Line data    Source code

       1             : //
       2             : // Copyright (c) 2023 Vinnie Falco (vinnie.falco@gmail.com)
       3             : //
       4             : // Distributed under the Boost Software License, Version 1.0. (See accompanying
       5             : // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
       6             : //
       7             : // Official repository: https://github.com/cppalliance/http_proto
       8             : //
       9             : 
      10             : #ifndef BOOST_HTTP_PROTO_BUFFERED_BASE_HPP
      11             : #define BOOST_HTTP_PROTO_BUFFERED_BASE_HPP
      12             : 
      13             : #include <boost/http_proto/detail/config.hpp>
      14             : #include <cstddef>
      15             : 
      16             : namespace boost {
      17             : namespace http_proto {
      18             : 
      19             : /** Base class for buffered algorithms
      20             : 
      21             :     Algorithms implementing @ref filter,
      22             :     @ref source, or @ref sink inherit from
      23             :     this common interface.
      24             : */
      25             : struct BOOST_HTTP_PROTO_DECL
      26          27 :     buffered_base
      27             : {
      28             :     /** Allocator for buffered algorithms.
      29             :     */
      30             :     class allocator;
      31             : 
      32             :     /** Destructor.
      33             :     */
      34             :     virtual
      35             :     ~buffered_base();
      36             : 
      37             :     /** Initialize the algorithm.
      38             : 
      39             :         The derived class must be initialized
      40             :         before invoking any other members,
      41             :         except destruction.
      42             :         The default implementation does nothing.
      43             :         The purpose of this function is to
      44             :         allow the derived class to optionally
      45             :         allocate temporary storage using the
      46             :         specified allocator, which could offer
      47             :         advantages.
      48             :         <br>
      49             :         Subclasses are still required to operate
      50             :         correctly even when insufficient storage
      51             :         is available from the allocator. In this
      52             :         case they should simply allocate normally.
      53             : 
      54             :         @par Preconditions
      55             :         Initialization has not already occurred.
      56             : 
      57             :         @param a The allocator to use.
      58             :     */
      59             :     void
      60          17 :     init(allocator& a)
      61             :     {
      62          17 :         on_init(a);
      63          14 :     }
      64             : 
      65             :     /** Initialize the algorithm.
      66             : 
      67             :         The derived class must be initialized
      68             :         before invoking any other members,
      69             :         except destruction.
      70             :         The default implementation does nothing.
      71             :         The purpose of this function is to
      72             :         allow the derived class to optionally
      73             :         allocate temporary storage using the
      74             :         specified allocator, which could offer
      75             :         advantages.
      76             :         <br>
      77             :         Subclasses are still required to operate
      78             :         correctly even when insufficient storage
      79             :         is available from the allocator. In this
      80             :         case they should simply allocate normally.
      81             : 
      82             :         @par Preconditions
      83             :         Initialization has not already occurred.
      84             : 
      85             :         @throws std::invalid_argument `max_size > a.max_size()`
      86             : 
      87             :         @param a The allocator to use.
      88             : 
      89             :         @param max_size The largest allowed
      90             :             total amount of bytes for the
      91             :             allocator.
      92             :     */
      93             :     void
      94             :     init(
      95             :         allocator& a,
      96             :         std::size_t max_size);
      97             : 
      98             : protected:
      99             :     /** Initialize the algorithm.
     100             : 
     101             :         The default implementation does nothing.
     102             :         The purpose of this function is to
     103             :         allow the derived class to optionally
     104             :         allocate temporary storage using the
     105             :         specified allocator, which could offer
     106             :         advantages.
     107             :         <br>
     108             :         Subclasses are still required to operate
     109             :         correctly even when insufficient storage
     110             :         is available from the allocator. In this
     111             :         case they should simply allocate normally.
     112             : 
     113             :         @par Preconditions
     114             :         Initialization has not already occurred.
     115             : 
     116             :         @param a The allocator to use.
     117             :     */
     118             :     virtual
     119             :     void
     120             :     on_init(allocator& a);
     121             : };
     122             : 
     123             : //------------------------------------------------
     124             : 
     125             : /** Provides memory to buffered algorithms.
     126             : */
     127             : class buffered_base::allocator
     128             : {
     129             : public:
     130             :     /** Constructor
     131             : 
     132             :         Default constructed objects return
     133             :         zero from @ref max_size.
     134             :     */
     135             :     allocator() = default;
     136             : 
     137             :     /** Constructor
     138             : 
     139             :         This function constructs an allocator
     140             :         which uses the specified contiguous
     141             :         buffer. Calls to allocate will return
     142             :         parcels of the buffer from either the
     143             :         beginning or the end depending on the
     144             :         value of `downwards`.
     145             : 
     146             :         @par Preconditions
     147             :         @code
     148             :         p != nullptr || n == 0
     149             :         @endcode
     150             : 
     151             :         @par Exception Safety
     152             :         Throws nothing.
     153             : 
     154             :         @param p A pointer to contiguous storage.
     155             :             This may be `nullptr` if `n == 0`.
     156             : 
     157             :         @param n The number of valid bytes of
     158             :             storage pointed to by p. This may
     159             :             be zero.
     160             : 
     161             :         @param downwards When true, calls to
     162             :             allocate will return storage from
     163             :             the end of the memory pointed to
     164             :             by `p` rather than the beginning.
     165             :     */
     166          12 :     allocator(
     167             :         void* p,
     168             :         std::size_t n,
     169             :         bool downwards) noexcept
     170          12 :         : base_(static_cast<
     171             :             unsigned char*>(p))
     172             :         , size_(n)
     173          12 :         , down_(downwards)
     174             :     {
     175          12 :     }
     176             : 
     177             :     /** The maximum amount that can be successfully returned from reserve
     178             :     */
     179             :     std::size_t
     180          38 :     max_size() const noexcept
     181             :     {
     182          38 :         return size_;
     183             :     }
     184             : 
     185             :     /** Return the total number of bytes allocated
     186             :     */
     187             :     std::size_t
     188          18 :     size_used() const noexcept
     189             :     {
     190          18 :         return size_used_;
     191             :     }
     192             : 
     193             :     /** Return a pointer to at least n bytes of contiguous storage
     194             : 
     195             :         Allocated storage will be automatically
     196             :         deallocated when the @ref filter,
     197             :         @ref sink, or @ref source is destroyed.
     198             : 
     199             :         @throws std::invalid_argument `n > max_size()`
     200             : 
     201             :         @return A pointer to uninitialized storage.
     202             : 
     203             :         @param n The number of bytes.
     204             :     */
     205             :     BOOST_HTTP_PROTO_DECL
     206             :     void*
     207             :     allocate(std::size_t n);
     208             : 
     209             : private:
     210             :     void
     211           7 :     remove(
     212             :         std::size_t n) noexcept
     213             :     {
     214           7 :         if(down_)
     215           2 :             base_ += n;
     216           7 :         size_ -= n;
     217           7 :     }
     218             : 
     219             :     void
     220           7 :     restore(
     221             :         std::size_t n) noexcept
     222             :     {
     223           7 :         if(down_)
     224           2 :             base_ -= n;
     225           7 :         size_ += n;
     226           7 :     }
     227             : 
     228             :     friend struct buffered_base;
     229             : 
     230             :     unsigned char* base_ = nullptr;
     231             :     std::size_t size_ = 0;
     232             :     std::size_t size_used_ = 0;
     233             :     bool down_ = false;
     234             : };
     235             : 
     236             : } // http_proto
     237             : } // boost
     238             : 
     239             : #endif