[Feature request] SFTP driver for Cloud Sync

[flavionm]

#15548 implemented the Cloud Sync functionality. Currently we have the WebDAV and the iCloud drivers. iCloud is platform specific, so for most platforms we only have the option of using WebDAV. While WebDAV is supported by many cloud storage providers, having at least a second multiplatform option would help a lot with compatibility, since while certain services might not support some protocols, they'll often support at least a couple popular ones.

One such protocol is SFTP. It is build on top of SSH, unlike WebDAV, which is based on HTTP, and it is often implemented by both SSH and FTP servers, making it also very likely to be supported. RetroArch doesn't currently implements SSH in any capacity, as far as I know, but SSH has a couple very mature C libraries that support SFTP, so it should be able to be included without sacrificing portability.

For instance, the provider I use, rsync.net, is very SSH-centric, and supports SFTP, but not WebDAV. The current implementation of Cloud Sync is very robust, and being able to use it across all my devices without requiring any local setup would improve the experience immensely.

[i30817]

If you don't want to wait and have the ability to keep a small computer running, it's relatively easy to run a webdav localhost server or even expose it to the internet with duckdns and modem dmz config as you figure out the right apache configs in Linux.

I do it for Android devices and RSAF plugin to allow some emulators with SAF support (not RetroArch unfortunately) to access (read only in the external internet) games in the device with the actual spacious storage. Don't see any reason why it wouldn't work for RetroArch cloud sync which only has to care about savegames and savestates iirc.

Hardest part after I figured out the apache config was to make the mount of the external disk early enough for the apache server to recognize it as a valid dir to expose. I actually didn't, what I did expose was the /media dir before the drives get mounted there, then on the client pass a url with the rest of the path from there, which works ironically. That only matters if you need to keep your server read/write dirs in a external drive, which isn't likely for most (but was for me). Maybe there is a apache webdav flag for a lazy mount for a more specific exposed dir that doesn't exist yet\not automounted yet, but if so I didn't find it.

[flavionm]

I found a provider that offers a bit of storage for free and supports WebDAV, for now. Since none of this data is really sensitive, and I keep a backup of everything anyway, any potential data loss is negligible.