transaction hash and id

...the hash is the usual hash, and the id is the reverse of that, which is what
is usually graphically displayed by bitcoind.

lib/transaction.js

@@ -3,6 +3,7 @@ var Txout = require('./txout');
 var BufferWriter = require('./bufferwriter');
 var BufferReader = require('./bufferreader');
 var Varint = require('./varint');
+var Hash = require('./hash');
 
 var Transaction = function Transaction(version, txinsvi, txins, txoutsvi, txouts, nlocktime) {
   if (!(this instanceof Transaction))
@@ -113,4 +114,12 @@ Transaction.prototype.toBufferWriter = function(bw) {
   return bw;
 };
 
+Transaction.prototype.hash = function() {
+  return Hash.sha256sha256(this.toBuffer());
+};
+
+Transaction.prototype.id = function() {
+  return BufferReader(this.hash()).reverse().read();
+};
+
 module.exports = Transaction;

test/transaction.js

@@ -124,4 +124,23 @@ describe('Transaction', function() {
 
   });
 
+  describe('#hash', function() {
+
+    it('should correctly calculate the hash of this known transaction', function() {
+      var tx = Transaction().fromBuffer(tx2buf);
+      var txhashbuf = new Buffer(Array.apply([], new Buffer(tx2idhex, 'hex')).reverse());
+      tx.hash().toString('hex').should.equal(txhashbuf.toString('hex'));
+    });
+
+  });
+
+  describe('#id', function() {
+
+    it('should correctly calculate the id of this known transaction', function() {
+      var tx = Transaction().fromBuffer(tx2buf);
+      tx.id().toString('hex').should.equal(tx2idhex);
+    });
+
+  });
+
 });