$_FILES and $_POST empty in PHP When Uploading Large Files

Posted in PHP

Today I came across an issue where when uploading large files my $_FILES and $_POST values returned empty arrays. Turns out this is expected (albeit stupid IMO) behavior.

You can test this by uploading a small then a huge file to this relatively simple PHP script:

<!DOCTYPE html>
<html>
<head>
<title>Upload test</title>
</head>
<body>
	<form action="?submit=true" role="form" method="POST" enctype="multipart/form-data">
		<input name="images" type="file">
		<input type="hidden" name="foo" value="bar">
		<input type="submit">
	</form>

	<pre>$_FILES:
<?php print_r($_FILES); ?>
	</pre>
	<pre>$_POST:
<?php print_r($_POST); ?>
	</pre>
</body>
</html>

After uploading a small file your $_FILES variable will contain the file details but with a huge file (one larger than your POST_MAX_SIZE ini setting) it will be empty.

To check if a user has uploaded a file larger than your POST_MAX_SIZE value you need to use the following if statement courtesy of stackoverflow:

if ( !empty($_SERVER['CONTENT_LENGTH']) && empty($_FILES) && empty($_POST) )
	echo 'The uploaded zip was too large. You must upload a file smaller than ' . ini_get("upload_max_filesize");

Here is an updated file that will notify the user if the file they uploaded is too large:

<!DOCTYPE html>
<html>
<head>
<title>Upload test</title>
</head>
<body>
	<form action="?submit=true" role="form" method="POST" enctype="multipart/form-data">
		<input name="images" type="file">
		<input type="hidden" name="foo" value="bar">
		<input type="submit">
	</form>

	<?php
		if ( !empty($_SERVER['CONTENT_LENGTH']) && empty($_FILES) && empty($_POST) )
			echo 'The uploaded zip was too large. You must upload a file smaller than ' . ini_get("upload_max_filesize");
	?>

	<pre>$_FILES:
<?php print_r($_FILES); ?>
	</pre>
	<pre>$_POST:
<?php print_r($_POST); ?>
	</pre>
</body>
</html>