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      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 <cassert>
     26 #include <cstdlib>
     27 #include <type_traits>
     28 
     29 namespace bssl {
     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   // 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 
    162 template <typename T>
    163 const size_t Span<T>::npos;
    164 
    165 template <typename T>
    166 Span<T> MakeSpan(T *ptr, size_t size) {
    167   return Span<T>(ptr, size);
    168 }
    169 
    170 template <typename C>
    171 auto MakeSpan(C &c) -> decltype(MakeSpan(c.data(), c.size())) {
    172   return MakeSpan(c.data(), c.size());
    173 }
    174 
    175 template <typename T>
    176 Span<const T> MakeConstSpan(T *ptr, size_t size) {
    177   return Span<const T>(ptr, size);
    178 }
    179 
    180 template <typename C>
    181 auto 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