Question

I’ve written an PHP page to dynamically resize an image stored as a BLOB in a MySQL database. I’m doing this on the fly without storing any temporary files. Is there any way to determine a Content-Length to send in the header?

I have the image created with imagecopyresampled() and use imagepng() (or the like) to output the image data.

$origImage = imagecreatefromstring($image['data']);
$newImage = imagecreatetruecolor($width, $height);

// preserve alpha
imagealphablending($newImage, false);
imagesavealpha($newImage, true);

$resizeSuccess = imagecopyresampled($newImage, $origImage, 0, 0, 0, 0, $width, $height, $image['width'], $image['height']);

header('Content-Type: image/png');
imagepng($newImage, null, $pngCompression, PNG_NO_FILTER);
imagedestroy($newImage);

Answer 1

Instead of your imagepng call, try this:

ob_start(function($c) {
    header("Content-Length: ".strlen($c));
    return $c;
});
imagepng($newImage, null, $pngCompression, PNG_NO_FILTER);
obj_end_flush();

Also, the server should handle Content-Length automatically for you.