improve code readability

lib/common/defaults.js

@@ -49,9 +49,18 @@ Defaults.FIAT_RATE_MAX_LOOK_BACK_TIME = 120; // In minutes
 
 Defaults.HISTORY_LIMIT = 100;
 
+// The maximum amount of an UTXO to be considered too big to be used in the tx before exploring smaller
+// alternatives (proportinal to tx amount).
 Defaults.UTXO_SELECTION_MAX_SINGLE_UTXO_FACTOR = 2;
-Defaults.UTXO_SELECTION_MAX_FEE_VS_SINGLE_UTXO_FEE_FACTOR = 5;
-Defaults.UTXO_SELECTION_MAX_FEE_VS_TX_AMOUNT_FACTOR = 0.002;
+
+// The minimum amount an UTXO need to contribute proportional to tx amount.
 Defaults.UTXO_SELECTION_MIN_TX_AMOUNT_VS_UTXO_FACTOR = 0.1;
 
+// The maximum threshold to consider fees non-significant in relation to tx amount.
+Defaults.UTXO_SELECTION_MAX_FEE_VS_TX_AMOUNT_FACTOR = 0.05;
+
+// The maximum amount to pay for using small inputs instead of one big input
+// when fees are significant (proportional to how much we would pay for using that big input only).
+Defaults.UTXO_SELECTION_MAX_FEE_VS_SINGLE_UTXO_FEE_FACTOR = 5;
+
 module.exports = Defaults;

lib/server.js

@@ -1357,12 +1357,10 @@ WalletService.prototype._selectTxInputs = function(txp, utxosToExclude, cb) {
       log.debug('Tx size: ' + Utils.formatSize(txpSize) + ', Tx fee: ' + Utils.formatAmountInBtc(fee));
 
       var feeVsAmountRatio = fee / txpAmount;
-      var feeVsSingleInputFeeRatio = fee / (baseTxpFee + feePerInput);
       var amountVsUtxoRatio = netInputAmount / txpAmount;
 
-      log.debug('Tx amount/Fee: ' + Utils.formatRatio(feeVsAmountRatio) + ' (max: ' + Utils.formatRatio(Defaults.UTXO_SELECTION_MAX_FEE_VS_TX_AMOUNT_FACTOR) + ')');
-      log.debug('Single-input fee/Multi-input fee: ' + Utils.formatRatio(feeVsSingleInputFeeRatio) + ' (max: ' + Utils.formatRatio(Defaults.UTXO_SELECTION_MAX_FEE_VS_SINGLE_UTXO_FEE_FACTOR) + ')' + ' loses wrt single-input tx: ' + Utils.formatAmountInBtc((selected.length - 1) * feePerInput));
-      log.debug('Tx amount/input amount:' + Utils.formatRatio(amountVsUtxoRatio) + ' (min: ' + Utils.formatRatio(Defaults.UTXO_SELECTION_MIN_TX_AMOUNT_VS_UTXO_FACTOR) + ')');
+      log.debug('Fee/Tx amount: ' + Utils.formatRatio(feeVsAmountRatio) + ' (max: ' + Utils.formatRatio(Defaults.UTXO_SELECTION_MAX_FEE_VS_TX_AMOUNT_FACTOR) + ')');
+      log.debug('Tx amount/Input amount:' + Utils.formatRatio(amountVsUtxoRatio) + ' (min: ' + Utils.formatRatio(Defaults.UTXO_SELECTION_MIN_TX_AMOUNT_VS_UTXO_FACTOR) + ')');
 
       if (txpSize / 1000. > Defaults.MAX_TX_SIZE_IN_KB) {
         log.debug('Breaking because tx size (' + Utils.formatSize(txpSize) + ') is too big (max: ' + Utils.formatSize(Defaults.MAX_TX_SIZE_IN_KB * 1000.) + ')');
@@ -1376,10 +1374,13 @@ WalletService.prototype._selectTxInputs = function(txp, utxosToExclude, cb) {
           return false;
         }
 
-        if ((feeVsAmountRatio > Defaults.UTXO_SELECTION_MAX_FEE_VS_TX_AMOUNT_FACTOR &&
-          feeVsSingleInputFeeRatio > Defaults.UTXO_SELECTION_MAX_FEE_VS_SINGLE_UTXO_FEE_FACTOR)) {
-          log.debug('Breaking because fee exceeded fee/amount ratio and fee is too expensive compared to single input tx');
-          return false;
+        if (feeVsAmountRatio > Defaults.UTXO_SELECTION_MAX_FEE_VS_TX_AMOUNT_FACTOR) {
+          var feeVsSingleInputFeeRatio = fee / (baseTxpFee + feePerInput);
+          log.debug('Fee/Single-input fee: ' + Utils.formatRatio(feeVsSingleInputFeeRatio) + ' (max: ' + Utils.formatRatio(Defaults.UTXO_SELECTION_MAX_FEE_VS_SINGLE_UTXO_FEE_FACTOR) + ')' + ' loses wrt single-input tx: ' + Utils.formatAmountInBtc((selected.length - 1) * feePerInput));
+          if (feeVsSingleInputFeeRatio > Defaults.UTXO_SELECTION_MAX_FEE_VS_SINGLE_UTXO_FEE_FACTOR) {
+            log.debug('Breaking because fee is too significant compared to tx amount and it is too expensive compared to using single input');
+            return false;
+          }
         }
       }