Add invariant to WitnessTransaction that says inputs.length == witnes… (#954)

* Add invariant to WitnessTransaction that says inputs.length == witnesses.length

* Remove println

* Address code review

core-test/src/test/scala/org/bitcoins/core/crypto/TransactionSignatureSerializerTest.scala

@@ -205,12 +205,13 @@ class TransactionSignatureSerializerTest extends FlatSpec with MustMatchers {
                                         oldInput.sequence)
 
     val updatedInputs = ubtx.inputs.updated(inputIndex.toInt, updatedInput)
+    val witness = EmptyWitness.fromInputs(updatedInputs)
 
-    val uwtx = WitnessTransaction(ubtx.version,
-                                  updatedInputs,
-                                  ubtx.outputs,
-                                  ubtx.lockTime,
-                                  EmptyWitness)
+    val uwtx = WitnessTransaction(version = ubtx.version,
+                                  inputs = updatedInputs,
+                                  outputs = ubtx.outputs,
+                                  lockTime = ubtx.lockTime,
+                                  witness = witness)
 
     val wtxSigComp = {
       WitnessTxSigComponentP2SH(transaction = uwtx,

core-test/src/test/scala/org/bitcoins/core/protocol/transaction/TransactionWitnessSpec.scala

@@ -20,7 +20,7 @@ class TransactionWitnessSpec extends BitcoinSUnitTest {
   }
 
   it must "be able to resize a witness to the given index" in {
-    val empty = EmptyWitness
+    val empty = EmptyWitness.fromN(0)
     val pubKey = ECPrivateKey.freshPrivateKey.publicKey
     val p2pkh = P2PKHScriptSignature(EmptyDigitalSignature, pubKey)
     val scriptWit = P2WPKHWitnessV0.fromP2PKHScriptSig(p2pkh)
@@ -31,7 +31,7 @@ class TransactionWitnessSpec extends BitcoinSUnitTest {
 
   it must "fail to update a negative index witness" in {
     intercept[IndexOutOfBoundsException] {
-      EmptyWitness.updated(-1, EmptyScriptWitness)
+      EmptyWitness.fromN(0).updated(-1, EmptyScriptWitness)
     }
   }
 

core/src/main/scala/org/bitcoins/core/protocol/transaction/Transaction.scala

@@ -119,6 +119,10 @@ case object EmptyTransaction extends BaseTransaction {
 }
 
 sealed abstract class WitnessTransaction extends Transaction {
+  require(
+    inputs.length == witness.witnesses.length,
+    s"Must have same amount of inputs and witnesses in witness tx, inputs=${inputs.length} witnesses=${witness.witnesses.length}"
+  )
 
   /** The txId for the witness transaction from satoshi's original serialization */
   override def txId: DoubleSha256Digest = {
@@ -224,7 +228,7 @@ object WitnessTransaction extends Factory[WitnessTransaction] {
                          btx.inputs,
                          btx.outputs,
                          btx.lockTime,
-                         EmptyWitness)
+                         EmptyWitness.fromInputs(btx.inputs))
     case wtx: WitnessTransaction => wtx
   }
 }

core/src/main/scala/org/bitcoins/core/protocol/transaction/TransactionWitness.scala

@@ -55,10 +55,26 @@ sealed abstract class TransactionWitness extends NetworkElement {
   }
 }
 
-/** Used to represent a transaction witness pre segwit, see BIP141 for details */
-case object EmptyWitness extends TransactionWitness {
-  override val bytes: ByteVector = ByteVector.low(1)
-  override val witnesses: Vector[ScriptWitness] = Vector.empty
+/** Each input (even if it does not spend a segwit output) needs to have a witness associated with it
+  * in a [[WitnessTransaction]]. This helper case class is used to "fill in" [[EmptyScriptWitness]] for
+  * the inputs that do not spend a [[org.bitcoins.core.protocol.script.WitnessScriptPubKeyV0 WitnessScriptPubKeyV0]]
+  *
+  * @see https://github.com/bitcoin/bips/blob/master/bip-0141.mediawiki#specification
+  * */
+case class EmptyWitness(witnesses: Vector[EmptyScriptWitness.type])
+    extends TransactionWitness
+
+object EmptyWitness {
+
+  /** Generates an empty witness with n [[EmptyScriptWitness]] inside it */
+  def fromN(n: Int): EmptyWitness = {
+    val wits = Vector.fill(n)(EmptyScriptWitness)
+    new EmptyWitness(wits)
+  }
+
+  def fromInputs(inputs: Seq[TransactionInput]): EmptyWitness = {
+    fromN(inputs.length)
+  }
 }
 
 object TransactionWitness {
@@ -69,7 +85,8 @@ object TransactionWitness {
     if (witnesses.exists(_ != EmptyScriptWitness)) {
       TransactionWitnessImpl(witnesses)
     } else {
-      EmptyWitness
+      //means that everything must be a empty ScriptWitness
+      EmptyWitness.fromN(witnesses.length)
     }
   }
 

core/src/main/scala/org/bitcoins/core/wallet/signer/Signer.scala

@@ -113,7 +113,8 @@ sealed abstract class Signer[-SpendingInfo <: UTXOSpendingInfo] {
               spendingInfo.scriptWitnessOpt.map(scriptWit =>
                 TransactionWitness(Vector(scriptWit)))
             val transactionWitness =
-              transactionWitnessOpt.getOrElse(EmptyWitness)
+              transactionWitnessOpt.getOrElse(
+                EmptyWitness.fromInputs(btx.inputs))
 
             WitnessTransaction(btx.version,
                                btx.inputs,
@@ -407,11 +408,7 @@ sealed abstract class P2WPKHSigner extends BitcoinSigner[P2WPKHV0SpendingInfo] {
 
           }
         case btx: BaseTransaction =>
-          val wtx = WitnessTransaction(btx.version,
-                                       btx.inputs,
-                                       btx.outputs,
-                                       btx.lockTime,
-                                       EmptyWitness)
+          val wtx = WitnessTransaction.toWitnessTx(btx)
 
           sign(spendingInfoToSatisfy, wtx, isDummySignature)
       }
@@ -433,15 +430,7 @@ sealed abstract class P2WSHSigner extends BitcoinSigner[P2WSHV0SpendingInfo] {
     } else {
       val (_, output, inputIndex, _) = relevantInfo(spendingInfo, unsignedTx)
 
-      val wtx = unsignedTx match {
-        case btx: BaseTransaction =>
-          WitnessTransaction(btx.version,
-                             btx.inputs,
-                             btx.outputs,
-                             btx.lockTime,
-                             EmptyWitness)
-        case wtx: WitnessTransaction => wtx
-      }
+      val wtx = WitnessTransaction.toWitnessTx(unsignedTx)
 
       val signedSigComponentF = BitcoinSigner.sign(
         spendingInfo,