How to: folder sync
sync folders to/from copyparty

NOTE: full bidirectional sync, like what [nextcloud](https://docs.nextcloud.com/server/latest/user_manual/sv/files/desktop_mobile_sync.html) and [syncthing](https://syncthing.net/) does, will never be supported! Only single-direction sync (server-to-client, or client-to-server) is possible with copyparty

* if you want bidirectional sync, then copyparty and syncthing *should* be entirely safe to combine; they should be able to collaborate on the same folders without causing any trouble for eachother. Many people do this, and there have been no issues so far. But, if you *do* encounter any problems, please [file a copyparty bug](https://github.com/9001/copyparty/issues/new/choose) and I'll try to help -- just keep in mind I've never used syncthing before :-)

the commandline uploader [u2c.py](https://github.com/9001/copyparty/tree/hovudstraum/bin#u2cpy) with `--dr` is the best way to sync a folder to copyparty; verifies checksums and does files in parallel, and deletes unexpected files on the server after upload has finished which makes file-renames really cheap (it'll rename serverside and skip uploading)

if you want to sync with `u2c.py` then:
* the `e2dsa` option (either globally or volflag) must be enabled on the server for the volumes you're syncing into
* ...but DON'T enable global-options `no-hash` or `no-idx` (or volflags `nohash` / `noidx`), or at least make sure they are configured so they do not affect anything you are syncing into
* ...and u2c needs the delete-permission, so either `rwd` at minimum, or just `A` which is the same as `rwmd.a`
  * quick reminder that `a` and `A` are different permissions, and `.` is very useful for sync

alternatively there is [rclone](./docs/rclone.md) which allows for bidirectional sync and is *way* more flexible (stream files straight from sftp/s3/gcs to copyparty, ...), although there is no integrity check and it won't work with files over 100 MiB if copyparty is behind cloudflare

* starting from rclone v1.63, rclone is faster than u2c.py on low-latency connections
  * but this is only true for the initial upload; u2c will be faster for periodic syncing