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 BSSL_NAMESPACE_BEGIN
30
31 template <typename T>
32 class Span;
33
34 namespace internal {
35 template <typename T>
36 class 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.
94 template <typename T>
95 class Span : private internal::SpanBase<const T> {
96 private:
97 static const size_t npos = static_cast<size_t>(-1);
98
99 // Heuristically test whether C is a container type that can be converted into
100 // a Span by checking for data() and size() member functions.
101 //
102 // TODO(davidben): Require C++17 support for std::is_convertible_v, etc.
103 template <typename C>
104 using EnableIfContainer = std::enable_if_t<
105 std::is_convertible<decltype(std::declval<C>().data()), T *>::value &&
106 std::is_integral<decltype(std::declval<C>().size())>::value>;
107
108 public:
Span()109 constexpr Span() : Span(nullptr, 0) {}
Span(T * ptr,size_t len)110 constexpr Span(T *ptr, size_t len) : data_(ptr), size_(len) {}
111
112 template <size_t N>
Span(T (& array)[N])113 constexpr Span(T (&array)[N]) : Span(array, N) {}
114
115 template <typename C, typename = EnableIfContainer<C>,
116 typename = std::enable_if_t<std::is_const<T>::value, C>>
Span(const C & container)117 Span(const C &container) : data_(container.data()), size_(container.size()) {}
118
119 template <typename C, typename = EnableIfContainer<C>,
120 typename = std::enable_if_t<!std::is_const<T>::value, C>>
Span(C & container)121 explicit Span(C &container)
122 : data_(container.data()), size_(container.size()) {}
123
data()124 T *data() const { return data_; }
size()125 size_t size() const { return size_; }
empty()126 bool empty() const { return size_ == 0; }
127
begin()128 T *begin() const { return data_; }
cbegin()129 const T *cbegin() const { return data_; }
end()130 T *end() const { return data_ + size_; }
cend()131 const T *cend() const { return end(); }
132
front()133 T &front() const {
134 if (size_ == 0) {
135 abort();
136 }
137 return data_[0];
138 }
back()139 T &back() const {
140 if (size_ == 0) {
141 abort();
142 }
143 return data_[size_ - 1];
144 }
145
146 T &operator[](size_t i) const {
147 if (i >= size_) {
148 abort();
149 }
150 return data_[i];
151 }
at(size_t i)152 T &at(size_t i) const { return (*this)[i]; }
153
154 Span subspan(size_t pos = 0, size_t len = npos) const {
155 if (pos > size_) {
156 // absl::Span throws an exception here. Note std::span and Chromium
157 // base::span additionally forbid pos + len being out of range, with a
158 // special case at npos/dynamic_extent, while absl::Span::subspan clips
159 // the span. For now, we align with absl::Span in case we switch to it in
160 // the future.
161 abort();
162 }
163 return Span(data_ + pos, std::min(size_ - pos, len));
164 }
165
first(size_t len)166 Span first(size_t len) {
167 if (len > size_) {
168 abort();
169 }
170 return Span(data_, len);
171 }
172
last(size_t len)173 Span last(size_t len) {
174 if (len > size_) {
175 abort();
176 }
177 return Span(data_ + size_ - len, len);
178 }
179
180 private:
181 T *data_;
182 size_t size_;
183 };
184
185 template <typename T>
186 const size_t Span<T>::npos;
187
188 template <typename T>
MakeSpan(T * ptr,size_t size)189 Span<T> MakeSpan(T *ptr, size_t size) {
190 return Span<T>(ptr, size);
191 }
192
193 template <typename C>
194 auto MakeSpan(C &c) -> decltype(MakeSpan(c.data(), c.size())) {
195 return MakeSpan(c.data(), c.size());
196 }
197
198 template <typename T>
MakeConstSpan(T * ptr,size_t size)199 Span<const T> MakeConstSpan(T *ptr, size_t size) {
200 return Span<const T>(ptr, size);
201 }
202
203 template <typename C>
204 auto MakeConstSpan(const C &c) -> decltype(MakeConstSpan(c.data(), c.size())) {
205 return MakeConstSpan(c.data(), c.size());
206 }
207
208 BSSL_NAMESPACE_END
209
210 } // extern C++
211
212 #endif // !defined(BORINGSSL_NO_CXX)
213
214 #endif // OPENSSL_HEADER_SSL_SPAN_H
215