devp2p: solve "DPT discovers nodes when open_slots = 0" (#1816)

* devp2p: remove OpenSlots check
in favor of queue length cap

* devp2p/rlpx: remove extraneous `peer:` label

Co-authored-by: Ryan Ghods <ryan@ryanio.com>

* devp2p/rlpx: add helper function
`_getOpenQueueSlots()`

Co-authored-by: Ryan Ghods <ryan@ryanio.com>

Author: ScottyPoi

packages/devp2p/src/rlpx/rlpx.ts

@@ -82,8 +82,11 @@ export class RLPx extends EventEmitter {
         if (this._peersLRU.has(peer.id!.toString('hex'))) return
         this._peersLRU.set(peer.id!.toString('hex'), true)
 
-        if (this._getOpenSlots() > 0) return this._connectToPeer(peer)
-        this._peersQueue.push({ peer: peer, ts: 0 }) // save to queue
+        if (this._getOpenSlots() > 0) {
+          return this._connectToPeer(peer)
+        } else if (this._getOpenQueueSlots() > 0) {
+          this._peersQueue.push({ peer, ts: 0 }) // save to queue
+        }
       })
       this._dpt.on('peer:removed', (peer: PeerInfo) => {
         // remove from queue
@@ -177,6 +180,10 @@ export class RLPx extends EventEmitter {
     return Math.max(this._maxPeers - this._peers.size, 0)
   }
 
+  _getOpenQueueSlots() {
+    return this._maxPeers * 2 - this._peersQueue.length
+  }
+
   _connectToPeer(peer: PeerInfo) {
     this.connect(peer).catch((err) => {
       if (this._dpt === null) return
@@ -244,14 +251,16 @@ export class RLPx extends EventEmitter {
 
       if (!disconnectWe && reason === DISCONNECT_REASONS.TOO_MANY_PEERS) {
         // hack
-        this._peersQueue.push({
-          peer: {
-            id: peer.getId()!,
-            address: peer._socket.remoteAddress,
-            tcpPort: peer._socket.remotePort,
-          },
-          ts: (Date.now() + ms('5m')) as number,
-        })
+        if (this._getOpenQueueSlots() > 0) {
+          this._peersQueue.push({
+            peer: {
+              id: peer.getId()!,
+              address: peer._socket.remoteAddress,
+              tcpPort: peer._socket.remotePort,
+            },
+            ts: (Date.now() + ms('5m')) as number,
+          })
+        }
       }
 
       const id = peer.getId()