KeyboardSettings: Add checkbox to enable Caps Lock mapping to Ctrl

This patch adds an additional control to KeyboardSettings allowing
the user to map Caps Lock to Ctrl. Previously, this was only possible
by writing to /sys/kernel/variables/caps_lock_to_ctrl.

Writing to /sys/kernel/variables/caps_lock_to_ctrl requires root
privileges, but KeyboardSettings will not attempt to elevate
the privilege of the user if they are not root. Instead, the
checkbox is rendered as un-editable.

4 files changed, 53 insertions, 0 deletions

diff --git a/Userland/Applications/KeyboardSettings/Keyboard.gml b/Userland/Applications/KeyboardSettings/Keyboard.gml
index 89ee28391d..a1b5588678 100644
--- a/Userland/Applications/KeyboardSettings/Keyboard.gml
+++ b/Userland/Applications/KeyboardSettings/Keyboard.gml
@@ -124,4 +124,18 @@
             name: "num_lock_checkbox"
         }
     }
+
+    @GUI::GroupBox {
+        title: "Caps Lock"
+        fixed_height: 60
+        layout: @GUI::HorizontalBoxLayout {
+            margins: [16, 8, 8]
+            spacing: 16
+        }
+
+        @GUI::CheckBox {
+            text: "Use Caps Lock as an additional Ctrl"
+            name: "caps_lock_remapped_to_ctrl_checkbox"
+        }
+    }
 }
diff --git a/Userland/Applications/KeyboardSettings/KeyboardSettingsWidget.cpp b/Userland/Applications/KeyboardSettings/KeyboardSettingsWidget.cpp
index 842018a569..eb97fa661f 100644
--- a/Userland/Applications/KeyboardSettings/KeyboardSettingsWidget.cpp
+++ b/Userland/Applications/KeyboardSettings/KeyboardSettingsWidget.cpp
@@ -1,6 +1,7 @@
 /*
  * Copyright (c) 2020, Hüseyin Aslıtürk <asliturk@hotmail.com>
  * Copyright (c) 2021-2023, Sam Atkins <atkinssj@serenityos.org>
+ * Copyright (c) 2022, Sam Cohen <sbcohen2000@gmail.com>
  * Copyright (c) 2022, the SerenityOS developers.
  *
  * SPDX-License-Identifier: BSD-2-Clause
@@ -255,6 +256,19 @@ KeyboardSettingsWidget::KeyboardSettingsWidget()
     m_num_lock_checkbox->on_checked = [&](auto) {
         set_modified(true);
     };
+
+    m_caps_lock_checkbox = find_descendant_of_type_named<GUI::CheckBox>("caps_lock_remapped_to_ctrl_checkbox");
+    auto caps_lock_is_remapped = read_caps_lock_to_ctrl_sys_variable();
+    if (caps_lock_is_remapped.is_error()) {
+        auto error_message = DeprecatedString::formatted("Could not determine if Caps Lock is remapped to Ctrl: {}", caps_lock_is_remapped.error());
+        GUI::MessageBox::show_error(window(), error_message);
+    } else {
+        m_caps_lock_checkbox->set_checked(caps_lock_is_remapped.value());
+    }
+    m_caps_lock_checkbox->set_enabled(getuid() == 0);
+    m_caps_lock_checkbox->on_checked = [&](auto) {
+        set_modified(true);
+    };
 }
 
 KeyboardSettingsWidget::~KeyboardSettingsWidget()
@@ -282,6 +296,7 @@ void KeyboardSettingsWidget::apply_settings()
     }
     m_initial_active_keymap = m_keymaps_list_model.active_keymap();
     Config::write_bool("KeyboardSettings"sv, "StartupEnable"sv, "NumLock"sv, m_num_lock_checkbox->is_checked());
+    write_caps_lock_to_ctrl_sys_variable(m_caps_lock_checkbox->is_checked());
 }
 
 void KeyboardSettingsWidget::set_keymaps(Vector<DeprecatedString> const& keymaps, DeprecatedString const& active_keymap)
@@ -289,3 +304,20 @@ void KeyboardSettingsWidget::set_keymaps(Vector<DeprecatedString> const& keymaps
     auto keymaps_string = DeprecatedString::join(',', keymaps);
     GUI::Process::spawn_or_show_error(window(), "/bin/keymap"sv, Array { "-s", keymaps_string.characters(), "-m", active_keymap.characters() });
 }
+
+void KeyboardSettingsWidget::write_caps_lock_to_ctrl_sys_variable(bool caps_lock_to_ctrl)
+{
+    if (getuid() != 0)
+        return;
+
+    auto write_command = DeprecatedString::formatted("caps_lock_to_ctrl={}", caps_lock_to_ctrl ? "1" : "0");
+    GUI::Process::spawn_or_show_error(window(), "/bin/sysctl"sv, Array { "-w", write_command.characters() });
+}
+
+ErrorOr<bool> KeyboardSettingsWidget::read_caps_lock_to_ctrl_sys_variable()
+{
+    auto file = TRY(Core::File::open("/sys/kernel/variables/caps_lock_to_ctrl"sv, Core::File::OpenMode::Read));
+    auto buffer = TRY(file->read_until_eof());
+    StringView contents_string((char const*)buffer.data(), min(1, buffer.size()));
+    return contents_string == "1";
+}
diff --git a/Userland/Applications/KeyboardSettings/KeyboardSettingsWidget.h b/Userland/Applications/KeyboardSettings/KeyboardSettingsWidget.h
index ff2dba31b9..25720b49d7 100644
--- a/Userland/Applications/KeyboardSettings/KeyboardSettingsWidget.h
+++ b/Userland/Applications/KeyboardSettings/KeyboardSettingsWidget.h
@@ -6,6 +6,7 @@
 
 #pragma once
 
+#include <AK/Error.h>
 #include <AK/Vector.h>
 #include <LibGUI/Button.h>
 #include <LibGUI/CheckBox.h>
@@ -28,6 +29,9 @@ private:
 
     void set_keymaps(Vector<DeprecatedString> const& keymaps, DeprecatedString const& active_keymap);
 
+    void write_caps_lock_to_ctrl_sys_variable(bool);
+    ErrorOr<bool> read_caps_lock_to_ctrl_sys_variable();
+
     Vector<DeprecatedString> m_initial_keymap_list;
 
     DeprecatedString m_initial_active_keymap;
@@ -35,6 +39,7 @@ private:
     RefPtr<GUI::ListView> m_selected_keymaps_listview;
     RefPtr<GUI::Label> m_active_keymap_label;
     RefPtr<GUI::CheckBox> m_num_lock_checkbox;
+    RefPtr<GUI::CheckBox> m_caps_lock_checkbox;
     RefPtr<GUI::Button> m_activate_keymap_button;
     RefPtr<GUI::Button> m_add_keymap_button;
     RefPtr<GUI::Button> m_remove_keymap_button;
diff --git a/Userland/Applications/KeyboardSettings/main.cpp b/Userland/Applications/KeyboardSettings/main.cpp
index 3d8fcb491e..b34c2ba13d 100644
--- a/Userland/Applications/KeyboardSettings/main.cpp
+++ b/Userland/Applications/KeyboardSettings/main.cpp
@@ -27,7 +27,9 @@ ErrorOr<int> serenity_main(Main::Arguments arguments)
     TRY(Core::System::pledge("stdio rpath recvfd sendfd proc exec"));
     TRY(Core::System::unveil("/res", "r"));
     TRY(Core::System::unveil("/bin/keymap", "x"));
+    TRY(Core::System::unveil("/bin/sysctl", "x"));
     TRY(Core::System::unveil("/sys/kernel/keymap", "r"));
+    TRY(Core::System::unveil("/sys/kernel/variables/caps_lock_to_ctrl", "r"));
     TRY(Core::System::unveil("/etc/Keyboard.ini", "r"));
     TRY(Core::System::unveil(nullptr, nullptr));