119 lines
4.1 KiB
C++
119 lines
4.1 KiB
C++
#ifndef BACKBUFFER_H
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#define BACKBUFFER_H
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#include "zipios-config.h"
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#include <algorithm>
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#include "meta-iostreams.h"
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#include <vector>
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#include "fcollexceptions.h"
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#include "ziphead.h"
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#include "zipheadio.h"
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#include "virtualseeker.h"
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#include "zipios_common.h"
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namespace zipios {
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using std::ios ;
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using std::cerr ;
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using std::endl ;
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/** A BackBuffer instance is useful for reading the last part of a
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file in an efficient manner, when it is not known exactly how far
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back (towards the front!) to go, to find the start of the desired
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data block. BackBuffer is a vector< unsigned char > that fills
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itself with data from a file by reading chunks from the end of the
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file progressing towards the start. Upon construction the
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BackBuffer instance is associated with a file and a chunksize can
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be specified. To read a chunk of the file into the BackBuffer call
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readChunk(). */
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class BackBuffer : public vector< unsigned char > {
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public:
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/** BackBuffer constructor.
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@param is The istream to read the data from. The stream must be
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seekable, as BackBuffer will reposition the file position to
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read chunks from the back of the file.
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@param vs
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@param chunk_size specifies the size of the chunks to read the file
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into the BackBuffer in.
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@throw FCollException Thrown if the VirtualSeeker vs that has been
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specified is invalid for the istream is. */
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inline explicit BackBuffer( istream &is, VirtualSeeker vs = VirtualSeeker(),
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int chunk_size = 1024 ) ;
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/** Reads another chunk and returns the size of the chunk that has
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been read. Returns 0 on I/O failure.
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@param read_pointer When a new chunk is read in the already
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stored bytes change position in the BackBuffer. read_pointer is
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assumed by readChunk() to be a pointer into a position in the
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BackBuffer, and is updated to point to the same position in the file
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as it pointed to before the new chunk was read. */
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inline int readChunk( int &read_pointer ) ;
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private:
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VirtualSeeker _vs ;
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int _chunk_size ;
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istream &_is ;
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streampos _file_pos ;
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};
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BackBuffer::BackBuffer( istream &is, VirtualSeeker vs, int chunk_size )
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: _vs ( vs ),
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_chunk_size( chunk_size ),
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_is ( is )
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{
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_vs.vseekg( is, 0, ios::end ) ;
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_file_pos = _vs.vtellg( is ) ;
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// Only happens if _vs.startOffset() is a position
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// in the file that lies after _vs.endOffset(), which
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// is clearly not a valid situation.
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if ( _file_pos < 0 )
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throw FCollException( "Invalid virtual file endings" ) ;
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}
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int BackBuffer::readChunk( int &read_pointer ) {
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// Update chunk_size and file position
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_chunk_size = min<int> ( static_cast< int >( _file_pos ), _chunk_size ) ;
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_file_pos -= _chunk_size ;
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_vs.vseekg( _is, _file_pos, ios::beg ) ;
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// Make space for _chunk_size new bytes first in buffer
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insert ( begin(), _chunk_size, static_cast< char > ( 0 ) ) ;
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// Read in the next _chunk_size of bytes
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readByteSeq ( _is, &( (*this)[ 0 ] ), _chunk_size ) ;
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read_pointer += _chunk_size ;
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if ( _is.good() )
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return _chunk_size ;
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else
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return 0 ;
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}
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}
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#endif
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/** \file
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The header file for BackBuffer
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*/
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/*
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Zipios++ - a small C++ library that provides easy access to .zip files.
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Copyright (C) 2000 Thomas Søndergaard
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This library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2 of the License, or (at your option) any later version.
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This library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with this library; if not, write to the Free Software
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Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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*/
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