How to transfer a file over the Internet?

Question

go

The question arose with how to write a program in go that can transfer a file between PCs via the Internet. I would like to know 2 aspects of the issue theoretical and practical. Theoretically, how the transfer is carried out in general, because you can connect directly to the same subnet, and only the address received via PAT is visible on the Internet. And on a practical issue, find out the libraries and, if possible, the implementation of such a transfer.

Answer 1

start with openvpn, you will quickly learn what when

The bottom subnet can be directly connected, and only the address received via PAT is visible to the Internet.

VPN only through an intermediate server
, and so on.
============ here is a layer on networking, sockets, networking in go, etc. =============