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
22 extern "C++" {
23
24 #include <stdlib.h>
25
26 #include <algorithm>
27 #include <type_traits>
28
29 #if __cplusplus >= 201703L
30 #include <string_view>
31 #endif
32
33 BSSL_NAMESPACE_BEGIN
34
35 template <typename T>
36 class Span;
37
38 namespace internal {
39 template <typename T>
40 class SpanBase {
41 // Put comparison operator implementations into a base class with const T, so
42 // they can be used with any type that implicitly converts into a Span.
43 static_assert(std::is_const<T>::value,
44 "Span<T> must be derived from SpanBase<const T>");
45
46 friend bool operator==(Span<T> lhs, Span<T> rhs) {
47 return std::equal(lhs.begin(), lhs.end(), rhs.begin(), rhs.end());
48 }
49
50 friend bool operator!=(Span<T> lhs, Span<T> rhs) { return !(lhs == rhs); }
51 };
52
53 // Heuristically test whether C is a container type that can be converted into
54 // a Span<T> by checking for data() and size() member functions.
55 //
56 // TODO(davidben): Require C++17 support for std::is_convertible_v, etc.
57 template <typename C, typename T>
58 using EnableIfContainer = std::enable_if_t<
59 std::is_convertible<decltype(std::declval<C>().data()), T *>::value &&
60 std::is_integral<decltype(std::declval<C>().size())>::value>;
61
62 } // namespace internal
63
64 // A Span<T> is a non-owning reference to a contiguous array of objects of type
65 // |T|. Conceptually, a Span is a simple a pointer to |T| and a count of
66 // elements accessible via that pointer. The elements referenced by the Span can
67 // be mutated if |T| is mutable.
68 //
69 // A Span can be constructed from container types implementing |data()| and
70 // |size()| methods. If |T| is constant, construction from a container type is
71 // implicit. This allows writing methods that accept data from some unspecified
72 // container type:
73 //
74 // // Foo views data referenced by v.
75 // void Foo(bssl::Span<const uint8_t> v) { ... }
76 //
77 // std::vector<uint8_t> vec;
78 // Foo(vec);
79 //
80 // For mutable Spans, conversion is explicit:
81 //
82 // // FooMutate mutates data referenced by v.
83 // void FooMutate(bssl::Span<uint8_t> v) { ... }
84 //
85 // FooMutate(bssl::Span<uint8_t>(vec));
86 //
87 // You can also use the |MakeSpan| and |MakeConstSpan| factory methods to
88 // construct Spans in order to deduce the type of the Span automatically.
89 //
90 // FooMutate(bssl::MakeSpan(vec));
91 //
92 // Note that Spans have value type sematics. They are cheap to construct and
93 // copy, and should be passed by value whenever a method would otherwise accept
94 // a reference or pointer to a container or array.
95 template <typename T>
96 class Span : private internal::SpanBase<const T> {
97 public:
98 static const size_t npos = static_cast<size_t>(-1);
99
100 using element_type = T;
101 using value_type = std::remove_cv_t<T>;
102 using size_type = size_t;
103 using difference_type = ptrdiff_t;
104 using pointer = T *;
105 using const_pointer = const T *;
106 using reference = T &;
107 using const_reference = const T &;
108 using iterator = T *;
109 using const_iterator = const T *;
110
Span()111 constexpr Span() : Span(nullptr, 0) {}
Span(T * ptr,size_t len)112 constexpr Span(T *ptr, size_t len) : data_(ptr), size_(len) {}
113
114 template <size_t N>
Span(T (& array)[N])115 constexpr Span(T (&array)[N]) : Span(array, N) {}
116
117 template <typename C, typename = internal::EnableIfContainer<C, T>,
118 typename = std::enable_if_t<std::is_const<T>::value, C>>
Span(const C & container)119 constexpr Span(const C &container)
120 : data_(container.data()), size_(container.size()) {}
121
122 template <typename C, typename = internal::EnableIfContainer<C, T>,
123 typename = std::enable_if_t<!std::is_const<T>::value, C>>
Span(C & container)124 constexpr explicit Span(C &container)
125 : data_(container.data()), size_(container.size()) {}
126
data()127 constexpr T *data() const { return data_; }
size()128 constexpr size_t size() const { return size_; }
empty()129 constexpr bool empty() const { return size_ == 0; }
130
begin()131 constexpr iterator begin() const { return data_; }
cbegin()132 constexpr const_iterator cbegin() const { return data_; }
end()133 constexpr iterator end() const { return data_ + size_; }
cend()134 constexpr const_iterator cend() const { return end(); }
135
front()136 constexpr T &front() const {
137 if (size_ == 0) {
138 abort();
139 }
140 return data_[0];
141 }
back()142 constexpr T &back() const {
143 if (size_ == 0) {
144 abort();
145 }
146 return data_[size_ - 1];
147 }
148
149 constexpr T &operator[](size_t i) const {
150 if (i >= size_) {
151 abort();
152 }
153 return data_[i];
154 }
at(size_t i)155 T &at(size_t i) const { return (*this)[i]; }
156
157 constexpr Span subspan(size_t pos = 0, size_t len = npos) const {
158 if (pos > size_) {
159 // absl::Span throws an exception here. Note std::span and Chromium
160 // base::span additionally forbid pos + len being out of range, with a
161 // special case at npos/dynamic_extent, while absl::Span::subspan clips
162 // the span. For now, we align with absl::Span in case we switch to it in
163 // the future.
164 abort();
165 }
166 return Span(data_ + pos, std::min(size_ - pos, len));
167 }
168
first(size_t len)169 constexpr Span first(size_t len) const {
170 if (len > size_) {
171 abort();
172 }
173 return Span(data_, len);
174 }
175
last(size_t len)176 constexpr Span last(size_t len) const {
177 if (len > size_) {
178 abort();
179 }
180 return Span(data_ + size_ - len, len);
181 }
182
183 private:
184 T *data_;
185 size_t size_;
186 };
187
188 template <typename T>
189 const size_t Span<T>::npos;
190
191 #if __cplusplus >= 201703L
192 template <typename T>
193 Span(T *, size_t) -> Span<T>;
194 template <typename T, size_t size>
195 Span(T (&array)[size]) -> Span<T>;
196 template <
197 typename C,
198 typename T = std::remove_pointer_t<decltype(std::declval<C>().data())>,
199 typename = internal::EnableIfContainer<C, T>>
200 Span(C &) -> Span<T>;
201 #endif
202
203 // C++17 callers can instead rely on CTAD and the deduction guides defined
204 // above.
205 template <typename T>
MakeSpan(T * ptr,size_t size)206 constexpr Span<T> MakeSpan(T *ptr, size_t size) {
207 return Span<T>(ptr, size);
208 }
209
210 template <typename C>
211 constexpr auto MakeSpan(C &c) -> decltype(MakeSpan(c.data(), c.size())) {
212 return MakeSpan(c.data(), c.size());
213 }
214
215 template <typename T>
MakeConstSpan(T * ptr,size_t size)216 constexpr Span<const T> MakeConstSpan(T *ptr, size_t size) {
217 return Span<const T>(ptr, size);
218 }
219
220 template <typename C>
221 constexpr auto MakeConstSpan(const C &c)
222 -> decltype(MakeConstSpan(c.data(), c.size())) {
223 return MakeConstSpan(c.data(), c.size());
224 }
225
226 template <typename T, size_t size>
MakeConstSpan(T (& array)[size])227 constexpr Span<const T> MakeConstSpan(T (&array)[size]) {
228 return array;
229 }
230
231 #if __cplusplus >= 201703L
StringAsBytes(std::string_view s)232 inline Span<const uint8_t> StringAsBytes(std::string_view s) {
233 return MakeConstSpan(reinterpret_cast<const uint8_t *>(s.data()), s.size());
234 }
235
BytesAsStringView(bssl::Span<const uint8_t> b)236 inline std::string_view BytesAsStringView(bssl::Span<const uint8_t> b) {
237 return std::string_view(reinterpret_cast<const char *>(b.data()), b.size());
238 }
239 #endif
240
241 BSSL_NAMESPACE_END
242
243 } // extern C++
244
245 #endif // !defined(BORINGSSL_NO_CXX)
246
247 #endif // OPENSSL_HEADER_SSL_SPAN_H
248