not letting someone submit a form more then once

[esthera]

I have a form and the problem is people are submitting then pressing the back key and submitting again.

What is the best way to stop this?

Should I check their IP?
Should I set a session variable?
Can we disable the back button or make the form empty on clicking back?

What do you suggest and how would I do it? (the form submits to a php page)

[96turnerri]

you could make it method=post so it expires, log there ip would be the best bet on the form action script use this

<?php

$ip = $_SERVER['REMOTE_ADDR'];

$handle = @fopen("ips.txt", "a");
if(!$handle)
{die("Error opening file to writing");}
fwrite($handle, $ip."\n");
fclose($handle);

?>

and on form page

use this

<?php

$ip = $_SERVER['REMOTE_ADDR'];
$iplist = file_get_contents('ips.txt');

if(preg_match("/\b".$ip."\b/", $iplist)) {
echo "Sorry you have already submitted this form";
} else {
//Form code or include
}

?>

[96turnerri]

o yes and if the form page is not php

use this in form action script


<?php

$ip = $_SERVER['REMOTE_ADDR'];
$iplist = file_get_contents('ips.txt');

if(preg_match("/\b".$ip."\b/", $iplist)) {
echo "Sorry you have already submitted this form";
} else {
$handle = @fopen("ips.txt", "a");
if(!$handle)
{die("Error opening file to writing");}
fwrite($handle, $ip."\n");
fclose($handle);
//current form action script
}

?>

Hope this helps