// // basic_streambuf.hpp // ~~~~~~~~~~~~~~~~~~~ // // Copyright (c) 2003-2016 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_buffers_1 const_buffers_type; typedef boost::asio::mutable_buffers_1 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 += buffer_size(buf); * } * @endcode */ std::size_t size() const { 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 { return max_size_; } /// 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 { 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) { if (pptr() + n > epptr()) 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())); } }; // Helper function to get the preferred size for reading data. Used for any // user-provided specialisations of basic_streambuf. template <typename Allocator> inline std::size_t read_size_helper( basic_streambuf<Allocator>& sb, std::size_t max_size) { return std::min<std::size_t>(512, std::min<std::size_t>(max_size, sb.max_size() - sb.size())); } } // namespace asio } // namespace boost #include <boost/asio/detail/pop_options.hpp> #endif // !defined(BOOST_ASIO_NO_IOSTREAM) #endif // BOOST_ASIO_BASIC_STREAMBUF_HPP