A WebSocket client in PHP is a program that uses a library such as textalk/websocket to connect to a WebSocket server and send and receive data in real-time.

WebSockets are a powerful tool for building real-time, interactive applications that run over the web. They allow for bidirectional communication between a client and a server, enabling the creation of chat apps, multiplayer games, and other applications that require real-time updates.

In PHP, there are several libraries available for working with WebSockets, such as textalk/websocket. This library provides a simple and easy-to-use interface for creating WebSocket client applications in PHP.

To get started with WebSockets in PHP using textalk/websocket, you’ll first need to install the library using Composer, a popular dependency manager for PHP:

composer require textalk/websocket

Once you have installed the library, you can use it to create a new WebSocket client and connect to a WebSocket server. Here is an example of a simple WebSocket client using textalk/websocket:

<?php
require 'vendor/autoload.php';

use WebSocket\Client;

$client = new Client("ws://echo.websocket.org");
$client->send("Hello WebSocket Server!");
echo $client->receive(); // will output 'Hello WebSocket Server!'

In this example, the WebSocket client is created with the Client class and the ws://echo.websocket.org url is passed as a parameter, this is a WebSocket echo server that will return the same message that is sent to it. The send() method is used to send a message to the server and the receive() method is used to receive the response from the server.

You can also use the onMessage method to handle incoming messages, the onMessage function is triggered each time the server sends a message to the client.

$client->onMessage(function ($message) {
    echo "Received message: $message\n";
});

In addition to the send() and receive() methods, the textalk/websocket library also provides several other methods for working with WebSockets, such as isConnected() to check the connection status and close() to close the connection.

Let’s see one more example. In this example we will fetch the crypto currency prices from the Binance websocket.

$client = new WebSocket\Client("wss://stream.binance.com:9443/ws/btcusdt@ticker");
$client->receive();

while ($client->isConnected()) {
    $response = json_decode($client->receive(), true);
    if (isset($response['c'])) {
        $price = $response['c'];
        echo "Current price: $price USDT\n";
    }
}
$client->close();

In conclusion, WebSockets are a powerful tool for building real-time, interactive applications that run over the web. With the help of libraries like textalk/websocket, it is relatively easy to create WebSocket client applications in PHP. This library provides a simple and easy-to-use interface for connecting to WebSocket servers and sending and receiving messages.