tx creation algorithm

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

@@ -13,6 +13,7 @@ import java.util.stream.Collectors;
 import static com.sparrowwallet.drongo.policy.PolicyType.*;
 import static com.sparrowwallet.drongo.protocol.Script.decodeFromOpN;
 import static com.sparrowwallet.drongo.protocol.ScriptOpCodes.*;
+import static com.sparrowwallet.drongo.protocol.Transaction.WITNESS_SCALE_FACTOR;
 
 public enum ScriptType {
     P2PK("P2PK", "m/44'/0'/0'") {
@@ -1030,6 +1031,10 @@ public enum ScriptType {
 
     public static final ScriptType[] SINGLE_HASH_TYPES = {P2PKH, P2SH, P2SH_P2WPKH, P2SH_P2WSH, P2WPKH, P2WSH};
 
+    public static final ScriptType[] NON_WITNESS_TYPES = {P2PK, P2PKH, P2SH};
+
+    public static final ScriptType[] WITNESS_TYPES = {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());
     }
@@ -1044,6 +1049,30 @@ public enum ScriptType {
         return null;
     }
 
+    /**
+     * Determines the dust threshold for this script type.
+     *
+     * @param output The output under consideration
+     * @param feeRate The fee rate at which the fee required will be calculated
+     * @return the minimum viable value than the provided output must have in order to not be dust
+     */
+    public long getDustThreshold(TransactionOutput output, Double feeRate) {
+        //Start with length of output
+        int totalLength = output.getLength();
+        if(Arrays.asList(WITNESS_TYPES).contains(this)) {
+            //Add length of spending input with 75% discount to script size
+            totalLength += (32 + 4 + 1 + (107 / WITNESS_SCALE_FACTOR) + 4);
+        } else if(Arrays.asList(NON_WITNESS_TYPES).contains(this)) {
+            //Add length of spending input with no discount
+            totalLength += (32 + 4 + 1 + 107 + 4);
+        } else {
+            throw new UnsupportedOperationException("Cannot determine dust threshold for script type " + this.getName());
+        }
+
+        //Return fee rate in sats/vbyte multiplied by the calculated total byte length
+        return (long)(feeRate * totalLength);
+    }
+
     @Override
     public String toString() {
         return name;

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

@@ -21,6 +21,8 @@ public class Transaction extends ChildMessage {
     public static final long MAX_BITCOIN = 21 * 1000 * 1000L;
     public static final long SATOSHIS_PER_BITCOIN = 100 * 1000 * 1000L;
     public static final long MAX_BLOCK_LOCKTIME = 500000000L;
+    public static final int WITNESS_SCALE_FACTOR = 4;
+    public static final double DEFAULT_DISCARD_FEE_RATE = 10000d / 1000;
 
     private long version;
     private long locktime;
@@ -147,6 +149,18 @@ public class Transaction extends ChildMessage {
         return false;
     }
 
+    public byte[] bitcoinSerialize() {
+        try {
+            ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
+            bitcoinSerializeToStream(outputStream);
+            return outputStream.toByteArray();
+        } catch (IOException e) {
+            //can't happen
+        }
+
+        return null;
+    }
+
     public void bitcoinSerializeToStream(OutputStream stream) throws IOException {
         boolean useSegwit = isSegwit();
         bitcoinSerializeToStream(stream, useSegwit);
@@ -253,19 +267,19 @@ public class Transaction extends ChildMessage {
         int wu = 0;
 
         // version
-        wu += 4*4;
+        wu += 4 * WITNESS_SCALE_FACTOR;
         // marker, flag
         if(isSegwit()) {
             wu += 2;
         }
         // txin_count, txins
-        wu += new VarInt(inputs.size()).getSizeInBytes() * 4;
+        wu += new VarInt(inputs.size()).getSizeInBytes() * WITNESS_SCALE_FACTOR;
         for (TransactionInput in : inputs)
-            wu += in.length * 4;
+            wu += in.length * WITNESS_SCALE_FACTOR;
         // txout_count, txouts
-        wu += new VarInt(outputs.size()).getSizeInBytes() * 4;
+        wu += new VarInt(outputs.size()).getSizeInBytes() * WITNESS_SCALE_FACTOR;
         for (TransactionOutput out : outputs)
-            wu += out.length * 4;
+            wu += out.length * WITNESS_SCALE_FACTOR;
         // script_witnesses
         if(isSegwit()) {
             for (TransactionInput in : inputs) {
@@ -275,9 +289,9 @@ public class Transaction extends ChildMessage {
             }
         }
         // lock_time
-        wu += 4*4;
+        wu += 4 * WITNESS_SCALE_FACTOR;
 
-        return (int)Math.ceil((double)wu / 4.0);
+        return (int)Math.ceil((double)wu / (double)WITNESS_SCALE_FACTOR);
     }
 
     public List<TransactionInput> getInputs() {

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

@@ -0,0 +1,11 @@
+package com.sparrowwallet.drongo.wallet;
+
+public class InsufficientFundsException extends Exception {
+    public InsufficientFundsException() {
+        super();
+    }
+
+    public InsufficientFundsException(String msg) {
+        super(msg);
+    }
+}

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

@@ -18,6 +18,9 @@ public class PriorityUtxoSelector implements UtxoSelector {
         List<BlockTransactionHashIndex> sorted = candidates.stream().filter(ref -> ref.getHeight() != 0).collect(Collectors.toList());
         sort(sorted);
 
+        //Testing only: remove
+        Collections.reverse(sorted);
+
         long total = 0;
         for(BlockTransactionHashIndex reference : sorted) {
             if(total > targetValue) {

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

@@ -151,17 +151,45 @@ public class Wallet {
         throw new IllegalStateException("Could not fill nodes to index " + index);
     }
 
+    public ECKey getPubKey(WalletNode node) {
+        return getPubKey(node.getKeyPurpose(), node.getIndex());
+    }
+
+    public ECKey getPubKey(KeyPurpose keyPurpose, int index) {
+        if(policyType == PolicyType.MULTI) {
+            throw new IllegalStateException("Attempting to retrieve a single key for a multisig policy wallet");
+        } else if(policyType == PolicyType.CUSTOM) {
+            throw new UnsupportedOperationException("Cannot determine a public key for a custom policy");
+        }
+
+        Keystore keystore = getKeystores().get(0);
+        return keystore.getKey(keyPurpose, index);
+    }
+
+    public List<ECKey> getPubKeys(WalletNode node) {
+        return getPubKeys(node.getKeyPurpose(), node.getIndex());
+    }
+
+    public List<ECKey> getPubKeys(KeyPurpose keyPurpose, int index) {
+        if(policyType == PolicyType.SINGLE) {
+            throw new IllegalStateException("Attempting to retrieve multiple keys for a singlesig policy wallet");
+        } else if(policyType == PolicyType.CUSTOM) {
+            throw new UnsupportedOperationException("Cannot determine public keys for a custom policy");
+        }
+
+        return getKeystores().stream().map(keystore -> keystore.getKey(keyPurpose, index)).collect(Collectors.toList());
+    }
+
     public Address getAddress(WalletNode node) {
         return getAddress(node.getKeyPurpose(), node.getIndex());
     }
 
     public Address getAddress(KeyPurpose keyPurpose, int index) {
         if(policyType == PolicyType.SINGLE) {
-            Keystore keystore = getKeystores().get(0);
-            DeterministicKey key = keystore.getKey(keyPurpose, index);
-            return scriptType.getAddress(key);
+            ECKey pubKey = getPubKey(keyPurpose, index);
+            return scriptType.getAddress(pubKey);
         } else if(policyType == PolicyType.MULTI) {
-            List<ECKey> pubKeys = getKeystores().stream().map(keystore -> keystore.getKey(keyPurpose, index)).collect(Collectors.toList());
+            List<ECKey> pubKeys = getPubKeys(keyPurpose, index);
             Script script = ScriptType.MULTISIG.getOutputScript(defaultPolicy.getNumSignaturesRequired(), pubKeys);
             return scriptType.getAddress(script);
         } else {
@@ -175,11 +203,10 @@ public class Wallet {
 
     public Script getOutputScript(KeyPurpose keyPurpose, int index) {
         if(policyType == PolicyType.SINGLE) {
-            Keystore keystore = getKeystores().get(0);
-            DeterministicKey key = keystore.getKey(keyPurpose, index);
-            return scriptType.getOutputScript(key);
+            ECKey pubKey = getPubKey(keyPurpose, index);
+            return scriptType.getOutputScript(pubKey);
         } else if(policyType == PolicyType.MULTI) {
-            List<ECKey> pubKeys = getKeystores().stream().map(keystore -> keystore.getKey(keyPurpose, index)).collect(Collectors.toList());
+            List<ECKey> pubKeys = getPubKeys(keyPurpose, index);
             Script script = ScriptType.MULTISIG.getOutputScript(defaultPolicy.getNumSignaturesRequired(), pubKeys);
             return scriptType.getOutputScript(script);
         } else {
@@ -193,11 +220,10 @@ public class Wallet {
 
     public String getOutputDescriptor(KeyPurpose keyPurpose, int index) {
         if(policyType == PolicyType.SINGLE) {
-            Keystore keystore = getKeystores().get(0);
-            DeterministicKey key = keystore.getKey(keyPurpose, index);
-            return scriptType.getOutputDescriptor(key);
+            ECKey pubKey = getPubKey(keyPurpose, index);
+            return scriptType.getOutputDescriptor(pubKey);
         } else if(policyType == PolicyType.MULTI) {
-            List<ECKey> pubKeys = getKeystores().stream().map(keystore -> keystore.getKey(keyPurpose, index)).collect(Collectors.toList());
+            List<ECKey> pubKeys = getPubKeys(keyPurpose, index);
             Script script = ScriptType.MULTISIG.getOutputScript(defaultPolicy.getNumSignaturesRequired(), pubKeys);
             return scriptType.getOutputDescriptor(script);
         } else {
@@ -222,6 +248,91 @@ public class Wallet {
         }
     }
 
+    public WalletTransaction createWalletTransaction(List<UtxoSelector> utxoSelectors, Address recipientAddress, long recipientAmount, double feeRate) throws InsufficientFundsException {
+        long valueRequiredAmt = recipientAmount;
+
+        while(true) {
+            Map<BlockTransactionHashIndex, WalletNode> selectedUtxos = selectInputs(utxoSelectors, valueRequiredAmt);
+            long totalSelectedAmt = selectedUtxos.keySet().stream().mapToLong(BlockTransactionHashIndex::getValue).sum();
+
+            //Add inputs
+            Transaction transaction = new Transaction();
+            for(Map.Entry<BlockTransactionHashIndex, WalletNode> selectedUtxo : selectedUtxos.entrySet()) {
+                Transaction prevTx = getTransactions().get(selectedUtxo.getKey().getHash()).getTransaction();
+                TransactionOutput prevTxOut = prevTx.getOutputs().get((int)selectedUtxo.getKey().getIndex());
+
+                if(getPolicyType().equals(PolicyType.SINGLE)) {
+                    ECKey pubKey = getPubKey(selectedUtxo.getValue());
+                    TransactionSignature signature = TransactionSignature.dummy();
+                    getScriptType().addSpendingInput(transaction, prevTxOut, pubKey, signature);
+                } else if(getPolicyType().equals(PolicyType.MULTI)) {
+                    List<ECKey> pubKeys = getPubKeys(selectedUtxo.getValue());
+                    int threshold = getDefaultPolicy().getNumSignaturesRequired();
+                    List<TransactionSignature> signatures = new ArrayList<>(threshold);
+                    for(int i = 0; i < threshold; i++) {
+                        signatures.add(TransactionSignature.dummy());
+                    }
+                    getScriptType().addMultisigSpendingInput(transaction, prevTxOut, threshold, pubKeys, signatures);
+                }
+            }
+
+            //Add recipient output
+            transaction.addOutput(recipientAmount, recipientAddress);
+            int noChangeVSize = transaction.getVirtualSize();
+            long noChangeFeeRequiredAmt = (long)(feeRate * noChangeVSize);
+
+            //Calculate what is left over from selected utxos after paying recipient
+            long differenceAmt = totalSelectedAmt - recipientAmount;
+
+            //If insufficient fee, increase value required from inputs to include the fee and try again
+            if(differenceAmt < noChangeFeeRequiredAmt) {
+                valueRequiredAmt = totalSelectedAmt + 1;
+                continue;
+            }
+
+            //Determine if a change output is required by checking if its value is greater than its dust threshold
+            long changeAmt = differenceAmt - noChangeFeeRequiredAmt;
+            WalletNode changeNode = getFreshNode(KeyPurpose.CHANGE);
+            TransactionOutput changeOutput = new TransactionOutput(transaction, changeAmt, getOutputScript(changeNode));
+            long dustThreshold = getScriptType().getDustThreshold(changeOutput, Transaction.DEFAULT_DISCARD_FEE_RATE);
+            if(changeAmt > dustThreshold) {
+                //Change output is required, determine new fee once change output has been added
+                int changeVSize = noChangeVSize + changeOutput.getLength();
+                long changeFeeRequiredAmt = (long)(feeRate * changeVSize);
+
+                //Recalculate the change amount with the new fee
+                changeAmt = differenceAmt - changeFeeRequiredAmt;
+                if(changeAmt < dustThreshold) {
+                    //The new fee has meant that the change output is now dust. We pay too high a fee without change, but change is dust when added. Increase value required from inputs and try again
+                    valueRequiredAmt = totalSelectedAmt + 1;
+                    continue;
+                }
+
+                //Add change output
+                transaction.addOutput(changeAmt, getOutputScript(changeNode));
+
+                return new WalletTransaction(this, transaction, selectedUtxos, recipientAddress, recipientAmount, changeNode, changeAmt, changeFeeRequiredAmt);
+            }
+
+            return new WalletTransaction(this, transaction, selectedUtxos, recipientAddress, recipientAmount, differenceAmt);
+        }
+    }
+
+    private Map<BlockTransactionHashIndex, WalletNode> selectInputs(List<UtxoSelector> utxoSelectors, Long targetValue) throws InsufficientFundsException {
+        Map<BlockTransactionHashIndex, WalletNode> utxos = getWalletUtxos();
+
+        for(UtxoSelector utxoSelector : utxoSelectors) {
+            Collection<BlockTransactionHashIndex> selectedInputs = utxoSelector.select(targetValue, utxos.keySet());
+            long total = selectedInputs.stream().mapToLong(BlockTransactionHashIndex::getValue).sum();
+            if(total > targetValue) {
+                utxos.keySet().retainAll(selectedInputs);
+                return utxos;
+            }
+        }
+
+        throw new InsufficientFundsException("Not enough combined value in UTXOs for output value " + targetValue);
+    }
+
     public void clearNodes() {
         purposeNodes.clear();
         transactions.clear();

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

@@ -0,0 +1,74 @@
+package com.sparrowwallet.drongo.wallet;
+
+import com.sparrowwallet.drongo.address.Address;
+import com.sparrowwallet.drongo.protocol.Transaction;
+import com.sparrowwallet.drongo.psbt.PSBT;
+
+import java.util.Map;
+
+/**
+ * WalletTransaction contains a draft transaction along with associated metadata. The draft transaction has empty signatures but is otherwise complete.
+ * This object represents an intermediate step before the transaction is signed or a PSBT is created from it.
+ */
+public class WalletTransaction {
+    private final Wallet wallet;
+    private final Transaction transaction;
+    private final Map<BlockTransactionHashIndex, WalletNode> selectedUtxos;
+    private final Address recipientAddress;
+    private final long recipientAmount;
+    private final WalletNode changeNode;
+    private final long changeAmount;
+    private final long fee;
+
+    public WalletTransaction(Wallet wallet, Transaction transaction, Map<BlockTransactionHashIndex, WalletNode> selectedUtxos, Address recipientAddress, long recipientAmount, long fee) {
+        this(wallet, transaction, selectedUtxos, recipientAddress, recipientAmount, null, 0L, fee);
+    }
+
+    public WalletTransaction(Wallet wallet, Transaction transaction, Map<BlockTransactionHashIndex, WalletNode> selectedUtxos, Address recipientAddress, long recipientAmount, WalletNode changeNode, long changeAmount, long fee) {
+        this.wallet = wallet;
+        this.transaction = transaction;
+        this.selectedUtxos = selectedUtxos;
+        this.recipientAddress = recipientAddress;
+        this.recipientAmount = recipientAmount;
+        this.changeNode = changeNode;
+        this.changeAmount = changeAmount;
+        this.fee = fee;
+    }
+
+    public PSBT createPSBT() {
+        //TODO: Create PSBT
+        return null;
+    }
+
+    public Wallet getWallet() {
+        return wallet;
+    }
+
+    public Transaction getTransaction() {
+        return transaction;
+    }
+
+    public Map<BlockTransactionHashIndex, WalletNode> getSelectedUtxos() {
+        return selectedUtxos;
+    }
+
+    public Address getRecipientAddress() {
+        return recipientAddress;
+    }
+
+    public long getRecipientAmount() {
+        return recipientAmount;
+    }
+
+    public WalletNode getChangeNode() {
+        return changeNode;
+    }
+
+    public long getChangeAmount() {
+        return changeAmount;
+    }
+
+    public long getFee() {
+        return fee;
+    }
+}