Add option `-permitrbf` to set transaction replacement policy

Add a configuration option `-permitrbf` to set transaction replacement policy
for the mempool.

Enabling it will enable (opt-in) RBF, disabling it will refuse all
conflicting transactions.

src/init.cpp

@@ -367,6 +367,7 @@ std::string HelpMessage(HelpMessageMode mode)
     strUsage += HelpMessageOpt("-onion=<ip:port>", strprintf(_("Use separate SOCKS5 proxy to reach peers via Tor hidden services (default: %s)"), "-proxy"));
     strUsage += HelpMessageOpt("-onlynet=<net>", _("Only connect to nodes in network <net> (ipv4, ipv6 or onion)"));
     strUsage += HelpMessageOpt("-permitbaremultisig", strprintf(_("Relay non-P2SH multisig (default: %u)"), DEFAULT_PERMIT_BAREMULTISIG));
+    strUsage += HelpMessageOpt("-permitrbf", strprintf(_("Permit transaction replacement (default: %u)"), DEFAULT_PERMIT_REPLACEMENT));
     strUsage += HelpMessageOpt("-peerbloomfilters", strprintf(_("Support filtering of blocks and transaction with bloom filters (default: %u)"), 1));
     if (showDebug)
         strUsage += HelpMessageOpt("-enforcenodebloom", strprintf("Enforce minimum protocol version to limit use of bloom filters (default: %u)", 0));
@@ -1029,6 +1030,7 @@ bool AppInit2(boost::thread_group& threadGroup, CScheduler& scheduler)
         nLocalServices |= NODE_BLOOM;
 
     nMaxTipAge = GetArg("-maxtipage", DEFAULT_MAX_TIP_AGE);
+    fPermitReplacement = GetBoolArg("-permitrbf", DEFAULT_PERMIT_REPLACEMENT);
 
     // ********************************************************* Step 4: application initialization: dir lock, daemonize, pidfile, debug log
 

src/main.cpp

@@ -78,6 +78,7 @@ bool fAlerts = DEFAULT_ALERTS;
 /* If the tip is older than this (in seconds), the node is considered to be in initial block download.
  */
 int64_t nMaxTipAge = DEFAULT_MAX_TIP_AGE;
+bool fPermitReplacement = DEFAULT_PERMIT_REPLACEMENT;
 
 /** Fees smaller than this (in satoshi) are considered zero fee (for relaying, mining and transaction creation) */
 CFeeRate minRelayTxFee = CFeeRate(DEFAULT_MIN_RELAY_TX_FEE);
@@ -868,6 +869,8 @@ bool AcceptToMemoryPoolWorker(CTxMemPool& pool, CValidationState &state, const C
                 // unconfirmed ancestors anyway; doing otherwise is hopelessly
                 // insecure.
                 bool fReplacementOptOut = true;
+                if (fPermitReplacement)
+                {
                     BOOST_FOREACH(const CTxIn &txin, ptxConflicting->vin)
                     {
                         if (txin.nSequence < std::numeric_limits<unsigned int>::max()-1)
@@ -876,6 +879,7 @@ bool AcceptToMemoryPoolWorker(CTxMemPool& pool, CValidationState &state, const C
                             break;
                         }
                     }
+                }
                 if (fReplacementOptOut)
                     return state.Invalid(false, REJECT_CONFLICT, "txn-mempool-conflict");
 

src/main.h

@@ -107,6 +107,8 @@ static const bool DEFAULT_TXINDEX = false;
 static const unsigned int DEFAULT_BANSCORE_THRESHOLD = 100;
 
 static const bool DEFAULT_TESTSAFEMODE = false;
+/** Default for -permitrbf */
+static const bool DEFAULT_PERMIT_REPLACEMENT = true;
 
 /** Maximum number of headers to announce when relaying blocks with headers message.*/
 static const unsigned int MAX_BLOCKS_TO_ANNOUNCE = 8;
@@ -139,6 +141,7 @@ extern size_t nCoinCacheUsage;
 extern CFeeRate minRelayTxFee;
 extern bool fAlerts;
 extern int64_t nMaxTipAge;
+extern bool fPermitReplacement;
 
 /** Best header we've seen so far (used for getheaders queries' starting points). */
 extern CBlockIndex *pindexBestHeader;