Comment 3 for bug 260748

The queue looks like the correct place for the crc check now, but according to your own logic, the whole file should be flagged as invalid, not just the source (any file with tth checked will be bad)...

There is of course a slight chance that something happens with a file while it's being saved to disk - maybe calculate tth along with crc and if tth is ok and crc not flag the file as bad, if tth mismatches repair / redownload file (we had some repair code somewhere, didn't we?)...