Handle when peers ask each other at the same time (#865)

libp2p/connmanager.nim

@@ -32,6 +32,7 @@ const
 
 type
   TooManyConnectionsError* = object of LPError
+  AlreadyExpectingConnectionError* = object of LPError
 
   ConnEventKind* {.pure.} = enum
     Connected,    # A connection was made and securely upgraded - there may be
@@ -79,7 +80,7 @@ type
     muxed: Table[Connection, MuxerHolder]
     connEvents: array[ConnEventKind, OrderedSet[ConnEventHandler]]
     peerEvents: array[PeerEventKind, OrderedSet[PeerEventHandler]]
-    expectedConnections: Table[PeerId, Future[Connection]]
+    expectedConnectionsOverLimit*: Table[(PeerId, Direction), Future[Connection]]
     peerStore*: PeerStore
 
   ConnectionSlot* = object
@@ -221,18 +222,19 @@ proc triggerPeerEvents*(c: ConnManager,
   except CatchableError as exc: # handlers should not raise!
     warn "Exception in triggerPeerEvents", exc = exc.msg, peer = peerId
 
-proc expectConnection*(c: ConnManager, p: PeerId): Future[Connection] {.async.} =
+proc expectConnection*(c: ConnManager, p: PeerId, dir: Direction): Future[Connection] {.async.} =
   ## Wait for a peer to connect to us. This will bypass the `MaxConnectionsPerPeer`
-  if p in c.expectedConnections:
-    raise LPError.newException("Already expecting a connection from that peer")
+  let key = (p, dir)
+  if key in c.expectedConnectionsOverLimit:
+    raise newException(AlreadyExpectingConnectionError, "Already expecting an incoming connection from that peer")
 
   let future = newFuture[Connection]()
-  c.expectedConnections[p] = future
+  c.expectedConnectionsOverLimit[key] = future
 
   try:
     return await future
   finally:
-    c.expectedConnections.del(p)
+    c.expectedConnectionsOverLimit.del(key)
 
 proc contains*(c: ConnManager, conn: Connection): bool =
   ## checks if a connection is being tracked by the
@@ -412,10 +414,12 @@ proc storeConn*(c: ConnManager, conn: Connection)
   let peerId = conn.peerId
 
   # we use getOrDefault in the if below instead of [] to avoid the KeyError
-  if peerId in c.expectedConnections and
-     not(c.expectedConnections.getOrDefault(peerId).finished):
-      c.expectedConnections.getOrDefault(peerId).complete(conn)
-  elif c.conns.getOrDefault(peerId).len > c.maxConnsPerPeer:
+  if c.conns.getOrDefault(peerId).len > c.maxConnsPerPeer:
+    let key = (peerId, conn.dir)
+    let expectedConn = c.expectedConnectionsOverLimit.getOrDefault(key)
+    if expectedConn != nil and not expectedConn.finished:
+        expectedConn.complete(conn)
+    else:
       debug "Too many connections for peer",
         conn, conns = c.conns.getOrDefault(peerId).len
 
@@ -562,8 +566,8 @@ proc close*(c: ConnManager) {.async.} =
   let muxed = c.muxed
   c.muxed.clear()
 
-  let expected = c.expectedConnections
-  c.expectedConnections.clear()
+  let expected = c.expectedConnectionsOverLimit
+  c.expectedConnectionsOverLimit.clear()
 
   for _, fut in expected:
     await fut.cancelAndWait()

libp2p/protocols/connectivity/autonat/client.nim

@@ -58,10 +58,14 @@ method dialMe*(self: AutonatClient, switch: Switch, pid: PeerId, addrs: seq[Mult
       raise newException(AutonatError, "Unexpected error when dialling: " & err.msg, err)
 
   # To bypass maxConnectionsPerPeer
-  let incomingConnection = switch.connManager.expectConnection(pid)
+  let incomingConnection = switch.connManager.expectConnection(pid, In)
+  if incomingConnection.failed() and incomingConnection.error of AlreadyExpectingConnectionError:
+    raise newException(AutonatError, incomingConnection.error.msg)
   defer:
     await conn.close()
     incomingConnection.cancel() # Safer to always try to cancel cause we aren't sure if the peer dialled us or not
+    if incomingConnection.completed():
+      await (await incomingConnection).close()
   trace "sending Dial", addrs = switch.peerInfo.addrs
   await conn.sendDial(switch.peerInfo.peerId, switch.peerInfo.addrs)
   let response = getResponseOrRaise(AutonatMsg.decode(await conn.readLp(1024)))

libp2p/protocols/connectivity/autonat/server.nim

@@ -63,7 +63,10 @@ proc tryDial(autonat: Autonat, conn: Connection, addrs: seq[MultiAddress]) {.asy
   var futs: seq[Future[Opt[MultiAddress]]]
   try:
     # This is to bypass the per peer max connections limit
-    let outgoingConnection = autonat.switch.connManager.expectConnection(conn.peerId)
+    let outgoingConnection = autonat.switch.connManager.expectConnection(conn.peerId, Out)
+    if outgoingConnection.failed() and outgoingConnection.error of AlreadyExpectingConnectionError:
+      await conn.sendResponseError(DialRefused, outgoingConnection.error.msg)
+      return
     # Safer to always try to cancel cause we aren't sure if the connection was established
     defer: outgoingConnection.cancel()
     # tryDial is to bypass the global max connections limit

libp2p/protocols/connectivity/autonat/service.nim

@@ -80,6 +80,9 @@ proc hasEnoughIncomingSlots(switch: Switch): bool =
   # we leave some margin instead of comparing to 0 as a peer could connect to us while we are asking for the dial back
   return switch.connManager.slotsAvailable(In) >= 2
 
+proc doesPeerHaveIncomingConn(switch: Switch, peerId: PeerId): bool =
+  return switch.connManager.selectConn(peerId, In) != nil
+
 proc handleAnswer(self: AutonatService, ans: NetworkReachability) {.async.} =
 
   if ans == Unknown:
@@ -104,6 +107,10 @@ proc handleAnswer(self: AutonatService, ans: NetworkReachability) {.async.} =
 proc askPeer(self: AutonatService, switch: Switch, peerId: PeerId): Future[NetworkReachability] {.async.} =
   logScope:
     peerId = $peerId
+
+  if doesPeerHaveIncomingConn(switch, peerId):
+    return Unknown
+
   if not hasEnoughIncomingSlots(switch):
     debug "No incoming slots available, not asking peer", incomingSlotsAvailable=switch.connManager.slotsAvailable(In)
     return Unknown
@@ -152,10 +159,7 @@ method setup*(self: AutonatService, switch: Switch): Future[bool] {.async.} =
   if hasBeenSetup:
     if self.askNewConnectedPeers:
       self.newConnectedPeerHandler = proc (peerId: PeerId, event: PeerEvent): Future[void] {.async.} =
-        if switch.connManager.selectConn(peerId, In) != nil: # no need to ask an incoming peer
-          return
         discard askPeer(self, switch, peerId)
-        await self.callHandler()
       switch.connManager.addPeerEventHandler(self.newConnectedPeerHandler, PeerEventKind.Joined)
     if self.scheduleInterval.isSome():
       self.scheduleHandle = schedule(self, switch, self.scheduleInterval.get())

tests/testautonatservice.nim

@@ -277,6 +277,94 @@ suite "Autonat Service":
     await allFuturesThrowing(
       switch1.stop(), switch2.stop())
 
+  asyncTest "Must work when peers ask each other at the same time with max 1 conn per peer":
+    let autonatService1 = AutonatService.new(AutonatClient.new(), newRng(), some(500.millis), maxQueueSize = 3)
+    let autonatService2 = AutonatService.new(AutonatClient.new(), newRng(), some(500.millis), maxQueueSize = 3)
+    let autonatService3 = AutonatService.new(AutonatClient.new(), newRng(), some(500.millis), maxQueueSize = 3)
+
+    let switch1 = createSwitch(autonatService1, maxConnsPerPeer = 0)
+    let switch2 = createSwitch(autonatService2, maxConnsPerPeer = 0)
+    let switch3 = createSwitch(autonatService2, maxConnsPerPeer = 0)
+
+    let awaiter1 = newFuture[void]()
+    let awaiter2 = newFuture[void]()
+    let awaiter3 = newFuture[void]()
+
+    proc statusAndConfidenceHandler1(networkReachability: NetworkReachability, confidence: Option[float]) {.gcsafe, async.} =
+      if networkReachability == NetworkReachability.Reachable and confidence.isSome() and confidence.get() == 1:
+        if not awaiter1.finished:
+          awaiter1.complete()
+
+    proc statusAndConfidenceHandler2(networkReachability: NetworkReachability, confidence: Option[float]) {.gcsafe, async.} =
+      if networkReachability == NetworkReachability.Reachable and confidence.isSome() and confidence.get() == 1:
+        if not awaiter2.finished:
+          awaiter2.complete()
+
+    check autonatService1.networkReachability() == NetworkReachability.Unknown
+    check autonatService2.networkReachability() == NetworkReachability.Unknown
+
+    autonatService1.statusAndConfidenceHandler(statusAndConfidenceHandler1)
+    autonatService2.statusAndConfidenceHandler(statusAndConfidenceHandler2)
+
+    await switch1.start()
+    await switch2.start()
+    await switch3.start()
+
+    await switch1.connect(switch2.peerInfo.peerId, switch2.peerInfo.addrs)
+    await switch2.connect(switch1.peerInfo.peerId, switch1.peerInfo.addrs)
+    await switch2.connect(switch3.peerInfo.peerId, switch3.peerInfo.addrs)
+
+    await awaiter1
+    await awaiter2
+
+    check autonatService1.networkReachability() == NetworkReachability.Reachable
+    check autonatService2.networkReachability() == NetworkReachability.Reachable
+    check libp2p_autonat_reachability_confidence.value(["Reachable"]) == 1
+
+    await allFuturesThrowing(
+      switch1.stop(), switch2.stop(), switch3.stop())
+
+  asyncTest "Must work for one peer when two peers ask each other at the same time with max 1 conn per peer":
+    let autonatService1 = AutonatService.new(AutonatClient.new(), newRng(), some(500.millis), maxQueueSize = 3)
+    let autonatService2 = AutonatService.new(AutonatClient.new(), newRng(), some(500.millis), maxQueueSize = 3)
+
+    let switch1 = createSwitch(autonatService1, maxConnsPerPeer = 0)
+    let switch2 = createSwitch(autonatService2, maxConnsPerPeer = 0)
+
+    let awaiter1 = newFuture[void]()
+
+    proc statusAndConfidenceHandler1(networkReachability: NetworkReachability, confidence: Option[float]) {.gcsafe, async.} =
+      if networkReachability == NetworkReachability.Reachable and confidence.isSome() and confidence.get() == 1:
+        if not awaiter1.finished:
+          awaiter1.complete()
+
+    check autonatService1.networkReachability() == NetworkReachability.Unknown
+
+    autonatService1.statusAndConfidenceHandler(statusAndConfidenceHandler1)
+
+    await switch1.start()
+    await switch2.start()
+
+    await switch1.connect(switch2.peerInfo.peerId, switch2.peerInfo.addrs)
+    try:
+      # We allow a temp conn for the peer to dial us. It could use this conn to just connect to us and not dial.
+      # We don't care if it fails at this point or not. But this conn must be closed eventually.
+      # Bellow we check that there's only one connection between the peers
+      await switch2.connect(switch1.peerInfo.peerId, switch1.peerInfo.addrs, reuseConnection = false)
+    except CatchableError:
+      discard
+
+    await awaiter1
+
+    check autonatService1.networkReachability() == NetworkReachability.Reachable
+    check libp2p_autonat_reachability_confidence.value(["Reachable"]) == 1
+
+    # Make sure remote peer can't create a connection to us
+    check switch1.connManager.connCount(switch2.peerInfo.peerId) == 1
+
+    await allFuturesThrowing(
+      switch1.stop(), switch2.stop())
+
   asyncTest "Must work with low maxConnections":
     let autonatService = AutonatService.new(AutonatClient.new(), newRng(), some(1.seconds), maxQueueSize = 1)
 

tests/testconnmngr.nim

@@ -208,15 +208,15 @@ suite "Connection Manager":
     expect TooManyConnectionsError:
       connMngr.storeConn(conns[0])
 
-    let waitedConn1 = connMngr.expectConnection(peerId)
+    let waitedConn1 = connMngr.expectConnection(peerId, In)
 
-    expect LPError:
-      discard await connMngr.expectConnection(peerId)
+    expect AlreadyExpectingConnectionError:
+      discard await connMngr.expectConnection(peerId, In)
 
     await waitedConn1.cancelAndWait()
     let
-      waitedConn2 = connMngr.expectConnection(peerId)
-      waitedConn3 = connMngr.expectConnection(PeerId.init(PrivateKey.random(ECDSA, (newRng())[]).tryGet()).tryGet())
+      waitedConn2 = connMngr.expectConnection(peerId, In)
+      waitedConn3 = connMngr.expectConnection(PeerId.init(PrivateKey.random(ECDSA, (newRng())[]).tryGet()).tryGet(), In)
       conn = getConnection(peerId)
     connMngr.storeConn(conn)
     check (await waitedConn2) == conn