LibIPC: Share most of the code between {Client,Server}Connection

This patch introduces IPC::Connection which becomes the new base class
of ClientConnection and ServerConnection. Most of the functionality
has been hoisted up to the base class since almost all of it is useful
on both sides.

This gives us the ability to send synchronous messages in both
directions, which is needed for the WebContent server process.
Unlike other servers, WebContent does not mind blocking on a response
from its client.

3 files changed, 267 insertions, 244 deletions

diff --git a/Libraries/LibIPC/ClientConnection.h b/Libraries/LibIPC/ClientConnection.h
index 0e2da07bf9..2b042db22d 100644
--- a/Libraries/LibIPC/ClientConnection.h
+++ b/Libraries/LibIPC/ClientConnection.h
@@ -32,6 +32,7 @@
 #include <LibCore/LocalSocket.h>
 #include <LibCore/Object.h>
 #include <LibCore/Timer.h>
+#include <LibIPC/Connection.h>
 #include <LibIPC/Endpoint.h>
 #include <LibIPC/Message.h>
 #include <errno.h>
@@ -75,133 +76,38 @@ NonnullRefPtr<T> new_client_connection(Args&&... args)
     return T::construct(forward<Args>(args)...) /* arghs */;
 }
 
-template<typename Endpoint>
-class ClientConnection : public Core::Object {
+template<typename ClientEndpoint, typename ServerEndpoint>
+class ClientConnection : public Connection<ServerEndpoint, ClientEndpoint> {
 public:
-    ClientConnection(Endpoint& endpoint, NonnullRefPtr<Core::LocalSocket> socket, int client_id)
-        : m_endpoint(endpoint)
-        , m_socket(move(socket))
+    ClientConnection(ServerEndpoint& endpoint, NonnullRefPtr<Core::LocalSocket> socket, int client_id)
+        : IPC::Connection<ServerEndpoint, ClientEndpoint>(endpoint, move(socket))
         , m_client_id(client_id)
     {
-        ASSERT(m_socket->is_connected());
-        ucred creds;
-        socklen_t creds_size = sizeof(creds);
-        if (getsockopt(m_socket->fd(), SOL_SOCKET, SO_PEERCRED, &creds, &creds_size) < 0) {
-            ASSERT_NOT_REACHED();
-        }
-        m_client_pid = creds.pid;
-        m_socket->on_ready_to_read = [this] { drain_messages_from_client(); };
-
-        m_responsiveness_timer = Core::Timer::create_single_shot(3000, [this] { may_have_become_unresponsive(); });
+        ASSERT(this->socket().is_connected());
+        this->socket().on_ready_to_read = [this] { this->drain_messages_from_peer(); };
+        this->initialize_peer_info();
     }
 
     virtual ~ClientConnection() override
     {
     }
 
-    virtual void may_have_become_unresponsive() { }
-    virtual void did_become_responsive() { }
-
-    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();
-
-        auto bytes_remaining = buffer.size();
-        while (bytes_remaining) {
-            auto nwritten = write(m_socket->fd(), buffer.data(), buffer.size());
-            if (nwritten < 0) {
-                switch (errno) {
-                case EPIPE:
-                    dbg() << *this << "::post_message: Disconnected from peer";
-                    shutdown();
-                    return;
-                case EAGAIN:
-                    dbg() << *this << "::post_message: Client buffer overflowed.";
-                    did_misbehave();
-                    return;
-                default:
-                    perror("Connection::post_message write");
-                    shutdown();
-                    return;
-                }
-            }
-            bytes_remaining -= nwritten;
-        }
-
-        m_responsiveness_timer->start();
-    }
-
-    void drain_messages_from_client()
-    {
-        if (!m_socket->is_open())
-            return;
-
-        Vector<u8> bytes;
-        for (;;) {
-            u8 buffer[4096];
-            ssize_t nread = recv(m_socket->fd(), buffer, sizeof(buffer), MSG_DONTWAIT);
-            if (nread == 0 || (nread == -1 && errno == EAGAIN)) {
-                if (bytes.is_empty()) {
-                    Core::EventLoop::current().post_event(*this, make<DisconnectedEvent>(client_id()));
-                    return;
-                }
-                break;
-            }
-            if (nread < 0) {
-                perror("recv");
-                shutdown();
-                return;
-            }
-            bytes.append(buffer, nread);
-        }
-
-        if (!bytes.is_empty()) {
-            m_responsiveness_timer->stop();
-            did_become_responsive();
-        }
-
-        size_t decoded_bytes = 0;
-        for (size_t index = 0; index < bytes.size(); index += decoded_bytes) {
-            auto remaining_bytes = ByteBuffer::wrap(bytes.data() + index, bytes.size() - index);
-            auto message = Endpoint::decode_message(remaining_bytes, decoded_bytes);
-            if (!message) {
-                dbg() << "drain_messages_from_client: Endpoint didn't recognize message";
-                did_misbehave();
-                return;
-            }
-            if (auto response = m_endpoint.handle(*message))
-                post_message(*response);
-            ASSERT(decoded_bytes);
-        }
-    }
-
     void did_misbehave()
     {
-        dbg() << *this << " (id=" << m_client_id << ", pid=" << m_client_pid << ") misbehaved, disconnecting.";
-        shutdown();
+        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=" << m_client_pid << ") misbehaved (" << message << "), disconnecting.";
-        shutdown();
-    }
-
-    void shutdown()
-    {
-        m_socket->close();
-        die();
+        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 m_client_pid; }
-    void set_client_pid(pid_t pid) { m_client_pid = pid; }
+    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;
 
@@ -213,7 +119,7 @@ protected:
             int client_id = static_cast<const DisconnectedEvent&>(event).client_id();
             dbg() << *this << ": Client disconnected: " << client_id;
 #endif
-            die();
+            this->die();
             return;
         }
 
@@ -221,11 +127,7 @@ protected:
     }
 
 private:
-    Endpoint& m_endpoint;
-    NonnullRefPtr<Core::LocalSocket> m_socket;
-    RefPtr<Core::Timer> m_responsiveness_timer;
     int m_client_id { -1 };
-    int m_client_pid { -1 };
 };
 
 }
diff --git a/Libraries/LibIPC/Connection.h b/Libraries/LibIPC/Connection.h
new file mode 100644
index 0000000000..d2df6ad71f
--- /dev/null
+++ b/Libraries/LibIPC/Connection.h
@@ -0,0 +1,235 @@
+/*
+ * 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/LocalSocket.h>
+#include <LibCore/Notifier.h>
+#include <LibCore/SyscallUtils.h>
+#include <LibCore/Timer.h>
+#include <LibIPC/Message.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(); });
+    }
+
+    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();
+
+        auto bytes_remaining = buffer.size();
+        while (bytes_remaining) {
+            auto nwritten = write(m_socket->fd(), buffer.data(), buffer.size());
+            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;
+                }
+            }
+            bytes_remaining -= 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_socket->close();
+        die();
+    }
+
+    virtual void die() { }
+
+protected:
+    Core::LocalSocket& socket() { return *m_socket; }
+    Core::Notifier& notifier() { return *m_notifier; }
+    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>();
+            }
+
+            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())
+                return nullptr;
+        }
+    }
+
+    bool drain_messages_from_peer()
+    {
+        Vector<u8> bytes;
+        for (;;) {
+            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) {
+                dbg() << "EOF on IPC fd";
+                if (bytes.is_empty()) {
+                    deferred_invoke([this](auto&) {
+                        dbg() << *this << " Disconnected";
+                        die();
+                    });
+                }
+                return false;
+            }
+            bytes.append(buffer, nread);
+        }
+
+        if (!bytes.is_empty()) {
+            m_responsiveness_timer->stop();
+            did_become_responsive();
+        }
+
+        size_t decoded_bytes = 0;
+        for (size_t index = 0; index < bytes.size(); index += decoded_bytes) {
+            auto remaining_bytes = ByteBuffer::wrap(bytes.data() + index, bytes.size() - index);
+            if (auto message = LocalEndpoint::decode_message(remaining_bytes, decoded_bytes)) {
+                m_unprocessed_messages.append(message.release_nonnull());
+            } else if (auto message = PeerEndpoint::decode_message(remaining_bytes, decoded_bytes)) {
+                m_unprocessed_messages.append(message.release_nonnull());
+            } else {
+                ASSERT_NOT_REACHED();
+            }
+            ASSERT(decoded_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;
+    pid_t m_peer_pid { -1 };
+};
+
+}
diff --git a/Libraries/LibIPC/ServerConnection.h b/Libraries/LibIPC/ServerConnection.h
index 1556b309dd..456d29964b 100644
--- a/Libraries/LibIPC/ServerConnection.h
+++ b/Libraries/LibIPC/ServerConnection.h
@@ -32,6 +32,7 @@
 #include <LibCore/LocalSocket.h>
 #include <LibCore/Notifier.h>
 #include <LibCore/SyscallUtils.h>
+#include <LibIPC/Connection.h>
 #include <LibIPC/Message.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -42,159 +43,44 @@
 
 namespace IPC {
 
-template<typename LocalEndpoint, typename PeerEndpoint>
-class ServerConnection : public Core::Object {
+template<typename ClientEndpoint, typename ServerEndpoint>
+class ServerConnection : public IPC::Connection<ClientEndpoint, ServerEndpoint> {
 public:
-    ServerConnection(LocalEndpoint& local_endpoint, const StringView& address)
-        : m_local_endpoint(local_endpoint)
-        , m_connection(Core::LocalSocket::construct(this))
-        , m_notifier(Core::Notifier::construct(m_connection->fd(), Core::Notifier::Read, this))
+    ServerConnection(ClientEndpoint& local_endpoint, const StringView& address)
+        : Connection<ClientEndpoint, ServerEndpoint>(local_endpoint, Core::LocalSocket::construct())
     {
         // We want to rate-limit our clients
-        m_connection->set_blocking(true);
-        m_notifier->on_ready_to_read = [this] {
-            drain_messages_from_server();
-            handle_messages();
+        this->socket().set_blocking(true);
+        this->notifier().on_ready_to_read = [this] {
+            this->drain_messages_from_peer();
+            this->handle_messages();
         };
 
-        if (!m_connection->connect(Core::SocketAddress::local(address))) {
+        if (!this->socket().connect(Core::SocketAddress::local(address))) {
             perror("connect");
             ASSERT_NOT_REACHED();
         }
 
-        ucred creds;
-        socklen_t creds_size = sizeof(creds);
-        if (getsockopt(m_connection->fd(), SOL_SOCKET, SO_PEERCRED, &creds, &creds_size) < 0) {
-            ASSERT_NOT_REACHED();
-        }
-        m_server_pid = creds.pid;
+        ASSERT(this->socket().is_connected());
 
-        ASSERT(m_connection->is_connected());
+        this->initialize_peer_info();
     }
 
     virtual void handshake() = 0;
 
-    pid_t server_pid() const { return m_server_pid; }
-    void set_server_pid(pid_t pid) { m_server_pid = pid; }
+    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; }
 
-    template<typename MessageType>
-    OwnPtr<MessageType> wait_for_specific_message()
-    {
-        return wait_for_specific_endpoint_message<MessageType, LocalEndpoint>();
-    }
-
-    bool post_message(const Message& message)
-    {
-        auto buffer = message.encode();
-        int nwritten = write(m_connection->fd(), buffer.data(), buffer.size());
-        if (nwritten < 0) {
-            perror("write");
-            ASSERT_NOT_REACHED();
-            return false;
-        }
-        ASSERT(static_cast<size_t>(nwritten) == buffer.size());
-        return true;
-    }
-
-    template<typename RequestType, typename... Args>
-    OwnPtr<typename RequestType::ResponseType> send_sync(Args&&... args)
+    virtual void die() override
     {
-        bool success = post_message(RequestType(forward<Args>(args)...));
-        ASSERT(success);
-        auto response = wait_for_specific_endpoint_message<typename RequestType::ResponseType, PeerEndpoint>();
-        ASSERT(response);
-        return response;
+        // Override this function if you don't want your app to exit if it loses the connection.
+        exit(0);
     }
 
 private:
-    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>();
-            }
-
-            fd_set rfds;
-            FD_ZERO(&rfds);
-            FD_SET(m_connection->fd(), &rfds);
-            int rc = Core::safe_syscall(select, m_connection->fd() + 1, &rfds, nullptr, nullptr, nullptr);
-            if (rc < 0) {
-                perror("select");
-            }
-            ASSERT(rc > 0);
-            ASSERT(FD_ISSET(m_connection->fd(), &rfds));
-            if (!drain_messages_from_server())
-                return nullptr;
-        }
-    }
-
-    bool drain_messages_from_server()
-    {
-        Vector<u8> bytes;
-        for (;;) {
-            u8 buffer[4096];
-            ssize_t nread = recv(m_connection->fd(), buffer, sizeof(buffer), MSG_DONTWAIT);
-            if (nread < 0) {
-                if (errno == EAGAIN)
-                    break;
-                perror("recv");
-                exit(1);
-                return false;
-            }
-            if (nread == 0) {
-                dbg() << "EOF on IPC fd";
-                // FIXME: Dying is definitely not always appropriate!
-                exit(1);
-                return false;
-            }
-            bytes.append(buffer, nread);
-        }
-
-        size_t decoded_bytes = 0;
-        for (size_t index = 0; index < bytes.size(); index += decoded_bytes) {
-            auto remaining_bytes = ByteBuffer::wrap(bytes.data() + index, bytes.size() - index);
-            if (auto message = LocalEndpoint::decode_message(remaining_bytes, decoded_bytes)) {
-                m_unprocessed_messages.append(message.release_nonnull());
-            } else if (auto message = PeerEndpoint::decode_message(remaining_bytes, decoded_bytes)) {
-                m_unprocessed_messages.append(message.release_nonnull());
-            } else {
-                ASSERT_NOT_REACHED();
-            }
-            ASSERT(decoded_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())
-                m_local_endpoint.handle(message);
-        }
-    }
-
-    LocalEndpoint& m_local_endpoint;
-    RefPtr<Core::LocalSocket> m_connection;
-    RefPtr<Core::Notifier> m_notifier;
-    NonnullOwnPtrVector<Message> m_unprocessed_messages;
-    int m_server_pid { -1 };
     int m_my_client_id { -1 };
 };