CSV export prints complete HTML - php

Question

I have this export button that needs to xport data fro my database to an excel(csv) file but when i press itthe complete html is shown in the csv file.
here is my ode for the export:
if (isset($_POST["export"])) {
header('Content-Type: text/csv; charset=utf-8');
header('Content-Disposition: attachment; filename=data.csv');
$output = fopen("php://output", "w");
fputcsv($output, array('example','example','example','example','example','example','example','example','example','example'));
$query = "SELECT example,example,example,example,example,example,example,example,example,example FROM user";
$stmt = $con->prepare($query);
$stmt->execute();
fclose($output);
exit();
}
Edit:
This is my complete file with the code in it, i tried both options that were given below and they didn't seem to work. It still prints the complete html into a csv file.
<?php
if (isset($_POST["export"])) {
header('Content-Type: text/csv; charset=utf-8');
header('Content-Disposition: attachment; filename=data.csv');
$output = fopen("php://output", "w");
fputcsv($output, array('example','example','example','example','example','example','example','example','example','example'));
$query = "SELECT example,example,example,example,example,example,example,example,example,example FROM user";
$stmt = $con->prepare($query);
$stmt->execute();
fclose($output);
exit();
}
print '<div class="dropdown">
<button class="dropbtn">Kies een Lijst... <i class="fa fa-caret-down"></i> </button>
<div class="dropdown-content">
Gehele Lijst
Namen/Social/Soort
Namen & Soort
Soort
Namen & Categorie Bordspellen
Namen & Categorie Bordspellen
Namen
</div>
</div> ';
function getKeys($con, $query)
{
$result = $con->query($query);
$row = $result->fetch(PDO::FETCH_ASSOC);
return array_keys($row);
}
function getValues($con, $query)
{
$data = $con->query($query);
$data->setFetchMode(PDO::FETCH_ASSOC);
return $data;
}
$query = "SELECT example,example,example,example,example,example,example,example,example,example FROM user";
//Tabel 1
print "<table id='een'>";
$array_keys = getKeys($con, $query);
print " <tr>";
foreach ($array_keys as $value) {
print " <th>$value</th>";
}
print " </tr> ";
//Values
$data = getValues($con, $query);
foreach ($data as $row) {
print " <tr> ";
foreach ($row as $name => $value) {
print " <td>$value</td> ";
}
print " </tr> ";
}
print '<form method="post" action="index.php?pages=export1"><button type="submit" name="export" value="export" style="width: 5%; height: 5%">Export</button></form>';
//export to csv
print "</table> ";
print '
<footer class="w3-center footer" style="margin-top: 25%">
<div class="w3-xlarge w3-section">
<?php $_SESSION["loggedin"] = true;
if ($_SESSION["loggedin"] === true) {
?>
<h6><br>&copy Big Bang 2020 Uitloggen</h6>
<?php
}
?>
</div>
</footer>';
Edit 2
maybe it helps that i show the result in the csv file.
csv file:
The header is a header.php file which is included in the index.php file automatically.

Answer 1

If you have other PHP and HTML in your script located earlier than the code shown, then that content will still be output by PHP - everything in the script will be output unless you specifically instruct it not to be. And you've decided to redirect all that output to a file download, so the result is inevitable - all the output goes into the file.
You need to make sure that other content doesn't get output when the user has chosen the export option. This is simple enough:
Either:
Just put the if (isset($_POST["export"])) {
as the first line of the script so that nothing else is output first. The script will already end after that due to your exit() command, so no other output would then be included in the download. (If you also have a header file which outputs HTML included before this, then this option won't be sufficient, you'll need to use the second option below - which is arguably a better separation of concerns anyway.)
OR
put the export code into a separate PHP script which doesn't have any other purpose or function, then there is no danger of other content being accidentally included in the file. Whatever form you are using to request the export should be changed to post back to that script instead.