WindowServer: Let clients mark windows as stealable by specific clients

This implements window stealing in WindowServer, which allows clients
to mark a window they own as 'stealable' by another client. Indicating
that the other client may use it for any purpose.

This also updates set_window_parent_from_id so that the client must
first mark its window as stealable before allowing other clients to
use it as a parent.

Userland/Services/WindowServer/ClientConnection.cpp

@@ -1129,7 +1129,11 @@ void ClientConnection::set_window_parent_from_client(i32 client_id, i32 parent_i
     if (!parent_window)
         did_misbehave("SetWindowParentFromClient: Bad parent window ID");
 
+    if (parent_window->is_stealable_by_client(this->client_id())) {
         child_window->set_parent_window(*parent_window);
+    } else {
+        did_misbehave("SetWindowParentFromClient: Window is not stealable");
+    }
 }
 
 Messages::WindowServer::GetWindowRectFromClientResponse ClientConnection::get_window_rect_from_client(i32 client_id, i32 window_id)
@@ -1145,4 +1149,36 @@ Messages::WindowServer::GetWindowRectFromClientResponse ClientConnection::get_wi
     return window->rect();
 }
 
+void ClientConnection::add_window_stealing_for_client(i32 client_id, i32 window_id)
+{
+    auto window = window_from_id(window_id);
+    if (!window)
+        did_misbehave("AddWindowStealingForClient: Bad window ID");
+
+    if (!from_client_id(client_id))
+        did_misbehave("AddWindowStealingForClient: Bad client ID");
+
+    window->add_stealing_for_client(client_id);
+}
+
+void ClientConnection::remove_window_stealing_for_client(i32 client_id, i32 window_id)
+{
+    auto window = window_from_id(window_id);
+    if (!window)
+        did_misbehave("RemoveWindowStealingForClient: Bad window ID");
+
+    // Don't check if the client exists, it may have died
+
+    window->remove_stealing_for_client(client_id);
+}
+
+void ClientConnection::remove_window_stealing(i32 window_id)
+{
+    auto window = window_from_id(window_id);
+    if (!window)
+        did_misbehave("RemoveWindowStealing: Bad window ID");
+
+    window->remove_all_stealing();
+}
+
 }

Userland/Services/WindowServer/ClientConnection.h

@@ -166,6 +166,9 @@ private:
     virtual void set_flash_flush(bool) override;
     virtual void set_window_parent_from_client(i32, i32, i32) override;
     virtual Messages::WindowServer::GetWindowRectFromClientResponse get_window_rect_from_client(i32, i32) override;
+    virtual void add_window_stealing_for_client(i32, i32) override;
+    virtual void remove_window_stealing_for_client(i32, i32) override;
+    virtual void remove_window_stealing(i32) override;
 
     Window* window_from_id(i32 window_id);
 

Userland/Services/WindowServer/Window.h

@@ -362,6 +362,16 @@ public:
     void set_moving_to_another_stack(bool value) { m_moving_to_another_stack = value; }
     bool is_moving_to_another_stack() const { return m_moving_to_another_stack; }
 
+    void add_stealing_for_client(i32 client_id) { m_stealable_by_client_ids.append(move(client_id)); }
+    void remove_stealing_for_client(i32 client_id)
+    {
+        m_stealable_by_client_ids.remove_all_matching([client_id](i32 approved_client_id) {
+            return approved_client_id == client_id;
+        });
+    }
+    void remove_all_stealing() { m_stealable_by_client_ids.clear(); }
+    bool is_stealable_by_client(i32 client_id) const { return m_stealable_by_client_ids.contains_slow(client_id); }
+
 private:
     Window(ClientConnection&, WindowType, int window_id, bool modal, bool minimizable, bool frameless, bool resizable, bool fullscreen, bool accessory, Window* parent_window = nullptr);
     Window(Core::Object&, WindowType);
@@ -418,6 +428,7 @@ private:
     bool m_pinned { false };
     bool m_moving_to_another_stack { false };
     bool m_invalidate_last_render_rects { false };
+    Vector<i32> m_stealable_by_client_ids;
     WindowTileType m_tiled { WindowTileType::None };
     Gfx::IntRect m_untiled_rect;
     bool m_occluded { false };

Userland/Services/WindowServer/WindowServer.ipc

@@ -150,4 +150,7 @@ endpoint WindowServer
 
     set_window_parent_from_client(i32 client_id, i32 parent_id, i32 child_id) =|
     get_window_rect_from_client(i32 client_id, i32 window_id) => (Gfx::IntRect rect)
+    add_window_stealing_for_client(i32 client_id, i32 window_id) =|
+    remove_window_stealing_for_client(i32 client_id, i32 window_id) =|
+    remove_window_stealing(i32 window_id) =|
 }