rpc: acquire global coin select lock in related RPCs

This ensures proper coin selection synchronization between lnd and users
of the RPC to avoid potential double spend errors.

lnrpc/walletrpc/config_active.go

@@ -38,6 +38,13 @@ type Config struct {
 	// any relevant requests to.
 	Wallet lnwallet.WalletController
 
+	// CoinSelectionLocker allows the caller to perform an operation, which
+	// is synchronized with all coin selection attempts. This can be used
+	// when an operation requires that all coin selection operations cease
+	// forward progress. Think of this as an exclusive lock on coin
+	// selection operations.
+	CoinSelectionLocker sweep.CoinSelectionLocker
+
 	// KeyRing is an interface that the WalletKit will use to derive any
 	// keys due to incoming client requests.
 	KeyRing keychain.KeyRing

lnrpc/walletrpc/walletkit_server.go

@@ -10,6 +10,7 @@ import (
 	"io/ioutil"
 	"os"
 	"path/filepath"
+	"time"
 
 	"github.com/btcsuite/btcd/chaincfg/chainhash"
 	"github.com/btcsuite/btcd/txscript"
@@ -258,7 +259,15 @@ func (w *WalletKit) ListUnspent(ctx context.Context,
 
 	// With our arguments validated, we'll query the internal wallet for
 	// the set of UTXOs that match our query.
-	utxos, err := w.cfg.Wallet.ListUnspentWitness(minConfs, maxConfs)
+	//
+	// We'll acquire the global coin selection lock to ensure there aren't
+	// any other concurrent processes attempting to lock any UTXOs which may
+	// be shown available to us.
+	var utxos []*lnwallet.Utxo
+	err = w.cfg.CoinSelectionLocker.WithCoinSelectLock(func() error {
+		utxos, err = w.cfg.Wallet.ListUnspentWitness(minConfs, maxConfs)
+		return err
+	})
 	if err != nil {
 		return nil, err
 	}
@@ -301,7 +310,13 @@ func (w *WalletKit) LeaseOutput(ctx context.Context,
 		return nil, err
 	}
 
-	expiration, err := w.cfg.Wallet.LeaseOutput(lockID, *op)
+	// Acquire the global coin selection lock to ensure there aren't any
+	// other concurrent processes attempting to lease the same UTXO.
+	var expiration time.Time
+	err = w.cfg.CoinSelectionLocker.WithCoinSelectLock(func() error {
+		expiration, err = w.cfg.Wallet.LeaseOutput(lockID, *op)
+		return err
+	})
 	if err != nil {
 		return nil, err
 	}
@@ -328,7 +343,12 @@ func (w *WalletKit) ReleaseOutput(ctx context.Context,
 		return nil, err
 	}
 
-	if err := w.cfg.Wallet.ReleaseOutput(lockID, *op); err != nil {
+	// Acquire the global coin selection lock to maintain consistency as
+	// it's acquired when we initially leased the output.
+	err = w.cfg.CoinSelectionLocker.WithCoinSelectLock(func() error {
+		return w.cfg.Wallet.ReleaseOutput(lockID, *op)
+	})
+	if err != nil {
 		return nil, err
 	}
 

rpcserver.go

@@ -950,7 +950,17 @@ func (r *rpcServer) ListUnspent(ctx context.Context,
 
 	// With our arguments validated, we'll query the internal wallet for
 	// the set of UTXOs that match our query.
-	utxos, err := r.server.cc.wallet.ListUnspentWitness(minConfs, maxConfs)
+	//
+	// We'll acquire the global coin selection lock to ensure there aren't
+	// any other concurrent processes attempting to lock any UTXOs which may
+	// be shown available to us.
+	var utxos []*lnwallet.Utxo
+	err = r.server.cc.wallet.WithCoinSelectLock(func() error {
+		utxos, err = r.server.cc.wallet.ListUnspentWitness(
+			minConfs, maxConfs,
+		)
+		return err
+	})
 	if err != nil {
 		return nil, err
 	}

subrpcserver_config.go

@@ -153,6 +153,9 @@ func (s *subRPCServerConfigs) PopulateDependencies(cfg *Config, cc *chainControl
 			subCfgValue.FieldByName("Wallet").Set(
 				reflect.ValueOf(cc.wallet),
 			)
+			subCfgValue.FieldByName("CoinSelectionLocker").Set(
+				reflect.ValueOf(cc.wallet),
+			)
 			subCfgValue.FieldByName("KeyRing").Set(
 				reflect.ValueOf(cc.keyRing),
 			)