note 102301 added to session.examples

(Improved version) It took me a while to find out how to use PHP sessions to prevent HTML form re-submits. A user can re-submit a form via the backspace key/back arrow and/or the F5/refresh key. I needed to control if/when a HTML form could be resubmitted. Here's what I came up with: <?php $SID = session_id(); if(empty($SID)) session_start() or exit(basename(__FILE__).'(): Could not start session'); $_SESSION['err'] = ''; $exit = false; do { // check if form was previously submitted if(isset($_POST['submit']) and isset($_POST['SID']) and ($_POST['SID'] !== session_id())) { $ret = null; $exit = true; break; } // break out of do-while if form has not been submitted yet if(empty($_POST['submit'])) break; // process form data if user hit form "submit" button if(isset($_POST['submit'])) { $ret = validate_form(); // ret will be error message if form validation failed if(is_string($ret)) { $_SESSION['err'] = $ret; break; } // ret will be array of cleaned form values if validation passed if(is_array($ret)) { session_regenerate_id(true); $exit = true; break; } } } while(false); if($exit) display_receipt($ret); $exit and exit; function validate_form() { $tmp = htmlspecialchars(strtoupper($_POST['name'])); // clean POST data if(stripos($_POST['great'], 'yes') !== false) return array('name' => $tmp, 'great' => 'YES!'); return 'Wrong answer!'; } function display_receipt($msg) { if($msg === null) echo 'You already answered the question!'; if(is_array($msg)) echo 'Your answer of '.$msg['great'].' is right '.$msg['name']; return; } ?> <html><body> <?php echo $_SESSION['err']; ?> <form name="form1" action="http://<?php echo $_SERVER['HTTP_HOST'], $_SERVER['PHP_SELF']; ?>" method="post"> Name: <input type="text" name="name" value="<?php isset($_SESSION["name"]) and print $_SESSION["name"]; ?>"> Is PHP great? <input type="text" name="great" value="<?php isset($_SESSION["great"]) and print $_SESSION["great"]; ?>"> <input type="hidden" name="SID" value="<?php echo session_id(); ?>"> <input type="submit" name="submit" value="Submit"> </form></body></html> ---- Server IP: 64.71.164.2 Probable Submitter: 65.41.147.195 ---- Manual Page -- http://www.php.net/manual/en/session.examples.php Edit -- https://master.php.net/note/edit/102301 Del: integrated -- https://master.php.net/note/delete/102301/integrated Del: useless -- https://master.php.net/note/delete/102301/useless Del: bad code -- https://master.php.net/note/delete/102301/bad+code Del: spam -- https://master.php.net/note/delete/102301/spam Del: non-english -- https://master.php.net/note/delete/102301/non-english Del: in docs -- https://master.php.net/note/delete/102301/in+docs Del: other reasons-- https://master.php.net/note/delete/102301 Reject -- https://master.php.net/note/reject/102301 Search -- https://master.php.net/manage/user-notes.php