lnwallet: add FeeEstimator interface, StaticFeeEstimator implementation

This commit adds the FeeEstimator interface, which can be used for
future fee calculation implementations. Currently, there is only the
StaticFeeEstimator implementation, which returns the same fee rate for
any transaction.

lnwallet/wallet.go

@@ -273,6 +273,10 @@ type LightningWallet struct {
 	// update the commitment state.
 	Signer Signer
 
+	// FeeEstimator is the implementation that the wallet will use for the
+	// calculation of on-chain transaction fees.
+	FeeEstimator FeeEstimator
+
 	// ChainIO is an instance of the BlockChainIO interface. ChainIO is
 	// used to lookup the existence of outputs within the UTXO set.
 	ChainIO BlockChainIO
@@ -320,12 +324,13 @@ type LightningWallet struct {
 // initialized/started before being passed as a function arugment.
 func NewLightningWallet(cdb *channeldb.DB, notifier chainntnfs.ChainNotifier,
 	wallet WalletController, signer Signer, bio BlockChainIO,
-	netParams *chaincfg.Params) (*LightningWallet, error) {
+	fe FeeEstimator, netParams *chaincfg.Params) (*LightningWallet, error) {
 
 	return &LightningWallet{
 		chainNotifier:    notifier,
 		Signer:           signer,
 		WalletController: wallet,
+		FeeEstimator:     fe,
 		ChainIO:          bio,
 		ChannelDB:        cdb,
 		msgChan:          make(chan interface{}, msgBufferSize),
@@ -490,6 +495,7 @@ func (l *LightningWallet) InitChannelReservation(capacity,
 
 	errChan := make(chan error, 1)
 	respChan := make(chan *ChannelReservation, 1)
+	minFeeRate := btcutil.Amount(l.FeeEstimator.EstimateFeePerWeight(1))
 
 	l.msgChan <- &initFundingReserveMsg{
 		capacity:      capacity,
@@ -497,6 +503,7 @@ func (l *LightningWallet) InitChannelReservation(capacity,
 		fundingAmount: ourFundAmt,
 		csvDelay:      csvDelay,
 		ourDustLimit:  ourDustLimit,
+		minFeeRate:    minFeeRate,
 		pushSat:       pushSat,
 		nodeID:        theirID,
 		nodeAddr:      theirAddr,
@@ -1434,3 +1441,28 @@ func coinSelect(feeRate uint64, amt btcutil.Amount,
 		return selectedUtxos, changeAmt, nil
 	}
 }
+
+// StaticFeeEstimator will return a static value for all fee calculation
+// requests. It is designed to be replaced by a proper fee calcuation
+// implementation.
+type StaticFeeEstimator struct {
+	FeeRate      uint64
+	Confirmation uint32
+}
+
+// EstimateFeePerByte will return a static value for fee calculations.
+func (e StaticFeeEstimator) EstimateFeePerByte(numBlocks uint32) uint64 {
+	return e.FeeRate
+}
+
+// EstimateFeePerWeight will return a static value for fee calculations.
+func (e StaticFeeEstimator) EstimateFeePerWeight(numBlocks uint32) uint64 {
+	return e.FeeRate * 4
+}
+
+// EstimateConfirmation will return a static value representing the estimated
+// number of blocks that will be required to confirm a transaction for the
+// given fee rate.
+func (e StaticFeeEstimator) EstimateConfirmation(satPerByte int64) uint32 {
+	return e.Confirmation
+}