Sftp SynchronizeDirectories should not just use the size of the file to sync/update

[manu-st]

Currently the implementation of SynchronizeDirectories from SftpClient uses the size of the file to know if it needs to override it. Unfortunately this is not good enough in most cases. There is a comment about using MD5, which would be nice indeed. In the meantime, could we use a some file stamp comparison?

[manu-st]

I'm proposing changing this line of code:
isDifferent = localFile.Length != dest.Length;
to read
isDifferent = (localFile.Length != dest.Length) || (dest.LastWriteTimeUtc.AddSeconds(-60.0) <= localFile.LastWriteTimeUtc);

The 60s is to avoid any potential clock differences between machines.

[raffaeler]

I would keep the difference in no more than 10 seconds. If you are actively working on some files, 1 minute is definitely too much