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post – PHP $_POST variables are sometimes empty

Posted by: admin July 12, 2020 Leave a comment

Questions:

I am a PHP novice and I am having a problem with POST variable sometimes being empty when I submit them. The part which is making this difficult for me to figure out is that this doesn’t happen every time, and I can usually get the post data in my PHP program by simply refreshing the page. Sometimes it will take a few times, but once the data has come through once, it will continue to come through fine.

Other PHP applications (WordPress and others) work fine and never give any errors, so I am pretty sure there is a problem with my php app.

I have PHP 4.2.9 installed on a CentOS 5.2 server, and have KeepAliveTimeout set to 1.

The code for the app in which I process the submitted data:

<?php
    session_start(); 
    if (isset($_SESSION['username'])) {
        $expire = time() + (60*60*24*30);
        setcookie("username", $_SESSION['username'], $expire);
    }

    header("Cache-control: no-cache");

    if (!isset($_SESSION['username'])) {
        header('Location: ./login.php');
        die();
    }

    if(empty($_SERVER['CONTENT_TYPE'])){
        $type = "application/x-www-form-urlencoded";
        $_SERVER['CONTENT_TYPE'] = $type;
    }

    var_dump($_POST);
    echo "\n";
    var_dump($_SERVER);
?>

Any help at all would be appreciated

Edit: I have found one difference between working post requests and the ones that fail. Firebug tells me that when the post fails, the status is a 302 redirect instead of 200 ok.
Im not really sure what can cause that, but I have the header cache control in sending form just as it appears in the above code snippet.

Any ideas?

How to&Answers:

You forgot the name= parameter on your INPUT tag.

<input type="text" id="xyz" name="xyz" value="123"/>

Answer:

You could check the $_REQUEST variable which is a combination of $_POST and $_GET arrays. If the variables aren’t there, they haven’t been sent and the problem is probably on the client side.

You can use network traffic analyzing tools e.g. Firebug’s Net tab to see what’s actually been sent to the server.

Answer:

The $_POST variable is filled by the PHP engine, not by any application. So, if it’s empty, it’s just empty and your code needs to take that into account, in the same way as you already do for the $_SESSION and $_SERVER variables.

Answer:

header('Location: ./login.php');

By default this will send the status code 302 as well. Most browsers will request the target of a 302 with a GET request, regardless of the original request type. If you want both requests to contain the POST data then you could try a 307:

header('Location: ./login.php', true, 307);

But you might this doesn’t work across all browsers (it should work in anything non-ancient). You might want to re-examine your logic here though, it’s not normal to require clients double-POST.

Also, are you aware that you read $_SESSION['username'] but don’t appear to ever write to it?