text: //
  // Copyright (c) 2016-2017 Vinnie Falco (vinnie dot falco at gmail dot com)
  //
  // Distributed under the Boost Software License, Version 1.0. (See accompanying
  // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
  //
  // Official repository: https://github.com/boostorg/beast
  //
  
  #ifndef BOOST_BEAST_HTTP_FIELDS_HPP
  #define BOOST_BEAST_HTTP_FIELDS_HPP
  
  #include <boost/beast/core/detail/config.hpp>
  #include <boost/beast/core/string_param.hpp>
  #include <boost/beast/core/string.hpp>
  #include <boost/beast/core/detail/allocator.hpp>
  #include <boost/beast/core/detail/empty_base_optimization.hpp>
  #include <boost/beast/http/field.hpp>
  #include <boost/asio/buffer.hpp>
  #include <boost/intrusive/list.hpp>
  #include <boost/intrusive/set.hpp>
  #include <boost/optional.hpp>
  #include <algorithm>
  #include <cctype>
  #include <cstring>
  #include <memory>
  #include <string>
  #include <type_traits>
  #include <utility>
  
  namespace boost {
  namespace beast {
  namespace http {
  
  /** A container for storing HTTP header fields.
  
      This container is designed to store the field value pairs that make
      up the fields and trailers in an HTTP message. Objects of this type
      are iterable, with each element holding the field name and field
      value.
  
      Field names are stored as-is, but comparisons are case-insensitive.
      The container behaves as a `std::multiset`; there will be a separate
      value for each occurrence of the same field name. When the container
      is iterated the fields are presented in the order of insertion, with
      fields having the same name following each other consecutively.
  
      Meets the requirements of @b Fields
  
      @tparam Allocator The allocator to use. This must meet the
      requirements of @b Allocator.
  */
  template<class Allocator>
  class basic_fields
  #ifndef BOOST_BEAST_DOXYGEN
      : private beast::detail::empty_base_optimization<Allocator>
  #endif
  {
      // Fancy pointers are not supported
      static_assert(std::is_pointer<typename
          std::allocator_traits<Allocator>::pointer>::value,
          "Allocator must use regular pointers");
  
      friend class fields_test; // for `header`
  
      static std::size_t constexpr max_static_buffer = 4096;
  
      using off_t = std::uint16_t;
  
  public:
      /// The type of allocator used.
      using allocator_type = Allocator;
  
      /// The type of element used to represent a field 
      class value_type
      {
          friend class basic_fields;
  
          boost::asio::const_buffer
          buffer() const;
  
          value_type(field name,
              string_view sname, string_view value);
  
          boost::intrusive::list_member_hook<
              boost::intrusive::link_mode<
                  boost::intrusive::normal_link>>
                      list_hook_;
          boost::intrusive::set_member_hook<
              boost::intrusive::link_mode<
                  boost::intrusive::normal_link>>
                      set_hook_;
          off_t off_;
          off_t len_;
          field f_;
  
      public:
          /// Constructor (deleted)
          value_type(value_type const&) = delete;
  
          /// Assignment (deleted)
          value_type& operator=(value_type const&) = delete;
  
          /// Returns the field enum, which can be @ref field::unknown
          field
          name() const;
  
          /// Returns the field name as a string
          string_view const
          name_string() const;
  
          /// Returns the value of the field
          string_view const
          value() const;
      };
  
      /** A strictly less predicate for comparing keys, using a case-insensitive comparison.
  
          The case-comparison operation is defined only for low-ASCII characters.
      */
      struct key_compare : beast::iless
      {
          /// Returns `true` if lhs is less than rhs using a strict ordering
          template<class String>
          bool
          operator()(
              String const& lhs,
              value_type const& rhs) const noexcept
          {
              if(lhs.size() < rhs.name_string().size())
                  return true;
              if(lhs.size() > rhs.name_string().size())
                  return false;
              return iless::operator()(lhs, rhs.name_string());
          }
  
          /// Returns `true` if lhs is less than rhs using a strict ordering
          template<class String>
          bool
          operator()(
              value_type const& lhs,
              String const& rhs) const noexcept
          {
              if(lhs.name_string().size() < rhs.size())
                  return true;
              if(lhs.name_string().size() > rhs.size())
                  return false;
              return iless::operator()(lhs.name_string(), rhs);
          }
  
          /// Returns `true` if lhs is less than rhs using a strict ordering
          bool
          operator()(
              value_type const& lhs,
              value_type const& rhs) const noexcept
          {
              if(lhs.name_string().size() < rhs.name_string().size())
                  return true;
              if(lhs.name_string().size() > rhs.name_string().size())
                  return false;
              return iless::operator()(lhs.name_string(), rhs.name_string());
          }
      };
  
      /// The algorithm used to serialize the header
  #if BOOST_BEAST_DOXYGEN
      using writer = implementation_defined;
  #else
      class writer;
  #endif
  
  private:
      using list_t = typename boost::intrusive::make_list<
          value_type, boost::intrusive::member_hook<
              value_type, boost::intrusive::list_member_hook<
                  boost::intrusive::link_mode<
                      boost::intrusive::normal_link>>,
                          &value_type::list_hook_>,
                              boost::intrusive::constant_time_size<
                                  false>>::type;
  
      using set_t = typename boost::intrusive::make_multiset<
          value_type, boost::intrusive::member_hook<value_type,
              boost::intrusive::set_member_hook<
                  boost::intrusive::link_mode<
                      boost::intrusive::normal_link>>,
                          &value_type::set_hook_>,
                              boost::intrusive::constant_time_size<true>,
                                  boost::intrusive::compare<key_compare>>::type;
  
      using align_type = typename
          boost::type_with_alignment<alignof(value_type)>::type;
  
      using rebind_type = typename
          beast::detail::allocator_traits<Allocator>::
              template rebind_alloc<align_type>;
  
      using alloc_traits =
          beast::detail::allocator_traits<rebind_type>;
  
      using size_type = typename
          beast::detail::allocator_traits<Allocator>::size_type;
  
  
  public:
      /// Destructor
      ~basic_fields();
  
      /// Constructor.
      basic_fields() = default;
  
      /** Constructor.
  
          @param alloc The allocator to use.
      */
      explicit
      basic_fields(Allocator const& alloc) noexcept;
  
      /** Move constructor.
  
          The state of the moved-from object is
          as if constructed using the same allocator.
      */
      basic_fields(basic_fields&&) noexcept;
  
      /** Move constructor.
  
          The state of the moved-from object is
          as if constructed using the same allocator.
  
          @param alloc The allocator to use.
      */
      basic_fields(basic_fields&&, Allocator const& alloc);
  
      /// Copy constructor.
      basic_fields(basic_fields const&);
  
      /** Copy constructor.
  
          @param alloc The allocator to use.
      */
      basic_fields(basic_fields const&, Allocator const& alloc);
  
      /// Copy constructor.
      template<class OtherAlloc>
      basic_fields(basic_fields<OtherAlloc> const&);
  
      /** Copy constructor.
  
          @param alloc The allocator to use.
      */
      template<class OtherAlloc>
      basic_fields(basic_fields<OtherAlloc> const&,
          Allocator const& alloc);
  
      /** Move assignment.
  
          The state of the moved-from object is
          as if constructed using the same allocator.
      */
      basic_fields& operator=(basic_fields&&) noexcept(
          alloc_traits::propagate_on_container_move_assignment::value);
  
      /// Copy assignment.
      basic_fields& operator=(basic_fields const&);
  
      /// Copy assignment.
      template<class OtherAlloc>
      basic_fields& operator=(basic_fields<OtherAlloc> const&);
  
  public:
      /// A constant iterator to the field sequence.
  #if BOOST_BEAST_DOXYGEN
      using const_iterator = implementation_defined;
  #else
      using const_iterator = typename list_t::const_iterator;
  #endif
  
      /// A constant iterator to the field sequence.
      using iterator = const_iterator;
  
      /// Return a copy of the allocator associated with the container.
      allocator_type
      get_allocator() const
      {
          return this->member();
      }
  
      //--------------------------------------------------------------------------
      //
      // Element access
      //
      //--------------------------------------------------------------------------
  
      /** Returns the value for a field, or throws an exception.
  
          If more than one field with the specified name exists, the
          first field defined by insertion order is returned.
  
          @param name The name of the field.
  
          @return The field value.
  
          @throws std::out_of_range if the field is not found.
      */
      string_view const
      at(field name) const;
  
      /** Returns the value for a field, or throws an exception.
  
          If more than one field with the specified name exists, the
          first field defined by insertion order is returned.
  
          @param name The name of the field.
  
          @return The field value.
  
          @throws std::out_of_range if the field is not found.
      */
      string_view const
      at(string_view name) const;
  
      /** Returns the value for a field, or `""` if it does not exist.
  
          If more than one field with the specified name exists, the
          first field defined by insertion order is returned.
  
          @param name The name of the field.
      */
      string_view const
      operator[](field name) const;
  
      /** Returns the value for a case-insensitive matching header, or `""` if it does not exist.
  
          If more than one field with the specified name exists, the
          first field defined by insertion order is returned.
  
          @param name The name of the field.
      */
      string_view const
      operator[](string_view name) const;
  
      //--------------------------------------------------------------------------
      //
      // Iterators
      //
      //--------------------------------------------------------------------------
  
      /// Return a const iterator to the beginning of the field sequence.
      const_iterator
      begin() const
      {
          return list_.cbegin();
      }
  
      /// Return a const iterator to the end of the field sequence.
      const_iterator
      end() const
      {
          return list_.cend();
      }
  
      /// Return a const iterator to the beginning of the field sequence.
      const_iterator
      cbegin() const
      {
          return list_.cbegin();
      }
  
      /// Return a const iterator to the end of the field sequence.
      const_iterator
      cend() const
      {
          return list_.cend();
      }
  
      //--------------------------------------------------------------------------
      //
      // Capacity
      //
      //--------------------------------------------------------------------------
  
  private:
      // VFALCO Since the header and message derive from Fields,
      //        what does the expression m.empty() mean? Its confusing.
      bool
      empty() const
      {
          return list_.empty();
      }
  public:
  
      //--------------------------------------------------------------------------
      //
      // Modifiers
      //
      //--------------------------------------------------------------------------
  
      /** Remove all fields from the container
  
          All references, pointers, or iterators referring to contained
          elements are invalidated. All past-the-end iterators are also
          invalidated.
  
          @par Postconditions:
          @code
              std::distance(this->begin(), this->end()) == 0
          @endcode
      */
      void
      clear();
  
      /** Insert a field.
  
          If one or more fields with the same name already exist,
          the new field will be inserted after the last field with
          the matching name, in serialization order.
  
          @param name The field name.
  
          @param value The value of the field, as a @ref string_param
      */
      void
      insert(field name, string_param const& value);
  
      /** Insert a field.
  
          If one or more fields with the same name already exist,
          the new field will be inserted after the last field with
          the matching name, in serialization order.
  
          @param name The field name.
  
          @param value The value of the field, as a @ref string_param
      */
      void
      insert(string_view name, string_param const& value);
  
      /** Insert a field.
  
          If one or more fields with the same name already exist,
          the new field will be inserted after the last field with
          the matching name, in serialization order.
  
          @param name The field name.
  
          @param name_string The literal text corresponding to the
          field name. If `name != field::unknown`, then this value
          must be equal to `to_string(name)` using a case-insensitive
          comparison, otherwise the behavior is undefined.
  
          @param value The value of the field, as a @ref string_param
      */
      void
      insert(field name, string_view name_string,
          string_param const& value);
  
      /** Set a field value, removing any other instances of that field.
  
          First removes any values with matching field names, then
          inserts the new field value.
  
          @param name The field name.
  
          @param value The value of the field, as a @ref string_param
  
          @return The field value.
      */
      void
      set(field name, string_param const& value);
  
      /** Set a field value, removing any other instances of that field.
  
          First removes any values with matching field names, then
          inserts the new field value.
  
          @param name The field name.
  
          @param value The value of the field, as a @ref string_param
      */
      void
      set(string_view name, string_param const& value);
  
      /** Remove a field.
  
          References and iterators to the erased elements are
          invalidated. Other references and iterators are not
          affected.
  
          @param pos An iterator to the element to remove.
  
          @return An iterator following the last removed element.
          If the iterator refers to the last element, the end()
          iterator is returned.
      */
      const_iterator
      erase(const_iterator pos);
  
      /** Remove all fields with the specified name.
  
          All fields with the same field name are erased from the
          container.
          References and iterators to the erased elements are
          invalidated. Other references and iterators are not
          affected.
  
          @param name The field name.
  
          @return The number of fields removed.
      */
      std::size_t
      erase(field name);
  
      /** Remove all fields with the specified name.
  
          All fields with the same field name are erased from the
          container.
          References and iterators to the erased elements are
          invalidated. Other references and iterators are not
          affected.
  
          @param name The field name.
  
          @return The number of fields removed.
      */
      std::size_t
      erase(string_view name);
  
      /** Return a buffer sequence representing the trailers.
  
          This function returns a buffer sequence holding the
          serialized representation of the trailer fields promised
          in the Accept field. Before calling this function the
          Accept field must contain the exact trailer fields
          desired. Each field must also exist.
      */
  
  
      /// Swap this container with another
      void
      swap(basic_fields& other);
  
      /// Swap two field containers
      template<class Alloc>
      friend
      void
      swap(basic_fields<Alloc>& lhs, basic_fields<Alloc>& rhs);
  
      //--------------------------------------------------------------------------
      //
      // Lookup
      //
      //--------------------------------------------------------------------------
  
      /** Return the number of fields with the specified name.
  
          @param name The field name.
      */
      std::size_t
      count(field name) const;
  
      /** Return the number of fields with the specified name.
  
          @param name The field name.
      */
      std::size_t
      count(string_view name) const;
  
      /** Returns an iterator to the case-insensitive matching field.
  
          If more than one field with the specified name exists, the
          first field defined by insertion order is returned.
  
          @param name The field name.
  
          @return An iterator to the matching field, or `end()` if
          no match was found.
      */
      const_iterator
      find(field name) const;
  
      /** Returns an iterator to the case-insensitive matching field name.
  
          If more than one field with the specified name exists, the
          first field defined by insertion order is returned.
  
          @param name The field name.
  
          @return An iterator to the matching field, or `end()` if
          no match was found.
      */
      const_iterator
      find(string_view name) const;
  
      /** Returns a range of iterators to the fields with the specified name.
  
          @param name The field name.
  
          @return A range of iterators to fields with the same name,
          otherwise an empty range.
      */
      std::pair<const_iterator, const_iterator>
      equal_range(field name) const;
  
      /** Returns a range of iterators to the fields with the specified name.
  
          @param name The field name.
  
          @return A range of iterators to fields with the same name,
          otherwise an empty range.
      */
      std::pair<const_iterator, const_iterator>
      equal_range(string_view name) const;
  
      //--------------------------------------------------------------------------
      //
      // Observers
      //
      //--------------------------------------------------------------------------
  
      /// Returns a copy of the key comparison function
      key_compare
      key_comp() const
      {
          return key_compare{};
      }
  
  protected:
      /** Returns the request-method string.
  
          @note Only called for requests.
      */
      string_view
      get_method_impl() const;
  
      /** Returns the request-target string.
  
          @note Only called for requests.
      */
      string_view
      get_target_impl() const;
  
      /** Returns the response reason-phrase string.
  
          @note Only called for responses.
      */
      string_view
      get_reason_impl() const;
  
      /** Returns the chunked Transfer-Encoding setting
      */
      bool
      get_chunked_impl() const;
  
      /** Returns the keep-alive setting
      */
      bool
      get_keep_alive_impl(unsigned version) const;
  
      /** Returns `true` if the Content-Length field is present.
      */
      bool
      has_content_length_impl() const;
  
      /** Set or clear the method string.
  
          @note Only called for requests.
      */
      void
      set_method_impl(string_view s);
  
      /** Set or clear the target string.
  
          @note Only called for requests.
      */
      void
      set_target_impl(string_view s);
  
      /** Set or clear the reason string.
  
          @note Only called for responses.
      */
      void
      set_reason_impl(string_view s);
  
      /** Adjusts the chunked Transfer-Encoding value
      */
      void
      set_chunked_impl(bool value);
  
      /** Sets or clears the Content-Length field
      */
      void
      set_content_length_impl(
          boost::optional<std::uint64_t> const& value);
  
      /** Adjusts the Connection field
      */
      void
      set_keep_alive_impl(
          unsigned version, bool keep_alive);
  
  private:
      template<class OtherAlloc>
      friend class basic_fields;
  
      value_type&
      new_element(field name,
          string_view sname, string_view value);
  
      void
      delete_element(value_type& e);
  
      void
      set_element(value_type& e);
  
      void
      realloc_string(string_view& dest, string_view s);
  
      void
      realloc_target(
          string_view& dest, string_view s);
  
      template<class OtherAlloc>
      void
      copy_all(basic_fields<OtherAlloc> const&);
  
      void
      clear_all();
  
      void
      delete_list();
  
      void
      move_assign(basic_fields&, std::true_type);
  
      void
      move_assign(basic_fields&, std::false_type);
  
      void
      copy_assign(basic_fields const&, std::true_type);
  
      void
      copy_assign(basic_fields const&, std::false_type);
  
      void
      swap(basic_fields& other, std::true_type);
  
      void
      swap(basic_fields& other, std::false_type);
  
      set_t set_;
      list_t list_;
      string_view method_;
      string_view target_or_reason_;
  };
  
  /// A typical HTTP header fields container
  using fields = basic_fields<std::allocator<char>>;
  
  } // http
  } // beast
  } // boost
  
  #include <boost/beast/http/impl/fields.ipp>
  
  #endif
  