sparse_file.hpp

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/*********************************************************************/
// dar - disk archive - a backup/restoration program
// Copyright (C) 2002-2052 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., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
//
// to contact the author : http://dar.linux.free.fr/email.html
/*********************************************************************/


#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:

            // this parameter is only used if "below" is in write-only mode
        sparse_file(generic_file *below, const infinint & hole_size = 15);

        void write_as_escape(bool mode) { escape_write = mode; }; // if set to true, inherited_write() call will not make any lookup for holes, the written data will simply be escaped if it could collide with a mark used to signal the start of a hole
        void read_as_escape(bool mode) { escape_read = mode; }; // if set to true, the data will be unescaped or eof will be signaled to the first mark met, instead of interpreting the mark and what follows as a hole data structure.
        void copy_to_without_skip(bool mode) { copy_to_no_skip = mode; }; // if set to true, the copy_to() methods, write zeroed data in place of skipping over a hole to restore it into the target generic_file

        bool has_seen_hole() const { return seen_hole; };
        bool has_escaped_data() const { return data_escaped; };


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

        void copy_to(generic_file & ref, const infinint & crc_size, crc * & value);

            // indirectly inherited from generic_file

        bool skip(const infinint & pos) { if(pos != offset) throw Efeature("skip in sparse_file"); else return true; };
        bool skip_to_eof() { throw Efeature("skip in sparse_file"); };
        bool skip_relative(S_I x)  { if(x != 0) throw Efeature("skip in sparse_file"); return true; };
        infinint get_position();

    protected:

            // hidden methods from the escape class

        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); };

            // redefined protected methods from generic_file

        U_I inherited_read(char *a, U_I size);
        void inherited_write(const char *a, U_I size);
        void inherited_sync_write();
        void inherited_terminate() { escape::inherited_terminate(); };

    private:
        static bool initialized;
        static unsigned char zeroed_field[SPARSE_FIXED_ZEROED_BLOCK]; // read-only, used when the sequence of zeros is too short for a hole

        enum { normal, hole } mode;
        infinint zero_count;     //< number of zeroed byte pending in the current hole
        infinint offset;         //< current offset in file (as if it was a plain file).
        infinint min_hole_size;  //< minimum size of hole to consider
        U_I UI_min_hole_size;    //< if possible store min_hole_size under U_I, if not this field is set to zero which disables the hole lookup inside buffers while writing data
        bool escape_write;       //< whether to behave like an escape object when writing down data
        bool escape_read;        //< whether to behave like an escape object when reading out data
        bool copy_to_no_skip;    //< whether to hide holes by zeored bytes in the copy_to() methods
        bool seen_hole;          //< whether a hole has been seen or this is a plain file so far
        bool data_escaped;       //< whether some data has been escaped to not collide with a mark (may occur even when no hole is met)

        void dump_pending_zeros();

        void write_hole(const infinint & length);


        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