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 <algorithm>
25 #include <cstdlib>
26 #include <type_traits>
27
28 BSSL_NAMESPACE_BEGIN
29
30 template <typename T>
31 class Span;
32
33 namespace internal {
34 template <typename T>
35 class SpanBase {
36 // Put comparison operator implementations into a base class with const T, so
37 // they can be used with any type that implicitly converts into a Span.
38 static_assert(std::is_const<T>::value,
39 "Span<T> must be derived from SpanBase<const T>");
40
41 friend bool operator==(Span<T> lhs, Span<T> rhs) {
42 // MSVC issues warning C4996 because std::equal is unsafe. The pragma to
43 // suppress the warning mysteriously has no effect, hence this
44 // implementation. See
45 // https://msdn.microsoft.com/en-us/library/aa985974.aspx.
46 if (lhs.size() != rhs.size()) {
47 return false;
48 }
49 for (T *l = lhs.begin(), *r = rhs.begin(); l != lhs.end() && r != rhs.end();
50 ++l, ++r) {
51 if (*l != *r) {
52 return false;
53 }
54 }
55 return true;
56 }
57
58 friend bool operator!=(Span<T> lhs, Span<T> rhs) { return !(lhs == rhs); }
59 };
60 } // namespace internal
61
62 // A Span<T> is a non-owning reference to a contiguous array of objects of type
63 // |T|. Conceptually, a Span is a simple a pointer to |T| and a count of
64 // elements accessible via that pointer. The elements referenced by the Span can
65 // be mutated if |T| is mutable.
66 //
67 // A Span can be constructed from container types implementing |data()| and
68 // |size()| methods. If |T| is constant, construction from a container type is
69 // implicit. This allows writing methods that accept data from some unspecified
70 // container type:
71 //
72 // // Foo views data referenced by v.
73 // void Foo(bssl::Span<const uint8_t> v) { ... }
74 //
75 // std::vector<uint8_t> vec;
76 // Foo(vec);
77 //
78 // For mutable Spans, conversion is explicit:
79 //
80 // // FooMutate mutates data referenced by v.
81 // void FooMutate(bssl::Span<uint8_t> v) { ... }
82 //
83 // FooMutate(bssl::Span<uint8_t>(vec));
84 //
85 // You can also use the |MakeSpan| and |MakeConstSpan| factory methods to
86 // construct Spans in order to deduce the type of the Span automatically.
87 //
88 // FooMutate(bssl::MakeSpan(vec));
89 //
90 // Note that Spans have value type sematics. They are cheap to construct and
91 // copy, and should be passed by value whenever a method would otherwise accept
92 // a reference or pointer to a container or array.
93 template <typename T>
94 class Span : private internal::SpanBase<const T> {
95 private:
96 // Heuristically test whether C is a container type that can be converted into
97 // a Span by checking for data() and size() member functions.
98 //
99 // TODO(davidben): Switch everything to std::enable_if_t when we remove
100 // support for MSVC 2015. Although we could write our own enable_if_t and MSVC
101 // 2015 has std::enable_if_t anyway, MSVC 2015's SFINAE implementation is
102 // problematic and does not work below unless we write the ::type at use.
103 template <typename C>
104 using EnableIfContainer = std::enable_if<
105 std::is_convertible<decltype(std::declval<C>().data()), T *>::value &&
106 std::is_integral<decltype(std::declval<C>().size())>::value>;
107
108 static const size_t npos = static_cast<size_t>(-1);
109
110 public:
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 <
118 typename C, typename = typename EnableIfContainer<C>::type,
119 typename = typename std::enable_if<std::is_const<T>::value, C>::type>
Span(const C & container)120 Span(const C &container) : data_(container.data()), size_(container.size()) {}
121
122 template <
123 typename C, typename = typename EnableIfContainer<C>::type,
124 typename = typename std::enable_if<!std::is_const<T>::value, C>::type>
Span(C & container)125 explicit Span(C &container)
126 : data_(container.data()), size_(container.size()) {}
127
data()128 T *data() const { return data_; }
size()129 size_t size() const { return size_; }
empty()130 bool empty() const { return size_ == 0; }
131
begin()132 T *begin() const { return data_; }
cbegin()133 const T *cbegin() const { return data_; }
end()134 T *end() const { return data_ + size_; }
cend()135 const T *cend() const { return end(); }
136
front()137 T &front() const {
138 if (size_ == 0) {
139 abort();
140 }
141 return data_[0];
142 }
back()143 T &back() const {
144 if (size_ == 0) {
145 abort();
146 }
147 return data_[size_ - 1];
148 }
149
150 T &operator[](size_t i) const {
151 if (i >= size_) {
152 abort();
153 }
154 return data_[i];
155 }
at(size_t i)156 T &at(size_t i) const { return (*this)[i]; }
157
158 Span subspan(size_t pos = 0, size_t len = npos) const {
159 if (pos > size_) {
160 abort(); // absl::Span throws an exception here.
161 }
162 return Span(data_ + pos, std::min(size_ - pos, len));
163 }
164
165 private:
166 T *data_;
167 size_t size_;
168 };
169
170 template <typename T>
171 const size_t Span<T>::npos;
172
173 template <typename T>
MakeSpan(T * ptr,size_t size)174 Span<T> MakeSpan(T *ptr, size_t size) {
175 return Span<T>(ptr, size);
176 }
177
178 template <typename C>
179 auto MakeSpan(C &c) -> decltype(MakeSpan(c.data(), c.size())) {
180 return MakeSpan(c.data(), c.size());
181 }
182
183 template <typename T>
MakeConstSpan(T * ptr,size_t size)184 Span<const T> MakeConstSpan(T *ptr, size_t size) {
185 return Span<const T>(ptr, size);
186 }
187
188 template <typename C>
189 auto MakeConstSpan(const C &c) -> decltype(MakeConstSpan(c.data(), c.size())) {
190 return MakeConstSpan(c.data(), c.size());
191 }
192
193 BSSL_NAMESPACE_END
194
195 } // extern C++
196
197 #endif // !defined(BORINGSSL_NO_CXX)
198
199 #endif // OPENSSL_HEADER_SSL_SPAN_H
200