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authorAnas Nashif <anas.nashif@intel.com>2012-10-30 12:57:26 -0700
committerAnas Nashif <anas.nashif@intel.com>2012-10-30 12:57:26 -0700
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+//
+// basic_streambuf.hpp
+// ~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2012 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_NO_IOSTREAM)
+
+#include <algorithm>
+#include <cstring>
+#include <stdexcept>
+#include <streambuf>
+#include <vector>
+#include <boost/limits.hpp>
+#include <boost/throw_exception.hpp>
+#include <boost/asio/basic_streambuf_fwd.hpp>
+#include <boost/asio/buffer.hpp>
+#include <boost/asio/detail/noncopyable.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.
+ *
+ * @throws std::length_error If @c n is greater than the size of the output
+ * sequence.
+ */
+ 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.
+ *
+ * @throws std::length_error If <tt>n > size()</tt>.
+ */
+ 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::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_NO_IOSTREAM)
+
+#endif // BOOST_ASIO_BASIC_STREAMBUF_HPP