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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 <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:
    111   constexpr Span() : Span(nullptr, 0) {}
    112   constexpr Span(T *ptr, size_t len) : data_(ptr), size_(len) {}
    113 
    114   template <size_t 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>
    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>
    125   explicit Span(C &container)
    126       : data_(container.data()), size_(container.size()) {}
    127 
    128   T *data() const { return data_; }
    129   size_t size() const { return size_; }
    130   bool empty() const { return size_ == 0; }
    131 
    132   T *begin() const { return data_; }
    133   const T *cbegin() const { return data_; }
    134   T *end() const { return data_ + size_; }
    135   const T *cend() const { return end(); }
    136 
    137   T &front() const {
    138     if (size_ == 0) {
    139       abort();
    140     }
    141     return data_[0];
    142   }
    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   }
    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>
    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>
    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