PHP：imagecopyresampled返回false和URL

Question

I'm trying to write a simple file uploader which can resize an image if needed and copy it into the server's file system. That works if I pass the file directly but I also want to be able to pass a URL via a GET parameter. And somehow imagecopyresampled seems to fail with the URL.

Here is my code:

if(isset($_FILES["file"]))
    $fn = $_FILES['file']['tmp_name'];
else
    $fn = urldecode($_GET['url']);
$fileMD5 = md5_file($fn);
$target = $basedir . $fileMD5 . ".png";
list($width, $height, $imgtype) = getimagesize($fn);
if ($imgtype == IMAGETYPE_PNG)
    $img = imagecreatefrompng($fn);
else if ($imgtype == IMAGETYPE_JPEG)
    $img = imagecreatefromjpeg($fn);
else if ($imgtype == IMAGETYPE_GIF)
    $img = imagecreatefromgif($fn);
else if ($imgtype == IMAGETYPE_BMP)
    $img = imagecreatefromwbmp($fn);
else {
    echo "unsupported file format";
        return;
}
// image resize
if($width > $maxwidth && $width >= $height) {
    $newwidth = $maxwidth;
    $newheight = ($height / $width) * $newwidth;
} else if($height > $maxheight) {
    $newheight = $maxheight;
    $newwidth = ($width / $height) * $newheight;
}
$tmp = imagecreatetruecolor($newwidth, $newheight);
imagecopyresampled($tmp, $img, 0, 0, 0, 0, $newwidth, $newheight, $width, $height);
imagepng($tmp, $target);

Everything seems to work fine until imagecopyresampled. I get the correct IMAGETYPE and also, something is created with imagecreatetruecolor. But imagecopyresampled returns false. I'm pretty confused since the script seems to be able to actually read the image and get it's first bits to determine the type of it. Any suspections what's going wrong?

Thanks in advance.

Answer 1

Your resize section seems to leave out some situations that could lead to an undefined $newheight and $newwidth.

Are you sure about imagecreatetruecolor returning an image?