From 3c8442b1bb453ef8ccfd00b18939c4287bacd3a3 Mon Sep 17 00:00:00 2001
From: Christopher Jeffrey <chjjeffrey@gmail.com>
Date: Tue, 12 Jan 2016 03:47:12 -0800
Subject: [PATCH] improve fee calculation.

---
 lib/bcoin/tx.js | 24 ++++++++++++++++++------
 1 file changed, 18 insertions(+), 6 deletions(-)

diff --git a/lib/bcoin/tx.js b/lib/bcoin/tx.js
index 387aff58..44e7ed81 100644
--- a/lib/bcoin/tx.js
+++ b/lib/bcoin/tx.js
@@ -153,7 +153,6 @@ TX.prototype._inputIndex = function _inputIndex(hash, index) {
   return -1;
 };
 
-// Build the scriptSigs for inputs, excluding the signatures
 TX.prototype.scriptInput = function scriptInput(index, pub, redeem) {
   var input, s, n, i;
 
@@ -206,10 +205,12 @@ TX.prototype.scriptInput = function scriptInput(index, pub, redeem) {
   }
 
   // P2SH requires the redeem script after signatures
-  if (redeem)
+  if (redeem) {
     input.script.push(redeem);
-
-  this._recalculateFee();
+    // The fee can be calculated more accurately
+    // now that the redeem script is available.
+    this._recalculateFee();
+  }
 };
 
 // Sign the now-built scriptSigs
@@ -702,6 +703,18 @@ TX.prototype.maxSize = function maxSize() {
     // Get the previous output's subscript
     s = input.out.tx.getSubscript(input.out.index);
 
+    // If we have access to the redeem script,
+    // we can use it to calculate size much easier.
+    if (this.inputs[i].script.length && bcoin.script.isScripthash(s)) {
+      s = this.inputs[i].script[this.inputs[i].script.length - 1];
+      // Need to add the redeem script size
+      // here since it will be ignored by
+      // the isMultisig clause.
+      // OP_PUSHDATA2 [redeem]
+      size += 3 + s.length;
+      s = bcoin.script.normalize(s);
+    }
+
     if (bcoin.script.isPubkey(s)) {
       // P2PK
       // OP_PUSHDATA0 [signature]
@@ -718,7 +731,6 @@ TX.prototype.maxSize = function maxSize() {
       m = s[0];
       if (Array.isArray(m))
         m = m[0];
-      assert(m >= 1 && m <= 3);
       // OP_0
       size += 1;
       // OP_PUSHDATA0 [signature] ...
@@ -880,7 +892,7 @@ TX.prototype._recalculateFee = function recalculateFee() {
     output = this.outputs[this.outputs.length - 1];
   }
 
-  size = this.render().length;
+  size = this.maxSize();
   real = Math.ceil(size / 1024) * constants.tx.fee;
   fee = this.getFee().toNumber();