# net_echo.ludic — N0: the transport seam (NETWORKING-DESIGN §5, §13 N0).
#
# The transport is two calls — net_send puts a datagram on the wire, net_poll
# takes the next one off. A production build binds them to a real socket with
# `extern fn net_send/net_poll` (UDP native, WebRTC/WebSocket wasm); absent that,
# the compiler supplies a built-in in-process loopback, so a program is networked
# end to end with NO foreign host — pure Ludic. This sends four bytes and polls
# them back through the loopback: prints 4, then 10 20 30 42.
program NetEcho {
  entry {
    let out = bytes(4)
    out[0] = '\n'
    out[1] = 20
    out[2] = 30
    out[3] = '*'
    net_send(0, out, 4)                  # onto the wire (the built-in loopback)

    let inb = bytes(64)
    let n = net_poll(inb, 64)            # take the next datagram back off
    print(n)                             # 4
    var i = 0
    while i < n { print(inb[i]);  i += 1 }   # 10 20 30 42
  }
}