record+routing/route: add AMP record

record/amp.go

@@ -0,0 +1,107 @@
+package record
+
+import (
+	"fmt"
+	"io"
+
+	"github.com/lightningnetwork/lnd/tlv"
+)
+
+// AMPOnionType is the type used in the onion to reference the AMP fields:
+// root_share, set_id, and child_index.
+const AMPOnionType tlv.Type = 10
+
+// AMP is a record that encodes the fields necessary for atomic multi-path
+// payments.
+type AMP struct {
+	rootShare  [32]byte
+	setID      [32]byte
+	childIndex uint16
+}
+
+// NewAMP generate a new AMP record with the given root_share, set_id, and
+// child_index.
+func NewAMP(rootShare, setID [32]byte, childIndex uint16) *AMP {
+	return &AMP{
+		rootShare:  rootShare,
+		setID:      setID,
+		childIndex: childIndex,
+	}
+}
+
+// RootShare returns the root share contained in the AMP record.
+func (a *AMP) RootShare() [32]byte {
+	return a.rootShare
+}
+
+// SetID returns the set id contained in the AMP record.
+func (a *AMP) SetID() [32]byte {
+	return a.setID
+}
+
+// ChildIndex returns the child index contained in the AMP record.
+func (a *AMP) ChildIndex() uint16 {
+	return a.childIndex
+}
+
+// AMPEncoder writes the AMP record to the provided io.Writer.
+func AMPEncoder(w io.Writer, val interface{}, buf *[8]byte) error {
+	if v, ok := val.(*AMP); ok {
+		if err := tlv.EBytes32(w, &v.rootShare, buf); err != nil {
+			return err
+		}
+
+		if err := tlv.EBytes32(w, &v.setID, buf); err != nil {
+			return err
+		}
+
+		return tlv.ETUint16T(w, v.childIndex, buf)
+	}
+	return tlv.NewTypeForEncodingErr(val, "AMP")
+}
+
+const (
+	// minAMPLength is the minimum length of a serialized AMP TLV record,
+	// which occurs when the truncated encoding of child_index takes 0
+	// bytes, leaving only the root_share and set_id.
+	minAMPLength = 64
+
+	// maxAMPLength is the maximum legnth of a serialized AMP TLV record,
+	// which occurs when the truncated endoing of a child_index takes 2
+	// bytes.
+	maxAMPLength = 66
+)
+
+// AMPDecoder reads the AMP record from the provided io.Reader.
+func AMPDecoder(r io.Reader, val interface{}, buf *[8]byte, l uint64) error {
+	if v, ok := val.(*AMP); ok && minAMPLength <= l && l <= maxAMPLength {
+		if err := tlv.DBytes32(r, &v.rootShare, buf, 32); err != nil {
+			return err
+		}
+
+		if err := tlv.DBytes32(r, &v.setID, buf, 32); err != nil {
+			return err
+		}
+
+		return tlv.DTUint16(r, &v.childIndex, buf, l-64)
+	}
+	return tlv.NewTypeForDecodingErr(val, "AMP", l, maxAMPLength)
+}
+
+// Record returns a tlv.Record that can be used to encode or decode this record.
+func (a *AMP) Record() tlv.Record {
+	return tlv.MakeDynamicRecord(
+		AMPOnionType, a, a.PayloadSize, AMPEncoder, AMPDecoder,
+	)
+}
+
+// PayloadSize returns the size this record takes up in encoded form.
+func (a *AMP) PayloadSize() uint64 {
+	return 32 + 32 + tlv.SizeTUint16(a.childIndex)
+}
+
+// String returns a human-readble description of the amp payload fields.
+func (a *AMP) String() string {
+	return fmt.Sprintf("root_share=%x set_id=%x child_index=%d",
+		a.rootShare, a.setID, a.childIndex)
+}

record/record_test.go

@@ -17,8 +17,11 @@ type recordEncDecTest struct {
 }
 
 var (
-	testTotal = lnwire.MilliSatoshi(45)
-	testAddr  = [32]byte{0x01, 0x02}
+	testTotal      = lnwire.MilliSatoshi(45)
+	testAddr       = [32]byte{0x01, 0x02}
+	testShare      = [32]byte{0x03, 0x04}
+	testSetID      = [32]byte{0x05, 0x06}
+	testChildIndex = uint16(17)
 )
 
 var recordEncDecTests = []recordEncDecTest{
@@ -40,6 +43,29 @@ var recordEncDecTests = []recordEncDecTest{
 			}
 		},
 	},
+	{
+		name: "amp",
+		encRecord: func() tlv.RecordProducer {
+			return record.NewAMP(
+				testShare, testSetID, testChildIndex,
+			)
+		},
+		decRecord: func() tlv.RecordProducer {
+			return new(record.AMP)
+		},
+		assert: func(t *testing.T, r interface{}) {
+			amp := r.(*record.AMP)
+			if amp.RootShare() != testShare {
+				t.Fatal("incorrect root share")
+			}
+			if amp.SetID() != testSetID {
+				t.Fatal("incorrect set id")
+			}
+			if amp.ChildIndex() != testChildIndex {
+				t.Fatal("incorrect child index")
+			}
+		},
+	},
 }
 
 // TestRecordEncodeDecode is a generic test framework for custom TLV records. It

routing/route/route.go

@@ -34,6 +34,10 @@ var (
 	// record to an intermediate hop, only final hops can receive MPP
 	// records.
 	ErrIntermediateMPPHop = errors.New("cannot send MPP to intermediate")
+
+	// ErrAMPMissingMPP is returned when the caller tries to attach an AMP
+	// record but no MPP record is presented for the final hop.
+	ErrAMPMissingMPP = errors.New("cannot send AMP without MPP record")
 )
 
 // Vertex is a simple alias for the serialization of a compressed Bitcoin
@@ -111,6 +115,10 @@ type Hop struct {
 	// only be set for the final hop.
 	MPP *record.MPP
 
+	// AMP encapsulates the data required for option_amp. This field should
+	// only be set for the final hop.
+	AMP *record.AMP
+
 	// CustomRecords if non-nil are a set of additional TLV records that
 	// should be included in the forwarding instructions for this node.
 	CustomRecords record.CustomSet
@@ -168,6 +176,18 @@ func (h *Hop) PackHopPayload(w io.Writer, nextChanID uint64) error {
 		}
 	}
 
+	// If an AMP record is destined for this hop, ensure that we only ever
+	// attach it if we also have an MPP record. We can infer that this is
+	// already a final hop if MPP is non-nil otherwise we would have exited
+	// above.
+	if h.AMP != nil {
+		if h.MPP != nil {
+			records = append(records, h.AMP.Record())
+		} else {
+			return ErrAMPMissingMPP
+		}
+	}
+
 	// Append any custom types destined for this hop.
 	tlvRecords := tlv.MapToRecords(h.CustomRecords)
 	records = append(records, tlvRecords...)
@@ -217,6 +237,11 @@ func (h *Hop) PayloadSize(nextChanID uint64) uint64 {
 		addRecord(record.MPPOnionType, h.MPP.PayloadSize())
 	}
 
+	// Add amp if present.
+	if h.AMP != nil {
+		addRecord(record.AMPOnionType, h.AMP.PayloadSize())
+	}
+
 	// Add custom records.
 	for k, v := range h.CustomRecords {
 		addRecord(tlv.Type(k), uint64(len(v)))

routing/route/route_test.go

@@ -71,8 +71,8 @@ var (
 	testAddr = [32]byte{0x01, 0x02}
 )
 
-// TestMPPHop asserts that a Hop will encode a non-nil to final nodes, and fail
-// when trying to send to intermediaries.
+// TestMPPHop asserts that a Hop will encode a non-nil MPP to final nodes, and
+// fail when trying to send to intermediaries.
 func TestMPPHop(t *testing.T) {
 	t.Parallel()
 
@@ -101,6 +101,47 @@ func TestMPPHop(t *testing.T) {
 	}
 }
 
+// TestAMPHop asserts that a Hop will encode a non-nil AMP to final nodes of an
+// MPP record is also present, and fail otherwise.
+func TestAMPHop(t *testing.T) {
+	t.Parallel()
+
+	hop := Hop{
+		ChannelID:        1,
+		OutgoingTimeLock: 44,
+		AmtToForward:     testAmt,
+		LegacyPayload:    false,
+		AMP:              record.NewAMP([32]byte{}, [32]byte{}, 3),
+	}
+
+	// Encoding an AMP record to an intermediate hop w/o an MPP record
+	// should result in a failure.
+	var b bytes.Buffer
+	err := hop.PackHopPayload(&b, 2)
+	if err != ErrAMPMissingMPP {
+		t.Fatalf("expected err: %v, got: %v",
+			ErrAMPMissingMPP, err)
+	}
+
+	// Encoding an AMP record to a final hop w/o an MPP record should result
+	// in a failure.
+	b.Reset()
+	err = hop.PackHopPayload(&b, 0)
+	if err != ErrAMPMissingMPP {
+		t.Fatalf("expected err: %v, got: %v",
+			ErrAMPMissingMPP, err)
+	}
+
+	// Encoding an AMP record to a final hop w/ an MPP record should be
+	// successful.
+	hop.MPP = record.NewMPP(testAmt, testAddr)
+	b.Reset()
+	err = hop.PackHopPayload(&b, 0)
+	if err != nil {
+		t.Fatalf("expected err: %v, got: %v", nil, err)
+	}
+}
+
 // TestPayloadSize tests the payload size calculation that is provided by Hop
 // structs.
 func TestPayloadSize(t *testing.T) {
@@ -123,6 +164,7 @@ func TestPayloadSize(t *testing.T) {
 			AmtToForward:     1200,
 			OutgoingTimeLock: 700000,
 			MPP:              record.NewMPP(500, [32]byte{}),
+			AMP:              record.NewAMP([32]byte{}, [32]byte{}, 8),
 			CustomRecords: map[uint64][]byte{
 				100000:  {1, 2, 3},
 				1000000: {4, 5},