Transaction: Added replace-by-fee (RBF) support

- Useful for bidding transactions as described in: https://bitpay.com/chaindb.pdf
- Reference: nSequence-based opt-in: https://github.com/bitcoin/bitcoin/pull/6871

lib/transaction/input/input.js

@@ -11,9 +11,10 @@ var Script = require('../../script');
 var Sighash = require('../sighash');
 var Output = require('../output');
 
-
-var DEFAULT_SEQNUMBER = 0xFFFFFFFF;
-var DEFAULT_LOCKTIME_SEQNUMBER = 0x00000000;
+var MAXINT = 0xffffffff; // Math.pow(2, 32) - 1;
+var DEFAULT_RBF_SEQNUMBER = MAXINT - 2;
+var DEFAULT_SEQNUMBER = MAXINT;
+var DEFAULT_LOCKTIME_SEQNUMBER = MAXINT - 1;
 
 function Input(params) {
   if (!(this instanceof Input)) {
@@ -24,8 +25,10 @@ function Input(params) {
   }
 }
 
+Input.MAXINT = MAXINT;
 Input.DEFAULT_SEQNUMBER = DEFAULT_SEQNUMBER;
 Input.DEFAULT_LOCKTIME_SEQNUMBER = DEFAULT_LOCKTIME_SEQNUMBER;
+Input.DEFAULT_RBF_SEQNUMBER = DEFAULT_RBF_SEQNUMBER;
 
 Object.defineProperty(Input.prototype, 'script', {
   configurable: false,

lib/transaction/transaction.js

@@ -544,7 +544,7 @@ Transaction.prototype.from = function(utxo, pubkeys, threshold) {
     return input.prevTxId.toString('hex') === utxo.txId && input.outputIndex === utxo.outputIndex;
   });
   if (exists) {
-    return;
+    return this;
   }
   if (pubkeys && threshold) {
     this._fromMultisigUtxo(utxo, pubkeys, threshold);
@@ -1195,5 +1195,34 @@ Transaction.prototype.isCoinbase = function() {
   return (this.inputs.length === 1 && this.inputs[0].isNull());
 };
 
+/**
+ * Determines if this transaction can be replaced in the mempool with another
+ * transaction that provides a sufficiently higher fee (RBF).
+ */
+Transaction.prototype.isRBF = function() {
+  for (var i = 0; i < this.inputs.length; i++) {
+    var input = this.inputs[i];
+    if (input.sequenceNumber < Input.MAXINT - 1) {
+      return true;
+    }
+  }
+  return false;
+};
+
+/**
+ * Enable this transaction to be replaced in the mempool (RBF) if a transaction
+ * includes a sufficiently higher fee. It will set the sequenceNumber to
+ * DEFAULT_RBF_SEQNUMBER for all inputs if the sequence number does not
+ * already enable RBF.
+ */
+Transaction.prototype.enableRBF = function() {
+  for (var i = 0; i < this.inputs.length; i++) {
+    var input = this.inputs[i];
+    if (input.sequenceNumber >= Input.MAXINT - 1) {
+      input.sequenceNumber = Input.DEFAULT_RBF_SEQNUMBER;
+    }
+  }
+  return this;
+};
 
 module.exports = Transaction;

test/transaction/transaction.js

@@ -180,7 +180,7 @@ describe('Transaction', function() {
   var simpleUtxoWith1BTC = {
     address: fromAddress,
     txId: 'a477af6b2667c29670467e4e0728b685ee07b240235771862318e29ddbe58458',
-    outputIndex: 0,
+    outputIndex: 1,
     script: Script.buildPublicKeyHashOut(fromAddress).toString(),
     satoshis: 1e8
   };
@@ -1086,6 +1086,106 @@ describe('Transaction', function() {
 
     });
   });
+  describe('Replace-by-fee', function() {
+    describe('#enableRBF', function() {
+      it('only enable inputs not already enabled (0xffffffff)', function() {
+        var tx = new Transaction()
+          .from(simpleUtxoWith1BTC)
+          .from(simpleUtxoWith100000Satoshis)
+          .to([{address: toAddress, satoshis: 50000}])
+          .fee(15000)
+          .change(changeAddress)
+          .sign(privateKey);
+        tx.inputs[0].sequenceNumber = 0x00000000;
+        tx.enableRBF();
+        tx.inputs[0].sequenceNumber.should.equal(0x00000000);
+        tx.inputs[1].sequenceNumber.should.equal(0xfffffffd);
+      });
+      it('enable for inputs with 0xffffffff and 0xfffffffe', function() {
+        var tx = new Transaction()
+          .from(simpleUtxoWith1BTC)
+          .from(simpleUtxoWith100000Satoshis)
+          .to([{address: toAddress, satoshis: 50000}])
+          .fee(15000)
+          .change(changeAddress)
+          .sign(privateKey);
+        tx.inputs[0].sequenceNumber = 0xffffffff;
+        tx.inputs[1].sequenceNumber = 0xfffffffe;
+        tx.enableRBF();
+        tx.inputs[0].sequenceNumber.should.equal(0xfffffffd);
+        tx.inputs[1].sequenceNumber.should.equal(0xfffffffd);
+      });
+    });
+    describe('#isRBF', function() {
+      it('enable and determine opt-in', function() {
+        var tx = new Transaction()
+          .from(simpleUtxoWith100000Satoshis)
+          .to([{address: toAddress, satoshis: 50000}])
+          .fee(15000)
+          .change(changeAddress)
+          .enableRBF()
+          .sign(privateKey);
+        tx.isRBF().should.equal(true);
+      });
+      it('determine opt-out with default sequence number', function() {
+        var tx = new Transaction()
+          .from(simpleUtxoWith100000Satoshis)
+          .to([{address: toAddress, satoshis: 50000}])
+          .fee(15000)
+          .change(changeAddress)
+          .sign(privateKey);
+        tx.isRBF().should.equal(false);
+      });
+      it('determine opt-out with 0xfffffffe', function() {
+        var tx = new Transaction()
+          .from(simpleUtxoWith1BTC)
+          .from(simpleUtxoWith100000Satoshis)
+          .to([{address: toAddress, satoshis: 50000 + 1e8}])
+          .fee(15000)
+          .change(changeAddress)
+          .sign(privateKey);
+        tx.inputs[0].sequenceNumber = 0xfffffffe;
+        tx.inputs[1].sequenceNumber = 0xfffffffe;
+        tx.isRBF().should.equal(false);
+      });
+      it('determine opt-out with 0xffffffff', function() {
+        var tx = new Transaction()
+          .from(simpleUtxoWith1BTC)
+          .from(simpleUtxoWith100000Satoshis)
+          .to([{address: toAddress, satoshis: 50000 + 1e8}])
+          .fee(15000)
+          .change(changeAddress)
+          .sign(privateKey);
+        tx.inputs[0].sequenceNumber = 0xffffffff;
+        tx.inputs[1].sequenceNumber = 0xffffffff;
+        tx.isRBF().should.equal(false);
+      });
+      it('determine opt-in with 0xfffffffd (first input)', function() {
+        var tx = new Transaction()
+          .from(simpleUtxoWith1BTC)
+          .from(simpleUtxoWith100000Satoshis)
+          .to([{address: toAddress, satoshis: 50000 + 1e8}])
+          .fee(15000)
+          .change(changeAddress)
+          .sign(privateKey);
+        tx.inputs[0].sequenceNumber = 0xfffffffd;
+        tx.inputs[1].sequenceNumber = 0xffffffff;
+        tx.isRBF().should.equal(true);
+      });
+      it('determine opt-in with 0xfffffffd (second input)', function() {
+        var tx = new Transaction()
+          .from(simpleUtxoWith1BTC)
+          .from(simpleUtxoWith100000Satoshis)
+          .to([{address: toAddress, satoshis: 50000 + 1e8}])
+          .fee(15000)
+          .change(changeAddress)
+          .sign(privateKey);
+        tx.inputs[0].sequenceNumber = 0xffffffff;
+        tx.inputs[1].sequenceNumber = 0xfffffffd;
+        tx.isRBF().should.equal(true);
+      });
+    });
+  });
 });