Add option 'mempooltxinputlimit' so the mempool can reject a transaction

based on the number of transparent inputs.

src/main.cpp

@@ -1057,6 +1057,17 @@ bool AcceptToMemoryPool(CTxMemPool& pool, CValidationState &state, const CTransa
     if (pfMissingInputs)
         *pfMissingInputs = false;
 
+    // Node operator can choose to reject tx by number of transparent inputs
+    static_assert(std::numeric_limits<size_t>::max() >= std::numeric_limits<int64_t>::max(), "size_t too small");
+    size_t limit = (size_t) GetArg("-mempooltxinputlimit", 0);
+    if (limit > 0) {
+        size_t n = tx.vin.size();
+        if (n > limit) {
+            LogPrint("mempool", "Dropping txid %s : too many transparent inputs %zu > limit %zu\n", tx.GetHash().ToString(), n, limit );
+            return false;
+        }
+    }
+
     auto verifier = libzcash::ProofVerifier::Strict();
     if (!CheckTransaction(tx, state, verifier))
         return error("AcceptToMemoryPool: CheckTransaction failed");