lnwire: convert the delivery addr in [Open+Accept]Channel to a TLV type in ExtraData

In this commit, we convert the delivery address in the open and accept
channel methods to be a TLV type. This works as an "empty" delivery
address is encoded using a two zero bytes (uint16 length zero), and a
tlv type of 0 is encoded in the same manner (byte for type, byte for
zero length). This change allows us to easily extend these messages in
the future, in a uniform manner.

When decoding the message we snip the bytes from the read TLV data.
Similarly, when encoding we concatenate the TLV record for the shutdown
script with the rest of the TLV data.

lnwire/accept_channel.go

@@ -1,6 +1,7 @@
 package lnwire
 
 import (
+	"fmt"
 	"io"
 
 	"github.com/btcsuite/btcd/btcec"
@@ -92,6 +93,17 @@ type AcceptChannel struct {
 	// and has a length prefix, so a zero will be written if it is not set
 	// and its length followed by the script will be written if it is set.
 	UpfrontShutdownScript DeliveryAddress
+
+	// ExtraData is the set of data that was appended to this message to
+	// fill out the full maximum transport message size. These fields can
+	// be used to specify optional data such as custom TLV fields.
+	//
+	// NOTE: Since the upfront shutdown script MUST be present (though can
+	// be zero-length) if any TLV data is available, the script will be
+	// extracted and removed from this blob when decoding. ExtraData will
+	// contain all TLV records _except_ the DeliveryAddress record in that
+	// case.
+	ExtraData ExtraOpaqueData
 }
 
 // A compile time check to ensure AcceptChannel implements the lnwire.Message
@@ -104,6 +116,15 @@ var _ Message = (*AcceptChannel)(nil)
 //
 // This is part of the lnwire.Message interface.
 func (a *AcceptChannel) Encode(w io.Writer, pver uint32) error {
+	// Since the upfront script is encoded as a TLV record, concatenate it
+	// with the ExtraData, and write them as one.
+	tlvRecords, err := packShutdownScript(
+		a.UpfrontShutdownScript, a.ExtraData,
+	)
+	if err != nil {
+		return err
+	}
+
 	return WriteElements(w,
 		a.PendingChannelID[:],
 		a.DustLimit,
@@ -119,7 +140,7 @@ func (a *AcceptChannel) Encode(w io.Writer, pver uint32) error {
 		a.DelayedPaymentPoint,
 		a.HtlcPoint,
 		a.FirstCommitmentPoint,
-		a.UpfrontShutdownScript,
+		tlvRecords,
 	)
 }
 
@@ -150,15 +171,82 @@ func (a *AcceptChannel) Decode(r io.Reader, pver uint32) error {
 		return err
 	}
 
-	// Check for the optional upfront shutdown script field. If it is not there,
-	// silence the EOF error.
-	err = ReadElement(r, &a.UpfrontShutdownScript)
-	if err != nil && err != io.EOF {
+	// For backwards compatibility, the optional extra data blob for
+	// AcceptChannel must contain an entry for the upfront shutdown script.
+	// We'll read it out and attempt to parse it.
+	var tlvRecords ExtraOpaqueData
+	if err := ReadElements(r, &tlvRecords); err != nil {
 		return err
 	}
+
+	a.UpfrontShutdownScript, a.ExtraData, err = parseShutdownScript(
+		tlvRecords,
+	)
+	if err != nil {
+		return err
+	}
+
 	return nil
 }
 
+// packShutdownScript takes an upfront shutdown script and an opaque data blob
+// and concatenates them.
+func packShutdownScript(addr DeliveryAddress, extraData ExtraOpaqueData) (
+	ExtraOpaqueData, error) {
+
+	// We'll always write the upfront shutdown script record, regardless of
+	// the script being empty.
+	var tlvRecords ExtraOpaqueData
+
+	// Pack it into a data blob as a TLV record.
+	err := tlvRecords.PackRecords(addr.NewRecord())
+	if err != nil {
+		return nil, fmt.Errorf("unable to pack upfront shutdown "+
+			"script as TLV record: %v", err)
+	}
+
+	// Concatenate the remaining blob with the shutdown script record.
+	tlvRecords = append(tlvRecords, extraData...)
+	return tlvRecords, nil
+}
+
+// parseShutdownScript reads and extract the upfront shutdown script from the
+// passe data blob. It returns the script, if any, and the remainder of the
+// data blob.
+//
+// This can be used to parse extra data for the OpenChannel and AcceptChannel
+// messages, where the shutdown script is mandatory if extra TLV data is
+// present.
+func parseShutdownScript(tlvRecords ExtraOpaqueData) (DeliveryAddress,
+	ExtraOpaqueData, error) {
+
+	// If no TLV data is present there can't be any script available.
+	if len(tlvRecords) == 0 {
+		return nil, tlvRecords, nil
+	}
+
+	// Otherwise the shutdown script MUST be present.
+	var addr DeliveryAddress
+	tlvs, err := tlvRecords.ExtractRecords(addr.NewRecord())
+	if err != nil {
+		return nil, nil, err
+	}
+
+	// Not among TLV records, this means the data was invalid.
+	if _, ok := tlvs[DeliveryAddrType]; !ok {
+		return nil, nil, fmt.Errorf("no shutdown script in non-empty " +
+			"data blob")
+	}
+
+	// Now that we have retrieved the address (which can be zero-length),
+	// we'll remove the bytes encoding it from the TLV data before
+	// returning it.
+	addrLen := len(addr)
+	tlvRecords = tlvRecords[addrLen+2:]
+
+	return addr, tlvRecords, nil
+}
+
 // MsgType returns the MessageType code which uniquely identifies this message
 // as an AcceptChannel on the wire.
 //
@@ -172,11 +260,5 @@ func (a *AcceptChannel) MsgType() MessageType {
 //
 // This is part of the lnwire.Message interface.
 func (a *AcceptChannel) MaxPayloadLength(uint32) uint32 {
-	// 32 + (8 * 4) + (4 * 1) + (2 * 2) + (33 * 6)
-	var length uint32 = 270 // base length
-
-	// Upfront shutdown script max length.
-	length += 2 + deliveryAddressMaxSize
-
-	return length
+	return MaxMsgBody
 }

lnwire/lnwire_test.go

@@ -376,6 +376,15 @@ func TestLightningWireProtocol(t *testing.T) {
 				req.UpfrontShutdownScript = []byte{}
 			}
 
+			// 1/2 chance how having more TLV data after the
+			// shutdown script.
+			if r.Intn(2) == 0 {
+				// TLV type 1 of length 2.
+				req.ExtraData = []byte{1, 2, 0xff, 0xff}
+			} else {
+				req.ExtraData = []byte{}
+			}
+
 			v[0] = reflect.ValueOf(req)
 		},
 		MsgAcceptChannel: func(v []reflect.Value, r *rand.Rand) {
@@ -436,6 +445,14 @@ func TestLightningWireProtocol(t *testing.T) {
 			} else {
 				req.UpfrontShutdownScript = []byte{}
 			}
+			// 1/2 chance how having more TLV data after the
+			// shutdown script.
+			if r.Intn(2) == 0 {
+				// TLV type 1 of length 2.
+				req.ExtraData = []byte{1, 2, 0xff, 0xff}
+			} else {
+				req.ExtraData = []byte{}
+			}
 
 			v[0] = reflect.ValueOf(req)
 		},

lnwire/open_channel.go

@@ -128,6 +128,17 @@ type OpenChannel struct {
 	// and has a length prefix, so a zero will be written if it is not set
 	// and its length followed by the script will be written if it is set.
 	UpfrontShutdownScript DeliveryAddress
+
+	// ExtraData is the set of data that was appended to this message to
+	// fill out the full maximum transport message size. These fields can
+	// be used to specify optional data such as custom TLV fields.
+	//
+	// NOTE: Since the upfront shutdown script MUST be present (though can
+	// be zero-length) if any TLV data is available, the script will be
+	// extracted and removed from this blob when decoding. ExtraData will
+	// contain all TLV records _except_ the DeliveryAddress record in that
+	// case.
+	ExtraData ExtraOpaqueData
 }
 
 // A compile time check to ensure OpenChannel implements the lnwire.Message
@@ -140,6 +151,15 @@ var _ Message = (*OpenChannel)(nil)
 //
 // This is part of the lnwire.Message interface.
 func (o *OpenChannel) Encode(w io.Writer, pver uint32) error {
+	// Since the upfront script is encoded as a TLV record, concatenate it
+	// with the ExtraData, and write them as one.
+	tlvRecords, err := packShutdownScript(
+		o.UpfrontShutdownScript, o.ExtraData,
+	)
+	if err != nil {
+		return err
+	}
+
 	return WriteElements(w,
 		o.ChainHash[:],
 		o.PendingChannelID[:],
@@ -159,7 +179,7 @@ func (o *OpenChannel) Encode(w io.Writer, pver uint32) error {
 		o.HtlcPoint,
 		o.FirstCommitmentPoint,
 		o.ChannelFlags,
-		o.UpfrontShutdownScript,
+		tlvRecords,
 	)
 }
 
@@ -169,7 +189,8 @@ func (o *OpenChannel) Encode(w io.Writer, pver uint32) error {
 //
 // This is part of the lnwire.Message interface.
 func (o *OpenChannel) Decode(r io.Reader, pver uint32) error {
-	if err := ReadElements(r,
+	// Read all the mandatory fields in the open message.
+	err := ReadElements(r,
 		o.ChainHash[:],
 		o.PendingChannelID[:],
 		&o.FundingAmount,
@@ -188,14 +209,23 @@ func (o *OpenChannel) Decode(r io.Reader, pver uint32) error {
 		&o.HtlcPoint,
 		&o.FirstCommitmentPoint,
 		&o.ChannelFlags,
-	); err != nil {
+	)
+	if err != nil {
 		return err
 	}
 
-	// Check for the optional upfront shutdown script field. If it is not there,
-	// silence the EOF error.
-	err := ReadElement(r, &o.UpfrontShutdownScript)
-	if err != nil && err != io.EOF {
+	// For backwards compatibility, the optional extra data blob for
+	// OpenChannel must contain an entry for the upfront shutdown script.
+	// We'll read it out and attempt to parse it.
+	var tlvRecords ExtraOpaqueData
+	if err := ReadElements(r, &tlvRecords); err != nil {
+		return err
+	}
+
+	o.UpfrontShutdownScript, o.ExtraData, err = parseShutdownScript(
+		tlvRecords,
+	)
+	if err != nil {
 		return err
 	}
 
@@ -215,11 +245,5 @@ func (o *OpenChannel) MsgType() MessageType {
 //
 // This is part of the lnwire.Message interface.
 func (o *OpenChannel) MaxPayloadLength(uint32) uint32 {
-	// (32 * 2) + (8 * 6) + (4 * 1) + (2 * 2) + (33 * 6) + 1
-	var length uint32 = 319 // base length
-
-	// Upfront shutdown script max length.
-	length += 2 + deliveryAddressMaxSize
-
-	return length
+	return MaxMsgBody
 }

lnwire/shutdown.go

@@ -22,20 +22,6 @@ type Shutdown struct {
 	ExtraData ExtraOpaqueData
 }
 
-// DeliveryAddress is used to communicate the address to which funds from a
-// closed channel should be sent. The address can be a p2wsh, p2pkh, p2sh or
-// p2wpkh.
-type DeliveryAddress []byte
-
-// deliveryAddressMaxSize is the maximum expected size in bytes of a
-// DeliveryAddress based on the types of scripts we know.
-// Following are the known scripts and their sizes in bytes.
-// - pay to witness script hash: 34
-// - pay to pubkey hash: 25
-// - pay to script hash: 22
-// - pay to witness pubkey hash: 22.
-const deliveryAddressMaxSize = 34
-
 // NewShutdown creates a new Shutdown message.
 func NewShutdown(cid ChannelID, addr DeliveryAddress) *Shutdown {
 	return &Shutdown{

lnwire/typed_delivery_addr.go

@@ -0,0 +1,41 @@
+package lnwire
+
+import (
+	"github.com/lightningnetwork/lnd/tlv"
+)
+
+const (
+	// DeliveryAddrType is the TLV record type for delivery addreses within
+	// the name space of the OpenChannel and AcceptChannel messages.
+	DeliveryAddrType = 0
+
+	// deliveryAddressMaxSize is the maximum expected size in bytes of a
+	// DeliveryAddress based on the types of scripts we know.
+	// Following are the known scripts and their sizes in bytes.
+	// - pay to witness script hash: 34
+	// - pay to pubkey hash: 25
+	// - pay to script hash: 22
+	// - pay to witness pubkey hash: 22.
+	deliveryAddressMaxSize = 34
+)
+
+// DeliveryAddress is used to communicate the address to which funds from a
+// closed channel should be sent. The address can be a p2wsh, p2pkh, p2sh or
+// p2wpkh.
+type DeliveryAddress []byte
+
+// NewRecord returns a TLV record that can be used to encode the delivery
+// address within the ExtraData TLV stream. This was intorudced in order to
+// allow the OpenChannel/AcceptChannel messages to properly be extended with
+// TLV types.
+func (d *DeliveryAddress) NewRecord() tlv.Record {
+	addrBytes := (*[]byte)(d)
+
+	return tlv.MakeDynamicRecord(
+		DeliveryAddrType, addrBytes,
+		func() uint64 {
+			return uint64(len(*addrBytes))
+		},
+		tlv.EVarBytes, tlv.DVarBytes,
+	)
+}

lnwire/typed_delivery_addr_test.go

@@ -0,0 +1,37 @@
+package lnwire
+
+import (
+	"bytes"
+	"testing"
+)
+
+// TestDeliveryAddressEncodeDecode tests that we're able to properly
+// encode and decode delivery addresses within TLV streams.
+func TestDeliveryAddressEncodeDecode(t *testing.T) {
+	t.Parallel()
+
+	addr := DeliveryAddress(
+		bytes.Repeat([]byte("a"), deliveryAddressMaxSize),
+	)
+
+	var extraData ExtraOpaqueData
+	err := extraData.PackRecords(addr.NewRecord())
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	var addr2 DeliveryAddress
+	tlvs, err := extraData.ExtractRecords(addr2.NewRecord())
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if _, ok := tlvs[DeliveryAddrType]; !ok {
+		t.Fatalf("DeliveryAddrType not found in records")
+	}
+
+	if !bytes.Equal(addr, addr2) {
+		t.Fatalf("addr mismatch: expected %x, got %x", addr[:],
+			addr2[:])
+	}
+}