From da20b02906e55a8b9727babf6cb583b029244813 Mon Sep 17 00:00:00 2001
From: Mike Hearn <mike@plan99.net>
Date: Thu, 9 Jul 2015 15:05:36 +0200
Subject: [PATCH] Implement special priority tx size calculation.

---
 .../java/org/bitcoinj/core/Transaction.java   | 17 ++++++++
 .../org/bitcoinj/core/TransactionTest.java    | 40 +++++++++++--------
 2 files changed, 40 insertions(+), 17 deletions(-)

diff --git a/core/src/main/java/org/bitcoinj/core/Transaction.java b/core/src/main/java/org/bitcoinj/core/Transaction.java
index e247735d..9d7adbd2 100644
--- a/core/src/main/java/org/bitcoinj/core/Transaction.java
+++ b/core/src/main/java/org/bitcoinj/core/Transaction.java
@@ -583,6 +583,23 @@ public class Transaction extends ChildMessage implements Serializable {
         return optimalEncodingMessageSize;
     }
 
+    /**
+     * The priority (coin age) calculation doesn't use the regular message size, but rather one adjusted downwards
+     * for the number of inputs. The goal is to incentivise cleaning up the UTXO set with free transactions, if one
+     * can do so.
+     */
+    public int getMessageSizeForPriorityCalc() {
+        int size = getMessageSize();
+        for (TransactionInput input : inputs) {
+            // 41: min size of an input
+            // 110: enough to cover a compressed pubkey p2sh redemption (somewhat arbitrary).
+            int benefit = 41 + Math.min(110, input.getScriptSig().getProgram().length);
+            if (size > benefit)
+                size -= benefit;
+        }
+        return size;
+    }
+
     /**
      * A coinbase transaction is one that creates a new coin. They are the first transaction in each block and their
      * value is determined by a formula that all implementations of Bitcoin share. In 2011 the value of a coinbase
diff --git a/core/src/test/java/org/bitcoinj/core/TransactionTest.java b/core/src/test/java/org/bitcoinj/core/TransactionTest.java
index 9fe4dfbc..8cde9464 100644
--- a/core/src/test/java/org/bitcoinj/core/TransactionTest.java
+++ b/core/src/test/java/org/bitcoinj/core/TransactionTest.java
@@ -1,24 +1,16 @@
 package org.bitcoinj.core;
 
-import org.bitcoinj.core.TransactionConfidence.ConfidenceType;
-import org.bitcoinj.params.UnitTestParams;
-import org.bitcoinj.script.Script;
-import org.bitcoinj.script.ScriptBuilder;
-import org.bitcoinj.testing.FakeTxBuilder;
-import org.junit.Before;
-import org.junit.Test;
-import org.easymock.EasyMock;
+import org.bitcoinj.core.TransactionConfidence.*;
+import org.bitcoinj.params.*;
+import org.bitcoinj.script.*;
+import org.bitcoinj.testing.*;
+import org.easymock.*;
+import org.junit.*;
 
-import static org.junit.Assert.assertEquals;
-import static org.easymock.EasyMock.createMock;
-import static org.easymock.EasyMock.replay;
+import java.util.*;
 
-import java.util.Calendar;
-import java.util.Date;
-import java.util.Iterator;
-import java.util.List;
-import java.util.SortedSet;
-import java.util.TreeSet;
+import static org.easymock.EasyMock.*;
+import static org.junit.Assert.*;
 
 /**
  * Just check the Transaction.verify() method. Most methods that have complicated logic in Transaction are tested
@@ -296,4 +288,18 @@ public class TransactionTest {
 
         tx.addSignedInput(fakeTx.getOutput(0).getOutPointFor(), script, key);
     }
+
+    @Test
+    public void testPrioSizeCalc() throws Exception {
+        Transaction tx1 = FakeTxBuilder.createFakeTx(PARAMS, Coin.COIN, ADDRESS);
+        int size1 = tx1.getMessageSize();
+        int size2 = tx1.getMessageSizeForPriorityCalc();
+        assertEquals(113, size1 - size2);
+        tx1.getInput(0).setScriptSig(new Script(new byte[109]));
+        assertEquals(78, tx1.getMessageSizeForPriorityCalc());
+        tx1.getInput(0).setScriptSig(new Script(new byte[110]));
+        assertEquals(78, tx1.getMessageSizeForPriorityCalc());
+        tx1.getInput(0).setScriptSig(new Script(new byte[111]));
+        assertEquals(79, tx1.getMessageSizeForPriorityCalc());
+    }
 }
\ No newline at end of file