From d1721c761e3dce78ceb27aaaba2ad7836e669306 Mon Sep 17 00:00:00 2001
From: Andreas Kling <kling@serenityos.org>
Date: Sun, 26 Jan 2020 16:24:57 +0100
Subject: [PATCH] LookupServer: Don't cache already-expired DNS answers

---
 Servers/LookupServer/LookupServer.cpp | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/Servers/LookupServer/LookupServer.cpp b/Servers/LookupServer/LookupServer.cpp
index cb36c1cc5f..a33bb4fce8 100644
--- a/Servers/LookupServer/LookupServer.cpp
+++ b/Servers/LookupServer/LookupServer.cpp
@@ -240,13 +240,18 @@ Vector<String> LookupServer::lookup(const String& hostname, bool& did_timeout, u
         return {};
     }
 
-    Vector<String> responses;
+    Vector<String, 8> responses;
+    Vector<DNSAnswer, 8> cacheable_answers;
     for (auto& answer : response.answers()) {
         responses.append(answer.record_data());
+        if (!answer.has_expired())
+            cacheable_answers.append(answer);
     }
 
-    if (m_lookup_cache.size() >= 256)
-        m_lookup_cache.remove(m_lookup_cache.begin());
-    m_lookup_cache.set(hostname, { request.questions()[0], response.answers() });
+    if (!cacheable_answers.is_empty()) {
+        if (m_lookup_cache.size() >= 256)
+            m_lookup_cache.remove(m_lookup_cache.begin());
+        m_lookup_cache.set(hostname, { request.questions()[0], move(cacheable_answers) });
+    }
     return responses;
 }