lnrpc/watchtowerrpc: add WatchtowerBackend configs

lnrpc/watchtowerrpc/config_active.go

@@ -0,0 +1,13 @@
+// +build watchtowerrpc
+
+package watchtowerrpc
+
+// Config is the primary configuration struct for the watchtower RPC server. It
+// contains all items required for the RPC server to carry out its duties. The
+// fields with struct tags are meant to parsed as normal configuration options,
+// while if able to be populated, the latter fields MUST also be specified.
+type Config struct {
+	// Tower is the active watchtower which serves as the primary source for
+	// information presented via RPC.
+	Tower WatchtowerBackend
+}

lnrpc/watchtowerrpc/config_default.go

@@ -0,0 +1,6 @@
+// +build !watchtowerrpc
+
+package watchtowerrpc
+
+// Config is empty for non-watchtowerrpc builds.
+type Config struct{}

lnrpc/watchtowerrpc/interface.go

@@ -0,0 +1,23 @@
+package watchtowerrpc
+
+import (
+	"net"
+
+	"github.com/btcsuite/btcd/btcec"
+)
+
+// WatchtowerBackend abstracts access to the watchtower information that is
+// served via RPC connections.
+type WatchtowerBackend interface {
+	// PubKey returns the public key for the watchtower used to
+	// authentication and encrypt traffic with clients.
+	PubKey() *btcec.PublicKey
+
+	// ListeningAddrs returns the listening addresses where the watchtower
+	// server can accept client connections.
+	ListeningAddrs() []net.Addr
+
+	// ExternalIPs returns the addresses where the watchtower can be reached
+	// by clients externally.
+	ExternalIPs() []net.Addr
+}