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Merge pull request #4018 from breez/intercept-forward-htlc
Intercept forward htlc
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package htlcswitch | ||
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import ( | ||
"fmt" | ||
"sync" | ||
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"github.com/go-errors/errors" | ||
"github.com/lightningnetwork/lnd/channeldb" | ||
"github.com/lightningnetwork/lnd/htlcswitch/hop" | ||
"github.com/lightningnetwork/lnd/lntypes" | ||
"github.com/lightningnetwork/lnd/lnwire" | ||
) | ||
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var ( | ||
// ErrFwdNotExists is an error returned when the caller tries to resolve | ||
// a forward that doesn't exist anymore. | ||
ErrFwdNotExists = errors.New("forward does not exist") | ||
) | ||
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// InterceptableSwitch is an implementation of ForwardingSwitch interface. | ||
// This implementation is used like a proxy that wraps the switch and | ||
// intercepts forward requests. A reference to the Switch is held in order | ||
// to communicate back the interception result where the options are: | ||
// Resume - forwards the original request to the switch as is. | ||
// Settle - routes UpdateFulfillHTLC to the originating link. | ||
// Fail - routes UpdateFailHTLC to the originating link. | ||
type InterceptableSwitch struct { | ||
sync.RWMutex | ||
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// htlcSwitch is the underline switch | ||
htlcSwitch *Switch | ||
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// fwdInterceptor is the callback that is called for each forward of | ||
// an incoming htlc. It should return true if it is interested in handling | ||
// it. | ||
fwdInterceptor ForwardInterceptor | ||
} | ||
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// NewInterceptableSwitch returns an instance of InterceptableSwitch. | ||
func NewInterceptableSwitch(s *Switch) *InterceptableSwitch { | ||
return &InterceptableSwitch{htlcSwitch: s} | ||
} | ||
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// SetInterceptor sets the ForwardInterceptor to be used. | ||
func (s *InterceptableSwitch) SetInterceptor( | ||
interceptor ForwardInterceptor) { | ||
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s.Lock() | ||
defer s.Unlock() | ||
s.fwdInterceptor = interceptor | ||
} | ||
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// ForwardPackets attempts to forward the batch of htlcs through the | ||
// switch, any failed packets will be returned to the provided | ||
// ChannelLink. The link's quit signal should be provided to allow | ||
// cancellation of forwarding during link shutdown. | ||
func (s *InterceptableSwitch) ForwardPackets(linkQuit chan struct{}, | ||
packets ...*htlcPacket) error { | ||
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var interceptor ForwardInterceptor | ||
s.Lock() | ||
interceptor = s.fwdInterceptor | ||
s.Unlock() | ||
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// Optimize for the case we don't have an interceptor. | ||
if interceptor == nil { | ||
return s.htlcSwitch.ForwardPackets(linkQuit, packets...) | ||
} | ||
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var notIntercepted []*htlcPacket | ||
for _, p := range packets { | ||
if !s.interceptForward(p, interceptor, linkQuit) { | ||
notIntercepted = append(notIntercepted, p) | ||
} | ||
} | ||
return s.htlcSwitch.ForwardPackets(linkQuit, notIntercepted...) | ||
} | ||
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// interceptForward checks if there is any external interceptor interested in | ||
// this packet. Currently only htlc type of UpdateAddHTLC that are forwarded | ||
// are being checked for interception. It can be extended in the future given | ||
// the right use case. | ||
func (s *InterceptableSwitch) interceptForward(packet *htlcPacket, | ||
interceptor ForwardInterceptor, linkQuit chan struct{}) bool { | ||
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switch htlc := packet.htlc.(type) { | ||
case *lnwire.UpdateAddHTLC: | ||
// We are not interested in intercepting initated payments. | ||
if packet.incomingChanID == hop.Source { | ||
return false | ||
} | ||
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intercepted := &interceptedForward{ | ||
linkQuit: linkQuit, | ||
htlc: htlc, | ||
packet: packet, | ||
htlcSwitch: s.htlcSwitch, | ||
} | ||
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// If this htlc was intercepted, don't handle the forward. | ||
return interceptor(intercepted) | ||
default: | ||
return false | ||
} | ||
} | ||
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// interceptedForward implements the InterceptedForward interface. | ||
// It is passed from the switch to external interceptors that are interested | ||
// in holding forwards and resolve them manually. | ||
type interceptedForward struct { | ||
linkQuit chan struct{} | ||
htlc *lnwire.UpdateAddHTLC | ||
packet *htlcPacket | ||
htlcSwitch *Switch | ||
} | ||
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// Packet returns the intercepted htlc packet. | ||
func (f *interceptedForward) Packet() lnwire.UpdateAddHTLC { | ||
return *f.htlc | ||
} | ||
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// CircuitKey returns the circuit key for the intercepted htlc. | ||
func (f *interceptedForward) CircuitKey() channeldb.CircuitKey { | ||
return channeldb.CircuitKey{ | ||
ChanID: f.packet.incomingChanID, | ||
HtlcID: f.packet.incomingHTLCID, | ||
} | ||
} | ||
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// Resume resumes the default behavior as if the packet was not intercepted. | ||
func (f *interceptedForward) Resume() error { | ||
return f.htlcSwitch.ForwardPackets(f.linkQuit, f.packet) | ||
} | ||
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// Fail forward a failed packet to the switch. | ||
func (f *interceptedForward) Fail() error { | ||
reason, err := f.packet.obfuscator.EncryptFirstHop(lnwire.NewTemporaryChannelFailure(nil)) | ||
if err != nil { | ||
return fmt.Errorf("failed to encrypt failure reason %v", err) | ||
} | ||
return f.resolve(&lnwire.UpdateFailHTLC{ | ||
Reason: reason, | ||
}) | ||
} | ||
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// Settle forwards a settled packet to the switch. | ||
func (f *interceptedForward) Settle(preimage lntypes.Preimage) error { | ||
if !preimage.Matches(f.htlc.PaymentHash) { | ||
return errors.New("preimage does not match hash") | ||
} | ||
return f.resolve(&lnwire.UpdateFulfillHTLC{ | ||
PaymentPreimage: preimage, | ||
}) | ||
} | ||
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// resolve is used for both Settle and Fail and forwards the message to the | ||
// switch. | ||
func (f *interceptedForward) resolve(message lnwire.Message) error { | ||
pkt := &htlcPacket{ | ||
incomingChanID: f.packet.incomingChanID, | ||
incomingHTLCID: f.packet.incomingHTLCID, | ||
outgoingChanID: f.packet.outgoingChanID, | ||
outgoingHTLCID: f.packet.outgoingHTLCID, | ||
isResolution: true, | ||
circuit: f.packet.circuit, | ||
htlc: message, | ||
obfuscator: f.packet.obfuscator, | ||
} | ||
return f.htlcSwitch.mailOrchestrator.Deliver(pkt.incomingChanID, pkt) | ||
} |
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