From 3a4da5aa0579c43c6126ddca11cd3f02205015a3 Mon Sep 17 00:00:00 2001
From: Andreas Kling <awesomekling@gmail.com>
Date: Wed, 16 Oct 2019 12:10:16 +0200
Subject: [PATCH] LookupServer: Cache successful DNS lookup responses for 1
 minute

This reduces DNS traffic spam during web browsing. We can definitely do
a lot better here, this is just a very low-hanging fruit.
---
 Servers/LookupServer/main.cpp | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/Servers/LookupServer/main.cpp b/Servers/LookupServer/main.cpp
index e636164122..c5c3821483 100644
--- a/Servers/LookupServer/main.cpp
+++ b/Servers/LookupServer/main.cpp
@@ -16,6 +16,7 @@
 #include <sys/select.h>
 #include <sys/socket.h>
 #include <sys/time.h>
+#include <time.h>
 #include <unistd.h>
 
 #define T_A 1
@@ -27,6 +28,13 @@
 
 #define C_IN 1
 
+struct CachedLookup {
+    time_t timestamp { 0 };
+    unsigned short record_type { 0 };
+    Vector<String> responses;
+};
+
+static HashMap<String, CachedLookup> lookup_cache;
 static HashMap<String, String> dns_custom_hostnames;
 
 static Vector<String> lookup(const String& hostname, bool& did_timeout, const String& DNS_IP, unsigned short record_type);
@@ -207,6 +215,14 @@ static u16 get_next_id()
 
 Vector<String> lookup(const String& hostname, bool& did_timeout, const String& DNS_IP, unsigned short record_type)
 {
+    if (auto it = lookup_cache.find(hostname); it != lookup_cache.end()) {
+        auto& cached_lookup = it->value;
+        if (cached_lookup.record_type == record_type && cached_lookup.timestamp < (time(nullptr) + 60)) {
+            return it->value.responses;
+        }
+        lookup_cache.remove(it);
+    }
+
     DNSPacket request_header;
     request_header.set_id(get_next_id());
     request_header.set_is_query();
@@ -335,6 +351,7 @@ Vector<String> lookup(const String& hostname, bool& did_timeout, const String& D
         // FIXME: Parse some other record types perhaps?
     }
 
+    lookup_cache.set(hostname, { time(nullptr), record_type, addresses });
     return addresses;
 }