1 files changed, 33 insertions, 0 deletions
diff --git a/Userland/Services/LookupServer/DNSName.cpp b/Userland/Services/LookupServer/DNSName.cpp
index 7385868076..ce9ad68f56 100644
--- a/Userland/Services/LookupServer/DNSName.cpp
+++ b/Userland/Services/LookupServer/DNSName.cpp
@@ -1,4 +1,5 @@
 /*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
  * Copyright (c) 2021, Sergey Bugaev <bugaevc@serenityos.org>
  * All rights reserved.
  *
@@ -36,4 +37,36 @@ DNSName::DNSName(const String& name)
         m_name = name;
 }
 
+DNSName DNSName::parse(const u8* data, size_t& offset, size_t max_offset, size_t recursion_level)
+{
+    if (recursion_level > 4)
+        return DNSName({});
+
+    StringBuilder builder;
+    while (true) {
+        if (offset >= max_offset)
+            return DNSName({});
+        u8 b = data[offset++];
+        if (b == '\0') {
+            // This terminates the name.
+            return builder.to_string();
+        } else if ((b & 0xc0) == 0xc0) {
+            // The two bytes tell us the offset when to continue from.
+            if (offset >= max_offset)
+                return DNSName({});
+            size_t dummy = (b & 0x3f) << 8 | data[offset++];
+            auto rest_of_name = parse(data, dummy, max_offset, recursion_level + 1);
+            builder.append(rest_of_name.as_string());
+            return builder.to_string();
+        } else {
+            // This is the length of a part.
+            if (offset + b >= max_offset)
+                return DNSName({});
+            builder.append((const char*)&data[offset], (size_t)b);
+            builder.append('.');
+            offset += b;
+        }
+    }
+}
+
 }