check double spend in inputs when add tx to pool.

src/lib/blockchain/validate_transaction.cpp

@@ -1339,6 +1339,18 @@ code validate_transaction::check_transaction_basic() const
     if (tx.serialized_size() > max_transaction_size)
         return error::size_limits;
 
+    // check double spend in inputs
+    std::set<std::string> set;
+    for (auto& input : tx.inputs) {
+        auto tx_hash = libbitcoin::encode_hash(input.previous_output.hash);
+        auto value = tx_hash + ":" + std::to_string(input.previous_output.index);
+        if (set.count(value)) {
+            return error::double_spend;
+        }
+
+        set.insert(value);
+    }
+
     // Check for negative or overflow output values
     uint64_t total_output_value = 0;