multi: accept memo note when opening channel

channeldb/channel.go

@@ -220,6 +220,10 @@ const (
 	// A tlv type definition used to serialize and deserialize the
 	// confirmed ShortChannelID for a zero-conf channel.
 	realScidType tlv.Type = 4
+
+	// A tlv type definition used to serialize and deserialize the
+	// Memo for the channel channel.
+	channelMemoType tlv.Type = 5
 )
 
 // indexStatus is an enum-like type that describes what state the
@@ -818,6 +822,10 @@ type OpenChannel struct {
 	// default ShortChannelID. This is only set for zero-conf channels.
 	confirmedScid lnwire.ShortChannelID
 
+	// Memo is any arbitrary information we wish to store locally about the
+	// channel that will be useful to our future selves.
+	Memo []byte
+
 	// TODO(roasbeef): eww
 	Db *ChannelStateDB
 
@@ -3642,6 +3650,7 @@ func putChanInfo(chanBucket kvdb.RwBucket, channel *OpenChannel) error {
 			initialRemoteBalanceType, &remoteBalance,
 		),
 		MakeScidRecord(realScidType, &channel.confirmedScid),
+		tlv.MakePrimitiveRecord(channelMemoType, &channel.Memo),
 	)
 	if err != nil {
 		return err
@@ -3839,10 +3848,11 @@ func fetchChanInfo(chanBucket kvdb.RBucket, channel *OpenChannel) error {
 		}
 	}
 
-	// Create balance fields in uint64.
+	// Create balance fields in uint64, and Memo field as byte slice.
 	var (
 		localBalance  uint64
 		remoteBalance uint64
+		memo          []byte
 	)
 
 	// Create the tlv stream.
@@ -3859,6 +3869,7 @@ func fetchChanInfo(chanBucket kvdb.RBucket, channel *OpenChannel) error {
 			initialRemoteBalanceType, &remoteBalance,
 		),
 		MakeScidRecord(realScidType, &channel.confirmedScid),
+		tlv.MakePrimitiveRecord(channelMemoType, &memo),
 	)
 	if err != nil {
 		return err
@@ -3872,6 +3883,11 @@ func fetchChanInfo(chanBucket kvdb.RBucket, channel *OpenChannel) error {
 	channel.InitialLocalBalance = lnwire.MilliSatoshi(localBalance)
 	channel.InitialRemoteBalance = lnwire.MilliSatoshi(remoteBalance)
 
+	// Attach the memo field if non-empty.
+	if len(memo) > 0 {
+		channel.Memo = memo
+	}
+
 	channel.Packager = NewChannelPackager(channel.ShortChannelID)
 
 	// Finally, read the optional shutdown scripts.

cmd/lncli/cmd_open_channel.go

@@ -93,7 +93,12 @@ var openChannelCommand = cli.Command{
 
 	One can manually set the fee to be used for the funding transaction via
 	either the --conf_target or --sat_per_vbyte arguments. This is
-	optional.`,
+	optional.
+
+	One can also specify a short string memo to record some useful
+	information about the channel using the --memo argument. This is stored
+	locally only, and is purely for reference. It has no bearing on the
+	channel's operation. Max allowed length is 500 characters.`,
 	ArgsUsage: "node-key local-amt push-amt",
 	Flags: []cli.Flag{
 		cli.StringFlag{
@@ -257,6 +262,14 @@ var openChannelCommand = cli.Command{
 				"payment. If not specified, a default of 1% " +
 				"of the channel capacity will be used.",
 		},
+		cli.StringFlag{
+			Name: "memo",
+			Usage: `(optional) a note-to-self containing some useful
+				information about the channel. This is stored
+				locally only, and is purely for reference. It
+				has no bearing on the channel's operation. Max
+				allowed length is 500 characters`,
+		},
 	},
 	Action: actionDecorator(openChannel),
 }
@@ -300,6 +313,7 @@ func openChannel(ctx *cli.Context) error {
 		ScidAlias:                  ctx.Bool("scid_alias"),
 		RemoteChanReserveSat:       ctx.Uint64("remote_reserve_sats"),
 		FundMax:                    ctx.Bool("fundmax"),
+		Memo:                       ctx.String("memo"),
 	}
 
 	switch {

docs/release-notes/release-notes-0.17.0.md

@@ -40,6 +40,11 @@ package](https://github.com/lightningnetwork/lnd/pull/7356)
   and `--protocol.custom-invoice` flags to set feature bits for various feature
   "sets", as defined in [BOLT 9](https://github.com/lightning/bolts/blob/master/09-features.md).
 
+* `OpenChannel` now accepts an [optional `memo`
+  argument](https://github.com/lightningnetwork/lnd/pull/7668) for specifying
+  a helpful note-to-self containing arbitrary useful information about the
+  channel.
+
 ## Misc
 
 * [Generate default macaroons

funding/manager.go

@@ -291,6 +291,10 @@ type InitFundingMsg struct {
 	// support explicit channel type negotiation.
 	ChannelType *lnwire.ChannelType
 
+	// Memo is any arbitrary information we wish to store locally about the
+	// channel that will be useful to our future selves.
+	Memo []byte
+
 	// Updates is a channel which updates to the opening status of the
 	// channel are sent on.
 	Updates chan *lnrpc.OpenStatusUpdate
@@ -4137,6 +4141,7 @@ func (f *Manager) handleInitFundingMsg(msg *InitFundingMsg) {
 		ZeroConf:          zeroConf,
 		OptionScidAlias:   scid,
 		ScidAliasFeature:  scidFeatureVal,
+		Memo:              msg.Memo,
 	}
 
 	reservation, err := f.cfg.Wallet.InitChannelReservation(req)

itest/lnd_open_channel_test.go

@@ -2,6 +2,7 @@ package itest
 
 import (
 	"fmt"
+	"strings"
 	"testing"
 
 	"github.com/btcsuite/btcd/btcjson"
@@ -373,16 +374,32 @@ func runBasicChannelCreationAndUpdates(ht *lntest.HarnessTest,
 	aliceChanSub := alice.RPC.SubscribeChannelEvents()
 
 	// Open the channels between Alice and Bob, asserting that the channels
-	// have been properly opened on-chain.
+	// have been properly opened on-chain. We also attach the optional Memo
+	// argument to one of the channels so we can test that it can be
+	// retrieved correctly when querying the created channel.
 	chanPoints := make([]*lnrpc.ChannelPoint, numChannels)
+	openChannelParams := []lntest.OpenChannelParams{
+		{Amt: amount, Memo: "bob is a good peer"},
+		{Amt: amount},
+	}
 	for i := 0; i < numChannels; i++ {
 		chanPoints[i] = ht.OpenChannel(
-			alice, bob, lntest.OpenChannelParams{
-				Amt: amount,
-			},
+			alice, bob, openChannelParams[i],
 		)
 	}
 
+	// Alice should see the memo when retrieving the first channel.
+	channel := ht.QueryChannelByChanPoint(alice, chanPoints[0])
+	require.Equal(ht, "bob is a good peer", channel.Memo)
+
+	// Bob shouldn't see the memo since it's for Alice only.
+	channel = ht.QueryChannelByChanPoint(bob, chanPoints[0])
+	require.Empty(ht, channel.Memo, "Memo is not empty")
+
+	// The second channel doesn't have a memo.
+	channel = ht.QueryChannelByChanPoint(alice, chanPoints[1])
+	require.Empty(ht, channel.Memo, "Memo is not empty")
+
 	// Since each of the channels just became open, Bob and Alice should
 	// each receive an open and an active notification for each channel.
 	const numExpectedOpenUpdates = 3 * numChannels
@@ -445,6 +462,16 @@ func runBasicChannelCreationAndUpdates(ht *lntest.HarnessTest,
 		}
 	}
 
+	// If Bob now tries to open a channel with an invalid memo, reject it.
+	invalidMemo := strings.Repeat("a", 501)
+	params := lntest.OpenChannelParams{
+		Amt:  funding.MaxBtcFundingAmount,
+		Memo: invalidMemo,
+	}
+	expErr := fmt.Errorf("provided memo (%s) is of length 501, exceeds 500",
+		invalidMemo)
+	ht.OpenChannelAssertErr(bob, alice, params, expErr)
+
 	// verifyCloseUpdatesReceived is used to verify that Alice and Bob
 	// receive the correct channel updates in order.
 	const numExpectedCloseUpdates = 3 * numChannels