tx input construction from script type

src/main/java/com/sparrowwallet/drongo/address/Address.java

@@ -2,6 +2,7 @@ package com.sparrowwallet.drongo.address;
 
 import com.sparrowwallet.drongo.protocol.Base58;
 import com.sparrowwallet.drongo.protocol.Bech32;
+import com.sparrowwallet.drongo.protocol.Script;
 import com.sparrowwallet.drongo.protocol.ScriptType;
 
 import java.util.Arrays;
@@ -31,6 +32,8 @@ public abstract class Address {
 
     public abstract ScriptType getScriptType();
 
+    public abstract Script getOutputScript();
+
     public abstract byte[] getOutputScriptData();
 
     public abstract String getOutputScriptDataType();

src/main/java/com/sparrowwallet/drongo/address/P2PKAddress.java

@@ -1,11 +1,9 @@
 package com.sparrowwallet.drongo.address;
 
 import com.sparrowwallet.drongo.Utils;
+import com.sparrowwallet.drongo.protocol.Script;
 import com.sparrowwallet.drongo.protocol.ScriptType;
 
-import java.util.ArrayList;
-import java.util.List;
-
 public class P2PKAddress extends Address {
     private byte[] pubKey;
 
@@ -22,6 +20,10 @@ public class P2PKAddress extends Address {
         return ScriptType.P2PK;
     }
 
+    public Script getOutputScript() {
+        return getScriptType().getOutputScript(pubKey);
+    }
+
     @Override
     public byte[] getOutputScriptData() {
         return pubKey;

src/main/java/com/sparrowwallet/drongo/address/P2PKHAddress.java

@@ -1,5 +1,6 @@
 package com.sparrowwallet.drongo.address;
 
+import com.sparrowwallet.drongo.protocol.Script;
 import com.sparrowwallet.drongo.protocol.ScriptType;
 
 public class P2PKHAddress extends Address {
@@ -15,6 +16,10 @@ public class P2PKHAddress extends Address {
         return ScriptType.P2PKH;
     }
 
+    public Script getOutputScript() {
+        return getScriptType().getOutputScript(hash);
+    }
+
     @Override
     public byte[] getOutputScriptData() {
         return hash;

src/main/java/com/sparrowwallet/drongo/address/P2SHAddress.java

@@ -1,6 +1,7 @@
 package com.sparrowwallet.drongo.address;
 
 import com.sparrowwallet.drongo.Utils;
+import com.sparrowwallet.drongo.protocol.Script;
 import com.sparrowwallet.drongo.protocol.ScriptType;
 
 public class P2SHAddress extends Address {
@@ -12,10 +13,16 @@ public class P2SHAddress extends Address {
         return 5;
     }
 
+    @Override
     public ScriptType getScriptType() {
         return ScriptType.P2SH;
     }
 
+    @Override
+    public Script getOutputScript() {
+        return getScriptType().getOutputScript(hash);
+    }
+
     @Override
     public byte[] getOutputScriptData() {
         return hash;

src/main/java/com/sparrowwallet/drongo/address/P2WPKHAddress.java

@@ -1,6 +1,7 @@
 package com.sparrowwallet.drongo.address;
 
 import com.sparrowwallet.drongo.protocol.Bech32;
+import com.sparrowwallet.drongo.protocol.Script;
 import com.sparrowwallet.drongo.protocol.ScriptType;
 
 public class P2WPKHAddress extends Address {
@@ -22,6 +23,11 @@ public class P2WPKHAddress extends Address {
         return ScriptType.P2WPKH;
     }
 
+    @Override
+    public Script getOutputScript() {
+        return getScriptType().getOutputScript(hash);
+    }
+
     @Override
     public byte[] getOutputScriptData() {
         return hash;

src/main/java/com/sparrowwallet/drongo/address/P2WSHAddress.java

@@ -21,6 +21,11 @@ public class P2WSHAddress extends Address {
         return ScriptType.P2WSH;
     }
 
+    @Override
+    public Script getOutputScript() {
+        return getScriptType().getOutputScript(hash);
+    }
+
     @Override
     public byte[] getOutputScriptData() {
         return hash;

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

@@ -4,7 +4,11 @@ public abstract class ChildMessage extends Message {
 
     protected Message parent;
 
-    public ChildMessage(byte[] rawtx, int offset) {
+    protected ChildMessage() {
+        super();
+    }
+
+    protected ChildMessage(byte[] rawtx, int offset) {
         super(rawtx, offset);
     }
 

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

@@ -23,7 +23,11 @@ public abstract class Message {
 
     protected int length = UNKNOWN_LENGTH;
 
-    public Message(byte[] payload, int offset) {
+    protected Message() {
+
+    }
+
+    protected Message(byte[] payload, int offset) {
         this.payload = payload;
         this.cursor = this.offset = offset;
 

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

@@ -41,10 +41,10 @@ public class Script {
     }
 
     private static final ScriptChunk[] STANDARD_TRANSACTION_SCRIPT_CHUNKS = {
-            new ScriptChunk(ScriptOpCodes.OP_DUP, null, 0),
+            new ScriptChunk(ScriptOpCodes.OP_DUP, null),
-            new ScriptChunk(ScriptOpCodes.OP_HASH160, null, 1),
+            new ScriptChunk(ScriptOpCodes.OP_HASH160, null),
-            new ScriptChunk(ScriptOpCodes.OP_EQUALVERIFY, null, 23),
+            new ScriptChunk(ScriptOpCodes.OP_EQUALVERIFY, null),
-            new ScriptChunk(ScriptOpCodes.OP_CHECKSIG, null, 24),
+            new ScriptChunk(ScriptOpCodes.OP_CHECKSIG, null),
     };
 
     void parse() {
@@ -52,7 +52,6 @@ public class Script {
         ByteArrayInputStream bis = new ByteArrayInputStream(program);
         int initialSize = bis.available();
         while (bis.available() > 0) {
-            int startLocationInProgram = initialSize - bis.available();
             int opcode = bis.read();
 
             long dataToRead = -1;
@@ -75,7 +74,7 @@ public class Script {
 
             ScriptChunk chunk;
             if (dataToRead == -1) {
-                chunk = new ScriptChunk(opcode, null, startLocationInProgram);
+                chunk = new ScriptChunk(opcode, null);
             } else {
                 if (dataToRead > bis.available())
                     throw new ProtocolException("Push of data element that is larger than remaining data");
@@ -84,7 +83,7 @@ public class Script {
                     throw new ProtocolException();
                 }
 
-                chunk = new ScriptChunk(opcode, data, startLocationInProgram);
+                chunk = new ScriptChunk(opcode, data);
             }
             // Save some memory by eliminating redundant copies of the same chunk objects.
             for (ScriptChunk c : STANDARD_TRANSACTION_SCRIPT_CHUNKS) {

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

@@ -22,16 +22,38 @@ public class ScriptChunk {
      */
     public final byte[] data;
 
-    private int startLocationInProgram;
-
     public ScriptChunk(int opcode, byte[] data) {
-        this(opcode, data, -1);
-    }
-
-    public ScriptChunk(int opcode, byte[] data, int startLocationInProgram) {
         this.opcode = opcode;
         this.data = data;
-        this.startLocationInProgram = startLocationInProgram;
+    }
+
+    public static ScriptChunk fromOpcode(int opcode) {
+        return new ScriptChunk(opcode, null);
+    }
+
+    public static ScriptChunk fromData(byte[] data) {
+        byte[] copy = Arrays.copyOf(data, data.length);
+        int opcode;
+        if (data.length == 0) {
+            opcode = OP_0;
+        } else if (data.length == 1) {
+            byte b = data[0];
+            if (b >= 1 && b <= 16) {
+                opcode = Script.encodeToOpN(b);
+            } else {
+                opcode = 1;
+            }
+        } else if (data.length < OP_PUSHDATA1) {
+            opcode = data.length;
+        } else if (data.length < 256) {
+            opcode = OP_PUSHDATA1;
+        } else if (data.length < 65536) {
+            opcode = OP_PUSHDATA2;
+        } else {
+            opcode = OP_PUSHDATA4;
+        }
+
+        return new ScriptChunk(opcode, copy);
     }
 
     public boolean equalsOpCode(int opcode) {

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

@@ -92,6 +92,33 @@ public enum ScriptType {
             return ECKey.fromPublicOnly(script.chunks.get(0).data);
         }
 
+        @Override
+        public Script getScriptSig(Script scriptPubKey, ECKey pubKey, TransactionSignature signature) {
+            if(!isScriptType(scriptPubKey)) {
+                throw new ProtocolException("Provided scriptPubKey is not a " + getName() + " script");
+            }
+
+            byte[] signatureBytes = signature.encodeToBitcoin();
+            ScriptChunk signatureChunk = ScriptChunk.fromData(signatureBytes);
+            return new Script(List.of(signatureChunk));
+        }
+
+        @Override
+        public TransactionInput addSpendingInput(Transaction transaction, TransactionOutput prevOutput, ECKey pubKey, TransactionSignature signature) {
+            Script scriptSig = getScriptSig(prevOutput.getScript(), pubKey, signature);
+            return transaction.addInput(prevOutput.getHash(), prevOutput.getIndex(), scriptSig);
+        }
+
+        @Override
+        public Script getMultisigScriptSig(Script scriptPubKey, int threshold, List<ECKey> pubKeys, List<TransactionSignature> signatures) {
+            throw new ProtocolException(getName() + " is not a multisig script type");
+        }
+
+        @Override
+        public TransactionInput addMultisigSpendingInput(Transaction transaction, TransactionOutput prevOutput, int threshold, List<ECKey> pubKeys, List<TransactionSignature> signatures) {
+            throw new ProtocolException(getName() + " is not a multisig script type");
+        }
+
         @Override
         public List<PolicyType> getAllowedPolicyTypes() {
             return List.of(SINGLE);
@@ -171,6 +198,35 @@ public enum ScriptType {
             return script.chunks.get(2).data;
         }
 
+        @Override
+        public Script getScriptSig(Script scriptPubKey, ECKey pubKey, TransactionSignature signature) {
+            if(!isScriptType(scriptPubKey)) {
+                throw new ProtocolException("Provided scriptPubKey is not a " + getName() + " script");
+            }
+
+            byte[] signatureBytes = signature.encodeToBitcoin();
+            ScriptChunk signatureChunk = ScriptChunk.fromData(signatureBytes);
+            byte[] pubKeyBytes = pubKey.getPubKey();
+            ScriptChunk pubKeyChunk = ScriptChunk.fromData(pubKeyBytes);
+            return new Script(List.of(signatureChunk, pubKeyChunk));
+        }
+
+        @Override
+        public TransactionInput addSpendingInput(Transaction transaction, TransactionOutput prevOutput, ECKey pubKey, TransactionSignature signature) {
+            Script scriptSig = getScriptSig(prevOutput.getScript(), pubKey, signature);
+            return transaction.addInput(prevOutput.getHash(), prevOutput.getIndex(), scriptSig);
+        }
+
+        @Override
+        public Script getMultisigScriptSig(Script scriptPubKey, int threshold, List<ECKey> pubKeys, List<TransactionSignature> signatures) {
+            throw new ProtocolException(getName() + " is not a multisig script type");
+        }
+
+        @Override
+        public TransactionInput addMultisigSpendingInput(Transaction transaction, TransactionOutput prevOutput, int threshold, List<ECKey> pubKeys, List<TransactionSignature> signatures) {
+            throw new ProtocolException(getName() + " is not a multisig script type");
+        }
+
         @Override
         public List<PolicyType> getAllowedPolicyTypes() {
             return List.of(SINGLE);
@@ -218,6 +274,10 @@ public enum ScriptType {
 
         @Override
         public Script getOutputScript(int threshold, List<ECKey> pubKeys) {
+            if(threshold > pubKeys.size()) {
+                throw new ProtocolException("Threshold of " + threshold + " is greater than number of pubKeys provided (" + pubKeys.size() + ")");
+            }
+
             List<byte[]> pubKeyBytes = new ArrayList<>();
             for(ECKey key : pubKeys) {
                 pubKeyBytes.add(key.getPubKey());
@@ -310,6 +370,42 @@ public enum ScriptType {
             return decodeFromOpN(script.chunks.get(0).opcode);
         }
 
+        @Override
+        public Script getScriptSig(Script scriptPubKey, ECKey pubKey, TransactionSignature signature) {
+            throw new ProtocolException(getName() + " is a multisig script type");
+        }
+
+        @Override
+        public TransactionInput addSpendingInput(Transaction transaction, TransactionOutput prevOutput, ECKey pubKey, TransactionSignature signature) {
+            throw new ProtocolException(getName() + " is a multisig script type");
+        }
+
+        @Override
+        public Script getMultisigScriptSig(Script scriptPubKey, int threshold, List<ECKey> pubKeys, List<TransactionSignature> signatures) {
+            if(!isScriptType(scriptPubKey)) {
+                throw new ProtocolException("Provided scriptPubKey is not a " + getName() + " script");
+            }
+            if(threshold != signatures.size()) {
+                throw new ProtocolException("Only " + signatures.size() + " signatures provided to meet a multisig threshold of " + threshold);
+            }
+
+            List<ScriptChunk> chunks = new ArrayList<>(signatures.size() + 1);
+            ScriptChunk opZero = ScriptChunk.fromOpcode(OP_0);
+            chunks.add(opZero);
+            for(TransactionSignature signature : signatures) {
+                byte[] signatureBytes = signature.encodeToBitcoin();
+                chunks.add(ScriptChunk.fromData(signatureBytes));
+            }
+
+            return new Script(chunks);
+        }
+
+        @Override
+        public TransactionInput addMultisigSpendingInput(Transaction transaction, TransactionOutput prevOutput, int threshold, List<ECKey> pubKeys, List<TransactionSignature> signatures) {
+            Script scriptSig = getMultisigScriptSig(prevOutput.getScript(), threshold, pubKeys, signatures);
+            return transaction.addInput(prevOutput.getHash(), prevOutput.getIndex(), scriptSig);
+        }
+
         @Override
         public List<PolicyType> getAllowedPolicyTypes() {
             return List.of(MULTI);
@@ -395,6 +491,41 @@ public enum ScriptType {
             return script.chunks.get(1).data;
         }
 
+        @Override
+        public Script getScriptSig(Script scriptPubKey, ECKey pubKey, TransactionSignature signature) {
+            throw new ProtocolException("Only multisig scriptSigs supported for " + getName() + " scriptPubKeys");
+        }
+
+        @Override
+        public TransactionInput addSpendingInput(Transaction transaction, TransactionOutput prevOutput, ECKey pubKey, TransactionSignature signature) {
+            throw new ProtocolException("Only multisig scriptSigs supported for " + getName() + " scriptPubKeys");
+        }
+
+        @Override
+        public Script getMultisigScriptSig(Script scriptPubKey, int threshold, List<ECKey> pubKeys, List<TransactionSignature> signatures) {
+            if(!isScriptType(scriptPubKey)) {
+                throw new ProtocolException("Provided scriptPubKey is not a " + getName() + " script");
+            }
+
+            Script redeemScript = MULTISIG.getOutputScript(threshold, pubKeys);
+            if(!scriptPubKey.equals(getOutputScript(redeemScript))) {
+                throw new ProtocolException("P2SH scriptPubKey hash does not match constructed redeem script hash");
+            }
+
+            Script multisigScript = MULTISIG.getMultisigScriptSig(redeemScript, threshold, pubKeys, signatures);
+            List<ScriptChunk> chunks = new ArrayList<>(multisigScript.getChunks());
+            ScriptChunk redeemScriptChunk = ScriptChunk.fromData(redeemScript.getProgram());
+            chunks.add(redeemScriptChunk);
+
+            return new Script(chunks);
+        }
+
+        @Override
+        public TransactionInput addMultisigSpendingInput(Transaction transaction, TransactionOutput prevOutput, int threshold, List<ECKey> pubKeys, List<TransactionSignature> signatures) {
+            Script scriptSig = getMultisigScriptSig(prevOutput.getScript(), threshold, pubKeys, signatures);
+            return transaction.addInput(prevOutput.getHash(), prevOutput.getIndex(), scriptSig);
+        }
+
         @Override
         public List<PolicyType> getAllowedPolicyTypes() {
             return List.of(MULTI);
@@ -461,6 +592,38 @@ public enum ScriptType {
             return P2SH.getHashFromScript(script);
         }
 
+        @Override
+        public Script getScriptSig(Script scriptPubKey, ECKey pubKey, TransactionSignature signature) {
+            if(!isScriptType(scriptPubKey)) {
+                throw new ProtocolException("Provided scriptPubKey is not a " + getName() + " script");
+            }
+
+            Script redeemScript = P2WPKH.getOutputScript(pubKey);
+            if(!scriptPubKey.equals(P2SH.getOutputScript(redeemScript))) {
+                throw new ProtocolException(getName() + " scriptPubKey hash does not match constructed redeem script hash");
+            }
+
+            ScriptChunk redeemScriptChunk = ScriptChunk.fromData(redeemScript.getProgram());
+            return new Script(List.of(redeemScriptChunk));
+        }
+
+        @Override
+        public TransactionInput addSpendingInput(Transaction transaction, TransactionOutput prevOutput, ECKey pubKey, TransactionSignature signature) {
+            Script scriptSig = getScriptSig(prevOutput.getScript(), pubKey, signature);
+            TransactionWitness witness = new TransactionWitness(transaction, pubKey, signature);
+            return transaction.addInput(prevOutput.getHash(), prevOutput.getIndex(), scriptSig, witness);
+        }
+
+        @Override
+        public Script getMultisigScriptSig(Script scriptPubKey, int threshold, List<ECKey> pubKeys, List<TransactionSignature> signatures) {
+            throw new ProtocolException(getName() + " is not a multisig script type");
+        }
+
+        @Override
+        public TransactionInput addMultisigSpendingInput(Transaction transaction, TransactionOutput prevOutput, int threshold, List<ECKey> pubKeys, List<TransactionSignature> signatures) {
+            throw new ProtocolException(getName() + " is not a multisig script type");
+        }
+
         @Override
         public List<PolicyType> getAllowedPolicyTypes() {
             return List.of(SINGLE);
@@ -523,6 +686,40 @@ public enum ScriptType {
             return P2SH.getHashFromScript(script);
         }
 
+        @Override
+        public Script getScriptSig(Script scriptPubKey, ECKey pubKey, TransactionSignature signature) {
+            throw new ProtocolException("Only multisig scriptSigs supported for " + getName() + " scriptPubKeys");
+        }
+
+        @Override
+        public TransactionInput addSpendingInput(Transaction transaction, TransactionOutput prevOutput, ECKey pubKey, TransactionSignature signature) {
+            throw new ProtocolException("Only multisig scriptSigs supported for " + getName() + " scriptPubKeys");
+        }
+
+        @Override
+        public Script getMultisigScriptSig(Script scriptPubKey, int threshold, List<ECKey> pubKeys, List<TransactionSignature> signatures) {
+            if(!isScriptType(scriptPubKey)) {
+                throw new ProtocolException("Provided scriptPubKey is not a " + getName() + " script");
+            }
+
+            Script witnessScript = MULTISIG.getOutputScript(threshold, pubKeys);
+            Script redeemScript = P2WSH.getOutputScript(witnessScript);
+            if(!scriptPubKey.equals(P2SH.getOutputScript(redeemScript))) {
+                throw new ProtocolException("P2SH scriptPubKey hash does not match constructed redeem script hash");
+            }
+
+            ScriptChunk redeemScriptChunk = ScriptChunk.fromData(redeemScript.getProgram());
+            return new Script(List.of(redeemScriptChunk));
+        }
+
+        @Override
+        public TransactionInput addMultisigSpendingInput(Transaction transaction, TransactionOutput prevOutput, int threshold, List<ECKey> pubKeys, List<TransactionSignature> signatures) {
+            Script scriptSig = getMultisigScriptSig(prevOutput.getScript(), threshold, pubKeys, signatures);
+            Script witnessScript = MULTISIG.getOutputScript(threshold, pubKeys);
+            TransactionWitness witness = new TransactionWitness(transaction, signatures, witnessScript);
+            return transaction.addInput(prevOutput.getHash(), prevOutput.getIndex(), scriptSig, witness);
+        }
+
         @Override
         public List<PolicyType> getAllowedPolicyTypes() {
             return List.of(MULTI, CUSTOM);
@@ -593,6 +790,36 @@ public enum ScriptType {
             return script.chunks.get(1).data;
         }
 
+        @Override
+        public Script getScriptSig(Script scriptPubKey, ECKey pubKey, TransactionSignature signature) {
+            if(!isScriptType(scriptPubKey)) {
+                throw new ProtocolException("Provided scriptPubKey is not a " + getName() + " script");
+            }
+
+            if(!scriptPubKey.equals(getOutputScript(pubKey))) {
+                throw new ProtocolException("P2WPKH scriptPubKey hash does not match constructed pubkey script hash");
+            }
+
+            return new Script(new byte[0]);
+        }
+
+        @Override
+        public TransactionInput addSpendingInput(Transaction transaction, TransactionOutput prevOutput, ECKey pubKey, TransactionSignature signature) {
+            Script scriptSig = getScriptSig(prevOutput.getScript(), pubKey, signature);
+            TransactionWitness witness = new TransactionWitness(transaction, pubKey, signature);
+            return transaction.addInput(prevOutput.getHash(), prevOutput.getIndex(), scriptSig, witness);
+        }
+
+        @Override
+        public Script getMultisigScriptSig(Script scriptPubKey, int threshold, List<ECKey> pubKeys, List<TransactionSignature> signatures) {
+            throw new ProtocolException(getName() + " is not a multisig script type");
+        }
+
+        @Override
+        public TransactionInput addMultisigSpendingInput(Transaction transaction, TransactionOutput prevOutput, int threshold, List<ECKey> pubKeys, List<TransactionSignature> signatures) {
+            throw new ProtocolException(getName() + " is not a multisig script type");
+        }
+
         @Override
         public List<PolicyType> getAllowedPolicyTypes() {
             return List.of(SINGLE);
@@ -667,6 +894,38 @@ public enum ScriptType {
             return script.chunks.get(1).data;
         }
 
+        @Override
+        public Script getScriptSig(Script scriptPubKey, ECKey pubKey, TransactionSignature signature) {
+            throw new ProtocolException("Only multisig scriptSigs supported for " + getName() + " scriptPubKeys");
+        }
+
+        @Override
+        public TransactionInput addSpendingInput(Transaction transaction, TransactionOutput prevOutput, ECKey pubKey, TransactionSignature signature) {
+            throw new ProtocolException("Only multisig scriptSigs supported for " + getName() + " scriptPubKeys");
+        }
+
+        @Override
+        public Script getMultisigScriptSig(Script scriptPubKey, int threshold, List<ECKey> pubKeys, List<TransactionSignature> signatures) {
+            if(!isScriptType(scriptPubKey)) {
+                throw new ProtocolException("Provided scriptPubKey is not a " + getName() + " script");
+            }
+
+            Script witnessScript = MULTISIG.getOutputScript(threshold, pubKeys);
+            if(!scriptPubKey.equals(P2WSH.getOutputScript(witnessScript))) {
+                throw new ProtocolException("P2WSH scriptPubKey hash does not match constructed witness script hash");
+            }
+
+            return new Script(new byte[0]);
+        }
+
+        @Override
+        public TransactionInput addMultisigSpendingInput(Transaction transaction, TransactionOutput prevOutput, int threshold, List<ECKey> pubKeys, List<TransactionSignature> signatures) {
+            Script scriptSig = getMultisigScriptSig(prevOutput.getScript(), threshold, pubKeys, signatures);
+            Script witnessScript = MULTISIG.getOutputScript(threshold, pubKeys);
+            TransactionWitness witness = new TransactionWitness(transaction, signatures, witnessScript);
+            return transaction.addInput(prevOutput.getHash(), prevOutput.getIndex(), scriptSig, witness);
+        }
+
         @Override
         public List<PolicyType> getAllowedPolicyTypes() {
             return List.of(MULTI, CUSTOM);
@@ -761,12 +1020,30 @@ public enum ScriptType {
         throw new ProtocolException("Script type " + this + " is not a multisig script");
     }
 
+    public abstract Script getScriptSig(Script scriptPubKey, ECKey pubKey, TransactionSignature signature);
+
+    public abstract TransactionInput addSpendingInput(Transaction transaction, TransactionOutput prevOutput, ECKey pubKey, TransactionSignature signature);
+
+    public abstract Script getMultisigScriptSig(Script scriptPubKey, int threshold, List<ECKey> pubKeys, List<TransactionSignature> signatures);
+
+    public abstract TransactionInput addMultisigSpendingInput(Transaction transaction, TransactionOutput prevOutput, int threshold, List<ECKey> pubKeys, List<TransactionSignature> signatures);
+
     public static final ScriptType[] SINGLE_HASH_TYPES = {P2PKH, P2SH, P2SH_P2WPKH, P2SH_P2WSH, P2WPKH, P2WSH};
 
     public static List<ScriptType> getScriptTypesForPolicyType(PolicyType policyType) {
         return Arrays.stream(values()).filter(scriptType -> scriptType.isAllowed(policyType)).collect(Collectors.toList());
     }
 
+    public static ScriptType getType(Script script) {
+        for(ScriptType type : values()) {
+            if(type.isScriptType(script)) {
+                return type;
+            }
+        }
+
+        return null;
+    }
+
     @Override
     public String toString() {
         return name;

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

@@ -33,6 +33,13 @@ public class Transaction extends ChildMessage {
     private ArrayList<TransactionInput> inputs;
     private ArrayList<TransactionOutput> outputs;
 
+    public Transaction() {
+        version = 1;
+        inputs = new ArrayList<>();
+        outputs = new ArrayList<>();
+        length = 8;
+    }
+
     public Transaction(byte[] rawtx) {
         super(rawtx, 0);
     }
@@ -125,6 +132,11 @@ public class Transaction extends ChildMessage {
     }
 
     public void setSegwitVersion(int segwitVersion) {
+        if(!segwit) {
+            adjustLength(2);
+            this.segwit = true;
+        }
+
         this.segwitVersion = segwitVersion;
     }
 
@@ -272,10 +284,44 @@ public class Transaction extends ChildMessage {
         return Collections.unmodifiableList(inputs);
     }
 
+    public TransactionInput addInput(Sha256Hash spendTxHash, long outputIndex, Script script) {
+        return addInput(new TransactionInput(this, new TransactionOutPoint(spendTxHash, outputIndex), script.getProgram()));
+    }
+
+    public TransactionInput addInput(Sha256Hash spendTxHash, long outputIndex, Script script, TransactionWitness witness) {
+        return addInput(new TransactionInput(this, new TransactionOutPoint(spendTxHash, outputIndex), script.getProgram(), witness));
+    }
+
+    public TransactionInput addInput(TransactionInput input) {
+        input.setParent(this);
+        inputs.add(input);
+        adjustLength(inputs.size(), input.length);
+        return input;
+    }
+
     public List<TransactionOutput> getOutputs() {
         return Collections.unmodifiableList(outputs);
     }
 
+    public TransactionOutput addOutput(long value, Script script) {
+        return addOutput(new TransactionOutput(this, value, script));
+    }
+
+    public TransactionOutput addOutput(long value, Address address) {
+        return addOutput(new TransactionOutput(this, value, address.getOutputScript()));
+    }
+
+    public TransactionOutput addOutput(long value, ECKey pubkey) {
+        return addOutput(new TransactionOutput(this, value, ScriptType.P2PK.getOutputScript(pubkey)));
+    }
+
+    public TransactionOutput addOutput(TransactionOutput output) {
+        output.setParent(this);
+        outputs.add(output);
+        adjustLength(outputs.size(), output.length);
+        return output;
+    }
+
     public void verify() throws VerificationException {
         if (inputs.size() == 0 || outputs.size() == 0)
             throw new VerificationException.EmptyInputsOrOutputs();

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

@@ -25,6 +25,23 @@ public class TransactionInput extends ChildMessage {
 
     private TransactionWitness witness;
 
+    public TransactionInput(Transaction transaction, TransactionOutPoint outpoint, byte[] scriptBytes) {
+        this(transaction, outpoint, scriptBytes, null);
+    }
+
+    public TransactionInput(Transaction transaction, TransactionOutPoint outpoint, byte[] scriptBytes, TransactionWitness witness) {
+        setParent(transaction);
+        this.sequence = SEQUENCE_LOCKTIME_DISABLED;
+        this.outpoint = outpoint;
+        this.outpoint.setParent(this);
+        this.scriptBytes = scriptBytes;
+        this.witness = witness;
+        length = 40 + (scriptBytes == null ? 1 : VarInt.sizeOf(scriptBytes.length) + scriptBytes.length);
+        if(witness != null) {
+            transaction.adjustLength(witness.getLength());
+        }
+    }
+
     public TransactionInput(Transaction transaction, byte[] rawtx, int offset) {
         super(rawtx, offset);
         setParent(transaction);

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

@@ -18,6 +18,12 @@ public class TransactionOutPoint extends ChildMessage {
 
     private Address[] addresses = new Address[0];
 
+    public TransactionOutPoint(Sha256Hash hash, long index) {
+        this.hash = hash;
+        this.index = index;
+        length = MESSAGE_LENGTH;
+    }
+
     public TransactionOutPoint(byte[] rawtx, int offset, Message parent) {
         super(rawtx, offset);
         setParent(parent);

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

@@ -3,7 +3,6 @@ package com.sparrowwallet.drongo.protocol;
 import com.sparrowwallet.drongo.Utils;
 import com.sparrowwallet.drongo.address.Address;
 
-import java.io.ByteArrayOutputStream;
 import java.io.IOException;
 import java.io.OutputStream;
 
@@ -19,27 +18,22 @@ public class TransactionOutput extends ChildMessage {
 
     private Address[] addresses = new Address[0];
 
+    public TransactionOutput(Transaction transaction, long value, Script script) {
+        this(transaction, value, script.getProgram());
+    }
+
+    public TransactionOutput(Transaction transaction, long value, byte[] scriptBytes) {
+        this.value = value;
+        this.scriptBytes = scriptBytes;
+        setParent(transaction);
+        length = 8 + VarInt.sizeOf(scriptBytes.length) + scriptBytes.length;
+    }
+
     public TransactionOutput(Transaction parent, byte[] rawtx, int offset) {
         super(rawtx, offset);
         setParent(parent);
     }
 
-    public TransactionOutput(Transaction parent, long value, byte[] scriptBytes) {
-        super(new byte[0], 0);
-        this.value = value;
-        this.scriptBytes = scriptBytes;
-        setParent(parent);
-        length = 8 + VarInt.sizeOf(scriptBytes.length) + scriptBytes.length;
-
-        try {
-            ByteArrayOutputStream baos = new ByteArrayOutputStream();
-            bitcoinSerializeToStream(baos);
-            payload = baos.toByteArray();
-        } catch(IOException e) {
-            //ignore
-        }
-    }
-
     protected void parse() throws ProtocolException {
         value = readInt64();
         int scriptLen = (int) readVarInt();
@@ -78,6 +72,11 @@ public class TransactionOutput extends ChildMessage {
         this.addresses = addresses;
     }
 
+    public Sha256Hash getHash() {
+        Transaction transaction = (Transaction)parent;
+        return transaction.getTxId();
+    }
+
     public int getIndex() {
         Transaction transaction = (Transaction)parent;
         return transaction.getOutputs().indexOf(this);

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

@@ -1,5 +1,6 @@
 package com.sparrowwallet.drongo.protocol;
 
+import com.sparrowwallet.drongo.crypto.ECKey;
 import org.bouncycastle.util.encoders.Hex;
 
 import java.io.ByteArrayOutputStream;
@@ -13,6 +14,30 @@ import java.util.List;
 public class TransactionWitness extends ChildMessage {
     private List<byte[]> pushes;
 
+    public TransactionWitness(Transaction transaction, ECKey pubKey, TransactionSignature signature) {
+        setParent(transaction);
+        this.pushes = new ArrayList<>();
+        pushes.add(signature.encodeToBitcoin());
+        pushes.add(pubKey.getPubKey());
+    }
+
+    public TransactionWitness(Transaction transaction, List<TransactionSignature> signatures, Script witnessScript) {
+        setParent(transaction);
+        this.pushes = new ArrayList<>();
+        if(ScriptType.MULTISIG.isScriptType(witnessScript)) {
+            pushes.add(new byte[] { ScriptOpCodes.OP_0 });
+        }
+        for(TransactionSignature signature : signatures) {
+            pushes.add(signature.encodeToBitcoin());
+        }
+        pushes.add(witnessScript.getProgram());
+    }
+
+    public TransactionWitness(Transaction transaction, List<byte[]> witnesses) {
+        setParent(transaction);
+        this.pushes = witnesses;
+    }
+
     public TransactionWitness(Transaction parent, byte[] rawtx, int offset) {
         super(rawtx, offset);
         setParent(parent);
@@ -53,9 +78,13 @@ public class TransactionWitness extends ChildMessage {
         int length = new VarInt(pushes.size()).getSizeInBytes();
         for (int i = 0; i < pushes.size(); i++) {
             byte[] push = pushes.get(i);
+            if(push.length == 1 && push[0] == 0) {
+                length++;
+            } else {
                 length += new VarInt(push.length).getSizeInBytes();
                 length += push.length;
             }
+        }
 
         return length;
     }
@@ -64,10 +93,14 @@ public class TransactionWitness extends ChildMessage {
         stream.write(new VarInt(pushes.size()).encode());
         for (int i = 0; i < pushes.size(); i++) {
             byte[] push = pushes.get(i);
+            if(push.length == 1 && push[0] == 0) {
+                stream.write(push);
+            } else {
                 stream.write(new VarInt(push.length).encode());
                 stream.write(push);
             }
         }
+    }
 
     public byte[] toByteArray() {
         ByteArrayOutputStream baos = new ByteArrayOutputStream();

src/main/java/com/sparrowwallet/drongo/wallet/PriorityUtxoSelector.java

@@ -0,0 +1,59 @@
+package com.sparrowwallet.drongo.wallet;
+
+import java.math.BigInteger;
+import java.util.*;
+import java.util.stream.Collectors;
+
+public class PriorityUtxoSelector implements UtxoSelector {
+    private final int currentBlockHeight;
+
+    public PriorityUtxoSelector(int currentBlockHeight) {
+        this.currentBlockHeight = currentBlockHeight;
+    }
+
+    @Override
+    public Collection<BlockTransactionHashIndex> select(long targetValue, Collection<BlockTransactionHashIndex> candidates) {
+        List<BlockTransactionHashIndex> selected = new ArrayList<>();
+
+        List<BlockTransactionHashIndex> sorted = candidates.stream().filter(ref -> ref.getHeight() != 0).collect(Collectors.toList());
+        sort(sorted);
+
+        long total = 0;
+        for(BlockTransactionHashIndex reference : sorted) {
+            if(total > targetValue) {
+                break;
+            }
+
+            selected.add(reference);
+            total += reference.getValue();
+        }
+
+        return selected;
+    }
+
+    private void sort(List<BlockTransactionHashIndex> outputs) {
+        outputs.sort((a, b) -> {
+            int depthA = currentBlockHeight - a.getHeight();
+            int depthB = currentBlockHeight - b.getHeight();
+
+            Long valueA = a.getValue();
+            Long valueB = b.getValue();
+
+            BigInteger coinDepthA = BigInteger.valueOf(depthA).multiply(BigInteger.valueOf(valueA));
+            BigInteger coinDepthB = BigInteger.valueOf(depthB).multiply(BigInteger.valueOf(valueB));
+
+            int coinDepthCompare = coinDepthB.compareTo(coinDepthA);
+            if (coinDepthCompare != 0) {
+                return coinDepthCompare;
+            }
+
+            // The "coin*days" destroyed are equal, sort by value alone to get the lowest transaction size.
+            int coinValueCompare = valueB.compareTo(valueA);
+            if (coinValueCompare != 0) {
+                return coinValueCompare;
+            }
+
+            return a.compareTo(b);
+        });
+    }
+}

src/main/java/com/sparrowwallet/drongo/wallet/Wallet.java

@@ -205,6 +205,23 @@ public class Wallet {
         }
     }
 
+    public Map<BlockTransactionHashIndex, WalletNode> getWalletUtxos() {
+        Map<BlockTransactionHashIndex, WalletNode> walletUtxos = new TreeMap<>();
+
+        getWalletUtxos(walletUtxos, getNode(KeyPurpose.RECEIVE));
+        getWalletUtxos(walletUtxos, getNode(KeyPurpose.CHANGE));
+
+        return walletUtxos;
+    }
+
+    private void getWalletUtxos(Map<BlockTransactionHashIndex, WalletNode> walletUtxos, WalletNode purposeNode) {
+        for(WalletNode addressNode : purposeNode.getChildren()) {
+            for(BlockTransactionHashIndex utxo : addressNode.getUnspentTransactionOutputs()) {
+                walletUtxos.put(utxo, addressNode);
+            }
+        }
+    }
+
     public void clearNodes() {
         purposeNodes.clear();
         transactions.clear();