Re: [Quickfix-developers] FileStore issues

[John M. <jg...@jg...>]

Kenny,

I think someone should implement a Berkeley DB store and use the =
transaction support.  Want to volunteer?

www.sleepycat.com

-John

-----Original Message-----
From: qui...@li... =
<qui...@li...>
To: qui...@li... =
<qui...@li...>
Sent: Mon Jan 12 22:17:38 2004
Subject: [Quickfix-developers] FileStore issues

Hi,
  I've noticed a few potential issues with the FileStore::set method.
Namely, that in the event of a write error, the files may be left in a =
bad
state leading to corruption.

The the method looks like:
  if ( fseek( m_msgFile, 0, SEEK_END ) ) throw IOException();
  if ( fseek( m_headerFile, 0, SEEK_END ) ) throw IOException();

  int offset =3D ftell( m_msgFile );
  if ( offset < 0 ) throw IOException();
  int size =3D msg.size();

  if ( fprintf( m_headerFile, "%d,%d,%d ", msgSeqNum, offset, size ) < 0 =
)
    throw IOException();
  m_offsets[ msgSeqNum ] =3D std::make_pair( offset, size );
  fwrite( msg.c_str(), sizeof( char ), msg.size(), m_msgFile );
  if ( ferror( m_msgFile ) ) throw IOException();
  if ( fflush( m_msgFile ) =3D=3D EOF ) throw IOException();
  if ( fflush( m_headerFile ) =3D=3D EOF ) throw IOException();
  return true;

So, first off, a file may not be more then 2GB, otherwise the ftell may =
return
a negative number.  No sweat, I'm not dealing with such large things =
yet.

  The real problems come in the last part where the actual writing is =
done.
If the fprintf fails by running out of space and doing a partial write, =
nothing
is cleaned up.  Since a seek to end of file is always done, any future =
writes
will also be affected by the superfluous characters.
  Same for the fwrite - no cleanup is done on error, thereby leaving the =
file
in a un-usable state.  Not only this, but also note that the header info =
is not
rolled-back in the event of failure to persist the message file - =
leading to
corrupt state on recovery.

  Having said this, I'm not sure I know the correct fix within the =
restrictions
of ANSI C.
  If this were a POSIX world, I'd use little guard objects to roll back
(ftruncate) the header and message files in the event of an error.

  Is there any interest in a FileStore-compatible POSIX-only =
MessageStore?

thanks,
-Kenny

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