From 476cc4870244dd74155bb31f7ea95142a7dbc02c Mon Sep 17 00:00:00 2001
From: Christopher Jeffrey <chjjeffrey@gmail.com>
Date: Mon, 3 Oct 2016 04:55:32 -0700
Subject: [PATCH] tx: improve witness parsing.

---
 lib/primitives/tx.js | 111 ++++++++++++++++++++++++-------------------
 1 file changed, 63 insertions(+), 48 deletions(-)

diff --git a/lib/primitives/tx.js b/lib/primitives/tx.js
index fbc31cca..77fe2356 100644
--- a/lib/primitives/tx.js
+++ b/lib/primitives/tx.js
@@ -2128,7 +2128,7 @@ TX.fromRaw = function fromRaw(data, enc) {
  */
 
 TX.prototype.fromRaw = function fromRaw(data) {
-  var p, i, inCount, outCount;
+  var p, i, count;
 
   if (TX.isWitness(data))
     return this.fromWitness(data);
@@ -2138,14 +2138,14 @@ TX.prototype.fromRaw = function fromRaw(data) {
 
   this.version = p.readU32(); // Technically signed
 
-  inCount = p.readVarint();
+  count = p.readVarint();
 
-  for (i = 0; i < inCount; i++)
+  for (i = 0; i < count; i++)
     this.inputs.push(Input.fromRaw(p));
 
-  outCount = p.readVarint();
+  count = p.readVarint();
 
-  for (i = 0; i < outCount; i++)
+  for (i = 0; i < count; i++)
     this.outputs.push(Output.fromRaw(p));
 
   this.locktime = p.readU32();
@@ -2170,48 +2170,60 @@ TX.prototype.fromRaw = function fromRaw(data) {
 
 TX.prototype.fromWitness = function fromWitness(data) {
   var p = BufferReader(data);
-  var i, marker, inCount, outCount, input, hasWitness, witnessSize;
+  var flag = 0;
+  var witnessSize = 0;
+  var hasWitness = false;
+  var i, count, input;
 
   p.start();
 
   this.version = p.readU32(); // Technically signed
 
-  marker = p.readU8();
-  this.flag = p.readU8();
+  assert(p.readU8() === 0, 'Non-zero marker.');
 
-  if (marker !== 0)
-    throw new Error('Invalid witness tx (marker != 0)');
+  flag = p.readU8();
 
-  if (this.flag === 0)
-    throw new Error('Invalid witness tx (flag == 0)');
+  assert(flag !== 0, 'Flag byte is zero.');
 
-  inCount = p.readVarint();
+  this.flag = flag;
 
-  for (i = 0; i < inCount; i++)
+  count = p.readVarint();
+
+  for (i = 0; i < count; i++)
     this.inputs.push(Input.fromRaw(p));
 
-  outCount = p.readVarint();
+  count = p.readVarint();
 
-  for (i = 0; i < outCount; i++)
+  for (i = 0; i < count; i++)
     this.outputs.push(Output.fromRaw(p));
 
-  p.start();
+  if (flag & 1) {
+    flag ^= 1;
 
-  for (i = 0; i < inCount; i++) {
-    input = this.inputs[i];
-    input.witness.fromRaw(p);
-    if (input.witness.items.length > 0)
-      hasWitness = true;
+    p.start();
+
+    for (i = 0; i < this.inputs.length; i++) {
+      input = this.inputs[i];
+      input.witness.fromRaw(p);
+      if (input.witness.items.length > 0)
+        hasWitness = true;
+    }
+
+    witnessSize = p.end() + 2;
   }
 
-  if (!hasWitness)
-    throw new Error('Witness tx has an empty witness.');
+  if (flag !== 0)
+    throw new Error('Unknown witness flag.');
 
-  witnessSize = p.end() + 2;
+  // We'll never be able to reserialize
+  // this to get the regular txid, and
+  // there's no way it's valid anyway.
+  if (this.inputs.length === 0 && this.outputs.length !== 0)
+    throw new Error('Zero input witness tx.');
 
   this.locktime = p.readU32();
 
-  if (!this.mutable) {
+  if (!this.mutable && hasWitness) {
     this._raw = p.endData();
     this._size = this._raw.length;
     this._witnessSize = witnessSize;
@@ -2222,27 +2234,6 @@ TX.prototype.fromWitness = function fromWitness(data) {
   return this;
 };
 
-/**
- * Test whether data is a witness transaction.
- * @param {Buffer|BufferReader} data
- * @returns {Boolean}
- */
-
-TX.isWitness = function isWitness(data) {
-  if (Buffer.isBuffer(data)) {
-    if (data.length < 12)
-      return false;
-
-    return data[4] === 0 && data[5] !== 0;
-  }
-
-  if (data.left() < 12)
-    return false;
-
-  return data.data[data.offset + 4] === 0
-    && data.data[data.offset + 5] !== 0;
-};
-
 /**
  * Serialize transaction without witness.
  * @private
@@ -2254,7 +2245,7 @@ TX.prototype.frameNormal = function frameNormal(writer) {
   var p = BufferWriter(writer);
   var i;
 
-  if (this.inputs.length === 0 && this.outputs.length === 1)
+  if (this.inputs.length === 0 && this.outputs.length !== 0)
     throw new Error('Cannot serialize zero-input tx.');
 
   p.write32(this.version);
@@ -2292,6 +2283,9 @@ TX.prototype.frameWitness = function frameWitness(writer) {
   var witnessSize = 0;
   var i, start;
 
+  if (this.inputs.length === 0 && this.outputs.length !== 0)
+    throw new Error('Cannot serialize zero-input tx.');
+
   p.write32(this.version);
   p.writeU8(0);
   p.writeU8(this.flag);
@@ -2326,6 +2320,27 @@ TX.prototype.frameWitness = function frameWitness(writer) {
   return p;
 };
 
+/**
+ * Test whether data is a witness transaction.
+ * @param {Buffer|BufferReader} data
+ * @returns {Boolean}
+ */
+
+TX.isWitness = function isWitness(data) {
+  if (Buffer.isBuffer(data)) {
+    if (data.length < 6)
+      return false;
+
+    return data[4] === 0 && data[5] !== 0;
+  }
+
+  if (data.left() < 6)
+    return false;
+
+  return data.data[data.offset + 4] === 0
+    && data.data[data.offset + 5] !== 0;
+};
+
 /**
  * Serialize a transaction to BCoin "extended format".
  * This is the serialization format BCoin uses internally