config: add a new --debughtlc config parameter

This commit adds a new configuration parameter to the deamon:
‘DebugHTLC’. When true, all outgoing HTLC’s sent via the RPC interface
will be sent paying to a special rHash value which all lnd nodes also
with the flag activated know the preimage to. Therefore all payments
sent to a 1-hop node will immediately be settled by that node.

By default, this flag is false, it it only intended to be used to
exercise local changes to 1-hop behavior manually.

config.go

@@ -68,6 +68,7 @@ type config struct {
 	TestNet3   bool   `long:"testnet" description:"Use the test network"`
 	SimNet     bool   `long:"simnet" description:"Use the simulation test network"`
 	SegNet     bool   `long:"segnet" description:"Use the segragated witness test network"`
+	DebugHTLC  bool   `long:"debughtlc" description:"Activate the debug htlc mode. With the debug HTLC mode, all payments sent use a pre-determined R-Hash. Additionally, all HTLC's sent to a node with the debug HTLC R-Hash are immediately settled in the next available state transition."`
 }
 
 // loadConfig initializes and parses the config using a config file and command

rpcserver.go

@@ -458,12 +458,22 @@ func (r *rpcServer) SendPayment(paymentStream lnrpc.Lightning_SendPaymentServer)
 				return err
 			}
 
+			// If we're in debug HTLC mode, then all outgoing
+			// HTLC's will pay to the same debug rHash. Otherwise,
+			// we pay to the rHash specified within the RPC
+			// request.
+			var rHash [32]byte
+			if cfg.DebugHTLC {
+				rHash = debugHash
+			} else {
+				copy(rHash[:], nextPayment.PaymentHash)
+			}
 			// Craft an HTLC packet to send to the routing sub-system. The
 			// meta-data within this packet will be used to route the
 			// payment through the network.
 			htlcAdd := &lnwire.HTLCAddRequest{
 				Amount:           lnwire.CreditsAmount(nextPayment.Amt),
-				RedemptionHashes: [][32]byte{debugHash},
+				RedemptionHashes: [][32]byte{rHash},
 			}
 			destAddr, err := wire.NewShaHash(nextPayment.Dest)
 			if err != nil {

server.go

@@ -104,6 +104,15 @@ func newServer(listenAddrs []string, notifier chainntnfs.ChainNotifier,
 		quit:          make(chan struct{}),
 	}
 
+	// If the debug HTLC flag is on, then we invoice a "master debug"
+	// invoice which all outgoing payments will be sent and all incoming
+	// HTLC's with the debug R-Hash immediately settled.
+	if cfg.DebugHTLC {
+		kiloCoin := btcutil.Amount(btcutil.SatoshiPerBitcoin * 1000)
+		s.invoices.AddDebugInvoice(kiloCoin, *debugPre)
+		srvrLog.Debugf("Debug HTLC invoice inserted, preimage=%x, hash=%x",
+			debugPre[:], debugHash[:])
+	}
 
 	s.utxoNursery = newUtxoNursery(notifier, wallet)