cmd, eth, p2p: introduce pending peer cli arg, add tests

p2p/server.go

@@ -22,9 +22,7 @@ const (
 	refreshPeersInterval    = 30 * time.Second
 	staticPeerCheckInterval = 15 * time.Second
 
-	// This is the maximum number of inbound connection
-	// that are allowed to linger between 'accepted' and
-	// 'added as peer'.
+	// Maximum number of concurrently handshaking inbound connections.
 	maxAcceptConns = 10
 
 	// Maximum number of concurrently dialing outbound connections.
@@ -55,6 +53,11 @@ type Server struct {
 	// connected. It must be greater than zero.
 	MaxPeers int
 
+	// MaxPendingPeers is the maximum number of peers that can be pending in the
+	// handshake phase, counted separately for inbound and outbound connections.
+	// Zero defaults to preset values.
+	MaxPendingPeers int
+
 	// Name sets the node name of this server.
 	// Use common.MakeName to create a name that follows existing conventions.
 	Name string
@@ -334,8 +337,12 @@ func (srv *Server) listenLoop() {
 	// This channel acts as a semaphore limiting
 	// active inbound connections that are lingering pre-handshake.
 	// If all slots are taken, no further connections are accepted.
-	slots := make(chan struct{}, maxAcceptConns)
-	for i := 0; i < maxAcceptConns; i++ {
+	tokens := maxAcceptConns
+	if srv.MaxPendingPeers > 0 {
+		tokens = srv.MaxPendingPeers
+	}
+	slots := make(chan struct{}, tokens)
+	for i := 0; i < tokens; i++ {
 		slots <- struct{}{}
 	}
 
@@ -405,8 +412,12 @@ func (srv *Server) dialLoop() {
 	defer refresh.Stop()
 
 	// Limit the number of concurrent dials
-	slots := make(chan struct{}, maxDialingConns)
-	for i := 0; i < maxDialingConns; i++ {
+	tokens := maxAcceptConns
+	if srv.MaxPendingPeers > 0 {
+		tokens = srv.MaxPendingPeers
+	}
+	slots := make(chan struct{}, tokens)
+	for i := 0; i < tokens; i++ {
 		slots <- struct{}{}
 	}
 	dial := func(dest *discover.Node) {