Script: add function for parsing multisig type scripts

Author: afk11

src/script.js

@@ -2,7 +2,6 @@ var bip66 = require('bip66')
 var bufferutils = require('./bufferutils')
 var typeforce = require('typeforce')
 var types = require('./types')
-
 var OPS = require('./opcodes.json')
 var REVERSE_OPS = (function () {
  var result = {}
@@ -251,27 +250,55 @@ function isMultisigInput (script, allowIncomplete) {
  return chunks.slice(1).every(isCanonicalSignature)
 }
 
-function isMultisigOutput (script) {
- var chunks = decompile(script)
- if (chunks.length < 4) return false
- if (chunks[chunks.length - 1] !== OPS.OP_CHECKMULTISIG) return false
-
- var mOp = chunks[0]
- var nOp = chunks[chunks.length - 2]
+function parseMultisigScript (scriptPubKey) {
+ var chunks = decompile(scriptPubKey)
+ if (chunks.length < 4) {
+ throw new Error('Multisig script should contain at least 4 elements')
+ }
+ if (chunks[chunks.length - 1] !== OPS.OP_CHECKMULTISIG) {
+ throw new Error('Final opcode should be OP_CHECKMULTISIG')
+ }
+ if (!types.Number(chunks[0])) {
+ throw new Error('First element must be a number-push opcode')
+ }
+ if (!types.Number(chunks[chunks.length - 2])) {
+ throw new Error('Second-last element must be a number-push opcode')
+ }
+ var m = chunks[0] - OP_INT_BASE
+ var n = chunks[chunks.length - 2] - OP_INT_BASE
 
- if (!types.Number(mOp)) return false
- if (!types.Number(nOp)) return false
+ if (m <= 0) {
+ throw new Error('Number of signatures required must be greater than zero')
+ }
+ if (n > 16) {
+ throw new Error('Number of public keys must be less than 17')
+ }
+ if (m > n) {
+ throw new Error('Number of signatures cannot exceed the number of public keys')
+ }
+ if (n !== chunks.length - 3) {
+ throw new Error('n does not match the number of public keys')
+ }
 
- var m = mOp - OP_INT_BASE
- var n = nOp - OP_INT_BASE
+ var keys = chunks.slice(1, -2)
+ if (!keys.every(isCanonicalPubKey)) {
+ throw new Error('Non-canonical pubic key found')
+ }
 
- // 0 < m <= n <= 16
- if (m <= 0) return false
- if (m > n) return false
- if (n > 16) return false
- if (n !== chunks.length - 3) return false
+ return {
+ nRequiredSigs: m,
+ nPublicKeys: n,
+ publicKeyBuffers: keys
+ }
+}
 
- return chunks.slice(1, -2).every(isCanonicalPubKey)
+function isMultisigOutput (script) {
+ try {
+ parseMultisigScript(script)
+ return true
+ } catch (e) {
+ return false
+ }
 }
 
 function isNullDataOutput (script) {
@@ -399,16 +426,9 @@ function witnessScriptHashInput (scriptSig, scriptPubKey) {
 // OP_0 [signatures ...]
 function multisigInput (signatures, scriptPubKey) {
  if (scriptPubKey) {
- var chunks = decompile(scriptPubKey)
- if (!isMultisigOutput(chunks)) throw new Error('Expected multisig scriptPubKey')
-
- var mOp = chunks[0]
- var nOp = chunks[chunks.length - 2]
- var m = mOp - OP_INT_BASE
- var n = nOp - OP_INT_BASE
-
- if (signatures.length < m) throw new Error('Not enough signatures provided')
- if (signatures.length > n) throw new Error('Too many signatures provided')
+ var scriptData = parseMultisigScript(scriptPubKey)
+ if (signatures.length < scriptData.nRequiredSigs) throw new Error('Not enough signatures provided')
+ if (signatures.length > scriptData.nPublicKeys) throw new Error('Too many signatures provided')
  }
 
  return compile([].concat(OPS.OP_0, signatures))
@@ -441,6 +461,7 @@ module.exports = {
  isMultisigOutput: isMultisigOutput,
  isNullDataOutput: isNullDataOutput,
 
+ parseMultisigScript: parseMultisigScript,
  classifyOutput: classifyOutput,
  classifyInput: classifyInput,
  pubKeyOutput: pubKeyOutput,