minios/key_reader.h

// Copyright 2021 The ChromiumOS Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef MINIOS_KEY_READER_H_
#define MINIOS_KEY_READER_H_

#include <linux/input.h>

#include <memory>
#include <string>
#include <vector>

#include <base/files/file_descriptor_watcher_posix.h>
#include <base/files/file_util.h>
#include <base/files/scoped_file.h>
#include <xkbcommon/xkbcommon.h>

namespace minios {

constexpr int kMaxInputLength = 64;

// Increasing `kRepeatedSensitivity` will slow key repeating speed.
constexpr int kRepeatedSensitivity = 3;

// Key state parameter.
extern const int kFdsMax;

// Input event values.
const int kKeyRelease = 0;
const int kKeyPress = 1;
const int kKeyHold = 2;

class KeyReader {
 public:
  // Default constructor can only access EvWaitForKeys.
  explicit KeyReader(bool include_usb);

  KeyReader(bool include_usb, std::string keyboard_layout);
  ~KeyReader();

  KeyReader(const KeyReader&) = delete;
  KeyReader& operator=(const KeyReader&) = delete;

  class Delegate {
   public:
    // Forward a key press to the currently displayed screen.
    virtual void OnKeyPress(int key) = 0;
  };

  // Initializes the `epfd_` and sets the callback. Listens for input keys based
  // on whether the device is detachable or not. Returns false on error.
  bool Init(const std::vector<int>& valid_keys);

  void SetDelegate(Delegate* delegate) { delegate_ = delegate; }

  // Creates the correct keyboard layout for a given country code.
  // Returns false for invalid keyboard layout, true otherwise.
  bool SetKeyboardContext();

  // Given a key code, does all the setup finding the available fds and events
  // and creating the proper keyboard layout.
  bool InputSetUp();

  // In order to be able to display the string as users are typing,
  // `GetUserInput` returns every time a char is added to the string buffer, but
  // only returns with true once the enter key is pressed. Press tab to toggle
  // between showing and hiding passwords. This is a blocking call, and any
  // active watchers must be disabled for the duration of this function.
  bool GetUserInput(bool* enter, bool* tab_toggle, std::string* user_input);

  // Sets the watcher to the `epfd`, has a callback to `OnKeyEvent`.
  // Note: Any input already present in `epfd` before watcher is enabled will be
  // read out during the next event.
  bool StartWatcher();

  // Stops the watcher.
  // Note: No file descriptors are closed here. Input that occurred after
  // StopWather can be read either via `GetUserInput` or after `StartWatcher`.
  void StopWatcher();

  // Wrapper that does not take in tab toggle key. Used for testing.
  bool GetCharForTest(const struct input_event& ev);

  // Returns the current key input as a string. Used for testing.
  std::string GetUserInputForTest();

 private:
  FRIEND_TEST(KeyReaderTest, OnKeyEventRepeat);

  // Checks whether all the keys in `keys_` are supported by the fd. Returns
  // false on failure.
  bool SupportsAllKeys(const int fd);

  // Checks all the valid files under `kDevInputEvent`, stores the valid
  // keyboard devices to `fds_`. Will check if all keys are supported if input
  // is true. Returns false if there are no available file descriptors.
  virtual bool GetValidFds(bool check_supported_keys);

  // Creates the epoll and gets event data. Sets epoll file descriptor and on
  // returns true on success.
  virtual bool EpollCreate(base::ScopedFD* epfd);

  // Waits for a valid key event and reads it into the input event struct.
  // Returns true on success.
  virtual bool GetEpEvent(int epfd, struct input_event* ev);

  // Get epoll event using `GetEpEvent`. If the event is a key event and is for
  // a valid key, it and calls the Delegate `OnKeyPress` function to modify the
  // screen and index.
  virtual void OnKeyEvent();

  // GetChar takes in an input event and adds to user input if the key press
  // is a valid, printable ASCII. Pressing tab key toggles boolean. Returns
  // false after enter key press, true otherwise.
  bool GetChar(const struct input_event& ev, bool* tab_toggle);

  std::string user_input_;
  // Records the most recent repeated key press
  int repeated_key_;
  // Counts and aggregates repeated key events.
  unsigned int repeated_counter_;
  // Checks that enter key down was recorded before returning on key up.
  bool return_pressed_;
  // Whether or not to include USB connections when scanning for events.
  bool include_usb_;
  // Keyboard layout for xkb common;
  std::string keyboard_layout_;
  // Stores open event connections.
  std::vector<base::ScopedFD> fds_;
  // Stores epoll file descriptor.
  base::ScopedFD epfd_;

  // Watches the epoll file descriptor and calls `OnKeyEvent`.
  std::unique_ptr<base::FileDescriptorWatcher::Controller> watcher_;

  // Allows class to only access the `EvWaitForKey` function. `GetInput` will
  // return false.
  bool use_only_evwaitkey_;

  // A list of keys to listen for on the blocking call.
  std::vector<int> keys_;

  Delegate* delegate_;

  // XKB common keyboard layout members.
  struct xkb_context* ctx_{nullptr};
  struct xkb_rule_names names_;
  struct xkb_keymap* keymap_{nullptr};
  struct xkb_state* state_{nullptr};
};

}  // namespace minios

#endif  // MINIOS_KEY_READER_H_