node_modules/engine.io/lib/server.js - devtools/devtools-frontend - Git at Google

 const qs = require("querystring");
 const parse = require("url").parse;
 const base64id = require("base64id");
 const transports = require("./transports");
 const EventEmitter = require("events").EventEmitter;
 const Socket = require("./socket");
 const debug = require("debug")("engine");
 const cookieMod = require("cookie");

 class Server extends EventEmitter {
   /**
    * Server constructor.
    *
    * @param {Object} options
    * @api public
    */
   constructor(opts = {}) {
     super();

     this.clients = {};
     this.clientsCount = 0;

     this.opts = Object.assign(
       {
         wsEngine: process.env.EIO_WS_ENGINE || "ws",
         pingTimeout: 5000,
         pingInterval: 25000,
         upgradeTimeout: 10000,
         maxHttpBufferSize: 1e6,
         transports: Object.keys(transports),
         allowUpgrades: true,
         httpCompression: {
           threshold: 1024
         },
         cors: false,
         allowEIO3: false
       },
       opts
     );

     if (opts.cookie) {
       this.opts.cookie = Object.assign(
         {
           name: "io",
           path: "/",
           httpOnly: opts.cookie.path !== false,
           sameSite: "lax"
         },
         opts.cookie
       );
     }

     if (this.opts.cors) {
       this.corsMiddleware = require("cors")(this.opts.cors);
     }

     if (opts.perMessageDeflate) {
       this.opts.perMessageDeflate = Object.assign(
         {
           threshold: 1024
         },
         opts.perMessageDeflate
       );
     }

     this.init();
   }

   /**
    * Initialize websocket server
    *
    * @api private
    */
   init() {
     if (!~this.opts.transports.indexOf("websocket")) return;

     if (this.ws) this.ws.close();

     // add explicit require for bundlers like webpack
     const wsModule =
       this.opts.wsEngine === "ws" ? require("ws") : require(this.opts.wsEngine);
     this.ws = new wsModule.Server({
       noServer: true,
       clientTracking: false,
       perMessageDeflate: this.opts.perMessageDeflate,
       maxPayload: this.opts.maxHttpBufferSize
     });
   }

   /**
    * Returns a list of available transports for upgrade given a certain transport.
    *
    * @return {Array}
    * @api public
    */
   upgrades(transport) {
     if (!this.opts.allowUpgrades) return [];
     return transports[transport].upgradesTo || [];
   }

   /**
    * Verifies a request.
    *
    * @param {http.IncomingMessage}
    * @return {Boolean} whether the request is valid
    * @api private
    */
   verify(req, upgrade, fn) {
     // transport check
     const transport = req._query.transport;
     if (!~this.opts.transports.indexOf(transport)) {
       debug('unknown transport "%s"', transport);
       return fn(Server.errors.UNKNOWN_TRANSPORT, false);
     }

     // 'Origin' header check
     const isOriginInvalid = checkInvalidHeaderChar(req.headers.origin);
     if (isOriginInvalid) {
       req.headers.origin = null;
       debug("origin header invalid");
       return fn(Server.errors.BAD_REQUEST, false);
     }

     // sid check
     const sid = req._query.sid;
     if (sid) {
       if (!this.clients.hasOwnProperty(sid)) {
         debug('unknown sid "%s"', sid);
         return fn(Server.errors.UNKNOWN_SID, false);
       }
       if (!upgrade && this.clients[sid].transport.name !== transport) {
         debug("bad request: unexpected transport without upgrade");
         return fn(Server.errors.BAD_REQUEST, false);
       }
     } else {
       // handshake is GET only
       if ("GET" !== req.method)
         return fn(Server.errors.BAD_HANDSHAKE_METHOD, false);
       if (!this.opts.allowRequest) return fn(null, true);
       return this.opts.allowRequest(req, fn);
     }

     fn(null, true);
   }

   /**
    * Prepares a request by processing the query string.
    *
    * @api private
    */
   prepare(req) {
     // 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) : {};
     }
   }

   /**
    * Closes all clients.
    *
    * @api public
    */
   close() {
     debug("closing all open clients");
     for (let i in this.clients) {
       if (this.clients.hasOwnProperty(i)) {
         this.clients[i].close(true);
       }
     }
     if (this.ws) {
       debug("closing webSocketServer");
       this.ws.close();
       // don't delete this.ws because it can be used again if the http server starts listening again
     }
     return this;
   }

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

     const callback = (err, success) => {
       if (!success) {
         sendErrorMessage(req, res, err);
         return;
       }

       if (req._query.sid) {
         debug("setting new request for existing client");
         this.clients[req._query.sid].transport.onRequest(req);
       } else {
         this.handshake(req._query.transport, req);
       }
     };

     if (this.corsMiddleware) {
       this.corsMiddleware.call(null, req, res, () => {
         this.verify(req, false, callback);
       });
     } else {
       this.verify(req, false, callback);
     }
   }

   /**
    * generate a socket id.
    * Overwrite this method to generate your custom socket id
    *
    * @param {Object} request object
    * @api public
    */
   generateId(req) {
     return base64id.generateId();
   }

   /**
    * Handshakes a new client.
    *
    * @param {String} transport name
    * @param {Object} request object
    * @api private
    */
   async handshake(transportName, req) {
     const protocol = req._query.EIO === "3" ? 3 : 4; // 4th revision by default
     if (protocol === 3 && !this.opts.allowEIO3) {
       debug("unsupported protocol version");
       sendErrorMessage(
         req,
         req.res,
         Server.errors.UNSUPPORTED_PROTOCOL_VERSION
       );
       return;
     }

     let id;
     try {
       id = await this.generateId(req);
     } catch (e) {
       debug("error while generating an id");
       sendErrorMessage(req, req.res, Server.errors.BAD_REQUEST);
       return;
     }

     debug('handshaking client "%s"', id);

     try {
       var transport = new transports[transportName](req);
       if ("polling" === transportName) {
         transport.maxHttpBufferSize = this.opts.maxHttpBufferSize;
         transport.httpCompression = this.opts.httpCompression;
       } else if ("websocket" === transportName) {
         transport.perMessageDeflate = this.opts.perMessageDeflate;
       }

       if (req._query && req._query.b64) {
         transport.supportsBinary = false;
       } else {
         transport.supportsBinary = true;
       }
     } catch (e) {
       debug('error handshaking to transport "%s"', transportName);
       sendErrorMessage(req, req.res, Server.errors.BAD_REQUEST);
       return;
     }
     const socket = new Socket(id, this, transport, req, protocol);
     const self = this;

     if (this.opts.cookie) {
       transport.on("headers", headers => {
         headers["Set-Cookie"] = cookieMod.serialize(
           this.opts.cookie.name,
           id,
           this.opts.cookie
         );
       });
     }

     transport.onRequest(req);

     this.clients[id] = socket;
     this.clientsCount++;

     socket.once("close", function() {
       delete self.clients[id];
       self.clientsCount--;
     });

     this.emit("connection", socket);
   }

   /**
    * Handles an Engine.IO HTTP Upgrade.
    *
    * @api public
    */
   handleUpgrade(req, socket, upgradeHead) {
     this.prepare(req);

     const self = this;
     this.verify(req, true, function(err, success) {
       if (!success) {
         abortConnection(socket, err);
         return;
       }

       const head = Buffer.from(upgradeHead); // eslint-disable-line node/no-deprecated-api
       upgradeHead = null;

       // delegate to ws
       self.ws.handleUpgrade(req, socket, head, function(conn) {
         self.onWebSocket(req, conn);
       });
     });
   }

   /**
    * Called upon a ws.io connection.
    *
    * @param {ws.Socket} websocket
    * @api private
    */
   onWebSocket(req, socket) {
     socket.on("error", onUpgradeError);

     if (
       transports[req._query.transport] !== undefined &&
       !transports[req._query.transport].prototype.handlesUpgrades
     ) {
       debug("transport doesnt handle upgraded requests");
       socket.close();
       return;
     }

     // get client id
     const id = req._query.sid;

     // keep a reference to the ws.Socket
     req.websocket = socket;

     if (id) {
       const client = this.clients[id];
       if (!client) {
         debug("upgrade attempt for closed client");
         socket.close();
       } else if (client.upgrading) {
         debug("transport has already been trying to upgrade");
         socket.close();
       } else if (client.upgraded) {
         debug("transport had already been upgraded");
         socket.close();
       } else {
         debug("upgrading existing transport");

         // transport error handling takes over
         socket.removeListener("error", onUpgradeError);

         const transport = new transports[req._query.transport](req);
         if (req._query && req._query.b64) {
           transport.supportsBinary = false;
         } else {
           transport.supportsBinary = true;
         }
         transport.perMessageDeflate = this.perMessageDeflate;
         client.maybeUpgrade(transport);
       }
     } else {
       // transport error handling takes over
       socket.removeListener("error", onUpgradeError);

       this.handshake(req._query.transport, req);
     }

     function onUpgradeError() {
       debug("websocket error before upgrade");
       // socket.close() not needed
     }
   }

   /**
    * Captures upgrade requests for a http.Server.
    *
    * @param {http.Server} server
    * @param {Object} options
    * @api public
    */
   attach(server, options) {
     const self = this;
     options = options || {};
     let path = (options.path || "/engine.io").replace(/\/$/, "");

     const destroyUpgradeTimeout = options.destroyUpgradeTimeout || 1000;

     // normalize path
     path += "/";

     function check(req) {
       return path === req.url.substr(0, path.length);
     }

     // cache and clean up listeners
     const listeners = server.listeners("request").slice(0);
     server.removeAllListeners("request");
     server.on("close", self.close.bind(self));
     server.on("listening", self.init.bind(self));

     // add request handler
     server.on("request", function(req, res) {
       if (check(req)) {
         debug('intercepting request for path "%s"', path);
         self.handleRequest(req, res);
       } else {
         let i = 0;
         const l = listeners.length;
         for (; i < l; i++) {
           listeners[i].call(server, req, res);
         }
       }
     });

     if (~self.opts.transports.indexOf("websocket")) {
       server.on("upgrade", function(req, socket, head) {
         if (check(req)) {
           self.handleUpgrade(req, socket, head);
         } else if (false !== options.destroyUpgrade) {
           // default node behavior is to disconnect when no handlers
           // but by adding a handler, we prevent that
           // and if no eio thing handles the upgrade
           // then the socket needs to die!
           setTimeout(function() {
             if (socket.writable && socket.bytesWritten <= 0) {
               return socket.end();
             }
           }, destroyUpgradeTimeout);
         }
       });
     }
   }
 }

 /**
  * Protocol errors mappings.
  */

 Server.errors = {
   UNKNOWN_TRANSPORT: 0,
   UNKNOWN_SID: 1,
   BAD_HANDSHAKE_METHOD: 2,
   BAD_REQUEST: 3,
   FORBIDDEN: 4,
   UNSUPPORTED_PROTOCOL_VERSION: 5
 };

 Server.errorMessages = {
   0: "Transport unknown",
   1: "Session ID unknown",
   2: "Bad handshake method",
   3: "Bad request",
   4: "Forbidden",
   5: "Unsupported protocol version"
 };

 /**
  * Sends an Engine.IO Error Message
  *
  * @param {http.ServerResponse} response
  * @param {code} error code
  * @api private
  */

 function sendErrorMessage(req, res, code) {
   const headers = { "Content-Type": "application/json" };

   const isForbidden = !Server.errorMessages.hasOwnProperty(code);
   if (isForbidden) {
     res.writeHead(403, headers);
     res.end(
       JSON.stringify({
         code: Server.errors.FORBIDDEN,
         message: code || Server.errorMessages[Server.errors.FORBIDDEN]
       })
     );
     return;
   }
   if (res !== undefined) {
     res.writeHead(400, headers);
     res.end(
       JSON.stringify({
         code: code,
         message: Server.errorMessages[code]
       })
     );
   }
 }

 /**
  * Closes the connection
  *
  * @param {net.Socket} socket
  * @param {code} error code
  * @api private
  */

 function abortConnection(socket, code) {
   socket.on("error", () => {
     debug("ignoring error from closed connection");
   });
   if (socket.writable) {
     const message = Server.errorMessages.hasOwnProperty(code)
       ? Server.errorMessages[code]
       : String(code || "");
     const length = Buffer.byteLength(message);
     socket.write(
       "HTTP/1.1 400 Bad Request\r\n" +
         "Connection: close\r\n" +
         "Content-type: text/html\r\n" +
         "Content-Length: " +
         length +
         "\r\n" +
         "\r\n" +
         message
     );
   }
   socket.destroy();
 }

 module.exports = Server;

 /* eslint-disable */

 /**
  * From https://github.com/nodejs/node/blob/v8.4.0/lib/_http_common.js#L303-L354
  *
  * True if val contains an invalid field-vchar
  *  field-value    = *( field-content / obs-fold )
  *  field-content  = field-vchar [ 1*( SP / HTAB ) field-vchar ]
  *  field-vchar    = VCHAR / obs-text
  *
  * checkInvalidHeaderChar() is currently designed to be inlinable by v8,
  * so take care when making changes to the implementation so that the source
  * code size does not exceed v8's default max_inlined_source_size setting.
  **/
 // prettier-ignore
 const validHdrChars = [
   0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, // 0 - 15
   0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // 16 - 31
   1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // 32 - 47
   1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // 48 - 63
   1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // 64 - 79
   1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // 80 - 95
   1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // 96 - 111
   1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, // 112 - 127
   1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // 128 ...
   1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
   1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
   1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
   1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
   1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
   1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
   1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1  // ... 255
 ]

 function checkInvalidHeaderChar(val) {
   val += "";
   if (val.length < 1) return false;
   if (!validHdrChars[val.charCodeAt(0)]) {
     debug('invalid header, index 0, char "%s"', val.charCodeAt(0));
     return true;
   }
   if (val.length < 2) return false;
   if (!validHdrChars[val.charCodeAt(1)]) {
     debug('invalid header, index 1, char "%s"', val.charCodeAt(1));
     return true;
   }
   if (val.length < 3) return false;
   if (!validHdrChars[val.charCodeAt(2)]) {
     debug('invalid header, index 2, char "%s"', val.charCodeAt(2));
     return true;
   }
   if (val.length < 4) return false;
   if (!validHdrChars[val.charCodeAt(3)]) {
     debug('invalid header, index 3, char "%s"', val.charCodeAt(3));
     return true;
   }
   for (let i = 4; i < val.length; ++i) {
     if (!validHdrChars[val.charCodeAt(i)]) {
       debug('invalid header, index "%i", char "%s"', i, val.charCodeAt(i));
       return true;
     }
   }
   return false;
 }
	const qs = require("querystring");
	const parse = require("url").parse;
	const base64id = require("base64id");
	const transports = require("./transports");
	const EventEmitter = require("events").EventEmitter;
	const Socket = require("./socket");
	const debug = require("debug")("engine");
	const cookieMod = require("cookie");

	class Server extends EventEmitter {
	/**
	* Server constructor.
	*
	* @param {Object} options
	* @api public
	*/
	constructor(opts = {}) {
	super();

	this.clients = {};
	this.clientsCount = 0;

	this.opts = Object.assign(
	{
	wsEngine: process.env.EIO_WS_ENGINE \|\| "ws",
	pingTimeout: 5000,
	pingInterval: 25000,
	upgradeTimeout: 10000,
	maxHttpBufferSize: 1e6,
	transports: Object.keys(transports),
	allowUpgrades: true,
	httpCompression: {
	threshold: 1024
	},
	cors: false,
	allowEIO3: false
	},
	opts
	);

	if (opts.cookie) {
	this.opts.cookie = Object.assign(
	{
	name: "io",
	path: "/",
	httpOnly: opts.cookie.path !== false,
	sameSite: "lax"
	},
	opts.cookie
	);
	}

	if (this.opts.cors) {
	this.corsMiddleware = require("cors")(this.opts.cors);
	}

	if (opts.perMessageDeflate) {
	this.opts.perMessageDeflate = Object.assign(
	{
	threshold: 1024
	},
	opts.perMessageDeflate
	);
	}

	this.init();
	}

	/**
	* Initialize websocket server
	*
	* @api private
	*/
	init() {
	if (!~this.opts.transports.indexOf("websocket")) return;

	if (this.ws) this.ws.close();

	// add explicit require for bundlers like webpack
	const wsModule =
	this.opts.wsEngine === "ws" ? require("ws") : require(this.opts.wsEngine);
	this.ws = new wsModule.Server({
	noServer: true,
	clientTracking: false,
	perMessageDeflate: this.opts.perMessageDeflate,
	maxPayload: this.opts.maxHttpBufferSize
	});
	}

	/**
	* Returns a list of available transports for upgrade given a certain transport.
	*
	* @return {Array}
	* @api public
	*/
	upgrades(transport) {
	if (!this.opts.allowUpgrades) return [];
	return transports[transport].upgradesTo \|\| [];
	}

	/**
	* Verifies a request.
	*
	* @param {http.IncomingMessage}
	* @return {Boolean} whether the request is valid
	* @api private
	*/
	verify(req, upgrade, fn) {
	// transport check
	const transport = req._query.transport;
	if (!~this.opts.transports.indexOf(transport)) {
	debug('unknown transport "%s"', transport);
	return fn(Server.errors.UNKNOWN_TRANSPORT, false);
	}

	// 'Origin' header check
	const isOriginInvalid = checkInvalidHeaderChar(req.headers.origin);
	if (isOriginInvalid) {
	req.headers.origin = null;
	debug("origin header invalid");
	return fn(Server.errors.BAD_REQUEST, false);
	}

	// sid check
	const sid = req._query.sid;
	if (sid) {
	if (!this.clients.hasOwnProperty(sid)) {
	debug('unknown sid "%s"', sid);
	return fn(Server.errors.UNKNOWN_SID, false);
	}
	if (!upgrade && this.clients[sid].transport.name !== transport) {
	debug("bad request: unexpected transport without upgrade");
	return fn(Server.errors.BAD_REQUEST, false);
	}
	} else {
	// handshake is GET only
	if ("GET" !== req.method)
	return fn(Server.errors.BAD_HANDSHAKE_METHOD, false);
	if (!this.opts.allowRequest) return fn(null, true);
	return this.opts.allowRequest(req, fn);
	}

	fn(null, true);
	}

	/**
	* Prepares a request by processing the query string.
	*
	* @api private
	*/
	prepare(req) {
	// 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) : {};
	}
	}

	/**
	* Closes all clients.
	*
	* @api public
	*/
	close() {
	debug("closing all open clients");
	for (let i in this.clients) {
	if (this.clients.hasOwnProperty(i)) {
	this.clients[i].close(true);
	}
	}
	if (this.ws) {
	debug("closing webSocketServer");
	this.ws.close();
	// don't delete this.ws because it can be used again if the http server starts listening again
	}
	return this;
	}

	/**
	* Handles an Engine.IO HTTP request.
	*
	* @param {http.IncomingMessage} request
	* @param {http.ServerResponse\|http.OutgoingMessage} response
	* @api public
	*/
	handleRequest(req, res) {
	debug('handling "%s" http request "%s"', req.method, req.url);
	this.prepare(req);
	req.res = res;

	const callback = (err, success) => {
	if (!success) {
	sendErrorMessage(req, res, err);
	return;
	}

	if (req._query.sid) {
	debug("setting new request for existing client");
	this.clients[req._query.sid].transport.onRequest(req);
	} else {
	this.handshake(req._query.transport, req);
	}
	};

	if (this.corsMiddleware) {
	this.corsMiddleware.call(null, req, res, () => {
	this.verify(req, false, callback);
	});
	} else {
	this.verify(req, false, callback);
	}
	}

	/**
	* generate a socket id.
	* Overwrite this method to generate your custom socket id
	*
	* @param {Object} request object
	* @api public
	*/
	generateId(req) {
	return base64id.generateId();
	}

	/**
	* Handshakes a new client.
	*
	* @param {String} transport name
	* @param {Object} request object
	* @api private
	*/
	async handshake(transportName, req) {
	const protocol = req._query.EIO === "3" ? 3 : 4; // 4th revision by default
	if (protocol === 3 && !this.opts.allowEIO3) {
	debug("unsupported protocol version");
	sendErrorMessage(
	req,
	req.res,
	Server.errors.UNSUPPORTED_PROTOCOL_VERSION
	);
	return;
	}

	let id;
	try {
	id = await this.generateId(req);
	} catch (e) {
	debug("error while generating an id");
	sendErrorMessage(req, req.res, Server.errors.BAD_REQUEST);
	return;
	}

	debug('handshaking client "%s"', id);

	try {
	var transport = new transports[transportName](req);
	if ("polling" === transportName) {
	transport.maxHttpBufferSize = this.opts.maxHttpBufferSize;
	transport.httpCompression = this.opts.httpCompression;
	} else if ("websocket" === transportName) {
	transport.perMessageDeflate = this.opts.perMessageDeflate;
	}

	if (req._query && req._query.b64) {
	transport.supportsBinary = false;
	} else {
	transport.supportsBinary = true;
	}
	} catch (e) {
	debug('error handshaking to transport "%s"', transportName);
	sendErrorMessage(req, req.res, Server.errors.BAD_REQUEST);
	return;
	}
	const socket = new Socket(id, this, transport, req, protocol);
	const self = this;

	if (this.opts.cookie) {
	transport.on("headers", headers => {
	headers["Set-Cookie"] = cookieMod.serialize(
	this.opts.cookie.name,
	id,
	this.opts.cookie
	);
	});
	}

	transport.onRequest(req);

	this.clients[id] = socket;
	this.clientsCount++;

	socket.once("close", function() {
	delete self.clients[id];
	self.clientsCount--;
	});

	this.emit("connection", socket);
	}

	/**
	* Handles an Engine.IO HTTP Upgrade.
	*
	* @api public
	*/
	handleUpgrade(req, socket, upgradeHead) {
	this.prepare(req);

	const self = this;
	this.verify(req, true, function(err, success) {
	if (!success) {
	abortConnection(socket, err);
	return;
	}

	const head = Buffer.from(upgradeHead); // eslint-disable-line node/no-deprecated-api
	upgradeHead = null;

	// delegate to ws
	self.ws.handleUpgrade(req, socket, head, function(conn) {
	self.onWebSocket(req, conn);
	});
	});
	}

	/**
	* Called upon a ws.io connection.
	*
	* @param {ws.Socket} websocket
	* @api private
	*/
	onWebSocket(req, socket) {
	socket.on("error", onUpgradeError);

	if (
	transports[req._query.transport] !== undefined &&
	!transports[req._query.transport].prototype.handlesUpgrades
	) {
	debug("transport doesnt handle upgraded requests");
	socket.close();
	return;
	}

	// get client id
	const id = req._query.sid;

	// keep a reference to the ws.Socket
	req.websocket = socket;

	if (id) {
	const client = this.clients[id];
	if (!client) {
	debug("upgrade attempt for closed client");
	socket.close();
	} else if (client.upgrading) {
	debug("transport has already been trying to upgrade");
	socket.close();
	} else if (client.upgraded) {
	debug("transport had already been upgraded");
	socket.close();
	} else {
	debug("upgrading existing transport");

	// transport error handling takes over
	socket.removeListener("error", onUpgradeError);

	const transport = new transports[req._query.transport](req);
	if (req._query && req._query.b64) {
	transport.supportsBinary = false;
	} else {
	transport.supportsBinary = true;
	}
	transport.perMessageDeflate = this.perMessageDeflate;
	client.maybeUpgrade(transport);
	}
	} else {
	// transport error handling takes over
	socket.removeListener("error", onUpgradeError);

	this.handshake(req._query.transport, req);
	}

	function onUpgradeError() {
	debug("websocket error before upgrade");
	// socket.close() not needed
	}
	}

	/**
	* Captures upgrade requests for a http.Server.
	*
	* @param {http.Server} server
	* @param {Object} options
	* @api public
	*/
	attach(server, options) {
	const self = this;
	options = options \|\| {};
	let path = (options.path \|\| "/engine.io").replace(/\/$/, "");

	const destroyUpgradeTimeout = options.destroyUpgradeTimeout \|\| 1000;

	// normalize path
	path += "/";

	function check(req) {
	return path === req.url.substr(0, path.length);
	}

	// cache and clean up listeners
	const listeners = server.listeners("request").slice(0);
	server.removeAllListeners("request");
	server.on("close", self.close.bind(self));
	server.on("listening", self.init.bind(self));

	// add request handler
	server.on("request", function(req, res) {
	if (check(req)) {
	debug('intercepting request for path "%s"', path);
	self.handleRequest(req, res);
	} else {
	let i = 0;
	const l = listeners.length;
	for (; i < l; i++) {
	listeners[i].call(server, req, res);
	}
	}
	});

	if (~self.opts.transports.indexOf("websocket")) {
	server.on("upgrade", function(req, socket, head) {
	if (check(req)) {
	self.handleUpgrade(req, socket, head);
	} else if (false !== options.destroyUpgrade) {
	// default node behavior is to disconnect when no handlers
	// but by adding a handler, we prevent that
	// and if no eio thing handles the upgrade
	// then the socket needs to die!
	setTimeout(function() {
	if (socket.writable && socket.bytesWritten <= 0) {
	return socket.end();
	}
	}, destroyUpgradeTimeout);
	}
	});
	}
	}
	}

	/**
	* Protocol errors mappings.
	*/

	Server.errors = {
	UNKNOWN_TRANSPORT: 0,
	UNKNOWN_SID: 1,
	BAD_HANDSHAKE_METHOD: 2,
	BAD_REQUEST: 3,
	FORBIDDEN: 4,
	UNSUPPORTED_PROTOCOL_VERSION: 5
	};

	Server.errorMessages = {
	0: "Transport unknown",
	1: "Session ID unknown",
	2: "Bad handshake method",
	3: "Bad request",
	4: "Forbidden",
	5: "Unsupported protocol version"
	};

	/**
	* Sends an Engine.IO Error Message
	*
	* @param {http.ServerResponse} response
	* @param {code} error code
	* @api private
	*/

	function sendErrorMessage(req, res, code) {
	const headers = { "Content-Type": "application/json" };

	const isForbidden = !Server.errorMessages.hasOwnProperty(code);
	if (isForbidden) {
	res.writeHead(403, headers);
	res.end(
	JSON.stringify({
	code: Server.errors.FORBIDDEN,
	message: code \|\| Server.errorMessages[Server.errors.FORBIDDEN]
	})
	);
	return;
	}
	if (res !== undefined) {
	res.writeHead(400, headers);
	res.end(
	JSON.stringify({
	code: code,
	message: Server.errorMessages[code]
	})
	);
	}
	}

	/**
	* Closes the connection
	*
	* @param {net.Socket} socket
	* @param {code} error code
	* @api private
	*/

	function abortConnection(socket, code) {
	socket.on("error", () => {
	debug("ignoring error from closed connection");
	});
	if (socket.writable) {
	const message = Server.errorMessages.hasOwnProperty(code)
	? Server.errorMessages[code]
	: String(code \|\| "");
	const length = Buffer.byteLength(message);
	socket.write(
	"HTTP/1.1 400 Bad Request\r\n" +
	"Connection: close\r\n" +
	"Content-type: text/html\r\n" +
	"Content-Length: " +
	length +
	"\r\n" +
	"\r\n" +
	message
	);
	}
	socket.destroy();
	}

	module.exports = Server;

	/* eslint-disable */

	/**
	* From https://github.com/nodejs/node/blob/v8.4.0/lib/_http_common.js#L303-L354
	*
	* True if val contains an invalid field-vchar
	* field-value = *( field-content / obs-fold )
	* field-content = field-vchar [ 1*( SP / HTAB ) field-vchar ]
	* field-vchar = VCHAR / obs-text
	*
	* checkInvalidHeaderChar() is currently designed to be inlinable by v8,
	* so take care when making changes to the implementation so that the source
	* code size does not exceed v8's default max_inlined_source_size setting.
	**/
	// prettier-ignore
	const validHdrChars = [
	0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, // 0 - 15
	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // 16 - 31
	1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // 32 - 47
	1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // 48 - 63
	1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // 64 - 79
	1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // 80 - 95
	1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // 96 - 111
	1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, // 112 - 127
	1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // 128 ...
	1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
	1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
	1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
	1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
	1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
	1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
	1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1 // ... 255
	]

	function checkInvalidHeaderChar(val) {
	val += "";
	if (val.length < 1) return false;
	if (!validHdrChars[val.charCodeAt(0)]) {
	debug('invalid header, index 0, char "%s"', val.charCodeAt(0));
	return true;
	}
	if (val.length < 2) return false;
	if (!validHdrChars[val.charCodeAt(1)]) {
	debug('invalid header, index 1, char "%s"', val.charCodeAt(1));
	return true;
	}
	if (val.length < 3) return false;
	if (!validHdrChars[val.charCodeAt(2)]) {
	debug('invalid header, index 2, char "%s"', val.charCodeAt(2));
	return true;
	}
	if (val.length < 4) return false;
	if (!validHdrChars[val.charCodeAt(3)]) {
	debug('invalid header, index 3, char "%s"', val.charCodeAt(3));
	return true;
	}
	for (let i = 4; i < val.length; ++i) {
	if (!validHdrChars[val.charCodeAt(i)]) {
	debug('invalid header, index "%i", char "%s"', i, val.charCodeAt(i));
	return true;
	}
	}
	return false;
	}