multi: Expose disablerelaytx

This setting allows the wallet to not sync mempool transactions when in
SPV mode. This is useful to reduce cpu, memory and bandwidth consumption
for wallets that see very few useful mempool transactions, such as
wallets meant for only occasional use or mobile wallets.

The setting is exposed as a CLI or config argument --spvdisablerelaytx.

config.go

@@ -148,8 +148,9 @@ type config struct {
 	Offline bool `long:"offline" description:"Do not sync the wallet"`
 
 	// SPV options
-	SPV        bool     `long:"spv" description:"Sync using simplified payment verification"`
-	SPVConnect []string `long:"spvconnect" description:"SPV sync only with specified peers; disables DNS seeding"`
+	SPV               bool     `long:"spv" description:"Sync using simplified payment verification"`
+	SPVConnect        []string `long:"spvconnect" description:"SPV sync only with specified peers; disables DNS seeding"`
+	SPVDisableRelayTx bool     `long:"spvdisablerelaytx" description:"Disable receiving mempool transactions when in SPV mode"`
 
 	// RPC server options
 	RPCCert                *cfgutil.ExplicitString `long:"rpccert" description:"RPC server TLS certificate"`

dcrwallet.go

@@ -546,6 +546,7 @@ func spvLoop(ctx context.Context, w *wallet.Wallet) {
 	amgr := addrmgr.New(amgrDir, cfg.lookup)
 	lp := p2p.NewLocalPeer(w.ChainParams(), addr, amgr)
 	lp.SetDialFunc(cfg.dial)
+	lp.SetDisableRelayTx(cfg.SPVDisableRelayTx)
 	syncer := spv.NewSyncer(w, lp)
 	if len(cfg.SPVConnect) > 0 {
 		syncer.SetPersistentPeers(cfg.SPVConnect)

p2p/peering.go

@@ -133,9 +133,10 @@ type LocalPeer struct {
 	announcedHeaders  chan *inMsg
 	receivedInitState chan *inMsg
 
-	extaddr     net.Addr
-	amgr        *addrmgr.AddrManager
-	chainParams *chaincfg.Params
+	extaddr        net.Addr
+	amgr           *addrmgr.AddrManager
+	chainParams    *chaincfg.Params
+	disableRelayTx bool
 
 	rpByID map[uint64]*RemotePeer
 	rpMu   sync.Mutex
@@ -168,6 +169,13 @@ func (lp *LocalPeer) SetDialFunc(dial DialFunc) {
 	lp.dial = dial
 }
 
+// SetDisableRelayTx sets whether remote peers will be asked to relay
+// transactions to the local peer. This must be called before the local peer
+// runs.
+func (lp *LocalPeer) SetDisableRelayTx(disableRelayTx bool) {
+	lp.disableRelayTx = disableRelayTx
+}
+
 func isCGNAT(ip net.IP) bool {
 	if ip4 := ip.To4(); ip4 != nil {
 		return ip4[0] == 100 && ip4[1]&0xc0 == 64 // 100.64.0.0/10
@@ -210,6 +218,7 @@ func (lp *LocalPeer) newMsgVersion(pver uint32, c net.Conn) (*wire.MsgVersion, e
 	v := wire.NewMsgVersion(la, ra, nonce, 0)
 	v.AddUserAgent(uaName, uaVersion)
 	v.ProtocolVersion = int32(pver)
+	v.DisableRelayTx = lp.disableRelayTx
 	return v, nil
 }
 
@@ -738,9 +747,7 @@ func (rp *RemotePeer) readMessages(ctx context.Context) error {
 			case *wire.MsgHeaders:
 				rp.receivedHeaders(ctx, m)
 			case *wire.MsgInv:
-				if rp.lp.messageIsMasked(MaskInv) {
-					rp.lp.receivedInv <- newInMsg(rp, msg)
-				}
+				rp.receivedInv(ctx, m)
 			case *wire.MsgGetMiningState:
 				rp.receivedGetMiningState(ctx)
 			case *wire.MsgGetInitState:
@@ -1847,3 +1854,37 @@ func (rp *RemotePeer) GetInitState(ctx context.Context, msg *wire.MsgGetInitStat
 		}
 	}
 }
+
+// invVecContainsTx returns true if at least one inv vector is of type
+// transaction.
+func invVecContainsTx(inv []*wire.InvVect) bool {
+	for i := range inv {
+		if inv[i].Type == wire.InvTypeTx {
+			return true
+		}
+	}
+	return false
+}
+
+// receivedInv is called when an inv message is received from the remote peer.
+func (rp *RemotePeer) receivedInv(ctx context.Context, inv *wire.MsgInv) {
+	const opf = "remotepeer(%v).receivedInv"
+
+	// When tx relay is disabled, we don't expect transactions on invs.
+	if rp.lp.disableRelayTx && invVecContainsTx(inv.InvList) {
+		op := errors.Opf(opf, rp.raddr)
+		err := errors.E(op, errors.Protocol, "received tx in msginv when tx relaying is disabled")
+		rp.Disconnect(err)
+		return
+	}
+
+	// Ignore if the user is not interested in invs.
+	if !rp.lp.messageIsMasked(MaskInv) {
+		return
+	}
+
+	select {
+	case rp.lp.receivedInv <- newInMsg(rp, inv):
+	case <-ctx.Done():
+	}
+}

sample-dcrwallet.conf

@@ -198,6 +198,24 @@
 ; dcrdpassword=
 
 
+; ------------------------------------------------------------------------------
+; SPV settings
+; ------------------------------------------------------------------------------
+
+; Enable SPV mode by setting SPV to 1.
+; spv=1
+
+; spvconnect may be used to specify specific peers to connect to, when using
+; SPV mode. Multiple peers may be specified. When spvconnect is set, the wallet
+; will connect _only_ to the listed peers.
+; spvconnect=
+
+; Set spvdisablerelaytx to 1 to disable receiving transactions from remote peers
+; in SPV mode. This reduces bandwidth consumption but effectively disables the
+; mempool.
+; spvdisablerelaytx=1
+
+
 ; ------------------------------------------------------------------------------
 ; Debug
 ; ------------------------------------------------------------------------------