text: /* Copyright (c) 2017, Google Inc.
   *
   * Permission to use, copy, modify, and/or distribute this software for any
   * purpose with or without fee is hereby granted, provided that the above
   * copyright notice and this permission notice appear in all copies.
   *
   * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
   * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
   * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
   * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
   * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
   * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
   * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */
  
  #ifndef OPENSSL_HEADER_SSL_SPAN_H
  #define OPENSSL_HEADER_SSL_SPAN_H
  
  #include <openssl/base.h>
  
  #if !defined(BORINGSSL_NO_CXX)
  
  extern "C++" {
  
  #include <stdlib.h>
  
  #include <algorithm>
  #include <type_traits>
  
  BSSL_NAMESPACE_BEGIN
  
  template <typename T>
  class Span;
  
  namespace internal {
  template <typename T>
  class SpanBase {
    // Put comparison operator implementations into a base class with const T, so
    // they can be used with any type that implicitly converts into a Span.
    static_assert(std::is_const<T>::value,
                  "Span<T> must be derived from SpanBase<const T>");
  
    friend bool operator==(Span<T> lhs, Span<T> rhs) {
      // MSVC issues warning C4996 because std::equal is unsafe. The pragma to
      // suppress the warning mysteriously has no effect, hence this
      // implementation. See
      // https://msdn.microsoft.com/en-us/library/aa985974.aspx.
      if (lhs.size() != rhs.size()) {
        return false;
      }
      for (T *l = lhs.begin(), *r = rhs.begin(); l != lhs.end() && r != rhs.end();
           ++l, ++r) {
        if (*l != *r) {
          return false;
        }
      }
      return true;
    }
  
    friend bool operator!=(Span<T> lhs, Span<T> rhs) { return !(lhs == rhs); }
  };
  }  // namespace internal
  
  // A Span<T> is a non-owning reference to a contiguous array of objects of type
  // |T|. Conceptually, a Span is a simple a pointer to |T| and a count of
  // elements accessible via that pointer. The elements referenced by the Span can
  // be mutated if |T| is mutable.
  //
  // A Span can be constructed from container types implementing |data()| and
  // |size()| methods. If |T| is constant, construction from a container type is
  // implicit. This allows writing methods that accept data from some unspecified
  // container type:
  //
  // // Foo views data referenced by v.
  // void Foo(bssl::Span<const uint8_t> v) { ... }
  //
  // std::vector<uint8_t> vec;
  // Foo(vec);
  //
  // For mutable Spans, conversion is explicit:
  //
  // // FooMutate mutates data referenced by v.
  // void FooMutate(bssl::Span<uint8_t> v) { ... }
  //
  // FooMutate(bssl::Span<uint8_t>(vec));
  //
  // You can also use the |MakeSpan| and |MakeConstSpan| factory methods to
  // construct Spans in order to deduce the type of the Span automatically.
  //
  // FooMutate(bssl::MakeSpan(vec));
  //
  // Note that Spans have value type sematics. They are cheap to construct and
  // copy, and should be passed by value whenever a method would otherwise accept
  // a reference or pointer to a container or array.
  template <typename T>
  class Span : private internal::SpanBase<const T> {
   private:
    // Heuristically test whether C is a container type that can be converted into
    // a Span by checking for data() and size() member functions.
    //
    // TODO(davidben): Switch everything to std::enable_if_t when we remove
    // support for MSVC 2015. Although we could write our own enable_if_t and MSVC
    // 2015 has std::enable_if_t anyway, MSVC 2015's SFINAE implementation is
    // problematic and does not work below unless we write the ::type at use.
    template <typename C>
    using EnableIfContainer = std::enable_if<
        std::is_convertible<decltype(std::declval<C>().data()), T *>::value &&
        std::is_integral<decltype(std::declval<C>().size())>::value>;
  
    static const size_t npos = static_cast<size_t>(-1);
  
   public:
    constexpr Span() : Span(nullptr, 0) {}
    constexpr Span(T *ptr, size_t len) : data_(ptr), size_(len) {}
  
    template <size_t N>
    constexpr Span(T (&array)[N]) : Span(array, N) {}
  
    template <
        typename C, typename = typename EnableIfContainer<C>::type,
        typename = typename std::enable_if<std::is_const<T>::value, C>::type>
    Span(const C &container) : data_(container.data()), size_(container.size()) {}
  
    template <
        typename C, typename = typename EnableIfContainer<C>::type,
        typename = typename std::enable_if<!std::is_const<T>::value, C>::type>
    explicit Span(C &container)
        : data_(container.data()), size_(container.size()) {}
  
    T *data() const { return data_; }
    size_t size() const { return size_; }
    bool empty() const { return size_ == 0; }
  
    T *begin() const { return data_; }
    const T *cbegin() const { return data_; }
    T *end() const { return data_ + size_; }
    const T *cend() const { return end(); }
  
    T &front() const {
      if (size_ == 0) {
        abort();
      }
      return data_[0];
    }
    T &back() const {
      if (size_ == 0) {
        abort();
      }
      return data_[size_ - 1];
    }
  
    T &operator[](size_t i) const {
      if (i >= size_) {
        abort();
      }
      return data_[i];
    }
    T &at(size_t i) const { return (*this)[i]; }
  
    Span subspan(size_t pos = 0, size_t len = npos) const {
      if (pos > size_) {
        abort();  // absl::Span throws an exception here.
      }
      return Span(data_ + pos, std::min(size_ - pos, len));
    }
  
   private:
    T *data_;
    size_t size_;
  };
  
  template <typename T>
  const size_t Span<T>::npos;
  
  template <typename T>
  Span<T> MakeSpan(T *ptr, size_t size) {
    return Span<T>(ptr, size);
  }
  
  template <typename C>
  auto MakeSpan(C &c) -> decltype(MakeSpan(c.data(), c.size())) {
    return MakeSpan(c.data(), c.size());
  }
  
  template <typename T>
  Span<const T> MakeConstSpan(T *ptr, size_t size) {
    return Span<const T>(ptr, size);
  }
  
  template <typename C>
  auto MakeConstSpan(const C &c) -> decltype(MakeConstSpan(c.data(), c.size())) {
    return MakeConstSpan(c.data(), c.size());
  }
  
  BSSL_NAMESPACE_END
  
  }  // extern C++
  
  #endif  // !defined(BORINGSSL_NO_CXX)
  
  #endif  // OPENSSL_HEADER_SSL_SPAN_H
  