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.

Conflicts:
	src/init.cpp
	src/main.cpp
	src/main.h

Github-Pull: #7386
Rebased-From: b768108d9c

src/init.cpp

@@ -366,6 +366,7 @@ 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));
@@ -1007,6 +1008,8 @@ bool AppInit2(boost::thread_group& threadGroup, CScheduler& scheduler)
     if (GetBoolArg("-peerbloomfilters", true))
         nLocalServices |= NODE_BLOOM;
 
+    fPermitReplacement = GetBoolArg("-permitrbf", DEFAULT_PERMIT_REPLACEMENT);
+
     // ********************************************************* Step 4: application initialization: dir lock, daemonize, pidfile, debug log
 
     // Initialize elliptic curve code

src/main.cpp

@@ -75,6 +75,7 @@ bool fCheckpointsEnabled = DEFAULT_CHECKPOINTS_ENABLED;
 size_t nCoinCacheUsage = 5000 * 300;
 uint64_t nPruneTarget = 0;
 bool fAlerts = DEFAULT_ALERTS;
+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);
@@ -865,12 +866,15 @@ bool AcceptToMemoryPoolWorker(CTxMemPool& pool, CValidationState &state, const C
                 // unconfirmed ancestors anyway; doing otherwise is hopelessly
                 // insecure.
                 bool fReplacementOptOut = true;
-                BOOST_FOREACH(const CTxIn &txin, ptxConflicting->vin)
+                if (fPermitReplacement)
                 {
-                    if (txin.nSequence < std::numeric_limits<unsigned int>::max()-1)
+                    BOOST_FOREACH(const CTxIn &txin, ptxConflicting->vin)
                     {
-                        fReplacementOptOut = false;
+                        if (txin.nSequence < std::numeric_limits<unsigned int>::max()-1)
-                        break;
+                        {
+                            fReplacementOptOut = false;
+                            break;
+                        }
                     }
                 }
                 if (fReplacementOptOut)

src/main.h

@@ -106,6 +106,8 @@ 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;
@@ -137,6 +139,7 @@ extern bool fCheckpointsEnabled;
 extern size_t nCoinCacheUsage;
 extern CFeeRate minRelayTxFee;
 extern bool fAlerts;
+extern bool fPermitReplacement;
 
 /** Best header we've seen so far (used for getheaders queries' starting points). */
 extern CBlockIndex *pindexBestHeader;