lspd/intercept.go

package main

import (
	"bytes"
	"context"
	"fmt"
	"log"
	"math/big"
	"os"
	"time"

	"github.com/btcsuite/btcd/btcec"
	"github.com/btcsuite/btcd/chaincfg/chainhash"
	"github.com/btcsuite/btcd/wire"
	"github.com/lightningnetwork/lnd/lnrpc"
	"github.com/lightningnetwork/lnd/lnrpc/routerrpc"
	"github.com/lightningnetwork/lnd/lnwire"
	"github.com/lightningnetwork/lnd/record"
	"github.com/lightningnetwork/lnd/routing/route"
	"google.golang.org/grpc/codes"
	"google.golang.org/grpc/metadata"
	"google.golang.org/grpc/status"

	sphinx "github.com/lightningnetwork/lightning-onion"
)

func openChannel(ctx context.Context, client lnrpc.LightningClient, paymentHash, destination []byte, incomingAmountMsat int64) ([]byte, uint32, error) {
	capacity := incomingAmountMsat/1000 + channelFeeStartAmount
	channelPoint, err := client.OpenChannelSync(ctx, &lnrpc.OpenChannelRequest{
		NodePubkey:         destination,
		LocalFundingAmount: capacity,
		TargetConf:         20,
		Private:            true,
	})
	if err != nil {
		return nil, 0, err
	}
	err = setFundingTx(paymentHash, channelPoint.GetFundingTxidBytes(), int(channelPoint.OutputIndex))
	return channelPoint.GetFundingTxidBytes(), channelPoint.OutputIndex, err
}

func getChannel(ctx context.Context, client lnrpc.LightningClient, node []byte, channelPoint string) uint64 {
	r, err := client.ListChannels(ctx, &lnrpc.ListChannelsRequest{Peer: node})
	if err != nil {
		log.Printf("client.ListChannels(%x) error: %v", node, err)
		return 0
	}
	for _, c := range r.Channels {
		log.Printf("getChannel(%x): %v", node, c.ChanId)
		if c.ChannelPoint == channelPoint && c.Active {
			return c.ChanId
		}
	}
	log.Printf("No channel found: getChannel(%x)", node)
	return 0
}

func intercept() {

	clientCtx := metadata.AppendToOutgoingContext(context.Background(), "macaroon", os.Getenv("LND_MACAROON_HEX"))
	interceptorClient, err := routerClient.HtlcInterceptor(clientCtx)
	if err != nil {
		log.Fatalf("routerClient.HtlcInterceptor(): %v", err)
	}

	for {
		request, err := interceptorClient.Recv()
		if err != nil {
			// If it is  just the error result of the context cancellation
			// the we exit silently.
			status, ok := status.FromError(err)
			if ok && status.Code() == codes.Canceled {
				break
			}
			// Otherwise it an unexpected error, we fail the test.
			log.Fatalf("unexpected error in interceptor.Recv() %v", err)
			break
		}
		fmt.Printf("htlc: %v\nchanID: %v\nincoming amount: %v\noutgoing amount: %v\nincomin expiry: %v\noutgoing expiry: %v\npaymentHash: %x\nonionBlob: %x\n\n",
			request.IncomingCircuitKey.HtlcId,
			request.IncomingCircuitKey.ChanId,
			request.IncomingAmountMsat,
			request.OutgoingAmountMsat,
			request.IncomingExpiry,
			request.OutgoingExpiry,
			request.PaymentHash,
			request.OnionBlob,
		)

		paymentSecret, destination, incomingAmountMsat, outgoingAmountMsat, fundingTxID, fundingTxOutnum, err := paymentInfo(request.PaymentHash)
		if err != nil {
			log.Printf("paymentInfo(%x) error: %v", request.PaymentHash, err)
		}
		log.Printf("paymentSecret: %x\ndestination:%x\nincomingAmountMsat:%v\noutgoingAmountMsat:%v\n\n",
			paymentSecret, destination, incomingAmountMsat, outgoingAmountMsat)
		if paymentSecret != nil {

			if fundingTxID == nil {
				fundingTxID, fundingTxOutnum, err = openChannel(clientCtx, client, request.PaymentHash, destination, incomingAmountMsat)
				log.Printf("openChannel(%x, %v) err: %v", destination, incomingAmountMsat, err)
				if err != nil {
					interceptorClient.Send(&routerrpc.ForwardHtlcInterceptResponse{
						IncomingCircuitKey: request.IncomingCircuitKey,
						Action:             routerrpc.ResolveHoldForwardAction_FAIL,
					})
					continue
				}
			}

			pubKey, err := btcec.ParsePubKey(destination, btcec.S256())
			log.Printf("btcec.ParsePubKey(%x): %v", destination, err)

			sessionKey, err := btcec.NewPrivateKey(btcec.S256())
			log.Printf("btcec.NewPrivateKey(): %v", err)

			var bigProd, bigAmt big.Int
			amt := (bigAmt.Div(bigProd.Mul(big.NewInt(outgoingAmountMsat), big.NewInt(int64(request.OutgoingAmountMsat))), big.NewInt(incomingAmountMsat))).Int64()

			var addr [32]byte
			copy(addr[:], paymentSecret)
			hop := route.Hop{
				AmtToForward:     lnwire.MilliSatoshi(amt),
				OutgoingTimeLock: request.OutgoingExpiry,
				MPP:              record.NewMPP(lnwire.MilliSatoshi(outgoingAmountMsat), addr),
				CustomRecords:    make(record.CustomSet),
			}

			var b bytes.Buffer
			err = hop.PackHopPayload(&b, uint64(0))
			log.Printf("hop.PackHopPayload(): %v", err)

			payload, err := sphinx.NewHopPayload(nil, b.Bytes())
			log.Printf("sphinx.NewHopPayload(): %v", err)

			var sphinxPath sphinx.PaymentPath
			sphinxPath[0] = sphinx.OnionHop{
				NodePub:    *pubKey,
				HopPayload: payload,
			}
			sphinxPacket, err := sphinx.NewOnionPacket(
				&sphinxPath, sessionKey, request.PaymentHash,
				sphinx.DeterministicPacketFiller,
			)
			var onionBlob bytes.Buffer
			err = sphinxPacket.Encode(&onionBlob)
			log.Printf("sphinxPacket.Encode(): %v", err)
			var h chainhash.Hash
			err = h.SetBytes(fundingTxID)
			if err != nil {
				log.Printf("h.SetBytes(%x) error: %v", fundingTxID, err)
				interceptorClient.Send(&routerrpc.ForwardHtlcInterceptResponse{
					IncomingCircuitKey: request.IncomingCircuitKey,
					Action:             routerrpc.ResolveHoldForwardAction_FAIL,
				})
				continue
			}
			channelPoint := wire.NewOutPoint(&h, fundingTxOutnum).String()
			go resumeOrCancel(
				clientCtx, interceptorClient, request.IncomingCircuitKey, destination,
				channelPoint, uint64(amt), onionBlob.Bytes(),
			)

		} else {
			interceptorClient.Send(&routerrpc.ForwardHtlcInterceptResponse{
				IncomingCircuitKey:      request.IncomingCircuitKey,
				Action:                  routerrpc.ResolveHoldForwardAction_RESUME,
				OutgoingAmountMsat:      request.OutgoingAmountMsat,
				OutgoingRequestedChanId: request.OutgoingRequestedChanId,
				OnionBlob:               request.OnionBlob,
			})
		}
	}
}

func resumeOrCancel(
	ctx context.Context,
	interceptorClient routerrpc.Router_HtlcInterceptorClient,
	incomingCircuitKey *routerrpc.CircuitKey,
	destination []byte,
	channelPoint string,
	outgoingAmountMsat uint64,
	onionBlob []byte,
) {
	deadline := time.Now().Add(10 * time.Second)
	for {
		chanID := getChannel(ctx, client, destination, channelPoint)
		if chanID != 0 {
			interceptorClient.Send(&routerrpc.ForwardHtlcInterceptResponse{
				IncomingCircuitKey:      incomingCircuitKey,
				Action:                  routerrpc.ResolveHoldForwardAction_RESUME,
				OutgoingAmountMsat:      outgoingAmountMsat,
				OutgoingRequestedChanId: chanID,
				OnionBlob:               onionBlob,
			})
			return
		}
		log.Printf("getChannel(%x, %v) returns 0", destination, channelPoint)
		if time.Now().After(deadline) {
			log.Printf("Stop retrying getChannel(%x, %v)", destination, channelPoint)
			break
		}
		time.Sleep(1 * time.Second)
	}
	interceptorClient.Send(&routerrpc.ForwardHtlcInterceptResponse{
		IncomingCircuitKey: incomingCircuitKey,
		Action:             routerrpc.ResolveHoldForwardAction_FAIL,
	})
}