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// 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/containers/span.h"
#include "base/hash/hash.h"
#include "third_party/abseil-cpp/absl/types/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) : words_{high, 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 words_.w0; }
constexpr uint64_t low() const { return words_.w1; }
constexpr bool is_zero() const { return words_.w0 == 0 && words_.w1 == 0; }
span<const uint8_t, 16> AsBytes() const {
return as_bytes(make_span(words_.arr));
}
constexpr bool operator==(const Token& other) const {
return words_.w0 == other.words_.w0 && words_.w1 == other.words_.w1;
}
constexpr bool operator!=(const Token& other) const {
return !(*this == other);
}
constexpr bool operator<(const Token& other) const {
return std::tie(words_.w0, words_.w1) <
std::tie(other.words_.w0, other.words_.w1);
}
// 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.
union {
uint64_t arr[2];
struct {
uint64_t w0;
uint64_t w1;
};
} words_ = {{0,0}};
};
// 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 absl::optional<Token> ReadTokenFromPickle(
PickleIterator* pickle_iterator);
} // namespace base
#endif // BASE_TOKEN_H_
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