nim-libp2p/libp2p/nameresolving/dnsresolver.nim

# Nim-LibP2P
# Copyright (c) 2023 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.

{.push raises: [].}

import
  std/[streams, strutils, sets, sequtils],
  chronos,
  chronicles,
  stew/byteutils,
  dnsclientpkg/[protocol, types],
  ../utility

import nameresolver

logScope:
  topics = "libp2p dnsresolver"

type DnsResolver* = ref object of NameResolver
  nameServers*: seq[TransportAddress]

proc questionToBuf(address: string, kind: QKind): seq[byte] =
  try:
    var
      header = initHeader()
      question = initQuestion(address, kind)

      requestStream = header.toStream()
    question.toStream(requestStream)

    let dataLen = requestStream.getPosition()
    requestStream.setPosition(0)

    var buf = newSeq[byte](dataLen)
    discard requestStream.readData(addr buf[0], dataLen)
    return buf
  except CatchableError as exc:
    info "Failed to created DNS buffer", description = exc.msg
    return newSeq[byte](0)

proc getDnsResponse(
    dnsServer: TransportAddress, address: string, kind: QKind
): Future[Response] {.async.} =
  var sendBuf = questionToBuf(address, kind)

  if sendBuf.len == 0:
    raise newException(ValueError, "Incorrect DNS query")

  let receivedDataFuture = newFuture[void]()

  proc datagramDataReceived(
      transp: DatagramTransport, raddr: TransportAddress
  ): Future[void] {.async, closure.} =
    receivedDataFuture.complete()

  let sock =
    if dnsServer.family == AddressFamily.IPv6:
      newDatagramTransport6(datagramDataReceived)
    else:
      newDatagramTransport(datagramDataReceived)

  try:
    await sock.sendTo(dnsServer, addr sendBuf[0], sendBuf.len)

    await receivedDataFuture or sleepAsync(5.seconds) #unix default

    if not receivedDataFuture.finished:
      raise newException(IOError, "DNS server timeout")

    let rawResponse = sock.getMessage()
    # parseResponse can has a raises: [Exception, ..] because of
    # https://github.com/nim-lang/Nim/commit/035134de429b5d99c5607c5fae912762bebb6008
    # it can't actually raise though
    return exceptionToAssert:
      parseResponse(string.fromBytes(rawResponse))
  finally:
    await sock.closeWait()

method resolveIp*(
    self: DnsResolver, address: string, port: Port, domain: Domain = Domain.AF_UNSPEC
): Future[seq[TransportAddress]] {.async.} =
  trace "Resolving IP using DNS", address, servers = self.nameServers.mapIt($it), domain
  for _ in 0 ..< self.nameServers.len:
    let server = self.nameServers[0]
    var responseFutures: seq[Future[Response]]
    if domain == Domain.AF_INET or domain == Domain.AF_UNSPEC:
      responseFutures.add(getDnsResponse(server, address, A))

    if domain == Domain.AF_INET6 or domain == Domain.AF_UNSPEC:
      let fut = getDnsResponse(server, address, AAAA)
      if server.family == AddressFamily.IPv6:
        trace "IPv6 DNS server, puting AAAA records first", server = $server
        responseFutures.insert(fut)
      else:
        responseFutures.add(fut)

    var
      resolvedAddresses: OrderedSet[string]
      resolveFailed = false
    for fut in responseFutures:
      try:
        let resp = await fut
        for answer in resp.answers:
          # toString can has a raises: [Exception, ..] because of
          # https://github.com/nim-lang/Nim/commit/035134de429b5d99c5607c5fae912762bebb6008
          # it can't actually raise though
          resolvedAddresses.incl(exceptionToAssert(answer.toString()))
      except CancelledError as e:
        raise e
      except ValueError as e:
        info "Invalid DNS query", address, error = e.msg
        return @[]
      except CatchableError as e:
        info "Failed to query DNS", address, error = e.msg
        resolveFailed = true
        break

    if resolveFailed:
      self.nameServers.add(self.nameServers[0])
      self.nameServers.delete(0)
      continue

    trace "Got IPs from DNS server", resolvedAddresses, server = $server
    return resolvedAddresses.toSeq().mapIt(initTAddress(it, port))

  debug "Failed to resolve address, returning empty set"
  return @[]

method resolveTxt*(self: DnsResolver, address: string): Future[seq[string]] {.async.} =
  trace "Resolving TXT using DNS", address, servers = self.nameServers.mapIt($it)
  for _ in 0 ..< self.nameServers.len:
    let server = self.nameServers[0]
    try:
      # toString can has a raises: [Exception, ..] because of
      # https://github.com/nim-lang/Nim/commit/035134de429b5d99c5607c5fae912762bebb6008
      # it can't actually raise though
      let response = await getDnsResponse(server, address, TXT)
      return exceptionToAssert:
        trace "Got TXT response",
          server = $server, answer = response.answers.mapIt(it.toString())
        response.answers.mapIt(it.toString())
    except CancelledError as e:
      raise e
    except CatchableError as e:
      info "Failed to query DNS", address, error = e.msg
      self.nameServers.add(self.nameServers[0])
      self.nameServers.delete(0)
      continue

  debug "Failed to resolve TXT, returning empty set"
  return @[]

proc new*(T: typedesc[DnsResolver], nameServers: seq[TransportAddress]): T =
  T(nameServers: nameServers)