Solve Output: take an output script, returns {type, script, solvedBy, requiredSigs, canSign}

src/templates/index.js

@@ -17,6 +17,9 @@ var types = {
   P2WSH: 'witnessscripthash'
 }
 
+var SIGNABLE_SCRIPTS = [types.MULTISIG, types.P2PKH, types.P2PK]
+var P2SH_SCRIPTS = SIGNABLE_SCRIPTS.concat([types.P2WPKH, types.P2WSH])
+
 function classifyOutput (script) {
   if (witnessPubKeyHash.output.check(script)) return types.P2WPKH
   if (witnessScriptHash.output.check(script)) return types.P2WSH
@@ -54,10 +57,61 @@ function classifyWitness (script, allowIncomplete) {
   return types.NONSTANDARD
 }
 
+function solveOutput (scriptCode) {
+  if (!(scriptCode instanceof Buffer)) {
+    throw new Error('Argument 0 for solveScript must be a Buffer')
+  }
+
+  var outputType = classifyOutput(scriptCode)
+  var solvedBy = null
+  var requiredSigs = null
+
+  switch (outputType) {
+    // We can only determine the relevant hash from these, not if it's signable
+    case types.P2SH:
+      solvedBy = scriptHash.output.decode(scriptCode)
+      break
+    case types.P2WSH:
+      solvedBy = witnessScriptHash.output.decode(scriptCode)
+      break
+
+    // P2WPKH is separate from other signable types, it's best viewed as a special case for P2PKH
+    // Not included in canSign.
+    case types.P2WPKH:
+      solvedBy = witnessPubKeyHash.output.decode(scriptCode)
+      requiredSigs = 1
+      break
+
+    // We can immediately solve signatures for these
+    // When adding a new script type, edit here
+    case types.P2PK:
+      solvedBy = pubKey.output.decode(scriptCode)
+      requiredSigs = 1
+      break
+    case types.P2PKH:
+      solvedBy = pubKeyHash.output.decode(scriptCode)
+      requiredSigs = 1
+      break
+    case types.MULTISIG:
+      solvedBy = multisig.output.decode(scriptCode)
+      requiredSigs = solvedBy.m
+      break
+  }
+
+  return {
+    type: outputType,
+    script: scriptCode,
+    solvedBy: solvedBy,
+    canSign: SIGNABLE_SCRIPTS.indexOf(outputType) !== -1,
+    requiredSigs: requiredSigs
+  }
+}
+
 module.exports = {
   classifyInput: classifyInput,
   classifyOutput: classifyOutput,
   classifyWitness: classifyWitness,
+  solveOutput: solveOutput,
   multisig: multisig,
   nullData: nullData,
   pubKey: pubKey,
@@ -65,5 +119,7 @@ module.exports = {
   scriptHash: scriptHash,
   witnessPubKeyHash: witnessPubKeyHash,
   witnessScriptHash: witnessScriptHash,
-  types: types
+  types: types,
+  SIGNABLE_SCRIPTS: SIGNABLE_SCRIPTS,
+  P2SH_SCRIPTS: P2SH_SCRIPTS
 }

test/script.js

@@ -105,6 +105,30 @@ describe('script', function () {
     })
   })
 
+  describe('solveOutput', function () {
+    fixtures.valid.forEach(function (f) {
+      var script
+      if (f.scriptPubKeyHex) {
+        script = new Buffer(f.scriptPubKeyHex, 'hex')
+      } else if (f.scriptPubKey) {
+        script = bscript.fromASM(f.scriptPubKey)
+      } else {
+        return
+      }
+
+      it('solves ' + bscript.toASM(script) + ' as ' + f.type, function () {
+        var solution = bscript.solveOutput(script)
+        assert.equal(solution.type, f.type)
+        if ([bscript.types.P2SH].concat(bscript.P2SH_SCRIPTS).indexOf(f.type) === -1) {
+          assert.equal(solution.solvedBy, null)
+        }
+        if (solution.canSign) {
+          assert.notEqual(solution.requiredSigs, null)
+        }
+      })
+    })
+  })
+
   describe('SCRIPT_VERIFY_MINIMALDATA policy', function () {
     fixtures.valid.forEach(function (f) {
       if (f.scriptSigHex) {