sparse_file.hpp

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/*********************************************************************/
// dar - disk archive - a backup/restoration program
// Copyright (C) 2002-2026 Denis Corbin
//
// This program is free software; you can redistribute it and/or
// modify it under the terms of the GNU General Public License
// as published by the Free Software Foundation; either version 2
// of the License, or (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program; if not, write to the Free Software
// Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
//
// to contact the author, see the AUTHOR file
/*********************************************************************/

 
#ifndef SPARSE_FILE_HPP
#define SPARSE_FILE_HPP
 
#include "../my_config.h"
 
extern "C"
{
#if HAVE_LIMITS_H
#include <limits.h>
#endif
}
 
#include "generic_file.hpp"
#include "escape.hpp"
 
#define SPARSE_FIXED_ZEROED_BLOCK 40960
#ifdef SSIZE_MAX
#if SSIZE_MAX < MAX_BUFFER_SIZE
#undef MAX_BUFFER_SIZE
#define SPARSE_FIXED_ZEROED_BLOCK SSIZE_MAX
#endif
#endif
 
namespace libdar
{

 
    class sparse_file : public escape
    {
    public:

    sparse_file(generic_file *below, const infinint & hole_size = 15);
    sparse_file(const sparse_file & ref) = default;
    sparse_file(sparse_file && ref) noexcept = default;
    sparse_file & operator = (const sparse_file & ref) = default;
    sparse_file & operator = (sparse_file && ref) noexcept = default;
    ~sparse_file() = default;

    void write_as_escape(bool mode) { escape_write = mode; };

    void read_as_escape(bool mode) { escape_read = mode; };

    void copy_to_without_skip(bool mode) { copy_to_no_skip = mode; };
 
    bool has_seen_hole() const { return seen_hole; };
    bool has_escaped_data() const { return data_escaped; };


    virtual void copy_to(generic_file & ref) override { crc *tmp = nullptr; copy_to(ref, 0, tmp); if(tmp != nullptr) throw SRC_BUG; };


    virtual void copy_to(generic_file & ref, const infinint & crc_size, crc * & value) override;
 
        // indirectly inherited from generic_file
    virtual bool skippable(skippability direction, const infinint & amount) override { return false; };
    virtual bool skip(const infinint & pos) override { if(pos != offset) throw Efeature("skip in sparse_file"); else return true; };
    virtual bool skip_to_eof() override { throw Efeature("skip in sparse_file"); };
    virtual bool skip_relative(S_I x) override { if(x != 0) throw Efeature("skip in sparse_file"); return true; };
    virtual infinint get_position() const override;
 
    protected:
 
        // methods from the escape class we hide from the (public) class interface
 
    void add_mark_at_current_position(sequence_type t) { escape::add_mark_at_current_position(t); };
    bool skip_to_next_mark(sequence_type t, bool jump) { return escape::skip_to_next_mark(t, jump); };
    bool next_to_read_is_mark(sequence_type t) { return escape::next_to_read_is_mark(t); };
    void add_unjumpable_mark(sequence_type t) { escape::add_unjumpable_mark(t); };
 
        // methods from generic_file redefined as protected
 
    virtual U_I inherited_read(char *a, U_I size) override;
    virtual void inherited_write(const char *a, U_I size) override;
    virtual void inherited_sync_write() override;
        // inherited_flush_read() kept as is from the escape class
        // inherited_terminate() kept as is from the escape class
 
    private:
    static bool initialized; 
        static unsigned char zeroed_field[SPARSE_FIXED_ZEROED_BLOCK]; 
 
    enum { normal, hole } mode; 
    infinint zero_count;     
    infinint offset;         
    infinint min_hole_size;  
    U_I UI_min_hole_size;    
    bool escape_write;       
    bool escape_read;        
    bool copy_to_no_skip;    
    bool seen_hole;          
    bool data_escaped;       

    void dump_pending_zeros();

    void write_hole(const infinint & length);

    void reset();
 


    static bool look_for_hole(const char *a, U_I size, U_I min_hole_size, U_I & start, U_I & length);


    static U_I count_initial_zeros(const char *a, U_I size);
    };

 
} // end of namespace
 
 
#endif