chainregistry+config: enable neutrino fee estimation from external api

Co-authored-by: Valentine Wallace <vwallace@protonmail.com>

chainregistry.go

@@ -208,6 +208,23 @@ func newChainControlFromConfig(cfg *config, chanDB *channeldb.DB,
 			return nil, err
 		}
 
+		// If the user provided an API for fee estimation, activate it now.
+		if cfg.NeutrinoMode.FeeURL != "" {
+			ltndLog.Infof("Using API fee estimator!")
+
+			estimator := lnwallet.NewWebAPIFeeEstimator(
+				lnwallet.SparseConfFeeSource{
+					URL: cfg.NeutrinoMode.FeeURL,
+				},
+				defaultBitcoinStaticFeePerKW,
+			)
+
+			if err := estimator.Start(); err != nil {
+				return nil, err
+			}
+			cc.feeEstimator = estimator
+		}
+
 		walletConfig.ChainSource = chain.NewNeutrinoClient(
 			activeNetParams.Params, neutrinoCS,
 		)

config.go

@@ -130,6 +130,7 @@ type neutrinoConfig struct {
 	MaxPeers     int           `long:"maxpeers" description:"Max number of inbound and outbound peers"`
 	BanDuration  time.Duration `long:"banduration" description:"How long to ban misbehaving peers.  Valid time units are {s, m, h}.  Minimum 1 second"`
 	BanThreshold uint32        `long:"banthreshold" description:"Maximum allowed ban score before disconnecting and banning misbehaving peers."`
+	FeeURL       string        `long:"feeurl" description:"Optional URL for fee estimation. If a URL is not specified, static fees will be used for estimation."`
 }
 
 type btcdConfig struct {

sample-lnd.conf

@@ -233,6 +233,9 @@ bitcoin.node=btcd
 ; Add a peer to connect with at startup.
 ; neutrino.addpeer=
 
+; Set a URL source for fee estimates.
+; neutrino.feeurl=
+
 
 [Litecoin]