Long Polling Example

Long polling is a technique used in web development to allow a client to receive an immediate response from a server, or to wait for a certain event to occur before receiving a response. It is often used in scenarios where real-time communication is required, such as chat applications or live updates.

Basic Concept

In a long polling scenario, the client sends a request to the server and the server holds the request open until a certain event occurs. Once the event occurs, the server sends a response back to the client, and the client then sends another request to the server, and so on.

Steps:

1. The client sends a request to the server.
2. The server holds the request open until a certain event occurs.
3. The server sends a response back to the client.
4. The client sends another request to the server.

Example

Here is a simple example of how long polling can be implemented using JavaScript and PHP:

// Client-side JavaScript
function longPolling() {
  var xhr = new XMLHttpRequest();
  xhr.open('GET', '/en/developer_docs/long_polling_example', true);
  xhr.onreadystatechange = function() {
    if (xhr.readyState === 4 && xhr.status === 200) {
      console.log(xhr.responseText);
      longPolling();
    }
  };
  xhr.send();
}

longPolling();

// Server-side PHP
<?php
if ($_SERVER['REQUEST_METHOD'] === 'GET') {
  // Simulate a delay
  sleep(5);

  // Simulate an event
  $event = "New message received";

  // Send the response back to the client
  echo $event;
}
?>

Conclusion

Long polling is a powerful technique for implementing real-time communication between a client and a server. It is simple to implement and can be used in a variety of scenarios. For more information on long polling, you can refer to the MDN Web Docs.

Long Polling Concept