RPC: indicate which transactions are replaceable

Add "bip125-replaceable" output field to listtransactions and gettransaction
which indicates if an unconfirmed transaction, or any unconfirmed parent, is
signaling opt-in RBF according to BIP 125.

src/Makefile.am

@@ -122,6 +122,7 @@ BITCOIN_CORE_H = \
   noui.h \
   policy/fees.h \
   policy/policy.h \
+  policy/rbf.h \
   pow.h \
   prevector.h \
   primitives/block.h \
@@ -239,6 +240,7 @@ libbitcoin_wallet_a_SOURCES = \
   wallet/wallet.cpp \
   wallet/wallet_ismine.cpp \
   wallet/walletdb.cpp \
+  policy/rbf.cpp \
   $(BITCOIN_CORE_H)
 
 # crypto primitives library

src/policy/rbf.cpp

@@ -0,0 +1,46 @@
+// Copyright (c) 2016 The Bitcoin developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include "policy/rbf.h"
+
+bool SignalsOptInRBF(const CTransaction &tx)
+{
+    BOOST_FOREACH(const CTxIn &txin, tx.vin) {
+        if (txin.nSequence < std::numeric_limits<unsigned int>::max()-1) {
+            return true;
+        }
+    }
+    return false;
+}
+
+bool IsRBFOptIn(const CTxMemPoolEntry &entry, CTxMemPool &pool)
+{
+    AssertLockHeld(pool.cs);
+
+    CTxMemPool::setEntries setAncestors;
+
+    // First check the transaction itself.
+    if (SignalsOptInRBF(entry.GetTx())) {
+        return true;
+    }
+
+    // If this transaction is not in our mempool, then we can't be sure
+    // we will know about all its inputs.
+    if (!pool.exists(entry.GetTx().GetHash())) {
+        throw std::runtime_error("Cannot determine RBF opt-in signal for non-mempool transaction\n");
+    }
+
+    // If all the inputs have nSequence >= maxint-1, it still might be
+    // signaled for RBF if any unconfirmed parents have signaled.
+    uint64_t noLimit = std::numeric_limits<uint64_t>::max();
+    std::string dummy;
+    pool.CalculateMemPoolAncestors(entry, setAncestors, noLimit, noLimit, noLimit, noLimit, dummy, false);
+
+    BOOST_FOREACH(CTxMemPool::txiter it, setAncestors) {
+        if (SignalsOptInRBF(it->GetTx())) {
+            return true;
+        }
+    }
+    return false;
+}

src/policy/rbf.h

@@ -0,0 +1,20 @@
+// Copyright (c) 2016 The Bitcoin developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef BITCOIN_POLICY_RBF_H
+#define BITCOIN_POLICY_RBF_H
+
+#include "txmempool.h"
+
+// Check whether the sequence numbers on this transaction are signaling
+// opt-in to replace-by-fee, according to BIP 125
+bool SignalsOptInRBF(const CTransaction &tx);
+
+// Determine whether an in-mempool transaction is signaling opt-in to RBF
+// according to BIP 125
+// This involves checking sequence numbers of the transaction, as well
+// as the sequence numbers of all in-mempool ancestors.
+bool IsRBFOptIn(const CTxMemPoolEntry &entry, CTxMemPool &pool);
+
+#endif // BITCOIN_POLICY_RBF_H

src/wallet/rpcwallet.cpp

@@ -11,6 +11,7 @@
 #include "main.h"
 #include "net.h"
 #include "netbase.h"
+#include "policy/rbf.h"
 #include "rpcserver.h"
 #include "timedata.h"
 #include "util.h"
@@ -76,6 +77,23 @@ void WalletTxToJSON(const CWalletTx& wtx, UniValue& entry)
     entry.push_back(Pair("walletconflicts", conflicts));
     entry.push_back(Pair("time", wtx.GetTxTime()));
     entry.push_back(Pair("timereceived", (int64_t)wtx.nTimeReceived));
+
+    // Add opt-in RBF status
+    std::string rbfStatus = "no";
+    if (confirms <= 0) {
+        LOCK(mempool.cs);
+        if (!mempool.exists(hash)) {
+            if (SignalsOptInRBF(wtx)) {
+                rbfStatus = "yes";
+            } else {
+                rbfStatus = "unknown";
+            }
+        } else if (IsRBFOptIn(*mempool.mapTx.find(hash), mempool)) {
+            rbfStatus = "yes";
+        }
+    }
+    entry.push_back(Pair("bip125-replaceable", rbfStatus));
+
     BOOST_FOREACH(const PAIRTYPE(string,string)& item, wtx.mapValue)
         entry.push_back(Pair(item.first, item.second));
 }
@@ -1439,6 +1457,8 @@ UniValue listtransactions(const UniValue& params, bool fHelp)
             "    \"otheraccount\": \"accountname\",  (string) For the 'move' category of transactions, the account the funds came \n"
             "                                          from (for receiving funds, positive amounts), or went to (for sending funds,\n"
             "                                          negative amounts).\n"
+            "    \"bip125-replaceable\": \"yes|no|unknown\"  (string) Whether this transaction could be replaced due to BIP125 (replace-by-fee);\n"
+            "                                                     may be unknown for unconfirmed transactions not in the mempool\n"
             "  }\n"
             "]\n"
 
@@ -1707,6 +1727,8 @@ UniValue gettransaction(const UniValue& params, bool fHelp)
             "  \"txid\" : \"transactionid\",   (string) The transaction id.\n"
             "  \"time\" : ttt,            (numeric) The transaction time in seconds since epoch (1 Jan 1970 GMT)\n"
             "  \"timereceived\" : ttt,    (numeric) The time received in seconds since epoch (1 Jan 1970 GMT)\n"
+            "  \"bip125-replaceable\": \"yes|no|unknown\"  (string) Whether this transaction could be replaced due to BIP125 (replace-by-fee);\n"
+            "                                                   may be unknown for unconfirmed transactions not in the mempool\n"
             "  \"details\" : [\n"
             "    {\n"
             "      \"account\" : \"accountname\",  (string) DEPRECATED. The account name involved in the transaction, can be \"\" for the default account.\n"