php session validation

Question

I want to achieve that a user cannot send the same input twice. I use a php script to submit user input.

My idea is to save his inputs in a session array and each time that he submits something check through the array if it matches one of the things he already submitted before.

The code looks like this:

    //Compare post with what user has posted so far; if the same, exit (spam protection)
    foreach($_SESSION['postarray'][] as $postarray) if($post=$postarray) exit;

    //Save post in session of all other posts
    $_SESSION['postarray'][]=$post;

I get the following error:

Fatal error: Cannot use [] for reading in /Applications/XAMPP/xamppfiles/htdocs/postish/action/post.php on line 32 (which refers to the line with the foreach() loop)

Even after changing the function to only $_SESSION['post array'], it doesn't work either.

Any help much appreciated :)

Dennis

the error message suggests that the "[]" syntax is wrong. Try removing the empty brackets. And = is for assignments. == is for conditions. — Nadir Sampaoli
– Nadir Sampaoli, Commented May 8, 2012 at 10:24
Premise is fundamentally flawed as is method of implementation. How do you deal with an ever-growing session? Why not at the storage tier? I suspect you really want to prevent the user submitting the same instance of a form multiple times - in which case this should be managed at the client. See also CSRF prevention. — symcbean
– symcbean, Commented May 8, 2012 at 12:07

VisioN · Accepted Answer · 2012-05-08 10:29:28Z

4

Operator [] adds a new element to array.

To get elements for foreach loop you have to use it without []:

foreach($_SESSION['postarray'] as $postarray)
    if ($post == $postarray) exit;

And pay attention to comparison operator == which is used to check the equality of the variables.

The better option to check if $post exists in $_SESSION['postarray'] is to use in_array function:

if (in_array($post, $_SESSION['postarray'])) exit;

edited May 8, 2012 at 10:29

answered May 8, 2012 at 10:23

VisioN

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ThiefMaster · Accepted Answer · 2012-05-08 10:24:07Z

2

You accidentally used the assignment operator = instead of the comparion operator == or ===.

So you need to replace if($post=$postarray) with if($post == $postarray)

You also need to remove the [] in foreach($_SESSION['postarray'][] as $postarray) as [] is only used when inserting a new array element.

answered May 8, 2012 at 10:24

ThiefMaster

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Community · Accepted Answer · 2017-05-23 12:11:28Z

0

If you want to stop a user from sending the same data twice, you need to look into using a nonce (number used once)

There are a few examples:

edited May 23, 2017 at 12:11

CommunityBot

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answered May 8, 2012 at 11:00

Petah

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