How to Implement Simple Long Polling Using Apache and PHP?

Implementing Simple Long Polling

Many resources describe the concept of long polling, but practical implementation examples remain elusive. Let's delve into a simplified version without relying on complex frameworks or server configurations.

Using Apache and PHP for Server Communication

To handle server requests, Apache is adequate. The PHP script below sends a random string after a random interval, simulating real-time message arrival. Occasionally, it returns an error for demonstration purposes.

<?php
if (rand(1, 3) == 1) {
    header("HTTP/1.0 404 Not Found");
    die();
}
sleep(rand(2, 10));
echo("Hi! Have a random number: " . rand(1, 10));
?>

JavaScript Client for Long Polling

In JavaScript, the long poller continually requests the above script and waits for a response:

<script type="text/javascript">
function waitForMsg() {
    $.ajax({
        type: "GET",
        url: "msgsrv.php",

        success: function(data) {
            // Display the message
            $("#messages").append("<div class='msg new'>" + data + "</div>");

            // Recursively invoke waitForMsg
            setTimeout(waitForMsg, 1000);
        },
        error: function() {
            // Display the error message and restart the process after 15 seconds
            $("#messages").append("<div class='msg error'>Error encountered</div>");
            setTimeout(waitForMsg, 15000);
        }
    });
}

$(document).ready(function() {
    waitForMsg();
});
</script>

This script continuously checks for server updates and displays incoming messages. Error handling is incorporated, and the long poller attempts to reconnect after a specified timeout period.

Strengths of Long Polling

Long polling offers several benefits:

• Resilience: In the event of an internet connection loss, the client can recover and reconnect automatically.
• Scalability: A standalone server can handle multiple simultaneous long polling requests without affecting website performance.
• Simplicity: The code, both server-side and client-side, is straightforward and easy to implement.

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