
-   *
-   * @api public.
   */
  constructor(req) {
    super(req);
@@ -35,8 +34,6 @@ export class Polling extends Transport {

  /**
   * Transport name
-   *
-   * @api public
   */
  get name() {
    return "polling";
@@ -45,10 +42,10 @@ export class Polling extends Transport {
  /**
   * Overrides onRequest.
   *
-   * @param {http.IncomingMessage}
-   * @api private
+   * @param {EngineRequest} req
+   * @package
   */
-  onRequest(req: IncomingMessage & { res: ServerResponse }) {
+  onRequest(req: EngineRequest) {
    const res = req.res;
    // remove the reference to the ServerResponse object (as the first request of the session is kept in memory by default)
    req.res = null;
@@ -66,9 +63,9 @@ export class Polling extends Transport {
  /**
   * The client sends a request awaiting for us to send data.
   *
-   * @api private
+   * @private
   */
-  onPollRequest(req, res) {
+  private onPollRequest(req: EngineRequest, res: ServerResponse) {
    if (this.req) {
      debug("request overlap");
      // assert: this.res, '.req and .res should be (un)set together'
@@ -108,9 +105,9 @@ export class Polling extends Transport {
  /**
   * The client sends a request with data.
   *
-   * @api private
+   * @private
   */
-  onDataRequest(req: IncomingMessage, res: ServerResponse) {
+  private onDataRequest(req: IncomingMessage, res: ServerResponse) {
    if (this.dataReq) {
      // assert: this.dataRes, '.dataReq and .dataRes should be (un)set together'
      this.onError("data request overlap from client");
@@ -165,7 +162,7 @@ export class Polling extends Transport {
        // text/html is required instead of text/plain to avoid an
        // unwanted download dialog on certain user-agents (GH-43)
        "Content-Type": "text/html",
-        "Content-Length": 2,
+        "Content-Length": "2",
      };

      res.writeHead(200, this.headers(req, headers));
@@ -182,10 +179,10 @@ export class Polling extends Transport {
  /**
   * Processes the incoming data payload.
   *
-   * @param {String} encoded payload
-   * @api private
+   * @param data - encoded payload
+   * @protected
   */
-  onData(data) {
+  override onData(data: RawData) {
    debug('received "%s"', data);
    const callback = (packet) => {
      if ("close" === packet.type) {
@@ -207,7 +204,7 @@ export class Polling extends Transport {
  /**
   * Overrides onClose.
   *
-   * @api private
+   * @private
   */
  onClose() {
    if (this.writable) {
@@ -217,13 +214,7 @@ export class Polling extends Transport {
    super.onClose();
  }

-  /**
-   * Writes a packet payload.
-   *
-   * @param {Object} packet
-   * @api private
-   */
-  send(packets) {
+  send(packets: Packet[]) {
    this.writable = false;

    if (this.shouldClose) {
@@ -252,9 +243,9 @@ export class Polling extends Transport {
   *
   * @param {String} data
   * @param {Object} options
-   * @api private
+   * @private
   */
-  write(data, options) {
+  private write(data, options) {
    debug('writing "%s"', data);
    this.doWrite(data, options, () => {
      this.req.cleanup();
@@ -265,9 +256,9 @@ export class Polling extends Transport {
  /**
   * Performs the write.
   *
-   * @api private
+   * @protected
   */
-  doWrite(data, options, callback) {
+  protected doWrite(data, options, callback) {
    // explicit UTF-8 is required for pages not served under utf
    const isString = typeof data === "string";
    const contentType = isString
@@ -319,9 +310,9 @@ export class Polling extends Transport {
  /**
   * Compresses data.
   *
-   * @api private
+   * @private
   */
-  compress(data, encoding, callback) {
+  private compress(data, encoding, callback) {
    debug("compressing");

    const buffers = [];
@@ -342,9 +333,9 @@ export class Polling extends Transport {
  /**
   * Closes the transport.
   *
-   * @api private
+   * @private
   */
-  doClose(fn) {
+  override doClose(fn: () => void) {
    debug("closing");

    let closeTimeoutTimer;
@@ -377,13 +368,11 @@ export class Polling extends Transport {
  /**
   * Returns headers for a response.
   *
-   * @param {http.IncomingMessage} request
-   * @param {Object} extra headers
-   * @api private
+   * @param {http.IncomingMessage} req
+   * @param {Object} headers - extra headers
+   * @private
   */
-  headers(req, headers) {
-    headers = headers || {};
-
+  private headers(req: IncomingMessage, headers: Record<string, string> = {}) {
    // prevent XSS warnings on IE
    // https://github.com/LearnBoost/socket.io/pull/1333
    const ua = req.headers["user-agent"];
--- a/lib/transports/websocket.ts
+++ b/lib/transports/websocket.ts
@@ -1,4 +1,4 @@
-import { Transport } from "../transport";
+import { EngineRequest, Transport } from "../transport";
 import debugModule from "debug";
 import type { Packet, RawData } from "engine.io-parser";

@@ -11,10 +11,9 @@ export class WebSocket extends Transport {
  /**
   * WebSocket transport
   *
-   * @param {http.IncomingMessage}
-   * @api public
+   * @param {EngineRequest} req
   */
-  constructor(req) {
+  constructor(req: EngineRequest) {
    super(req);
    this.socket = req.websocket;
    this.socket.on("message", (data, isBinary) => {
@@ -30,8 +29,6 @@ export class WebSocket extends Transport {

  /**
   * Transport name
-   *
-   * @api public
   */
  get name() {
    return "websocket";
@@ -39,8 +36,6 @@ export class WebSocket extends Transport {

  /**
   * Advertise upgrade support.
-   *
-   * @api public
   */
  get handlesUpgrades() {
    return true;
--- a/lib/userver.ts
+++ b/lib/userver.ts
@@ -30,7 +30,7 @@ export class uServer extends BaseServer {
  /**
   * Prepares a request by processing the query string.
   *
-   * @api private
+   * @private
   */
  private prepare(req, res: HttpResponse) {
    req.method = req.getMethod().toUpperCase();