From c081b386d26aa6e838eed7cd5abad9911506ed72 Mon Sep 17 00:00:00 2001
From: Olaoluwa Osuntokun <laolu32@gmail.com>
Date: Thu, 30 Nov 2017 22:52:28 -0800
Subject: [PATCH] funding: when crafting our ChannelUpdate use the remote
 party's minHTLC

In this commit, we implement a recent spec change that require nodes to
advertise the minHTLC of the remote node within their ChannelUpdate. We
do this as it will be the remote node which carries the HTLC towards
us, therefore we should advertise *their* minHTLC value.
---
 fundingmanager.go | 41 +++++++++++++++++++++++++++--------------
 1 file changed, 27 insertions(+), 14 deletions(-)

diff --git a/fundingmanager.go b/fundingmanager.go
index d4192151..c1e7216f 100644
--- a/fundingmanager.go
+++ b/fundingmanager.go
@@ -1650,11 +1650,18 @@ func (f *fundingManager) sendChannelAnnouncement(completeChan *channeldb.OpenCha
 	fndgLog.Infof("Announcing ChannelPoint(%v), short_chan_id=%v",
 		&fundingPoint, spew.Sdump(shortChanID))
 
+	// We'll obtain their min HTLC as we'll use this value within our
+	// ChannelUpdate. We use this value isn't of ours, as the remote party
+	// will be the one that's carrying the HTLC towards us.
+	remoteMinHTLC := completeChan.RemoteChanCfg.MinHTLC
+
 	// Register the new link with the L3 routing manager so this new
 	// channel can be utilized during path finding.
 	err := f.announceChannel(f.cfg.IDKey, completeChan.IdentityPub,
 		completeChan.LocalChanCfg.MultiSigKey,
-		completeChan.RemoteChanCfg.MultiSigKey, *shortChanID, chanID)
+		completeChan.RemoteChanCfg.MultiSigKey, *shortChanID, chanID,
+		remoteMinHTLC,
+	)
 	if err != nil {
 		return fmt.Errorf("channel announcement failed: %v", err)
 	}
@@ -1853,8 +1860,8 @@ type chanAnnouncement struct {
 // channel.
 func (f *fundingManager) newChanAnnouncement(localPubKey, remotePubKey *btcec.PublicKey,
 	localFundingKey, remoteFundingKey *btcec.PublicKey,
-	shortChanID lnwire.ShortChannelID,
-	chanID lnwire.ChannelID) (*chanAnnouncement, error) {
+	shortChanID lnwire.ShortChannelID, chanID lnwire.ChannelID,
+	remoteMinHTLC lnwire.MilliSatoshi) (*chanAnnouncement, error) {
 
 	chainHash := *f.cfg.Wallet.Cfg.NetParams.GenesisHash
 
@@ -1871,7 +1878,7 @@ func (f *fundingManager) newChanAnnouncement(localPubKey, remotePubKey *btcec.Pu
 	// being updated within the ChannelUpdateAnnouncement announcement
 	// below. A value of zero means it's the edge of the "first" node and 1
 	// being the other node.
-	var chanFlags uint16
+	var chanFlags lnwire.ChanUpdateFlag
 
 	// The lexicographical ordering of the two identity public keys of the
 	// nodes indicates which of the nodes is "first". If our serialized
@@ -1900,14 +1907,18 @@ func (f *fundingManager) newChanAnnouncement(localPubKey, remotePubKey *btcec.Pu
 	}
 
 	chanUpdateAnn := &lnwire.ChannelUpdate{
-		ShortChannelID:  shortChanID,
-		ChainHash:       chainHash,
-		Timestamp:       uint32(time.Now().Unix()),
-		Flags:           chanFlags,
-		TimeLockDelta:   uint16(f.cfg.DefaultRoutingPolicy.TimeLockDelta),
-		HtlcMinimumMsat: f.cfg.DefaultRoutingPolicy.MinHTLC,
-		BaseFee:         uint32(f.cfg.DefaultRoutingPolicy.BaseFee),
-		FeeRate:         uint32(f.cfg.DefaultRoutingPolicy.FeeRate),
+		ShortChannelID: shortChanID,
+		ChainHash:      chainHash,
+		Timestamp:      uint32(time.Now().Unix()),
+		Flags:          chanFlags,
+		TimeLockDelta:  uint16(f.cfg.DefaultRoutingPolicy.TimeLockDelta),
+
+		// We use the *remote* party's HtlcMinimumMsat, as they'll be
+		// the ones carrying the HTLC routed *towards* us.
+		HtlcMinimumMsat: remoteMinHTLC,
+
+		BaseFee: uint32(f.cfg.DefaultRoutingPolicy.BaseFee),
+		FeeRate: uint32(f.cfg.DefaultRoutingPolicy.FeeRate),
 	}
 
 	// With the channel update announcement constructed, we'll generate a
@@ -1972,14 +1983,16 @@ func (f *fundingManager) newChanAnnouncement(localPubKey, remotePubKey *btcec.Pu
 // finish, either successfully or with an error.
 func (f *fundingManager) announceChannel(localIDKey, remoteIDKey, localFundingKey,
 	remoteFundingKey *btcec.PublicKey, shortChanID lnwire.ShortChannelID,
-	chanID lnwire.ChannelID) error {
+	chanID lnwire.ChannelID, remoteMinHTLC lnwire.MilliSatoshi) error {
 
 	// First, we'll create the batch of announcements to be sent upon
 	// initial channel creation. This includes the channel announcement
 	// itself, the channel update announcement, and our half of the channel
 	// proof needed to fully authenticate the channel.
 	ann, err := f.newChanAnnouncement(localIDKey, remoteIDKey,
-		localFundingKey, remoteFundingKey, shortChanID, chanID)
+		localFundingKey, remoteFundingKey, shortChanID, chanID,
+		remoteMinHTLC,
+	)
 	if err != nil {
 		fndgLog.Errorf("can't generate channel announcement: %v", err)
 		return err