"Safe" Copy Mechanism?

Does anybody know of a program (or preferably some sort of Finder extension) that'll automatically verify that when a file is copied, what's written is the same as the original file?

I've recently had my external Firewire drive start to spit out random SMART errors and seen the end results of this in files which, when copied from A to B, managed to change in the process. When the copying concerned is moving stuff into a disk image I've created to burn to DVD for backup purposes, this is generally a bad thing. Fortunately the errors are very intermittent, but I've already lost at least one program that I've bought via electronic download which became corrupted before I could get it burned to an external backup.

My ideal solution to the problem would be invisible, or near invisible - doing a drag and drop the way you would normally do it, only with some new and exotic combination of keys held down. With the exception of truly huge files, it'd be fairly simple to implement the verification - calculate something like an MD5 digest of the file as you read it, then read back the copy, generate its MD5, and compare them. Re-reading and re-calculating the checksum for both files would help to verify whether you had a problem with read errors or write errors. I'm assuming the hooks exist to add something like this seamlessly, if not the user interface for this would be very simple.

Does something like this already exist? I know all the various manual methods that exist to do this (running md5 or diff, fr'example) but ideally I'd like transparency - the option to have this as the Finder's default copy behavior, even, if I was willing to live with the performance hit - rather than mucking around wiith dedicated programs. Before I add writing something like this to my project list, I'd like to make sure that I'm not re-inventing the wheel.

Al

 

Getting a new drive is exactly what I am doing, but the drive seems to have gone through a lengthy flaking out period before the problem became obvious, corrupting files here and there. I just think that some sort of verified-copy mechanism would have its uses - in my case, I had 30GB of data to move off the drive. I've no idea how many files got damaged in the process.

Hmm, if it is a situation where most people don't need it, maybe I'd be better off developing it as something for my specific situation - getting files safely off dying drives. Plus, as you mention, there's always folder actions.