ScriptSignature from P2WSH Witness (#1605)

core-test/src/test/scala/org/bitcoins/core/protocol/script/ScriptWitnessSpec.scala

@@ -19,4 +19,12 @@ class ScriptWitnessSpec extends Properties("ScriptWitnessSpec") {
         P2WSHWitnessV0(spk).redeemScript == spk
     }
   }
+
+  property("pull script signature out of p2wsh witness") = {
+    Prop.forAll(ScriptGenerators.rawScriptPubKey,
+                ScriptGenerators.rawScriptSignature) {
+      case ((spk, _), scriptSig) =>
+        P2WSHWitnessV0(spk, scriptSig).scriptSignature == scriptSig
+    }
+  }
 }

core/src/main/scala/org/bitcoins/core/protocol/script/ScriptWitness.scala

@@ -1,7 +1,11 @@
 package org.bitcoins.core.protocol.script
 
 import org.bitcoins.core.protocol.CompactSizeUInt
-import org.bitcoins.core.serializers.script.RawScriptWitnessParser
+import org.bitcoins.core.script.constant.{OP_0, ScriptNumberOperation}
+import org.bitcoins.core.serializers.script.{
+  RawScriptWitnessParser,
+  ScriptParser
+}
 import org.bitcoins.core.util.{BitcoinScriptUtil, BytesUtil}
 import org.bitcoins.crypto.{
   ECDigitalSignature,
@@ -106,6 +110,21 @@ sealed abstract class P2WSHWitnessV0 extends ScriptWitnessV0 {
     relevantStack.map(ECDigitalSignature.fromBytes)
   }
 
+  // Note that this is not guaranteed to work for non-standard script signatures
+  lazy val scriptSignature: ScriptSignature = {
+    val asm = stack.toVector.tail.reverse.flatMap { bytes =>
+      if (bytes.isEmpty) {
+        Vector(OP_0)
+      } else if (bytes.length == 1 && bytes.head <= 16 && bytes.head >= -1) {
+        ScriptNumberOperation.fromNumber(bytes.head.toLong).toVector
+      } else {
+        ScriptParser.fromBytes(CompactSizeUInt.calc(bytes).bytes ++ bytes)
+      }
+    }
+
+    ScriptSignature.fromAsm(asm)
+  }
+
   override def toString =
     s"P2WSHWitnessV0(${stack.map(BytesUtil.encodeHex(_)).toString})"
 }

testkit/src/main/scala/org/bitcoins/testkit/core/gen/ScriptGenerators.scala

@@ -539,6 +539,17 @@ sealed abstract class ScriptGenerators extends BitcoinSLogger {
     )
   }
 
+  def rawScriptSignature: Gen[ScriptSignature] = {
+    Gen.oneOf(
+      p2pkScriptSignature,
+      p2pkhScriptSignature,
+      p2pkWithTimeoutScriptSignature,
+      multiSignatureScriptSignature,
+      emptyScriptSignature,
+      conditionalScriptSignature
+    )
+  }
+
   /**
     * Generates a `ScriptSignature` corresponding to the type of
     * `ScriptPubKey` given.