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+//
+// basic_streambuf.hpp
+// ~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2018 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 ASIO_BASIC_STREAMBUF_HPP
+#define ASIO_BASIC_STREAMBUF_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+
+#if !defined(ASIO_NO_IOSTREAM)
+
+#include <algorithm>
+#include <cstring>
+#include <stdexcept>
+#include <streambuf>
+#include <vector>
+#include "asio/basic_streambuf_fwd.hpp"
+#include "asio/buffer.hpp"
+#include "asio/detail/limits.hpp"
+#include "asio/detail/noncopyable.hpp"
+#include "asio/detail/throw_exception.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+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
+ * 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
+ * asio::streambuf b;
+ *
+ * // reserve 512 bytes in output sequence
+ * 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 ASIO_CONST_BUFFER const_buffers_type;
+  typedef 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 ASIO_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 ASIO_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 ASIO_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 ASIO_NOEXCEPT
+  {
+    return asio::buffer(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 asio::buffer(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("asio::streambuf too long");
+        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) ASIO_NOEXCEPT
+    : sb_(other.sb_)
+  {
+  }
+
+#if defined(ASIO_HAS_MOVE) || defined(GENERATING_DOCUMENTATION)
+  /// Move construct a basic_streambuf_ref.
+  basic_streambuf_ref(basic_streambuf_ref&& other) ASIO_NOEXCEPT
+    : sb_(other.sb_)
+  {
+  }
+#endif // defined(ASIO_HAS_MOVE) || defined(GENERATING_DOCUMENTATION)
+
+  /// Get the size of the input sequence.
+  std::size_t size() const ASIO_NOEXCEPT
+  {
+    return sb_.size();
+  }
+
+  /// Get the maximum size of the dynamic buffer.
+  std::size_t max_size() const ASIO_NOEXCEPT
+  {
+    return sb_.max_size();
+  }
+
+  /// Get the current capacity of the dynamic buffer.
+  std::size_t capacity() const ASIO_NOEXCEPT
+  {
+    return sb_.capacity();
+  }
+
+  /// Get a list of buffers that represents the input sequence.
+  const_buffers_type data() const ASIO_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
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // !defined(ASIO_NO_IOSTREAM)
+
+#endif // ASIO_BASIC_STREAMBUF_HPP