Services: Move to Userland/Services/

Userland/Services/LookupServer/CMakeLists.txt

@@ -0,0 +1,10 @@
+set(SOURCES
+    DNSAnswer.cpp
+    DNSRequest.cpp
+    DNSResponse.cpp
+    LookupServer.cpp
+    main.cpp
+)
+
+serenity_bin(LookupServer)
+target_link_libraries(LookupServer LibCore)

Userland/Services/LookupServer/DNSAnswer.cpp

@@ -0,0 +1,46 @@
+/*
+ * Copyright (c) 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 "DNSAnswer.h"
+#include <time.h>
+
+DNSAnswer::DNSAnswer(const String& name, u16 type, u16 class_code, u32 ttl, const String& record_data)
+    : m_name(name)
+    , m_type(type)
+    , m_class_code(class_code)
+    , m_ttl(ttl)
+    , m_record_data(record_data)
+{
+    auto now = time(nullptr);
+    m_expiration_time = now + m_ttl;
+    if (m_expiration_time < now)
+        m_expiration_time = 0;
+}
+
+bool DNSAnswer::has_expired() const
+{
+    return time(nullptr) >= m_expiration_time;
+}

Userland/Services/LookupServer/DNSAnswer.h

@@ -0,0 +1,51 @@
+/*
+ * Copyright (c) 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.
+ */
+
+#pragma once
+
+#include <AK/String.h>
+#include <AK/Types.h>
+
+class DNSAnswer {
+public:
+    DNSAnswer(const String& name, u16 type, u16 class_code, u32 ttl, const String& record_data);
+
+    const String& name() const { return m_name; }
+    u16 type() const { return m_type; }
+    u16 class_code() const { return m_class_code; }
+    u32 ttl() const { return m_ttl; }
+    const String& record_data() const { return m_record_data; }
+
+    bool has_expired() const;
+
+private:
+    String m_name;
+    u16 m_type { 0 };
+    u16 m_class_code { 0 };
+    u32 m_ttl { 0 };
+    time_t m_expiration_time { 0 };
+    String m_record_data;
+};

Userland/Services/LookupServer/DNSPacket.h

@@ -0,0 +1,115 @@
+/*
+ * 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.
+ */
+
+#pragma once
+
+#include <AK/Endian.h>
+#include <AK/Types.h>
+
+class [[gnu::packed]] DNSPacket {
+public:
+    DNSPacket()
+        : m_recursion_desired(false)
+        , m_truncated(false)
+        , m_authoritative_answer(false)
+        , m_opcode(0)
+        , m_query_or_response(false)
+        , m_response_code(0)
+        , m_checking_disabled(false)
+        , m_authenticated_data(false)
+        , m_zero(false)
+        , m_recursion_available(false)
+    {
+    }
+
+    u16 id() const { return m_id; }
+    void set_id(u16 w) { m_id = w; }
+
+    bool recursion_desired() const { return m_recursion_desired; }
+    void set_recursion_desired(bool b) { m_recursion_desired = b; }
+
+    bool is_truncated() const { return m_truncated; }
+    void set_truncated(bool b) { m_truncated = b; }
+
+    bool is_authoritative_answer() const { return m_authoritative_answer; }
+    void set_authoritative_answer(bool b) { m_authoritative_answer = b; }
+
+    u8 opcode() const { return m_opcode; }
+    void set_opcode(u8 b) { m_opcode = b; }
+
+    bool is_query() const { return !m_query_or_response; }
+    bool is_response() const { return m_query_or_response; }
+    void set_is_query() { m_query_or_response = false; }
+    void set_is_response() { m_query_or_response = true; }
+
+    u8 response_code() const { return m_response_code; }
+    void set_response_code(u8 b) { m_response_code = b; }
+
+    bool checking_disabled() const { return m_checking_disabled; }
+    void set_checking_disabled(bool b) { m_checking_disabled = b; }
+
+    bool is_authenticated_data() const { return m_authenticated_data; }
+    void set_authenticated_data(bool b) { m_authenticated_data = b; }
+
+    bool is_recursion_available() const { return m_recursion_available; }
+    void set_recursion_available(bool b) { m_recursion_available = b; }
+
+    u16 question_count() const { return m_question_count; }
+    void set_question_count(u16 w) { m_question_count = w; }
+
+    u16 answer_count() const { return m_answer_count; }
+    void set_answer_count(u16 w) { m_answer_count = w; }
+
+    u16 authority_count() const { return m_authority_count; }
+    void set_authority_count(u16 w) { m_authority_count = w; }
+
+    u16 additional_count() const { return m_additional_count; }
+    void set_additional_count(u16 w) { m_additional_count = w; }
+
+    void* payload() { return this + 1; }
+    const void* payload() const { return this + 1; }
+
+private:
+    NetworkOrdered<u16> m_id;
+
+    bool m_recursion_desired : 1;
+    bool m_truncated : 1;
+    bool m_authoritative_answer : 1;
+    u8 m_opcode : 4;
+    bool m_query_or_response : 1;
+    u8 m_response_code : 4;
+    bool m_checking_disabled : 1;
+    bool m_authenticated_data : 1;
+    bool m_zero : 1;
+    bool m_recursion_available : 1;
+
+    NetworkOrdered<u16> m_question_count;
+    NetworkOrdered<u16> m_answer_count;
+    NetworkOrdered<u16> m_authority_count;
+    NetworkOrdered<u16> m_additional_count;
+};
+
+static_assert(sizeof(DNSPacket) == 12);

Userland/Services/LookupServer/DNSQuestion.h

@@ -0,0 +1,59 @@
+/*
+ * Copyright (c) 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.
+ */
+
+#pragma once
+
+#include <AK/String.h>
+#include <AK/Types.h>
+
+class DNSQuestion {
+public:
+    DNSQuestion(const String& name, u16 record_type, u16 class_code)
+        : m_name(name)
+        , m_record_type(record_type)
+        , m_class_code(class_code)
+    {
+    }
+
+    u16 record_type() const { return m_record_type; }
+    u16 class_code() const { return m_class_code; }
+    const String& name() const { return m_name; }
+
+    bool operator==(const DNSQuestion& other) const
+    {
+        return m_name == other.m_name && m_record_type == other.m_record_type && m_class_code == other.m_class_code;
+    }
+
+    bool operator!=(const DNSQuestion& other) const
+    {
+        return !(*this == other);
+    }
+
+private:
+    String m_name;
+    u16 m_record_type { 0 };
+    u16 m_class_code { 0 };
+};

Userland/Services/LookupServer/DNSRequest.cpp

@@ -0,0 +1,96 @@
+/*
+ * 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/MemoryStream.h>
+#include <AK/StringBuilder.h>
+#include <arpa/inet.h>
+#include <ctype.h>
+#include <stdlib.h>
+
+const u16 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());
+
+    DuplexMemoryStream stream;
+
+    stream << ReadonlyBytes { &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.bytes();
+        }
+        stream << '\0';
+        stream << htons(question.record_type());
+        stream << htons(question.class_code());
+    }
+
+    return stream.copy_into_contiguous_buffer();
+}

Userland/Services/LookupServer/DNSRequest.h

@@ -0,0 +1,65 @@
+/*
+ * Copyright (c) 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.
+ */
+
+#pragma once
+
+#include "DNSQuestion.h"
+#include <AK/Types.h>
+#include <AK/Vector.h>
+
+#define T_A 1
+#define T_NS 2
+#define T_CNAME 5
+#define T_SOA 6
+#define T_PTR 12
+#define T_MX 15
+
+enum class ShouldRandomizeCase {
+    No = 0,
+    Yes
+};
+
+class DNSRequest {
+public:
+    DNSRequest();
+
+    void add_question(const String& name, u16 record_type, ShouldRandomizeCase);
+
+    const Vector<DNSQuestion>& questions() const { return m_questions; }
+
+    u16 question_count() const
+    {
+        ASSERT(m_questions.size() < UINT16_MAX);
+        return m_questions.size();
+    }
+
+    u16 id() const { return m_id; }
+    ByteBuffer to_byte_buffer() const;
+
+private:
+    u16 m_id { 0 };
+    Vector<DNSQuestion> m_questions;
+};

Userland/Services/LookupServer/DNSResponse.cpp

@@ -0,0 +1,152 @@
+/*
+ * 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 "DNSResponse.h"
+#include "DNSPacket.h"
+#include "DNSRequest.h"
+#include <AK/IPv4Address.h>
+#include <AK/StringBuilder.h>
+
+static String parse_dns_name(const u8* data, size_t& offset, size_t max_offset, size_t recursion_level = 0);
+
+class [[gnu::packed]] DNSRecordWithoutName {
+public:
+    DNSRecordWithoutName() { }
+
+    u16 type() const { return m_type; }
+    u16 record_class() const { return m_class; }
+    u32 ttl() const { return m_ttl; }
+    u16 data_length() const { return m_data_length; }
+
+    void* data() { return this + 1; }
+    const void* data() const { return this + 1; }
+
+private:
+    NetworkOrdered<u16> m_type;
+    NetworkOrdered<u16> m_class;
+    NetworkOrdered<u32> m_ttl;
+    NetworkOrdered<u16> m_data_length;
+};
+
+static_assert(sizeof(DNSRecordWithoutName) == 10);
+
+Optional<DNSResponse> DNSResponse::from_raw_response(const u8* raw_data, size_t raw_size)
+{
+    if (raw_size < sizeof(DNSPacket)) {
+        dbgln("DNS response not large enough ({} out of {}) to be a DNS packet.", raw_size, sizeof(DNSPacket));
+        return {};
+    }
+
+    auto& response_header = *(const DNSPacket*)(raw_data);
+#ifdef LOOKUPSERVER_DEBUG
+    dbgln("Got response (ID: {})", response_header.id());
+    dbgln("  Question count: {}", response_header.question_count());
+    dbgln("    Answer count: {}", response_header.answer_count());
+    dbgln(" Authority count: {}", response_header.authority_count());
+    dbgln("Additional count: {}", response_header.additional_count());
+#endif
+
+    DNSResponse response;
+    response.m_id = response_header.id();
+    response.m_code = response_header.response_code();
+
+    if (response.code() != DNSResponse::Code::NOERROR)
+        return response;
+
+    size_t offset = sizeof(DNSPacket);
+
+    for (u16 i = 0; i < response_header.question_count(); ++i) {
+        auto name = parse_dns_name(raw_data, offset, raw_size);
+        struct RawDNSAnswerQuestion {
+            NetworkOrdered<u16> record_type;
+            NetworkOrdered<u16> class_code;
+        };
+        auto& record_and_class = *(const RawDNSAnswerQuestion*)&raw_data[offset];
+        response.m_questions.empend(name, record_and_class.record_type, record_and_class.class_code);
+        offset += 4;
+#ifdef LOOKUPSERVER_DEBUG
+        auto& question = response.m_questions.last();
+        dbgln("Question #{}: name=_{}_, type={}, class={}", i, question.name(), question.record_type(), question.class_code());
+#endif
+    }
+
+    for (u16 i = 0; i < response_header.answer_count(); ++i) {
+        auto name = parse_dns_name(raw_data, offset, raw_size);
+
+        auto& record = *(const DNSRecordWithoutName*)(&raw_data[offset]);
+
+        String data;
+
+        offset += sizeof(DNSRecordWithoutName);
+        if (record.type() == T_PTR) {
+            size_t dummy_offset = offset;
+            data = parse_dns_name(raw_data, dummy_offset, raw_size);
+        } else if (record.type() == T_A) {
+            auto ipv4_address = IPv4Address((const u8*)record.data());
+            data = ipv4_address.to_string();
+        } else {
+            // FIXME: Parse some other record types perhaps?
+            dbgln("data=(unimplemented record type {})", record.type());
+        }
+#ifdef LOOKUPSERVER_DEBUG
+        dbgln("Answer   #{}: name=_{}_, type={}, ttl={}, length={}, data=_{}_", i, name, record.type(), record.ttl(), record.data_length(), data);
+#endif
+        response.m_answers.empend(name, record.type(), record.record_class(), record.ttl(), data);
+        offset += record.data_length();
+    }
+
+    return response;
+}
+
+String parse_dns_name(const u8* data, size_t& offset, size_t max_offset, size_t recursion_level)
+{
+    if (recursion_level > 4)
+        return {};
+    Vector<char, 128> buf;
+    while (offset < max_offset) {
+        u8 ch = data[offset];
+        if (ch == '\0') {
+            ++offset;
+            break;
+        }
+        if ((ch & 0xc0) == 0xc0) {
+            if ((offset + 1) >= max_offset)
+                return {};
+            size_t dummy = (ch & 0x3f) << 8 | data[offset + 1];
+            offset += 2;
+            StringBuilder builder;
+            builder.append(buf.data(), buf.size());
+            auto okay = parse_dns_name(data, dummy, max_offset, recursion_level + 1);
+            builder.append(okay);
+            return builder.to_string();
+        }
+        for (size_t i = 0; i < ch; ++i)
+            buf.append(data[offset + i + 1]);
+        buf.append('.');
+        offset += ch + 1;
+    }
+    return String::copy(buf);
+}

Userland/Services/LookupServer/DNSResponse.h

@@ -0,0 +1,77 @@
+/*
+ * Copyright (c) 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.
+ */
+
+#pragma once
+
+#include "DNSAnswer.h"
+#include "DNSQuestion.h"
+#include <AK/Optional.h>
+#include <AK/Types.h>
+#include <AK/Vector.h>
+
+class DNSResponse {
+public:
+    static Optional<DNSResponse> from_raw_response(const u8*, size_t);
+
+    u16 id() const { return m_id; }
+    const Vector<DNSQuestion>& questions() const { return m_questions; }
+    const Vector<DNSAnswer>& answers() const { return m_answers; }
+
+    u16 question_count() const
+    {
+        ASSERT(m_questions.size() <= UINT16_MAX);
+        return m_questions.size();
+    }
+
+    u16 answer_count() const
+    {
+        ASSERT(m_answers.size() <= UINT16_MAX);
+        return m_answers.size();
+    }
+
+    enum class Code : u8 {
+        NOERROR = 0,
+        FORMERR = 1,
+        SERVFAIL = 2,
+        NXDOMAIN = 3,
+        NOTIMP = 4,
+        REFUSED = 5,
+        YXDOMAIN = 6,
+        XRRSET = 7,
+        NOTAUTH = 8,
+        NOTZONE = 9,
+    };
+
+    Code code() const { return (Code)m_code; }
+
+private:
+    DNSResponse() { }
+
+    u16 m_id { 0 };
+    u8 m_code { 0 };
+    Vector<DNSQuestion> m_questions;
+    Vector<DNSAnswer> m_answers;
+};

Userland/Services/LookupServer/LookupServer.cpp

@@ -0,0 +1,278 @@
+/*
+ * 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 "LookupServer.h"
+#include "DNSRequest.h"
+#include "DNSResponse.h"
+#include <AK/ByteBuffer.h>
+#include <AK/HashMap.h>
+#include <AK/String.h>
+#include <AK/StringBuilder.h>
+#include <LibCore/ConfigFile.h>
+#include <LibCore/File.h>
+#include <LibCore/LocalServer.h>
+#include <LibCore/LocalSocket.h>
+#include <LibCore/UDPSocket.h>
+#include <stdio.h>
+#include <sys/time.h>
+#include <unistd.h>
+
+//#define LOOKUPSERVER_DEBUG
+
+LookupServer::LookupServer()
+{
+    auto config = Core::ConfigFile::get_for_system("LookupServer");
+    dbgln("Using network config file at {}", config->file_name());
+    m_nameservers = config->read_entry("DNS", "Nameservers", "1.1.1.1,1.0.0.1").split(',');
+
+    load_etc_hosts();
+
+    m_local_server = Core::LocalServer::construct(this);
+    m_local_server->on_ready_to_accept = [this]() {
+        auto socket = m_local_server->accept();
+        socket->on_ready_to_read = [this, socket]() {
+            service_client(socket);
+            RefPtr<Core::LocalSocket> keeper = socket;
+            const_cast<Core::LocalSocket&>(*socket).on_ready_to_read = [] {};
+        };
+    };
+    bool ok = m_local_server->take_over_from_system_server();
+    ASSERT(ok);
+}
+
+void LookupServer::load_etc_hosts()
+{
+    auto file = Core::File::construct("/etc/hosts");
+    if (!file->open(Core::IODevice::ReadOnly))
+        return;
+    while (!file->eof()) {
+        auto line = file->read_line(1024);
+        if (line.is_empty())
+            break;
+        auto fields = line.split('\t');
+
+        auto sections = fields[0].split('.');
+        IPv4Address addr {
+            (u8)atoi(sections[0].characters()),
+            (u8)atoi(sections[1].characters()),
+            (u8)atoi(sections[2].characters()),
+            (u8)atoi(sections[3].characters()),
+        };
+
+        auto name = fields[1];
+        m_etc_hosts.set(name, addr.to_string());
+
+        IPv4Address reverse_addr {
+            (u8)atoi(sections[3].characters()),
+            (u8)atoi(sections[2].characters()),
+            (u8)atoi(sections[1].characters()),
+            (u8)atoi(sections[0].characters()),
+        };
+        StringBuilder builder;
+        builder.append(reverse_addr.to_string());
+        builder.append(".in-addr.arpa");
+        m_etc_hosts.set(builder.to_string(), name);
+    }
+}
+
+void LookupServer::service_client(RefPtr<Core::LocalSocket> socket)
+{
+    u8 client_buffer[1024];
+    int nrecv = socket->read(client_buffer, sizeof(client_buffer) - 1);
+    if (nrecv < 0) {
+        perror("read");
+        return;
+    }
+
+    client_buffer[nrecv] = '\0';
+
+    char lookup_type = client_buffer[0];
+    if (lookup_type != 'L' && lookup_type != 'R') {
+        dbgln("Invalid lookup_type '{}'", lookup_type);
+        return;
+    }
+    auto hostname = String((const char*)client_buffer + 1, nrecv - 1, Chomp);
+#ifdef LOOKUPSERVER_DEBUG
+    dbgln("Got request for '{}'", hostname);
+#endif
+
+    Vector<String> responses;
+
+    if (auto known_host = m_etc_hosts.get(hostname); known_host.has_value()) {
+        responses.append(known_host.value());
+    } else if (!hostname.is_empty()) {
+        for (auto& nameserver : m_nameservers) {
+#ifdef LOOKUPSERVER_DEBUG
+            dbgln("Doing lookup using nameserver '{}'", nameserver);
+#endif
+            bool did_get_response = false;
+            int retries = 3;
+            do {
+                if (lookup_type == 'L')
+                    responses = lookup(hostname, nameserver, did_get_response, T_A);
+                else if (lookup_type == 'R')
+                    responses = lookup(hostname, nameserver, did_get_response, T_PTR);
+                if (did_get_response)
+                    break;
+            } while (--retries);
+            if (!responses.is_empty()) {
+                break;
+            } else {
+                if (!did_get_response)
+                    dbgln("Never got a response from '{}', trying next nameserver", nameserver);
+                else
+                    dbgln("Received response from '{}' but no result(s), trying next nameserver", nameserver);
+            }
+        }
+        if (responses.is_empty()) {
+            fprintf(stderr, "LookupServer: Tried all nameservers but never got a response :(\n");
+            return;
+        }
+    }
+
+    if (responses.is_empty()) {
+        int nsent = socket->write("Not found.\n");
+        if (nsent < 0)
+            perror("write");
+        return;
+    }
+    for (auto& response : responses) {
+        auto line = String::format("%s\n", response.characters());
+        int nsent = socket->write(line);
+        if (nsent < 0) {
+            perror("write");
+            break;
+        }
+    }
+}
+
+Vector<String> LookupServer::lookup(const String& hostname, const String& nameserver, bool& did_get_response, unsigned short record_type, ShouldRandomizeCase should_randomize_case)
+{
+    if (auto it = m_lookup_cache.find(hostname); it != m_lookup_cache.end()) {
+        auto& cached_lookup = it->value;
+        if (cached_lookup.question.record_type() == record_type) {
+            Vector<String> responses;
+            for (auto& cached_answer : cached_lookup.answers) {
+#ifdef LOOKUPSERVER_DEBUG
+                dbgln("Cache hit: {} -> {}, expired: {}", hostname, cached_answer.record_data(), cached_answer.has_expired());
+#endif
+                if (!cached_answer.has_expired())
+                    responses.append(cached_answer.record_data());
+            }
+            if (!responses.is_empty())
+                return responses;
+        }
+        m_lookup_cache.remove(it);
+    }
+
+    DNSRequest request;
+    request.add_question(hostname, record_type, should_randomize_case);
+
+    auto buffer = request.to_byte_buffer();
+
+    auto udp_socket = Core::UDPSocket::construct();
+    udp_socket->set_blocking(true);
+
+    struct timeval timeout {
+        1, 0
+    };
+
+    int rc = setsockopt(udp_socket->fd(), SOL_SOCKET, SO_RCVTIMEO, &timeout, sizeof(timeout));
+    if (rc < 0) {
+        perror("setsockopt(SOL_SOCKET, SO_RCVTIMEO)");
+        return {};
+    }
+
+    if (!udp_socket->connect(nameserver, 53))
+        return {};
+
+    if (!udp_socket->write(buffer))
+        return {};
+
+    u8 response_buffer[4096];
+    int nrecv = udp_socket->read(response_buffer, sizeof(response_buffer));
+    if (nrecv == 0)
+        return {};
+
+    did_get_response = true;
+
+    auto o_response = DNSResponse::from_raw_response(response_buffer, nrecv);
+    if (!o_response.has_value())
+        return {};
+
+    auto& response = o_response.value();
+
+    if (response.id() != request.id()) {
+        dbgln("LookupServer: ID mismatch ({} vs {}) :(", response.id(), request.id());
+        return {};
+    }
+
+    if (response.code() == DNSResponse::Code::REFUSED) {
+        if (should_randomize_case == ShouldRandomizeCase::Yes) {
+            // Retry with 0x20 case randomization turned off.
+            return lookup(hostname, nameserver, did_get_response, record_type, ShouldRandomizeCase::No);
+        }
+        return {};
+    }
+
+    if (response.question_count() != request.question_count()) {
+        dbgln("LookupServer: Question count ({} vs {}) :(", response.question_count(), request.question_count());
+        return {};
+    }
+
+    for (size_t i = 0; i < request.question_count(); ++i) {
+        auto& request_question = request.questions()[i];
+        auto& response_question = response.questions()[i];
+        if (request_question != response_question) {
+            dbgln("Request and response questions do not match");
+            dbgln("   Request: name=_{}_, type={}, class={}", request_question.name(), response_question.record_type(), response_question.class_code());
+            dbgln("  Response: name=_{}_, type={}, class={}", response_question.name(), response_question.record_type(), response_question.class_code());
+            return {};
+        }
+    }
+
+    if (response.answer_count() < 1) {
+        dbgln("LookupServer: Not enough answers ({}) :(", response.answer_count());
+        return {};
+    }
+
+    Vector<String, 8> responses;
+    Vector<DNSAnswer, 8> cacheable_answers;
+    for (auto& answer : response.answers()) {
+        if (answer.type() != T_A)
+            continue;
+        responses.append(answer.record_data());
+        if (!answer.has_expired())
+            cacheable_answers.append(answer);
+    }
+
+    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;
+}

Userland/Services/LookupServer/LookupServer.h

@@ -0,0 +1,56 @@
+/*
+ * 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.
+ */
+
+#pragma once
+
+#include "DNSRequest.h"
+#include "DNSResponse.h"
+#include <AK/HashMap.h>
+#include <LibCore/Object.h>
+
+class DNSAnswer;
+
+class LookupServer final : public Core::Object {
+    C_OBJECT(LookupServer)
+
+public:
+    LookupServer();
+
+private:
+    void load_etc_hosts();
+    void service_client(RefPtr<Core::LocalSocket>);
+    Vector<String> lookup(const String& hostname, const String& nameserver, bool& did_get_response, unsigned short record_type, ShouldRandomizeCase = ShouldRandomizeCase::Yes);
+
+    struct CachedLookup {
+        DNSQuestion question;
+        Vector<DNSAnswer> answers;
+    };
+
+    RefPtr<Core::LocalServer> m_local_server;
+    Vector<String> m_nameservers;
+    HashMap<String, String> m_etc_hosts;
+    HashMap<String, CachedLookup> m_lookup_cache;
+};

Userland/Services/LookupServer/main.cpp

@@ -0,0 +1,50 @@
+/*
+ * 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 "LookupServer.h"
+#include <LibCore/EventLoop.h>
+#include <LibCore/LocalServer.h>
+#include <stdio.h>
+
+int main([[maybe_unused]] int argc, [[maybe_unused]] char** argv)
+{
+    if (pledge("stdio accept unix inet cpath rpath fattr", nullptr) < 0) {
+        perror("pledge");
+        return 1;
+    }
+
+    Core::EventLoop event_loop;
+    LookupServer server;
+
+    if (pledge("stdio accept inet", nullptr) < 0) {
+        perror("pledge");
+        return 1;
+    }
+
+    unveil(nullptr, nullptr);
+
+    return event_loop.exec();
+}