Refuse to create transactions larger than the max standard size.

core/src/main/java/com/google/bitcoin/core/Transaction.java

@@ -47,8 +47,12 @@ public class Transaction extends ChildMessage implements Serializable {
     private static final Logger log = LoggerFactory.getLogger(Transaction.class);
     private static final long serialVersionUID = -8567546957352643140L;
     
-    // Threshold for lockTime: below this value it is interpreted as block number, otherwise as timestamp.
+    /** Threshold for lockTime: below this value it is interpreted as block number, otherwise as timestamp. **/
-    static final int LOCKTIME_THRESHOLD = 500000000; // Tue Nov  5 00:53:20 1985 UTC
+    public static final int LOCKTIME_THRESHOLD = 500000000; // Tue Nov  5 00:53:20 1985 UTC
+
+    /** How many bytes a transaction can be before it won't be relayed anymore. */
+    public static final int MAX_STANDARD_TX_SIZE = 100 * 1024;
+
 
     // These are serialized in both bitcoin and java serialization.
     private long version;

core/src/main/java/com/google/bitcoin/core/Wallet.java

@@ -1751,6 +1751,14 @@ public class Wallet implements Serializable, BlockChainListener {
             throw new RuntimeException(e);
         }
 
+        // Check size.
+        int size = req.tx.bitcoinSerialize().length;
+        if (size > Transaction.MAX_STANDARD_TX_SIZE) {
+            // TODO: Throw an exception here.
+            log.error("Transaction could not be created without exceeding max size: {} vs {}", size, Transaction.MAX_STANDARD_TX_SIZE);
+            return false;
+        }
+
         // Label the transaction as being self created. We can use this later to spend its change output even before
         // the transaction is confirmed.
         req.tx.getConfidence().setSource(TransactionConfidence.Source.SELF);

core/src/test/java/com/google/bitcoin/core/WalletTest.java

@@ -32,6 +32,7 @@ import java.net.InetAddress;
 import java.util.ArrayList;
 import java.util.LinkedList;
 import java.util.List;
+import java.util.Random;
 import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.TimeUnit;
 
@@ -896,6 +897,22 @@ public class WalletTest {
         }
     }
 
+    @Test
+    public void respectMaxStandardSize() throws Exception {
+        // Check that we won't create txns > 100kb. Average tx size is ~220 bytes so this would have to be enormous.
+        sendMoneyToWallet(Utils.toNanoCoins(100, 0), AbstractBlockChain.NewBlockType.BEST_CHAIN);
+        Transaction tx = new Transaction(params);
+        byte[] bits = new byte[20];
+        new Random().nextBytes(bits);
+        BigInteger v = Utils.toNanoCoins(0, 1);
+        // 3100 outputs to a random address.
+        for (int i = 0; i < 3100; i++) {
+            tx.addOutput(v, new Address(params, bits));
+        }
+        Wallet.SendRequest req = Wallet.SendRequest.forTx(tx);
+        assertFalse(wallet.completeTx(req));
+    }
+
     // There is a test for spending a coinbase transaction as it matures in BlockChainTest#coinbaseTransactionAvailability
 
     // Support for offline spending is tested in PeerGroupTest