Easy way to close connections to the browser and continue processing on the server.

closeConnection.php

<?php
/**
 * Close the connection to the browser but continue processing the operation
 * @param $body
 */
public function closeConnection($body, $responseCode){
    // Cause we are clever and don't want the rest of the script to be bound by a timeout.
    // Set to zero so no time limit is imposed from here on out.
    set_time_limit(0);
    
    // if using (u)sleep in an XHR the next requests are still hanging until sleep finishes
    session_write_close();

    // Client disconnect should NOT abort our script execution
    ignore_user_abort(true);

    // Clean (erase) the output buffer and turn off output buffering
    // in case there was anything up in there to begin with.
    ob_end_clean();

    // Turn on output buffering, because ... we just turned it off ...
    // if it was on.
    ob_start();

    echo $body;

    // Return the length of the output buffer
    $size = ob_get_length();

    // send headers to tell the browser to close the connection
    // remember, the headers must be called prior to any actual
    // input being sent via our flush(es) below.
    header("Connection: close\r\n");
    header("Content-Encoding: none\r\n");
    header("Content-Length: $size");

    // Set the HTTP response code
    // this is only available in PHP 5.4.0 or greater
    http_response_code($responseCode);

    // Flush (send) the output buffer and turn off output buffering
    ob_end_flush();

    // Flush (send) the output buffer
    // This looks like overkill, but trust me. I know, you really don't need this
    // unless you do need it, in which case, you will be glad you had it!
    @ob_flush();

    // Flush system output buffer
    // I know, more over kill looking stuff, but this
    // Flushes the system write buffers of PHP and whatever backend PHP is using
    // (CGI, a web server, etc). This attempts to push current output all the way
    // to the browser with a few caveats.
    flush();
}

https://www.php.net/manual/en/features.connection-handling.php#71172

https://www.php.net/manual/en/features.connection-handling.php#93441