ballerina/websocket

Package Overview

This package provides an implementation for connecting and interacting with WebSocket endpoints. The package facilitates three types of network entry points as ‘Client’, ‘AsyncClient’, and ‘Listener’.

The websocket:Client reads text and binary messages synchronously. A callback service with the two onPing and onPong remote functions can be registered at the initialization of the client to receive ping/pong control frames. The websocket:AsyncClient, which behaves asynchronously also has a callback websocket:Service that can be registered at the initialization of the client. It has a fixed set of remote methods in this service and they get called on the receipt of messages from the server.

On the server-side, an initial WebSocket service is there to handle upgrade requests. It has a single get resource, which takes in an http:Request optionally. The get resource returns a websocket:Service to which incoming messages get dispatched after a successful WebSocket connection upgrade. This resource can be used to intercept the initial HTTP upgrade with custom headers or to cancel the WebSocket upgrade by returning an error. The returning websocket:Service has a fixed set of remote methods.

WebSocket upgrade: During a WebSocket upgrade, the initial message received is an HTTP request.

service /ws on new websocket:Listener(21003) {
    resource function get .(http:Request req) returns websocket:Service|websocket:UpgradeError {
        return new WsService();
}
        
service class WsService {
  *websocket:Service;
  remote isolated function onTextMessage(websocket:Caller caller, string data) returns websocket:Error? {
      check caller->writeTextMessage(data);
  }
}

Remote methods associated with websocket:Service

onOpen: As soon as the WebSocket handshake is completed and the connection is established, the onOpen remote method is dispatched.

onTextMessage: The received text messages are dispatched to this remote method.

onBinaryMessage: The received binary messages are dispatched to this remote method.

onPing and onPong: The received ping and pong messages are dispatched to these remote methods respectively.

onIdleTimeout: This remote method is dispatched when the idle timeout is reached. The idleTimeout has to be configured either in the WebSocket service or the client configuration.

onClose: This remote method is dispatched when a close frame with a statusCode and a reason is received.

onError: This remote method is dispatched when an error occurs in the WebSocket connection. This will always be preceded by a connection closure with an appropriate close frame.

Remote methods associated with websocket:Client service

onPing: The received ping messages are dispatched to this remote method.

onPong: The received pong messages are dispatched to this remote method.

For more information, see the following.

• Server Example
• Client