ByteIO.h

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//# ByteIO.h: Abstract base class for IO on a byte stream
//# Copyright (C) 1996,1999,2001
//# Associated Universities, Inc. Washington DC, USA.
//#
//# This library is free software; you can redistribute it and/or modify it
//# under the terms of the GNU Library General Public License as published by
//# the Free Software Foundation; either version 2 of the License, or (at your
//# option) any later version.
//#
//# This library 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 Library General Public
//# License for more details.
//#
//# You should have received a copy of the GNU Library General Public License
//# along with this library; if not, write to the Free Software Foundation,
//# Inc., 675 Massachusetts Ave, Cambridge, MA 02139, USA.
//#
//# Correspondence concerning AIPS++ should be addressed as follows:
//#        Internet email: aips2-request@nrao.edu.
//#        Postal address: AIPS++ Project Office
//#                        National Radio Astronomy Observatory
//#                        520 Edgemont Road
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//#
//# $Id$

#ifndef CASA_BYTEIO_H
#define CASA_BYTEIO_H

//# Includes
#include <casacore/casa/aips.h>
#include <casacore/casa/BasicSL/String.h>


namespace casacore { //# NAMESPACE CASACORE - BEGIN

// <summary>Abstract base class for IO on a byte stream.</summary>

// <use visibility=export>

// <reviewed reviewer="Friso Olnon" date="1996/11/06" tests="tByteIO" demos="">
// </reviewed>

// <synopsis> 
// ByteIO is the abstract base class for all classes doing IO on
// byte streams. Examples of derived classes are
// <linkto class=RegularFileIO>RegularFileIO</linkto> and
// <linkto class=MemoryIO>MemoryIO</linkto>.
// <p>
// ByteIO contains two enumerations, which define the possible
// open and seek options on byte streams. These enumerations
// are used throughout the IO framework.
// </synopsis>

// <motivation> 
// Make polymorphic operations on byte streams possible.
// </motivation>


class ByteIO
{
public:
    // Define the possible ByteIO open options.
    enum OpenOption {
        Old=1,
        // read/write; file must exist.
        Update,
        // read/write; create file if not exist.
        Append,
        // read/write; create file if not exist.
        New,
        // read/write; file may not exist yet.
        NewNoReplace,
        // read/write; delete file at close.
        Scratch,
        // read/write; file must exist; delete at close.
        Delete
    };

    // Define the possible seek options.
    enum SeekOption {
        // Seek from beginning of file.
        Begin=1,
        // Seek from current position.
        Current,
        // Seek from the end of the file.
        End
    };


    // The constructor does nothing.
    ByteIO();

    virtual ~ByteIO();

    // Write <src>size</src> bytes to the byte stream.
    virtual void write (Int64 size, const void* buf) = 0;

    // Write <src>size</src> bytes to the byte stream at <src>offset</src>.
    // The file offset is not changed
    virtual void pwrite (Int64 size, Int64 offset, const void* buf);

    // Read <src>size</src> bytes from the byte stream. Returns the number of
    // bytes actually read, or a negative number if an error occurred. Will also
    // throw an Exception (AipsError) if the requested number of bytes could
    // not be read unless throwException is set to False.
    virtual Int64 read (Int64 size, void* buf, Bool throwException=True) = 0;    

    // Like read but reads from offset of start of the file
    // The file offset is not changed
    virtual Int64 pread (Int64 size, Int64 offset, void* buf, Bool throwException=True);

    // Reopen the underlying IO stream for read/write access.
    // Nothing will be done if the stream is writable already.
    // Otherwise it will be reopened and an exception will be thrown
    // if it is not possible to reopen it for read/write access.
    // The default implementation in this base class throws a "not possible"
    // exception if a reopen has to be done.
    virtual void reopenRW();

    // This function sets the position on the given offset.
    // The seek option defines from which file position the seek is done.
    // -1 is returned if not seekable.
    // <group>
    Int64 seek (Int offset, ByteIO::SeekOption = ByteIO::Begin);
    Int64 seek (Int64 offset, ByteIO::SeekOption = ByteIO::Begin);
    // </group>

    // Flush the data to the file.
    // The default implementation does nothing.
    virtual void flush();

    // Fsync the file (i.e. force the data to be physically written).
    // The default implementation does nothing.
    virtual void fsync();

    // Resync the file (i.e. empty the current buffer).
    // The default implementation does nothing.
    virtual void resync();
  
    // Get the file name of the file attached.
    // The default implementation returns an empty string.
    virtual String fileName() const;

    // Get the length of the byte stream.
    virtual Int64 length() = 0;
    
    // Is the byte stream readable?
    virtual Bool isReadable() const = 0;

    // Is the byte stream writable?
    virtual Bool isWritable() const = 0;

    // Is the byte stream seekable?
    virtual Bool isSeekable() const = 0;


protected:
    // Make copy constructor and assignment protected, so a user cannot
    // use them (but a derived class can).
    // <group>
    ByteIO (const ByteIO& byteIO);
    ByteIO& operator= (const ByteIO& byteIO);
    // </group>

    virtual Int64 doSeek (Int64 offset, ByteIO::SeekOption) = 0;
};



inline ByteIO::ByteIO()
{}

inline ByteIO::ByteIO (const ByteIO&)
{}

inline ByteIO& ByteIO::operator= (const ByteIO&)
{
   return *this;
}

inline Int64 ByteIO::seek (Int64 offset, ByteIO::SeekOption option)
{
    return doSeek (offset, option);
}
inline Int64 ByteIO::seek (Int offset, ByteIO::SeekOption option)
{
    return doSeek (Int64(offset), option);
}


} //# NAMESPACE CASACORE - END

#endif