FileMemoryStream.h

// This file is part of libigl, a simple c++ geometry processing library.
//
// Copyright (C) 2020 Jérémie Dumas <jeremie.dumas@ens-lyon.org>
// Copyright (C) 2021 Alec Jacobson <alecjacobson@gmail.com>
//
// This Source Code Form is subject to the terms of the Mozilla Public License
// v. 2.0. If a copy of the MPL was not distributed with this file, You can
// obtain one at http://mozilla.org/MPL/2.0/.
#ifndef IGL_FILEMEMORYSTREAM_H
#define IGL_FILEMEMORYSTREAM_H

#include "igl_inline.h"

#include <streambuf>
#include <istream>
#include <string>

namespace igl {
  struct FileMemoryBuffer : public std::streambuf 
  {
    char *p_start{nullptr};
    char *p_end{nullptr};
    size_t size;
  
    FileMemoryBuffer(char const *first_elem, size_t size)
      : p_start(const_cast<char *>(first_elem)), p_end(p_start + size),
        size(size) 
    {
      setg(p_start, p_start, p_end);
    }
  
    pos_type seekoff(
      off_type off, 
      std::ios_base::seekdir dir,
      std::ios_base::openmode /*which*/) override 
    {
      if (dir == std::ios_base::cur) 
      {
        gbump(static_cast<int>(off));
      }else
      {
        setg(p_start,(dir==std::ios_base::beg ? p_start : p_end) + off,p_end);
      }
      return gptr() - p_start;
    }
  
    pos_type seekpos(pos_type pos, std::ios_base::openmode which) override 
    {
      return seekoff(pos, std::ios_base::beg, which);
    }
  };
  
  /// Class to convert a FILE * to an std::istream
  struct FileMemoryStream : virtual FileMemoryBuffer, public std::istream 
  {
    FileMemoryStream( char const *first_elem, size_t size)
      : FileMemoryBuffer(first_elem, size), 
        std::istream( static_cast<std::streambuf *>(this))
    {}
  };
} 

#endif