Merge pull request #1271 from isocolsky/fix/fee_estimation

Fix/fee estimation

lib/transaction/transaction.js

@@ -205,7 +205,7 @@ Transaction.prototype.getSerializationError = function(opts) {
     unspentError = this._hasFeeError(opts, unspent);
   }
 
-  return  unspentError ||
+  return unspentError ||
     this._hasDustOutputs(opts) ||
     this._isMissingSignatures(opts);
 };
@@ -394,7 +394,7 @@ Transaction.prototype._checkConsistency = function() {
     $.checkState(this._changeScript);
     $.checkState(this.outputs[this._changeIndex]);
     $.checkState(this.outputs[this._changeIndex].script.toString() ===
-                 this._changeScript.toString());
+      this._changeScript.toString());
   }
   // TODO: add other checks
 };
@@ -634,6 +634,21 @@ Transaction.prototype.fee = function(amount) {
   return this;
 };
 
+/**
+ * Manually set the fee per KB for this transaction. Beware that this resets all the signatures
+ * for inputs (in further versions, SIGHASH_SINGLE or SIGHASH_NONE signatures will not
+ * be reset).
+ *
+ * @param {number} amount satoshis per KB to be sent
+ * @return {Transaction} this, for chaining
+ */
+Transaction.prototype.feePerKb = function(amount) {
+  $.checkArgument(_.isNumber(amount), 'amount must be a number');
+  this._feePerKb = amount;
+  this._updateChangeOutput();
+  return this;
+};
+
 /* Output management */
 
 /**
@@ -831,7 +846,7 @@ Transaction.prototype.getFee = function() {
 Transaction.prototype._estimateFee = function() {
   var estimatedSize = this._estimateSize();
   var available = this._getUnspentValue();
-  return Transaction._estimateFee(estimatedSize, available);
+  return Transaction._estimateFee(estimatedSize, available, this._feePerKb);
 };
 
 Transaction.prototype._getUnspentValue = function() {
@@ -844,12 +859,12 @@ Transaction.prototype._clearSignatures = function() {
   });
 };
 
-Transaction._estimateFee = function(size, amountAvailable) {
+Transaction._estimateFee = function(size, amountAvailable, feePerKb) {
-  var fee = Math.ceil(size / Transaction.FEE_PER_KB);
+  var fee = Math.ceil(size / 1000) * (feePerKb || Transaction.FEE_PER_KB);
   if (amountAvailable > fee) {
     size += Transaction.CHANGE_OUTPUT_MAX_SIZE;
   }
-  return Math.ceil(size / 1000) * Transaction.FEE_PER_KB;
+  return Math.ceil(size / 1000) * (feePerKb || Transaction.FEE_PER_KB);
 };
 
 Transaction.prototype._estimateSize = function() {

test/transaction/transaction.js

@@ -257,6 +257,22 @@ describe('Transaction', function() {
       transaction.outputs.length.should.equal(2);
       transaction.outputs[1].satoshis.should.equal(10000);
     });
+    it('fee per kb can be set up manually', function() {
+      var inputs = _.map(_.range(10), function(i) {
+        var utxo = _.clone(simpleUtxoWith100000Satoshis);
+        utxo.outputIndex = i;
+        return utxo;
+      });
+      var transaction = new Transaction()
+        .from(inputs)
+        .to(toAddress, 950000)
+        .feePerKb(8000)
+        .change(changeAddress)
+        .sign(privateKey);
+      transaction._estimateSize().should.be.within(1000, 1999);
+      transaction.outputs.length.should.equal(2);
+      transaction.outputs[1].satoshis.should.equal(34000);
+    });
     it('if satoshis are invalid', function() {
       var transaction = new Transaction()
         .from(simpleUtxoWith100000Satoshis)
@@ -406,7 +422,9 @@ describe('Transaction', function() {
         .fee(10000000);
 
       expect(function() {
-        return transaction.serialize({disableMoreOutputThanInput: true});
+        return transaction.serialize({
+          disableMoreOutputThanInput: true
+        });
       }).to.throw(errors.Transaction.FeeError.TooLarge);
     });
     describe('skipping checks', function() {