server.bal

import ballerina/http;
import ballerina/log;
import ballerina/io;

// Annotations specifying the webSocket service.
@http:WebSocketServiceConfig {
    path: "/websocket"
}

// Define the backend service with port 15300.
service server on new http:Listener(9090) {

    resource function onOpen(http:WebSocketCaller caller) {
        log:printInfo("WebSocket client connect wih the server. The Connection ID: "
        + caller.getConnectionId());
        checkpanic caller->pushText("Hi");
    }

    // This resource gets invoked when a server is receiving a text message from the client
    resource function onText(http:WebSocketCaller caller, string text, boolean finalFrame) {
        io:println(text);
        var err = caller->pushText(text, finalFrame);
        if (err is http:WebSocketError) {
            log:printError("Error occurred when sending text message", err);
        }
    }
}