FiledesIO.h

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// # FiledesIO.h: Class for unbuffered IO on a file
// # Copyright (C) 1996,1997,1999,2001
// # 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: casa-feedback@nrao.edu.
// #        Postal address: AIPS++ Project Office
// #                        National Radio Astronomy Observatory
// #                        520 Edgemont Road
// #                        Charlottesville, VA 22903-2475 USA
 
#ifndef CASA_FILEDESIO_H
#define CASA_FILEDESIO_H
 
// # Includes
#include <casacore/casa/aips.h>
#include <casacore/casa/IO/ByteIO.h>
#include <casacore/casa/BasicSL/String.h>
 
namespace casacore {  // # NAMESPACE CASACORE - BEGIN
 
// <summary>
// Class for unbuffered IO on a file.
// </summary>
 
// <use visibility=export>
 
// <reviewed reviewer="Friso Olnon" date="1996/11/06" tests="tByteIO" demos="">
// </reviewed>
 
// <prerequisite>
//    <li> <linkto class=ByteIO>ByteIO</linkto> class
//    <li> file descriptors
// </prerequisite>
 
// <synopsis>
// This class is a specialization of class
// <linkto class=ByteIO>ByteIO</linkto>. It uses a file descriptor
// to read/write data.
// <p>
// The file associated with the file descriptor has to be opened
// before hand.
// The constructor will determine automatically if the file is
// readable, writable and seekable.
// Note that on destruction the file descriptor is NOT closed.
// </synopsis>
 
// <example>
// This example shows how FiledesIO can be used with an fd.
// It uses the fd for a regular file, which could be done in an easier
// way using class <linkto class=RegularFileIO>RegularFileIO</linkto>.
// However, when using pipes or sockets, this would be the only way.
// <srcblock>
//    // Get a file descriptor for the file.
//    int fd = open ("file.name");
//    // Use that as the source of AipsIO (which will also use CanonicalIO).
//    FiledesIO fio (fd);
//    AipsIO stream (&fio);
//    // Read the data.
//    Int vali;
//    Bool valb;
//    stream >> vali >> valb;
// </srcblock>
// </example>
 
// <motivation>
// Make it possible to use the Casacore IO functionality on any file.
// In this way any device can be hooked to the IO framework.
// </motivation>
 
class FiledesIO : public ByteIO {
 public:
  // Default constructor.
  // A stream can be attached using the attach function.
  FiledesIO();
 
  // Construct from the given file descriptor.
  // The file name is only used in possible error messages.
  explicit FiledesIO(int fd, const String& fileName = String());
 
  // Attach to the given file descriptor.
  // An exception is thrown if it is not in a detached state.
  // The file name is only used in error messages.
  void attach(int fd, const String& fileName);
 
  // Detach from the file descriptor. The file is not closed.
  void detach();
 
  // The destructor detaches, but does not close the file.
  virtual ~FiledesIO();
 
  // Write the number of bytes.
  virtual void write(Int64 size, const void* buf);
 
  // Write the number of bytes at offset from start of the file.
  // The file offset is not changed
  virtual void pwrite(Int64 size, Int64 offset, const void* buf);
 
  // Read <src>size</src> bytes from the descriptor. Returns the number of
  // bytes actually read or a negative number if an error occurred. Will throw
  // an Exception (AipsError) if the requested number of bytes could not be
  // read, or an error occured, unless throwException is set to False. Will
  // always throw an exception if the descriptor is not readable or the
  // system call returned an undocumented value.
  virtual Int64 read(Int64 size, void* buf, Bool throwException = True);
 
  // Like read except reads from offset of the start of the file.
  // The file offset is not changed
  virtual Int64 pread(Int64 size, Int64 offset, void* buf, Bool throwException = True);
 
  // Get the length of the byte stream.
  virtual Int64 length();
 
  // Is the IO stream readable?
  virtual Bool isReadable() const;
 
  // Is the IO stream writable?
  virtual Bool isWritable() const;
 
  // Is the IO stream seekable?
  virtual Bool isSeekable() const;
 
  // Set that the IO stream is writable.
  void setWritable() { itsWritable = True; }
 
  // Get the file name of the file attached.
  virtual String fileName() const;
 
  // Fsync the file (i.e. force the data to be physically written).
  virtual void fsync();
 
  // Truncate the file to the given size.
  virtual void truncate(Int64 size);
 
  // Some static convenience functions for file create/open/close.
  // Close is only done if the fd is non-negative.
  // <group>
  static int create(const Char* name, int mode = 0666);
  static int open(const Char* name, Bool writable = False, Bool throwExcp = True);
  static void close(int fd);
  // </group>
 
 protected:
  // Get the file descriptor.
  int fd() const { return itsFile; }
 
  // Determine if the file descriptor is readable and/or writable.
  void fillRWFlags(int fd);
 
  // Determine if the file is seekable.
  void fillSeekable();
 
  // Reset the position pointer to the given value. It returns the
  // new position.
  virtual Int64 doSeek(Int64 offset, ByteIO::SeekOption);
 
 private:
  Bool itsSeekable;
  Bool itsReadable;
  Bool itsWritable;
  int itsFile;
  String itsFileName;
 
  // Copy constructor, should not be used.
  FiledesIO(const FiledesIO& that);
 
  // Assignment, should not be used.
  FiledesIO& operator=(const FiledesIO& that);
};
 
}  // namespace casacore
 
#endif