watchtower/multi: switch over to wtpolicy

migrate to using wtpolicy.Policy in wtwire messages and wtserver

watchtower/blob/justice_kit.go

@@ -17,12 +17,6 @@ import (
 )
 
 const (
-	// MinVersion is the minimum blob version supported by this package.
-	MinVersion = 0
-
-	// MaxVersion is the maximumm blob version supported by this package.
-	MaxVersion = 0
-
 	// NonceSize is the length of a chacha20poly1305 nonce, 24 bytes.
 	NonceSize = chacha20poly1305.NonceSizeX
 
@@ -53,14 +47,14 @@ const (
 //   nonce:                24 bytes
 //   enciphered plaintext:  n bytes
 //   MAC:                  16 bytes
-func Size(ver uint16) int {
+func Size(blobType Type) int {
-	return NonceSize + PlaintextSize(ver) + CiphertextExpansion
+	return NonceSize + PlaintextSize(blobType) + CiphertextExpansion
 }
 
 // PlaintextSize returns the size of the encoded-but-unencrypted blob in bytes.
-func PlaintextSize(ver uint16) int {
+func PlaintextSize(blobType Type) int {
-	switch ver {
+	switch {
-	case 0:
+	case blobType.Has(FlagCommitOutputs):
 		return V0PlaintextSize
 	default:
 		return 0
@@ -71,9 +65,9 @@ var (
 	// byteOrder specifies a big-endian encoding of all integer values.
 	byteOrder = binary.BigEndian
 
-	// ErrUnknownBlobVersion signals that we don't understand the requested
+	// ErrUnknownBlobType signals that we don't understand the requested
 	// blob encoding scheme.
-	ErrUnknownBlobVersion = errors.New("unknown blob version")
+	ErrUnknownBlobType = errors.New("unknown blob type")
 
 	// ErrCiphertextTooSmall is a decryption error signaling that the
 	// ciphertext is smaller than the ciphertext expansion factor.
@@ -229,7 +223,7 @@ func (b *JusticeKit) CommitToRemoteWitnessStack() ([][]byte, error) {
 //
 // NOTE: It is the caller's responsibility to ensure that this method is only
 // called once for a given (nonce, key) pair.
-func (b *JusticeKit) Encrypt(key []byte, version uint16) ([]byte, error) {
+func (b *JusticeKit) Encrypt(key []byte, blobType Type) ([]byte, error) {
 	// Fail if the nonce is not 32-bytes.
 	if len(key) != KeySize {
 		return nil, ErrKeySize
@@ -238,7 +232,7 @@ func (b *JusticeKit) Encrypt(key []byte, version uint16) ([]byte, error) {
 	// Encode the plaintext using the provided version, to obtain the
 	// plaintext bytes.
 	var ptxtBuf bytes.Buffer
-	err := b.encode(&ptxtBuf, version)
+	err := b.encode(&ptxtBuf, blobType)
 	if err != nil {
 		return nil, err
 	}
@@ -252,7 +246,7 @@ func (b *JusticeKit) Encrypt(key []byte, version uint16) ([]byte, error) {
 	// Allocate the ciphertext, which will contain the nonce, encrypted
 	// plaintext and MAC.
 	plaintext := ptxtBuf.Bytes()
-	ciphertext := make([]byte, Size(version))
+	ciphertext := make([]byte, Size(blobType))
 
 	// Generate a random  24-byte nonce in the ciphertext's prefix.
 	nonce := ciphertext[:NonceSize]
@@ -270,7 +264,7 @@ func (b *JusticeKit) Encrypt(key []byte, version uint16) ([]byte, error) {
 // Decrypt unenciphers a blob of justice by decrypting the ciphertext using
 // chacha20poly1305 with the chosen (nonce, key) pair. The internal plaintext is
 // then deserialized using the given encoding version.
-func Decrypt(key, ciphertext []byte, version uint16) (*JusticeKit, error) {
+func Decrypt(key, ciphertext []byte, blobType Type) (*JusticeKit, error) {
 	switch {
 
 	// Fail if the blob's overall length is less than required for the nonce
@@ -305,7 +299,7 @@ func Decrypt(key, ciphertext []byte, version uint16) (*JusticeKit, error) {
 	// If decryption succeeded, we will then decode the plaintext bytes
 	// using the specified blob version.
 	boj := &JusticeKit{}
-	err = boj.decode(bytes.NewReader(plaintext), version)
+	err = boj.decode(bytes.NewReader(plaintext), blobType)
 	if err != nil {
 		return nil, err
 	}
@@ -315,23 +309,23 @@ func Decrypt(key, ciphertext []byte, version uint16) (*JusticeKit, error) {
 
 // encode serializes the JusticeKit according to the version, returning an
 // error if the version is unknown.
-func (b *JusticeKit) encode(w io.Writer, ver uint16) error {
+func (b *JusticeKit) encode(w io.Writer, blobType Type) error {
-	switch ver {
+	switch {
-	case 0:
+	case blobType.Has(FlagCommitOutputs):
 		return b.encodeV0(w)
 	default:
-		return ErrUnknownBlobVersion
+		return ErrUnknownBlobType
 	}
 }
 
 // decode deserializes the JusticeKit according to the version, returning an
 // error if the version is unknown.
-func (b *JusticeKit) decode(r io.Reader, ver uint16) error {
+func (b *JusticeKit) decode(r io.Reader, blobType Type) error {
-	switch ver {
+	switch {
-	case 0:
+	case blobType.Has(FlagCommitOutputs):
 		return b.decodeV0(r)
 	default:
-		return ErrUnknownBlobVersion
+		return ErrUnknownBlobType
 	}
 }
 

watchtower/blob/justice_kit_test.go

@@ -38,8 +38,8 @@ func makeAddr(size int) []byte {
 
 type descriptorTest struct {
 	name                 string
-	encVersion           uint16
+	encVersion           blob.Type
-	decVersion           uint16
+	decVersion           blob.Type
 	sweepAddr            []byte
 	revPubKey            blob.PubKey
 	delayPubKey          blob.PubKey
@@ -52,11 +52,15 @@ type descriptorTest struct {
 	decErr               error
 }
 
+var rewardAndCommitType = blob.TypeFromFlags(
+	blob.FlagReward, blob.FlagCommitOutputs,
+)
+
 var descriptorTests = []descriptorTest{
 	{
 		name:             "to-local only",
-		encVersion:       0,
+		encVersion:       blob.TypeDefault,
-		decVersion:       0,
+		decVersion:       blob.TypeDefault,
 		sweepAddr:        makeAddr(22),
 		revPubKey:        makePubKey(0),
 		delayPubKey:      makePubKey(1),
@@ -65,8 +69,8 @@ var descriptorTests = []descriptorTest{
 	},
 	{
 		name:                 "to-local and p2wkh",
-		encVersion:           0,
+		encVersion:           rewardAndCommitType,
-		decVersion:           0,
+		decVersion:           rewardAndCommitType,
 		sweepAddr:            makeAddr(22),
 		revPubKey:            makePubKey(0),
 		delayPubKey:          makePubKey(1),
@@ -78,30 +82,30 @@ var descriptorTests = []descriptorTest{
 	},
 	{
 		name:             "unknown encrypt version",
-		encVersion:       1,
+		encVersion:       0,
-		decVersion:       0,
+		decVersion:       blob.TypeDefault,
 		sweepAddr:        makeAddr(34),
 		revPubKey:        makePubKey(0),
 		delayPubKey:      makePubKey(1),
 		csvDelay:         144,
 		commitToLocalSig: makeSig(1),
-		encErr:           blob.ErrUnknownBlobVersion,
+		encErr:           blob.ErrUnknownBlobType,
 	},
 	{
 		name:             "unknown decrypt version",
-		encVersion:       0,
+		encVersion:       blob.TypeDefault,
-		decVersion:       1,
+		decVersion:       0,
 		sweepAddr:        makeAddr(34),
 		revPubKey:        makePubKey(0),
 		delayPubKey:      makePubKey(1),
 		csvDelay:         144,
 		commitToLocalSig: makeSig(1),
-		decErr:           blob.ErrUnknownBlobVersion,
+		decErr:           blob.ErrUnknownBlobType,
 	},
 	{
 		name:             "sweep addr length zero",
-		encVersion:       0,
+		encVersion:       blob.TypeDefault,
-		decVersion:       0,
+		decVersion:       blob.TypeDefault,
 		sweepAddr:        makeAddr(0),
 		revPubKey:        makePubKey(0),
 		delayPubKey:      makePubKey(1),
@@ -110,8 +114,8 @@ var descriptorTests = []descriptorTest{
 	},
 	{
 		name:             "sweep addr max size",
-		encVersion:       0,
+		encVersion:       blob.TypeDefault,
-		decVersion:       0,
+		decVersion:       blob.TypeDefault,
 		sweepAddr:        makeAddr(blob.MaxSweepAddrSize),
 		revPubKey:        makePubKey(0),
 		delayPubKey:      makePubKey(1),
@@ -120,8 +124,8 @@ var descriptorTests = []descriptorTest{
 	},
 	{
 		name:             "sweep addr too long",
-		encVersion:       0,
+		encVersion:       blob.TypeDefault,
-		decVersion:       0,
+		decVersion:       blob.TypeDefault,
 		sweepAddr:        makeAddr(blob.MaxSweepAddrSize + 1),
 		revPubKey:        makePubKey(0),
 		delayPubKey:      makePubKey(1),

watchtower/lookout/justice_descriptor_test.go

@@ -19,6 +19,7 @@ import (
 	"github.com/lightningnetwork/lnd/watchtower/blob"
 	"github.com/lightningnetwork/lnd/watchtower/lookout"
 	"github.com/lightningnetwork/lnd/watchtower/wtdb"
+	"github.com/lightningnetwork/lnd/watchtower/wtpolicy"
 )
 
 const csvDelay uint32 = 144
@@ -170,8 +171,10 @@ func TestJusticeDescriptor(t *testing.T) {
 	// parameters that should be used in constructing the justice
 	// transaction.
 	sessionInfo := &wtdb.SessionInfo{
-		SweepFeeRate:  2000,
+		Policy: wtpolicy.Policy{
-		RewardRate:    900000,
+			SweepFeeRate: 2000,
+			RewardRate:   900000,
+		},
 		RewardAddress: makeAddrSlice(22),
 	}
 

watchtower/lookout/lookout.go

@@ -210,7 +210,7 @@ func (l *Lookout) processEpoch(epoch *chainntnfs.BlockEpoch,
 		// sweep the breached commitment outputs.
 		justiceKit, err := blob.Decrypt(
 			commitTxID[:], match.EncryptedBlob,
-			match.SessionInfo.Version,
+			match.SessionInfo.Policy.BlobType,
 		)
 		if err != nil {
 			// If the decryption fails, this implies either that the

watchtower/lookout/lookout_test.go

@@ -15,6 +15,7 @@ import (
 	"github.com/lightningnetwork/lnd/watchtower/blob"
 	"github.com/lightningnetwork/lnd/watchtower/lookout"
 	"github.com/lightningnetwork/lnd/watchtower/wtdb"
+	"github.com/lightningnetwork/lnd/watchtower/wtpolicy"
 )
 
 type mockPunisher struct {
@@ -86,15 +87,25 @@ func TestLookoutBreachMatching(t *testing.T) {
 		t.Fatalf("unable to start watcher: %v", err)
 	}
 
+	rewardAndCommitType := blob.TypeFromFlags(
+		blob.FlagReward, blob.FlagCommitOutputs,
+	)
+
 	// Create two sessions, representing two distinct clients.
 	sessionInfo1 := &wtdb.SessionInfo{
-		ID:            makeArray33(1),
+		ID: makeArray33(1),
-		MaxUpdates:    10,
+		Policy: wtpolicy.Policy{
+			BlobType:   rewardAndCommitType,
+			MaxUpdates: 10,
+		},
 		RewardAddress: makeAddrSlice(22),
 	}
 	sessionInfo2 := &wtdb.SessionInfo{
-		ID:            makeArray33(2),
+		ID: makeArray33(2),
-		MaxUpdates:    10,
+		Policy: wtpolicy.Policy{
+			BlobType:   rewardAndCommitType,
+			MaxUpdates: 10,
+		},
 		RewardAddress: makeAddrSlice(22),
 	}
 
@@ -137,13 +148,13 @@ func TestLookoutBreachMatching(t *testing.T) {
 	}
 
 	// Encrypt the first justice kit under the txid of the first txn.
-	encBlob1, err := blob1.Encrypt(hash1[:], 0)
+	encBlob1, err := blob1.Encrypt(hash1[:], blob.FlagCommitOutputs.Type())
 	if err != nil {
 		t.Fatalf("unable to encrypt sweep detail 1: %v", err)
 	}
 
 	// Encrypt the second justice kit under the txid of the second txn.
-	encBlob2, err := blob2.Encrypt(hash2[:], 0)
+	encBlob2, err := blob2.Encrypt(hash2[:], blob.FlagCommitOutputs.Type())
 	if err != nil {
 		t.Fatalf("unable to encrypt sweep detail 2: %v", err)
 	}

watchtower/wtdb/session_info.go

@@ -4,7 +4,7 @@ import (
 	"errors"
 
 	"github.com/btcsuite/btcutil"
-	"github.com/lightningnetwork/lnd/lnwallet"
+	"github.com/lightningnetwork/lnd/watchtower/wtpolicy"
 )
 
 var (
@@ -49,12 +49,8 @@ type SessionInfo struct {
 	// ID is the remote public key of the watchtower client.
 	ID SessionID
 
-	// Version specifies the plaintext blob encoding of all state updates.
+	// Policy holds the negotiated session parameters.
-	Version uint16
+	Policy wtpolicy.Policy
-
-	// MaxUpdates is the total number of updates the client can send for
-	// this session.
-	MaxUpdates uint16
 
 	// LastApplied the sequence number of the last successful state update.
 	LastApplied uint16
@@ -62,14 +58,6 @@ type SessionInfo struct {
 	// ClientLastApplied the last last-applied the client has echoed back.
 	ClientLastApplied uint16
 
-	// RewardRate the fraction of the swept amount that goes to the tower,
-	// expressed in millionths of the swept balance.
-	RewardRate uint32
-
-	// SweepFeeRate is the agreed upon fee rate used to sign any sweep
-	// transactions.
-	SweepFeeRate lnwallet.SatPerKWeight
-
 	// RewardAddress the address that the tower's reward will be deposited
 	// to if a sweep transaction confirms.
 	RewardAddress []byte
@@ -96,7 +84,7 @@ func (s *SessionInfo) AcceptUpdateSequence(seqNum, lastApplied uint16) error {
 		return ErrLastAppliedReversion
 
 	// Client update exceeds capacity of session.
-	case seqNum > s.MaxUpdates:
+	case seqNum > s.Policy.MaxUpdates:
 		return ErrSessionConsumed
 
 	// Client update does not match our expected next seqnum.
@@ -117,7 +105,7 @@ func (s *SessionInfo) AcceptUpdateSequence(seqNum, lastApplied uint16) error {
 func (s *SessionInfo) ComputeSweepOutputs(totalAmt btcutil.Amount,
 	txVSize int64) (btcutil.Amount, btcutil.Amount, error) {
 
-	txFee := s.SweepFeeRate.FeeForWeight(txVSize)
+	txFee := s.Policy.SweepFeeRate.FeeForWeight(txVSize)
 	if txFee > totalAmt {
 		return 0, 0, ErrFeeExceedsInputs
 	}
@@ -126,7 +114,8 @@ func (s *SessionInfo) ComputeSweepOutputs(totalAmt btcutil.Amount,
 
 	// Apply the reward rate to the remaining total, specified in millionths
 	// of the available balance.
-	rewardAmt := (totalAmt*btcutil.Amount(s.RewardRate) + 999999) / 1000000
+	rewardRate := btcutil.Amount(s.Policy.RewardRate)
+	rewardAmt := (totalAmt*rewardRate + 999999) / 1000000
 	sweepAmt := totalAmt - rewardAmt
 
 	// TODO(conner): check dustiness

watchtower/wtserver/server.go

@@ -14,6 +14,7 @@ import (
 	"github.com/btcsuite/btcutil"
 	"github.com/lightningnetwork/lnd/lnwire"
 	"github.com/lightningnetwork/lnd/watchtower/wtdb"
+	"github.com/lightningnetwork/lnd/watchtower/wtpolicy"
 	"github.com/lightningnetwork/lnd/watchtower/wtwire"
 )
 
@@ -246,14 +247,14 @@ func (s *Server) handleClient(peer Peer) {
 
 			log.Infof("Received CreateSession from %s, "+
 				"version=%d nupdates=%d rewardrate=%d "+
-				"sweepfeerate=%d", id, msg.BlobVersion,
+				"sweepfeerate=%d", id, msg.BlobType,
 				msg.MaxUpdates, msg.RewardRate,
 				msg.SweepFeeRate)
 
 			// Attempt to open a new session for this client.
 			err := s.handleCreateSession(peer, &id, msg)
 			if err != nil {
-				log.Errorf("unable to handle CreateSession "+
+				log.Errorf("Unable to handle CreateSession "+
 					"from %s: %v", id, err)
 			}
 
@@ -327,7 +328,7 @@ func (s *Server) handleInit(localInit, remoteInit *wtwire.Init) error {
 // session info is known about the session id. If an existing session is found,
 // the reward address is returned in case the client lost our reply.
 func (s *Server) handleCreateSession(peer Peer, id *wtdb.SessionID,
-	init *wtwire.CreateSession) error {
+	req *wtwire.CreateSession) error {
 
 	// TODO(conner): validate accept against policy
 
@@ -375,11 +376,13 @@ func (s *Server) handleCreateSession(peer Peer, id *wtdb.SessionID,
 	// address, and session id.
 	info := wtdb.SessionInfo{
 		ID:            *id,
-		Version:       init.BlobVersion,
-		MaxUpdates:    init.MaxUpdates,
-		RewardRate:    init.RewardRate,
-		SweepFeeRate:  init.SweepFeeRate,
 		RewardAddress: rewardAddrBytes,
+		Policy: wtpolicy.Policy{
+			BlobType:     req.BlobType,
+			MaxUpdates:   req.MaxUpdates,
+			RewardRate:   req.RewardRate,
+			SweepFeeRate: req.SweepFeeRate,
+		},
 	}
 
 	// Insert the session info into the watchtower's database. If

watchtower/wtserver/server_test.go

@@ -12,6 +12,7 @@ import (
 	"github.com/btcsuite/btcd/chaincfg"
 	"github.com/btcsuite/btcutil"
 	"github.com/lightningnetwork/lnd/lnwire"
+	"github.com/lightningnetwork/lnd/watchtower/blob"
 	"github.com/lightningnetwork/lnd/watchtower/wtdb"
 	"github.com/lightningnetwork/lnd/watchtower/wtserver"
 	"github.com/lightningnetwork/lnd/watchtower/wtwire"
@@ -155,7 +156,7 @@ var createSessionTests = []createSessionTestCase{
 			lnwire.NewRawFeatureVector(),
 		),
 		createMsg: &wtwire.CreateSession{
-			BlobVersion:  0,
+			BlobType:     blob.TypeDefault,
 			MaxUpdates:   1000,
 			RewardRate:   0,
 			SweepFeeRate: 1,
@@ -258,7 +259,7 @@ var stateUpdateTests = []stateUpdateTestCase{
 			GlobalFeatures: lnwire.NewRawFeatureVector(),
 		}},
 		createMsg: &wtwire.CreateSession{
-			BlobVersion:  0,
+			BlobType:     blob.TypeDefault,
 			MaxUpdates:   3,
 			RewardRate:   0,
 			SweepFeeRate: 1,
@@ -287,7 +288,7 @@ var stateUpdateTests = []stateUpdateTestCase{
 			GlobalFeatures: lnwire.NewRawFeatureVector(),
 		}},
 		createMsg: &wtwire.CreateSession{
-			BlobVersion:  0,
+			BlobType:     blob.TypeDefault,
 			MaxUpdates:   4,
 			RewardRate:   0,
 			SweepFeeRate: 1,
@@ -310,7 +311,7 @@ var stateUpdateTests = []stateUpdateTestCase{
 			GlobalFeatures: lnwire.NewRawFeatureVector(),
 		}},
 		createMsg: &wtwire.CreateSession{
-			BlobVersion:  0,
+			BlobType:     blob.TypeDefault,
 			MaxUpdates:   4,
 			RewardRate:   0,
 			SweepFeeRate: 1,
@@ -337,7 +338,7 @@ var stateUpdateTests = []stateUpdateTestCase{
 			GlobalFeatures: lnwire.NewRawFeatureVector(),
 		}},
 		createMsg: &wtwire.CreateSession{
-			BlobVersion:  0,
+			BlobType:     blob.TypeDefault,
 			MaxUpdates:   4,
 			RewardRate:   0,
 			SweepFeeRate: 1,
@@ -364,7 +365,7 @@ var stateUpdateTests = []stateUpdateTestCase{
 			GlobalFeatures: lnwire.NewRawFeatureVector(),
 		}},
 		createMsg: &wtwire.CreateSession{
-			BlobVersion:  0,
+			BlobType:     blob.TypeDefault,
 			MaxUpdates:   4,
 			RewardRate:   0,
 			SweepFeeRate: 1,
@@ -393,7 +394,7 @@ var stateUpdateTests = []stateUpdateTestCase{
 			GlobalFeatures: lnwire.NewRawFeatureVector(),
 		}},
 		createMsg: &wtwire.CreateSession{
-			BlobVersion:  0,
+			BlobType:     blob.TypeDefault,
 			MaxUpdates:   4,
 			RewardRate:   0,
 			SweepFeeRate: 1,
@@ -421,7 +422,7 @@ var stateUpdateTests = []stateUpdateTestCase{
 			GlobalFeatures: lnwire.NewRawFeatureVector(),
 		}},
 		createMsg: &wtwire.CreateSession{
-			BlobVersion:  0,
+			BlobType:     blob.TypeDefault,
 			MaxUpdates:   3,
 			RewardRate:   0,
 			SweepFeeRate: 1,
@@ -450,7 +451,7 @@ var stateUpdateTests = []stateUpdateTestCase{
 			GlobalFeatures: lnwire.NewRawFeatureVector(),
 		}},
 		createMsg: &wtwire.CreateSession{
-			BlobVersion:  0,
+			BlobType:     blob.TypeDefault,
 			MaxUpdates:   3,
 			RewardRate:   0,
 			SweepFeeRate: 1,

watchtower/wtwire/create_session.go

@@ -4,6 +4,7 @@ import (
 	"io"
 
 	"github.com/lightningnetwork/lnd/lnwallet"
+	"github.com/lightningnetwork/lnd/watchtower/blob"
 )
 
 // CreateSession is sent from a client to tower when to negotiate a session, which
@@ -11,9 +12,9 @@ import (
 // An update is consumed by uploading an encrypted blob that contains
 // information required to sweep a revoked commitment transaction.
 type CreateSession struct {
-	// BlobVersion specifies the blob format that must be used by all
+	// BlobType specifies the blob format that must be used by all updates sent
-	// updates sent under the session key used to negotiate this session.
+	// under the session key used to negotiate this session.
-	BlobVersion uint16
+	BlobType blob.Type
 
 	// MaxUpdates is the maximum number of updates the watchtower will honor
 	// for this session.
@@ -41,7 +42,7 @@ var _ Message = (*CreateSession)(nil)
 // This is part of the wtwire.Message interface.
 func (m *CreateSession) Decode(r io.Reader, pver uint32) error {
 	return ReadElements(r,
-		&m.BlobVersion,
+		&m.BlobType,
 		&m.MaxUpdates,
 		&m.RewardRate,
 		&m.SweepFeeRate,
@@ -54,7 +55,7 @@ func (m *CreateSession) Decode(r io.Reader, pver uint32) error {
 // This is part of the wtwire.Message interface.
 func (m *CreateSession) Encode(w io.Writer, pver uint32) error {
 	return WriteElements(w,
-		m.BlobVersion,
+		m.BlobType,
 		m.MaxUpdates,
 		m.RewardRate,
 		m.SweepFeeRate,

watchtower/wtwire/wtwire.go

@@ -8,6 +8,7 @@ import (
 	"github.com/btcsuite/btcd/btcec"
 	"github.com/btcsuite/btcd/wire"
 	"github.com/lightningnetwork/lnd/lnwallet"
+	"github.com/lightningnetwork/lnd/watchtower/blob"
 )
 
 // WriteElement is a one-stop shop to write the big endian representation of
@@ -30,6 +31,13 @@ func WriteElement(w io.Writer, element interface{}) error {
 			return err
 		}
 
+	case blob.Type:
+		var b [2]byte
+		binary.BigEndian.PutUint16(b[:], uint16(e))
+		if _, err := w.Write(b[:]); err != nil {
+			return err
+		}
+
 	case uint32:
 		var b [4]byte
 		binary.BigEndian.PutUint32(b[:], e)
@@ -127,6 +135,13 @@ func ReadElement(r io.Reader, element interface{}) error {
 		}
 		*e = binary.BigEndian.Uint16(b[:])
 
+	case *blob.Type:
+		var b [2]byte
+		if _, err := io.ReadFull(r, b[:]); err != nil {
+			return err
+		}
+		*e = blob.Type(binary.BigEndian.Uint16(b[:]))
+
 	case *uint32:
 		var b [4]byte
 		if _, err := io.ReadFull(r, b[:]); err != nil {