p2p: add network simulation framework (#14982)

This commit introduces a network simulation framework which
can be used to run simulated networks of devp2p nodes. The
intention is to use this for testing protocols, performing
benchmarks and visualising emergent network behaviour.

p2p/dial.go

@@ -47,6 +47,24 @@ const (
 	maxResolveDelay     = time.Hour
 )
 
+// NodeDialer is used to connect to nodes in the network, typically by using
+// an underlying net.Dialer but also using net.Pipe in tests
+type NodeDialer interface {
+	Dial(*discover.Node) (net.Conn, error)
+}
+
+// TCPDialer implements the NodeDialer interface by using a net.Dialer to
+// create TCP connections to nodes in the network
+type TCPDialer struct {
+	*net.Dialer
+}
+
+// Dial creates a TCP connection to the node
+func (t TCPDialer) Dial(dest *discover.Node) (net.Conn, error) {
+	addr := &net.TCPAddr{IP: dest.IP, Port: int(dest.TCP)}
+	return t.Dialer.Dial("tcp", addr.String())
+}
+
 // dialstate schedules dials and discovery lookups.
 // it get's a chance to compute new tasks on every iteration
 // of the main loop in Server.run.
@@ -318,14 +336,13 @@ func (t *dialTask) resolve(srv *Server) bool {
 
 // dial performs the actual connection attempt.
 func (t *dialTask) dial(srv *Server, dest *discover.Node) bool {
-	addr := &net.TCPAddr{IP: dest.IP, Port: int(dest.TCP)}
-	fd, err := srv.Dialer.Dial("tcp", addr.String())
+	fd, err := srv.Dialer.Dial(dest)
 	if err != nil {
 		log.Trace("Dial error", "task", t, "err", err)
 		return false
 	}
 	mfd := newMeteredConn(fd, false)
-	srv.setupConn(mfd, t.flags, dest)
+	srv.SetupConn(mfd, t.flags, dest)
 	return true
 }