script convenience methods

src/main/java/com/sparrowwallet/drongo/protocol/Script.java

@@ -106,6 +106,10 @@ public class Script {
         return Hex.toHexString(getProgram());
     }
 
+    public boolean isEmpty() {
+        return chunks.isEmpty();
+    }
+
     public List<ScriptChunk> getChunks() {
         return Collections.unmodifiableList(chunks);
     }
@@ -165,6 +169,16 @@ public class Script {
         throw new NonStandardScriptException("Cannot find number of required signatures for non standard script: " + toString());
     }
 
+    public Script getFirstNestedScript() {
+        for(ScriptChunk chunk : chunks) {
+            if(chunk.isScript()) {
+                return new Script(chunk.getData());
+            }
+        }
+
+        return null;
+    }
+
     public static int decodeFromOpN(int opcode) {
         if((opcode != OP_0 && opcode != OP_1NEGATE) && (opcode < OP_1 || opcode > OP_16)) {
             throw new ProtocolException("decodeFromOpN called on non OP_N opcode: " + opcode);

src/main/java/com/sparrowwallet/drongo/protocol/ScriptChunk.java

@@ -42,7 +42,7 @@ public class ScriptChunk {
      * If this chunk is a single byte of non-pushdata content (could be OP_RESERVED or some invalid Opcode)
      */
     public boolean isOpCode() {
-        return opcode > OP_PUSHDATA4;
+        return opcode == ScriptOpCodes.OP_0 || opcode > OP_PUSHDATA4;
     }
 
     public void write(OutputStream stream) throws IOException {
@@ -146,6 +146,9 @@ public class ScriptChunk {
     }
 
     static int getOpcodeForLength(int length) {
+        if(length == 0) {
+            return OP_0;
+        }
         if(length <= 0xFF) {
             return OP_PUSHDATA1;
         }

src/main/java/com/sparrowwallet/drongo/protocol/TransactionWitness.java

@@ -71,13 +71,13 @@ public class TransactionWitness {
         return builder.toString().trim();
     }
 
-    public String toDisplayString() {
+    public List<ScriptChunk> asScriptChunks() {
         List<ScriptChunk> scriptChunks = new ArrayList<>(pushes.size());
         for(byte[] push : pushes) {
            scriptChunks.add(new ScriptChunk(ScriptChunk.getOpcodeForLength(push.length), push));
         }
 
-        return Script.toDisplayString(scriptChunks);
+        return scriptChunks;
     }
 
     @Override