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 public:
Span()100 constexpr Span() : Span(nullptr, 0) {}
Span(T * ptr,size_t len)101 constexpr Span(T *ptr, size_t len) : data_(ptr), size_(len) {}
102
103 template <size_t N>
Span(T (& array)[N])104 constexpr Span(T (&array)[N]) : Span(array, N) {}
105
106 template <
107 typename C,
108 // TODO(davidben): Switch everything to std::enable_if_t when we remove
109 // support for MSVC 2015. Although we could write our own enable_if_t and
110 // MSVC 2015 has std::enable_if_t anyway, MSVC 2015's SFINAE
111 // implementation is problematic and does not work below unless we write
112 // the ::type at use.
113 //
114 // TODO(davidben): Move this and the identical copy below into an
115 // EnableIfContainer alias when we drop MSVC 2015 support. MSVC 2015's
116 // SFINAE support cannot handle type aliases.
117 typename = typename std::enable_if<
118 std::is_convertible<decltype(std::declval<C>().data()), T *>::value &&
119 std::is_integral<decltype(std::declval<C>().size())>::value>::type,
120 typename = typename std::enable_if<std::is_const<T>::value, C>::type>
Span(const C & container)121 Span(const C &container) : data_(container.data()), size_(container.size()) {}
122
123 template <
124 typename C,
125 typename = typename std::enable_if<
126 std::is_convertible<decltype(std::declval<C>().data()), T *>::value &&
127 std::is_integral<decltype(std::declval<C>().size())>::value>::type,
128 typename = typename std::enable_if<!std::is_const<T>::value, C>::type>
Span(C & container)129 explicit Span(C &container)
130 : data_(container.data()), size_(container.size()) {}
131
data()132 T *data() const { return data_; }
size()133 size_t size() const { return size_; }
empty()134 bool empty() const { return size_ == 0; }
135
begin()136 T *begin() const { return data_; }
cbegin()137 const T *cbegin() const { return data_; }
end()138 T *end() const { return data_ + size_; }
cend()139 const T *cend() const { return end(); }
140
front()141 T &front() const {
142 if (size_ == 0) {
143 abort();
144 }
145 return data_[0];
146 }
back()147 T &back() const {
148 if (size_ == 0) {
149 abort();
150 }
151 return data_[size_ - 1];
152 }
153
154 T &operator[](size_t i) const {
155 if (i >= size_) {
156 abort();
157 }
158 return data_[i];
159 }
at(size_t i)160 T &at(size_t i) const { return (*this)[i]; }
161
162 Span subspan(size_t pos = 0, size_t len = npos) const {
163 if (pos > size_) {
164 // absl::Span throws an exception here. Note std::span and Chromium
165 // base::span additionally forbid pos + len being out of range, with a
166 // special case at npos/dynamic_extent, while absl::Span::subspan clips
167 // the span. For now, we align with absl::Span in case we switch to it in
168 // the future.
169 abort();
170 }
171 return Span(data_ + pos, std::min(size_ - pos, len));
172 }
173
first(size_t len)174 Span first(size_t len) {
175 if (len > size_) {
176 abort();
177 }
178 return Span(data_, len);
179 }
180
last(size_t len)181 Span last(size_t len) {
182 if (len > size_) {
183 abort();
184 }
185 return Span(data_ + size_ - len, len);
186 }
187
188 private:
189 T *data_;
190 size_t size_;
191 };
192
193 template <typename T>
194 const size_t Span<T>::npos;
195
196 template <typename T>
MakeSpan(T * ptr,size_t size)197 Span<T> MakeSpan(T *ptr, size_t size) {
198 return Span<T>(ptr, size);
199 }
200
201 template <typename C>
202 auto MakeSpan(C &c) -> decltype(MakeSpan(c.data(), c.size())) {
203 return MakeSpan(c.data(), c.size());
204 }
205
206 template <typename T>
MakeConstSpan(T * ptr,size_t size)207 Span<const T> MakeConstSpan(T *ptr, size_t size) {
208 return Span<const T>(ptr, size);
209 }
210
211 template <typename C>
212 auto MakeConstSpan(const C &c) -> decltype(MakeConstSpan(c.data(), c.size())) {
213 return MakeConstSpan(c.data(), c.size());
214 }
215
216 BSSL_NAMESPACE_END
217
218 } // extern C++
219
220 #endif // !defined(BORINGSSL_NO_CXX)
221
222 #endif // OPENSSL_HEADER_SSL_SPAN_H
223