Any way to verify an uploaded file is complete/not corrupt?

bunner_bob

I'm working on a site which receives jpeg still images via FTP from a webcam. I have a script which each day copies a certain image (the one sent between 3pm and 4pm) to the "live" site.

Is there any way to check the source image file before copying to ensure it is complete - i.e. it wasn't only partially transferrered, or isn't corrupt?

etully

I've never tried this but maybe if you brought the image into Image Magick and tried to manipulate it, you would get an error message if it fails and you'd know that the image was broken.

Another, less sexy, way to do it might be to transfer the image twice and compare them. If they are not the same, transfer again twice and check. Keep looping until you get two identical files. The ImageMagick solution would be cooler if it works.

maxxd

getimagesize() will return an error if the file in question isn't a valid image - I would think (though I've not tested it) that if the image were corrupted or only partial, it would register as not a valid image file. Thus kicking an error out of a getimagesize() function call. Could use this as a test?

bunner_bob

getimagesize seems to work - though I only tested it on a text file renamed to imitate a jpeg.

Wonder how I could get hold of a corrupt jpeg...

etully

Apparently there are different ways to corrupt a JPG. The first time I tried, I removed random bytes from the beginning of the JPG and it simply would not open. (I wrecked the headers).

The next time, I removed random bytes from the middle. This time, when I opened the JPG, it actually displayed but an error message appeared that said, "JPG was corrupt... insufficient byte count".

So, I guess you'll need to test getimagesize to make sure it can spot different types of corrupt JPG's.

etully

corrupt.jpg (in my post above) was the one that will open but has an error message.

The JPG in this post, corrupt2.jpg, is the one where I wrecked the headers.

Scratch that!!! Apparently the upload tool for PHPBuilder won't let me upload the image if it's not a valid JPG. Too funny,

Anyway, to make a JPG corrupt, find a text editor that will edit binary files (like vi) and open the file, do some damage, and then save the file. If you had a Windows machine, I suppose you could try FTP'ing the file to another server in ASCII mode. That should wreck it pretty badly.

mjax

You should check the 'error' index of the $_FILES hash directly after uploading to check for corrupt uploads.

Like this:

if($_FILES['picture']['error']  == UPLOAD_ERR_OK) {
  // file is uploaded correctly
} else {
  // file is not uploaded correctly
}

bunner_bob

Not sure that'll work in my setup - the files are coming in via FTP to a receiving directory - no PHP involved.

Periodically a cron script will run that will copy particular files (with resizing, etc.) to a "live" directory, but that's not using $_FILES.