LibGUI+WindowServer: Separate window manager IPC from regular IPC

With this patch the window manager related functionality is split out
onto a new endpoint pair named WindowManagerServer/Client.  This allows
window manager functionality to be potentially privilege separated in
the future.  To this end, a new client named WMConnectionClient
is used to maintain a window manager connection.  When a process
connects to the endpoint and greets the WindowServer as a window manager
(via Window::make_window_manager(int)), they're subscribed to the events
they requested via the WM event mask.

This patch also removes the hardcoding of the Taskbar WindowType to
receive WM events automatically.  However, being a window manager still
requires having an active window, at the moment.

Userland/Services/WindowServer/WMClientConnection.cpp

@@ -0,0 +1,174 @@
+/*
+ * Copyright (c) 2021, the SerenityOS developers.
+ * 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 <WindowServer/AppletManager.h>
+#include <WindowServer/ClientConnection.h>
+#include <WindowServer/Screen.h>
+#include <WindowServer/WMClientConnection.h>
+
+namespace WindowServer {
+
+HashMap<int, NonnullRefPtr<WMClientConnection>> WMClientConnection::s_connections {};
+
+WMClientConnection::WMClientConnection(NonnullRefPtr<Core::LocalSocket> client_socket, int client_id)
+    : IPC::ClientConnection<WindowManagerClientEndpoint, WindowManagerServerEndpoint>(*this, move(client_socket), client_id)
+{
+    s_connections.set(client_id, *this);
+}
+
+WMClientConnection::~WMClientConnection()
+{
+    // The WM has gone away, so take away the applet manager (cause there's nowhere
+    // to draw it in).
+    AppletManager::the().set_position({});
+}
+
+void WMClientConnection::die()
+{
+    deferred_invoke([this](auto&) {
+        s_connections.remove(client_id());
+    });
+}
+
+OwnPtr<Messages::WindowManagerServer::SetAppletAreaPositionResponse> WMClientConnection::handle(const Messages::WindowManagerServer::SetAppletAreaPosition& message)
+{
+    if (m_window_id < 0) {
+        did_misbehave("SetAppletAreaPosition: WM didn't assign window as manager yet");
+        // FIXME: return ok boolean?
+        return make<Messages::WindowManagerServer::SetAppletAreaPositionResponse>();
+    }
+
+    AppletManager::the().set_position(message.position());
+    return make<Messages::WindowManagerServer::SetAppletAreaPositionResponse>();
+}
+
+void WMClientConnection::handle(const Messages::WindowManagerServer::SetActiveWindow& message)
+{
+    auto* client = WindowServer::ClientConnection::from_client_id(message.client_id());
+    if (!client) {
+        did_misbehave("SetActiveWindow: Bad client ID");
+        return;
+    }
+    auto it = client->m_windows.find(message.window_id());
+    if (it == client->m_windows.end()) {
+        did_misbehave("SetActiveWindow: Bad window ID");
+        return;
+    }
+    auto& window = *(*it).value;
+    WindowManager::the().minimize_windows(window, false);
+    WindowManager::the().move_to_front_and_make_active(window);
+}
+
+void WMClientConnection::handle(const Messages::WindowManagerServer::PopupWindowMenu& message)
+{
+    auto* client = WindowServer::ClientConnection::from_client_id(message.client_id());
+    if (!client) {
+        did_misbehave("PopupWindowMenu: Bad client ID");
+        return;
+    }
+    auto it = client->m_windows.find(message.window_id());
+    if (it == client->m_windows.end()) {
+        did_misbehave("PopupWindowMenu: Bad window ID");
+        return;
+    }
+    auto& window = *(*it).value;
+    if (auto* modal_window = window.blocking_modal_window()) {
+        modal_window->popup_window_menu(message.screen_position(), WindowMenuDefaultAction::BasedOnWindowState);
+    } else {
+        window.popup_window_menu(message.screen_position(), WindowMenuDefaultAction::BasedOnWindowState);
+    }
+}
+
+void WMClientConnection::handle(const Messages::WindowManagerServer::StartWindowResize& request)
+{
+    auto* client = WindowServer::ClientConnection::from_client_id(request.client_id());
+    if (!client) {
+        did_misbehave("WM_StartWindowResize: Bad client ID");
+        return;
+    }
+    auto it = client->m_windows.find(request.window_id());
+    if (it == client->m_windows.end()) {
+        did_misbehave("WM_StartWindowResize: Bad window ID");
+        return;
+    }
+    auto& window = *(*it).value;
+    // FIXME: We are cheating a bit here by using the current cursor location and hard-coding the left button.
+    //        Maybe the client should be allowed to specify what initiated this request?
+    WindowManager::the().start_window_resize(window, Screen::the().cursor_location(), MouseButton::Left);
+}
+
+void WMClientConnection::handle(const Messages::WindowManagerServer::SetWindowMinimized& message)
+{
+    auto* client = WindowServer::ClientConnection::from_client_id(message.client_id());
+    if (!client) {
+        did_misbehave("WM_SetWindowMinimized: Bad client ID");
+        return;
+    }
+    auto it = client->m_windows.find(message.window_id());
+    if (it == client->m_windows.end()) {
+        did_misbehave("WM_SetWindowMinimized: Bad window ID");
+        return;
+    }
+    auto& window = *(*it).value;
+    WindowManager::the().minimize_windows(window, message.minimized());
+}
+
+OwnPtr<Messages::WindowManagerServer::SetEventMaskResponse> WMClientConnection::handle(const Messages::WindowManagerServer::SetEventMask& message)
+{
+    m_event_mask = message.event_mask();
+    return make<Messages::WindowManagerServer::SetEventMaskResponse>();
+}
+
+OwnPtr<Messages::WindowManagerServer::SetManagerWindowResponse> WMClientConnection::handle(const Messages::WindowManagerServer::SetManagerWindow& message)
+{
+    m_window_id = message.window_id();
+
+    // Let the window manager know that we obtained a manager window, and should
+    // receive information about other windows.
+    WindowManager::the().greet_window_manager(*this);
+
+    return make<Messages::WindowManagerServer::SetManagerWindowResponse>();
+}
+
+void WMClientConnection::handle(const Messages::WindowManagerServer::SetWindowTaskbarRect& message)
+{
+    // Because the Taskbar (which should be the only user of this API) does not own the
+    // window or the client id, there is a possibility that it may send this message for
+    // a window or client that may have been destroyed already. This is not an error,
+    // and we should not call did_misbehave() for either.
+    auto* client = WindowServer::ClientConnection::from_client_id(message.client_id());
+    if (!client)
+        return;
+
+    auto it = client->m_windows.find(message.window_id());
+    if (it == client->m_windows.end())
+        return;
+
+    auto& window = *(*it).value;
+    window.set_taskbar_rect(message.rect());
+}
+
+}