From 5cab304a590c88b02029229b88dfea26d1dd04d5 Mon Sep 17 00:00:00 2001
From: Christopher Jeffrey <chjjeffrey@gmail.com>
Date: Thu, 31 Mar 2016 05:14:54 -0700
Subject: [PATCH] more coin selection.

---
 lib/bcoin/mtx.js | 66 ++++++++++++++++++++++++------------------------
 1 file changed, 33 insertions(+), 33 deletions(-)

diff --git a/lib/bcoin/mtx.js b/lib/bcoin/mtx.js
index b5bc3884..d81abdda 100644
--- a/lib/bcoin/mtx.js
+++ b/lib/bcoin/mtx.js
@@ -786,12 +786,11 @@ MTX.prototype.maxSize = function maxSize(maxM, maxN) {
 };
 
 MTX.prototype.selectCoins = function selectCoins(coins, options) {
-  var dustThreshold = constants.tx.dustThreshold;
   var tx = this.clone();
   var outputValue = tx.getOutputValue();
   var chosen = [];
   var lastAdded = 0;
-  var i, size, change, fee;
+  var tryFree, minValue, i, size, change, fee;
 
   assert(tx.inputs.length === 0);
 
@@ -802,6 +801,8 @@ MTX.prototype.selectCoins = function selectCoins(coins, options) {
     };
   }
 
+  tryFree = options.free;
+
   if (!options.selection || options.selection === 'age') {
     // Oldest unspents first
     coins = coins.slice().sort(function(a, b) {
@@ -871,12 +872,12 @@ MTX.prototype.selectCoins = function selectCoins(coins, options) {
       // Calculate max possible size after signing.
       size = tx.maxSize(options.m, options.n);
 
-      if (options.free) {
+      if (tryFree) {
         if (tx.isFree(network.height + 1, size)) {
           fee = new bn(0);
           break;
         }
-        options.free = false;
+        tryFree = false;
       }
 
       if (options.accurate)
@@ -892,40 +893,39 @@ MTX.prototype.selectCoins = function selectCoins(coins, options) {
 
   if (!isFull()) {
     // Still failing to get enough funds.
-    chosen = null;
-  } else {
-    // How much money is left after filling outputs.
-    change = tx.getInputValue().sub(total());
-
-    // Attempt to subtract fee.
-    if (options.subtractFee != null) {
-      if (typeof options.subtractFee === 'number') {
-        i = options.subtractFee;
-        assert(tx.outputs[i], 'Subtraction index does not exist.');
-        if (tx.outputs[i].value.cmp(fee.addn(dustThreshold)) >= 0)
-          tx.outputs[i].value.isub(fee);
-        else
-          chosen = null;
-      } else {
-        for (i = 0; i < tx.outputs.length; i++) {
-          if (tx.outputs[i].value.cmp(fee.addn(dustThreshold)) >= 0) {
-            tx.outputs[i].value.isub(fee);
-            break;
-          }
-        }
-        // Could not subtract fee
-        if (i === tx.outputs.length)
-          chosen = null;
-      }
-    }
-  }
-
-  if (!chosen) {
     err = new Error('Could not select coins.');
     err.requiredFunds = total();
     throw err;
   }
 
+  // How much money is left after filling outputs.
+  change = tx.getInputValue().sub(total());
+
+  // Attempt to subtract fee.
+  if (options.subtractFee != null) {
+    minValue = fee.addn(constants.tx.dustThreshold);
+    if (typeof options.subtractFee === 'number') {
+      i = options.subtractFee;
+
+      if (i > tx.outputs.length - 1)
+        throw new Error('Subtraction index does not exist.');
+
+      if (tx.outputs[i].value.cmp(minValue) < 0)
+        throw new Error('Could not subtract fee.');
+
+      tx.outputs[i].value.isub(fee);
+    } else {
+      for (i = 0; i < tx.outputs.length; i++) {
+        if (tx.outputs[i].value.cmp(minValue) >= 0) {
+          tx.outputs[i].value.isub(fee);
+          break;
+        }
+      }
+      if (i === tx.outputs.length)
+        throw new Error('Could not subtract fee.');
+    }
+  }
+
   // Return necessary inputs and change.
   return {
     coins: chosen,