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//
// basic_streambuf.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 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 const_buffer const_buffers_type;
typedef 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 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) 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
#include "asio/detail/pop_options.hpp"
#endif // !defined(ASIO_NO_IOSTREAM)
#endif // ASIO_BASIC_STREAMBUF_HPP