Merge pull request #603 from bitcoinjs/txbuffer

Transaction: allow parameterizable buffer

src/transaction.js

@@ -241,7 +241,7 @@ Transaction.prototype.hashForSignature = function (inIndex, prevOutScript, hashT
   // serialize and hash
   var buffer = new Buffer(txTmp.byteLength() + 4)
   buffer.writeInt32LE(hashType, buffer.length - 4)
-  txTmp.toBuffer().copy(buffer, 0)
+  txTmp.toBuffer(buffer, 0)
 
   return bcrypto.hash256(buffer)
 }
@@ -255,10 +255,10 @@ Transaction.prototype.getId = function () {
   return bufferReverse(this.getHash()).toString('hex')
 }
 
-Transaction.prototype.toBuffer = function () {
-  var buffer = new Buffer(this.byteLength())
+Transaction.prototype.toBuffer = function (buffer, initialOffset) {
+  if (!buffer) buffer = new Buffer(this.byteLength())
 
-  var offset = 0
+  var offset = initialOffset || 0
   function writeSlice (slice) {
     slice.copy(buffer, offset)
     offset += slice.length
@@ -304,6 +304,9 @@ Transaction.prototype.toBuffer = function () {
 
   writeUInt32(this.locktime)
 
+  // avoid slicing unless necessary
+  if (initialOffset !== undefined) return buffer.slice(initialOffset, offset)
+
   return buffer
 }
 

test/transaction.js

@@ -67,6 +67,24 @@ describe('Transaction', function () {
         assert.strictEqual(actual.toHex(), f.hex, actual.toHex())
       })
     })
+
+    it('accepts target Buffer and offset parameters', function () {
+      var f = fixtures.valid[0]
+      var actual = fromRaw(f.raw)
+      var byteLength = actual.byteLength()
+
+      var target = new Buffer(byteLength * 2)
+      var a = actual.toBuffer(target, 0)
+      var b = actual.toBuffer(target, byteLength)
+
+      assert.strictEqual(a.length, byteLength)
+      assert.strictEqual(b.length, byteLength)
+      assert.strictEqual(a.toString('hex'), f.hex)
+      assert.strictEqual(b.toString('hex'), f.hex)
+      assert.deepEqual(a, b)
+      assert.deepEqual(a, target.slice(0, byteLength))
+      assert.deepEqual(b, target.slice(byteLength))
+    })
   })
 
   describe('addInput', function () {