<?php

// FILENAME: the_form.php

if( $_POST )
{    // form submitted
    $success = process_form_data();
    
    // if $success, now we re-direct the user to the page he came from
    if( $success )
    {
        if( !$_POST['referredby'] ) // if there was no referer information, we redirect them to our homepage.
            $_POST['referredby'] = 'http://www.example.com/'; //i.e. our homepage.

        header( "Location: $_POST[referredby]" );
        exit;
    }
}
else
{    // show the form.
    echo '<form method="post" etc...>';
    
    // get referrer data.
    $referredby = null;
    if( isset($_SERVER['HTTP_REFERER'])  &&  $_SERVER['HTTP_REFERER'] )
        $referredby = htmlspecialchars( $_SERVER['HTTP_REFERER'] );
    
    echo '<input type="hidden" name="referredby" id="inputReferredBy" value="',
            $referredby,
            "\" />\n";
    echo "</form>\n";
}
?>