PHP Cookie not storing on users browser, php 7.4, Google App Engine

Question

I am creating a cloud based php application and When I use the code below in the top of my PHP document it creates the cookie perfectly.

setcookie("lgUsr",'admin', time() + (3600 * 24 * 30), "/");

But when I put it like below as a form submission it does not create the cookie in the browser.

    <?php
        if(isset($_POST['login-submit'])){
            $usrName = $_POST['username'];
            if($usrName == 'admin'){
                    setcookie("lgUsr",'admin', time() + (3600 * 24 * 30), "/");
                ?>
                <script>
                    var resP = document.getElementById('result');
                    resP.classList.add('success-text');
                    resP.innerHTML = 'Successfully Logged In.';
                </script>
                <?php
                header("Location: admin-dashboard.php");
            } else{
                ?>
                <script>
                    var resP = document.getElementById('result');
                    resP.classList.add('error-text');
                    resP.innerHTML = 'Error Occured while logging in.';
                </script>
                <?php
            }
        }
    ?>

What could be the problem? Any kind of help is really appreciated. Both codes above works perfectly in the localhost, GAE is the one that gives the problem.

Have you checked the PHP error log? Have you also enabled debug logging? — hakre, Oct 09 '21 at 21:38
`"PHP message: PHP Warning: Cannot modify header information - headers already sent by (output started at /workspace/admin.php:8) in /workspace/admin.php on line 59"` This is what it returns `line 8` is ` ` and `line 58` is where I have the `setcookie`. — Dulan Pabasara, Oct 09 '21 at 21:48
Have you seen this: https://stackoverflow.com/a/8028987/231316 — Chris Haas, Oct 09 '21 at 21:52
Okay, was a quick guess, (but/and) me assumed something in that direction. So what @ChrisHaas said. — hakre, Oct 09 '21 at 22:02
@ChrisHaas Adding the form submission catch to the top of the doc did the trick for now. — Dulan Pabasara, Oct 09 '21 at 22:10
Hi @DulanPabasara, If you managed to solve the issue, please post your solution as an answer, so other community members can upvote it if they encountered the same problem. Thank you. — Marc Anthony B, Oct 11 '21 at 05:58

score 0 · Answer 1 · edited Oct 12 '21 at 18:08

Apparently, App Engine only allow once to modify the headers. So, adding the setcookie() function containing code block to the top of the refresh page does the trick. Even a space in front of <?php tag can stop the page from modifying the header. More information can be taken from this Stack Overflow answer

Adding into this, according to the setcookie PHP manual:

setcookie() defines a cookie to be sent along with the rest of the HTTP headers. Like other headers, cookies must be sent before any output from your script (this is a protocol restriction). This requires that you place calls to this function prior to any output, including <html> and <head> tags as well as any whitespace.

Your answer could be improved with additional supporting information. Please [edit] to add further details, such as citations or documentation, so that others can confirm that your answer is correct. You can find more information on how to write good answers [in the help center](/help/how-to-answer). — Community, Oct 11 '21 at 14:13

PHP Cookie not storing on users browser, php 7.4, Google App Engine

1 Answers1