text: // Copyright 2018 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 BASE_TOKEN_H_
  #define BASE_TOKEN_H_
  
  #include <stdint.h>
  
  #include <string>
  #include <tuple>
  
  #include "base/base_export.h"
  #include "base/hash/hash.h"
  #include "base/optional.h"
  
  namespace base {
  
  // A Token is a randomly chosen 128-bit integer. This class supports generation
  // from a cryptographically strong random source, or constexpr construction over
  // fixed values (e.g. to store a pre-generated constant value). Tokens are
  // similar in spirit and purpose to UUIDs, without many of the constraints and
  // expectations (such as byte layout and string representation) clasically
  // associated with UUIDs.
  class BASE_EXPORT Token {
   public:
    // Constructs a zero Token.
    constexpr Token() = default;
  
    // Constructs a Token with |high| and |low| as its contents.
    constexpr Token(uint64_t high, uint64_t low) : high_(high), low_(low) {}
  
    constexpr Token(const Token&) = default;
    constexpr Token& operator=(const Token&) = default;
    constexpr Token(Token&&) noexcept = default;
    constexpr Token& operator=(Token&&) = default;
  
    // Constructs a new Token with random |high| and |low| values taken from a
    // cryptographically strong random source.
    static Token CreateRandom();
  
    // The high and low 64 bits of this Token.
    constexpr uint64_t high() const { return high_; }
    constexpr uint64_t low() const { return low_; }
  
    constexpr bool is_zero() const { return high_ == 0 && low_ == 0; }
  
    constexpr bool operator==(const Token& other) const {
      return high_ == other.high_ && low_ == other.low_;
    }
  
  #if __cplusplus <= 201703L
    constexpr bool operator!=(const Token& other) const {
      return !(*this == other);
    }
  #endif
  
    constexpr bool operator<(const Token& other) const {
      return std::tie(high_, low_) < std::tie(other.high_, other.low_);
    }
  
    // Generates a string representation of this Token useful for e.g. logging.
    std::string ToString() const;
  
   private:
    // Note: Two uint64_t are used instead of uint8_t[16] in order to have a
    // simpler implementation, paricularly for |ToString()|, |is_zero()|, and
    // constexpr value construction.
    uint64_t high_ = 0;
    uint64_t low_ = 0;
  };
  
  // For use in std::unordered_map.
  struct TokenHash {
    size_t operator()(const base::Token& token) const {
      return base::HashInts64(token.high(), token.low());
    }
  };
  
  class Pickle;
  class PickleIterator;
  
  // For serializing and deserializing Token values.
  BASE_EXPORT void WriteTokenToPickle(Pickle* pickle, const Token& token);
  BASE_EXPORT Optional<Token> ReadTokenFromPickle(
      PickleIterator* pickle_iterator);
  
  }  // namespace base
  
  #endif  // BASE_TOKEN_H_
  