How to Implement Basic Long Polling Using Apache and JavaScript?

Achieving Basic Long Polling Implementation

Long Polling is a polling technique that keeps connections open for an extended period, facilitating instant response when server updates become available. Its implementation can be quite straightforward.

Apache as a Request Handler

To serve requests using Apache, create a PHP script like msgsrv.php. Here's a simple example:

// Simulate data availability after a random delay
sleep(rand(2, 10));
echo("Hi! Here's a random number: " . rand(1, 10));

Run this script on Apache. Note that using a high-volume webserver like Apache may result in exhausted worker threads.

Using a JavaScript Script

In JavaScript, you can use a script like long_poller.htm to initiate polling requests:

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

      async: true,
      cache: false,
      timeout: 50000,

      success: function(data) {
        // Append the response to a div
        addmsg("new", data);
        // Continue polling after 1 second
        setTimeout(waitForMsg, 1000);
      },
      error: function(..., errorThrown) {
        // Append error to div
        addmsg("error", textStatus + " (" + errorThrown + ")");
        // Retry after 15 seconds
        setTimeout(waitForMsg, 15000);
      }
    });
  }

  $(document).ready(function() {
    waitForMsg(); // Start the initial request
  });
</script>

This script continuously makes requests to msgsrv.php, displaying responses in a div. It uses a simple rate limiter to prevent excessive requests.

Benefits of Long Polling

Long Polling offers resilience and simplicity. In case of network interruptions, the client retries automatically. It's a suitable choice for applications requiring immediate updates from the server, such as instant messaging or chat applications.

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