channeldb: use BigSize to encode htlc amount

This commit uses bigsize record to encode the htlc amount, which could
save us 3 more bytes if the encoded value is no greater than roughly
0.043 bitcoin. The uint test has been updated with a more realistic
values to reflect the actual gain.

channeldb/revocation_log.go

@@ -8,6 +8,7 @@ import (
 
 	"github.com/btcsuite/btcd/btcutil"
 	"github.com/lightningnetwork/lnd/kvdb"
+	"github.com/lightningnetwork/lnd/lntypes"
 	"github.com/lightningnetwork/lnd/tlv"
 )
 
@@ -43,6 +44,16 @@ var (
 // HTLCEntry specifies the minimal info needed to be stored on disk for ALL the
 // historical HTLCs, which is useful for constructing RevocationLog when a
 // breach is detected.
+// The actual size of each HTLCEntry varies based on its RHash and Amt(sat),
+// summarized as follows,
+//
+//   | RHash empty | Amt<=252 | Amt<=65,535 | Amt<=4,294,967,295 | otherwise |
+//   |:-----------:|:--------:|:-----------:|:------------------:|:---------:|
+//   |     true    |    19    |      21     |         23         |     26    |
+//   |     false   |    51    |      53     |         55         |     58    |
+//
+// So the size varies from 19 bytes to 58 bytes, where most likely to be 23 or
+// 55 bytes.
 //
 // NOTE: all the fields saved to disk use the primitive go types so they can be
 // made into tlv records without further conversion.
@@ -86,6 +97,46 @@ type HTLCEntry struct {
 	incomingTlv uint8
 }
 
+// RHashLen is used by MakeDynamicRecord to return the size of the RHash.
+//
+// NOTE: for zero hash, we return a length 0.
+func (h *HTLCEntry) RHashLen() uint64 {
+	if h.RHash == lntypes.ZeroHash {
+		return 0
+	}
+	return 32
+}
+
+// RHashEncoder is the customized encoder which skips encoding the empty hash.
+func RHashEncoder(w io.Writer, val interface{}, buf *[8]byte) error {
+	v, ok := val.(*[32]byte)
+	if !ok {
+		return tlv.NewTypeForEncodingErr(val, "RHash")
+	}
+
+	// If the value is an empty hash, we will skip encoding it.
+	if *v == lntypes.ZeroHash {
+		return nil
+	}
+
+	return tlv.EBytes32(w, v, buf)
+}
+
+// RHashDecoder is the customized decoder which skips decoding the empty hash.
+func RHashDecoder(r io.Reader, val interface{}, buf *[8]byte, l uint64) error {
+	v, ok := val.(*[32]byte)
+	if !ok {
+		return tlv.NewTypeForEncodingErr(val, "RHash")
+	}
+
+	// If the length is zero, we will skip encoding the empty hash.
+	if l == 0 {
+		return nil
+	}
+
+	return tlv.DBytes32(r, v, buf, 32)
+}
+
 // toTlvStream converts an HTLCEntry record into a tlv representation.
 func (h *HTLCEntry) toTlvStream() (*tlv.Stream, error) {
 	const (
@@ -103,7 +154,10 @@ func (h *HTLCEntry) toTlvStream() (*tlv.Stream, error) {
 	)
 
 	return tlv.NewStream(
-		tlv.MakePrimitiveRecord(rHashType, &h.RHash),
+		tlv.MakeDynamicRecord(
+			rHashType, &h.RHash, h.RHashLen,
+			RHashEncoder, RHashDecoder,
+		),
 		tlv.MakePrimitiveRecord(
 			refundTimeoutType, &h.RefundTimeout,
 		),
@@ -111,7 +165,9 @@ func (h *HTLCEntry) toTlvStream() (*tlv.Stream, error) {
 			outputIndexType, &h.OutputIndex,
 		),
 		tlv.MakePrimitiveRecord(incomingType, &h.incomingTlv),
-		tlv.MakePrimitiveRecord(amtType, &h.amtTlv),
+		// We will save 3 bytes if the amount is less or equal to
+		// 4,294,967,295 msat, or roughly 0.043 bitcoin.
+		tlv.MakeBigSizeRecord(amtType, &h.amtTlv),
 	)
 }
 

channeldb/revocation_log_test.go

@@ -34,30 +34,26 @@ var (
 	}
 
 	testHTLCEntry = HTLCEntry{
-		RefundTimeout: 100,
+		RefundTimeout: 740_000,
 		OutputIndex:   10,
 		Incoming:      true,
-		Amt:           255,
-		amtTlv:        255,
+		Amt:           1000_000,
+		amtTlv:        1000_000,
 		incomingTlv:   1,
 	}
 	testHTLCEntryBytes = []byte{
-		// Body length 58.
-		0x39,
+		// Body length 23.
+		0x16,
 		// Rhash tlv.
-		0x0, 0x20,
-		0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0,
-		0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0,
-		0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0,
-		0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0,
+		0x0, 0x0,
 		// RefundTimeout tlv.
-		0x1, 0x4, 0x0, 0x0, 0x0, 0x64,
+		0x1, 0x4, 0x0, 0xb, 0x4a, 0xa0,
 		// OutputIndex tlv.
 		0x2, 0x2, 0x0, 0xa,
 		// Incoming tlv.
 		0x3, 0x1, 0x1,
 		// Amt tlv.
-		0x4, 0x8, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0xff,
+		0x4, 0x5, 0xfe, 0x0, 0xf, 0x42, 0x40,
 	}
 
 	testChannelCommit = ChannelCommitment{
@@ -161,7 +157,7 @@ func TestReadTLVStreamErr(t *testing.T) {
 	require.Zero(t, valueRead)
 }
 
-func TestSerializeHTLCEntries(t *testing.T) {
+func TestSerializeHTLCEntriesEmptyRHash(t *testing.T) {
 	t.Parallel()
 
 	// Copy the testHTLCEntry.
@@ -181,6 +177,37 @@ func TestSerializeHTLCEntries(t *testing.T) {
 	require.Equal(t, testHTLCEntryBytes, buf.Bytes())
 }
 
+func TestSerializeHTLCEntries(t *testing.T) {
+	t.Parallel()
+
+	// Copy the testHTLCEntry.
+	entry := testHTLCEntry
+
+	// Create a fake rHash.
+	rHashBytes := bytes.Repeat([]byte{10}, 32)
+	copy(entry.RHash[:], rHashBytes)
+
+	// Construct the serialized bytes.
+	//
+	// Exclude the first 3 bytes, which are total length, RHash type and
+	// RHash length(0).
+	partialBytes := testHTLCEntryBytes[3:]
+
+	// Write the total length and RHash tlv.
+	expectedBytes := []byte{0x36, 0x0, 0x20}
+	expectedBytes = append(expectedBytes, rHashBytes...)
+
+	// Append the rest.
+	expectedBytes = append(expectedBytes, partialBytes...)
+
+	buf := bytes.NewBuffer([]byte{})
+	err := serializeHTLCEntries(buf, []*HTLCEntry{&entry})
+	require.NoError(t, err)
+
+	// Check the bytes are read as expected.
+	require.Equal(t, expectedBytes, buf.Bytes())
+}
+
 func TestSerializeRevocationLog(t *testing.T) {
 	t.Parallel()
 
@@ -197,7 +224,7 @@ func TestSerializeRevocationLog(t *testing.T) {
 	require.Equal(t, testRevocationLogBytes, buf.Bytes()[:bodyIndex])
 }
 
-func TestDerializeHTLCEntries(t *testing.T) {
+func TestDerializeHTLCEntriesEmptyRHash(t *testing.T) {
 	t.Parallel()
 
 	// Read the tlv stream.
@@ -210,6 +237,38 @@ func TestDerializeHTLCEntries(t *testing.T) {
 	require.Equal(t, &testHTLCEntry, htlcs[0])
 }
 
+func TestDerializeHTLCEntries(t *testing.T) {
+	t.Parallel()
+
+	// Copy the testHTLCEntry.
+	entry := testHTLCEntry
+
+	// Create a fake rHash.
+	rHashBytes := bytes.Repeat([]byte{10}, 32)
+	copy(entry.RHash[:], rHashBytes)
+
+	// Construct the serialized bytes.
+	//
+	// Exclude the first 3 bytes, which are total length, RHash type and
+	// RHash length(0).
+	partialBytes := testHTLCEntryBytes[3:]
+
+	// Write the total length and RHash tlv.
+	testBytes := append([]byte{0x36, 0x0, 0x20}, rHashBytes...)
+
+	// Append the rest.
+	testBytes = append(testBytes, partialBytes...)
+
+	// Read the tlv stream.
+	buf := bytes.NewBuffer(testBytes)
+	htlcs, err := deserializeHTLCEntries(buf)
+	require.NoError(t, err)
+
+	// Check the bytes are read as expected.
+	require.Len(t, htlcs, 1)
+	require.Equal(t, &entry, htlcs[0])
+}
+
 func TestDerializeRevocationLog(t *testing.T) {
 	t.Parallel()