chainntnfs+chainreg: add interface MempoolWatcher

This commit adds the interface `MempoolWatcher` and uses it in the chain
registry.

chainntnfs/bitcoindnotify/bitcoind.go

@@ -80,6 +80,10 @@ type BitcoindNotifier struct {
 // time.
 var _ chainntnfs.ChainNotifier = (*BitcoindNotifier)(nil)
 
+// Ensure BitcoindNotifier implements the MempoolWatcher interface at compile
+// time.
+var _ chainntnfs.MempoolWatcher = (*BitcoindNotifier)(nil)
+
 // New returns a new BitcoindNotifier instance. This function assumes the
 // bitcoind node detailed in the passed configuration is already running, and
 // willing to accept RPC requests and new zmq clients.

chainntnfs/btcdnotify/btcd.go

@@ -96,6 +96,9 @@ type BtcdNotifier struct {
 // Ensure BtcdNotifier implements the ChainNotifier interface at compile time.
 var _ chainntnfs.ChainNotifier = (*BtcdNotifier)(nil)
 
+// Ensure BtcdNotifier implements the MempoolWatcher interface at compile time.
+var _ chainntnfs.MempoolWatcher = (*BtcdNotifier)(nil)
+
 // New returns a new BtcdNotifier instance. This function assumes the btcd node
 // detailed in the passed configuration is already running, and willing to
 // accept new websockets clients.

chainntnfs/interface.go

@@ -808,3 +808,16 @@ type ConfirmHintCache interface {
 	// the cache.
 	PurgeConfirmHint(confRequests ...ConfRequest) error
 }
+
+// MempoolWatcher defines an interface that allows the caller to query
+// information in the mempool.
+type MempoolWatcher interface {
+	// SubscribeMempoolSpent allows the caller to register a subscription
+	// to watch for a spend of an outpoint in the mempool.The event will be
+	// dispatched once the outpoint is spent in the mempool.
+	SubscribeMempoolSpent(op wire.OutPoint) (*MempoolSpendEvent, error)
+
+	// CancelMempoolSpendEvent allows the caller to cancel a subscription to
+	// watch for a spend of an outpoint in the mempool.
+	CancelMempoolSpendEvent(sub *MempoolSpendEvent)
+}

chainreg/chainregistry.go

@@ -182,6 +182,10 @@ type PartialChainControl struct {
 	// interested in.
 	ChainNotifier chainntnfs.ChainNotifier
 
+	// MempoolNotifier is used to watch for spending events happened in
+	// mempool.
+	MempoolNotifier chainntnfs.MempoolWatcher
+
 	// ChainView is used in the router for maintaining an up-to-date graph.
 	ChainView chainview.FilteredChainView
 
@@ -433,10 +437,14 @@ func NewPartialChainControl(cfg *Config) (*PartialChainControl, func(), error) {
 				"bitcoind: %v", err)
 		}
 
-		cc.ChainNotifier = bitcoindnotify.New(
+		chainNotifier := bitcoindnotify.New(
 			bitcoindConn, cfg.ActiveNetParams.Params, hintCache,
 			hintCache, cfg.BlockCache,
 		)
+
+		cc.ChainNotifier = chainNotifier
+		cc.MempoolNotifier = chainNotifier
+
 		cc.ChainView = chainview.NewBitcoindFilteredChainView(
 			bitcoindConn, cfg.BlockCache,
 		)
@@ -655,7 +663,8 @@ func NewPartialChainControl(cfg *Config) (*PartialChainControl, func(), error) {
 			DisableConnectOnNew:  true,
 			DisableAutoReconnect: false,
 		}
-		cc.ChainNotifier, err = btcdnotify.New(
+
+		chainNotifier, err := btcdnotify.New(
 			rpcConfig, cfg.ActiveNetParams.Params, hintCache,
 			hintCache, cfg.BlockCache,
 		)
@@ -663,6 +672,9 @@ func NewPartialChainControl(cfg *Config) (*PartialChainControl, func(), error) {
 			return nil, nil, err
 		}
 
+		cc.ChainNotifier = chainNotifier
+		cc.MempoolNotifier = chainNotifier
+
 		// Finally, we'll create an instance of the default chain view
 		// to be used within the routing layer.
 		cc.ChainView, err = chainview.NewBtcdFilteredChainView(