Repository: bitcoinjs/bitcoinjs-lib
Pull request #722 (2016-12-13 11:06:24)

Script templates: add witness commitment template

dcousens: If you could add the necessary function witness commitment hash creation function to `Block`,  tests for that,  then a final integration test that checks segnet,  downloads a segwit block and verifies it... this feature is good to go :+1: 
dcousens: ACK 6c78b36 good to merge,  but will leave PR open for the above
dcousens: @afk11 can you rebase this?  We'll merge it now and I'll add an issue for:

> Needs an integration test showing how this would be used... and potentially a Block method to build the commitment hash

Patch:
diff --git a/src/templates/index.js b/src/templates/index.js
index 78a8eba9..fa7c4eac 100644
--- a/src/templates/index.js
+++ b/src/templates/index.js
@@ -6,6 +6,8 @@ var pubKeyHash = require('./pubkeyhash')
 var scriptHash = require('./scripthash')
 var witnessPubKeyHash = require('./witnesspubkeyhash')
 var witnessScriptHash = require('./witnessscripthash')
+var witnessCommitment = require('./witnesscommitment')
+
 var types = {
   MULTISIG: 'multisig',
   NONSTANDARD: 'nonstandard',
@@ -14,7 +16,8 @@ var types = {
   P2PKH: 'pubkeyhash',
   P2SH: 'scripthash',
   P2WPKH: 'witnesspubkeyhash',
-  P2WSH: 'witnessscripthash'
+  P2WSH: 'witnessscripthash',
+  WITNESS_COMMITMENT: 'witnesscommitment'
 }
 
 function classifyOutput (script) {
@@ -27,6 +30,7 @@ function classifyOutput (script) {
   var chunks = decompile(script)
   if (multisig.output.check(chunks)) return types.MULTISIG
   if (pubKey.output.check(chunks)) return types.P2PK
+  if (witnessCommitment.output.check(chunks)) return types.WITNESS_COMMITMENT
   if (nullData.output.check(chunks)) return types.NULLDATA
 
   return types.NONSTANDARD
@@ -65,5 +69,6 @@ module.exports = {
   scriptHash: scriptHash,
   witnessPubKeyHash: witnessPubKeyHash,
   witnessScriptHash: witnessScriptHash,
+  witnessCommitment: witnessCommitment,
   types: types
 }
diff --git a/src/templates/witnesscommitment/index.js b/src/templates/witnesscommitment/index.js
new file mode 100644
index 00000000..d4590381
--- /dev/null
+++ b/src/templates/witnesscommitment/index.js
@@ -0,0 +1,3 @@
+module.exports = {
+  output: require('./output')
+}
diff --git a/src/templates/witnesscommitment/output.js b/src/templates/witnesscommitment/output.js
new file mode 100644
index 00000000..e07f4016
--- /dev/null
+++ b/src/templates/witnesscommitment/output.js
@@ -0,0 +1,36 @@
+// OP_RETURN 36bytes:[0xaa21a9ed, Hash256(witnessRoot )]
+
+var bscript = require('../../script')
+var types = require('../../types')
+var typeforce = require('typeforce')
+var OPS = require('bitcoin-ops')
+
+function check (script) {
+  var buffer = bscript.compile(script)
+
+  return buffer.length > 37 &&
+    buffer[0] === OPS.OP_RETURN &&
+    buffer[1] === 0x24 &&
+    buffer.slice(2, 6).toString('hex') === 'aa21a9ed'
+}
+
+check.toJSON = function () { return 'Witness commitment output' }
+
+function encode (commitment) {
+  // hash256 0x21 hash160 0xed
+  typeforce(types.Hash256bit, commitment)
+
+  return bscript.compile([OPS.OP_RETURN, new Buffer('aa21a9ed' + commitment.toString('hex'), 'hex')])
+}
+
+function decode (buffer) {
+  typeforce(check, buffer)
+
+  return bscript.decompile(buffer)[1].slice(4, 36)
+}
+
+module.exports = {
+  check: check,
+  decode: decode,
+  encode: encode
+}


Test patch:
diff --git a/test/fixtures/script.json b/test/fixtures/script.json
index e0ef536e..b5286cfa 100644
--- a/test/fixtures/script.json
+++ b/test/fixtures/script.json
@@ -165,6 +165,10 @@
       "stack": [
         "000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
       ]
+    },
+    {
+      "asm": "OP_RETURN aa21a9ed4db4fb830efe3e804337413ffe8ad7393af301e0ec8e71b6e6f2b860a56f4dcd",
+      "script": "6a24aa21a9ed4db4fb830efe3e804337413ffe8ad7393af301e0ec8e71b6e6f2b860a56f4dcd"
     }
   ],
   "invalid": {
diff --git a/test/fixtures/templates.json b/test/fixtures/templates.json
index 17568211..d7873dd5 100644
--- a/test/fixtures/templates.json
+++ b/test/fixtures/templates.json
@@ -494,6 +494,27 @@
           "hash": "ffffff"
         }
       ]
+    },
+    "witnessCommitment": {
+      "inputs": [],
+      "outputs": [
+        {
+          "exception": "",
+          "commitment": "abcd1234abcd1234abcd1234abcd1234abcd1234abcd1234abcd1234abcd"
+        },
+        {
+          "description": "wrong OPCODE at the start",
+          "scriptPubKeyHex": "6024aa21a9ed4db4fb830efe3e804337413ffe8ad7393af301e0ec8e71b6e6f2b860a56f4dcd"
+        },
+        {
+          "description": "wrong length marker",
+          "scriptPubKeyHex": "6a23aa21a9ed4db4fb830efe3e804337413ffe8ad7393af301e0ec8e71b6e6f2b860a56f4dcd"
+        },
+        {
+          "description": "commitment of wrong length",
+          "scriptPubKeyHex": "6a23aa21a9ed4db4fb830efe3e804337413ffe8ad7393af301e0ec8e71b6e6f2b860a56f4d"
+        }
+      ]
     }
   }
 }
diff --git a/test/templates.js b/test/templates.js
index 33e36f30..6e9a5b1b 100644
--- a/test/templates.js
+++ b/test/templates.js
@@ -53,7 +53,8 @@ describe('script-templates', function () {
     'witnessPubKeyHash',
     'witnessScriptHash',
     'multisig',
-    'nullData'
+    'nullData',
+    'witnessCommitment'
   ].forEach(function (name) {
     var inputType = bscript[name].input
     var outputType = bscript[name].output
@@ -106,6 +107,12 @@ describe('script-templates', function () {
           it('returns ' + expected + ' for ' + f.output, function () {
             var output = bscript.fromASM(f.output)
 
+            if (name.toLowerCase() === 'nulldata' && f.type === bscript.types.WITNESS_COMMITMENT) {
+              return
+            }
+            if (name.toLowerCase() === 'witnesscommitment' && f.type === bscript.types.NULLDATA) {
+              return
+            }
             assert.strictEqual(outputType.check(output), expected)
           })
         }
@@ -401,6 +408,43 @@ describe('script-templates', function () {
     })
   })
 
+  describe('witnessCommitment.output', function () {
+    fixtures.valid.forEach(function (f) {
+      if (f.type !== 'witnesscommitment') return
+      if (!f.scriptPubKey) return
+
+      var commitment = new Buffer(f.witnessCommitment, 'hex')
+      var scriptPubKey = bscript.witnessCommitment.output.encode(commitment)
+
+      it('encodes to ' + f.scriptPubKey, function () {
+        assert.strictEqual(bscript.toASM(scriptPubKey), f.scriptPubKey)
+      })
+
+      it('decodes to ' + commitment.toString('hex'), function () {
+        assert.deepEqual(bscript.witnessCommitment.output.decode(scriptPubKey), commitment)
+      })
+    })
+
+    fixtures.invalid.witnessCommitment.outputs.forEach(function (f) {
+      if (f.commitment) {
+        var hash = new Buffer(f.commitment, 'hex')
+        it('throws on bad encode data', function () {
+          assert.throws(function () {
+            bscript.witnessCommitment.output.encode(hash)
+          }, new RegExp(f.exception))
+        })
+      }
+
+      if (f.scriptPubKeyHex) {
+        it('.decode throws on ' + f.description, function () {
+          assert.throws(function () {
+            bscript.witnessCommitment.output.decode(new Buffer(f.scriptPubKeyHex, 'hex'))
+          }, new RegExp(f.exception))
+        })
+      }
+    })
+  })
+
   describe('nullData.output', function () {
     fixtures.valid.forEach(function (f) {
       if (f.type !== 'nulldata') return