quicp2p/puncher.nim

import asyncdispatch, asyncnet, net, port_prediction, strformat

from nativesockets import
  SockAddr,
  SockAddr_storage,
  SockLen,
  getSockOptInt,
  setSockOptInt
from sequtils import any

type
  Attempt* = object
    ## A hole punching attempt.
    srcPort*: Port
    dstIp*: IpAddress
    dstPorts*: seq[Port]
    future*: Future[Port]

  Puncher* = ref object
    sock: AsyncSocket
    attempts: seq[Attempt]

  PunchHoleError* = object of ValueError

var IPPROTO_IP {.importc: "IPPROTO_IP", header: "<netinet/in.h>".}: cint
var IP_TTL {.importc: "IP_TTL", header: "<netinet/in.h>".}: cint

const Timeout = 3000

proc `==`(a, b: Attempt): bool =
  ## ``==`` for hole punching attempts.
  ##
  ## Two hole punching attempts are considered equal if their ``srcPort`` and
  ## ``dstIp`` are equal and their ``dstPorts`` overlap.
  a.srcPort == b.srcPort and a.dstIp == b.dstIp and
  a.dstPorts.any(proc (p: Port): bool = p in b.dstPorts)

proc initPuncher*(sock: AsyncSocket): Puncher =
  Puncher(sock: sock)

proc punch(puncher: Puncher, peerIp: IpAddress, peerPort: Port,
           peerProbedPorts: seq[Port], lowTTL: bool, msg: string):
          Future[Attempt] {.async.} =
  let punchFuture = newFuture[Port]("punch")
  let predictedDstPorts = predictPortRange(peerPort, peerProbedPorts)
  let (_, myPort) = puncher.sock.getLocalAddr()
  result = Attempt(srcPort: myPort, dstIp: peerIp, dstPorts: predictedDstPorts,
                   future: punchFuture)
  if puncher.attempts.contains(result):
    raise newException(PunchHoleError,
                       "hole punching for given parameters already active")
  puncher.attempts.add(result)
  echo &"sending msg {msg} to {peerIp}, predicted ports: {result.dstPorts}"
  var peerAddr: Sockaddr_storage
  var peerSockLen: SockLen
  try:
    var defaultTTL: int
    if lowTTL:
      defaultTTL = puncher.sock.getFd.getSockOptInt(IPPROTO_IP, IP_TTL)
      puncher.sock.getFd.setSockOptInt(IPPROTO_IP, IP_TTL, 2)
    for dstPort in result.dstPorts:
      toSockAddr(result.dstIp, dstPort, peerAddr, peerSockLen)
      # TODO: replace asyncdispatch.sendTo with asyncnet.sendTo (Nim 1.4 required)
      await sendTo(puncher.sock.getFd().AsyncFD, msg.cstring, msg.len,
                   cast[ptr SockAddr](addr peerAddr), peerSockLen)
    if lowTTL:
      puncher.sock.getFd.setSockOptInt(IPPROTO_IP, IP_TTL, defaultTTL)
  except OSError as e:
    raise newException(PunchHoleError, e.msg)

proc initiate*(puncher: Puncher, peerIp: IpAddress, peerPort: Port,
               peerProbedPorts: seq[Port]): Future[Attempt] =
  punch(puncher, peerIp, peerPort, peerProbedPorts, true, "SYN")
  
proc respond*(puncher: Puncher, peerIp: IpAddress, peerPort: Port,
              peerProbedPorts: seq[Port]): Future[Attempt] =
  punch(puncher, peerIp, peerPort, peerProbedPorts, false, "ACK")

proc finalize*(attempt: Attempt): Future[Port] {.async.} =
  await attempt.future or sleepAsync(Timeout)
  if attempt.future.finished:
    result = attempt.future.read()
  else:
    raise newException(PunchHoleError, "timeout")

proc handleMsg*(puncher: Puncher, msg: string, peerIp: IpAddress,
                peerPort: Port) =
  ## Handles an incoming UDP message which may complete the Futures returned by
  ## ``initiate`` and ``respond``.
  if msg == "SYN":
    # We received a SYN packet. We ignore it because we expected it to be
    # filtered by our NAT.
    return
  let (_, myPort) = puncher.sock.getLocalAddr()
  let query = Attempt(srcPort: myPort, dstIp: peerIp, dstPorts: @[peerPort])
  let i = puncher.attempts.find(query)
  if i != -1:
    if msg == "ACK":
      echo &"handling ACK message from {peerIp}:{peerPort}"
    else:
      echo &"handling QUIC message from {peerIp}:{peerPort}"
    puncher.attempts[i].future.complete(peerPort)
    puncher.attempts.del(i)
  else:
    echo &"received unexpected packet from {peerIp}:{peerPort}"

proc handleMsg*(puncher: Puncher, msg: string,
                peerAddr: SockAddr | Sockaddr_storage, peerSockLen: SockLen) =
  var peerIp: IpAddress
  var peerPort: Port
  fromSockAddr(peerAddr, peerSockLen, peerIp, peerPort)
  handleMsg(puncher, msg, peerIp, peerPort)