Services: Renamed from Servers

It didn't feel right to have a "DHCPClient" in a "Servers" directory.
Rename this to Services to better reflect the type of programs we'll
be putting in there.

Services/LookupServer/DNSRequest.cpp

@@ -0,0 +1,98 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "DNSRequest.h"
+#include "DNSPacket.h"
+#include <AK/BufferStream.h>
+#include <AK/StringBuilder.h>
+#include <arpa/inet.h>
+#include <ctype.h>
+#include <stdlib.h>
+
+#define C_IN 1
+
+DNSRequest::DNSRequest()
+    : m_id(arc4random_uniform(UINT16_MAX))
+{
+}
+
+void DNSRequest::add_question(const String& name, u16 record_type, ShouldRandomizeCase should_randomize_case)
+{
+    ASSERT(m_questions.size() <= UINT16_MAX);
+
+    if (name.is_empty())
+        return;
+
+    StringBuilder builder;
+    for (size_t i = 0; i < name.length(); ++i) {
+        u8 ch = name[i];
+        if (should_randomize_case == ShouldRandomizeCase::Yes) {
+            // Randomize the 0x20 bit in every ASCII character.
+            if (isalpha(ch)) {
+                if (arc4random_uniform(2))
+                    ch |= 0x20;
+                else
+                    ch &= ~0x20;
+            }
+        }
+        builder.append(ch);
+    }
+
+    if (name[name.length() - 1] != '.')
+        builder.append('.');
+
+    m_questions.empend(builder.to_string(), record_type, C_IN);
+}
+
+ByteBuffer DNSRequest::to_byte_buffer() const
+{
+    DNSPacket request_header;
+    request_header.set_id(m_id);
+    request_header.set_is_query();
+    request_header.set_opcode(0);
+    request_header.set_truncated(false);
+    request_header.set_recursion_desired(true);
+    request_header.set_question_count(m_questions.size());
+
+    auto buffer = ByteBuffer::create_uninitialized(m_questions.size() * 4096);
+    BufferStream stream(buffer);
+
+    stream << ByteBuffer::wrap(&request_header, sizeof(request_header));
+
+    for (auto& question : m_questions) {
+        auto parts = question.name().split('.');
+        for (auto& part : parts) {
+            stream << (u8)part.length();
+            stream << part;
+        }
+        stream << '\0';
+        stream << htons(question.record_type());
+        stream << htons(question.class_code());
+    }
+    stream.snip();
+
+    return buffer;
+}