nim-eth/eth/p2p/discoveryv5/messages_encoding.nim

# nim-eth - Node Discovery Protocol v5
# Copyright (c) 2020-2023 Status Research & Development GmbH
# Licensed and distributed under either of
#   * MIT license (license terms in the root directory or at https://opensource.org/licenses/MIT).
#   * Apache v2 license (license terms in the root directory or at https://www.apache.org/licenses/LICENSE-2.0).
# at your option. This file may not be copied, modified, or distributed except according to those terms.
#
## Discovery v5 Protocol Messages RLP Encoding

{.push raises: [].}

import
  std/net,
  stew/[arrayops, results],
  ../../rlp,
  "."/[messages, enr]

from stew/objects import checkedEnumAssign

export messages, rlp, results

func read*(rlp: var Rlp, T: type RequestId): T
    {.raises: [ValueError, RlpError].} =
  mixin read
  var reqId: RequestId
  reqId.id = rlp.toBytes()
  if reqId.id.len > 8:
    raise newException(ValueError, "RequestId is > 8 bytes")
  rlp.skipElem()

  reqId

func append*(writer: var RlpWriter, value: RequestId) =
  writer.append(value.id)

func read*(rlp: var Rlp, T: type IpAddress): T
    {.raises: [RlpError].} =
  let ipBytes = rlp.toBytes()
  rlp.skipElem()

  if ipBytes.len == 4:
    var ip: array[4, byte]
    discard copyFrom(ip, ipBytes)
    IpAddress(family: IPv4, address_v4: ip)
  elif ipBytes.len == 16:
    var ip: array[16, byte]
    discard copyFrom(ip, ipBytes)
    IpAddress(family: IPv6, address_v6: ip)
  else:
    raise newException(RlpTypeMismatch,
      "Amount of bytes for IP address is different from 4 or 16")

func append*(writer: var RlpWriter, ip: IpAddress) =
  case ip.family:
  of IpAddressFamily.IPv4:
    writer.append(ip.address_v4)
  of IpAddressFamily.IPv6:
    writer.append(ip.address_v6)

func numFields(T: typedesc): int =
  for k, v in fieldPairs(default(T)): inc result

func encodeMessage*[T: SomeMessage](p: T, reqId: RequestId): seq[byte] =
  ## Encodes a message with provided `reqId`.
  var bytes = newSeqOfCap[byte](64)
  bytes.add(messageKind(T).ord)

  const sz = numFields(T)
  var writer = initRlpList(sz + 1)
  writer.append(reqId)
  for k, v in fieldPairs(p):
    writer.append(v)

  bytes.add(writer.finish())

  bytes

func decodeMessage*(body: openArray[byte]): Result[Message, cstring] =
  ## Decodes to the specific `Message` type.
  if body.len < 1:
    return err("No message data")

  var kind: MessageKind
  if not checkedEnumAssign(kind, body[0]):
    return err("Invalid message type")

  var message = Message(kind: kind)
  var rlp = rlpFromBytes(body.toOpenArray(1, body.high))
  if rlp.enterList:
    try:
      message.reqId = rlp.read(RequestId)
    except RlpError, ValueError:
      return err("Invalid request-id")

    func decode[T](rlp: var Rlp, v: var T)
        {.nimcall, raises: [RlpError, ValueError].} =
      for k, v in v.fieldPairs:
        v = rlp.read(typeof(v))

    try:
      case kind
      of unused: return err("Invalid message type")
      of ping: rlp.decode(message.ping)
      of pong: rlp.decode(message.pong)
      of findNode: rlp.decode(message.findNode)
      of nodes: rlp.decode(message.nodes)
      of talkReq: rlp.decode(message.talkReq)
      of talkResp: rlp.decode(message.talkResp)
      of regTopic, ticket, regConfirmation, topicQuery:
        # We just pass the empty type of this message without attempting to
        # decode, so that the protocol knows what was received.
        # But we ignore the message as per specification as "the content and
        # semantics of this message are not final".
        discard
    except RlpError, ValueError:
      return err("Invalid message encoding")

    ok(message)
  else:
    err("Invalid message encoding: no rlp list")