txb: enforce outputs exist when signing

src/transaction_builder.js

@@ -633,6 +633,8 @@ TransactionBuilder.prototype.sign = function (vin, keyPair, redeemScript, hashTy
   // TODO: remove keyPair.network matching in 4.0.0
   if (keyPair.network && keyPair.network !== this.network) throw new TypeError('Inconsistent network')
   if (!this.__inputs[vin]) throw new Error('No input at index: ' + vin)
+  if (this.__needsOutputs()) throw new Error('Transaction needs outputs')
+
   hashType = hashType || Transaction.SIGHASH_ALL
 
   const input = this.__inputs[vin]
@@ -694,8 +696,7 @@ function signatureHashType (buffer) {
 
 TransactionBuilder.prototype.__canModifyInputs = function () {
   return this.__inputs.every(function (input) {
-    // any signatures?
+    if (!input.signatures) return true
-    if (input.signatures === undefined) return true
 
     return input.signatures.every(function (signature) {
       if (!signature) return true
@@ -708,6 +709,20 @@ TransactionBuilder.prototype.__canModifyInputs = function () {
   })
 }
 
+TransactionBuilder.prototype.__needsOutputs = function () {
+  // if any signature is not SIGHASH_NONE,
+  // we need outputs
+  return (this.__tx.outs.length === 0) && this.__inputs.some(function (input) {
+    if (!input.signatures) return false
+
+    return input.signatures.some(function (signature) {
+      if (!signature) return false
+      const hashType = signatureHashType(signature)
+      return ~(hashType & Transaction.SIGHASH_NONE)
+    })
+  })
+}
+
 TransactionBuilder.prototype.__canModifyOutputs = function () {
   const nInputs = this.__tx.ins.length
   const nOutputs = this.__tx.outs.length

test/fixtures/transaction_builder.json

@@ -2336,6 +2336,22 @@
             "value": 1000
           }
         ]
+      },
+      {
+        "description": "Transaction w/ no outputs",
+        "exception": "Transaction needs outputs",
+        "inputs": [
+          {
+            "txId": "ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff",
+            "vout": 0,
+            "signs": [
+              {
+                "keyPair": "KwDiBf89QgGbjEhKnhXJuH7LrciVrZi3qYjgd9M7rFU73sVHnoWn"
+              }
+            ]
+          }
+        ],
+        "outputs": []
       }
     ],
     "fromTransaction": [

test/transaction_builder.js

@@ -289,6 +289,7 @@ describe('TransactionBuilder', function () {
     it('throws if if there exist any scriptSigs', function () {
       const txb = new TransactionBuilder()
       txb.addInput(txHash, 0)
+      txb.addOutput(scripts[0], 100)
       txb.sign(0, keyPair)
 
       assert.throws(function () {