[Remoting Host] Handle text event characters that are not presented on the keyboard

remoting/host/linux/x_server_key_mapper.h

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef REMOTING_HOST_LINUX_X_SERVER_KEY_MAPPER_H_
+#define REMOTING_HOST_LINUX_X_SERVER_KEY_MAPPER_H_
+
+#include <stdint.h>
+#include <X11/Xlib.h>
+
+#include <queue>
+#include <unordered_set>
+
+#include "base/macros.h"
+
+namespace remoting {
+
+/**
+ * This is a helper class for assigning unused keycodes to characters. When all
+ * keycodes are used, newly added character will take the keycode of the oldest
+ * character.
+ * When the key mapper is destructed, all keycodes used by the mapper will be
+ * reset to map NoSymbol.
+ * The key mapper must be used on single thread thread.
+ */
+class XServerKeyMapper {
+ public:
+  explicit XServerKeyMapper(Display* display);
+  ~XServerKeyMapper();
+
+  // |code_point|: The Unicode code point for the character.
+  // Returns the keycode for the new character. Returns -1 when failed to map
+  // the character.
+  int AddNewCharacter(uint32_t code_point);
+
+ private:
+  // X11 graphics context.
+  Display* display_;
+
+  // TODO(yuweih): Consider better data structure, e.g. LRU.

[Sergey Ulanov, 2016/09/19 21:39:00]

To implement the current solution you can just have a vector and an index that
gets incremented when a keycode is used.

[Yuwei, 2016/09/21 03:47:40]

For LRU I think we should count use of KeySym rather than the KeyCode, which is
not feasible for this class since AddNewCharacter() won't be called if the
character is already mapped.

+  std::queue<uint32_t> available_keycodes_;
+
+  std::unordered_set<uint32_t> used_keycodes_;

[Sergey Ulanov, 2016/09/19 21:39:00]

keycodes are always in range [8..255] so this can be a boolean array.

[Yuwei, 2016/09/21 03:47:40]

Obsolete. The |last_used| field of KeyInfo is enough to tell whether a keycode
has been used.

+
+  DISALLOW_COPY_AND_ASSIGN(XServerKeyMapper);
+};
+
+}  // namespace remoting
+
+#endif  // REMOTING_HOST_LINUX_X_SERVER_KEY_MAPPER_H_