feat: scp middleware

[caarlos0]

✨✨✨ SCP Middleware for Wish! ✨✨✨

what can it do?

the basic features:

• copy to and from a server
• recursive and non recursive
• globbing

what it can't do?

basically, tectia and advanced, rarely used, features. For example:

• copy preserving permissions (scp -p)
• "secure move" (scp -u)
• dry run mode (scp -n)
• bandwidth control (scp -l)

what else can I do with this?

Out of the box, you can server files from/to a folder with something like:

// ...
scph := scp.NewFileSystemHandler("/path/to/the/folder")
// ...
scp.Middleware(scph, scph),
// ...

You can also allow read-only access to any fs.FS implementation, using scp.NewFSHandler(fsys).

If these options don't fit what you're trying to achieve, you can also implement CopyToClientHandler and/or CopyFromClientHandler, to, for example, namespace files by SSH key fingerprint.

Please let me know your thoughts.

Feel free to check out examples/scp/main.go to see it in action.