file type validation

[Anon]

I have a problem for validation of jpeg file while uploading.Will anybody help me out how to check the file whether it is jpeg or not while uploading??

Ameer

[Anon]

A JPEG file begins with :

FF D8 FF E0

[Anon]

Olivier,
Where in the JPEG file is this "FF D8 FF E0" found? How would one write a code to validate this "FF D8 FF E0" value? Is there a list somewhere that gives the codes (like "FF D8 FF E0" ) for different file types (like .gif or even .txt).
Thanks
Allen

[Anon]

Well, my knowledge in that matter is purely experimental ;-) i.e. I open the files in binary mode and look at them... A signature is always at the beginning. I can give you some more (in ASCII this time ) :

.gif : GIF
.bmp : BM
.pdf : %PDF

No signature for txt files, all you can do to recognize them is check for non-alphanumeric characters.

A little function in PHP to check signatures :

function CheckSignature($filename,$signature)
{
$f=fopen($filename,"r");
$s=fread($f,strlen($signature));
$Ok=($s==$signature);
fclose($f);
return $Ok;
}

print CheckSignature("somegif.gif","GIF");
print CheckSignature("somjpg.jpg",chr(0xFF).chr(0xD8).chr(0xFF).chr(0xE0));

[Anon]

Thanks for the additional info, Olivier!!
Allen