Clean up syn_cookies class and add syn_cookies::cookie method which gets the cookie associated with an endpoint and erases that cookie from this container.

nano/node/network.cpp

@@ -810,6 +810,10 @@ void nano::tcp_message_manager::stop ()
 	producer_condition.notify_all ();
 }
 
+/*
+ * syn_cookies
+ */
+
 nano::syn_cookies::syn_cookies (std::size_t max_cookies_per_ip_a) :
 	max_cookies_per_ip (max_cookies_per_ip_a)
 {
@@ -888,6 +892,30 @@ void nano::syn_cookies::purge (std::chrono::steady_clock::time_point const & cut
 	}
 }
 
+std::optional<nano::uint256_union> nano::syn_cookies::cookie (const nano::endpoint & endpoint_a)
+{
+	auto ip_addr (endpoint_a.address ());
+	debug_assert (ip_addr.is_v6 ());
+	nano::lock_guard<nano::mutex> lock{ syn_cookie_mutex };
+	auto cookie_it (cookies.find (endpoint_a));
+	if (cookie_it != cookies.end ())
+	{
+		auto cookie = cookie_it->second.cookie;
+		cookies.erase (cookie_it);
+		unsigned & ip_cookies = cookies_per_ip[ip_addr];
+		if (ip_cookies > 0)
+		{
+			--ip_cookies;
+		}
+		else
+		{
+			debug_assert (false && "More SYN cookies deleted than created for IP");
+		}
+		return cookie;
+	}
+	return std::nullopt;
+}
+
 std::size_t nano::syn_cookies::cookies_size ()
 {
 	nano::lock_guard<nano::mutex> lock{ syn_cookie_mutex };

nano/node/network.hpp

@@ -14,6 +14,7 @@
 namespace nano
 {
 class node;
+
 class tcp_message_manager final
 {
 public:
@@ -34,13 +35,15 @@ private:
 
 	friend class network_tcp_message_manager_Test;
 };
+
 /**
  * Node ID cookies for node ID handshakes
  */
 class syn_cookies final
 {
 public:
-	syn_cookies (std::size_t);
+	explicit syn_cookies (std::size_t);
+
 	void purge (std::chrono::steady_clock::time_point const &);
 	// Returns boost::none if the IP is rate capped on syn cookie requests,
 	// or if the endpoint already has a syn cookie query
@@ -48,6 +51,9 @@ public:
 	// Returns false if valid, true if invalid (true on error convention)
 	// Also removes the syn cookie from the store if valid
 	bool validate (nano::endpoint const &, nano::account const &, nano::signature const &);
+	/** Get cookie associated with endpoint and erases that cookie from this container */
+	std::optional<nano::uint256_union> cookie (nano::endpoint const &);
+
 	std::unique_ptr<container_info_component> collect_container_info (std::string const &);
 	std::size_t cookies_size ();