remotely-save/docs/sync_algorithm.md
2021-11-15 00:30:30 +08:00

3.5 KiB

Sync Algorithm

Sources

We have three record sources:

  1. Local files
  2. Remote files
  3. Local "delete-or-rename" history.

Assuming all sources are reliable.

Deal with them

We list all combinations mutually exclusive and collectively exhaustive.

ID Remote Files Local files Local delete rename history Extra Decision
1 exist exist ignore mtime_remote > mtime_local download remote file, create local folder if not exists, clear local history if exists
2 exist exist ignore mtime_remote < mtime_local upload local file, create remote folder if not exists, clear local history if exists
3 exist exist ignore mtime_remote === mtime_local && password === "" && size_remote === size_local clear local history if exists (the file was synced and no changes after last sync)
4 exist exist ignore mtime_remote === mtime_local && password === "" && size_remote !== size_local upload local file, clear local history if exists (we always prefer local to remote)
5 exist exist ignore mtime_remote === mtime_local && password !== "" clear local history if exists (in encryption mode, file sizes are unequal. we can only rely on mtime(s))
6 exist exist ignore If local is a folder. mtime_local === undefined clear local history if exists. TODO: what if a folder and a previous file share the same name?
7 exist not exist exist mtime_remote >= delete_time_local download remote file, create folder if not exists
8 exist not exist exist mtime_remote < delete_time_local delete remote file, clear local history
9 exist not exist not exist download remote file, create folder if not exists
10 not exist exist ignore local may be folder or file upload local files recursively, create remote folder if not exists, clear local history if exists
11 not exist not exist ignore clear local history if exists