1 // Copyright 2018 The Chromium Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file.
13 #include "base/base_export.h"
14 #include "base/containers/span.h"
15 #include "base/hash/hash.h"
16 #include "third_party/abseil-cpp/absl/types/optional.h"
20 // A Token is a randomly chosen 128-bit integer. This class supports generation
21 // from a cryptographically strong random source, or constexpr construction over
22 // fixed values (e.g. to store a pre-generated constant value). Tokens are
23 // similar in spirit and purpose to UUIDs, without many of the constraints and
24 // expectations (such as byte layout and string representation) clasically
25 // associated with UUIDs.
26 class BASE_EXPORT Token {
28 // Constructs a zero Token.
29 constexpr Token() = default;
31 // Constructs a Token with |high| and |low| as its contents.
32 constexpr Token(uint64_t high, uint64_t low) : words_{high, low} {}
34 constexpr Token(const Token&) = default;
35 constexpr Token& operator=(const Token&) = default;
36 constexpr Token(Token&&) noexcept = default;
37 constexpr Token& operator=(Token&&) = default;
39 // Constructs a new Token with random |high| and |low| values taken from a
40 // cryptographically strong random source.
41 static Token CreateRandom();
43 // The high and low 64 bits of this Token.
44 constexpr uint64_t high() const { return words_[0]; }
45 constexpr uint64_t low() const { return words_[1]; }
47 constexpr bool is_zero() const { return words_[0] == 0 && words_[1] == 0; }
49 span<const uint8_t, 16> AsBytes() const {
50 return as_bytes(make_span(words_));
53 constexpr bool operator==(const Token& other) const {
54 return words_[0] == other.words_[0] && words_[1] == other.words_[1];
57 constexpr bool operator!=(const Token& other) const {
58 return !(*this == other);
61 constexpr bool operator<(const Token& other) const {
62 return std::tie(words_[0], words_[1]) <
63 std::tie(other.words_[0], other.words_[1]);
66 // Generates a string representation of this Token useful for e.g. logging.
67 std::string ToString() const;
70 // Note: Two uint64_t are used instead of uint8_t[16] in order to have a
71 // simpler implementation, paricularly for |ToString()|, |is_zero()|, and
72 // constexpr value construction.
74 uint64_t words_[2] = {0, 0};
77 // For use in std::unordered_map.
79 size_t operator()(const base::Token& token) const {
80 return base::HashInts64(token.high(), token.low());
87 // For serializing and deserializing Token values.
88 BASE_EXPORT void WriteTokenToPickle(Pickle* pickle, const Token& token);
89 BASE_EXPORT absl::optional<Token> ReadTokenFromPickle(
90 PickleIterator* pickle_iterator);
94 #endif // BASE_TOKEN_H_