Privacy improvement by sorting inputs and outputs

See BIP69 for more details:
https://github.com/bitcoin/bips/blob/master/bip-0069.mediawiki

lib/transaction/transaction.js

@@ -905,6 +905,41 @@ Transaction.prototype.removeOutput = function(index) {
   this._updateChangeOutput();
 };
 
+/**
+ * Sort a transaction's inputs and outputs according to BIP69
+ *
+ * @see {https://github.com/bitcoin/bips/blob/master/bip-0069.mediawiki}
+ * @return {Transaction} this
+ */
+Transaction.prototype.sort = function() {
+  this.sortOutputs(function(outputs) {
+    var copy = Array.prototype.concat.apply([], outputs);
+    copy.sort(function compare(first, second) {
+      if (first.satoshis < second.satoshis) {
+        return -1;
+      } else if (first.satoshis === second.satoshis) {
+        return Buffer.compare(first.script.toBuffer(), second.script.toBuffer());
+      } else {
+        return 1;
+      }
+    });
+    return copy;
+  });
+  this.sortInputs(function(inputs) {
+    var copy = Array.prototype.concat.apply([], inputs);
+    copy.sort(function compare(first, second) {
+      var compareTx = Buffer.compare(first.script.toBuffer(), second.script.toBuffer());
+      if (compareTx === 0) {
+        return first.outputIndex < second.outputIndex ? -1 : 1;
+      } else {
+        return compareTx;
+      }
+    });
+    return copy;
+  });
+  return this;
+};
+
 /**
  * Randomize this transaction's outputs ordering. The shuffling algorithm is a
  * version of the Fisher-Yates shuffle, provided by lodash's _.shuffle().
@@ -929,6 +964,20 @@ Transaction.prototype.sortOutputs = function(sortingFunction) {
   return this._newOutputOrder(outs);
 };
 
+/**
+ * Sort this transaction's inputs, according to a given sorting function that
+ * takes an array as argument and returns a new array, with the same elements
+ * but with a different order.
+ *
+ * @param {Function} sortingFunction
+ * @return {Transaction} this
+ */
+Transaction.prototype.sortInputs = function(sortingFunction) {
+  this.inputs = sortingFunction(this.inputs);
+  this._clearSignatures();
+  return this;
+};
+
 Transaction.prototype._newOutputOrder = function(newOutputs) {
   var isInvalidSorting = (this.outputs.length !== newOutputs.length ||
                           _.difference(this.outputs, newOutputs).length !== 0);

test/transaction/transaction.js

@@ -14,6 +14,7 @@ var PrivateKey = bitcore.PrivateKey;
 var Script = bitcore.Script;
 var Address = bitcore.Address;
 var Networks = bitcore.Networks;
+var Opcode = bitcore.Opcode;
 var errors = bitcore.errors;
 
 var transactionVector = require('../data/tx_creation');
@@ -919,6 +920,64 @@ describe('Transaction', function() {
     });
 
   });
+
+  describe('BIP69 Sorting', function() {
+
+    it('sorts inputs correctly', function() {
+      var from1 = {
+        txId: '0000000000000000000000000000000000000000000000000000000000000000',
+        outputIndex: 0,
+        script: Script.buildPublicKeyHashOut(fromAddress).toString(),
+        satoshis: 100000
+      };
+      var from2 = {
+        txId: '0000000000000000000000000000000000000000000000000000000000000001',
+        outputIndex: 0,
+        script: Script.buildPublicKeyHashOut(fromAddress).toString(),
+        satoshis: 100000
+      };
+      var from3 = {
+        txId: '0000000000000000000000000000000000000000000000000000000000000001',
+        outputIndex: 1,
+        script: Script.buildPublicKeyHashOut(fromAddress).toString(),
+        satoshis: 100000
+      };
+      var tx = new Transaction()
+        .from(from3)
+        .from(from2)
+        .from(from1);
+      tx.sort();
+      tx.inputs[0].prevTxId.toString('hex').should.equal(from1.txId);
+      tx.inputs[1].prevTxId.toString('hex').should.equal(from2.txId);
+      tx.inputs[2].prevTxId.toString('hex').should.equal(from3.txId);
+      tx.inputs[0].outputIndex.should.equal(from1.outputIndex);
+      tx.inputs[1].outputIndex.should.equal(from2.outputIndex);
+      tx.inputs[2].outputIndex.should.equal(from3.outputIndex);
+    });
+
+    it('sorts outputs correctly', function() {
+      var tx = new Transaction()
+        .addOutput(new Transaction.Output({
+          script: new Script().add(Opcode(0)),
+          satoshis: 2
+        }))
+        .addOutput(new Transaction.Output({
+          script: new Script().add(Opcode(1)),
+          satoshis: 2
+        }))
+        .addOutput(new Transaction.Output({
+          script: new Script().add(Opcode(0)),
+          satoshis: 1
+        }));
+      tx.sort();
+      tx.outputs[0].satoshis.should.equal(1);
+      tx.outputs[1].satoshis.should.equal(2);
+      tx.outputs[2].satoshis.should.equal(2);
+      tx.outputs[0].script.toString().should.equal('OP_0');
+      tx.outputs[1].script.toString().should.equal('OP_0');
+      tx.outputs[2].script.toString().should.equal('0x01');
+    });
+  });
 });
 
 var tx_empty_hex = '01000000000000000000';