nim-libp2p/libp2p/muxers/mplex.nim

## Nim-LibP2P
## Copyright (c) 2018 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 tables, sequtils
import chronos
import ../varint, ../connection, 
       ../vbuffer, ../protocol,
       ../stream/bufferstream, ../stream/lpstream, 
       muxer

const MaxMsgSize* = 1 shl 20 # 1mb
const MaxChannels* = 1000
const MplexCodec* = "/mplex/6.7.0"

type 
  MplexUnknownMsgError* = object of CatchableError
  MessageType* {.pure.} = enum
    New,
    MsgIn,
    MsgOut,
    CloseIn,
    CloseOut,
    ResetIn,
    ResetOut

  StreamHandler = proc(conn: Connection): Future[void] {.gcsafe.}
  Mplex* = ref object of Muxer
    remote*: Table[int, Channel]
    local*: Table[int, Channel]
    currentId*: int
    maxChannels*: uint
    streamHandler*: StreamHandler

  Channel* = ref object of BufferStream
    id*: int
    initiator*: bool
    isReset*: bool
    closedLocal*: bool
    closedRemote*: bool
    mplex*: Mplex

proc newMplexUnknownMsgError*(): ref MplexUnknownMsgError =
  result = newException(MplexUnknownMsgError, "Unknown mplex message type")

##########################################
##           Read/Write Helpers
##########################################

proc readHeader*(conn: Connection): Future[(uint, MessageType)] {.async, gcsafe.} = 
  var
    header: uint
    length: int
    res: VarintStatus
  var buffer = newSeq[byte](10)
  try:
    for i in 0..<len(buffer):
      await conn.readExactly(addr buffer[i], 1)
      res = LP.getUVarint(buffer.toOpenArray(0, i), length, header)
      if res == VarintStatus.Success:
        return (header shr 3, MessageType(header and 0x7))
    if res != VarintStatus.Success:
      buffer.setLen(0)
      return
  except LPStreamIncompleteError:
    buffer.setLen(0)

proc writeHeader*(conn: Connection,
                  id: int,
                  msgType: MessageType, 
                  size: int) {.async, gcsafe.} =
  ## write lenght prefixed
  var buf = initVBuffer()
  buf.writeVarint(LPSomeUVarint(id.uint shl 3 or msgType.uint))
  if size > 0:
    buf.writeVarint(LPSomeUVarint(size.uint))
  buf.finish()
  result = conn.write(buf.buffer)

##########################################
##               Channel
##########################################

proc newChannel*(mplex: Mplex,
                 id: int,
                 initiator: bool,
                 handler: WriteHandler,
                 size: int = MaxMsgSize): Channel = 
  new result
  result.id = id
  result.mplex = mplex
  result.initiator = initiator
  result.initBufferStream(handler, size)

proc closed*(s: Channel): bool = s.closedLocal and s.closedRemote
proc close*(s: Channel) {.async.} = discard
proc reset*(s: Channel) {.async.} = discard

##########################################
##               Mplex
##########################################

proc getChannelList(m: Mplex, initiator: bool): var Table[int, Channel] =
  if initiator:
    result = m.remote
  else:
    result = m.local

proc newStreamInternal*(m: Mplex,
                        initiator: bool = true,
                        chanId: int):
                        Future[Channel] {.async, gcsafe.} = 
  ## create new channel/stream
  let id = if initiator: m.currentId.inc(); m.currentId else: chanId
  proc writeHandler(data: seq[byte]): Future[void] {.async, gcsafe.} = 
    let msgType = if initiator: MessageType.MsgOut else: MessageType.MsgIn
    await m.connection.writeHeader(id, msgType, data.len) # write header
    await m.connection.write(data) # write data

  result = newChannel(m, id, initiator, writeHandler)
  m.getChannelList(initiator)[id] = result

proc newStreamInternal*(m: Mplex): Future[Channel] {.gcsafe.} = 
  result = m.newStreamInternal(true, 0)

proc handle*(m: Mplex): Future[void] {.async, gcsafe.} = 
  try:
    while not m.connection.closed:
      let (id, msgType) = await m.connection.readHeader()
      let initiator = bool(ord(msgType) and 1)
      case msgType:
        of MessageType.New:
          let channel = await m.newStreamInternal(false, id.int)
          await m.streamHandler(newConnection(channel))
        of MessageType.MsgIn, MessageType.MsgOut:
          let channel = m.getChannelList(initiator)[id.int]
          let msg = await m.connection.readLp()
          await channel.pushTo(msg)
        of MessageType.CloseIn, MessageType.CloseOut:
          let channel = m.getChannelList(initiator)[id.int]
          await channel.close()
        of MessageType.ResetIn, MessageType.ResetOut:
          let channel = m.getChannelList(initiator)[id.int]
          await channel.reset()
        else: raise newMplexUnknownMsgError()
  except Exception as exc:
    #TODO: add proper loging
    discard
  finally:
    await m.connection.close()

proc newMplex*(conn: Connection, 
               streamHandler: StreamHandler, 
               maxChanns: uint = MaxChannels): Mplex =
  new result
  result.connection = conn
  result.maxChannels = maxChanns
  result.streamHandler = streamHandler
  result.remote = initTable[int, Channel]()
  result.local = initTable[int, Channel]()

method newStream*(m: Mplex): Future[Connection] {.async, gcsafe.} =
  let channel = await m.newStreamInternal()
  await m.connection.writeHeader(channel.id, MessageType.New, 0)
  result = newConnection(channel)

method close*(m: Mplex) {.async, gcsafe.} = 
    await allFutures(@[allFutures(toSeq(m.remote.values).mapIt(it.close())),
                       allFutures(toSeq(m.local.values).mapIt(it.close()))])
    await m.connection.close()