Auto merge of #2342 - bitcartel:1081__mempoolpatch, r=str4d

Add ability for node to reject tx from mempool by number of tx inputs

Implement short-term solution described in #2343 so that users can respond promptly to critical short-term problems caused by quadratic validation scaling, such as the getblocktemplate latency, block propagation latency, and mempool size inflation issues described in #2333.

src/init.cpp

@@ -352,6 +352,7 @@ std::string HelpMessage(HelpMessageMode mode)
     strUsage += HelpMessageOpt("-dbcache=<n>", strprintf(_("Set database cache size in megabytes (%d to %d, default: %d)"), nMinDbCache, nMaxDbCache, nDefaultDbCache));
     strUsage += HelpMessageOpt("-loadblock=<file>", _("Imports blocks from external blk000??.dat file") + " " + _("on startup"));
     strUsage += HelpMessageOpt("-maxorphantx=<n>", strprintf(_("Keep at most <n> unconnectable transactions in memory (default: %u)"), DEFAULT_MAX_ORPHAN_TRANSACTIONS));
+    strUsage += HelpMessageOpt("-mempooltxinputlimit=<n>", _("Set the maximum number of transparent inputs in a transaction that the mempool will accept (default: 0 = no limit applied)"));
     strUsage += HelpMessageOpt("-par=<n>", strprintf(_("Set the number of script verification threads (%u to %d, 0 = auto, <0 = leave that many cores free, default: %d)"),
         -GetNumCores(), MAX_SCRIPTCHECK_THREADS, DEFAULT_SCRIPTCHECK_THREADS));
 #ifndef WIN32
@@ -1036,6 +1037,17 @@ bool AppInit2(boost::thread_group& threadGroup, CScheduler& scheduler)
     }
 #endif
 
+    // Default value of 0 for mempooltxinputlimit means no limit is applied
+    if (mapArgs.count("-mempooltxinputlimit")) {
+        int64_t limit = GetArg("-mempooltxinputlimit", 0);
+        if (limit < 0) {
+            return InitError(_("Mempool limit on transparent inputs to a transaction cannot be negative"));
+        } else if (limit > 0) {
+            LogPrintf("Mempool configured to reject transactions with greater than %lld transparent inputs\n", limit);
+        }
+    }
+
+
     // ********************************************************* Step 4: application initialization: dir lock, daemonize, pidfile, debug log
 
     // Initialize libsodium