Version: 20

WebSocketServer

The WebSocketServer class allows you to create and configure a WebSocket server in 4D. Once the 4D WebSocket server is active, you can open and use WebSocket connections between 4D and clients using the WebSocketConnection class.

History

Release	Changes
20	Added

About WebSocket Servers

The WebSocket protocol provides full-duplex communication channel between a WebSocket Server and a client (e.g. a Web browser). For more information on WebSocket servers, read this page on Wikipedia.

Requirements

To create and handle your WebSocket Server in 4D, you will have to use two 4D build-in classes:

this class (4D.WebSocketServer) to manage the server itself,
the 4D.WebSocketConnection class to manage connections and messages.

In addition, you will have to create two user classes that will contain callback functions:

a user class to handle server connections,
a user class to handle messages.

You must create the WebSocket server within a worker to keep the connection alive.

The 4D Web Server must be started.

Example

In this basic example, our WebSocket server will return messages in uppercase.

Create the WebSocket server using a worker (mandatory) and pass your server connection class as parameter:

	//create an instance of the user class
	//that will handle the connections to the server
var $handler:cs.myServerHandler
$handler:=cs.myServerHandler.new()

CALL WORKER("WebSocketServer"; Formula(wss:=4D.WebSocketServer.new($handler)))  
	//assign a variable (wss) to the WebSocket allows you  
	//to call wss.terminate() afterwards

Define the myServerHandler user class containing callback function(s) used to handle connections to the server:

//myServerHandler class

Function onConnection($wss : Object; $event : Object) : Object
	//returns an instance of the user class
	//that will handle the messages
	return cs.myConnectionHandler.new()

Define the myConnectionHandler user class containing callback function(s) used to handle messages:

// myConnectionHandler class

Function onMessage($ws : 4D.WebSocketConnection; $message : Object)
	//resends the message in uppercase
	$ws.send(Uppercase($message.data))

Client-Side JS

See this blog post for an example of client-side Javascript code handling a WebSocket connection.

WebSocketServer object

WebSocket server objects provide the following properties and functions:


.connections : Collection all current connections handled by the WebSocket server
.dataType : Text the type of the data received or sent
.handler : Object the accessor that gets the `WSSHandler` object used to initiate the WebSocket server
.path : Text the pattern of the path to access the WebSocket server
.terminate() .terminate( timeout : Integer ) closes the WebSocket server
.terminated : Boolean True if the WebSocket server is closed

4D.WebSocketServer.new()

4D.WebSocketServer.new( WSSHandler : Object { ; options : Object } ) : 4D.WebSocketServer

Parameter	Type		Description
WSSHandler	Object	->	Object of the user class declaring the WebSocket Server callbacks
options	Object	->	WebSocket configuration parameters
Result	4D.WebSocketServer	<-	New WebSocketServer object

The 4D.WebSocketServer.new() function creates and starts a WebSocket server that will use the specified WSSHandler callbacks and (optionally) options, and returns a 4D.WebSocketServer object.

Calling this function requires that the 4D Web Server is started. The host and port of the WebSocket server are the same as the host and port of the 4D Web Server.

WSSHandler parameter

In the WSSHandler parameter, pass an instance of a user class that will be called every time an event occurs on the WebSocket server --essentially, connection events. The class should define the following callback functions (only onConnection is mandatory):

Property	Type	Description	Default
onConnection	Function	(mandatory) Callback when a new client connection is started (see below)	undefined
onOpen	Function	Callback when the WebSocket server is started (see below)	undefined
onTerminate	Function	Callback when the WebSocket server is terminated (see below)	undefined
onError	Function	Callback when an error has occurred (see below)	undefined

WSHandler.onConnection(WSServer : Object ; event : Object) : Object | null

Parameter		Type		Description
WSServer		4D.WebSocketServer	<-	Current WebSocket server object
event		Object	<-	Parameters
	type	Text		"connection"
	request	Object		`request` object. Contains information on the connection request (see below)
Function result		Object	->	`connectionHandler` object (see below). If this function returns a `connectionHandler` object, a `4D.WebSocketConnection` object is automatically created and added to the collection of connections. This object is then received as parameter in each function of the `connectionHandler` object. If the returned value is null or undefined, the connection is cancelled.

This callback is called when the handshake is complete. It must be called with a valid connectionHandler object to create the WebSocket connection, otherwise the connection is cancelled.

WSHandler.onOpen(WSServer : Object ; event : Object)

Parameter		Type		Description
WSServer		4D.WebSocketServer	<-	Current WebSocket server object
event		Object	<-	Parameters
	type	Text		"open"

Event emitted when the websocket server is started.

WSHandler.onTerminate(WSServer : Object ; event : Object)

Parameter		Type		Description
WSServer		4D.WebSocketServer	<-	Current WebSocket server object
event		Object	<-	Parameters
	type	Text		"terminate"

Event emitted when the HTTP server or the WebSocket server is closed.

WSHandler.onError(WSServer : Object ; event : Object)

Parameter		Type		Description
WSServer		4D.WebSocketServer	<-	Current WebSocket server object
event		Object	<-	Parameters
	type	Text		"error"
	errors	Collection		Collection of 4D error stack in case of execution error [].errCode (number) - 4D error code [].message (text) - Description of the 4D error [].componentSignature (text) - Signature of the internal component which returned the error

Event emitted when an error occurs on the WebSocket server.

Example of `WSSHandler` class

This example of a basic chat feature illustrates how to handle WebSocket server connections in a WSSHandler class.

//myWSServerHandler class

Function onConnection($wss : Object; $event : Object) : Object

	If (VerifyAddress($event.request.remoteAddress))
		// The VerifyAddress method validates the client address
		// The returned WSConnectionHandler object will be used
		// by 4D to instantiate the 4D.WebSocketConnection object
		// related to this connection
		return cs.myConnectionHandler.new()   
		// See connectionHandler object
	Else
		// The connection is cancelled		
		return Null
	End if

Function onOpen($wss : Object; $event : Object)
LogFile("*** Server started")

Function onTerminate($wss : Object; $event : Object)
LogFile("*** Server closed")

Function onError($wss : Object; $event : Object)
LogFile("!!! Server error: "+$event.errors.first().message)

`request` object

A request object contains the following properties:

Parameter	Type	Description
headers	Object	The client HTTP GET request. `headers.key=value` (value can be a collection if the same key appears multiple times)
query	Object	Object that contains the URL parameters. For example, if parameters are: `?key1=value1&key2=value2` -> `query.key1=value1`, `query.key2=value2`
url	Text	contains only the URL that is present in the actual HTTP request. Ex: `GET /status?name=ryan HTTP/1.1` -> url="/status?name=ryan"
remoteAddress	Text	IP Address of the client

`connectionHandler` object

As a result of the WSHandler.onConnection callback, pass a connectionHandler object, which is an instance of a user class that will be called every time an event occurs in the WebSocket connection --essentially, messages received. The class should define the following callback functions (only onMessage is mandatory):

Parameter	Type	Description
onMessage	Function	(mandatory) Function called when a new message is received from this connection
onOpen	Function	Function called when the `4D.WebSocketConnection` is created
onTerminate	Function	Function called when this connection is terminated
onError	Function	Function called when an error occured

connectionHandler.onMessage(ws : 4D.WebSocketConnection ; event : Object)

Parameter		Type		Description
ws		`4D.WebSocketConnection`	<-	Current WebSocket connection object
event		Object	<-	Parameters
	type	Text		"message"
	data	Text / Blob / Object		data sent by the client

This Callback for WebSocket data. Called each time the WebSocket receives data.

connectionHandler.onOpen(ws : 4D.WebSocketConnection ; event : Object)

Parameter		Type		Description
ws		`4D.WebSocketConnection`	<-	Current WebSocket connection object
event		Object	<-	Parameters
	type	Text		"open"

Called when the connectionHandler object is created (after WSS.onConnection event).

connectionHandler.onTerminate(ws : 4D.WebSocketConnection ; event : Object)

Parameter		Type		Description
ws		`4D.WebSocketConnection`	<-	Current WebSocket connection object
event		Object	<-	Parameters
	type	Text		"terminate"
	code	Number		Status code indicating why the connection has been closed. If the WebSocket does not return an error code, `code` is set to 1005 if no error occurred or to 1006 if there was an error.
	reason	Text		String explaining why the connection has been closed. If the websocket doesn't return an reason, code is undefined

Function called when the WebSocket is closed.

connectionHandler.onError(ws : 4D.WebSocketConnection ; event : Object)

Parameter			Type		Description
ws			`4D.WebSocketConnection`	<-	Current WebSocket connection object
event			Object	<-	Parameters
	type		Text		"error"
	errors	Collection		Collection of 4D errors stack in case of execution error [].errCode (number) - 4D error code [].message (text) - Description of the 4D error [].componentSignature (text) - Signature of the internal component which returned the error

Function called when an error has occurred.

Example of `connectionHandler` class

This example of a basic chat feature illustrates how to handle messages in a connectionHandler class.

// myConnectionHandler Class

Function onMessage($ws : 4D.WebSocketConnection; $message : Object)
	// Resend the message to all chat clients
	This.broadcast($ws;$message.data)

Function onOpen($ws : 4D.WebSocketConnection; $message : Object)
	// Send a message to new connected users
	$ws.send("Welcome on the chat!")
	// Send "New client connected" message to all other chat clients
	This.broadcast($ws;"New client connected")

Function onTerminate($ws : 4D.WebSocketConnection; $message : Object)
	// Send "Client disconnected" message to all other chat clients
	This.broadcast($ws;"Client disconnected")

Function broadcast($ws : 4D.WebSocketConnection; $message:text)
	var $client:4D.WebSocketConnection
	// Resend the message to all chat clients
	For each ($client; $ws.wss.connections)
		// Check that the id is not the current connection
		If ($client.id#$ws.id)
			$client.send($message)
		End if
	End for each

options parameter

In the optional options parameter, pass an object that contains the following properties:

Property	Type	Description	Default
path	Text	Represents the path to access the WebSocket server. If no path is defined, the WebSocket server manages all the connections	undefined
dataType	Text	Type of the data received through the `connectionHandler.onMessage` and the data send by `WebSocketConnection.send()` function. Values: "text", "blob","object"). If "object": (send) transforms object into a json format and sends it; (reception): receives json format and transforms it into object	text

.connections

.connections : Collection

Description

The .connections property contains all current connections handled by the WebSocket server. Each element of the collection is a WebSocketConnection object.

When a connection is terminated, its status changes to "Closed" and it is removed from this collection.

.dataType

.dataType : Text

Description

The .dataType property contains the type of the data received or sent.

This property is read-only.

.handler

.handler : Object

Description

The .handler property contains the accessor that gets the WSSHandler object used to initiate the WebSocket server.

.path

.path : Text

Description

The .path property contains the pattern of the path to access the WebSocket server. If no path was defined, the WebSocket server manages all connections.

This property is read-only.

.terminate()

.terminate()
.terminate( timeout : Integer )

Parameter	Type		Description
timeout	Integer	->	Waiting time in seconds before terminating the WebSocket server

Description

The .terminate() function closes the WebSocket server.

By default, if no timeout value is set, the function initializes close handshake and waits to receive close frame from the peer, after that sending FIN packet in attempt to perform a clean socket close. When answer received, the socket is destroyed.

If a timeout value is set:

when the waiting time is reached, forcibly destroys the socket.
if timeout = 0, forcibly destroys the socket without closing frames or fin packets exchange, and does it instantly without waiting time.

.terminated

.terminated : Boolean

Description

The .terminated property contains True if the WebSocket server is closed.

This property is read-only.

Requirements​

Example​

WebSocketServer object​

4D.WebSocketServer.new()​

WSSHandler parameter​

Example of WSSHandler class​

request object​

connectionHandler object​

Example of connectionHandler class​

options parameter​

.connections​

Description​

.dataType​

Description​

.handler​

Description​

.path​

Description​

.terminate()​

Description​

.terminated​

Description​

Requirements

Example

WebSocketServer object

4D.WebSocketServer.new()

WSSHandler parameter

Example of `WSSHandler` class

`request` object

`connectionHandler` object

Example of `connectionHandler` class

options parameter

.connections

Description

.dataType

Description

.handler

Description

.path

Description

.terminate()

Description

.terminated

Description