1 // Copyright 2018 The Chromium Authors
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/strings/string_piece_forward.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. The result's |is_zero()| is
41 // guaranteed to be false.
42 static Token CreateRandom();
44 // The high and low 64 bits of this Token.
45 constexpr uint64_t high() const { return words_[0]; }
46 constexpr uint64_t low() const { return words_[1]; }
48 constexpr bool is_zero() const { return words_[0] == 0 && words_[1] == 0; }
50 span<const uint8_t, 16> AsBytes() const {
51 return as_bytes(make_span(words_));
54 constexpr bool operator==(const Token& other) const {
55 return words_[0] == other.words_[0] && words_[1] == other.words_[1];
58 constexpr bool operator!=(const Token& other) const {
59 return !(*this == other);
62 constexpr bool operator<(const Token& other) const {
63 return std::tie(words_[0], words_[1]) <
64 std::tie(other.words_[0], other.words_[1]);
67 // Generates a string representation of this Token useful for e.g. logging.
68 std::string ToString() const;
70 // FromString is the opposite of ToString. It returns absl::nullopt if the
71 // |string_representation| is invalid.
72 static absl::optional<Token> FromString(StringPiece string_representation);
75 // Note: Two uint64_t are used instead of uint8_t[16] in order to have a
76 // simpler implementation, paricularly for |ToString()|, |is_zero()|, and
77 // constexpr value construction.
79 uint64_t words_[2] = {0, 0};
82 // For use in std::unordered_map.
83 struct BASE_EXPORT TokenHash {
84 size_t operator()(const Token& token) const;
90 // For serializing and deserializing Token values.
91 BASE_EXPORT void WriteTokenToPickle(Pickle* pickle, const Token& token);
92 BASE_EXPORT absl::optional<Token> ReadTokenFromPickle(
93 PickleIterator* pickle_iterator);
97 #endif // BASE_TOKEN_H_