Fix gossipsub dOut handling (#883)

libp2p/protocols/pubsub/gossipsub/behavior.nim

@@ -164,7 +164,8 @@ proc handleGraft*(g: GossipSub,
     # If they send us a graft before they send us a subscribe, what should
     # we do? For now, we add them to mesh but don't add them to gossipsub.
     if topic in g.topics:
-      if g.mesh.peers(topic) < g.parameters.dHigh or peer.outbound:
+      if g.mesh.peers(topic) < g.parameters.dHigh or
+          (peer.outbound and g.mesh.outboundPeers(topic) < g.parameters.dOut):
         # In the spec, there's no mention of DHi here, but implicitly, a
         # peer will be removed from the mesh on next rebalance, so we don't want
         # this peer to push someone else out
@@ -328,10 +329,11 @@ proc rebalanceMesh*(g: GossipSub, topic: string, metrics: ptr MeshMetrics = nil)
   var
     prunes, grafts: seq[PubSubPeer]
     npeers = g.mesh.peers(topic)
+    nOutPeers = g.mesh.outboundPeers(topic)
     defaultMesh: HashSet[PubSubPeer]
     backingOff = g.backingOff.getOrDefault(topic)
 
-  if npeers  < g.parameters.dLow:
+  if npeers < g.parameters.dLow:
     trace "replenishing mesh", peers = npeers
     # replenish the mesh if we're below Dlo
 
@@ -370,7 +372,7 @@ proc rebalanceMesh*(g: GossipSub, topic: string, metrics: ptr MeshMetrics = nil)
           g.fanout.removePeer(topic, peer)
           grafts &= peer
 
-  else:
+  elif nOutPeers < g.parameters.dOut:
     trace "replenishing mesh outbound quota", peers = g.mesh.peers(topic)
 
     var
@@ -398,8 +400,8 @@ proc rebalanceMesh*(g: GossipSub, topic: string, metrics: ptr MeshMetrics = nil)
     # sort peers by score, high score first, we are grafting
     candidates.sort(byScore, SortOrder.Descending)
 
-    # Graft peers so we reach a count of D
-    candidates.setLen(min(candidates.len, g.parameters.dOut))
+    # Graft outgoing peers so we reach a count of dOut
+    candidates.setLen(min(candidates.len, g.parameters.dOut - nOutPeers))
 
     trace "grafting outbound peers", topic, peers = candidates.len
 

libp2p/protocols/pubsub/peertable.nim

@@ -12,7 +12,7 @@ when (NimMajor, NimMinor) < (1, 4):
 else:
   {.push raises: [].}
 
-import std/[tables, sets]
+import std/[tables, sets, sequtils]
 import ./pubsubpeer, ../../peerid
 
 export tables, sets
@@ -53,3 +53,10 @@ func peers*(table: PeerTable, topic: string): int =
     except KeyError: raiseAssert "checked with in"
   else:
     0
+
+func outboundPeers*(table: PeerTable, topic: string): int =
+  if topic in table:
+    try: table[topic].countIt(it.outbound)
+    except KeyError: raiseAssert "checked with in"
+  else:
+    0