backend.php
Código PHP:
<?php
$filename = dirname(__FILE__).'/data.txt';
// store new message in the file
$msg = isset($_GET['msg']) ? $_GET['msg'] : '';
if ($msg != '')
{
file_put_contents($filename,$msg);
die();
}
// infinite loop until the data file is not modified
$lastmodif = isset($_GET['timestamp']) ? $_GET['timestamp'] : 0;
$currentmodif = filemtime($filename);
while ($currentmodif <= $lastmodif) // check if the data file has been modified
{
usleep(10000); // sleep 10ms to unload the CPU
clearstatcache();
$currentmodif = filemtime($filename);
}
// return a json array
$response = array();
$response['msg'] = file_get_contents($filename);
$response['timestamp'] = $currentmodif;
echo json_encode($response);
flush();
?>
index.html
Código:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>Comet demo</title>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<script type="text/javascript" src="prototype.js"></script>
</head>
<body>
<div id="content">
</div>
<p>
<form action="" method="get" onsubmit="comet.doRequest($('word').value);$('word').value='';return false;">
<input type="text" name="word" id="word" value="" />
<input type="submit" name="submit" value="Send" />
</form>
</p>
<script type="text/javascript">
var Comet = Class.create();
Comet.prototype = {
timestamp: 0,
url: './backend.php',
noerror: true,
initialize: function() { },
connect: function()
{
this.ajax = new Ajax.Request(this.url, {
method: 'get',
parameters: { 'timestamp' : this.timestamp },
onSuccess: function(transport) {
// handle the server response
var response = transport.responseText.evalJSON();
this.comet.timestamp = response['timestamp'];
this.comet.handleResponse(response);
this.comet.noerror = true;
},
onComplete: function(transport) {
// send a new ajax request when this request is finished
if (!this.comet.noerror)
// if a connection problem occurs, try to reconnect each 5 seconds
setTimeout(function(){ comet.connect() }, 5000);
else
this.comet.connect();
this.comet.noerror = false;
}
});
this.ajax.comet = this;
},
disconnect: function()
{
},
handleResponse: function(response)
{
$('content').innerHTML += '<div>' + response['msg'] + '</div>';
},
doRequest: function(request)
{
new Ajax.Request(this.url, {
method: 'get',
parameters: { 'msg' : request }
});
}
}
var comet = new Comet();
comet.connect();
</script>
</body>
</html>
NOTA: Se debe descargar prototype y colocarlo en el mismo directorio con todos los archivos.
Crear un archivo plano de nombre: data.txt.
Una vez ejecuta la pagina, editar el archivo data.txt y notar que la pagina se actualiza por si sola.
Técnica: BOSH...usada por facebook.
Respuestas del formulario PHP 
. Voy a probar ahora mismo el code que hay arriba asique lo pruebo y os digo, muchas gracias a todos. 
