channeldb: introduce ChannelConfig and ChannelConstraints

This commit introduces two new structs to the channeled package:
ChannelConfig and ChannelConstraints.

The ChannelConfig struct will eliminate many of the fields on the
OpenChannel struct (ours vs theirs), in favor of having a single config
for both sides (local and remote).

The ChannelConstraints struct will house the channel flow control and
HTLC policies for both sides. The fields of this struct will be used to
control the flow of HTLC’s within the channel. In the occasion that any
of these constraints are violated, either the connection, or the
channel entirely is to be failed.

channeldb/channel.go

@@ -123,6 +123,98 @@ const (
 	DualFunder = 1
 )
 
+// ChannelConstraints represents a set of constraints meant to allow a node to
+// limit their exposure, enact flow control and ensure that all HTLC's 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 is static for the duration of the channel, meaning the channel
+// must be teared down for them to change.
+type ChannelConstraints struct {
+	// DustLimit is the min satoshis/kilo-weight that should be paid within
+	// the commitment transaction for the entire duration of the channel's
+	// lifetime. This field may be updated during normal operation of the
+	// channel as on-chain conditions change.
+	DustLimit btcutil.Amount
+
+	// MaxPendingAmount is the maximum pending HTLC value that can be
+	// present within the channel at a particular time. This value is set
+	// by the initiator of the channel and must be upheld at all times.
+	//
+	// TODO(roasbeef): in mSAT
+	MaxPendingAmount btcutil.Amount
+
+	// ChanReserve is an absolute reservation on the channel for this
+	// particular node. This means that the current settled balance for
+	// this node CANNOT dip below the reservation amount. This acts as a
+	// defense against costless attacks when either side no longer has any
+	// skin in the game.
+	//
+	// TODO(roasbeef): need to swap above, i tell them what reserve, then
+	// other way around
+	ChanReserve btcutil.Amount
+
+	// MinHTLC is the minimum HTLC accepted for a direction of the channel.
+	// If any HTLC's below this amount are offered, then the HTLC will be
+	// rejected. This, in tandem with the dust limit allows a node to
+	// regulate the smallest HTLC that it deems economically relevant.
+	//
+	// TODO(roasbeef): in mSAT
+	MinHTLC btcutil.Amount
+
+	// MaxAcceptedHtlcs is the maximum amount of HTLC's that are to be
+	// accepted by the owner of this set of constraints. This allows each
+	// node to limit their over all exposure to HTLC's that may need to be
+	// acted upon in the case of a unilateral channel closure or a contract
+	// breach.
+	MaxAcceptedHtlcs uint16
+}
+
+// ChannelConfig is a struct that houses the various configuration opens for
+// channels. Each side maintains an instance of this configuration file as it
+// governs: how the funding and commitment transaction to be created, the
+// 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 ths 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
+
+	// CsvDelay is the relative time lock delay expressed in blocks. Any
+	// settled outputs that pay to the owner of this channel configuration
+	// MUST ensure that the delay branch uses this value as the relative
+	// time lock. Similarly, any HTLC's offered by this node should use
+	// this value as well.
+	CsvDelay uint16
+
+	// MultiSigKey is the key to be used within the 2-of-2 output script
+	// for the owner of this channel config.
+	MultiSigKey *btcec.PublicKey
+
+	// RevocationBasePoint is the base public key to be used when deriving
+	// revocation keys for the remote node's commitment transaction. This
+	// will be combined along with a per commitment secret to derive a
+	// unique revocation key for each state.
+	RevocationBasePoint *btcec.PublicKey
+
+	// PaymentBasePoint is the based public key to be used when deriving
+	// the key used within the non-delayed pay-to-self output on the
+	// commitment transaction for a node. This will be combined with a
+	// tweak derived from the per-commitment point to ensure unique keys
+	// for each commitment transaction.
+	PaymentBasePoint *btcec.PublicKey
+
+	// DelayBasePoint is the based public key to be used when deriving the
+	// key used within the delayed pay-to-self output on the commitment
+	// transaction for a node. This will be combined with a tweak derived
+	// from the per-commitment point to ensure unique keys for each
+	// commitment transaction.
+	DelayBasePoint *btcec.PublicKey
+}
+
 // OpenChannel encapsulates the persistent and dynamic state of an open channel
 // with a remote node. An open channel supports several options for on-disk
 // serialization depending on the exact context. Full (upon channel creation)