connmgr: Implement inbound connection handling.

This modifies the connection manager to provide support for accepting
inbound connections on a caller-provided set of listeners and notify the
caller via a callback.

This is only the minimum work necessary to get inbound support into the
connection manager.  The intention for future commits is to move more
connection-related logic such as limiting the maximum number of overall
connections and banned peer tracking into the connection manager.

connmgr/connmanager.go

@@ -96,6 +96,29 @@ func (c *ConnReq) String() string {
 
 // Config holds the configuration options related to the connection manager.
 type Config struct {
+	// Listeners defines a slice of listeners for which the connection
+	// manager will take ownership of and accept connections.  When a
+	// connection is accepted, the OnAccept handler will be invoked with the
+	// connection.  Since the connection manager takes ownership of these
+	// listeners, they will be closed when the connection manager is
+	// stopped.
+	//
+	// This field will not have any effect if the OnAccept field is not
+	// also specified.  It may be nil if the caller does not wish to listen
+	// for incoming connections.
+	Listeners []net.Listener
+
+	// OnAccept is a callback that is fired when an inbound connection is
+	// accepted.  It is the caller's responsibility to close the connection.
+	// Failure to close the connection will result in the connection manager
+	// believing the connection is still active and thus have undesirable
+	// side effects such as still counting toward maximum connection limits.
+	//
+	// This field will not have any effect if the Listeners field is not
+	// also specified since there couldn't possibly be any accepted
+	// connections in that case.
+	OnAccept func(net.Conn)
+
 	// TargetOutbound is the number of outbound network connections to
 	// maintain. Defaults to 8.
 	TargetOutbound uint32
@@ -306,6 +329,26 @@ func (cm *ConnManager) Remove(id uint64) {
 	cm.requests <- handleDisconnected{id, false}
 }
 
+// listenHandler accepts incoming connections on a given listener.  It must be
+// run as a goroutine.
+func (cm *ConnManager) listenHandler(listener net.Listener) {
+	log.Infof("Server listening on %s", listener.Addr())
+	for atomic.LoadInt32(&cm.stop) == 0 {
+		conn, err := listener.Accept()
+		if err != nil {
+			// Only log the error if not forcibly shutting down.
+			if atomic.LoadInt32(&cm.stop) == 0 {
+				log.Errorf("Can't accept connection: %v", err)
+			}
+			continue
+		}
+		go cm.cfg.OnAccept(conn)
+	}
+
+	cm.wg.Done()
+	log.Tracef("Listener handler done for %s", listener.Addr())
+}
+
 // Start launches the connection manager and begins connecting to the network.
 func (cm *ConnManager) Start() {
 	// Already started?
@@ -317,6 +360,15 @@ func (cm *ConnManager) Start() {
 	cm.wg.Add(1)
 	go cm.connHandler()
 
+	// Start all the listeners so long as the caller requested them and
+	// provided a callback to be invoked when connections are accepted.
+	if cm.cfg.OnAccept != nil {
+		for _, listner := range cm.cfg.Listeners {
+			cm.wg.Add(1)
+			go cm.listenHandler(listner)
+		}
+	}
+
 	for i := atomic.LoadUint64(&cm.connReqCount); i < uint64(cm.cfg.TargetOutbound); i++ {
 		go cm.NewConnReq()
 	}
@@ -333,6 +385,15 @@ func (cm *ConnManager) Stop() {
 		log.Warnf("Connection manager already stopped")
 		return
 	}
+
+	// Stop all the listeners.  There will not be any listeners if
+	// listening is disabled.
+	for _, listener := range cm.cfg.Listeners {
+		// Ignore the error since this is shutdown and there is no way
+		// to recover anyways.
+		_ = listener.Close()
+	}
+
 	close(cm.quit)
 	log.Trace("Connection manager stopped")
 }

server.go

@@ -145,7 +145,6 @@ type server struct {
 	shutdown      int32
 	shutdownSched int32
 
-	listeners            []net.Listener
 	chainParams          *chaincfg.Params
 	addrManager          *addrmgr.AddrManager
 	connManager          *connmgr.ConnManager
@@ -1582,27 +1581,16 @@ func newPeerConfig(sp *serverPeer) *peer.Config {
 	}
 }
 
-// listenHandler is the main listener which accepts incoming connections for the
-// server.  It must be run as a goroutine.
-func (s *server) listenHandler(listener net.Listener) {
-	srvrLog.Infof("Server listening on %s", listener.Addr())
-	for atomic.LoadInt32(&s.shutdown) == 0 {
-		conn, err := listener.Accept()
-		if err != nil {
-			// Only log the error if we're not forcibly shutting down.
-			if atomic.LoadInt32(&s.shutdown) == 0 {
-				srvrLog.Errorf("Can't accept connection: %v", err)
-			}
-			continue
-		}
+// inboundPeerConnected is invoked by the connection manager when a new inbound
+// connection is established.  It initializes a new inbound server peer
+// instance, associates it with the connection, and starts a goroutine to wait
+// for disconnection.
+func (s *server) inboundPeerConnected(conn net.Conn) {
 	sp := newServerPeer(s, false)
 	sp.Peer = peer.NewInboundPeer(newPeerConfig(sp))
 	sp.AssociateConnection(conn)
 	go s.peerDoneHandler(sp)
 }
-	s.wg.Done()
-	srvrLog.Tracef("Listener handler done for %s", listener.Addr())
-}
 
 // outboundPeerConnected is invoked by the connection manager when a new
 // outbound connection is established.  It initializes a new outbound server
@@ -1966,13 +1954,6 @@ func (s *server) Start() {
 
 	srvrLog.Trace("Starting server")
 
-	// Start all the listeners.  There will not be any if listening is
-	// disabled.
-	for _, listener := range s.listeners {
-		s.wg.Add(1)
-		go s.listenHandler(listener)
-	}
-
 	// Start the peer handler which in turn starts the address and block
 	// managers.
 	s.wg.Add(1)
@@ -2010,15 +1991,6 @@ func (s *server) Stop() error {
 
 	srvrLog.Warnf("Server shutting down")
 
-	// Stop all the listeners.  There will not be any listeners if
-	// listening is disabled.
-	for _, listener := range s.listeners {
-		err := listener.Close()
-		if err != nil {
-			return err
-		}
-	}
-
 	// Stop the CPU miner if needed
 	s.cpuMiner.Stop()
 
@@ -2317,7 +2289,6 @@ func newServer(listenAddrs []string, db database.DB, chainParams *chaincfg.Param
 	}
 
 	s := server{
-		listeners:            listeners,
 		chainParams:          chainParams,
 		addrManager:          amgr,
 		newPeers:             make(chan *serverPeer, cfg.MaxPeers),
@@ -2469,6 +2440,8 @@ func newServer(listenAddrs []string, db database.DB, chainParams *chaincfg.Param
 		targetOutbound = cfg.MaxPeers
 	}
 	cmgr, err := connmgr.New(&connmgr.Config{
+		Listeners:      listeners,
+		OnAccept:       s.inboundPeerConnected,
 		RetryDuration:  connectionRetryInterval,
 		TargetOutbound: uint32(targetOutbound),
 		Dial:           btcdDial,