How to build event-based applications using PHP

Methods for building event-based applications in PHP include using the EventSource API to create an event source and using an EventSource object on the client to listen for events. Send events using Server Sent Events (SSE) and listen for events on the client side using the XMLHttpRequest object. A practical example is to use EventSource in an e-commerce website to update inventory counts in real time. This is achieved on the server side by randomly changing the inventory and sending updates, and the client listens for inventory updates through EventSource and displays them in real time.

How to build event-based applications using PHP

In modern web development, event-based applications are becoming more and more Becoming more and more popular. They allow developers to create applications that respond to user interactions, server events, and other triggers. PHP, as a popular server-side programming language, provides powerful support for building event-based applications.

EventSource API

PHP provides the EventSource API, which allows the browser to establish a persistent connection with the server and receive data when an event occurs on the server side.

To use an EventSource, you first need to create the event source on the server side:

<?php
header('Content-Type: text/event-stream');
header('Cache-Control: no-cache');

$count = 0;
while (true) {
    echo "data: {$count}\n\n";
    $count++;
    flush();
    sleep(1);
}
?>

This will create an event source that sends a number to the client every second.

Using EventSource on the client

Next, you can use EventSource on the client to listen to the event source:

var source = new EventSource('/events');

source.onmessage = function(event) {
    console.log(event.data);
};

This will create an EventSource instance and Listen for events from the server. When the server sends data, it is printed to the console.

Push-based Server Sent Events (SSE)

SSE is another method for creating event-based applications that provides a Function. To use SSE, you first need to send an event response on the server side using PHP:

<?php
header('Content-Type: text/event-stream');
header('Cache-Control: no-cache');

while (true) {
    $event = json_encode(['data' => 'some data']);
    echo "event: {$event}\n\n";
    flush();
    sleep(1);
}
?>

This will send one server-side event every second.

Using SSE on the client

You can use XMLHttpRequest (XHR) on the client to listen for SSE events:

var xhr = new XMLHttpRequest();

xhr.addEventListener('message', function(event) {
    console.log(event.data);
});

xhr.open('GET', '/sse', true);
xhr.send();

This will open a link to SSE GET request to the endpoint and print the data when the event is received.

Practical case: updating inventory in real time

Consider an e-commerce website with real-time inventory counts. Using event-based applications, websites can send updates to customers when inventory changes.

On the server side, you can use PHP to create an event source and send updates when the inventory changes:

<?php
header('Content-Type: text/event-stream');
header('Cache-Control: no-cache');

$stock = 100;

while (true) {
    // 随机更改库存
    $stock += rand(-10, 10);

    $event = json_encode(['stock' => $stock]);
    echo "event: {$event}\n\n";
    flush();
    sleep(1);
}
?>

On the client side, you can use an EventSource to listen for inventory updates:

var source = new EventSource('/stock-updates');

source.onmessage = function(event) {
    var data = JSON.parse(event.data);
    document.getElementById('stock-count').innerHTML = data.stock;
};

This will update the page's inventory count in real time.

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