Libraries: Move to Userland/Libraries/

Userland/Libraries/LibIPC/CMakeLists.txt

@@ -0,0 +1,9 @@
+set(SOURCES
+    Decoder.cpp
+    Encoder.cpp
+    Endpoint.cpp
+    Message.cpp
+)
+
+serenity_lib(LibIPC ipc)
+target_link_libraries(LibIPC LibC LibCore)

Userland/Libraries/LibIPC/ClientConnection.h

@@ -0,0 +1,78 @@
+/*
+ * 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 <LibIPC/Connection.h>
+
+namespace IPC {
+
+template<typename T, class... Args>
+NonnullRefPtr<T> new_client_connection(Args&&... args)
+{
+    return T::construct(forward<Args>(args)...) /* arghs */;
+}
+
+template<typename ClientEndpoint, typename ServerEndpoint>
+class ClientConnection : public Connection<ServerEndpoint, ClientEndpoint> {
+public:
+    ClientConnection(ServerEndpoint& endpoint, NonnullRefPtr<Core::LocalSocket> socket, int client_id)
+        : IPC::Connection<ServerEndpoint, ClientEndpoint>(endpoint, move(socket))
+        , m_client_id(client_id)
+    {
+        ASSERT(this->socket().is_connected());
+        this->socket().on_ready_to_read = [this] { this->drain_messages_from_peer(); };
+        this->initialize_peer_info();
+    }
+
+    virtual ~ClientConnection() override
+    {
+    }
+
+    void did_misbehave()
+    {
+        dbg() << *this << " (id=" << m_client_id << ", pid=" << client_pid() << ") misbehaved, disconnecting.";
+        this->shutdown();
+    }
+
+    void did_misbehave(const char* message)
+    {
+        dbg() << *this << " (id=" << m_client_id << ", pid=" << client_pid() << ") misbehaved (" << message << "), disconnecting.";
+        this->shutdown();
+    }
+
+    int client_id() const { return m_client_id; }
+
+    pid_t client_pid() const { return this->peer_pid(); }
+    void set_client_pid(pid_t pid) { this->set_peer_pid(pid); }
+
+    virtual void die() = 0;
+
+private:
+    int m_client_id { -1 };
+};
+
+}

Userland/Libraries/LibIPC/Connection.h

@@ -0,0 +1,281 @@
+/*
+ * 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/ByteBuffer.h>
+#include <AK/NonnullOwnPtrVector.h>
+#include <LibCore/Event.h>
+#include <LibCore/EventLoop.h>
+#include <LibCore/LocalSocket.h>
+#include <LibCore/Notifier.h>
+#include <LibCore/SyscallUtils.h>
+#include <LibCore/Timer.h>
+#include <LibIPC/Message.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/select.h>
+#include <sys/socket.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+namespace IPC {
+
+template<typename LocalEndpoint, typename PeerEndpoint>
+class Connection : public Core::Object {
+public:
+    Connection(LocalEndpoint& local_endpoint, NonnullRefPtr<Core::LocalSocket> socket)
+        : m_local_endpoint(local_endpoint)
+        , m_socket(move(socket))
+        , m_notifier(Core::Notifier::construct(m_socket->fd(), Core::Notifier::Read, this))
+    {
+        m_responsiveness_timer = Core::Timer::create_single_shot(3000, [this] { may_have_become_unresponsive(); });
+        m_notifier->on_ready_to_read = [this] {
+            drain_messages_from_peer();
+            handle_messages();
+        };
+    }
+
+    pid_t peer_pid() const { return m_peer_pid; }
+
+    template<typename MessageType>
+    OwnPtr<MessageType> wait_for_specific_message()
+    {
+        return wait_for_specific_endpoint_message<MessageType, LocalEndpoint>();
+    }
+
+    void post_message(const Message& message)
+    {
+        // NOTE: If this connection is being shut down, but has not yet been destroyed,
+        //       the socket will be closed. Don't try to send more messages.
+        if (!m_socket->is_open())
+            return;
+
+        auto buffer = message.encode();
+        // Prepend the message size.
+        uint32_t message_size = buffer.data.size();
+        buffer.data.prepend(reinterpret_cast<const u8*>(&message_size), sizeof(message_size));
+
+#ifdef __serenity__
+        for (int fd : buffer.fds) {
+            auto rc = sendfd(m_socket->fd(), fd);
+            if (rc < 0) {
+                perror("sendfd");
+                shutdown();
+            }
+        }
+#else
+        if (!buffer.fds.is_empty())
+            warnln("fd passing is not supported on this platform, sorry :(");
+#endif
+
+        size_t total_nwritten = 0;
+        while (total_nwritten < buffer.data.size()) {
+            auto nwritten = write(m_socket->fd(), buffer.data.data() + total_nwritten, buffer.data.size() - total_nwritten);
+            if (nwritten < 0) {
+                switch (errno) {
+                case EPIPE:
+                    dbg() << *this << "::post_message: Disconnected from peer";
+                    shutdown();
+                    return;
+                case EAGAIN:
+                    dbg() << *this << "::post_message: Peer buffer overflowed";
+                    shutdown();
+                    return;
+                default:
+                    perror("Connection::post_message write");
+                    shutdown();
+                    return;
+                }
+            }
+            total_nwritten += nwritten;
+        }
+
+        m_responsiveness_timer->start();
+    }
+
+    template<typename RequestType, typename... Args>
+    OwnPtr<typename RequestType::ResponseType> send_sync(Args&&... args)
+    {
+        post_message(RequestType(forward<Args>(args)...));
+        auto response = wait_for_specific_endpoint_message<typename RequestType::ResponseType, PeerEndpoint>();
+        ASSERT(response);
+        return response;
+    }
+
+    virtual void may_have_become_unresponsive() { }
+    virtual void did_become_responsive() { }
+
+    void shutdown()
+    {
+        m_notifier->close();
+        m_socket->close();
+        die();
+    }
+
+    virtual void die() { }
+
+protected:
+    Core::LocalSocket& socket() { return *m_socket; }
+    void set_peer_pid(pid_t pid) { m_peer_pid = pid; }
+
+    template<typename MessageType, typename Endpoint>
+    OwnPtr<MessageType> wait_for_specific_endpoint_message()
+    {
+        for (;;) {
+            // Double check we don't already have the event waiting for us.
+            // Otherwise we might end up blocked for a while for no reason.
+            for (size_t i = 0; i < m_unprocessed_messages.size(); ++i) {
+                auto& message = m_unprocessed_messages[i];
+                if (message.endpoint_magic() != Endpoint::static_magic())
+                    continue;
+                if (message.message_id() == MessageType::static_message_id())
+                    return m_unprocessed_messages.take(i).template release_nonnull<MessageType>();
+            }
+
+            if (!m_socket->is_open())
+                break;
+            fd_set rfds;
+            FD_ZERO(&rfds);
+            FD_SET(m_socket->fd(), &rfds);
+            int rc = Core::safe_syscall(select, m_socket->fd() + 1, &rfds, nullptr, nullptr, nullptr);
+            if (rc < 0) {
+                perror("select");
+            }
+            ASSERT(rc > 0);
+            ASSERT(FD_ISSET(m_socket->fd(), &rfds));
+            if (!drain_messages_from_peer())
+                break;
+        }
+        return {};
+    }
+
+    bool drain_messages_from_peer()
+    {
+        Vector<u8> bytes;
+
+        if (!m_unprocessed_bytes.is_empty()) {
+            bytes.append(m_unprocessed_bytes.data(), m_unprocessed_bytes.size());
+            m_unprocessed_bytes.clear();
+        }
+
+        while (m_socket->is_open()) {
+            u8 buffer[4096];
+            ssize_t nread = recv(m_socket->fd(), buffer, sizeof(buffer), MSG_DONTWAIT);
+            if (nread < 0) {
+                if (errno == EAGAIN)
+                    break;
+                perror("recv");
+                exit(1);
+                return false;
+            }
+            if (nread == 0) {
+                if (bytes.is_empty()) {
+                    deferred_invoke([this](auto&) { die(); });
+                }
+                return false;
+            }
+            bytes.append(buffer, nread);
+        }
+
+        if (!bytes.is_empty()) {
+            m_responsiveness_timer->stop();
+            did_become_responsive();
+        }
+
+        size_t index = 0;
+        uint32_t message_size = 0;
+        for (; index + sizeof(message_size) < bytes.size(); index += message_size) {
+            message_size = *reinterpret_cast<uint32_t*>(bytes.data() + index);
+            if (message_size == 0 || bytes.size() - index - sizeof(uint32_t) < message_size)
+                break;
+            index += sizeof(message_size);
+            auto remaining_bytes = ReadonlyBytes { bytes.data() + index, bytes.size() - index };
+            if (auto message = LocalEndpoint::decode_message(remaining_bytes, m_socket->fd())) {
+                m_unprocessed_messages.append(message.release_nonnull());
+            } else if (auto message = PeerEndpoint::decode_message(remaining_bytes, m_socket->fd())) {
+                m_unprocessed_messages.append(message.release_nonnull());
+            } else {
+                dbgln("Failed to parse a message");
+                break;
+            }
+        }
+
+        if (index < bytes.size()) {
+            // Sometimes we might receive a partial message. That's okay, just stash away
+            // the unprocessed bytes and we'll prepend them to the next incoming message
+            // in the next run of this function.
+            auto remaining_bytes = ByteBuffer::copy(bytes.data() + index, bytes.size() - index);
+            if (!m_unprocessed_bytes.is_empty()) {
+                dbg() << *this << "::drain_messages_from_peer: Already have unprocessed bytes";
+                shutdown();
+                return false;
+            }
+            m_unprocessed_bytes = remaining_bytes;
+        }
+
+        if (!m_unprocessed_messages.is_empty()) {
+            deferred_invoke([this](auto&) {
+                handle_messages();
+            });
+        }
+        return true;
+    }
+
+    void handle_messages()
+    {
+        auto messages = move(m_unprocessed_messages);
+        for (auto& message : messages) {
+            if (message.endpoint_magic() == LocalEndpoint::static_magic())
+                if (auto response = m_local_endpoint.handle(message))
+                    post_message(*response);
+        }
+    }
+
+protected:
+    void initialize_peer_info()
+    {
+        ucred creds;
+        socklen_t creds_size = sizeof(creds);
+        if (getsockopt(this->socket().fd(), SOL_SOCKET, SO_PEERCRED, &creds, &creds_size) < 0) {
+            // FIXME: We should handle this more gracefully.
+            ASSERT_NOT_REACHED();
+        }
+        m_peer_pid = creds.pid;
+    }
+
+    LocalEndpoint& m_local_endpoint;
+    NonnullRefPtr<Core::LocalSocket> m_socket;
+    RefPtr<Core::Timer> m_responsiveness_timer;
+
+    RefPtr<Core::Notifier> m_notifier;
+    NonnullOwnPtrVector<Message> m_unprocessed_messages;
+    ByteBuffer m_unprocessed_bytes;
+    pid_t m_peer_pid { -1 };
+};
+
+}

Userland/Libraries/LibIPC/Decoder.cpp

@@ -0,0 +1,186 @@
+/*
+ * 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 <AK/MemoryStream.h>
+#include <AK/URL.h>
+#include <LibIPC/Decoder.h>
+#include <LibIPC/Dictionary.h>
+#include <LibIPC/File.h>
+#include <string.h>
+#include <sys/socket.h>
+
+namespace IPC {
+
+bool Decoder::decode(bool& value)
+{
+    m_stream >> value;
+    return !m_stream.handle_any_error();
+}
+
+bool Decoder::decode(u8& value)
+{
+    m_stream >> value;
+    return !m_stream.handle_any_error();
+}
+
+bool Decoder::decode(u16& value)
+{
+    m_stream >> value;
+    return !m_stream.handle_any_error();
+}
+
+bool Decoder::decode(u32& value)
+{
+    m_stream >> value;
+    return !m_stream.handle_any_error();
+}
+
+bool Decoder::decode(u64& value)
+{
+    m_stream >> value;
+    return !m_stream.handle_any_error();
+}
+
+bool Decoder::decode(i8& value)
+{
+    m_stream >> value;
+    return !m_stream.handle_any_error();
+}
+
+bool Decoder::decode(i16& value)
+{
+    m_stream >> value;
+    return !m_stream.handle_any_error();
+}
+
+bool Decoder::decode(i32& value)
+{
+    m_stream >> value;
+    return !m_stream.handle_any_error();
+}
+
+bool Decoder::decode(i64& value)
+{
+    m_stream >> value;
+    return !m_stream.handle_any_error();
+}
+
+bool Decoder::decode(float& value)
+{
+    m_stream >> value;
+    return !m_stream.handle_any_error();
+}
+
+bool Decoder::decode(String& value)
+{
+    i32 length = 0;
+    m_stream >> length;
+    if (m_stream.handle_any_error())
+        return false;
+    if (length < 0) {
+        value = {};
+        return true;
+    }
+    if (length == 0) {
+        value = String::empty();
+        return true;
+    }
+    char* text_buffer = nullptr;
+    auto text_impl = StringImpl::create_uninitialized(static_cast<size_t>(length), text_buffer);
+    m_stream >> Bytes { text_buffer, static_cast<size_t>(length) };
+    value = *text_impl;
+    return !m_stream.handle_any_error();
+}
+
+bool Decoder::decode(ByteBuffer& value)
+{
+    i32 length = 0;
+    m_stream >> length;
+    if (m_stream.handle_any_error())
+        return false;
+    if (length < 0) {
+        value = {};
+        return true;
+    }
+    if (length == 0) {
+        value = ByteBuffer::create_uninitialized(0);
+        return true;
+    }
+    value = ByteBuffer::create_uninitialized(length);
+    m_stream >> value.bytes();
+    return !m_stream.handle_any_error();
+}
+
+bool Decoder::decode(URL& value)
+{
+    String string;
+    if (!decode(string))
+        return false;
+    value = URL(string);
+    return true;
+}
+
+bool Decoder::decode(Dictionary& dictionary)
+{
+    u64 size = 0;
+    m_stream >> size;
+    if (m_stream.handle_any_error())
+        return false;
+    if (size >= (size_t)NumericLimits<i32>::max()) {
+        ASSERT_NOT_REACHED();
+    }
+
+    for (size_t i = 0; i < size; ++i) {
+        String key;
+        if (!decode(key))
+            return false;
+        String value;
+        if (!decode(value))
+            return false;
+        dictionary.add(move(key), move(value));
+    }
+
+    return true;
+}
+
+bool Decoder::decode([[maybe_unused]] File& file)
+{
+#ifdef __serenity__
+    int fd = recvfd(m_sockfd);
+    if (fd < 0) {
+        dbgln("recvfd: {}", strerror(errno));
+        return false;
+    }
+    file = File(fd);
+    return true;
+#else
+    [[maybe_unused]] auto fd = m_sockfd;
+    warnln("fd passing is not supported on this platform, sorry :(");
+    return false;
+#endif
+}
+
+}

Userland/Libraries/LibIPC/Decoder.h

@@ -0,0 +1,132 @@
+/*
+ * 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/Forward.h>
+#include <AK/NumericLimits.h>
+#include <AK/StdLibExtras.h>
+#include <AK/String.h>
+#include <LibIPC/Forward.h>
+#include <LibIPC/Message.h>
+
+namespace IPC {
+
+template<typename T>
+inline bool decode(Decoder&, T&)
+{
+    static_assert(DependentFalse<T>, "Base IPC::decoder() instantiated");
+    ASSERT_NOT_REACHED();
+}
+
+class Decoder {
+public:
+    Decoder(InputMemoryStream& stream, int sockfd)
+        : m_stream(stream)
+        , m_sockfd(sockfd)
+    {
+    }
+
+    bool decode(bool&);
+    bool decode(u8&);
+    bool decode(u16&);
+    bool decode(u32&);
+    bool decode(u64&);
+    bool decode(i8&);
+    bool decode(i16&);
+    bool decode(i32&);
+    bool decode(i64&);
+    bool decode(float&);
+    bool decode(String&);
+    bool decode(ByteBuffer&);
+    bool decode(URL&);
+    bool decode(Dictionary&);
+    bool decode(File&);
+    template<typename K, typename V>
+    bool decode(HashMap<K, V>& hashmap)
+    {
+        u32 size;
+        if (!decode(size) || size > NumericLimits<i32>::max())
+            return false;
+
+        for (size_t i = 0; i < size; ++i) {
+            K key;
+            if (!decode(key))
+                return false;
+
+            V value;
+            if (!decode(value))
+                return false;
+
+            hashmap.set(move(key), move(value));
+        }
+        return true;
+    }
+
+    template<typename T>
+    bool decode(T& value)
+    {
+        return IPC::decode(*this, value);
+    }
+
+    template<typename T>
+    bool decode(Vector<T>& vector)
+    {
+        u64 size;
+        if (!decode(size) || size > NumericLimits<i32>::max())
+            return false;
+        for (size_t i = 0; i < size; ++i) {
+            T value;
+            if (!decode(value))
+                return false;
+            vector.append(move(value));
+        }
+        return true;
+    }
+
+    template<typename T>
+    bool decode(Optional<T>& optional)
+    {
+        bool has_value;
+        if (!decode(has_value))
+            return false;
+        if (!has_value) {
+            optional = {};
+            return true;
+        }
+        T value;
+        if (!decode(value))
+            return false;
+        optional = move(value);
+        return true;
+    }
+
+private:
+    InputMemoryStream& m_stream;
+    int m_sockfd { -1 };
+};
+
+}

Userland/Libraries/LibIPC/Dictionary.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 <AK/HashMap.h>
+#include <AK/String.h>
+
+namespace IPC {
+
+class Dictionary {
+public:
+    Dictionary() { }
+
+    Dictionary(const HashMap<String, String>& initial_entries)
+        : m_entries(initial_entries)
+    {
+    }
+
+    bool is_empty() const { return m_entries.is_empty(); }
+    size_t size() const { return m_entries.size(); }
+
+    void add(String key, String value)
+    {
+        m_entries.set(move(key), move(value));
+    }
+
+    template<typename Callback>
+    void for_each_entry(Callback callback) const
+    {
+        for (auto& it : m_entries) {
+            callback(it.key, it.value);
+        }
+    }
+
+    const HashMap<String, String>& entries() const { return m_entries; }
+
+private:
+    HashMap<String, String> m_entries;
+};
+
+}

Userland/Libraries/LibIPC/Encoder.cpp

@@ -0,0 +1,173 @@
+/*
+ * 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 <AK/ByteBuffer.h>
+#include <AK/String.h>
+#include <AK/URL.h>
+#include <LibIPC/Dictionary.h>
+#include <LibIPC/Encoder.h>
+#include <LibIPC/File.h>
+
+namespace IPC {
+
+Encoder& Encoder::operator<<(bool value)
+{
+    return *this << (u8)value;
+}
+
+Encoder& Encoder::operator<<(u8 value)
+{
+    m_buffer.data.append(value);
+    return *this;
+}
+
+Encoder& Encoder::operator<<(u16 value)
+{
+    m_buffer.data.ensure_capacity(m_buffer.data.size() + 2);
+    m_buffer.data.unchecked_append((u8)value);
+    m_buffer.data.unchecked_append((u8)(value >> 8));
+    return *this;
+}
+
+Encoder& Encoder::operator<<(u32 value)
+{
+    m_buffer.data.ensure_capacity(m_buffer.data.size() + 4);
+    m_buffer.data.unchecked_append((u8)value);
+    m_buffer.data.unchecked_append((u8)(value >> 8));
+    m_buffer.data.unchecked_append((u8)(value >> 16));
+    m_buffer.data.unchecked_append((u8)(value >> 24));
+    return *this;
+}
+
+Encoder& Encoder::operator<<(u64 value)
+{
+    m_buffer.data.ensure_capacity(m_buffer.data.size() + 8);
+    m_buffer.data.unchecked_append((u8)value);
+    m_buffer.data.unchecked_append((u8)(value >> 8));
+    m_buffer.data.unchecked_append((u8)(value >> 16));
+    m_buffer.data.unchecked_append((u8)(value >> 24));
+    m_buffer.data.unchecked_append((u8)(value >> 32));
+    m_buffer.data.unchecked_append((u8)(value >> 40));
+    m_buffer.data.unchecked_append((u8)(value >> 48));
+    m_buffer.data.unchecked_append((u8)(value >> 56));
+    return *this;
+}
+
+Encoder& Encoder::operator<<(i8 value)
+{
+    m_buffer.data.append((u8)value);
+    return *this;
+}
+
+Encoder& Encoder::operator<<(i16 value)
+{
+    m_buffer.data.ensure_capacity(m_buffer.data.size() + 2);
+    m_buffer.data.unchecked_append((u8)value);
+    m_buffer.data.unchecked_append((u8)(value >> 8));
+    return *this;
+}
+
+Encoder& Encoder::operator<<(i32 value)
+{
+    m_buffer.data.ensure_capacity(m_buffer.data.size() + 4);
+    m_buffer.data.unchecked_append((u8)value);
+    m_buffer.data.unchecked_append((u8)(value >> 8));
+    m_buffer.data.unchecked_append((u8)(value >> 16));
+    m_buffer.data.unchecked_append((u8)(value >> 24));
+    return *this;
+}
+
+Encoder& Encoder::operator<<(i64 value)
+{
+    m_buffer.data.ensure_capacity(m_buffer.data.size() + 8);
+    m_buffer.data.unchecked_append((u8)value);
+    m_buffer.data.unchecked_append((u8)(value >> 8));
+    m_buffer.data.unchecked_append((u8)(value >> 16));
+    m_buffer.data.unchecked_append((u8)(value >> 24));
+    m_buffer.data.unchecked_append((u8)(value >> 32));
+    m_buffer.data.unchecked_append((u8)(value >> 40));
+    m_buffer.data.unchecked_append((u8)(value >> 48));
+    m_buffer.data.unchecked_append((u8)(value >> 56));
+    return *this;
+}
+
+Encoder& Encoder::operator<<(float value)
+{
+    union bits {
+        float as_float;
+        u32 as_u32;
+    } u;
+    u.as_float = value;
+    return *this << u.as_u32;
+}
+
+Encoder& Encoder::operator<<(const char* value)
+{
+    return *this << StringView(value);
+}
+
+Encoder& Encoder::operator<<(const StringView& value)
+{
+    m_buffer.data.append((const u8*)value.characters_without_null_termination(), value.length());
+    return *this;
+}
+
+Encoder& Encoder::operator<<(const String& value)
+{
+    if (value.is_null())
+        return *this << (i32)-1;
+    *this << static_cast<i32>(value.length());
+    return *this << value.view();
+}
+
+Encoder& Encoder::operator<<(const ByteBuffer& value)
+{
+    *this << static_cast<i32>(value.size());
+    m_buffer.data.append(value.data(), value.size());
+    return *this;
+}
+
+Encoder& Encoder::operator<<(const URL& value)
+{
+    return *this << value.to_string();
+}
+
+Encoder& Encoder::operator<<(const Dictionary& dictionary)
+{
+    *this << (u64)dictionary.size();
+    dictionary.for_each_entry([this](auto& key, auto& value) {
+        *this << key << value;
+    });
+    return *this;
+}
+
+Encoder& Encoder::operator<<(const File& file)
+{
+    m_buffer.fds.append(file.fd());
+    return *this;
+}
+
+}

Userland/Libraries/LibIPC/Encoder.h

@@ -0,0 +1,111 @@
+/*
+ * 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 <LibIPC/Forward.h>
+#include <LibIPC/Message.h>
+
+namespace IPC {
+
+template<typename T>
+bool encode(Encoder&, T&)
+{
+    static_assert(DependentFalse<T>, "Base IPC::encode() was instantiated");
+    ASSERT_NOT_REACHED();
+}
+
+class Encoder {
+public:
+    explicit Encoder(MessageBuffer& buffer)
+        : m_buffer(buffer)
+    {
+    }
+
+    Encoder& operator<<(bool);
+    Encoder& operator<<(u8);
+    Encoder& operator<<(u16);
+    Encoder& operator<<(u32);
+    Encoder& operator<<(u64);
+    Encoder& operator<<(i8);
+    Encoder& operator<<(i16);
+    Encoder& operator<<(i32);
+    Encoder& operator<<(i64);
+    Encoder& operator<<(float);
+    Encoder& operator<<(const char*);
+    Encoder& operator<<(const StringView&);
+    Encoder& operator<<(const String&);
+    Encoder& operator<<(const ByteBuffer&);
+    Encoder& operator<<(const URL&);
+    Encoder& operator<<(const Dictionary&);
+    Encoder& operator<<(const File&);
+    template<typename K, typename V>
+    Encoder& operator<<(const HashMap<K, V>& hashmap)
+    {
+        *this << (u32)hashmap.size();
+        for (auto it : hashmap) {
+            *this << it.key;
+            *this << it.value;
+        }
+        return *this;
+    }
+
+    template<typename T>
+    Encoder& operator<<(const Vector<T>& vector)
+    {
+        *this << (u64)vector.size();
+        for (auto& value : vector)
+            *this << value;
+        return *this;
+    }
+
+    template<typename T>
+    Encoder& operator<<(const T& value)
+    {
+        encode(value);
+        return *this;
+    }
+
+    template<typename T>
+    Encoder& operator<<(const Optional<T>& optional)
+    {
+        *this << optional.has_value();
+        if (optional.has_value())
+            *this << optional.value();
+        return *this;
+    }
+
+    template<typename T>
+    void encode(const T& value)
+    {
+        IPC::encode(*this, value);
+    }
+
+private:
+    MessageBuffer& m_buffer;
+};
+
+}

Userland/Libraries/LibIPC/Endpoint.cpp

@@ -0,0 +1,39 @@
+/*
+ * 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 <LibIPC/Endpoint.h>
+
+namespace IPC {
+
+Endpoint::Endpoint()
+{
+}
+
+Endpoint::~Endpoint()
+{
+}
+
+}

Userland/Libraries/LibIPC/Endpoint.h

@@ -0,0 +1,55 @@
+/*
+ * 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/OwnPtr.h>
+#include <AK/String.h>
+
+namespace AK {
+class BufferStream;
+}
+
+namespace IPC {
+
+class Message;
+
+class Endpoint {
+public:
+    virtual ~Endpoint();
+
+    virtual int magic() const = 0;
+    virtual String name() const = 0;
+    virtual OwnPtr<Message> handle(const Message&) = 0;
+
+protected:
+    Endpoint();
+
+private:
+    String m_name;
+};
+
+}

Userland/Libraries/LibIPC/File.h

@@ -0,0 +1,49 @@
+/*
+ * Copyright (c) 2020, Sergey Bugaev <bugaevc@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
+
+namespace IPC {
+
+class File {
+public:
+    // Must have a default constructor, because LibIPC
+    // default-constructs arguments prior to decoding them.
+    File() { }
+
+    // Intentionally not `explicit`.
+    File(int fd)
+        : m_fd(fd)
+    {
+    }
+
+    int fd() const { return m_fd; }
+
+private:
+    int m_fd { -1 };
+};
+
+}

Userland/Libraries/LibIPC/Forward.h

@@ -0,0 +1,37 @@
+/*
+ * 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
+
+namespace IPC {
+
+class Decoder;
+class Dictionary;
+class Encoder;
+class Message;
+class File;
+
+}

Userland/Libraries/LibIPC/Message.cpp

@@ -0,0 +1,41 @@
+/*
+ * 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 <LibIPC/Message.h>
+
+namespace IPC {
+
+Message::Message()
+{
+}
+
+Message::~Message()
+{
+    if (on_destruction)
+        on_destruction();
+}
+
+}

Userland/Libraries/LibIPC/Message.h

@@ -0,0 +1,54 @@
+/*
+ * 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/Function.h>
+#include <AK/Vector.h>
+
+namespace IPC {
+
+struct MessageBuffer {
+    Vector<u8, 1024> data;
+    Vector<int> fds;
+};
+
+class Message {
+public:
+    virtual ~Message();
+
+    virtual int endpoint_magic() const = 0;
+    virtual int message_id() const = 0;
+    virtual const char* message_name() const = 0;
+    virtual MessageBuffer encode() const = 0;
+
+    Function<void()> on_destruction;
+
+protected:
+    Message();
+};
+
+}

Userland/Libraries/LibIPC/ServerConnection.h

@@ -0,0 +1,70 @@
+/*
+ * 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 <LibIPC/Connection.h>
+
+namespace IPC {
+
+template<typename ClientEndpoint, typename ServerEndpoint>
+class ServerConnection : public IPC::Connection<ClientEndpoint, ServerEndpoint> {
+public:
+    ServerConnection(ClientEndpoint& local_endpoint, const StringView& address)
+        : Connection<ClientEndpoint, ServerEndpoint>(local_endpoint, Core::LocalSocket::construct())
+    {
+        // We want to rate-limit our clients
+        this->socket().set_blocking(true);
+
+        if (!this->socket().connect(Core::SocketAddress::local(address))) {
+            perror("connect");
+            ASSERT_NOT_REACHED();
+        }
+
+        ASSERT(this->socket().is_connected());
+
+        this->initialize_peer_info();
+    }
+
+    virtual void handshake() = 0;
+
+    pid_t server_pid() const { return this->peer_pid(); }
+    void set_server_pid(pid_t pid) { this->set_peer_pid(pid); }
+
+    void set_my_client_id(int id) { m_my_client_id = id; }
+    int my_client_id() const { return m_my_client_id; }
+
+    virtual void die() override
+    {
+        // Override this function if you don't want your app to exit if it loses the connection.
+        exit(0);
+    }
+
+private:
+    int m_my_client_id { -1 };
+};
+
+}