Check if File Exists on Amazon s3 Signed URL - php

Question

I have create a signed $URL for Amazon s3 and it opens perfectly in the browser.
http://testbucket.com.s3.amazonaws.com/100-game-play-intro-1.m4v?AWSAccessKeyId=AKIAJUAjhkhkjhMO73BF5Q&Expires=1378465934&Signature=ttmsAUDgJjCXepwEXvl8JdFu%2F60%3D
**Bucket name and accesskey changed in this example
I am however trying to then use the function below to check (using curl) that the file exists. It fails the CURL connection. If I replace $URL above with the url of an image outside of s3 then this code works perfectly.
I know the file exists in amazon but can't work out why this code fails if using a signed url as above
Any ideas?
Thanks
Here is my code.
function remoteFileExists($url) {
$ch = curl_init();
curl_setopt($ch, CURLOPT_RETURNTRANSFER, false);
curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
//don't fetch the actual file, only get header to check if file exists
curl_setopt($ch, CURLOPT_HEADER, 1);
curl_setopt($ch, CURLOPT_NOBODY, true);
$result = curl_exec($ch);
curl_close($ch);
if ($result !== false) {
$statusCode = curl_getinfo($ch, CURLINFO_HTTP_CODE);
if ($statusCode == 200) {
$ret = true;
} else {
$ret = false;
}
} else {
$ret='connection failed';
}
return $ret;
}

Answer 1

When using CURLOPT_NOBODY, libcurl sends an HTTP HEAD request, not a GET request.
...the string to be signed is formed by appending the REST verb, content-md5 value, content-type value, expires parameter value, canonicalized x-amz headers (see recipe below), and the resource; all separated by newlines.
— http://s3.amazonaws.com/doc/s3-developer-guide/RESTAuthentication.html
The "REST verb" -- e.g., GET vs HEAD -- must be consistent between the signature you generate, and the request that make, so a signature that is valid for GET will not be valid for HEAD and vice versa.
You will need to sign a HEAD request instead of a GET request in order to validate a file in this way.

Answer 2

You can check by the header part.
$full_url = 'https://www.example.com/image.jpg';
$file_headers = #get_headers($full_url);
if($file_headers && strpos($file_headers[0], '200 OK')){
// enter code here
}
Or If you are using AWS S3 then you can also use this one.
if(!class_exists('S3')){
require('../includes/s3/S3.php');
}
S3::setAuth(awsAccessKey, awsSecretKey);
$info = S3::getObjectInfo($bucketName, $s3_furl);
// check for $info value and apply your condition.