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From Miroslav Pokorny <miroslav.poko...@gmail.com>
Subject Re: [vfs]
Date Thu, 21 Jul 2011 00:31:17 GMT
Hi Gary,

While it is true that FTP is typically thought of as a streaming rather than
random access file system, VFS does support random access reading. This is
confirmed of course by the list of capabilities and code. I have a hacked
version which supports random writing and does so using the following
strategy.


   - all read
      - if outputstream present flush and closeand clear
      - continue with reading byte(s)
      - seek
      - if outputstream present flush and closeand clear
      - perform seek.
      - // input and output streams are clear(nulled) and will be recreated
      by the next read / write
   - write methods
      - if outputstream is absent connect to server and restart at file
      pointer position
      - write byte(s).

While it appears to work, i thought there might have been some deeper
reasoning behinid the lack of inbuilt support in FtpFileProvider. After all
that the same strategy is used for reading as i have described for writing.
My code is however a mess as i have only implemented writing for some
RandomAccessContent.

If anyone is interested id be happy to share.

On Jul 20, 2011, at 0:45, "Miroslav Pokorny" <miroslav.pokorny@gmail.com>
> wrote:
>
> > Hiho
> >
> > I was just playing with Apache Commons VFS (thanks guys) and noticed that
> >> Ftp FileSystem< does not support random access writing as confirmed by
> > examining the capabilities.
> >
> > [LIST_CHILDREN, URI, GET_LAST_MODIFIED, RENAME, APPEND_CONTENT, DELETE,
> > GET_TYPE, RANDOM_ACCESS_READ, READ_CONTENT, WRITE_CONTENT, CREATE]
> >
> > It does however support random accesss reading and im just wondering is
> > there a particular reason why writing is not supported ?
> >
>
> Hello,
>
> The reason is probably as simple as the protocol is not a natural match for
> the feature. With FTP you stream the whole file up or down, not a random
> piece.
>
> Gary
>
> > tya
> >
> > mP
>
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-- 
mP

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