watchtower/wtpolicy/policy: adds watchtower policy

watchtower/wtpolicy/policy.go

@@ -0,0 +1,68 @@
+package wtpolicy
+
+import (
+	"fmt"
+
+	"github.com/lightningnetwork/lnd/lnwallet"
+	"github.com/lightningnetwork/lnd/watchtower/blob"
+)
+
+const (
+	// DefaultMaxUpdates specifies the number of encrypted blobs a client
+	// can send to the tower in a single session.
+	DefaultMaxUpdates = 1024
+
+	// DefaultRewardRate specifies the fraction of the channel that the
+	// tower takes if it successfully sweeps a breach. The value is
+	// expressed in millionths of the channel capacity.
+	DefaultRewardRate = 10000
+
+	// DefaultSweepFeeRate specifies the fee rate used to construct justice
+	// transactions. The value is expressed in satoshis per kilo-weight.
+	DefaultSweepFeeRate = 3000
+)
+
+// DefaultPolicy returns a Policy containing the default parameters that can be
+// used by clients or servers.
+func DefaultPolicy() Policy {
+	return Policy{
+		BlobType:   blob.TypeDefault,
+		MaxUpdates: DefaultMaxUpdates,
+		RewardRate: DefaultRewardRate,
+		SweepFeeRate: lnwallet.SatPerKWeight(
+			DefaultSweepFeeRate,
+		),
+	}
+}
+
+// Policy defines the negotiated parameters for a session between a client and
+// server. The parameters specify the format of encrypted blobs sent to the
+// tower, the reward schedule for the tower, and the number of encrypted blobs a
+// client can send in one session.
+type Policy struct {
+	// BlobType specifies the blob format that must be used by all updates sent
+	// under the session key used to negotiate this session.
+	BlobType blob.Type
+
+	// MaxUpdates is the maximum number of updates the watchtower will honor
+	// for this session.
+	MaxUpdates uint16
+
+	// RewardRate is the fraction of the total balance of the revoked
+	// commitment that the watchtower is entitled to. This value is
+	// expressed in millionths of the total balance.
+	RewardRate uint32
+
+	// SweepFeeRate expresses the intended fee rate to be used when
+	// constructing the justice transaction. All sweep transactions created
+	// for this session must use this value during construction, and the
+	// signatures must implicitly commit to the resulting output values.
+	SweepFeeRate lnwallet.SatPerKWeight
+}
+
+// String returns a human-readable description of the current policy.
+func (p Policy) String() string {
+	return fmt.Sprintf("(blob-type=%b max-updates=%d reward-rate=%d "+
+		"sweep-fee-rate=%d)", p.BlobType, p.MaxUpdates, p.RewardRate,
+		p.SweepFeeRate)
+}