How to set up a VPN for a single app on macOS?

Question

VPN

How to redirect all traffic of a specific application to VPN? macOS 10.13.4

Answer 1

It is possible to "wrap" all traffic of a certain application in a socks proxy. This is done by the tsocks utility (available in homebrew) or proxycap, they work on the same principle, replacing the application's network calls. It doesn't always work, but it generally works.
Further options are possible on how to use it:
1) use shadowsock as a local socks proxy and vpn tunnel to the server
2) configure a regular local socks proxy so that it uses an existing VPN channel.