PHP: form redirection after validating its fields

Question

I have done a simple form like this:

index.php:

<!DOCTYPE HTML>
<html>
  <head></head>
  <body>
<?php
  $name = "";
  if ($_SERVER["REQUEST_METHOD"] == "POST") {
    if (empty($_POST["name"])) {
      // handle missing field
    } else {
      $name = $_POST["name"];
    }
  }
  if($name != '') {
    header('location: http://localhost/new_page.php');
    exit();
  }
?>
    <form method="post" action="<?php echo htmlspecialchars($_SERVER['PHP_SELF']);?>">
      <span class="label">Name</span>
      <input type="text" name="name">
      <button><span>Validate</span></button>
    </form>
  </body>
</html>

I would like the following behaviour:

staying on the form if the name field is not set by the user
going to new_page.php if name field is set

I have the following error right now: if I set the name, I am redirected to a blank.php page. Can someone help me on this ? Or at least give me some tips to debug this as I am not really a PHP specialist.

Thank you !

either give input field required validation or need to use ajax — Devsi Odedra, Dec 11 '19 at 13:26
Ok, so I can simply use "required" in input fields and the above is correct ? — klaus, Dec 11 '19 at 13:29
on server side also redirect on same page if not getting value in any case, dont rely all time on required — Devsi Odedra, Dec 11 '19 at 13:30
I tried using required. But if all fields are set, I am still redirected to a blank page and I do not know why... — klaus, Dec 11 '19 at 13:31

score 2 · Accepted Answer · answered Dec 11 '19 at 13:45

Your header call comes too late.

an HTTP Response first has a header, then a body. HTML code is the body.

You need to put all output AFTER your PHP code. Since you start with <html>, headers will already have been sent and so your redirect will not work.

Also, regarding white pages (White screen of death or WSOD):

For the best error logging experience, set error_reporting to -1, turn display_errors off, and set a custom error_log. Then in the terminal, type 'tail -f /path/to/error_log'. Your notices, warnings and errors will now scroll past in real time, without distorting your web page's display.

you're very welcome :-) – delboy1978uk Dec 11 '19 at 13:52 — delboy1978uk, Dec 11 '19 at 13:52

score 0 · Answer 2 · answered Dec 11 '19 at 13:52

The answer given by @delboy1978uk is correct. All you have to do is change your file content to:

<?php
  $name = "";
  if ($_SERVER["REQUEST_METHOD"] == "POST") {
    if (empty($_POST["name"])) {
      // handle missing field
    } else {
      $name = $_POST["name"];
    }
    if($name != '') {
      header('location: http://localhost/new_page.php');
      exit();
    }
  }

?><!DOCTYPE HTML>
<html>
  <head></head>
  <body>
    <form method="post" action="<?php echo htmlspecialchars($_SERVER['PHP_SELF']);?>">
      <span class="label">Name</span>
      <input type="text" name="name">
      <button><span>Validate</span></button>
    </form>
  </body>
</html>

PHP: form redirection after validating its fields

2 Answers2