fix(@libp2p/tcp): race condition in onSocket

This fixes a race condition in the onSocket listener method.
onSocket gets a net.Socket parameter that needs to be closed later
before the tcp server can close.
The net.Socket is used to create a MultiaddrConnection but the
connection is not tracked with this.connections until after it has been
upgraded.
If the tcp listener.close is called while a the MultiaddrConnection is waiting
to be upgraded, then the MultiaddrConnection socket cannot be closed as
it does not exist in this.connections.

Instead of adding the MultiaddrConnection to this.connections on
creation I decided to create a separate property named
this.maConnections. I decided to track the non-upgraded connections
separately because I was unsure how this.connections must be used with other things
like metrics.

packages/transport-tcp/src/listener.ts

@@ -69,6 +69,7 @@ export class TCPListener extends TypedEventEmitter<ListenerEvents> implements Li
   private readonly server: net.Server
   /** Keep track of open connections to destroy in case of timeout */
   private readonly connections = new Set<MultiaddrConnection>()
+  private readonly maConnections = new Set<MultiaddrConnection>()
   private status: Status = { code: TCPListenerStatusCode.INACTIVE }
   private metrics?: TCPListenerMetrics
   private addr: string
@@ -195,11 +196,13 @@ export class TCPListener extends TypedEventEmitter<ListenerEvents> implements Li
     }
 
     this.log('new inbound connection %s', maConn.remoteAddr)
+    this.maConnections.add(maConn)
 
     this.context.upgrader.upgradeInbound(maConn)
       .then((conn) => {
         this.log('inbound connection upgraded %s', maConn.remoteAddr)
         this.connections.add(maConn)
+        this.maConnections.delete(maConn)
 
         socket.once('close', () => {
           this.connections.delete(maConn)
@@ -307,6 +310,11 @@ export class TCPListener extends TypedEventEmitter<ListenerEvents> implements Li
       conn.abort(err)
     })
 
+    // cleanup connections that have not been upgraded
+    this.maConnections.forEach(conn => {
+      conn.abort(err)
+    })
+
     // shut down the server socket, permanently
     await this.pause(true)
   }