Feature Request: Don't overwrite already downloaded files but delete/flag unfinished files about crunchyroll-dl

[Noctunus]

For this the target file size has to be known up-front and at least the HTTP standard allows chunked transfer of files where you only know that the file is completed if it's returned as completed in the last chunk. Therefore a fail-proof way to receive files would be to save it to a temporary filename and only if it's finished successful rename it to the target filename. This would solve several things at once:

1. You can be sure that the target filename is a complete file instead of only a part in an error case.
2. If the target filename is already present you can just skip it without looking at sizes.
3. Resuming a download would be possible as you know that the temp filename only consists of a part - to keep it simple you could just skip this and re-download the whole file with the same temp filename just overwriting the old data.

Also the implementation should be pretty simple (assuming the target filename is $name) :

1. If $name already exists just skip the current file
2. For the downloading just add a ".tmp" as suffix
3. On successful download rename $name.tmp to $name

[Platypuschan]

Mhm i´m just a scriptkiddie, but what´s about a more elaborated thingy like

if $already-existing-file-size != $size-of-file-to-download {
    rm $already-existing-file && download $new-file