dynamic fee

Transaction.js

@@ -16,7 +16,7 @@ var WalletKey          = imports.WalletKey || require('./WalletKey');
 var PrivateKey         = imports.PrivateKey || require('./PrivateKey');
 
 var COINBASE_OP = Buffer.concat([util.NULL_HASH, new Buffer('FFFFFFFF', 'hex')]);
-var DEFAULT_FEE = 0.001;
+var FEE_PER_1000B_SAT = parseInt(0.0001 * util.COIN); 
 
 function TransactionIn(data) {
   if ("object" !== typeof data) {
@@ -777,7 +777,7 @@ Transaction._sumOutputs = function(outs) {
 Transaction.prepare = function (ins, outs, opts) {
   opts = opts || {};
 
-  var feeSat = opts.feeSat || util.parseValue(opts.fee || DEFAULT_FEE);
+  var feeSat = opts.feeSat || (opts.fee? util.parseValue(opts.fee) : FEE_PER_1000B_SAT );
   var txobj = {};
   txobj.version = 1;
   txobj.lock_time = opts.lockTime || 0;
@@ -815,27 +815,27 @@ Transaction.prepare = function (ins, outs, opts) {
                     inv + ' < '+ouv + ' [SAT]');
   }
 
-  var remainderSat = valueInSat.sub(valueOutSat);
-
-  if (remainderSat.cmp(0)>0) {
-    var remainderAddress = opts.remainderAddress || ins[0].address;
-
-    outs.push({
-      address: remainderAddress,
-      amountSat: remainderSat,
-    });
-  }
-
   for(var i=0;i<outs.length;i++) {
     var amountSat = outs[i].amountSat || util.parseValue(outs[i].amount);
     var value = util.bigIntToValue(amountSat);
     var script = Transaction._scriptForAddress(outs[i].address);
-
     var txout = {
       v: value,
       s: script.getBuffer(),
     };
+    txobj.outs.push(txout);
+  }
 
+  // add remainder (without modifiying outs[])
+  var remainderSat = valueInSat.sub(valueOutSat);
+  if (remainderSat.cmp(0)>0) {
+    var remainderAddress = opts.remainderAddress || ins[0].address;
+    var value = util.bigIntToValue(remainderSat);
+    var script = Transaction._scriptForAddress(remainderAddress);
+    var txout = {
+      v: value,
+      s: script.getBuffer(),
+    };
     txobj.outs.push(txout);
   }
 
@@ -843,6 +843,31 @@ Transaction.prepare = function (ins, outs, opts) {
   return  new Transaction(txobj);
 };
 
+Transaction.prototype.calcSize = function () {
+  var totalSize = 8; // version + lock_time
+  totalSize += util.getVarIntSize(this.ins.length); // tx_in count
+  this.ins.forEach(function (txin) {
+    totalSize += 36 + util.getVarIntSize(txin.s.length) +
+      txin.s.length + 4; // outpoint + script_len + script + sequence
+  });
+
+  totalSize += util.getVarIntSize(this.outs.length);
+  this.outs.forEach(function (txout) {
+    totalSize += util.getVarIntSize(txout.s.length) +
+      txout.s.length + 8; // script_len + script + value
+  });
+  this.size = totalSize;
+  return totalSize;
+};
+
+Transaction.prototype.getSize = function getHash() {
+  if (!this.size) {
+    this.size = this.calcSize();
+  }
+  return this.size;
+};
+
+
 Transaction.prototype.isComplete = function () {
   var l = this.ins.length;
 
@@ -1021,9 +1046,24 @@ Transaction.prototype.sign = function (selectedUtxos, keys, opts) {
 
 Transaction.create = function (utxos, outs, keys, opts) {
 
+    //starting size estimation
+    var size    = 500;
+    var opts    = opts || {};
+
+    var givenFeeSat;
+    if (opts.fee || opts.feeSat) {
+      givenFeeSat = opts.fee ? opts.fee * util.COIN : opts.feeSat;
+    }
+
+    do {
+      // based on https://en.bitcoin.it/wiki/Transaction_fees
+      maxSizeK     = parseInt(size/1000) + 1;
+      var feeSat  = givenFeeSat
+        ? givenFeeSat : maxSizeK * FEE_PER_1000B_SAT ;
+
       var valueOutSat = Transaction
         ._sumOutputs(outs)
-      .add(DEFAULT_FEE * util.COIN);
+        .add(feeSat);
 
       var selectedUtxos = Transaction
         .selectUnspent(utxos,valueOutSat / util.COIN, opts.allowUnconfirmed);
@@ -1032,12 +1072,19 @@ Transaction.create = function (utxos, outs, keys, opts) {
         throw new Error(
           'the given UTXOs dont sum up the given outputs: ' 
           + valueOutSat.toString() 
-        + ' SAT'
+          + ' (fee is ' + feeSat
+          + ' )SAT'
         );
       }
+      var tx = Transaction.prepare(selectedUtxos, outs, {
+        feeSat: feeSat,
+        remainderAddress: opts.remainderAddress,
+        lockTime: opts.lockTime,
+      });
+
+      size = tx.getSize();
+    } while (size > (maxSizeK+1)*1000 );
 
-    var tx = Transaction.prepare(selectedUtxos, outs, opts);
-    //TODO interate with the new TX fee
     if (keys) tx.sign(selectedUtxos, keys);
     return tx;
 };

test/data/unspentSign.json

@@ -5,7 +5,7 @@
       "txid": "2ac165fa7a3a2b535d106a0041c7568d03b531e58aeccdd3199d7289ab12cfc1",
       "scriptPubKey": "76a914fe021bac469a5c49915b2a8ffa7390a9ce5580f988ac",
       "vout": 1,
-      "amount": 1.01,
+      "amount": 1.0101,
       "confirmations":7
     },
     {

test/test.Transaction.js

@@ -94,8 +94,9 @@ describe('Transaction', function() {
     tx.outs.length.should.equal(2);
 
     util.valueToBigInt(tx.outs[0].v).cmp(8000000).should.equal(0);
+
     // remainder is 0.0299 here because unspent select utxos in order
-    util.valueToBigInt(tx.outs[1].v).cmp(2900000).should.equal(0);
+    util.valueToBigInt(tx.outs[1].v).cmp(2990000).should.equal(0);
     tx.isComplete().should.equal(false);
   });
 
@@ -106,6 +107,12 @@ describe('Transaction', function() {
       .create
       .bind(utxos, outs, null, opts)
       .should.throw();
+
+    var outs2 = [{address:'mrPnbY1yKDBsdgbHbS7kJ8GVm8F66hWHLE', amount:0.5}];
+    should.exist( Transaction.create(utxos, outs2, null, opts));
+
+    // do not allow unconfirmed
+    Transaction.create.bind(utxos, outs2).should.throw();
   });
 
 
@@ -116,7 +123,7 @@ describe('Transaction', function() {
 
 
     // string output generated from: bitcoind createrawtransaction '[{"txid": "2ac165fa7a3a2b535d106a0041c7568d03b531e58aeccdd3199d7289ab12cfc1","vout":1},{"txid":"2ac165fa7a3a2b535d106a0041c7568d03b531e58aeccdd3199d7289ab12cfc2","vout":0}  ]' '{"mrPnbY1yKDBsdgbHbS7kJ8GVm8F66hWHLE":0.08,"mwZabyZXg8JzUtFX1pkGygsMJjnuqiNhgd":0.0299}'
-    tx.serialize().toString('hex').should.equal('0100000002c1cf12ab89729d19d3cdec8ae531b5038d56c741006a105d532b3a7afa65c12a0100000000ffffffffc2cf12ab89729d19d3cdec8ae531b5038d56c741006a105d532b3a7afa65c12a0000000000ffffffff0200127a00000000001976a914774e603bafb717bd3f070e68bbcccfd907c77d1388ac20402c00000000001976a914b00127584485a7cff0949ef0f6bc5575f06ce00d88ac00000000');
+    tx.serialize().toString('hex').should.equal('0100000002c1cf12ab89729d19d3cdec8ae531b5038d56c741006a105d532b3a7afa65c12a0100000000ffffffffc2cf12ab89729d19d3cdec8ae531b5038d56c741006a105d532b3a7afa65c12a0000000000ffffffff0200127a00000000001976a914774e603bafb717bd3f070e68bbcccfd907c77d1388acb09f2d00000000001976a914b00127584485a7cff0949ef0f6bc5575f06ce00d88ac00000000');
 
     // no remainder
     outs = [{address:'mrPnbY1yKDBsdgbHbS7kJ8GVm8F66hWHLE', amount:0.08}];
@@ -132,10 +139,14 @@ describe('Transaction', function() {
     var outs = [{address:'mrPnbY1yKDBsdgbHbS7kJ8GVm8F66hWHLE', amount:0.08}];
     var tx = Transaction.create(utxos, outs, testdata.dataUnspentSign.keyStrings, opts); 
     tx.isComplete().should.equal(true);
+    tx.ins.length.should.equal(1);
+    tx.outs.length.should.equal(2);
 
     var outs2 = [{address:'mrPnbY1yKDBsdgbHbS7kJ8GVm8F66hWHLE', amount:16}];
     var tx2 = Transaction.create(utxos, outs2, testdata.dataUnspentSign.keyStrings, opts); 
     tx2.isComplete().should.equal(true);
+    tx2.ins.length.should.equal(3);
+    tx2.outs.length.should.equal(2);
   });
 
   it('#sign should sign an incomplete tx ', function() {
@@ -143,6 +154,8 @@ describe('Transaction', function() {
     var utxos =testdata.dataUnspentSign.unspent;
     var outs = [{address:'mrPnbY1yKDBsdgbHbS7kJ8GVm8F66hWHLE', amount:0.08}];
     var tx = Transaction.create(utxos, outs, keys, opts); 
+    tx.ins.length.should.equal(1);
+    tx.outs.length.should.equal(2);
     tx.isComplete().should.equal(false);
   });
   it('#sign should sign a tx in multiple steps', function() {
@@ -165,6 +178,51 @@ describe('Transaction', function() {
  
   });
 
+  it('#create: should generate dynamic fee and readjust (and not) the selected UTXOs', function() {
+    //this cases exceeds the input by 1mbtc AFTEr calculating the dynamic fee,
+    //so, it should trigger adding a new 10BTC utxo
+    var utxos =testdata.dataUnspentSign.unspent;
+    var outs = [];
+    var n =101;
+    for (var i=0; i<n; i++) {
+      outs.push({address:'mrPnbY1yKDBsdgbHbS7kJ8GVm8F66hWHLE', amount:0.01});
+    }
+
+    var tx = Transaction.create(utxos, outs, testdata.dataUnspentSign.keyStrings, opts); 
+    tx.getSize().should.equal(3560);
+
+    // ins = 11.0101 BTC (2 inputs: 1.0101 + 10 );
+    tx.ins.length.should.equal(2);
+    // outs = 101 outs:
+    // 101 * 0.01 = 1.01BTC; + 0.0004 fee = 1.0104btc
+    // remainder = 11.0101-1.0104 = 9.9997
+    tx.outs.length.should.equal(102);
+    util.valueToBigInt(tx.outs[n].v).cmp(999970000).should.equal(0);
+    tx.isComplete().should.equal(true);
+
+
+    //this is the complementary case, it does not trigger a new utxo
+    var utxos =testdata.dataUnspentSign.unspent;
+    var outs = [];
+    var n =100;
+    for (var i=0; i<n; i++) {
+      outs.push({address:'mrPnbY1yKDBsdgbHbS7kJ8GVm8F66hWHLE', amount:0.01});
+    }
+
+    var tx = Transaction.create(utxos, outs, testdata.dataUnspentSign.keyStrings, opts); 
+    tx.getSize().should.equal(3485);
+
+    // ins = 1.0101 BTC (1 inputs: 1.0101);
+    tx.ins.length.should.equal(1);
+    // outs = 100 outs:
+    // 100 * 0.01 = 1BTC; + 0.0004 fee = 1.0004btc
+    // remainder = 1.0101-1.0004 = 0.0097
+    tx.outs.length.should.equal(101);
+    util.valueToBigInt(tx.outs[n].v).cmp(970000).should.equal(0);
+    tx.isComplete().should.equal(true);
+  });
+
+
   // Read tests from test/data/tx_valid.json
   // Format is an array of arrays
   // Inner arrays are either [ "comment" ]