package yggdrasil

// This manages the tun driver to send/recv packets to/from applications

import water "github.com/songgao/water"

const IPv6_HEADER_LENGTH = 40

type tunDevice struct {
  core *Core
  send chan<- []byte
  recv <-chan []byte
  mtu int
  iface *water.Interface
}

func (tun *tunDevice) init(core *Core) {
  tun.core = core
}

func (tun *tunDevice) write() error {
  for {
    data := <-tun.recv
    if _, err := tun.iface.Write(data); err != nil { return err }
    util_putBytes(data)
  }
}

func (tun *tunDevice) read() error {
  buf := make([]byte, tun.mtu)
  for {
    n, err := tun.iface.Read(buf)
    if err != nil { return err }
    if buf[0] & 0xf0 != 0x60 ||
       n != 256*int(buf[4]) + int(buf[5]) + IPv6_HEADER_LENGTH {
      // Either not an IPv6 packet or not the complete packet for some reason
      //panic("Should not happen in testing")
      continue
    }
    packet := append(util_getBytes(), buf[:n]...)
    tun.send<-packet
  }
}

func (tun *tunDevice) close() error {
  return tun.iface.Close()
}