How do I create a TCP socket in Lean 4 and accept an incoming connection or connect to a remote address? In other words, how do I implement a TCP server or client in Lean 4?
You need to wrap the socket types and functions to use them in Lean 4.
Lean 4 is still in an early stage, even without a stable release. There is very few packages for Lean now, so you cannot expect production level packages like Python's socket or Rust's std::net/mio.
But if you just want to take a try, you can look at my lean4-socket package, which is a toy implementation. There are also simple examples e.g. sending HTTP request (which is based on TCP) in the examples folder.