Implemented user duplicate input message check.

src/util.cpp

@@ -1,8 +1,45 @@
 #include "pchheader.hpp"
+#include "util.hpp"
 
 namespace util
 {
 
+// rollover_hashset class methods
+
+rollover_hashset::rollover_hashset(uint32_t maxsize)
+{
+    this->maxsize = maxsize == 0 ? 1 : maxsize;
+}
+
+/**
+ * Inserts the given hash to the list.
+ * @return True on succesful insertion. False if hash already exists.
+ */
+bool rollover_hashset::try_emplace(std::string hash)
+{
+    auto itr = recent_hashes.find(hash);
+    if (itr == recent_hashes.end()) // Not found
+    {
+        // Add the new message hash to the set.
+        auto [newitr, success] = recent_hashes.emplace(hash);
+
+        // Insert a pointer to the stored hash value to the back of the ordered list of hashes.
+        recent_hashes_list.push_back(&(*newitr));
+
+        // Remove oldest hash if exceeding max size.
+        if (recent_hashes_list.size() > maxsize)
+        {
+            const std::string &oldest_hash = *recent_hashes_list.front();
+            recent_hashes.erase(oldest_hash);
+            recent_hashes_list.pop_front();
+        }
+
+        return true; // Hash was inserted successfuly.
+    }
+
+    return false; // Hash already exists.
+}
+
 /**
  * Encodes provided bytes to hex string.
  *