1 // Copyright 2017 The Abseil Authors.
2 //
3 // Licensed under the Apache License, Version 2.0 (the "License");
4 // you may not use this file except in compliance with the License.
5 // You may obtain a copy of the License at
6 //
7 //      https://www.apache.org/licenses/LICENSE-2.0
8 //
9 // Unless required by applicable law or agreed to in writing, software
10 // distributed under the License is distributed on an "AS IS" BASIS,
11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12 // See the License for the specific language governing permissions and
13 // limitations under the License.
14 
15 #ifndef ABSL_RANDOM_INTERNAL_NONSECURE_BASE_H_
16 #define ABSL_RANDOM_INTERNAL_NONSECURE_BASE_H_
17 
18 #include <algorithm>
19 #include <cstdint>
20 #include <iostream>
21 #include <iterator>
22 #include <random>
23 #include <string>
24 #include <type_traits>
25 #include <vector>
26 
27 #include "absl/base/macros.h"
28 #include "absl/meta/type_traits.h"
29 #include "absl/random/internal/pool_urbg.h"
30 #include "absl/random/internal/salted_seed_seq.h"
31 #include "absl/random/internal/seed_material.h"
32 #include "absl/types/optional.h"
33 #include "absl/types/span.h"
34 
35 namespace absl {
36 ABSL_NAMESPACE_BEGIN
37 namespace random_internal {
38 
39 // Each instance of NonsecureURBGBase<URBG> will be seeded by variates produced
40 // by a thread-unique URBG-instance.
41 template <typename URBG>
42 class NonsecureURBGBase {
43  public:
44   using result_type = typename URBG::result_type;
45 
46   // Default constructor
NonsecureURBGBase()47   NonsecureURBGBase() : urbg_(ConstructURBG()) {}
48 
49   // Copy disallowed, move allowed.
50   NonsecureURBGBase(const NonsecureURBGBase&) = delete;
51   NonsecureURBGBase& operator=(const NonsecureURBGBase&) = delete;
52   NonsecureURBGBase(NonsecureURBGBase&&) = default;
53   NonsecureURBGBase& operator=(NonsecureURBGBase&&) = default;
54 
55   // Constructor using a seed
56   template <class SSeq, typename = typename absl::enable_if_t<
57                             !std::is_same<SSeq, NonsecureURBGBase>::value>>
NonsecureURBGBase(SSeq && seq)58   explicit NonsecureURBGBase(SSeq&& seq)
59       : urbg_(ConstructURBG(std::forward<SSeq>(seq))) {}
60 
61   // Note: on MSVC, min() or max() can be interpreted as MIN() or MAX(), so we
62   // enclose min() or max() in parens as (min)() and (max)().
63   // Additionally, clang-format requires no space before this construction.
64 
65   // NonsecureURBGBase::min()
result_type(min)66   static constexpr result_type(min)() { return (URBG::min)(); }
67 
68   // NonsecureURBGBase::max()
result_type(max)69   static constexpr result_type(max)() { return (URBG::max)(); }
70 
71   // NonsecureURBGBase::operator()()
operator()72   result_type operator()() { return urbg_(); }
73 
74   // NonsecureURBGBase::discard()
discard(unsigned long long values)75   void discard(unsigned long long values) {  // NOLINT(runtime/int)
76     urbg_.discard(values);
77   }
78 
79   bool operator==(const NonsecureURBGBase& other) const {
80     return urbg_ == other.urbg_;
81   }
82 
83   bool operator!=(const NonsecureURBGBase& other) const {
84     return !(urbg_ == other.urbg_);
85   }
86 
87  private:
88   // Seeder is a custom seed sequence type where generate() fills the provided
89   // buffer via the RandenPool entropy source.
90   struct Seeder {
91     using result_type = uint32_t;
92 
sizeSeeder93     size_t size() { return 0; }
94 
95     template <typename OutIterator>
paramSeeder96     void param(OutIterator) const {}
97 
98     template <typename RandomAccessIterator>
generateSeeder99     void generate(RandomAccessIterator begin, RandomAccessIterator end) {
100       if (begin != end) {
101         // begin, end must be random access iterators assignable from uint32_t.
102         generate_impl(
103             std::integral_constant<bool, sizeof(*begin) == sizeof(uint32_t)>{},
104             begin, end);
105       }
106     }
107 
108     // Commonly, generate is invoked with a pointer to a buffer which
109     // can be cast to a uint32_t.
110     template <typename RandomAccessIterator>
generate_implSeeder111     void generate_impl(std::integral_constant<bool, true>,
112                        RandomAccessIterator begin, RandomAccessIterator end) {
113       auto buffer = absl::MakeSpan(begin, end);
114       auto target = absl::MakeSpan(reinterpret_cast<uint32_t*>(buffer.data()),
115                                    buffer.size());
116       RandenPool<uint32_t>::Fill(target);
117     }
118 
119     // The non-uint32_t case should be uncommon, and involves an extra copy,
120     // filling the uint32_t buffer and then mixing into the output.
121     template <typename RandomAccessIterator>
generate_implSeeder122     void generate_impl(std::integral_constant<bool, false>,
123                        RandomAccessIterator begin, RandomAccessIterator end) {
124       const size_t n = std::distance(begin, end);
125       absl::InlinedVector<uint32_t, 8> data(n, 0);
126       RandenPool<uint32_t>::Fill(absl::MakeSpan(data.begin(), data.end()));
127       std::copy(std::begin(data), std::end(data), begin);
128     }
129   };
130 
ConstructURBG()131   static URBG ConstructURBG() {
132     Seeder seeder;
133     return URBG(seeder);
134   }
135 
136   template <typename SSeq>
ConstructURBG(SSeq && seq)137   static URBG ConstructURBG(SSeq&& seq) {  // NOLINT(runtime/references)
138     auto salted_seq =
139         random_internal::MakeSaltedSeedSeq(std::forward<SSeq>(seq));
140     return URBG(salted_seq);
141   }
142 
143   URBG urbg_;
144 };
145 
146 }  // namespace random_internal
147 ABSL_NAMESPACE_END
148 }  // namespace absl
149 
150 #endif  // ABSL_RANDOM_INTERNAL_NONSECURE_BASE_H_
151