Handle interception probing payments

probing payments uses a probing payment hash which is:
sha256("probing-01:" || payment_hash).

When the interceptor detects such a hash for a payment which is supposed
to trigger a channel creation , it checks if the destination is online,
and if online, fails with INCORRECT_OR_UNKNOWN_PAYMENT_DETAILS error in
order to let the payer knows that the payment would be successful.

db.go

@@ -24,25 +24,25 @@ func pgConnect() error {
 	return nil
 }
 
-func paymentInfo(paymentHash []byte) ([]byte, []byte, int64, int64, []byte, uint32, error) {
+func paymentInfo(htlcPaymentHash []byte) ([]byte, []byte, []byte, int64, int64, []byte, uint32, error) {
 	var (
-		paymentSecret, destination             []byte
+		paymentHash, paymentSecret, destination []byte
 		incomingAmountMsat, outgoingAmountMsat  int64
 		fundingTxID                             []byte
 		fundingTxOutnum                         pgtype.Int4
 	)
 	err := pgxPool.QueryRow(context.Background(),
-		`SELECT payment_secret, destination, incoming_amount_msat, outgoing_amount_msat, funding_tx_id, funding_tx_outnum
+		`SELECT payment_hash, payment_secret, destination, incoming_amount_msat, outgoing_amount_msat, funding_tx_id, funding_tx_outnum
 			FROM payments
-			WHERE payment_hash=$1`,
-		paymentHash).Scan(&paymentSecret, &destination, &incomingAmountMsat, &outgoingAmountMsat, &fundingTxID, &fundingTxOutnum)
+			WHERE payment_hash=$1 OR sha256('probing-01:' || payment_hash)=$1`,
+		htlcPaymentHash).Scan(&paymentHash, &paymentSecret, &destination, &incomingAmountMsat, &outgoingAmountMsat, &fundingTxID, &fundingTxOutnum)
 	if err != nil {
 		if err == pgx.ErrNoRows {
 			err = nil
 		}
-		return nil, nil, 0, 0, nil, 0, err
+		return nil, nil, nil, 0, 0, nil, 0, err
 	}
-	return paymentSecret, destination, incomingAmountMsat, outgoingAmountMsat, fundingTxID, uint32(fundingTxOutnum.Int), nil
+	return paymentHash, paymentSecret, destination, incomingAmountMsat, outgoingAmountMsat, fundingTxID, uint32(fundingTxOutnum.Int), nil
 }
 
 func setFundingTx(paymentHash, fundingTxID []byte, fundingTxOutnum int) error {

go.mod

@@ -4,16 +4,16 @@ go 1.14
 
 require (
 	github.com/aws/aws-sdk-go v1.30.20
-	github.com/btcsuite/btcd v0.20.1-beta
+	github.com/btcsuite/btcd v0.20.1-beta.0.20200730232343-1db1b6f8217f
 	github.com/caddyserver/certmagic v0.11.2
 	github.com/golang/protobuf v1.4.2
 	github.com/grpc-ecosystem/go-grpc-middleware v1.0.0
 	github.com/jackc/pgtype v1.4.2
 	github.com/jackc/pgx/v4 v4.8.1
-	github.com/lightningnetwork/lightning-onion v1.0.1
-	github.com/lightningnetwork/lnd v0.10.0-beta
+	github.com/lightningnetwork/lightning-onion v1.0.2-0.20200501022730-3c8c8d0b89ea
+	github.com/lightningnetwork/lnd v0.11.0-beta
 	golang.org/x/sync v0.0.0-20190911185100-cd5d95a43a6e
 	google.golang.org/grpc v1.31.0
 )
 
-replace github.com/lightningnetwork/lnd v0.10.0-beta => github.com/breez/lnd v0.10.0-beta.rc6.0.20200727142715-f67a1052c0e0
+replace github.com/lightningnetwork/lnd v0.11.0-beta => github.com/breez/lnd v0.11.0-beta.rc4.0.20201101122458-227226f00b18

intercept.go

@@ -3,6 +3,7 @@ package main
 import (
 	"bytes"
 	"context"
+	"encoding/hex"
 	"fmt"
 	"log"
 	"math/big"
@@ -32,6 +33,23 @@ func checkPayment(incomingAmountMsat, outgoingAmountMsat int64) error {
 	return nil
 }
 
+func isConnected(ctx context.Context, client lnrpc.LightningClient, destination []byte) error {
+	pubKey := hex.EncodeToString(destination)
+	r, err := client.ListPeers(ctx, &lnrpc.ListPeersRequest{LatestError: true})
+	if err != nil {
+		log.Printf("client.ListPeers() error: %v", err)
+		return fmt.Errorf("client.ListPeers() error: %w", err)
+	}
+	for _, peer := range r.Peers {
+		if pubKey == peer.PubKey {
+			log.Printf("destination online: %x", destination)
+			return nil
+		}
+	}
+	log.Printf("destination offline: %x", destination)
+	return fmt.Errorf("destination offline")
+}
+
 func openChannel(ctx context.Context, client lnrpc.LightningClient, paymentHash, destination []byte, incomingAmountMsat int64) ([]byte, uint32, error) {
 	capacity := incomingAmountMsat/1000 + additionalChannelCapacity
 	channelPoint, err := client.OpenChannelSync(ctx, &lnrpc.OpenChannelRequest{
@@ -104,15 +122,16 @@ func intercept() {
 			request.OnionBlob,
 		)
 
-		paymentSecret, destination, incomingAmountMsat, outgoingAmountMsat, fundingTxID, fundingTxOutnum, err := paymentInfo(request.PaymentHash)
+		paymentHash, 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)
+		log.Printf("paymentHash:%x\npaymentSecret:%x\ndestination:%x\nincomingAmountMsat:%v\noutgoingAmountMsat:%v\n\n",
+			paymentHash, paymentSecret, destination, incomingAmountMsat, outgoingAmountMsat)
 		if paymentSecret != nil {
 
 			if fundingTxID == nil {
+				if bytes.Compare(paymentHash, request.PaymentHash) == 0 {
 					fundingTxID, fundingTxOutnum, err = openChannel(clientCtx, client, request.PaymentHash, destination, incomingAmountMsat)
 					log.Printf("openChannel(%x, %v) err: %v", destination, incomingAmountMsat, err)
 					if err != nil {
@@ -122,6 +141,18 @@ func intercept() {
 						})
 						continue
 					}
+				} else { //probing
+					failureCode := routerrpc.ForwardHtlcInterceptResponse_TEMPORARY_CHANNEL_FAILURE
+					if err := isConnected(clientCtx, client, destination); err == nil {
+						failureCode = routerrpc.ForwardHtlcInterceptResponse_INCORRECT_OR_UNKNOWN_PAYMENT_DETAILS
+					}
+					interceptorClient.Send(&routerrpc.ForwardHtlcInterceptResponse{
+						IncomingCircuitKey: request.IncomingCircuitKey,
+						Action:             routerrpc.ResolveHoldForwardAction_FAIL,
+						FailureCode:        failureCode,
+					})
+					continue
+				}
 			}
 
 			pubKey, err := btcec.ParsePubKey(destination, btcec.S256())

postgresql/migrations/000004_create_probe_payments_hash_index.down.sql

@@ -0,0 +1 @@
+DROP INDEX probe_payment_hash;

postgresql/migrations/000004_create_probe_payments_hash_index.up.sql

@@ -0,0 +1 @@
+CREATE INDEX probe_payment_hash ON public.payments (sha256('probing-01:' || payment_hash));