nat.nim

# Copyright (c) 2019 Status Research & Development GmbH
# Licensed under either of
#  * Apache License, version 2.0, ([LICENSE-APACHE](LICENSE-APACHE))
#  * MIT license ([LICENSE-MIT](LICENSE-MIT))
# at your option.
# This file may not be copied, modified, or distributed except according to
# those terms.

import
  net, options, os, strutils, times,
  result, nat_traversal/[miniupnpc, natpmp], chronicles

type
  NatStrategy* = enum
    NatAny
    NatUpnp
    NatPmp
    NatNone

const
  UPNP_TIMEOUT = 200 # ms
  PORT_MAPPING_INTERVAL = 20 * 60 # seconds
  NATPMP_LIFETIME = 60 * 60 # in seconds, must be longer than PORT_MAPPING_INTERVAL

var
  upnp {.threadvar.}: Miniupnp
  npmp {.threadvar.}: NatPmp
  strategy = NatNone
  externalIP {.threadvar.}: IPAddress
  internalTcpPort: Port
  externalTcpPort: Port
  internalUdpPort: Port
  externalUdpPort: Port

logScope:
  topics = "nat"

## Also does threadvar initialisation.
## Must be called before redirectPorts() in each thread.
proc getExternalIP*(natStrategy: NatStrategy): Option[IpAddress] =
  if natStrategy == NatAny or natStrategy == NatUpnp:
    upnp = newMiniupnp()
    upnp.discoverDelay = UPNP_TIMEOUT
    let dres = upnp.discover()
    if dres.isErr:
      debug "UPnP", msg = dres.error
    else:
      var
        msg: cstring
        canContinue = true
      case upnp.selectIGD():
        of IGDNotFound:
          msg = "Internet Gateway Device not found. Giving up."
          canContinue = false
        of IGDFound:
          msg = "Internet Gateway Device found."
        of IGDNotConnected:
          msg = "Internet Gateway Device found but it's not connected. Trying anyway."
        of NotAnIGD:
          msg = "Some device found, but it's not recognised as an Internet Gateway Device. Trying anyway."
      debug "UPnP", msg
      if canContinue:
        let ires = upnp.externalIPAddress()
        if ires.isErr:
          debug "UPnP", msg = ires.error
        else:
          # if we got this far, UPnP is working and we don't need to try NAT-PMP
          try:
            externalIP = parseIpAddress(ires.value)
            strategy = NatUpnp
            return some(externalIP)
          except:
            error "parseIpAddress() exception", err = getCurrentExceptionMsg()
            return

  if natStrategy == NatAny or natStrategy == NatPmp:
    npmp = newNatPmp()
    let nres = npmp.init()
    if nres.isErr:
      debug "NAT-PMP", msg = nres.error
    else:
      let nires = npmp.externalIPAddress()
      if nires.isErr:
        debug "NAT-PMP", msg = nires.error
      else:
        try:
          externalIP = parseIpAddress($(nires.value))
          strategy = NatPmp
          return some(externalIP)
        except:
          error "parseIpAddress() exception", err = getCurrentExceptionMsg()
          return

proc doPortMapping(tcpPort, udpPort: Port, description: string): Option[(Port, Port)] {.gcsafe.} =
  var
    extTcpPort: Port
    extUdpPort: Port

  if strategy == NatUpnp:
    for t in [(tcpPort, UPNPProtocol.TCP), (udpPort, UPNPProtocol.UDP)]:
      let
        (port, protocol) = t
        pmres = upnp.addPortMapping(externalPort = $port,
                                    protocol = protocol,
                                    internalHost = upnp.lanAddr,
                                    internalPort = $port,
                                    desc = description,
                                    leaseDuration = 0,
                                    externalIP = $externalIP)
      if pmres.isErr:
        error "UPnP port mapping", msg = pmres.error
        return
      else:
        # let's check it
        let cres = upnp.getSpecificPortMapping(externalPort = $port,
                                                protocol = protocol)
        if cres.isErr:
          error "UPnP port mapping check", msg = cres.error
          return
        else:
          let extPort = Port(parseUInt(cres.value.externalPort))
          debug "UPnP: added port mapping", externalPort = extPort, internalPort = port, protocol = protocol
          case protocol:
            of UPNPProtocol.TCP:
              extTcpPort = extPort
            of UPNPProtocol.UDP:
              extUdpPort = extPort
  elif strategy == NatPmp:
    for t in [(tcpPort, NatPmpProtocol.TCP), (udpPort, NatPmpProtocol.UDP)]:
      let
        (port, protocol) = t
        pmres = npmp.addPortMapping(eport = port.cushort,
                                    iport = port.cushort,
                                    protocol = protocol,
                                    lifetime = NATPMP_LIFETIME)
      if pmres.isErr:
        error "NAT-PMP port mapping", msg = pmres.error
        return
      else:
        let extPort = Port(pmres.value)
        debug "NAT-PMP: added port mapping", externalPort = extPort, internalPort = port, protocol = protocol
        case protocol:
          of NatPmpProtocol.TCP:
            extTcpPort = extPort
          of NatPmpProtocol.UDP:
            extUdpPort = extPort
  return some((extTcpPort, extUdpPort))

type PortMappingArgs = tuple[tcpPort, udpPort: Port, description: string]
var
  natThread: Thread[PortMappingArgs]
  natCloseChan: Channel[bool]

proc repeatPortMapping(args: PortMappingArgs) {.thread.} =
  let
    (tcpPort, udpPort, description) = args
    interval = initDuration(seconds = PORT_MAPPING_INTERVAL)
    sleepDuration = 1_000 # in ms, also the maximum delay after pressing Ctrl-C

  var lastUpdate = now()

  # We can't use copies of Miniupnp and NatPmp objects in this thread, because they share
  # C pointers with other instances that have already been garbage collected, so
  # we use threadvars instead and initialise them again with getExternalIP().
  let ipres = getExternalIP(strategy)
  if ipres.isSome:
    externalIP = ipres.get()
    while true:
      # we're being silly here with this channel polling because we can't
      # select on Nim channels like on Go ones
      let (dataAvailable, data) = natCloseChan.tryRecv()
      if dataAvailable:
        return
      else:
        let currTime = now()
        if currTime >= (lastUpdate + interval):
          discard doPortMapping(tcpPort, udpPort, description)
          lastUpdate = currTime
        sleep(sleepDuration)

var mainThreadId = getThreadId()

proc stopNatThread() {.noconv.} =
  if getThreadId() == mainThreadId:
    # stop the thread
    natCloseChan.send(true)
    natThread.joinThread()
    natCloseChan.close()
    # delete our port mappings
    if strategy == NatUpnp:
      for t in [(externalTcpPort, internalTcpPort, UPNPProtocol.TCP), (externalUdpPort, internalUdpPort, UPNPProtocol.UDP)]:
        let
          (eport, iport, protocol) = t
          pmres = upnp.deletePortMapping(externalPort = $eport,
                                          protocol = protocol)
        if pmres.isErr:
          error "UPnP port mapping deletion", msg = pmres.error
        else:
          debug "UPnP: deleted port mapping", externalPort = eport, internalPort = iport, protocol = protocol
    elif strategy == NatPmp:
      for t in [(externalTcpPort, internalTcpPort, NatPmpProtocol.TCP), (externalUdpPort, internalUdpPort, NatPmpProtocol.UDP)]:
        let
          (eport, iport, protocol) = t
          pmres = npmp.deletePortMapping(eport = eport.cushort,
                                          iport = iport.cushort,
                                          protocol = protocol)
        if pmres.isErr:
          error "NAT-PMP port mapping deletion", msg = pmres.error
        else:
          debug "NAT-PMP: deleted port mapping", externalPort = eport, internalPort = iport, protocol = protocol

proc redirectPorts*(tcpPort, udpPort: Port, description: string): Option[(Port, Port)] =
  result = doPortMapping(tcpPort, udpPort, description)
  if result.isSome:
    (externalTcpPort, externalUdpPort) = result.get()
    # needed by NAT-PMP on port mapping deletion
    internalTcpPort = tcpPort
    internalUdpPort = udpPort
    # Port mapping works. Let's launch a thread that repeats it, in case the
    # NAT-PMP lease expires or the router is rebooted and forgets all about
    # these mappings.
    natCloseChan.open()
    natThread.createThread(repeatPortMapping, (externalTcpPort, externalUdpPort, description))
    # atexit() in disguise
    addQuitProc(stopNatThread)