Merge pull request #1 from twostack/1-2-0-SNAPSHOT

Fee calculation fixes.

Author: stephanfeb

build.gradle

@@ -6,7 +6,7 @@ plugins {
 }
 
 group 'org.twostack'
-version '1.1.0'
+version '1.2.0-SNAPSHOT'
 
 repositories {
     mavenCentral()

src/main/java/org/twostack/bitcoin4j/transaction/TransactionBuilder.java

@@ -40,7 +40,7 @@ public class TransactionBuilder {
 
     private final long DEFAULT_FEE_PER_KB = 512; //amount in satoshis
 
-    static final BigInteger DUST_AMOUNT = BigInteger.valueOf(546);
+    static final BigInteger DUST_AMOUNT = BigInteger.valueOf(256);
 
     /// Margin of error to allow fees in the vecinity of the expected value but doesn't allow a big difference
     private static final BigInteger FEE_SECURITY_MARGIN = BigInteger.valueOf(150);
@@ -264,6 +264,10 @@ public Transaction build(boolean performChecks) throws TransactionException {
         //add transaction outputs
         tx.addOutputs(outputs);
 
+        if (changeScriptBuilder != null) {
+            tx.addOutput(getChangeOutput());
+        }
+
         tx.setLockTime(nLockTime);
 
         return tx;
@@ -309,6 +313,12 @@ private void checkForDustErrors() throws TransactionException {
                 throw new TransactionException("You have outputs with spending values below the dust limit of " + DUST_AMOUNT.toString());
             }
         }
+
+        //check for dust on change output
+        if (getChangeOutput() != null && (getChangeOutput().getAmount().compareTo(DUST_AMOUNT) == -1)){
+            throw new TransactionException("You have a change output with spending value below the dust limit of " + DUST_AMOUNT.toString());
+        }
+
     }
 
 
@@ -358,6 +368,9 @@ private void updateChangeOutput(){
         //spent amount equals input amount. No change generated. Return.
         if (calcRecipientTotals() == calcInputTotals()) return;
 
+        //clear change outputs
+        changeOutput = null;
+
         changeAmount = calculateChange();
         TransactionOutput output = getChangeOutput();
         output.setAmount(changeAmount);
@@ -399,6 +412,13 @@ private BigInteger estimateFee(){
 
         BigInteger fee = BigInteger.valueOf(new Float(size / 1000 * feePerKb).longValue());
 
+        //if fee is less that 256, set fee at 256 satoshis
+        //this is current minimum we set automatically if no explicit fee given
+        //FIXME: Make this configurable
+        if (fee.compareTo(BigInteger.valueOf(256)) == -1){
+            fee = BigInteger.valueOf(256);
+        }
+
         return fee;
     }
 
@@ -433,6 +453,12 @@ private BigInteger calcRecipientTotals() {
             amount = amount.add(output.getAmount());
         };
 
+        //deduct change output
+        if (changeScriptBuilder != null){
+            TransactionOutput changeOutput = getChangeOutput();
+            amount = amount.add(changeOutput.getAmount());
+        }
+
         return amount;
     }
 

src/test/java/org/twostack/bitcoin4j/transaction/TransactionTest.java

@@ -155,6 +155,7 @@ public void test_transaction_serialization_vectors() throws IOException, Transac
             //txHex
             String serializedTx = serializedTxNode.asText();
 
+            System.out.println(txId);
 
             builder.spendFromUtxoMap(utxoMap, new P2PKHUnlockBuilder(privateKey.getPublicKey()));
             builder.withFeePerKb(100000);