nim-libp2p/libp2p/switch.nim

## Nim-LibP2P
## 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 std/[tables,
            options,
            sets,
            oids,
            sugar,
            math]

import chronos,
       chronicles,
       metrics

import stream/connection,
       transports/transport,
       upgrademngrs/[upgrade, muxedupgrade],
       multistream,
       multiaddress,
       protocols/protocol,
       protocols/secure/secure,
       peerinfo,
       protocols/identify,
       muxers/muxer,
       utils/semaphore,
       connmanager,
       peerid,
       errors

export connmanager, upgrade

logScope:
  topics = "libp2p switch"

#TODO: General note - use a finite state machine to manage the different
# steps of connections establishing and upgrading. This makes everything
# more robust and less prone to ordering attacks - i.e. muxing can come if
# and only if the channel has been secured (i.e. if a secure manager has been
# previously provided)

declareCounter(libp2p_total_dial_attempts, "total attempted dials")
declareCounter(libp2p_successful_dials, "dialed successful peers")
declareCounter(libp2p_failed_dials, "failed dials")
declareCounter(libp2p_failed_upgrades_incoming, "incoming connections failed upgrades")
declareCounter(libp2p_failed_upgrades_outgoing, "outgoing connections failed upgrades")

const
  ConcurrentUpgrades* = 4

type
    DialFailedError* = object of CatchableError

    Switch* = ref object of RootObj
      peerInfo*: PeerInfo
      connManager*: ConnManager
      transports*: seq[Transport]
      ms*: MultistreamSelect
      dialLock: Table[PeerID, AsyncLock]
      acceptFuts: seq[Future[void]]
      upgrade: Upgrade

proc addConnEventHandler*(s: Switch,
                          handler: ConnEventHandler,
                          kind: ConnEventKind) =
  s.connManager.addConnEventHandler(handler, kind)

proc removeConnEventHandler*(s: Switch,
                             handler: ConnEventHandler,
                             kind: ConnEventKind) =
  s.connManager.removeConnEventHandler(handler, kind)

proc addPeerEventHandler*(s: Switch,
                          handler: PeerEventHandler,
                          kind: PeerEventKind) =
  s.connManager.addPeerEventHandler(handler, kind)

proc removePeerEventHandler*(s: Switch,
                             handler: PeerEventHandler,
                             kind: PeerEventKind) =
  s.connManager.removePeerEventHandler(handler, kind)

proc isConnected*(s: Switch, peerId: PeerID): bool =
  ## returns true if the peer has one or more
  ## associated connections (sockets)
  ##

  peerId in s.connManager

proc disconnect*(s: Switch, peerId: PeerID): Future[void] {.gcsafe.} =
  s.connManager.dropPeer(peerId)

proc dialAndUpgrade(s: Switch,
                    peerId: PeerID,
                    addrs: seq[MultiAddress]):
                    Future[Connection] {.async.} =
  debug "Dialing peer", peerId

  # Avoid "cannot be captured as it would violate memory safety" errors in Nim-1.4.x.
  var
    transport: Transport
    address: MultiAddress

  for t in s.transports: # for each transport
    transport = t
    for a in addrs:      # for each address
      address = a
      if t.handles(a):   # check if it can dial it
        trace "Dialing address", address = $a, peerId
        let dialed = try:
            libp2p_total_dial_attempts.inc()
            # await a connection slot when the total
            # connection count is equal to `maxConns`
            await s.connManager.trackOutgoingConn(
              () => transport.dial(address)
            )
          except TooManyConnectionsError as exc:
            trace "Connection limit reached!"
            raise exc
          except CancelledError as exc:
            debug "Dialing canceled", msg = exc.msg, peerId
            raise exc
          except CatchableError as exc:
            debug "Dialing failed", msg = exc.msg, peerId
            libp2p_failed_dials.inc()
            continue # Try the next address

        # make sure to assign the peer to the connection
        dialed.peerInfo = PeerInfo.init(peerId, addrs)

        # also keep track of the connection's bottom unsafe transport direction
        # required by gossipsub scoring
        dialed.transportDir = Direction.Out

        libp2p_successful_dials.inc()

        let conn = try:
            await s.upgrade.upgradeOutgoing(dialed)
          except CatchableError as exc:
            # If we failed to establish the connection through one transport,
            # we won't succeeded through another - no use in trying again
            await dialed.close()
            debug "Upgrade failed", msg = exc.msg, peerId
            if exc isnot CancelledError:
              libp2p_failed_upgrades_outgoing.inc()
            raise exc

        doAssert not isNil(conn), "connection died after upgradeOutgoing"
        debug "Dial successful", conn, peerInfo = conn.peerInfo
        return conn

proc internalConnect(s: Switch,
                     peerId: PeerID,
                     addrs: seq[MultiAddress]):
                     Future[Connection] {.async.} =
  if s.peerInfo.peerId == peerId:
    raise newException(CatchableError, "can't dial self!")

  # Ensure there's only one in-flight attempt per peer
  let lock = s.dialLock.mgetOrPut(peerId, newAsyncLock())
  try:
    await lock.acquire()

    # Check if we have a connection already and try to reuse it
    var conn = s.connManager.selectConn(peerId)
    if conn != nil:
      if conn.atEof or conn.closed:
        # This connection should already have been removed from the connection
        # manager - it's essentially a bug that we end up here - we'll fail
        # for now, hoping that this will clean themselves up later...
        warn "dead connection in connection manager", conn
        await conn.close()
        raise newException(DialFailedError, "Zombie connection encountered")

      trace "Reusing existing connection", conn, direction = $conn.dir
      return conn

    conn = await s.dialAndUpgrade(peerId, addrs)
    if isNil(conn): # None of the addresses connected
      raise newException(DialFailedError, "Unable to establish outgoing link")

    # We already check for this in Connection manager
    # but a disconnect could have happened right after
    # we've added the connection so we check again
    # to prevent races due to that.
    if conn.closed() or conn.atEof():
      # This can happen when the other ends drops us
      # before we get a chance to return the connection
      # back to the dialer.
      trace "Connection dead on arrival", conn
      raise newLPStreamClosedError()

    return conn
  finally:
    if lock.locked():
      lock.release()

proc connect*(s: Switch, peerId: PeerID, addrs: seq[MultiAddress]) {.async.} =
  ## attempt to create establish a connection
  ## with a remote peer
  ##

  if s.connManager.connCount(peerId) > 0:
    return

  discard await s.internalConnect(peerId, addrs)

proc negotiateStream(s: Switch, conn: Connection, protos: seq[string]): Future[Connection] {.async.} =
  trace "Negotiating stream", conn, protos
  let selected = await s.ms.select(conn, protos)
  if not protos.contains(selected):
    await conn.closeWithEOF()
    raise newException(DialFailedError, "Unable to select sub-protocol " & $protos)

  return conn

proc dial*(s: Switch,
           peerId: PeerID,
           protos: seq[string]): Future[Connection] {.async.} =
  trace "Dialing (existing)", peerId, protos
  let stream = await s.connManager.getStream(peerId)
  if stream.isNil:
    raise newException(DialFailedError, "Couldn't get muxed stream")

  return await s.negotiateStream(stream, protos)

proc dial*(s: Switch,
           peerId: PeerID,
           proto: string): Future[Connection] =
  dial(s, peerId, @[proto])

proc dial*(s: Switch,
           peerId: PeerID,
           addrs: seq[MultiAddress],
           protos: seq[string]):
           Future[Connection] {.async.} =
  var
    conn: Connection
    stream: Connection

  proc cleanup() {.async.} =
    if not(isNil(stream)):
      await stream.closeWithEOF()

    if not(isNil(conn)):
      await conn.close()

  try:
    trace "Dialing (new)", peerId, protos
    conn = await s.internalConnect(peerId, addrs)
    trace "Opening stream", conn
    stream = await s.connManager.getStream(conn)

    if isNil(stream):
      raise newException(DialFailedError,
        "Couldn't get muxed stream")

    return await s.negotiateStream(stream, protos)
  except CancelledError as exc:
    trace "Dial canceled", conn
    await cleanup()
    raise exc
  except CatchableError as exc:
    debug "Error dialing", conn, msg = exc.msg
    await cleanup()
    raise exc

proc dial*(s: Switch,
           peerId: PeerID,
           addrs: seq[MultiAddress],
           proto: string):
           Future[Connection] = dial(s, peerId, addrs, @[proto])

proc mount*[T: LPProtocol](s: Switch, proto: T, matcher: Matcher = nil) {.gcsafe.} =
  if isNil(proto.handler):
    raise newException(CatchableError,
      "Protocol has to define a handle method or proc")

  if proto.codec.len == 0:
    raise newException(CatchableError,
      "Protocol has to define a codec string")

  s.ms.addHandler(proto.codecs, proto, matcher)
  s.peerInfo.protocols.add(proto.codec)

proc upgradeMonitor(conn: Connection, upgrades: AsyncSemaphore) {.async.} =
  ## monitor connection for upgrades
  ##
  try:
    # Since we don't control the flow of the
    # upgrade, this timeout guarantees that a
    # "hanged" remote doesn't hold the upgrade
    # forever
    await conn.onUpgrade.wait(30.seconds) # wait for connection to be upgraded
    trace "Connection upgrade succeeded"
  except CatchableError as exc:
    libp2p_failed_upgrades_incoming.inc()
    if not isNil(conn):
      await conn.close()

    trace "Exception awaiting connection upgrade", exc = exc.msg, conn
  finally:
    upgrades.release() # don't forget to release the slot!

proc accept(s: Switch, transport: Transport) {.async.} = # noraises
  ## switch accept loop, ran for every transport
  ##

  let upgrades = newAsyncSemaphore(ConcurrentUpgrades)
  while transport.running:
    var conn: Connection
    try:
      debug "About to accept incoming connection"
      # remember to always release the slot when
      # the upgrade succeeds or fails, this is
      # currently done by the `upgradeMonitor`
      await upgrades.acquire()    # first wait for an upgrade slot to become available
      conn = await s.connManager  # next attempt to get an incoming connection
      .trackIncomingConn(
        () => transport.accept()
      )
      if isNil(conn):
        # A nil connection means that we might have hit a
        # file-handle limit (or another non-fatal error),
        # we can get one on the next try, but we should
        # be careful to not end up in a thigh loop that
        # will starve the main event loop, thus we sleep
        # here before retrying.
        trace "Unable to get a connection, sleeping"
        await sleepAsync(100.millis) # TODO: should be configurable?
        upgrades.release()
        continue

      # set the direction of this bottom level transport
      # in order to be able to consume this information in gossipsub if required
      # gossipsub gives priority to connections we make
      conn.transportDir = Direction.In

      debug "Accepted an incoming connection", conn
      asyncSpawn upgradeMonitor(conn, upgrades)
      asyncSpawn s.upgrade.upgradeIncoming(conn)
    except CancelledError as exc:
      trace "releasing semaphore on cancellation"
      upgrades.release() # always release the slot
    except CatchableError as exc:
      debug "Exception in accept loop, exiting", exc = exc.msg
      upgrades.release() # always release the slot
      if not isNil(conn):
        await conn.close()
      return

proc start*(s: Switch): Future[seq[Future[void]]] {.async, gcsafe.} =
  trace "starting switch for peer", peerInfo = s.peerInfo
  var startFuts: seq[Future[void]]
  for t in s.transports: # for each transport
    for i, a in s.peerInfo.addrs:
      if t.handles(a): # check if it handles the multiaddr
        var server = t.start(a)
        s.peerInfo.addrs[i] = t.ma # update peer's address
        s.acceptFuts.add(s.accept(t))
        startFuts.add(server)

  debug "Started libp2p node", peer = s.peerInfo
  return startFuts # listen for incoming connections

proc stop*(s: Switch) {.async.} =
  trace "Stopping switch"

  # close and cleanup all connections
  await s.connManager.close()

  for t in s.transports:
    try:
      await t.stop()
    except CancelledError as exc:
      raise exc
    except CatchableError as exc:
      warn "error cleaning up transports", msg = exc.msg

  try:
    await allFutures(s.acceptFuts)
      .wait(1.seconds)
  except CatchableError as exc:
    trace "Exception while stopping accept loops", exc = exc.msg

  # check that all futures were properly
  # stopped and otherwise cancel them
  for a in s.acceptFuts:
    if not a.finished:
      a.cancel()

  trace "Switch stopped"

proc newSwitch*(peerInfo: PeerInfo,
                transports: seq[Transport],
                identity: Identify,
                muxers: Table[string, MuxerProvider],
                secureManagers: openarray[Secure] = [],
                maxConnections = MaxConnections,
                maxIn = -1,
                maxOut = -1,
                maxConnsPerPeer = MaxConnectionsPerPeer): Switch =
  if secureManagers.len == 0:
    raise (ref CatchableError)(msg: "Provide at least one secure manager")

  let ms = newMultistream()
  let connManager = ConnManager.init(maxConnsPerPeer, maxConnections, maxIn, maxOut)
  let upgrade = MuxedUpgrade.init(identity, muxers, secureManagers, connManager, ms)

  let switch = Switch(
    peerInfo: peerInfo,
    ms: ms,
    transports: transports,
    connManager: connManager,
    upgrade: upgrade,
  )

  switch.mount(identity)
  return switch

proc isConnected*(s: Switch, peerInfo: PeerInfo): bool
  {.deprecated: "Use PeerID version".} =
  not isNil(peerInfo) and isConnected(s, peerInfo.peerId)

proc disconnect*(s: Switch, peerInfo: PeerInfo): Future[void]
  {.deprecated: "Use PeerID version", gcsafe.} =
  disconnect(s, peerInfo.peerId)

proc connect*(s: Switch, peerInfo: PeerInfo): Future[void]
  {.deprecated: "Use PeerID version".} =
  connect(s, peerInfo.peerId, peerInfo.addrs)

proc dial*(s: Switch,
           peerInfo: PeerInfo,
           proto: string):
           Future[Connection]
  {.deprecated: "Use PeerID version".} =
  dial(s, peerInfo.peerId, peerInfo.addrs, proto)