ludic/packages/ludic.net/receive.ludic

# receive.ludic - what arrived, unwrapped from the relay, checked, acknowledged and put in order
# on the inbox. A reliable message is taken strictly in order; one that arrives early is dropped
# and comes again.
function net__pump(net_st: mut NetState) -> void {
  if net_st.net__sock <= 0 { return }
  for guard in 0 .. 200 {
    let n = NetSocket.recv(net_st.net__sock, net_st.net__in, NET_MTU + 64)
    if n <= 0 { return }
    let n2 = net__unwrap(net_st, n, NetSocket.from_ip(net_st.net__sock), NetSocket.from_port(net_st.net__sock))
    if n2 > 0 { net__packet(net_st, n2, net_st.net__from_ip, net_st.net__from_port) }
  }
}

function net__packet(net_st: mut NetState, n: int, ip: int, port: int) -> void {
  if NetWorld.trace() { net__log(`in {n} bytes from {Udp.ip_text(ip)}:{port}`) }
  if n < 20 { return }
  if net__stun_packet(net_st, n) { return }                # what the router looks like from outside
  if nb_get8(net_st.net__in, 0) != 'M' or nb_get8(net_st.net__in, 1) != 'L' { return }   # a punch ("MP") or noise
  if nb_get8(net_st.net__in, 2) != net__conf(net_st).proto { return }
  let slot = net__slot_for(net_st, n, ip, port)
  if slot < 0 { return }
  let p = net_st.net__peers[slot]
  p.heard = net_st.net__time
  # only what this connection has sent can be acknowledged: a packet from the one before it
  # (a re-join) carries the old numbers and would drop the new hello as already taken
  let ack = nb_get32(net_st.net__in, 12)
  if ack > p.acked and ack < p.next_id { p.acked = ack }
  net__messages(net_st, slot, n)
}

# the known peer at that address, a stranger's new slot (a host, and only with a hello), or -1
function net__slot_for(net_st: mut NetState, n: int, ip: int, port: int) -> int {
  let token = nb_get32(net_st.net__in, 4)
  var slot = net__find(net_st, ip, port)
  if slot >= 0 {
    if token != net_st.net__token and net_st.net__state != NET_JOINING and net_st.net__peers[slot].pid != 0 { return -1 }
    return slot
  }
  if net_st.net__state != NET_HOSTING { return -1 }
  if n < 28 or nb_get8(net_st.net__in, 20) != NET_HELLO { return -1 }
  for i in 1 .. NET_PEERS {
    if not net_st.net__peers[i].on {
      net__open(net_st, i, ip, port, 0)
      return i
    }
  }
  return -1
}

function net__messages(net_st: mut NetState, slot: int, n: int) -> void {
  let p = net_st.net__peers[slot]
  let from = nb_get32(net_st.net__in, 8)
  let count = nb_get32(net_st.net__in, 16)
  var o = 20
  for c in 0 .. count {
    if o + 4 > n { return }
    let kind = nb_get8(net_st.net__in, o)
    let rel = nb_get8(net_st.net__in, o + 1) == 1
    o += 2
    var id = 0
    if rel {
      if o + 4 > n { return }
      id = nb_get32(net_st.net__in, o)
      o += 4
    }
    let ml = nb_get8(net_st.net__in, o) | (nb_get8(net_st.net__in, o + 1) << 8)
    o += 2
    if ml < 0 or o + ml > n { return }
    var take = true
    if rel {
      p.ack_due = true
      if id != p.recv_id + 1 { take = false } else { p.recv_id = id }
    }
    if take { net__deliver(net_st, slot, from, kind, o, ml) }
    o += ml
  }
}

# onto the inbox - except a heartbeat, and on a host anything but a hello before its welcome
function net__deliver(net_st: mut NetState, slot: int, from: int, kind: int, o: int, ml: int) -> void {
  if kind == NET_BEAT { return }
  if net_st.net__state == NET_HOSTING and net_st.net__peers[slot].pid < 2 and kind != NET_HELLO { return }
  let m = net__in_take(net_st)
  m.slot = slot
  m.from = from
  m.kind = kind
  m.len = ml
  nb_copy(m.data, 0, net_st.net__in, o, ml)
  q_push(net_inbox(net_st), m)
}