ceph/src/boost/libs/asio/include/boost/asio/basic_streambuf.hpp

   1 //
   2 // basic_streambuf.hpp
   3 // ~~~~~~~~~~~~~~~~~~~
   4 //
   5 // Copyright (c) 2003-2016 Christopher M. Kohlhoff (chris at kohlhoff dot com)
   6 //
   7 // Distributed under the Boost Software License, Version 1.0. (See accompanying
   8 // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
   9 //
  10
  11 #ifndef BOOST_ASIO_BASIC_STREAMBUF_HPP
  12 #define BOOST_ASIO_BASIC_STREAMBUF_HPP
  13
  14 #if defined(_MSC_VER) && (_MSC_VER >= 1200)
  15 # pragma once
  16 #endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
  17
  18 #include <boost/asio/detail/config.hpp>
  19
  20 #if !defined(BOOST_ASIO_NO_IOSTREAM)
  21
  22 #include <algorithm>
  23 #include <cstring>
  24 #include <stdexcept>
  25 #include <streambuf>
  26 #include <vector>
  27 #include <boost/asio/basic_streambuf_fwd.hpp>
  28 #include <boost/asio/buffer.hpp>
  29 #include <boost/asio/detail/limits.hpp>
  30 #include <boost/asio/detail/noncopyable.hpp>
  31 #include <boost/asio/detail/throw_exception.hpp>
  32
  33 #include <boost/asio/detail/push_options.hpp>
  34
  35 namespace boost {
  36 namespace asio {
  37
  38 /// Automatically resizable buffer class based on std::streambuf.
  39 /**
  40  * The @c basic_streambuf class is derived from @c std::streambuf to associate
  41  * the streambuf's input and output sequences with one or more character
  42  * arrays. These character arrays are internal to the @c basic_streambuf
  43  * object, but direct access to the array elements is provided to permit them
  44  * to be used efficiently with I/O operations. Characters written to the output
  45  * sequence of a @c basic_streambuf object are appended to the input sequence
  46  * of the same object.
  47  *
  48  * The @c basic_streambuf class's public interface is intended to permit the
  49  * following implementation strategies:
  50  *
  51  * @li A single contiguous character array, which is reallocated as necessary
  52  * to accommodate changes in the size of the character sequence. This is the
  53  * implementation approach currently used in Asio.
  54  *
  55  * @li A sequence of one or more character arrays, where each array is of the
  56  * same size. Additional character array objects are appended to the sequence
  57  * to accommodate changes in the size of the character sequence.
  58  *
  59  * @li A sequence of one or more character arrays of varying sizes. Additional
  60  * character array objects are appended to the sequence to accommodate changes
  61  * in the size of the character sequence.
  62  *
  63  * The constructor for basic_streambuf accepts a @c size_t argument specifying
  64  * the maximum of the sum of the sizes of the input sequence and output
  65  * sequence. During the lifetime of the @c basic_streambuf object, the following
  66  * invariant holds:
  67  * @code size() <= max_size()@endcode
  68  * Any member function that would, if successful, cause the invariant to be
  69  * violated shall throw an exception of class @c std::length_error.
  70  *
  71  * The constructor for @c basic_streambuf takes an Allocator argument. A copy
  72  * of this argument is used for any memory allocation performed, by the
  73  * constructor and by all member functions, during the lifetime of each @c
  74  * basic_streambuf object.
  75  *
  76  * @par Examples
  77  * Writing directly from an streambuf to a socket:
  78  * @code
  79  * boost::asio::streambuf b;
  80  * std::ostream os(&b);
  81  * os << "Hello, World!\n";
  82  *
  83  * // try sending some data in input sequence
  84  * size_t n = sock.send(b.data());
  85  *
  86  * b.consume(n); // sent data is removed from input sequence
  87  * @endcode
  88  *
  89  * Reading from a socket directly into a streambuf:
  90  * @code
  91  * boost::asio::streambuf b;
  92  *
  93  * // reserve 512 bytes in output sequence
  94  * boost::asio::streambuf::mutable_buffers_type bufs = b.prepare(512);
  95  *
  96  * size_t n = sock.receive(bufs);
  97  *
  98  * // received data is "committed" from output sequence to input sequence
  99  * b.commit(n);
 100  *
 101  * std::istream is(&b);
 102  * std::string s;
 103  * is >> s;
 104  * @endcode
 105  */
 106 #if defined(GENERATING_DOCUMENTATION)
 107 template <typename Allocator = std::allocator<char> >
 108 #else
 109 template <typename Allocator>
 110 #endif
 111 class basic_streambuf
 112   : public std::streambuf,
 113     private noncopyable
 114 {
 115 public:
 116 #if defined(GENERATING_DOCUMENTATION)
 117   /// The type used to represent the input sequence as a list of buffers.
 118   typedef implementation_defined const_buffers_type;
 119
 120   /// The type used to represent the output sequence as a list of buffers.
 121   typedef implementation_defined mutable_buffers_type;
 122 #else
 123   typedef boost::asio::const_buffers_1 const_buffers_type;
 124   typedef boost::asio::mutable_buffers_1 mutable_buffers_type;
 125 #endif
 126
 127   /// Construct a basic_streambuf object.
 128   /**
 129    * Constructs a streambuf with the specified maximum size. The initial size
 130    * of the streambuf's input sequence is 0.
 131    */
 132   explicit basic_streambuf(
 133       std::size_t maximum_size = (std::numeric_limits<std::size_t>::max)(),
 134       const Allocator& allocator = Allocator())
 135     : max_size_(maximum_size),
 136       buffer_(allocator)
 137   {
 138     std::size_t pend = (std::min<std::size_t>)(max_size_, buffer_delta);
 139     buffer_.resize((std::max<std::size_t>)(pend, 1));
 140     setg(&buffer_[0], &buffer_[0], &buffer_[0]);
 141     setp(&buffer_[0], &buffer_[0] + pend);
 142   }
 143
 144   /// Get the size of the input sequence.
 145   /**
 146    * @returns The size of the input sequence. The value is equal to that
 147    * calculated for @c s in the following code:
 148    * @code
 149    * size_t s = 0;
 150    * const_buffers_type bufs = data();
 151    * const_buffers_type::const_iterator i = bufs.begin();
 152    * while (i != bufs.end())
 153    * {
 154    *   const_buffer buf(*i++);
 155    *   s += buffer_size(buf);
 156    * }
 157    * @endcode
 158    */
 159   std::size_t size() const
 160   {
 161     return pptr() - gptr();
 162   }
 163
 164   /// Get the maximum size of the basic_streambuf.
 165   /**
 166    * @returns The allowed maximum of the sum of the sizes of the input sequence
 167    * and output sequence.
 168    */
 169   std::size_t max_size() const
 170   {
 171     return max_size_;
 172   }
 173
 174   /// Get a list of buffers that represents the input sequence.
 175   /**
 176    * @returns An object of type @c const_buffers_type that satisfies
 177    * ConstBufferSequence requirements, representing all character arrays in the
 178    * input sequence.
 179    *
 180    * @note The returned object is invalidated by any @c basic_streambuf member
 181    * function that modifies the input sequence or output sequence.
 182    */
 183   const_buffers_type data() const
 184   {
 185     return boost::asio::buffer(boost::asio::const_buffer(gptr(),
 186           (pptr() - gptr()) * sizeof(char_type)));
 187   }
 188
 189   /// Get a list of buffers that represents the output sequence, with the given
 190   /// size.
 191   /**
 192    * Ensures that the output sequence can accommodate @c n characters,
 193    * reallocating character array objects as necessary.
 194    *
 195    * @returns An object of type @c mutable_buffers_type that satisfies
 196    * MutableBufferSequence requirements, representing character array objects
 197    * at the start of the output sequence such that the sum of the buffer sizes
 198    * is @c n.
 199    *
 200    * @throws std::length_error If <tt>size() + n > max_size()</tt>.
 201    *
 202    * @note The returned object is invalidated by any @c basic_streambuf member
 203    * function that modifies the input sequence or output sequence.
 204    */
 205   mutable_buffers_type prepare(std::size_t n)
 206   {
 207     reserve(n);
 208     return boost::asio::buffer(boost::asio::mutable_buffer(
 209           pptr(), n * sizeof(char_type)));
 210   }
 211
 212   /// Move characters from the output sequence to the input sequence.
 213   /**
 214    * Appends @c n characters from the start of the output sequence to the input
 215    * sequence. The beginning of the output sequence is advanced by @c n
 216    * characters.
 217    *
 218    * Requires a preceding call <tt>prepare(x)</tt> where <tt>x >= n</tt>, and
 219    * no intervening operations that modify the input or output sequence.
 220    *
 221    * @note If @c n is greater than the size of the output sequence, the entire
 222    * output sequence is moved to the input sequence and no error is issued.
 223    */
 224   void commit(std::size_t n)
 225   {
 226     if (pptr() + n > epptr())
 227       n = epptr() - pptr();
 228     pbump(static_cast<int>(n));
 229     setg(eback(), gptr(), pptr());
 230   }
 231
 232   /// Remove characters from the input sequence.
 233   /**
 234    * Removes @c n characters from the beginning of the input sequence.
 235    *
 236    * @note If @c n is greater than the size of the input sequence, the entire
 237    * input sequence is consumed and no error is issued.
 238    */
 239   void consume(std::size_t n)
 240   {
 241     if (egptr() < pptr())
 242       setg(&buffer_[0], gptr(), pptr());
 243     if (gptr() + n > pptr())
 244       n = pptr() - gptr();
 245     gbump(static_cast<int>(n));
 246   }
 247
 248 protected:
 249   enum { buffer_delta = 128 };
 250
 251   /// Override std::streambuf behaviour.
 252   /**
 253    * Behaves according to the specification of @c std::streambuf::underflow().
 254    */
 255   int_type underflow()
 256   {
 257     if (gptr() < pptr())
 258     {
 259       setg(&buffer_[0], gptr(), pptr());
 260       return traits_type::to_int_type(*gptr());
 261     }
 262     else
 263     {
 264       return traits_type::eof();
 265     }
 266   }
 267
 268   /// Override std::streambuf behaviour.
 269   /**
 270    * Behaves according to the specification of @c std::streambuf::overflow(),
 271    * with the specialisation that @c std::length_error is thrown if appending
 272    * the character to the input sequence would require the condition
 273    * <tt>size() > max_size()</tt> to be true.
 274    */
 275   int_type overflow(int_type c)
 276   {
 277     if (!traits_type::eq_int_type(c, traits_type::eof()))
 278     {
 279       if (pptr() == epptr())
 280       {
 281         std::size_t buffer_size = pptr() - gptr();
 282         if (buffer_size < max_size_ && max_size_ - buffer_size < buffer_delta)
 283         {
 284           reserve(max_size_ - buffer_size);
 285         }
 286         else
 287         {
 288           reserve(buffer_delta);
 289         }
 290       }
 291
 292       *pptr() = traits_type::to_char_type(c);
 293       pbump(1);
 294       return c;
 295     }
 296
 297     return traits_type::not_eof(c);
 298   }
 299
 300   void reserve(std::size_t n)
 301   {
 302     // Get current stream positions as offsets.
 303     std::size_t gnext = gptr() - &buffer_[0];
 304     std::size_t pnext = pptr() - &buffer_[0];
 305     std::size_t pend = epptr() - &buffer_[0];
 306
 307     // Check if there is already enough space in the put area.
 308     if (n <= pend - pnext)
 309     {
 310       return;
 311     }
 312
 313     // Shift existing contents of get area to start of buffer.
 314     if (gnext > 0)
 315     {
 316       pnext -= gnext;
 317       std::memmove(&buffer_[0], &buffer_[0] + gnext, pnext);
 318     }
 319
 320     // Ensure buffer is large enough to hold at least the specified size.
 321     if (n > pend - pnext)
 322     {
 323       if (n <= max_size_ && pnext <= max_size_ - n)
 324       {
 325         pend = pnext + n;
 326         buffer_.resize((std::max<std::size_t>)(pend, 1));
 327       }
 328       else
 329       {
 330         std::length_error ex("boost::asio::streambuf too long");
 331         boost::asio::detail::throw_exception(ex);
 332       }
 333     }
 334
 335     // Update stream positions.
 336     setg(&buffer_[0], &buffer_[0], &buffer_[0] + pnext);
 337     setp(&buffer_[0] + pnext, &buffer_[0] + pend);
 338   }
 339
 340 private:
 341   std::size_t max_size_;
 342   std::vector<char_type, Allocator> buffer_;
 343
 344   // Helper function to get the preferred size for reading data.
 345   friend std::size_t read_size_helper(
 346       basic_streambuf& sb, std::size_t max_size)
 347   {
 348     return std::min<std::size_t>(
 349         std::max<std::size_t>(512, sb.buffer_.capacity() - sb.size()),
 350         std::min<std::size_t>(max_size, sb.max_size() - sb.size()));
 351   }
 352 };
 353
 354 // Helper function to get the preferred size for reading data. Used for any
 355 // user-provided specialisations of basic_streambuf.
 356 template <typename Allocator>
 357 inline std::size_t read_size_helper(
 358     basic_streambuf<Allocator>& sb, std::size_t max_size)
 359 {
 360   return std::min<std::size_t>(512,
 361       std::min<std::size_t>(max_size, sb.max_size() - sb.size()));
 362 }
 363
 364 } // namespace asio
 365 } // namespace boost
 366
 367 #include <boost/asio/detail/pop_options.hpp>
 368
 369 #endif // !defined(BOOST_ASIO_NO_IOSTREAM)
 370
 371 #endif // BOOST_ASIO_BASIC_STREAMBUF_HPP