lnwallet: adds RequiredReserve method

lntest/mock/walletcontroller.go

@@ -105,6 +105,11 @@ func (w *WalletController) ListAccounts(string,
 	return nil, nil
 }
 
+// RequiredReserve currently returns a dummy value.
+func (w *WalletController) RequiredReserve(uint32) btcutil.Amount {
+	return 0
+}
+
 // ImportAccount currently returns a dummy value.
 func (w *WalletController) ImportAccount(string, *hdkeychain.ExtendedKey,
 	uint32, *waddrmgr.AddressType, bool) (*waddrmgr.AccountProperties,

lnwallet/btcwallet/btcwallet.go

@@ -711,6 +711,22 @@ func (b *BtcWallet) ListAccounts(name string,
 	return res, nil
 }
 
+// RequiredReserve returns the minimum amount of satoshis that should be
+// kept in the wallet in order to fee bump anchor channels if necessary.
+// The value scales with the number of public anchor channels but is
+// capped at a maximum.
+func (b *BtcWallet) RequiredReserve(
+	numAnchorChans uint32) btcutil.Amount {
+
+	anchorChanReservedValue := lnwallet.AnchorChanReservedValue
+	reserved := btcutil.Amount(numAnchorChans) * anchorChanReservedValue
+	if reserved > lnwallet.MaxAnchorChanReservedValue {
+		reserved = lnwallet.MaxAnchorChanReservedValue
+	}
+
+	return reserved
+}
+
 // ImportAccount imports an account backed by an account extended public key.
 // The master key fingerprint denotes the fingerprint of the root key
 // corresponding to the account public key (also known as the key with

lnwallet/interface.go

@@ -244,6 +244,12 @@ type WalletController interface {
 	ListAccounts(string, *waddrmgr.KeyScope) ([]*waddrmgr.AccountProperties,
 		error)
 
+	// RequiredReserve returns the minimum amount of satoshis that should be
+	// kept in the wallet in order to fee bump anchor channels if necessary.
+	// The value scales with the number of public anchor channels but is
+	// capped at a maximum.
+	RequiredReserve(uint32) btcutil.Amount
+
 	// ImportAccount imports an account backed by an account extended public
 	// key. The master key fingerprint denotes the fingerprint of the root
 	// key corresponding to the account public key (also known as the key