multi: add zeroconfacceptor that default rejects if no rpc acceptors

This is a safety mechanism so that zero-conf channels are not accepted
by default if no rpc acceptor exists.

chanacceptor/chainedacceptor.go

@@ -23,6 +23,8 @@ func NewChainedAcceptor() *ChainedAcceptor {
 }
 
 // AddAcceptor adds a ChannelAcceptor to this ChainedAcceptor.
+//
+// NOTE: Part of the MultiplexAcceptor interface.
 func (c *ChainedAcceptor) AddAcceptor(acceptor ChannelAcceptor) uint64 {
 	id := atomic.AddUint64(&c.acceptorID, 1)
 
@@ -36,12 +38,22 @@ func (c *ChainedAcceptor) AddAcceptor(acceptor ChannelAcceptor) uint64 {
 
 // RemoveAcceptor removes a ChannelAcceptor from this ChainedAcceptor given
 // an ID.
+//
+// NOTE: Part of the MultiplexAcceptor interface.
 func (c *ChainedAcceptor) RemoveAcceptor(id uint64) {
 	c.acceptorsMtx.Lock()
 	delete(c.acceptors, id)
 	c.acceptorsMtx.Unlock()
 }
 
+// numAcceptors returns the number of acceptors contained in the
+// ChainedAcceptor.
+func (c *ChainedAcceptor) numAcceptors() int {
+	c.acceptorsMtx.RLock()
+	defer c.acceptorsMtx.RUnlock()
+	return len(c.acceptors)
+}
+
 // Accept evaluates the results of all ChannelAcceptors in the acceptors map
 // and returns the conjunction of all these predicates.
 //
@@ -91,5 +103,5 @@ func (c *ChainedAcceptor) Accept(req *ChannelAcceptRequest) *ChannelAcceptRespon
 }
 
 // A compile-time constraint to ensure ChainedAcceptor implements the
-// ChannelAcceptor interface.
-var _ ChannelAcceptor = (*ChainedAcceptor)(nil)
+// MultiplexAcceptor interface.
+var _ MultiplexAcceptor = (*ChainedAcceptor)(nil)

chanacceptor/interface.go

@@ -118,3 +118,16 @@ func (c *ChannelAcceptResponse) RejectChannel() bool {
 type ChannelAcceptor interface {
 	Accept(req *ChannelAcceptRequest) *ChannelAcceptResponse
 }
+
+// MultiplexAcceptor is an interface that abstracts the ability of a
+// ChannelAcceptor to contain sub-ChannelAcceptors.
+type MultiplexAcceptor interface {
+	// Embed the ChannelAcceptor.
+	ChannelAcceptor
+
+	// AddAcceptor nests a ChannelAcceptor inside the MultiplexAcceptor.
+	AddAcceptor(acceptor ChannelAcceptor) uint64
+
+	// Remove a sub-ChannelAcceptor.
+	RemoveAcceptor(id uint64)
+}

chanacceptor/zeroconfacceptor.go

@@ -0,0 +1,68 @@
+package chanacceptor
+
+import "github.com/lightningnetwork/lnd/lnwire"
+
+// ZeroConfAcceptor wraps a regular ChainedAcceptor. If no acceptors are in the
+// ChainedAcceptor, then Accept will reject all channel open requests. This
+// should only be enabled when the zero-conf feature bit is set and is used to
+// protect users from a malicious counter-party double-spending the zero-conf
+// funding tx.
+type ZeroConfAcceptor struct {
+	chainedAcceptor *ChainedAcceptor
+}
+
+// NewZeroConfAcceptor initializes a ZeroConfAcceptor.
+func NewZeroConfAcceptor() *ZeroConfAcceptor {
+	return &ZeroConfAcceptor{
+		chainedAcceptor: NewChainedAcceptor(),
+	}
+}
+
+// AddAcceptor adds a sub-ChannelAcceptor to the internal ChainedAcceptor.
+func (z *ZeroConfAcceptor) AddAcceptor(acceptor ChannelAcceptor) uint64 {
+	return z.chainedAcceptor.AddAcceptor(acceptor)
+}
+
+// RemoveAcceptor removes a sub-ChannelAcceptor from the internal
+// ChainedAcceptor.
+func (z *ZeroConfAcceptor) RemoveAcceptor(id uint64) {
+	z.chainedAcceptor.RemoveAcceptor(id)
+}
+
+// Accept will deny the channel open request if the internal ChainedAcceptor is
+// empty. If the internal ChainedAcceptor has any acceptors, then Accept will
+// instead be called on it.
+//
+// NOTE: Part of the ChannelAcceptor interface.
+func (z *ZeroConfAcceptor) Accept(
+	req *ChannelAcceptRequest) *ChannelAcceptResponse {
+
+	// Alias for less verbosity.
+	channelType := req.OpenChanMsg.ChannelType
+
+	// Check if the channel type sets the zero-conf bit.
+	var zeroConfSet bool
+
+	if channelType != nil {
+		channelFeatures := lnwire.RawFeatureVector(*channelType)
+		zeroConfSet = channelFeatures.IsSet(lnwire.ZeroConfRequired)
+	}
+
+	// If there are no acceptors and the counter-party is requesting a zero
+	// conf channel, reject the attempt.
+	if z.chainedAcceptor.numAcceptors() == 0 && zeroConfSet {
+		// Deny the channel open request.
+		rejectChannel := NewChannelAcceptResponse(
+			false, nil, nil, 0, 0, 0, 0, 0, 0, false,
+		)
+		return rejectChannel
+	}
+
+	// Otherwise, the ChainedAcceptor has sub-acceptors, so call Accept on
+	// it.
+	return z.chainedAcceptor.Accept(req)
+}
+
+// A compile-time constraint to ensure ZeroConfAcceptor implements the
+// MultiplexAcceptor interface.
+var _ MultiplexAcceptor = (*ZeroConfAcceptor)(nil)

chanacceptor/zeroconfacceptor_test.go

@@ -0,0 +1,83 @@
+package chanacceptor
+
+import (
+	"testing"
+
+	"github.com/lightningnetwork/lnd/lnwire"
+	"github.com/stretchr/testify/require"
+)
+
+// dummyAcceptor is a ChannelAcceptor that will never return a failure.
+type dummyAcceptor struct{}
+
+func (d *dummyAcceptor) Accept(
+	req *ChannelAcceptRequest) *ChannelAcceptResponse {
+
+	return &ChannelAcceptResponse{}
+}
+
+// TestZeroConfAcceptorNormal verifies that the ZeroConfAcceptor will let
+// requests go through for non-zero-conf channels if there are no
+// sub-acceptors.
+func TestZeroConfAcceptorNormal(t *testing.T) {
+	t.Parallel()
+
+	// Create the zero-conf acceptor.
+	zeroAcceptor := NewZeroConfAcceptor()
+
+	// Assert that calling Accept won't return a failure.
+	req := &ChannelAcceptRequest{
+		OpenChanMsg: &lnwire.OpenChannel{},
+	}
+	resp := zeroAcceptor.Accept(req)
+	require.False(t, resp.RejectChannel())
+
+	// Add a dummyAcceptor to the zero-conf acceptor. Assert that Accept
+	// does not return a failure.
+	dummy := &dummyAcceptor{}
+	dummyID := zeroAcceptor.AddAcceptor(dummy)
+	resp = zeroAcceptor.Accept(req)
+	require.False(t, resp.RejectChannel())
+
+	// Remove the dummyAcceptor from the zero-conf acceptor and assert that
+	// Accept doesn't return a failure.
+	zeroAcceptor.RemoveAcceptor(dummyID)
+	resp = zeroAcceptor.Accept(req)
+	require.False(t, resp.RejectChannel())
+}
+
+// TestZeroConfAcceptorZC verifies that the ZeroConfAcceptor will fail
+// zero-conf channel opens unless a sub-acceptor exists.
+func TestZeroConfAcceptorZC(t *testing.T) {
+	t.Parallel()
+
+	// Create the zero-conf acceptor.
+	zeroAcceptor := NewZeroConfAcceptor()
+
+	channelType := new(lnwire.ChannelType)
+	*channelType = lnwire.ChannelType(*lnwire.NewRawFeatureVector(
+		lnwire.ZeroConfRequired,
+	))
+
+	// Assert that calling Accept results in failure.
+	req := &ChannelAcceptRequest{
+		OpenChanMsg: &lnwire.OpenChannel{
+			ChannelType: channelType,
+		},
+	}
+	resp := zeroAcceptor.Accept(req)
+	require.True(t, resp.RejectChannel())
+
+	// Add a dummyAcceptor to the zero-conf acceptor. Assert that Accept
+	// does not return a failure.
+	dummy := &dummyAcceptor{}
+	dummyID := zeroAcceptor.AddAcceptor(dummy)
+	resp = zeroAcceptor.Accept(req)
+	require.False(t, resp.RejectChannel())
+
+	// Remove the dummyAcceptor from the zero-conf acceptor and assert that
+	// Accept returns a failure.
+	zeroAcceptor.RemoveAcceptor(dummyID)
+	resp = zeroAcceptor.Accept(req)
+	require.True(t, resp.RejectChannel())
+}