src/IO/Source.hpp

   1 /*
   2 Copyright_License {
   3
   4   XCSoar Glide Computer - http://www.xcsoar.org/
   5   Copyright (C) 2000-2013 The XCSoar Project
   6   A detailed list of copyright holders can be found in the file "AUTHORS".
   7
   8   This program is free software; you can redistribute it and/or
   9   modify it under the terms of the GNU General Public License
  10   as published by the Free Software Foundation; either version 2
  11   of the License, or (at your option) any later version.
  12
  13   This program is distributed in the hope that it will be useful,
  14   but WITHOUT ANY WARRANTY; without even the implied warranty of
  15   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16   GNU General Public License for more details.
  17
  18   You should have received a copy of the GNU General Public License
  19   along with this program; if not, write to the Free Software
  20   Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
  21 }
  22 */
  23
  24 #ifndef XCSOAR_IO_SOURCE_HPP
  25 #define XCSOAR_IO_SOURCE_HPP
  26
  27 #include "Compiler.h"
  28
  29 #include <utility>
  30
  31 /**
  32  * A data source.  This object provides a buffer, which may be
  33  * modified in-place by the caller, to do zero-copy parsing.
  34  */
  35 template<class T>
  36 class Source {
  37 public:
  38   /**
  39    * A portion of this object's buffer.  The first item is the start
  40    * of the buffer, and the second item is the number of available
  41    * words.
  42    */
  43   struct Range {
  44     T *data;
  45
  46     unsigned length;
  47
  48     Range() = default;
  49
  50     constexpr
  51     Range(T *_data, unsigned _length):data(_data), length(_length) {}
  52
  53     constexpr
  54     bool IsEmpty() const {
  55       return length == 0;
  56     }
  57   };
  58
  59 public:
  60   virtual ~Source() {}
  61
  62   /**
  63    * Returns words from this source.  After you have used them, call
  64    * the method consume().  This method Invalidates any range returned
  65    * by a previous call.
  66    *
  67    * This object will always return as many words as possible; calling
  68    * read() subsequently (without consume()) will not get you more
  69    * data.  An empty range marks the end of the stream.
  70    */
  71   virtual Range Read() = 0;
  72
  73   /**
  74    * Marks words as "consumed".  The buffer returned by read() is not
  75    * yet Invalidated, and may be used until the next read() call is
  76    * issued.
  77    */
  78   virtual void Consume(unsigned n) = 0;
  79
  80   /**
  81    * Determins the size of the file.  Returns -1 if the size is
  82    * unknown.
  83    */
  84   gcc_pure
  85   virtual long GetSize() const {
  86     return -1;
  87   }
  88
  89   /**
  90    * Determins the current position within the file.  Returns -1 if
  91    * this is unknown.
  92    */
  93   gcc_pure
  94   virtual long Tell() const {
  95     return -1;
  96   }
  97 };
  98
  99 #endif