php script to cache images with memcache in Sina App Engine

index.php

<?php

//ini_set('display_errors',1);
//ini_set('display_startup_errors',1);
//error_reporting(-1);

// this is naive
function isValidUrl($url) {

	return strpos($url, 'http://') === 0 || strpos($url, 'https://') === 0;

}

// ref: http://stackoverflow.com/questions/28846006/php-create-thumbnail-image-from-url
function thumbnailJpeg($url, $width = 150, $height = true) {

	$image = ImageCreateFromString(file_get_contents($url));

	$height = $height === true ? (ImageSY($image) * $width / ImageSX($image)) : $height;

	$output = ImageCreateTrueColor($width, $height);
	ImageCopyResampled($output, $image, 0, 0, 0, 0, $width, $height, ImageSX($image), ImageSY($image));

	return $output;

}

function imageToString($image) {

	ob_start();
	ImageJpeg($image);
	$content = ob_get_clean();

	return $content;

}

$url = $_GET['url'];
if (!isValidUrl($url))
	exit(0);

$key = md5($url);

$mmc = memcache_init();

$str = memcache_get($mmc, $key);
if (!$str) {
	$image = thumbnailJpeg($url, 320);
	$str = imageToString($image);
	memcache_set($mmc, $key, base64_encode($str));
}
else {
	$image = ImageCreateFromString(base64_decode($str));
}

header("Cache-Control: max-age=31556926");
header("Content-type: image/jpeg");
ImageJpeg($image);

?>