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.

1 files changed, 48 insertions, 8 deletions

diff --git a/p2p/server.go b/p2p/server.go
index d7909d53a..d1d578401 100644
--- a/p2p/server.go
+++ b/p2p/server.go
@@ -27,6 +27,7 @@ import (
 
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/common/mclock"
+	"github.com/ethereum/go-ethereum/event"
 	"github.com/ethereum/go-ethereum/log"
 	"github.com/ethereum/go-ethereum/p2p/discover"
 	"github.com/ethereum/go-ethereum/p2p/discv5"
@@ -130,10 +131,14 @@ type Config struct {
 
 	// If Dialer is set to a non-nil value, the given Dialer
 	// is used to dial outbound peer connections.
-	Dialer *net.Dialer `toml:"-"`
+	Dialer NodeDialer `toml:"-"`
 
 	// If NoDial is true, the server will not dial any peers.
 	NoDial bool `toml:",omitempty"`
+
+	// If EnableMsgEvents is set then the server will emit PeerEvents
+	// whenever a message is sent to or received from a peer
+	EnableMsgEvents bool
 }
 
 // Server manages all peer connections.
@@ -166,6 +171,7 @@ type Server struct {
 	addpeer       chan *conn
 	delpeer       chan peerDrop
 	loopWG        sync.WaitGroup // loop, listenLoop
+	peerFeed      event.Feed
 }
 
 type peerOpFunc func(map[discover.NodeID]*Peer)
@@ -191,7 +197,7 @@ type conn struct {
 	fd net.Conn
 	transport
 	flags connFlag
-	cont  chan error      // The run loop uses cont to signal errors to setupConn.
+	cont  chan error      // The run loop uses cont to signal errors to SetupConn.
 	id    discover.NodeID // valid after the encryption handshake
 	caps  []Cap           // valid after the protocol handshake
 	name  string          // valid after the protocol handshake
@@ -291,6 +297,11 @@ func (srv *Server) RemovePeer(node *discover.Node) {
 	}
 }
 
+// SubscribePeers subscribes the given channel to peer events
+func (srv *Server) SubscribeEvents(ch chan *PeerEvent) event.Subscription {
+	return srv.peerFeed.Subscribe(ch)
+}
+
 // Self returns the local node's endpoint information.
 func (srv *Server) Self() *discover.Node {
 	srv.lock.Lock()
@@ -358,7 +369,7 @@ func (srv *Server) Start() (err error) {
 		srv.newTransport = newRLPX
 	}
 	if srv.Dialer == nil {
-		srv.Dialer = &net.Dialer{Timeout: defaultDialTimeout}
+		srv.Dialer = TCPDialer{&net.Dialer{Timeout: defaultDialTimeout}}
 	}
 	srv.quit = make(chan struct{})
 	srv.addpeer = make(chan *conn)
@@ -536,7 +547,11 @@ running:
 				c.flags |= trustedConn
 			}
 			// TODO: track in-progress inbound node IDs (pre-Peer) to avoid dialing them.
-			c.cont <- srv.encHandshakeChecks(peers, c)
+			select {
+			case c.cont <- srv.encHandshakeChecks(peers, c):
+			case <-srv.quit:
+				break running
+			}
 		case c := <-srv.addpeer:
 			// At this point the connection is past the protocol handshake.
 			// Its capabilities are known and the remote identity is verified.
@@ -544,6 +559,11 @@ running:
 			if err == nil {
 				// The handshakes are done and it passed all checks.
 				p := newPeer(c, srv.Protocols)
+				// If message events are enabled, pass the peerFeed
+				// to the peer
+				if srv.EnableMsgEvents {
+					p.events = &srv.peerFeed
+				}
 				name := truncateName(c.name)
 				log.Debug("Adding p2p peer", "id", c.id, "name", name, "addr", c.fd.RemoteAddr(), "peers", len(peers)+1)
 				peers[c.id] = p
@@ -552,7 +572,11 @@ running:
 			// The dialer logic relies on the assumption that
 			// dial tasks complete after the peer has been added or
 			// discarded. Unblock the task last.
-			c.cont <- err
+			select {
+			case c.cont <- err:
+			case <-srv.quit:
+				break running
+			}
 		case pd := <-srv.delpeer:
 			// A peer disconnected.
 			d := common.PrettyDuration(mclock.Now() - pd.created)
@@ -665,16 +689,16 @@ func (srv *Server) listenLoop() {
 		// Spawn the handler. It will give the slot back when the connection
 		// has been established.
 		go func() {
-			srv.setupConn(fd, inboundConn, nil)
+			srv.SetupConn(fd, inboundConn, nil)
 			slots <- struct{}{}
 		}()
 	}
 }
 
-// setupConn runs the handshakes and attempts to add the connection
+// SetupConn runs the handshakes and attempts to add the connection
 // as a peer. It returns when the connection has been added as a peer
 // or the handshakes have failed.
-func (srv *Server) setupConn(fd net.Conn, flags connFlag, dialDest *discover.Node) {
+func (srv *Server) SetupConn(fd net.Conn, flags connFlag, dialDest *discover.Node) {
 	// Prevent leftover pending conns from entering the handshake.
 	srv.lock.Lock()
 	running := srv.running
@@ -755,7 +779,23 @@ func (srv *Server) runPeer(p *Peer) {
 	if srv.newPeerHook != nil {
 		srv.newPeerHook(p)
 	}
+
+	// broadcast peer add
+	srv.peerFeed.Send(&PeerEvent{
+		Type: PeerEventTypeAdd,
+		Peer: p.ID(),
+	})
+
+	// run the protocol
 	remoteRequested, err := p.run()
+
+	// broadcast peer drop
+	srv.peerFeed.Send(&PeerEvent{
+		Type:  PeerEventTypeDrop,
+		Peer:  p.ID(),
+		Error: err.Error(),
+	})
+
 	// Note: run waits for existing peers to be sent on srv.delpeer
 	// before returning, so this send should not select on srv.quit.
 	srv.delpeer <- peerDrop{p, err, remoteRequested}