Be aware of opt-in full replace-by-fee.

core/src/main/java/org/bitcoinj/core/Transaction.java

@@ -24,6 +24,8 @@ import org.bitcoinj.script.ScriptBuilder;
 import org.bitcoinj.script.ScriptOpCodes;
 import org.bitcoinj.utils.ExchangeRate;
 import org.bitcoinj.wallet.WalletTransaction.Pool;
+
+import com.google.common.base.Joiner;
 import com.google.common.collect.ImmutableMap;
 import com.google.common.primitives.Ints;
 import com.google.common.primitives.Longs;
@@ -641,6 +643,9 @@ public class Transaction extends ChildMessage {
             }
             s.append(String.format(Locale.US, "  time locked until %s%n", time));
         }
+        if (isOptInFullRBF()) {
+            s.append("  opts into full replace-by-fee%n");
+        }
         if (inputs.size() == 0) {
             s.append(String.format(Locale.US, "  INCOMPLETE: No inputs!%n"));
             return s.toString();
@@ -680,6 +685,10 @@ public class Transaction extends ChildMessage {
                         s.append(Utils.HEX.encode(scriptPubKey.getPubKeyHash()));
                     }
                 }
+                String flags = Joiner.on(", ").skipNulls().join(in.hasSequence() ? "has sequence" : null,
+                        in.isOptInFullRBF() ? "opts into full RBF" : null);
+                if (!flags.isEmpty())
+                    s.append("\n          (").append(flags).append(')');
             } catch (Exception e) {
                 s.append("[exception: ").append(e.getMessage()).append("]");
             }
@@ -1281,6 +1290,17 @@ public class Transaction extends ChildMessage {
         return false;
     }
 
+    /**
+     * Returns whether this transaction will opt into the
+     * <a href="https://github.com/bitcoin/bips/blob/master/bip-0125.mediawiki">full replace-by-fee </a> semantics.
+     */
+    public boolean isOptInFullRBF() {
+        for (TransactionInput input : getInputs())
+            if (input.isOptInFullRBF())
+                return true;
+        return false;
+    }
+
     /**
      * <p>Returns true if this transaction is considered finalized and can be placed in a block. Non-finalized
      * transactions won't be included by miners and can be replaced with newer versions using sequence numbers.

core/src/main/java/org/bitcoinj/core/TransactionInput.java

@@ -21,6 +21,8 @@ import org.bitcoinj.script.Script;
 import org.bitcoinj.wallet.DefaultRiskAnalysis;
 import org.bitcoinj.wallet.KeyBag;
 import org.bitcoinj.wallet.RedeemData;
+
+import com.google.common.base.Joiner;
 import com.google.common.base.Objects;
 
 import javax.annotation.Nullable;
@@ -46,7 +48,7 @@ public class TransactionInput extends ChildMessage {
     // Magic outpoint index that indicates the input is in fact unconnected.
     private static final long UNCONNECTED = 0xFFFFFFFFL;
 
-    // Allows for altering transactions after they were broadcast.
+    // Allows for altering transactions after they were broadcast. Values below NO_SEQUENCE-1 mean it can be altered.
     private long sequence;
     // Data needed to connect to the output of the transaction we're gathering coins from.
     private TransactionOutPoint outpoint;
@@ -259,18 +261,6 @@ public class TransactionInput extends ChildMessage {
         return value;
     }
 
-    /**
-     * Returns a human readable debug string.
-     */
-    @Override
-    public String toString() {
-        try {
-            return isCoinBase() ? "TxIn: COINBASE" : "TxIn for [" + outpoint + "]: " + getScriptSig();
-        } catch (ScriptException e) {
-            throw new RuntimeException(e);
-        }
-    }
-
     public enum ConnectionResult {
         NO_SUCH_TX,
         ALREADY_SPENT,
@@ -385,6 +375,14 @@ public class TransactionInput extends ChildMessage {
         return sequence != NO_SEQUENCE;
     }
 
+    /**
+     * Returns whether this input will cause a transaction to opt into the
+     * <a href="https://github.com/bitcoin/bips/blob/master/bip-0125.mediawiki">full replace-by-fee </a> semantics.
+     */
+    public boolean isOptInFullRBF() {
+        return sequence < NO_SEQUENCE - 1;
+    }
+
     /**
      * For a connected transaction, runs the script against the connected pubkey and verifies they are correct.
      * @throws ScriptException if the script did not verify.
@@ -467,4 +465,26 @@ public class TransactionInput extends ChildMessage {
     public int hashCode() {
         return Objects.hashCode(sequence, outpoint, Arrays.hashCode(scriptBytes));
     }
+
+    /**
+     * Returns a human readable debug string.
+     */
+    @Override
+    public String toString() {
+        StringBuilder s = new StringBuilder("TxIn");
+        try {
+            if (isCoinBase()) {
+                s.append(": COINBASE");
+            } else {
+                s.append(" for [").append(outpoint).append("]: ").append(getScriptSig());
+                String flags = Joiner.on(", ").skipNulls().join(hasSequence() ? "has sequence" : null,
+                        isOptInFullRBF() ? "opts into full RBF" : null);
+                if (!flags.isEmpty())
+                    s.append(" (").append(flags).append(')');
+            }
+            return s.toString();
+        } catch (ScriptException e) {
+            throw new RuntimeException(e);
+        }
+    }
 }

core/src/test/java/org/bitcoinj/core/TransactionTest.java

@@ -403,4 +403,14 @@ public class TransactionTest {
         final Transaction transaction = PARAMS.getDefaultSerializer().makeTransaction(transactionBytes);
         transaction.checkCoinBaseHeight(height);
     }
+
+    @Test
+    public void optInFullRBF() {
+        // a standard transaction as wallets would create
+        Transaction tx = FakeTxBuilder.createFakeTx(PARAMS);
+        assertFalse(tx.isOptInFullRBF());
+
+        tx.getInputs().get(0).setSequenceNumber(TransactionInput.NO_SEQUENCE - 2);
+        assertTrue(tx.isOptInFullRBF());
+    }
 }