chain: use gettxspendingprevout in RPC clients

This commit creates a new method `getTxSpendingPrevOut` that's used by
both ZMQ and RPC clients to lookup mempool spend for a given input.

chain/bitcoind_events.go

@@ -44,6 +44,15 @@ func NewBitcoindEventSubscriber(cfg *BitcoindConfig, client *rpcclient.Client,
 			"should be specified, not both")
 	}
 
+	// Check if the bitcoind node is on a version that has the
+	// gettxspendingprevout RPC. If it does, then we don't need to maintain
+	// a mempool for ZMQ clients and can maintain a smaller mempool for RPC
+	// clients.
+	hasRPC, err := hasSpendingPrevoutRPC(client)
+	if err != nil {
+		return nil, err
+	}
+
 	if cfg.PollingConfig != nil {
 		if client == nil {
 			return nil, fmt.Errorf("rpc client must be given " +
@@ -52,7 +61,7 @@ func NewBitcoindEventSubscriber(cfg *BitcoindConfig, client *rpcclient.Client,
 		}
 
 		pollingEvents := newBitcoindRPCPollingEvents(
-			cfg.PollingConfig, client, bClient,
+			cfg.PollingConfig, client, bClient, hasRPC,
 		)
 
 		return pollingEvents, nil
@@ -63,14 +72,6 @@ func NewBitcoindEventSubscriber(cfg *BitcoindConfig, client *rpcclient.Client,
 			"rpcpolling is disabled")
 	}
 
-	// Check if the bitcoind node is on a version that has the
-	// gettxspendingprevout RPC. If it does, then we don't need to maintain
-	// a mempool for ZMQ clients.
-	hasRPC, err := hasSpendingPrevoutRPC(client)
-	if err != nil {
-		return nil, err
-	}
-
 	return newBitcoindZMQEvents(cfg.ZMQConfig, client, bClient, hasRPC)
 }
 

chain/bitcoind_rpc_events.go

@@ -77,7 +77,7 @@ var _ BitcoindEvents = (*bitcoindRPCPollingEvents)(nil)
 // newBitcoindRPCPollingEvents instantiates a new bitcoindRPCPollingEvents
 // object.
 func newBitcoindRPCPollingEvents(cfg *PollingConfig, client *rpcclient.Client,
-	bClient batchClient) *bitcoindRPCPollingEvents {
+	bClient batchClient, hasRPC bool) *bitcoindRPCPollingEvents {
 
 	if cfg.BlockPollingInterval == 0 {
 		cfg.BlockPollingInterval = defaultBlockPollInterval
@@ -100,6 +100,7 @@ func newBitcoindRPCPollingEvents(cfg *PollingConfig, client *rpcclient.Client,
 		client:            bClient,
 		getRawTxBatchSize: cfg.RPCBatchSize,
 		batchWaitInterval: cfg.RPCBatchInterval,
+		hasPrevoutRPC:     hasRPC,
 	}
 
 	if cfg.RPCBatchSize == 0 {
@@ -165,8 +166,16 @@ func (b *bitcoindRPCPollingEvents) LookupInputSpend(
 	b.mempool.RLock()
 	defer b.mempool.RUnlock()
 
-	// Check whether the input is in mempool.
-	return b.mempool.containsInput(op)
+	// If `gettxspendingprevout` is not supported, we need to loop it up in
+	// our local mempool.
+	if !b.mempool.cfg.hasPrevoutRPC {
+		// Check whether the input is in mempool.
+		return b.mempool.containsInput(op)
+	}
+
+	// Otherwise, we can use the `gettxspendingprevout` RPC to look up the
+	// input.
+	return getTxSpendingPrevOut(op, b.client)
 }
 
 // blockEventHandlerRPC is a goroutine that uses the rpc client to check if we

chain/bitcoind_zmq_events.go

@@ -249,54 +249,8 @@ func (b *bitcoindZMQEvents) LookupInputSpend(
 	}
 
 	// Otherwise, we aren't maintaining a mempool and can use the
-	// gettxspendingprevout RPC. Create an RPC-style prevout that will be
-	// the lone item in an array.
-	prevoutReq := &getTxSpendingPrevOutReq{
-		Txid: op.Hash.String(), Vout: op.Index,
-	}
-
-	// The RPC takes an array of prevouts so we have an array with a single
-	// item since we don't yet batch calls to LookupInputSpend.
-	prevoutArr := []*getTxSpendingPrevOutReq{prevoutReq}
-
-	req, err := json.Marshal(prevoutArr)
-	if err != nil {
-		return chainhash.Hash{}, false
-	}
-
-	resp, err := b.client.RawRequest(
-		"gettxspendingprevout", []json.RawMessage{req},
-	)
-	if err != nil {
-		return chainhash.Hash{}, false
-	}
-
-	var prevoutResps []getTxSpendingPrevOutResp
-	err = json.Unmarshal(resp, &prevoutResps)
-	if err != nil {
-		return chainhash.Hash{}, false
-	}
-
-	// We should only get a single item back since we only requested with a
-	// single item.
-	if len(prevoutResps) != 1 {
-		return chainhash.Hash{}, false
-	}
-
-	result := prevoutResps[0]
-
-	// If the "spendingtxid" field is empty, then the utxo has no spend in
-	// the mempool at the moment.
-	if result.SpendingTxid == "" {
-		return chainhash.Hash{}, false
-	}
-
-	spendHash, err := chainhash.NewHashFromStr(result.SpendingTxid)
-	if err != nil {
-		return chainhash.Hash{}, false
-	}
-
-	return *spendHash, true
+	// gettxspendingprevout RPC.
+	return getTxSpendingPrevOut(op, b.client)
 }
 
 // blockEventHandler reads raw blocks events from the ZMQ block socket and
@@ -541,3 +495,56 @@ func (b *bitcoindZMQEvents) mempoolPoller() {
 		}
 	}
 }
+
+// getTxSpendingPrevOut makes an RPC call to `gettxspendingprevout` and returns
+// the result.
+func getTxSpendingPrevOut(op wire.OutPoint,
+	client *rpcclient.Client) (chainhash.Hash, bool) {
+
+	prevoutReq := &getTxSpendingPrevOutReq{
+		Txid: op.Hash.String(), Vout: op.Index,
+	}
+
+	// The RPC takes an array of prevouts so we have an array with a single
+	// item since we don't yet batch calls to LookupInputSpend.
+	prevoutArr := []*getTxSpendingPrevOutReq{prevoutReq}
+
+	req, err := json.Marshal(prevoutArr)
+	if err != nil {
+		return chainhash.Hash{}, false
+	}
+
+	resp, err := client.RawRequest(
+		"gettxspendingprevout", []json.RawMessage{req},
+	)
+	if err != nil {
+		return chainhash.Hash{}, false
+	}
+
+	var prevoutResps []getTxSpendingPrevOutResp
+	err = json.Unmarshal(resp, &prevoutResps)
+	if err != nil {
+		return chainhash.Hash{}, false
+	}
+
+	// We should only get a single item back since we only requested with a
+	// single item.
+	if len(prevoutResps) != 1 {
+		return chainhash.Hash{}, false
+	}
+
+	result := prevoutResps[0]
+
+	// If the "spendingtxid" field is empty, then the utxo has no spend in
+	// the mempool at the moment.
+	if result.SpendingTxid == "" {
+		return chainhash.Hash{}, false
+	}
+
+	spendHash, err := chainhash.NewHashFromStr(result.SpendingTxid)
+	if err != nil {
+		return chainhash.Hash{}, false
+	}
+
+	return *spendHash, true
+}