1/* Copyright (c) 2017, Google Inc.
2 *
3 * Permission to use, copy, modify, and/or distribute this software for any
4 * purpose with or without fee is hereby granted, provided that the above
5 * copyright notice and this permission notice appear in all copies.
6 *
7 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
8 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
9 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
10 * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
11 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
12 * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
13 * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */
14
15#ifndef OPENSSL_HEADER_SSL_SPAN_H
16#define OPENSSL_HEADER_SSL_SPAN_H
17
18#include <openssl/base.h>
19
20#if !defined(BORINGSSL_NO_CXX)
21
22extern "C++" {
23
24#include <algorithm>
25#include <cassert>
26#include <cstdlib>
27#include <type_traits>
28
29namespace bssl {
30
31template <typename T>
32class Span;
33
34namespace internal {
35template <typename T>
36class SpanBase {
37  // Put comparison operator implementations into a base class with const T, so
38  // they can be used with any type that implicitly converts into a Span.
39  static_assert(std::is_const<T>::value,
40                "Span<T> must be derived from SpanBase<const T>");
41
42  friend bool operator==(Span<T> lhs, Span<T> rhs) {
43    // MSVC issues warning C4996 because std::equal is unsafe. The pragma to
44    // suppress the warning mysteriously has no effect, hence this
45    // implementation. See
46    // https://msdn.microsoft.com/en-us/library/aa985974.aspx.
47    if (lhs.size() != rhs.size()) {
48      return false;
49    }
50    for (T *l = lhs.begin(), *r = rhs.begin(); l != lhs.end() && r != rhs.end();
51         ++l, ++r) {
52      if (*l != *r) {
53        return false;
54      }
55    }
56    return true;
57  }
58
59  friend bool operator!=(Span<T> lhs, Span<T> rhs) { return !(lhs == rhs); }
60};
61}  // namespace internal
62
63// A Span<T> is a non-owning reference to a contiguous array of objects of type
64// |T|. Conceptually, a Span is a simple a pointer to |T| and a count of
65// elements accessible via that pointer. The elements referenced by the Span can
66// be mutated if |T| is mutable.
67//
68// A Span can be constructed from container types implementing |data()| and
69// |size()| methods. If |T| is constant, construction from a container type is
70// implicit. This allows writing methods that accept data from some unspecified
71// container type:
72//
73// // Foo views data referenced by v.
74// void Foo(bssl::Span<const uint8_t> v) { ... }
75//
76// std::vector<uint8_t> vec;
77// Foo(vec);
78//
79// For mutable Spans, conversion is explicit:
80//
81// // FooMutate mutates data referenced by v.
82// void FooMutate(bssl::Span<uint8_t> v) { ... }
83//
84// FooMutate(bssl::Span<uint8_t>(vec));
85//
86// You can also use the |MakeSpan| and |MakeConstSpan| factory methods to
87// construct Spans in order to deduce the type of the Span automatically.
88//
89// FooMutate(bssl::MakeSpan(vec));
90//
91// Note that Spans have value type sematics. They are cheap to construct and
92// copy, and should be passed by value whenever a method would otherwise accept
93// a reference or pointer to a container or array.
94template <typename T>
95class Span : private internal::SpanBase<const T> {
96 private:
97  // Heuristically test whether C is a container type that can be converted into
98  // a Span by checking for data() and size() member functions.
99  //
100  // TODO(davidben): Switch everything to std::enable_if_t when we remove
101  // support for MSVC 2015. Although we could write our own enable_if_t and MSVC
102  // 2015 has std::enable_if_t anyway, MSVC 2015's SFINAE implementation is
103  // problematic and does not work below unless we write the ::type at use.
104  template <typename C>
105  using EnableIfContainer = std::enable_if<
106      std::is_convertible<decltype(std::declval<C>().data()), T *>::value &&
107      std::is_integral<decltype(std::declval<C>().size())>::value>;
108
109  static const size_t npos = static_cast<size_t>(-1);
110
111 public:
112  constexpr Span() : Span(nullptr, 0) {}
113  constexpr Span(T *ptr, size_t len) : data_(ptr), size_(len) {}
114
115  template <size_t N>
116  constexpr Span(T (&array)[N]) : Span(array, N) {}
117
118  template <
119      typename C, typename = typename EnableIfContainer<C>::type,
120      typename = typename std::enable_if<std::is_const<T>::value, C>::type>
121  Span(const C &container) : data_(container.data()), size_(container.size()) {}
122
123  template <
124      typename C, typename = typename EnableIfContainer<C>::type,
125      typename = typename std::enable_if<!std::is_const<T>::value, C>::type>
126  explicit Span(C &container)
127      : data_(container.data()), size_(container.size()) {}
128
129  T *data() const { return data_; }
130  size_t size() const { return size_; }
131  bool empty() const { return size_ == 0; }
132
133  T *begin() const { return data_; }
134  const T *cbegin() const { return data_; }
135  T *end() const { return data_ + size_; };
136  const T *cend() const { return end(); };
137
138  T &front() const {
139    assert(size_ != 0);
140    return data_[0];
141  }
142  T &back() const {
143    assert(size_ != 0);
144    return data_[size_ - 1];
145  }
146
147  T &operator[](size_t i) const { return data_[i]; }
148  T &at(size_t i) const { return data_[i]; }
149
150  Span subspan(size_t pos = 0, size_t len = npos) const {
151    if (pos > size_) {
152      abort();  // absl::Span throws an exception here.
153    }
154    return Span(data_ + pos, std::min(size_ - pos, len));
155  }
156
157 private:
158  T *data_;
159  size_t size_;
160};
161
162template <typename T>
163const size_t Span<T>::npos;
164
165template <typename T>
166Span<T> MakeSpan(T *ptr, size_t size) {
167  return Span<T>(ptr, size);
168}
169
170template <typename C>
171auto MakeSpan(C &c) -> decltype(MakeSpan(c.data(), c.size())) {
172  return MakeSpan(c.data(), c.size());
173}
174
175template <typename T>
176Span<const T> MakeConstSpan(T *ptr, size_t size) {
177  return Span<const T>(ptr, size);
178}
179
180template <typename C>
181auto MakeConstSpan(const C &c) -> decltype(MakeConstSpan(c.data(), c.size())) {
182  return MakeConstSpan(c.data(), c.size());
183}
184
185}  // namespace bssl
186
187}  // extern C++
188
189#endif  // !defined(BORINGSSL_NO_CXX)
190
191#endif  // OPENSSL_HEADER_SSL_SPAN_H
192