lnwire+peer: clamp pong bytes, make ping handler more effcieint

This was not properly enforced and would be a spec violation on the
peer's end. Also re-use a pong buffer to save on heap allocations if
there are a lot of peers. The pong buffer is only read from, so this
is concurrent safe.

lnwire/lnwire_test.go

@@ -864,6 +864,22 @@ func TestLightningWireProtocol(t *testing.T) {
 					NewShortChanIDFromInt(uint64(r.Int63())))
 			}
 
+			v[0] = reflect.ValueOf(req)
+		},
+		MsgPing: func(v []reflect.Value, r *rand.Rand) {
+			// We use a special message generator here to ensure we
+			// don't generate ping messages that are too large,
+			// which'll cause the test to fail.
+			//
+			// We'll allow the test to generate padding bytes up to
+			// the max message limit, factoring in the 2 bytes for
+			// the num pong bytes.
+			paddingBytes := make([]byte, r.Intn(MaxMsgBody-1))
+			req := Ping{
+				NumPongBytes: uint16(r.Intn(MaxPongBytes + 1)),
+				PaddingBytes: paddingBytes,
+			}
+
 			v[0] = reflect.ValueOf(req)
 		},
 	}

lnwire/ping.go

@@ -38,9 +38,16 @@ var _ Message = (*Ping)(nil)
 //
 // This is part of the lnwire.Message interface.
 func (p *Ping) Decode(r io.Reader, pver uint32) error {
-	return ReadElements(r,
-		&p.NumPongBytes,
-		&p.PaddingBytes)
+	err := ReadElements(r, &p.NumPongBytes, &p.PaddingBytes)
+	if err != nil {
+		return err
+	}
+
+	if p.NumPongBytes > MaxPongBytes {
+		return ErrMaxPongBytesExceeded
+	}
+
+	return nil
 }
 
 // Encode serializes the target Ping into the passed io.Writer observing the

lnwire/pong.go

@@ -2,9 +2,19 @@ package lnwire
 
 import (
 	"bytes"
+	"fmt"
 	"io"
 )
 
+// MaxPongBytes is the maximum number of extra bytes a pong can be requested to
+// send. The type of the message (19) takes 2 bytes, the length field takes up
+// 2 bytes, leaving 65531 bytes.
+const MaxPongBytes = 65531
+
+// ErrMaxPongBytesExceeded indicates that the NumPongBytes field from the ping
+// message has exceeded MaxPongBytes.
+var ErrMaxPongBytesExceeded = fmt.Errorf("pong bytes exceeded")
+
 // PongPayload is a set of opaque bytes sent in response to a ping message.
 type PongPayload []byte
 

peer/brontide.go

@@ -327,6 +327,12 @@ type Config struct {
 	// from the peer.
 	HandleCustomMessage func(peer [33]byte, msg *lnwire.Custom) error
 
+	// PongBuf is a slice we'll reuse instead of allocating memory on the
+	// heap. Since only reads will occur and no writes, there is no need
+	// for any synchronization primitives. As a result, it's safe to share
+	// this across multiple Peer struct instances.
+	PongBuf []byte
+
 	// Quit is the server's quit channel. If this is closed, we halt operation.
 	Quit chan struct{}
 }
@@ -1394,10 +1400,8 @@ out:
 
 			// Next, we'll send over the amount of specified pong
 			// bytes.
-			//
-			// TODO(roasbeef): read out from pong scratch instead?
-			pongBytes := make([]byte, msg.NumPongBytes)
-			p.queueMsg(lnwire.NewPong(pongBytes), nil)
+			pong := lnwire.NewPong(p.cfg.PongBuf[0:msg.NumPongBytes])
+			p.queueMsg(pong, nil)
 
 		case *lnwire.OpenChannel,
 			*lnwire.AcceptChannel,

peer/brontide_test.go

@@ -999,6 +999,7 @@ func TestStaticRemoteDowngrade(t *testing.T) {
 					Features:       test.features,
 					Conn:           mockConn,
 					WritePool:      writePool,
+					PongBuf:        make([]byte, lnwire.MaxPongBytes),
 				},
 			}
 
@@ -1103,6 +1104,7 @@ func TestPeerCustomMessage(t *testing.T) {
 			}
 			return nil
 		},
+		PongBuf: make([]byte, lnwire.MaxPongBytes),
 	})
 
 	// Set up the init sequence.

server.go

@@ -229,6 +229,12 @@ type server struct {
 	// intended to replace it.
 	scheduledPeerConnection map[string]func()
 
+	// pongBuf is a shared pong reply buffer we'll use across all active
+	// peer goroutines. We know the max size of a pong message
+	// (lnwire.MaxPongBytes), so we can allocate this ahead of time, and
+	// avoid allocations each time we need to send a pong message.
+	pongBuf []byte
+
 	cc *chainreg.ChainControl
 
 	fundingMgr *funding.Manager
@@ -582,6 +588,7 @@ func newServer(cfg *Config, listenAddrs []net.Addr,
 		peerErrors:              make(map[string]*queue.CircularBuffer),
 		ignorePeerTermination:   make(map[*peer.Brontide]struct{}),
 		scheduledPeerConnection: make(map[string]func()),
+		pongBuf:                 make([]byte, lnwire.MaxPongBytes),
 
 		peersByPub:                make(map[string]*peer.Brontide),
 		inboundPeers:              make(map[string]*peer.Brontide),
@@ -3491,6 +3498,8 @@ func (s *server) peerConnected(conn net.Conn, connReq *connmgr.ConnReq,
 		DisconnectPeer:          s.DisconnectPeer,
 		GenNodeAnnouncement:     s.genNodeAnnouncement,
 
+		PongBuf: s.pongBuf,
+
 		PrunePersistentPeerConnection: s.prunePersistentPeerConnection,
 
 		FetchLastChanUpdate: s.fetchLastChanUpdate(),