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 //
 // basic_streambuf.hpp
 // ~~~~~~~~~~~~~~~~~~~
 //
 // Copyright (c) 2003-2023 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_BASIC_STREAMBUF_HPP
 #define BOOST_ASIO_BASIC_STREAMBUF_HPP
 
 #if defined(_MSC_VER) && (_MSC_VER >= 1200)
 # pragma once
 #endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
 
 #include <boost/asio/detail/config.hpp>
 
 #if !defined(BOOST_ASIO_NO_IOSTREAM)
 
 #include <algorithm>
 #include <cstring>
 #include <stdexcept>
 #include <streambuf>
 #include <vector>
 #include <boost/asio/basic_streambuf_fwd.hpp>
 #include <boost/asio/buffer.hpp>
 #include <boost/asio/detail/limits.hpp>
 #include <boost/asio/detail/noncopyable.hpp>
 #include <boost/asio/detail/throw_exception.hpp>
 
 #include <boost/asio/detail/push_options.hpp>
 
 namespace boost {
 namespace asio {
 
 /// Automatically resizable buffer class based on std::streambuf.
 /**
  * The @c basic_streambuf class is derived from @c std::streambuf to associate
  * the streambuf's input and output sequences with one or more character
  * arrays. These character arrays are internal to the @c basic_streambuf
  * object, but direct access to the array elements is provided to permit them
  * to be used efficiently with I/O operations. Characters written to the output
  * sequence of a @c basic_streambuf object are appended to the input sequence
  * of the same object.
  *
  * The @c basic_streambuf class's public interface is intended to permit the
  * following implementation strategies:
  *
  * @li A single contiguous character array, which is reallocated as necessary
  * to accommodate changes in the size of the character sequence. This is the
  * implementation approach currently used in Asio.
  *
  * @li A sequence of one or more character arrays, where each array is of the
  * same size. Additional character array objects are appended to the sequence
  * to accommodate changes in the size of the character sequence.
  *
  * @li A sequence of one or more character arrays of varying sizes. Additional
  * character array objects are appended to the sequence to accommodate changes
  * in the size of the character sequence.
  *
  * The constructor for basic_streambuf accepts a @c size_t argument specifying
  * the maximum of the sum of the sizes of the input sequence and output
  * sequence. During the lifetime of the @c basic_streambuf object, the following
  * invariant holds:
  * @code size() <= max_size()@endcode
  * Any member function that would, if successful, cause the invariant to be
  * violated shall throw an exception of class @c std::length_error.
  *
  * The constructor for @c basic_streambuf takes an Allocator argument. A copy
  * of this argument is used for any memory allocation performed, by the
  * constructor and by all member functions, during the lifetime of each @c
  * basic_streambuf object.
  *
  * @par Examples
  * Writing directly from an streambuf to a socket:
  * @code
  * boost::asio::streambuf b;
  * std::ostream os(&b);
  * os << "Hello, World!\n";
  *
  * // try sending some data in input sequence
  * size_t n = sock.send(b.data());
  *
  * b.consume(n); // sent data is removed from input sequence
  * @endcode
  *
  * Reading from a socket directly into a streambuf:
  * @code
  * boost::asio::streambuf b;
  *
  * // reserve 512 bytes in output sequence
  * boost::asio::streambuf::mutable_buffers_type bufs = b.prepare(512);
  *
  * size_t n = sock.receive(bufs);
  *
  * // received data is "committed" from output sequence to input sequence
  * b.commit(n);
  *
  * std::istream is(&b);
  * std::string s;
  * is >> s;
  * @endcode
  */
 #if defined(GENERATING_DOCUMENTATION)
 template <typename Allocator = std::allocator<char>>
 #else
 template <typename Allocator>
 #endif
 class basic_streambuf
   : public std::streambuf,
     private noncopyable
 {
 public:
 #if defined(GENERATING_DOCUMENTATION)
   /// The type used to represent the input sequence as a list of buffers.
   typedef implementation_defined const_buffers_type;
 
   /// The type used to represent the output sequence as a list of buffers.
   typedef implementation_defined mutable_buffers_type;
 #else
   typedef BOOST_ASIO_CONST_BUFFER const_buffers_type;
   typedef BOOST_ASIO_MUTABLE_BUFFER mutable_buffers_type;
 #endif
 
   /// Construct a basic_streambuf object.
   /**
    * Constructs a streambuf with the specified maximum size. The initial size
    * of the streambuf's input sequence is 0.
    */
   explicit basic_streambuf(
       std::size_t maximum_size = (std::numeric_limits<std::size_t>::max)(),
       const Allocator& allocator = Allocator())
     : max_size_(maximum_size),
       buffer_(allocator)
   {
     std::size_t pend = (std::min<std::size_t>)(max_size_, buffer_delta);
     buffer_.resize((std::max<std::size_t>)(pend, 1));
     setg(&buffer_[0], &buffer_[0], &buffer_[0]);
     setp(&buffer_[0], &buffer_[0] + pend);
   }
 
   /// Get the size of the input sequence.
   /**
    * @returns The size of the input sequence. The value is equal to that
    * calculated for @c s in the following code:
    * @code
    * size_t s = 0;
    * const_buffers_type bufs = data();
    * const_buffers_type::const_iterator i = bufs.begin();
    * while (i != bufs.end())
    * {
    *   const_buffer buf(*i++);
    *   s += buf.size();
    * }
    * @endcode
    */
   std::size_t size() const noexcept
   {
     return pptr() - gptr();
   }
 
   /// Get the maximum size of the basic_streambuf.
   /**
    * @returns The allowed maximum of the sum of the sizes of the input sequence
    * and output sequence.
    */
   std::size_t max_size() const noexcept
   {
     return max_size_;
   }
 
   /// Get the current capacity of the basic_streambuf.
   /**
    * @returns The current total capacity of the streambuf, i.e. for both the
    * input sequence and output sequence.
    */
   std::size_t capacity() const noexcept
   {
     return buffer_.capacity();
   }
 
   /// Get a list of buffers that represents the input sequence.
   /**
    * @returns An object of type @c const_buffers_type that satisfies
    * ConstBufferSequence requirements, representing all character arrays in the
    * input sequence.
    *
    * @note The returned object is invalidated by any @c basic_streambuf member
    * function that modifies the input sequence or output sequence.
    */
   const_buffers_type data() const noexcept
   {
     return boost::asio::buffer(boost::asio::const_buffer(gptr(),
           (pptr() - gptr()) * sizeof(char_type)));
   }
 
   /// Get a list of buffers that represents the output sequence, with the given
   /// size.
   /**
    * Ensures that the output sequence can accommodate @c n characters,
    * reallocating character array objects as necessary.
    *
    * @returns An object of type @c mutable_buffers_type that satisfies
    * MutableBufferSequence requirements, representing character array objects
    * at the start of the output sequence such that the sum of the buffer sizes
    * is @c n.
    *
    * @throws std::length_error If <tt>size() + n > max_size()</tt>.
    *
    * @note The returned object is invalidated by any @c basic_streambuf member
    * function that modifies the input sequence or output sequence.
    */
   mutable_buffers_type prepare(std::size_t n)
   {
     reserve(n);
     return boost::asio::buffer(boost::asio::mutable_buffer(
           pptr(), n * sizeof(char_type)));
   }
 
   /// Move characters from the output sequence to the input sequence.
   /**
    * Appends @c n characters from the start of the output sequence to the input
    * sequence. The beginning of the output sequence is advanced by @c n
    * characters.
    *
    * Requires a preceding call <tt>prepare(x)</tt> where <tt>x >= n</tt>, and
    * no intervening operations that modify the input or output sequence.
    *
    * @note If @c n is greater than the size of the output sequence, the entire
    * output sequence is moved to the input sequence and no error is issued.
    */
   void commit(std::size_t n)
   {
     n = std::min<std::size_t>(n, epptr() - pptr());
     pbump(static_cast<int>(n));
     setg(eback(), gptr(), pptr());
   }
 
   /// Remove characters from the input sequence.
   /**
    * Removes @c n characters from the beginning of the input sequence.
    *
    * @note If @c n is greater than the size of the input sequence, the entire
    * input sequence is consumed and no error is issued.
    */
   void consume(std::size_t n)
   {
     if (egptr() < pptr())
       setg(&buffer_[0], gptr(), pptr());
     if (gptr() + n > pptr())
       n = pptr() - gptr();
     gbump(static_cast<int>(n));
   }
 
 protected:
   enum { buffer_delta = 128 };
 
   /// Override std::streambuf behaviour.
   /**
    * Behaves according to the specification of @c std::streambuf::underflow().
    */
   int_type underflow()
   {
     if (gptr() < pptr())
     {
       setg(&buffer_[0], gptr(), pptr());
       return traits_type::to_int_type(*gptr());
     }
     else
     {
       return traits_type::eof();
     }
   }
 
   /// Override std::streambuf behaviour.
   /**
    * Behaves according to the specification of @c std::streambuf::overflow(),
    * with the specialisation that @c std::length_error is thrown if appending
    * the character to the input sequence would require the condition
    * <tt>size() > max_size()</tt> to be true.
    */
   int_type overflow(int_type c)
   {
     if (!traits_type::eq_int_type(c, traits_type::eof()))
     {
       if (pptr() == epptr())
       {
         std::size_t buffer_size = pptr() - gptr();
         if (buffer_size < max_size_ && max_size_ - buffer_size < buffer_delta)
         {
           reserve(max_size_ - buffer_size);
         }
         else
         {
           reserve(buffer_delta);
         }
       }
 
       *pptr() = traits_type::to_char_type(c);
       pbump(1);
       return c;
     }
 
     return traits_type::not_eof(c);
   }
 
   void reserve(std::size_t n)
   {
     // Get current stream positions as offsets.
     std::size_t gnext = gptr() - &buffer_[0];
     std::size_t pnext = pptr() - &buffer_[0];
     std::size_t pend = epptr() - &buffer_[0];
 
     // Check if there is already enough space in the put area.
     if (n <= pend - pnext)
     {
       return;
     }
 
     // Shift existing contents of get area to start of buffer.
     if (gnext > 0)
     {
       pnext -= gnext;
       std::memmove(&buffer_[0], &buffer_[0] + gnext, pnext);
     }
 
     // Ensure buffer is large enough to hold at least the specified size.
     if (n > pend - pnext)
     {
       if (n <= max_size_ && pnext <= max_size_ - n)
       {
         pend = pnext + n;
         buffer_.resize((std::max<std::size_t>)(pend, 1));
       }
       else
       {
         std::length_error ex("boost::asio::streambuf too long");
         boost::asio::detail::throw_exception(ex);
       }
     }
 
     // Update stream positions.
     setg(&buffer_[0], &buffer_[0], &buffer_[0] + pnext);
     setp(&buffer_[0] + pnext, &buffer_[0] + pend);
   }
 
 private:
   std::size_t max_size_;
   std::vector<char_type, Allocator> buffer_;
 
   // Helper function to get the preferred size for reading data.
   friend std::size_t read_size_helper(
       basic_streambuf& sb, std::size_t max_size)
   {
     return std::min<std::size_t>(
         std::max<std::size_t>(512, sb.buffer_.capacity() - sb.size()),
         std::min<std::size_t>(max_size, sb.max_size() - sb.size()));
   }
 };
 
 /// Adapts basic_streambuf to the dynamic buffer sequence type requirements.
 #if defined(GENERATING_DOCUMENTATION)
 template <typename Allocator = std::allocator<char>>
 #else
 template <typename Allocator>
 #endif
 class basic_streambuf_ref
 {
 public:
   /// The type used to represent the input sequence as a list of buffers.
   typedef typename basic_streambuf<Allocator>::const_buffers_type
     const_buffers_type;
 
   /// The type used to represent the output sequence as a list of buffers.
   typedef typename basic_streambuf<Allocator>::mutable_buffers_type
     mutable_buffers_type;
 
   /// Construct a basic_streambuf_ref for the given basic_streambuf object.
   explicit basic_streambuf_ref(basic_streambuf<Allocator>& sb)
     : sb_(sb)
   {
   }
 
   /// Copy construct a basic_streambuf_ref.
   basic_streambuf_ref(const basic_streambuf_ref& other) noexcept
     : sb_(other.sb_)
   {
   }
 
   /// Move construct a basic_streambuf_ref.
   basic_streambuf_ref(basic_streambuf_ref&& other) noexcept
     : sb_(other.sb_)
   {
   }
 
   /// Get the size of the input sequence.
   std::size_t size() const noexcept
   {
     return sb_.size();
   }
 
   /// Get the maximum size of the dynamic buffer.
   std::size_t max_size() const noexcept
   {
     return sb_.max_size();
   }
 
   /// Get the current capacity of the dynamic buffer.
   std::size_t capacity() const noexcept
   {
     return sb_.capacity();
   }
 
   /// Get a list of buffers that represents the input sequence.
   const_buffers_type data() const noexcept
   {
     return sb_.data();
   }
 
   /// Get a list of buffers that represents the output sequence, with the given
   /// size.
   mutable_buffers_type prepare(std::size_t n)
   {
     return sb_.prepare(n);
   }
 
   /// Move bytes from the output sequence to the input sequence.
   void commit(std::size_t n)
   {
     return sb_.commit(n);
   }
 
   /// Remove characters from the input sequence.
   void consume(std::size_t n)
   {
     return sb_.consume(n);
   }
 
 private:
   basic_streambuf<Allocator>& sb_;
 };
 
 } // namespace asio
 } // namespace boost
 
 #include <boost/asio/detail/pop_options.hpp>
 
 #endif // !defined(BOOST_ASIO_NO_IOSTREAM)
 
 #endif // BOOST_ASIO_BASIC_STREAMBUF_HPP

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