getimagesize() on stream instead of string - php

Question

I'm using Valum's file uploader to upload images with AJAX. This script submits the file to my server in a way that I don't fully understand, so it's probably best to explain by showing my server-side code:
$pathToFile = $path . $filename;
//Here I get a file not found error, because the file is not yet at this address
getimagesize($pathToFile);
$input = fopen('php://input', 'r');
$temp = tmpfile();
$realSize = stream_copy_to_stream($input, $temp);
//Here I get a string expected, resource given error
getimagesize($input);
fclose($input);
$target = fopen($pathToFile, 'w');
fseek($temp, 0, SEEK_SET);
//Here I get a file not found error, because the image is not at the $target yet
getimagesize($pathToFile);
stream_copy_to_stream($temp, $target);
fclose($target);
//Here it works, because the image is at the desired location so I'm able to access it with $pathToFile. However, the (potentially) malicious file is already in my server.
getimagesize($pathToFile);
The problem is that I want to perform some file validation here, using getimagesize(). getimagesize only supports a string, and I only have resources available, which result in the error: getimagesize expects a string, resource given.
It does work when I perform getimagesize($pathTofile) at the end of the script, but then the image is already uploaded and the damage could already have been done. Doing this and performing the check afterwards and then maybe deleting te file seems like bad practice to me.
The only thing thats in $_REQUEST is the filename, which i use for the var $pathToFile. $_FILES is empty.
How can I perform file validation on streams?
EDIT:
the solution is to first place the file in a temporary directory, and perform the validation on the temporary file before copying it to the destination directory.
// Store the file in tmp dir, to validate it before storing it in destination dir
$input = fopen('php://input', 'r');
$tmpPath = tempnam(sys_get_temp_dir(), 'upl'); // upl is 3-letter prefix for upload
$tmpStream = fopen($tmpPath, 'w'); // For writing it to tmp dir
stream_copy_to_stream($input, $tmpStream);
fclose($input);
fclose($tmpStream);
// Store the file in destination dir, after validation
$pathToFile = $path . $filename;
$destination = fopen($pathToFile, 'w');
$tmpStream = fopen($tmpPath, 'r'); // For reading it from tmp dir
stream_copy_to_stream($tmpStream, $destination);
fclose($destination);
fclose($tmpStream);

Answer 1

PHP 5.4 now supports getimagesizefromstring
See the docs:
http://php.net/manual/pt_BR/function.getimagesizefromstring.php
You could try:
$input = fopen('php://input', 'r');
$string = stream_get_contents($input);
fclose($input);
getimagesizefromstring($string);

Answer 2

Instead of using tmpfile() you could make use of tempnam() and sys_get_temp_dir() to create a temporary path.
Then use fopen() to get a handle to it, copy over the stream.
Then you've got a string and a handle for the operations you need to do.
//Copy PHP's input stream data into a temporary file
$inputStream = fopen('php://input', 'r');
$tempDir = sys_get_temp_dir();
$tempExtension = '.upload';
$tempFile = tempnam($tempDir, $tempExtension);
$tempStream = fopen($tempFile, "w");
$realSize = stream_copy_to_stream($inputStream, $tempStream);
fclose($tempStream);
getimagesize($tempFile);