rfqmsg: shift SCID alias into custom range

A recent change to the lnd SCID alias RPCs requires us to generate SCID
aliases in a certain range. Because we derive the alias from the
randomly generated RFQ ID, we need to do some shifting arithmetic to
arrive at an acceptable alias.

Author: guggero

rfqmsg/messages.go

@@ -8,6 +8,7 @@ import (
 	"io"
 	"math"
 
+	"github.com/lightningnetwork/lnd/aliasmgr"
 	"github.com/lightningnetwork/lnd/lnwire"
 	"github.com/lightningnetwork/lnd/routing/route"
 	"github.com/lightningnetwork/lnd/tlv"
@@ -32,7 +33,27 @@ func (id ID) Scid() SerialisedScid {
 	scidBytes := id[24:]
 
 	scidInteger := binary.BigEndian.Uint64(scidBytes)
-	return SerialisedScid(scidInteger)
+
+	// We need to make sure the block height is within the range of valid
+	// SCID block heights.
+	scid := lnwire.NewShortChanIDFromInt(scidInteger)
+
+	minBlock := uint32(aliasmgr.AliasStartBlockHeight)
+	maxBlock := uint32(aliasmgr.AliasEndBlockHeight)
+
+	// If we're within the valid range, we can return the SCID as is.
+	if aliasmgr.IsAlias(scid) {
+		return SerialisedScid(scid.ToUint64())
+	}
+
+	// Normalize the value relative to min, then wrap within blockRange, and
+	// finally shift back by min. Generated by ChatGPT and I couldn't find a
+	// better way to do this.
+	blockRange := maxBlock - minBlock + 1
+	scid.BlockHeight = ((scid.BlockHeight-minBlock)%blockRange+blockRange)%
+		blockRange + minBlock
+
+	return SerialisedScid(scid.ToUint64())
 }
 
 // Record returns a TLV record that can be used to encode/decode an ID to/from a

rfqmsg/messages_test.go

@@ -0,0 +1,129 @@
+package rfqmsg
+
+import (
+	"encoding/binary"
+	"testing"
+
+	"github.com/lightningnetwork/lnd/aliasmgr"
+	"github.com/lightningnetwork/lnd/lnwire"
+	"github.com/stretchr/testify/require"
+)
+
+func intToID(scid uint64) ID {
+	var id ID
+	binary.BigEndian.PutUint64(id[24:], scid)
+	return id
+}
+
+func shortChannelIDToID(scid lnwire.ShortChannelID) ID {
+	return intToID(scid.ToUint64())
+}
+
+// TestIDSerializedScid tests that an RFQ ID can be correctly converted into a
+// custom SCID alias that lies within the valid SCID block height range.
+func TestIDSerializedScid(t *testing.T) {
+	tests := []struct {
+		id       ID
+		expected lnwire.ShortChannelID
+	}{
+		{
+			id: intToID(123456),
+			expected: lnwire.ShortChannelID{
+				BlockHeight: 16200181,
+				TxIndex:     1,
+				TxPosition:  57920,
+			},
+		},
+		{
+			id: intToID(0),
+			expected: lnwire.ShortChannelID{
+				BlockHeight: 16200181,
+			},
+		},
+		{
+			id: shortChannelIDToID(lnwire.ShortChannelID{
+				BlockHeight: uint32(
+					aliasmgr.AliasStartBlockHeight,
+				),
+			}),
+			expected: lnwire.ShortChannelID{
+				BlockHeight: uint32(
+					aliasmgr.AliasStartBlockHeight,
+				),
+			},
+		},
+		{
+			id: intToID(1),
+			expected: lnwire.ShortChannelID{
+				BlockHeight: 16200181,
+				TxPosition:  1,
+			},
+		},
+		{
+			id: intToID(123456789),
+			expected: lnwire.ShortChannelID{
+				BlockHeight: 16200181,
+				TxIndex:     1883,
+				TxPosition:  52501,
+			},
+		},
+		{
+			id: shortChannelIDToID(lnwire.ShortChannelID{
+				BlockHeight: uint32(
+					aliasmgr.AliasEndBlockHeight + 1,
+				),
+				TxIndex:    123,
+				TxPosition: 123,
+			}),
+			expected: lnwire.ShortChannelID{
+				BlockHeight: uint32(
+					aliasmgr.AliasStartBlockHeight,
+				),
+				TxIndex:    123,
+				TxPosition: 123,
+			},
+		},
+		{
+			id: shortChannelIDToID(lnwire.ShortChannelID{
+				BlockHeight: 10561306,
+				TxIndex:     5698083,
+				TxPosition:  53702,
+			}),
+			expected: lnwire.ShortChannelID{
+				BlockHeight: 16011444,
+				TxIndex:     5698083,
+				TxPosition:  53702,
+			},
+		},
+		{
+			id: ID{
+				0xd3, 0x62, 0x2a, 0xa3, 0x9b, 0x51, 0x53, 0x88,
+				0x84, 0x2a, 0xa9, 0x78, 0x40, 0x65, 0xb3, 0x15,
+				0x80, 0x56, 0xb3, 0x09, 0x80, 0xeb, 0xbb, 0x50,
+				0xb8, 0xdf, 0x1a, 0x56, 0xf2, 0x23, 0xd1, 0xc6,
+			},
+			expected: lnwire.ShortChannelID{
+				BlockHeight: 16065870,
+				TxIndex:     5698083,
+				TxPosition:  53702,
+			},
+		},
+	}
+
+	for idx, test := range tests {
+		t.Logf("Running test #%d", idx)
+		scid := test.id.Scid()
+		shortChanID := lnwire.NewShortChanIDFromInt(uint64(scid))
+		require.Equal(t, test.expected, shortChanID)
+
+		require.GreaterOrEqual(
+			t, shortChanID.BlockHeight,
+			uint32(aliasmgr.AliasStartBlockHeight),
+		)
+		require.Less(
+			t, shortChanID.BlockHeight,
+			uint32(aliasmgr.AliasEndBlockHeight),
+		)
+		require.True(t, aliasmgr.IsAlias(shortChanID))
+	}
+}