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 //
 // detail/consuming_buffers.hpp
 // ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 //
 // Copyright (c) 2003-2025 Christopher M. Kohlhoff (chris at kohlhoff 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)
 //
 
 #ifndef BOOST_ASIO_DETAIL_CONSUMING_BUFFERS_HPP
 #define BOOST_ASIO_DETAIL_CONSUMING_BUFFERS_HPP
 
 #if defined(_MSC_VER) && (_MSC_VER >= 1200)
 # pragma once
 #endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
 
 #include <boost/asio/detail/config.hpp>
 #include <cstddef>
 #include <boost/asio/buffer.hpp>
 #include <boost/asio/detail/buffer_sequence_adapter.hpp>
 #include <boost/asio/detail/limits.hpp>
 #include <boost/asio/registered_buffer.hpp>
 
 #include <boost/asio/detail/push_options.hpp>
 
 namespace boost {
 namespace asio {
 namespace detail {
 
 // Helper template to determine the maximum number of prepared buffers.
 template <typename Buffers>
 struct prepared_buffers_max
 {
   enum { value = buffer_sequence_adapter_base::max_buffers };
 };
 
 template <typename Elem, std::size_t N>
 struct prepared_buffers_max<boost::array<Elem, N>>
 {
   enum { value = N };
 };
 
 template <typename Elem, std::size_t N>
 struct prepared_buffers_max<std::array<Elem, N>>
 {
   enum { value = N };
 };
 
 // A buffer sequence used to represent a subsequence of the buffers.
 template <typename Buffer, std::size_t MaxBuffers>
 struct prepared_buffers
 {
   typedef Buffer value_type;
   typedef const Buffer* const_iterator;
 
   enum { max_buffers = MaxBuffers < 16 ? MaxBuffers : 16 };
 
   prepared_buffers() : count(0) {}
   const_iterator begin() const { return elems; }
   const_iterator end() const { return elems + count; }
 
   Buffer elems[max_buffers];
   std::size_t count;
 };
 
 // A proxy for a sub-range in a list of buffers.
 template <typename Buffer, typename Buffers, typename Buffer_Iterator>
 class consuming_buffers
 {
 public:
   typedef prepared_buffers<Buffer, prepared_buffers_max<Buffers>::value>
     prepared_buffers_type;
 
   // Construct to represent the entire list of buffers.
   explicit consuming_buffers(const Buffers& buffers)
     : buffers_(buffers),
       total_consumed_(0),
       next_elem_(0),
       next_elem_offset_(0)
   {
     using boost::asio::buffer_size;
     total_size_ = buffer_size(buffers);
   }
 
   // Determine if we are at the end of the buffers.
   bool empty() const
   {
     return total_consumed_ >= total_size_;
   }
 
   // Get the buffer for a single transfer, with a size.
   prepared_buffers_type prepare(std::size_t max_size)
   {
     prepared_buffers_type result;
 
     Buffer_Iterator next = boost::asio::buffer_sequence_begin(buffers_);
     Buffer_Iterator end = boost::asio::buffer_sequence_end(buffers_);
 
     std::advance(next, next_elem_);
     std::size_t elem_offset = next_elem_offset_;
     while (next != end && max_size > 0 && (result.count) < result.max_buffers)
     {
       Buffer next_buf = Buffer(*next) + elem_offset;
       result.elems[result.count] = boost::asio::buffer(next_buf, max_size);
       max_size -= result.elems[result.count].size();
       elem_offset = 0;
       if (result.elems[result.count].size() > 0)
         ++result.count;
       ++next;
     }
 
     return result;
   }
 
   // Consume the specified number of bytes from the buffers.
   void consume(std::size_t size)
   {
     total_consumed_ += size;
 
     Buffer_Iterator next = boost::asio::buffer_sequence_begin(buffers_);
     Buffer_Iterator end = boost::asio::buffer_sequence_end(buffers_);
 
     std::advance(next, next_elem_);
     while (next != end && size > 0)
     {
       Buffer next_buf = Buffer(*next) + next_elem_offset_;
       if (size < next_buf.size())
       {
         next_elem_offset_ += size;
         size = 0;
       }
       else
       {
         size -= next_buf.size();
         next_elem_offset_ = 0;
         ++next_elem_;
         ++next;
       }
     }
   }
 
   // Get the total number of bytes consumed from the buffers.
   std::size_t total_consumed() const
   {
     return total_consumed_;
   }
 
 private:
   Buffers buffers_;
   std::size_t total_size_;
   std::size_t total_consumed_;
   std::size_t next_elem_;
   std::size_t next_elem_offset_;
 };
 
 // Base class of all consuming_buffers specialisations for single buffers.
 template <typename Buffer>
 class consuming_single_buffer
 {
 public:
   // Construct to represent the entire list of buffers.
   template <typename Buffer1>
   explicit consuming_single_buffer(const Buffer1& buffer)
     : buffer_(buffer),
       total_consumed_(0)
   {
   }
 
   // Determine if we are at the end of the buffers.
   bool empty() const
   {
     return total_consumed_ >= buffer_.size();
   }
 
   // Get the buffer for a single transfer, with a size.
   Buffer prepare(std::size_t max_size)
   {
     return boost::asio::buffer(buffer_ + total_consumed_, max_size);
   }
 
   // Consume the specified number of bytes from the buffers.
   void consume(std::size_t size)
   {
     total_consumed_ += size;
   }
 
   // Get the total number of bytes consumed from the buffers.
   std::size_t total_consumed() const
   {
     return total_consumed_;
   }
 
 private:
   Buffer buffer_;
   std::size_t total_consumed_;
 };
 
 template <>
 class consuming_buffers<mutable_buffer, mutable_buffer, const mutable_buffer*>
   : public consuming_single_buffer<mutable_buffer>
 {
 public:
   explicit consuming_buffers(const mutable_buffer& buffer)
     : consuming_single_buffer<mutable_buffer>(buffer)
   {
   }
 };
 
 template <>
 class consuming_buffers<const_buffer, mutable_buffer, const mutable_buffer*>
   : public consuming_single_buffer<const_buffer>
 {
 public:
   explicit consuming_buffers(const mutable_buffer& buffer)
     : consuming_single_buffer<const_buffer>(buffer)
   {
   }
 };
 
 template <>
 class consuming_buffers<const_buffer, const_buffer, const const_buffer*>
   : public consuming_single_buffer<const_buffer>
 {
 public:
   explicit consuming_buffers(const const_buffer& buffer)
     : consuming_single_buffer<const_buffer>(buffer)
   {
   }
 };
 
 template <>
 class consuming_buffers<mutable_buffer,
     mutable_registered_buffer, const mutable_buffer*>
   : public consuming_single_buffer<mutable_registered_buffer>
 {
 public:
   explicit consuming_buffers(const mutable_registered_buffer& buffer)
     : consuming_single_buffer<mutable_registered_buffer>(buffer)
   {
   }
 };
 
 template <>
 class consuming_buffers<const_buffer,
     mutable_registered_buffer, const mutable_buffer*>
   : public consuming_single_buffer<mutable_registered_buffer>
 {
 public:
   explicit consuming_buffers(const mutable_registered_buffer& buffer)
     : consuming_single_buffer<mutable_registered_buffer>(buffer)
   {
   }
 };
 
 template <>
 class consuming_buffers<const_buffer,
     const_registered_buffer, const const_buffer*>
   : public consuming_single_buffer<const_registered_buffer>
 {
 public:
   explicit consuming_buffers(const const_registered_buffer& buffer)
     : consuming_single_buffer<const_registered_buffer>(buffer)
   {
   }
 };
 
 template <typename Buffer, typename Elem>
 class consuming_buffers<Buffer, boost::array<Elem, 2>,
     typename boost::array<Elem, 2>::const_iterator>
 {
 public:
   // Construct to represent the entire list of buffers.
   explicit consuming_buffers(const boost::array<Elem, 2>& buffers)
     : buffers_(buffers),
       total_consumed_(0)
   {
   }
 
   // Determine if we are at the end of the buffers.
   bool empty() const
   {
     return total_consumed_ >=
       Buffer(buffers_[0]).size() + Buffer(buffers_[1]).size();
   }
 
   // Get the buffer for a single transfer, with a size.
   boost::array<Buffer, 2> prepare(std::size_t max_size)
   {
     boost::array<Buffer, 2> result = {{
       Buffer(buffers_[0]), Buffer(buffers_[1]) }};
     std::size_t buffer0_size = result[0].size();
     result[0] = boost::asio::buffer(result[0] + total_consumed_, max_size);
     result[1] = boost::asio::buffer(
         result[1] + (total_consumed_ < buffer0_size
           ? 0 : total_consumed_ - buffer0_size),
         max_size - result[0].size());
     return result;
   }
 
   // Consume the specified number of bytes from the buffers.
   void consume(std::size_t size)
   {
     total_consumed_ += size;
   }
 
   // Get the total number of bytes consumed from the buffers.
   std::size_t total_consumed() const
   {
     return total_consumed_;
   }
 
 private:
   boost::array<Elem, 2> buffers_;
   std::size_t total_consumed_;
 };
 
 template <typename Buffer, typename Elem>
 class consuming_buffers<Buffer, std::array<Elem, 2>,
     typename std::array<Elem, 2>::const_iterator>
 {
 public:
   // Construct to represent the entire list of buffers.
   explicit consuming_buffers(const std::array<Elem, 2>& buffers)
     : buffers_(buffers),
       total_consumed_(0)
   {
   }
 
   // Determine if we are at the end of the buffers.
   bool empty() const
   {
     return total_consumed_ >=
       Buffer(buffers_[0]).size() + Buffer(buffers_[1]).size();
   }
 
   // Get the buffer for a single transfer, with a size.
   std::array<Buffer, 2> prepare(std::size_t max_size)
   {
     std::array<Buffer, 2> result = {{
       Buffer(buffers_[0]), Buffer(buffers_[1]) }};
     std::size_t buffer0_size = result[0].size();
     result[0] = boost::asio::buffer(result[0] + total_consumed_, max_size);
     result[1] = boost::asio::buffer(
         result[1] + (total_consumed_ < buffer0_size
           ? 0 : total_consumed_ - buffer0_size),
         max_size - result[0].size());
     return result;
   }
 
   // Consume the specified number of bytes from the buffers.
   void consume(std::size_t size)
   {
     total_consumed_ += size;
   }
 
   // Get the total number of bytes consumed from the buffers.
   std::size_t total_consumed() const
   {
     return total_consumed_;
   }
 
 private:
   std::array<Elem, 2> buffers_;
   std::size_t total_consumed_;
 };
 
 // Specialisation for null_buffers to ensure that the null_buffers type is
 // always passed through to the underlying read or write operation.
 template <typename Buffer>
 class consuming_buffers<Buffer, null_buffers, const mutable_buffer*>
   : public boost::asio::null_buffers
 {
 public:
   consuming_buffers(const null_buffers&)
   {
     // No-op.
   }
 
   bool empty()
   {
     return false;
   }
 
   null_buffers prepare(std::size_t)
   {
     return null_buffers();
   }
 
   void consume(std::size_t)
   {
     // No-op.
   }
 
   std::size_t total_consumed() const
   {
     return 0;
   }
 };
 
 } // namespace detail
 } // namespace asio
 } // namespace boost
 
 #include <boost/asio/detail/pop_options.hpp>
 
 #endif // BOOST_ASIO_DETAIL_CONSUMING_BUFFERS_HPP

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