WebUi

Backend - WebSocket module

WebSocket server communicates with the connected clients via RFC 6455 protocol. The server requires each new connection and message to be singed with JWT token. In addition, it allows filtering messages broadcast to connected clients.

Instance

const {WebSocket, WebSocketMessage} = require('@aliceo2/web-ui');
WebSocket(HTTP_SERVER);

Where:

• HTTP_SERVER - instance of HTTP server

Public methods

bind

broadcast

unfilteredBroadcast

shutdown

WebSocketMessage class

The WebSocket messages are represented as WebSocketMessage objects. The object consists of following fields:

• command - message name
• code - optional code that indicates type of message (same as HTTP status code)
• broadcast - flag that states whether the message shoud be broadcast to all connected clients
• payload - message payload, for users logic
• message - message that might be set internally
• id - CERN ID (comes from token)
• username - CERN username (comes from token)

A message can be constructed in following way:

WebSocketMessage(code = 200);

The message can be manipulated using setters:

setPayload
setBroadcast
setCommand

…and getters:

getPayload
getBroadcast
getProperty
getCode
getToken

In addition two methods for encoding and decoding messages to/from JSON are avaialble:

json
parse

Broadcast filtering

Connecting clients may decide which broadcast messages they receive from server. This can be done by sending “filter” command (use setFilter of frontends’ WebSocketClient). The filter must be passed as stringified JavaScript function receiving WebSocketMessage object and returning true or false.

Example

// Prepare http server
...

// Create instance of WebSocket server
const ws = new WebSocket(http);

// Print all messages with command 'print'
ws.bind('print', (message) => {
  console.log(message.payload);
  // ...and send back 'print-response'
  return new WebSocketMessage().setCommand('print-response').setPayload('hi');
});

This site is open source. Improve this page.