From 27fbdb42ad07f9e95d1fc3d5dabfc4daf8b0e32b Mon Sep 17 00:00:00 2001
From: "Ryan X. Charles" <ryanxcharles@gmail.com>
Date: Fri, 19 Sep 2014 21:59:19 -0700
Subject: [PATCH] isOpReturn

standard OP_RETURN scripts contain either just an OP_RETURN or an OP_RETURN
followed by a single pushdata OP with not more than 40 bytes.
---
 lib/script.js  | 16 ++++++++++++++++
 test/script.js | 20 ++++++++++++++++++++
 2 files changed, 36 insertions(+)

diff --git a/lib/script.js b/lib/script.js
index 18bd2b800..4b2f2aa86 100644
--- a/lib/script.js
+++ b/lib/script.js
@@ -137,6 +137,8 @@ Script.prototype.fromString = function(str) {
         throw new Error('Invalid script');
       }
     } else if (opcodenum === Opcode.map.OP_PUSHDATA1 || opcodenum === Opcode.map.OP_PUSHDATA2 || opcodenum === Opcode.map.OP_PUSHDATA4) {
+      if (tokens[i + 2].slice(0, 2) != '0x')
+        throw new Error('Pushdata data must start with 0x');
       this.chunks.push({
         buf: new Buffer(tokens[i + 2].slice(2), 'hex'),
         len: parseInt(tokens[i + 1]),
@@ -171,4 +173,18 @@ Script.prototype.toString = function() {
   return str.substr(0, str.length - 1);
 };
 
+Script.prototype.isOpReturn = function() {
+  if (this.chunks[0] === Opcode('OP_RETURN').toNumber()
+    &&
+    (this.chunks.length === 1
+    ||
+    (this.chunks.length === 2
+    && this.chunks[1].buf
+    && this.chunks[1].buf.length <= 40
+    && this.chunks[1].length === this.chunks.len)))
+    return true;
+  else
+    return false;
+};
+
 module.exports = Script;
diff --git a/test/script.js b/test/script.js
index 739f7dd0e..11f98cc0e 100644
--- a/test/script.js
+++ b/test/script.js
@@ -196,4 +196,24 @@ describe('Script', function() {
 
   });
 
+  describe('#isOpReturn', function() {
+    
+    it('should know this is a (blank) OP_RETURN script', function() {
+      Script('OP_RETURN').isOpReturn().should.equal(true);
+    });
+
+    it('should know this is an OP_RETURN script', function() {
+      var buf = new Buffer(40);
+      buf.fill(0);
+      Script('OP_RETURN 40 0x' + buf.toString('hex')).isOpReturn().should.equal(true);
+    });
+
+    it('should know this is not an OP_RETURN script', function() {
+      var buf = new Buffer(40);
+      buf.fill(0);
+      Script('OP_CHECKMULTISIG 40 0x' + buf.toString('hex')).isOpReturn().should.equal(false);
+    });
+
+  });
+
 });