contractcourt: add HtlcBlobs to taprootBriefcase

In this commit, we add the set of HtlcBlobs to the taprootBriefcase
struct. This new field will store all the resolution blobs for a given
HTLC. We also add some new property based tests along the way for
adequate test coverage.

contractcourt/taproot_briefcase.go

@@ -39,7 +39,9 @@ type taprootBriefcase struct {
 	// used to sweep a remote party's breached output.
 	BreachedCommitBlob tlv.OptionalRecordT[tlv.TlvType3, tlv.Blob]
 
-	// TODO(roasbeef): htlc blobs
+	// HtlcBlobs is an optikonal record that contains the opaque blobs for
+	// the set of active HTLCs on the commitment transaction.
+	HtlcBlobs tlv.OptionalRecordT[tlv.TlvType4, htlcAuxBlobs]
 }
 
 // TODO(roasbeef): morph into new tlv record
@@ -70,6 +72,9 @@ func (t *taprootBriefcase) EncodeRecords() []tlv.Record {
 			records = append(records, r.Record())
 		},
 	)
+	t.HtlcBlobs.WhenSome(func(r tlv.RecordT[tlv.TlvType4, htlcAuxBlobs]) {
+		records = append(records, r.Record())
+	})
 
 	return records
 }
@@ -96,10 +101,11 @@ func (t *taprootBriefcase) Encode(w io.Writer) error {
 func (t *taprootBriefcase) Decode(r io.Reader) error {
 	settledCommitBlob := t.SettledCommitBlob.Zero()
 	breachedCommitBlob := t.BreachedCommitBlob.Zero()
+	htlcBlobs := t.HtlcBlobs.Zero()
+
 	records := append(
-		t.DecodeRecords(),
-		settledCommitBlob.Record(),
-		breachedCommitBlob.Record(),
+		t.DecodeRecords(), settledCommitBlob.Record(),
+		breachedCommitBlob.Record(), htlcBlobs.Record(),
 	)
 	stream, err := tlv.NewStream(records...)
 	if err != nil {
@@ -117,6 +123,9 @@ func (t *taprootBriefcase) Decode(r io.Reader) error {
 	if v, ok := typeMap[t.BreachedCommitBlob.TlvType()]; ok && v == nil {
 		t.BreachedCommitBlob = tlv.SomeRecordT(breachedCommitBlob)
 	}
+	if v, ok := typeMap[t.HtlcBlobs.TlvType()]; ok && v == nil {
+		t.HtlcBlobs = tlv.SomeRecordT(htlcBlobs)
+	}
 
 	return nil
 }
@@ -686,3 +695,110 @@ func (t *tapTweaks) Decode(r io.Reader) error {
 
 	return stream.Decode(r)
 }
+
+// htlcAuxBlobs is a map of resolver IDs to their corresponding HTLC blobs.
+// This is used to store the resolution blobs for HTLCs that are not yet
+// resolved.
+type htlcAuxBlobs map[resolverID]tlv.Blob
+
+// newAuxHtlcBlobs returns a new instance of the htlcAuxBlobs struct.
+func newAuxHtlcBlobs() htlcAuxBlobs {
+	return make(htlcAuxBlobs)
+}
+
+// Encode encodes the set of HTLC blobs into the target writer.
+func (h *htlcAuxBlobs) Encode(w io.Writer) error {
+	var buf [8]byte
+
+	numBlobs := uint64(len(*h))
+	if err := tlv.WriteVarInt(w, numBlobs, &buf); err != nil {
+		return err
+	}
+
+	for id, blob := range *h {
+		if _, err := w.Write(id[:]); err != nil {
+			return err
+		}
+
+		if err := varBytesEncoder(w, &blob, &buf); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+// Decode decodes the set of HTLC blobs from the target reader.
+func (h *htlcAuxBlobs) Decode(r io.Reader) error {
+	var buf [8]byte
+
+	numBlobs, err := tlv.ReadVarInt(r, &buf)
+	if err != nil {
+		return err
+	}
+
+	for i := uint64(0); i < numBlobs; i++ {
+		var id resolverID
+		if _, err := io.ReadFull(r, id[:]); err != nil {
+			return err
+		}
+
+		var blob tlv.Blob
+		if err := varBytesDecoder(r, &blob, &buf, 0); err != nil {
+			return err
+		}
+
+		(*h)[id] = blob
+	}
+
+	return nil
+}
+
+// eHtlcAuxBlobsEncoder is a custom TLV encoder for the htlcAuxBlobs struct.
+func htlcAuxBlobsEncoder(w io.Writer, val any, _ *[8]byte) error {
+	if t, ok := val.(*htlcAuxBlobs); ok {
+		return (*t).Encode(w)
+	}
+
+	return tlv.NewTypeForEncodingErr(val, "htlcAuxBlobs")
+}
+
+// dHtlcAuxBlobsDecoder is a custom TLV decoder for the htlcAuxBlobs struct.
+func htlcAuxBlobsDecoder(r io.Reader, val any, _ *[8]byte,
+	l uint64) error {
+
+	if typ, ok := val.(*htlcAuxBlobs); ok {
+		blobReader := io.LimitReader(r, int64(l))
+
+		htlcBlobs := newAuxHtlcBlobs()
+		err := htlcBlobs.Decode(blobReader)
+		if err != nil {
+			return err
+		}
+
+		*typ = htlcBlobs
+
+		return nil
+	}
+
+	return tlv.NewTypeForDecodingErr(val, "htlcAuxBlobs", l, l)
+}
+
+// Record returns a tlv.Record for the htlcAuxBlobs struct.
+func (h *htlcAuxBlobs) Record() tlv.Record {
+	recordSize := func() uint64 {
+		var (
+			b   bytes.Buffer
+			buf [8]byte
+		)
+		if err := htlcAuxBlobsEncoder(&b, h, &buf); err != nil {
+			panic(err)
+		}
+
+		return uint64(len(b.Bytes()))
+	}
+
+	return tlv.MakeDynamicRecord(
+		0, h, recordSize, htlcAuxBlobsEncoder, htlcAuxBlobsDecoder,
+	)
+}

contractcourt/taproot_briefcase_test.go

@@ -7,6 +7,7 @@ import (
 
 	"github.com/lightningnetwork/lnd/tlv"
 	"github.com/stretchr/testify/require"
+	"pgregory.net/rapid"
 )
 
 func randResolverCtrlBlocks(t *testing.T) resolverCtrlBlocks {
@@ -53,6 +54,25 @@ func randHtlcTweaks(t *testing.T) htlcTapTweaks {
 	return tweaks
 }
 
+func randHtlcAuxBlobs(t *testing.T) htlcAuxBlobs {
+	numBlobs := rand.Int() % 256
+	blobs := make(htlcAuxBlobs, numBlobs)
+
+	for i := 0; i < numBlobs; i++ {
+		var id resolverID
+		_, err := rand.Read(id[:])
+		require.NoError(t, err)
+
+		var blob [100]byte
+		_, err = rand.Read(blob[:])
+		require.NoError(t, err)
+
+		blobs[id] = blob[:]
+	}
+
+	return blobs
+}
+
 // TestTaprootBriefcase tests the encode/decode methods of the taproot
 // briefcase extension.
 func TestTaprootBriefcase(t *testing.T) {
@@ -93,6 +113,9 @@ func TestTaprootBriefcase(t *testing.T) {
 		BreachedCommitBlob: tlv.SomeRecordT(
 			tlv.NewPrimitiveRecord[tlv.TlvType3](commitBlob[:]),
 		),
+		HtlcBlobs: tlv.SomeRecordT(
+			tlv.NewRecordT[tlv.TlvType4](randHtlcAuxBlobs(t)),
+		),
 	}
 
 	var b bytes.Buffer
@@ -103,3 +126,21 @@ func TestTaprootBriefcase(t *testing.T) {
 
 	require.Equal(t, testCase, &decodedCase)
 }
+
+// TestHtlcAuxBlobEncodeDecode tests the encode/decode methods of the HTLC aux
+// blobs.
+func TestHtlcAuxBlobEncodeDecode(t *testing.T) {
+	t.Parallel()
+
+	rapid.Check(t, func(t *rapid.T) {
+		htlcBlobs := rapid.Make[htlcAuxBlobs]().Draw(t, "htlcAuxBlobs")
+
+		var b bytes.Buffer
+		require.NoError(t, htlcBlobs.Encode(&b))
+
+		decodedBlobs := newAuxHtlcBlobs()
+		require.NoError(t, decodedBlobs.Decode(&b))
+
+		require.Equal(t, htlcBlobs, decodedBlobs)
+	})
+}

contractcourt/testdata/rapid/TestHtlcAuxBlobEncodeDecode/TestHtlcAuxBlobEncodeDecode-20240902140253-81338.fail

@@ -0,0 +1,78 @@
+# 2024/09/02 14:02:53.354676 [TestHtlcAuxBlobEncodeDecode] [rapid] draw htlcAuxBlobs: contractcourt.htlcAuxBlobs{contractcourt.resolverID{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, 0x0, 0x0}:[]uint8{}}
+# 
+v0.4.8#15807814492030881602
+0x5555555555555
+0x0
+0x0
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go.mod

@@ -64,6 +64,7 @@ require (
 	google.golang.org/protobuf v1.33.0
 	gopkg.in/macaroon-bakery.v2 v2.0.1
 	gopkg.in/macaroon.v2 v2.0.0
+	pgregory.net/rapid v1.1.0
 )
 
 require (

go.sum

@@ -1076,6 +1076,8 @@ modernc.org/strutil v1.2.0 h1:agBi9dp1I+eOnxXeiZawM8F4LawKv4NzGWSaLfyeNZA=
 modernc.org/strutil v1.2.0/go.mod h1:/mdcBmfOibveCTBxUl5B5l6W+TTH1FXPLHZE6bTosX0=
 modernc.org/token v1.1.0 h1:Xl7Ap9dKaEs5kLoOQeQmPWevfnk/DM5qcLcYlA8ys6Y=
 modernc.org/token v1.1.0/go.mod h1:UGzOrNV1mAFSEB63lOFHIpNRUVMvYTc6yu1SMY/XTDM=
+pgregory.net/rapid v1.1.0 h1:CMa0sjHSru3puNx+J0MIAuiiEV4N0qj8/cMWGBBCsjw=
+pgregory.net/rapid v1.1.0/go.mod h1:PY5XlDGj0+V1FCq0o192FdRhpKHGTRIWBgqjDBTrq04=
 rsc.io/binaryregexp v0.2.0/go.mod h1:qTv7/COck+e2FymRvadv62gMdZztPaShugOCi3I+8D8=
 rsc.io/quote/v3 v3.1.0/go.mod h1:yEA65RcK8LyAZtP9Kv3t0HmxON59tX3rD+tICJqUlj0=
 rsc.io/sampler v1.3.0/go.mod h1:T1hPZKmBbMNahiBKFy5HrXp6adAjACjK9JXDnKaTXpA=