multi: break ChannelConstraints into two sub-structures

This commit breaks the ChannelConstraints structure into two
sub-structures that reflect the fundamental differences in how
these parameters are used. On its face it may not seem necessary,
however the distinction introduced here is relevant for how we
will be implementing the Dynamic Commitments proposal.

channeldb/channel.go

@@ -395,19 +395,11 @@ func (c ChannelType) IsTaproot() bool {
 	return c&SimpleTaprootFeatureBit == SimpleTaprootFeatureBit
 }
 
-// ChannelConstraints represents a set of constraints meant to allow a node to
-// limit their exposure, enact flow control and ensure that all HTLCs are
-// economically relevant. This struct will be mirrored for both sides of the
-// channel, as each side will enforce various constraints that MUST be adhered
-// to for the life time of the channel. The parameters for each of these
-// constraints are static for the duration of the channel, meaning the channel
-// must be torn down for them to change.
-type ChannelConstraints struct {
-	// DustLimit is the threshold (in satoshis) below which any outputs
-	// should be trimmed. When an output is trimmed, it isn't materialized
-	// as an actual output, but is instead burned to miner's fees.
-	DustLimit btcutil.Amount
-
+// ChannelStateBounds are the parameters from OpenChannel and AcceptChannel
+// that are responsible for providing bounds on the state space of the abstract
+// channel state. These values must be remembered for normal channel operation
+// but they do not impact how we compute the commitment transactions themselves.
+type ChannelStateBounds struct {
 	// ChanReserve is an absolute reservation on the channel for the
 	// owner of this set of constraints. This means that the current
 	// settled balance for this node CANNOT dip below the reservation
@@ -433,6 +425,19 @@ type ChannelConstraints struct {
 	// acted upon in the case of a unilateral channel closure or a contract
 	// breach.
 	MaxAcceptedHtlcs uint16
+}
+
+// CommitmentParams are the parameters from OpenChannel and
+// AcceptChannel that are required to render an abstract channel state to a
+// concrete commitment transaction. These values are necessary to (re)compute
+// the commitment transaction. We treat these differently than the state space
+// bounds because their history needs to be stored in order to properly handle
+// chain resolution.
+type CommitmentParams struct {
+	// DustLimit is the threshold (in satoshis) below which any outputs
+	// should be trimmed. When an output is trimmed, it isn't materialized
+	// as an actual output, but is instead burned to miner's fees.
+	DustLimit btcutil.Amount
 
 	// CsvDelay is the relative time lock delay expressed in blocks. Any
 	// settled outputs that pay to the owner of this channel configuration
@@ -448,12 +453,17 @@ type ChannelConstraints struct {
 // nature of HTLC's allotted, the keys to be used for delivery, and relative
 // time lock parameters.
 type ChannelConfig struct {
-	// ChannelConstraints is the set of constraints that must be upheld for
-	// the duration of the channel for the owner of this channel
+	// ChannelStateBounds is the set of constraints that must be
+	// upheld for the duration of the channel for the owner of this channel
 	// configuration. Constraints govern a number of flow control related
 	// parameters, also including the smallest HTLC that will be accepted
 	// by a participant.
-	ChannelConstraints
+	ChannelStateBounds
+
+	// CommitmentParams is an embedding of the parameters
+	// required to render an abstract channel state into a concrete
+	// commitment transaction.
+	CommitmentParams
 
 	// MultiSigKey is the key to be used within the 2-of-2 output script
 	// for the owner of this channel config.

channeldb/channel_test.go

@@ -235,15 +235,21 @@ func createTestChannelState(t *testing.T, cdb *ChannelStateDB) *OpenChannel {
 		}
 	}
 
+	localStateBounds := ChannelStateBounds{
+		MaxPendingAmount: lnwire.MilliSatoshi(rand.Int63()),
+		ChanReserve:      btcutil.Amount(rand.Int63()),
+		MinHTLC:          lnwire.MilliSatoshi(rand.Int63()),
+		MaxAcceptedHtlcs: uint16(rand.Int31()),
+	}
+
+	localRenderingParams := CommitmentParams{
+		DustLimit: btcutil.Amount(rand.Int63()),
+		CsvDelay:  uint16(rand.Int31()),
+	}
+
 	localCfg := ChannelConfig{
-		ChannelConstraints: ChannelConstraints{
-			DustLimit:        btcutil.Amount(rand.Int63()),
-			MaxPendingAmount: lnwire.MilliSatoshi(rand.Int63()),
-			ChanReserve:      btcutil.Amount(rand.Int63()),
-			MinHTLC:          lnwire.MilliSatoshi(rand.Int63()),
-			MaxAcceptedHtlcs: uint16(rand.Int31()),
-			CsvDelay:         uint16(rand.Int31()),
-		},
+		ChannelStateBounds: localStateBounds,
+		CommitmentParams:   localRenderingParams,
 		MultiSigKey: keychain.KeyDescriptor{
 			PubKey: privKey.PubKey(),
 		},
@@ -260,15 +266,22 @@ func createTestChannelState(t *testing.T, cdb *ChannelStateDB) *OpenChannel {
 			PubKey: privKey.PubKey(),
 		},
 	}
+
+	remoteStateBounds := ChannelStateBounds{
+		MaxPendingAmount: lnwire.MilliSatoshi(rand.Int63()),
+		ChanReserve:      btcutil.Amount(rand.Int63()),
+		MinHTLC:          lnwire.MilliSatoshi(rand.Int63()),
+		MaxAcceptedHtlcs: uint16(rand.Int31()),
+	}
+
+	remoteRenderingParams := CommitmentParams{
+		DustLimit: btcutil.Amount(rand.Int63()),
+		CsvDelay:  uint16(rand.Int31()),
+	}
+
 	remoteCfg := ChannelConfig{
-		ChannelConstraints: ChannelConstraints{
-			DustLimit:        btcutil.Amount(rand.Int63()),
-			MaxPendingAmount: lnwire.MilliSatoshi(rand.Int63()),
-			ChanReserve:      btcutil.Amount(rand.Int63()),
-			MinHTLC:          lnwire.MilliSatoshi(rand.Int63()),
-			MaxAcceptedHtlcs: uint16(rand.Int31()),
-			CsvDelay:         uint16(rand.Int31()),
-		},
+		ChannelStateBounds: remoteStateBounds,
+		CommitmentParams:   remoteRenderingParams,
 		MultiSigKey: keychain.KeyDescriptor{
 			PubKey: privKey.PubKey(),
 			KeyLocator: keychain.KeyLocator{

channeldb/db_test.go

@@ -292,6 +292,10 @@ func genRandomChannelShell() (*ChannelShell, error) {
 	}
 	shaChainProducer := shachain.NewRevocationProducer(*revRoot)
 
+	commitParams := CommitmentParams{
+		CsvDelay: uint16(rand.Int63()),
+	}
+
 	return &ChannelShell{
 		NodeAddrs: []net.Addr{&net.TCPAddr{
 			IP:   net.ParseIP("127.0.0.1"),
@@ -306,9 +310,7 @@ func genRandomChannelShell() (*ChannelShell, error) {
 			),
 			IdentityPub: pub,
 			LocalChanCfg: ChannelConfig{
-				ChannelConstraints: ChannelConstraints{
-					CsvDelay: uint16(rand.Int63()),
-				},
+				CommitmentParams: commitParams,
 				PaymentBasePoint: keychain.KeyDescriptor{
 					KeyLocator: keychain.KeyLocator{
 						Family: keychain.KeyFamily(rand.Int63()),