error using readfile php function - php

Question

I have this function which outputs an image to the browser. However i get an error image cannot be displayed because it contains errors.
I've done the file_exists check and the image headers are all applied correctly.
function sendImage(string $file, int $browser_cache = 2592000) {
if (file_exists($file)) {
header("Content-Type: ". mime_content_type($file));
header("Cache-Control: private, max-age=".$browser_cache);
header('Expires: '.gmdate('D, d M Y H:i:s', time()+$browser_cache).' GMT');
header('Content-Length: '.filesize($file));
readfile($file);
exit;
} else {
echo 'file does not exist';
}
}
Call the function
$file = $_SERVER['DOCUMENT_ROOT'] . '/images/image.png';
sendImage($file);
The image opens in my browser just fine. But displays an error with this function.

Answer 1

What I can tell from experience is that readfile does not work with large files.
And sometimes, even when you got the PHP part right there are other points of failures.
I suggest using the X-Sendfile header instead of manually outputting the file:
function sendImage(string $file, int $browser_cache = 2592000) {
$path = realpath($file);
if ($path !== false) {
header("Content-Type: ". mime_content_type($file));
header("Cache-Control: private, max-age=".$browser_cache);
header('Expires: '.gmdate('D, d M Y H:i:s', time()+$browser_cache).' GMT');
header('Content-Length: '.filesize($file));
header('X-Sendfile: '.$path);
exit;
} else {
echo 'file does not exist';
}
}
Of course you have to enable it in your webserver configuration for it to work.