ws-wrapper

Lightweight Web Socket lib with socket.io-like event handling, Promise-based requests, and channels.

What?

Much like Socket.io, this library provides a protocol and API that sits on top of native WebSockets. Rather than passing raw messages through the WebSocket via WebSocket.send(), this library allows you to pass JSON data over the sockets and trigger event handlers on the remote end. There is also a Promise-based request/response API, as well.

Why?

Because lightweight is sometimes what you want.

This lib might be useful if you want some socket.io functionality (i.e. namespaces, event handling, etc.), but you don't want all of the engine.io transports. When using this library in conjunction with a library like ws, your real-time web application can be pretty darn lightweight without giving up some nice bare-bones functionality.

ws + ws-wrapper is a good combination for mobile apps, desktop apps (i.e. electron), or other browser-targeted web applications.

Install

npm install ws-wrapper

Usage

WebSocketWrapper is a CommonJS module, so it works in Node.js and in the browser if you use a tool like browserify or module-concat.

Check out the example-app for a sample chat application.

Note: This module uses ES6 classes. If you need this to work in IE or another old, decrepit browser, try using a code transpiler like Babel.

Client-side

// Assuming WebSocketWrapper is available to this scope...
var socket = new WebSocketWrapper(new WebSocket(...) );
// Now use the WebSocketWrapper API... `socket.emit` for example
// See examples below...

Server-side

Use ws-server-wrapper to wrap the WebSocketServer. Or, you can wrap the WebSocket once a new WebSocket connects like this:

const WebSocketServer = require("ws").Server
	, WebSocketWrapper = require("ws-wrapper");
var wss = new WebSocketServer({port: 3000});
wss.on("connection", (socket) => {
	socket = new WebSocketWrapper(socket);
	// ...
});

Event Handling

Call on or once to bind an event handler to the wrapper or to a channel. Call emit to send an event.

Server-side Example:

const WebSocketServer = require("ws").Server
	, WebSocketWrapper = require("ws-wrapper");
var wss = new WebSocketServer({port: 3000});
var sockets = new Set();
wss.on("connection", (socket) => {
	var socket = new WebSocketWrapper(socket);
	sockets.add(socket);
	socket.on("msg", function(from, msg) {
		// `this` refers to the WebSocketWrapper instance
		console.log(`Received message from ${from}: ${msg}`);
		// Relay message to all clients
		sockets.forEach((socket) => {
			socket.emit("msg", from, msg);
		});
	});
	socket.on("disconnect", () => {
		sockets.delete(socket);
	});
});

Client-side:

// Assuming WebSocketWrapper is somehow available to this scope...
var socket = new WebSocketWrapper(
	new WebSocket("ws://" + location.host)
);
socket.on("msg", function(from, msg) {
	console.log(`Received message from ${from}: ${msg}`);
});
socket.emit("msg", "my_name", "This is a test message");

Channels

Just like in socket.io, you can "namespace" your sockets using channels. When sending messages to multiple channels, the same WebSocket connection is still used, but the events are separated into the appropriate channels.

By default, calling emit directly on a WebSocketWrapper instance will send the message to the "default" channel. To send a message over a channel named "foo", just call socket.of("foo").emit("eventName", "yourData").

Request / Response

Event handlers can return values or Promises to respond to requests. The response is sent back to the remote end.

The example below shows the client requesting data from the server, but ws-wrapper also allows servers to request data from the client.

Server-side:

const fs = require("fs")
	, WebSocketServer = require("ws").Server
	, WebSocketWrapper = require("ws-wrapper");
var wss = new WebSocketServer({port: 3000});
var sockets = new Set();
wss.on("connection", (socket) => {
	socket = new WebSocketWrapper(socket);
	sockets.add(socket);
	socket.on("userCount", () => {
		// Return value is sent back to the client
		return sockets.size;
	});
	socket.on("readFile", (path) => {
		// We can return a Promise that eventually resolves
		return new Promise((resolve, reject) => {
			// `path` should obviously be sanitized, but just go with it...
			fs.readFile(path, (err, data) => {
				// `err` or `data` are now sent back to the client
				if(err)
					reject(err);
				else
					resolve(data.toString("utf8") );
			});
		});
	});
	socket.on("disconnect", () => {
		sockets.delete(socket);
	});
});

Client-side:

// Assuming WebSocketWrapper is somehow available to this scope...
var socket = new WebSocketWrapper(
	new WebSocket("ws://" + location.host)
);
var p = socket.request("userCount");
// `p` is a Promise that will resolve when the server responds...
p.then((count) => {
	console.log("User count: " + count);
}).catch((err) => {
	console.error("An error occurred while getting the user count:", err);
});
socket.request("readFile", "/etc/issue").then((data) => {
	console.log("File contents:", data);
}).catch((err) => {
	console.error("Error reading file:", err);
});

API

Class: WebSocketWrapper

A WebSocketWrapper simply wraps around a WebSocket to give you well-deserved functionality. :)

socket = new WebSocketWrapper(webSocketInstance[, options]);

Constructs a new WebSocketWrapper, and binds it to the native WebSocket instance.

• webSocketInstance - the native WebSocket instance
• options
  • debug - set to true to print debugging messages to console.log
  • errorToJSON - function to serialize Errors over the WebSocket. In Node.js, the default is to send only the message property of the Error (for security reasons). Errors that occur on the browser include all properties.
  • requestTimeout - maximum delay in ms. that the WebSocketWrapper will wait until rejecting the Promise of a pending request. Defaults to null, which means that there will be no timeout. This option is recommended for servers because clients who do not fulfill pending requests can cause memory leaks.

Events

• Event: "open"
  • event - The (worthless) event from the native WebSocket instance
• Event: "error"
  • event - The Error event from the native WebSocket instance
• Event: "message"
  • event - The Message event from the native WebSocket instance
  • data - The message data (same as event.data)
• Event: "close" / "disconnect"
  • event - The Close event from the native WebSocket instance
  • wasOpen - true if the "open" event was fired on the native WebSocket instance before the "close" event was fired.

The EventEmitter-like API looks like this:

• socket.on(eventName, listener) Adds the listener function to the end of the listeners array for the event named eventName. When an event or request matching the eventName is received by the WebSocket, the listener is called.

  Values returned by the listener callback are used to respond to requests (see socket.request). If the return value of the listener is a Promise, the response to the request will be sent once the Promise is resolved or rejected; otherwise, the return value of the listener is sent back to the remote end immediately.

  If the inbound message is a simple event (see socket.emit), the return value of the listener is ignored. It is also "safe" for the listener to return a Promise even if the inbound message is a "simple" event. If the returned Promise is rejected, an unhandled rejection will not occur; rather, the result of the Promise is just ignored.

  If the listener throws an Error, this Error will propagate up the stack as expected, and if the inbound message was a request, the Error is sent back to the remote end as a response rejection.

• socket.once(eventName, listener) Adds a one time listener function for the event named eventName.

• socket.removeListener(eventName, listener) Removes the specified listener from the listener array for the event named eventName.

• socket.removeAllListeners([eventName]) Removes all listeners, or those of the specified eventName.

• socket.eventNames() Returns an array listing the events for which the emitter has registered listeners.

• socket.listeners(eventName) Returns a copy of the array of listeners for the event named eventName.

• socket.emit(eventName[, ...args]) Sends an event down the WebSocket with the specified eventName calling all listeners for eventName on the remote end, in the order they were registered, passing the supplied arguments to each.

• socket.request(eventName[, ...args]) Sends a request down the WebSocket with the specified eventName and returns a Promise that will resolve once the remote event listener responds.

  Note: While it is common design for only one event listener to exist on the remote end, all listeners for eventName on the remote end are called, in the order they were registered, passing the supplied arguments to each. Since Promises can only be resolved or rejected once, only the data from the first event listener is used to generate the response for this request.

  Note: If a request is sent, but there is no remote event listener to respond to the request, a response rejection is immediately sent back by the remote end.

• socket.timeout(tempTimeoutInMs) Temporarily sets the requestTimeout to tempTimeoutInMs for the next request only. This returns socket to allow chaining. Typical usage:

  // The next request will be rejected if there is no response for 5 secs.
  let promise = socket.timeout(5 * 1000).request("readFile", "/etc/issue");

The above EventEmitter functions like on and once are chainable (as appropriate).

Channel API:

• socket.of(channelName) Returns the channel with the specified channelName. Every channel has the same EventEmitter-like API as described above for sending and handling channel-specific events and requests.

Other methods and properties:

By default, the WebSocketWrapper provides a queue for data to be sent. Once the WebSocket is open, this queue is flushed until the connection is lost. The following methods allow one to re-bind a new WebSocket or clear the send queue.

• socket.abort() Clears the send queue for this WebSocketWrapper and rejects all Promises for pending requests.
• socket.bind(nativeWebSocket) Binds this WebSocketWrapper to a new WebSocket. This can be useful when socket reconnection logic needs to be implemented. Instead of creating a new WebSocketWrapper each time a WebSocket is disconnected, one can simply bind a new WebSocket to the WebSocketWrapper. In this way, data queued to be sent while the connection was dead will be sent over the new WebSocket passed to the bind function.
• socket.isConnecting - checks the native WebSocket readyState and is true if and only if the state is CONNECTING.
• socket.isConnected - checks the native WebSocket readyState is true if and only if the state is CONNECTED.
• socket.send(data) If connected, calls the native WebSocket's send method; otherwise, the data is added to the WebSocketWrapper's send queue.
• socket.disconnect() Closes the native WebSocket
• socket.set(key, value) Saves user data specific to this WebSocketWrapper
• socket.get(key) Retrieves user data. See socket.set(key, value) above.

WebSocketWrapper.MAX_SEND_QUEUE_SIZE The maximum number of items allowed in the send queue. If a user tries to send more messages than this number while a WebSocket is not connected, errors will be thrown. Defaults to 10; changes affect all WebSocketWrapper instances.

Protocol

All data passed over the native WebSocket should be valid JSON. ws-wrapper will parse the JSON string and determine the message type based on the properties in the parsed Object.

The following message types are defined by ws-wrapper:

1. Simple Event - Identified by an Object with a key but no i key. The channel name is optional.

   {
   	"c": "channel_name",
   	"a": ["event_name", "first_arg", "second_arg", "last_arg"]
   }

   The client or server can send events. Events are nothing more than an event name and some data, passed as arguments to the event handler.

2. Request - Identified by an Object with a and i keys where i refers to the unique request identifier. The channel name is optional.

   {
   	"i": 123,
   	"c": "channel_name",
   	"a": ["event_name", "first_arg", "second_arg", "last_arg"]
   }

   The client or server can send a Request, which is essentially an Event that needs some sort of server Response.

3. Response (Resolution) - Identified by an Object with i and d keys where i is the request identifier and d is the response data.

   {
   	"i": 123,
   	"d": {"resolved": "data", "hello": "world"}
   }

4. Response (Rejection) - Identified by an Object with i and e keys where i is the request identifier and e is the error Object to be used when rejecting the response Promise. If _ is set, the e Object is converted into an Error instance upon receipt.

   {
   	"i": 123,
   	"e": {"message": "error message"},
   	"_": 1
   }

If the message received by the WebSocket is not valid JSON or if the parsed Object does not match one of the above message types, then the message is simply ignored by ws-wrapper. Also if the JSON message contains a ws-wrapper property with the value false, the message will be ignored. This allows other libraries to use the same WebSocket and send messages that will not be processed by ws-wrapper.