support detection of utf8 string script chunks

src/main/java/com/sparrowwallet/drongo/Utils.java

@@ -13,6 +13,7 @@ import java.io.InputStream;
 import java.io.OutputStream;
 import java.math.BigInteger;
 import java.nio.ByteBuffer;
+import java.nio.charset.CharsetDecoder;
 import java.nio.charset.StandardCharsets;
 import java.util.*;
 
@@ -31,6 +32,16 @@ public class Utils {
         return s.matches(BASE64_REGEX);
     }
 
+    public static boolean isUtf8(byte[] bytes) {
+        try {
+            CharsetDecoder decoder = StandardCharsets.UTF_8.newDecoder();
+            decoder.decode(java.nio.ByteBuffer.wrap(bytes));
+            return true;
+        } catch(Exception e) {
+            return false;
+        }
+    }
+
     public static String bytesToHex(byte[] bytes) {
         char[] hexChars = new char[bytes.length * 2];
         for ( int j = 0; j < bytes.length; j++ ) {

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

@@ -7,6 +7,8 @@ import org.bouncycastle.util.encoders.Hex;
 import java.io.ByteArrayOutputStream;
 import java.io.IOException;
 import java.io.OutputStream;
+import java.nio.charset.Charset;
+import java.nio.charset.StandardCharsets;
 import java.util.Arrays;
 import java.util.Objects;
 
@@ -28,7 +30,11 @@ public class ScriptChunk {
     }
 
     public static ScriptChunk fromOpcode(int opcode) {
-        return new ScriptChunk(opcode, null);
+        return new ScriptChunk(opcode, opcode == ScriptOpCodes.OP_0 ? new byte[0] : null);
+    }
+
+    public static ScriptChunk fromString(String strData, Charset charset) {
+        return fromData(strData.getBytes(charset));
     }
 
     public static ScriptChunk fromData(byte[] data) {
@@ -68,7 +74,7 @@ public class ScriptChunk {
     }
 
     public void write(OutputStream stream) throws IOException {
-        if (isOpCode()) {
+        if (isOpCode() && opcode != ScriptOpCodes.OP_0) {
             if(data != null) throw new IllegalStateException("Data must be null for opcode chunk");
             stream.write(opcode);
         } else if (data != null) {
@@ -126,6 +132,18 @@ public class ScriptChunk {
         }
     }
 
+    public boolean isString() {
+        if(data == null || data.length == 0) {
+            return false;
+        }
+
+        if(isSignature() || isPubKey()) {
+            return false;
+        }
+
+        return Utils.isUtf8(data);
+    }
+
     public boolean isScript() {
         if(data == null || data.length == 0) {
             return false;
@@ -213,6 +231,9 @@ public class ScriptChunk {
         if (data.length == 0) {
             return "OP_0";
         }
+        if(Utils.isUtf8(data)) {
+            return new String(data, StandardCharsets.UTF_8);
+        }
 
         return Hex.toHexString(data);
     }