adding channel limits to mplex (#309)

libp2p/muxers/mplex/mplex.nim

@@ -23,10 +23,16 @@ export muxer
 logScope:
   topics = "mplex"
 
+const
+  MaxChannelCount = 200
+
 when defined(libp2p_expensive_metrics):
-  declareGauge(libp2p_mplex_channels, "mplex channels", labels = ["initiator", "peer"])
+  declareGauge(libp2p_mplex_channels,
+    "mplex channels", labels = ["initiator", "peer"])
 
 type
+  TooManyChannels* = object of CatchableError
+
   Mplex* = ref object of Muxer
     remote: Table[uint64, LPChannel]
     local: Table[uint64, LPChannel]
@@ -36,6 +42,10 @@ type
     outChannTimeout: Duration
     isClosed: bool
     oid*: Oid
+    maxChannCount: int
+
+proc newTooManyChannels(): ref TooManyChannels =
+  newException(TooManyChannels, "max allowed channel count exceeded")
 
 proc getChannelList(m: Mplex, initiator: bool): var Table[uint64, LPChannel] =
   if initiator:
@@ -151,6 +161,10 @@ method handle*(m: Mplex) {.async, gcsafe.} =
       case msgType:
         of MessageType.New:
           let name = string.fromBytes(data)
+          if m.getChannelList(false).len > m.maxChannCount - 1:
+            warn "too many channels created by remote peer", allowedMax = MaxChannelCount
+            raise newTooManyChannels()
+
           channel = await m.newStreamInternal(
             false,
             id,
@@ -208,14 +222,16 @@ method handle*(m: Mplex) {.async, gcsafe.} =
 proc init*(M: type Mplex,
            conn: Connection,
            maxChanns: uint = MaxChannels,
-           inTimeout, outTimeout: Duration = DefaultChanTimeout): Mplex =
+           inTimeout, outTimeout: Duration = DefaultChanTimeout,
+           maxChannCount: int = MaxChannelCount): Mplex =
   M(connection: conn,
     maxChannels: maxChanns,
     inChannTimeout: inTimeout,
     outChannTimeout: outTimeout,
     remote: initTable[uint64, LPChannel](),
     local: initTable[uint64, LPChannel](),
-    oid: genOid())
+    oid: genOid(),
+    maxChannCount: maxChannCount)
 
 method newStream*(m: Mplex,
                   name: string = "",