Re: [pclasses-devel] IOFilters / ZLibIOFilter

[stephan b. <st...@s1...>]

On Thursday 06 January 2005 18:46, Christian Prochnow wrote:
> Description:
> IOFilters are proxies which will be called by IODevice's to serve the
> actual I/O requests. The default implementation of IOFilter directly
> calls the real I/O methods (_read, _write, _....).

Don't forget to update the manual ;).
(Just kidding - i'll do that if you don't want to.)

> IOFilters work on any type of IODevice. however I/O filters may
> change the return value of IODevice::isSeekable(). Therefore you
> cannot rely on assumptions like "Files are always seekable".


> Since this is a "raw" zlib deflate stream I/O filter it cannot be
> directly used to decompress/compress gzip files.
> Processing gzip files require an additional header and a trailer
> (http://www.faqs.org/rfcs/rfc1952.html).

AFAIK zlib has gzip_xxx() functions, but i *think* it only has file 
variants, not in-memory variants.

> Maybe we should also add an GZipIOFilter ?
> or if it isn't possible a GZipFile() ?

That's exactly what i'm thinking. i have LGPL code for std::i/ostreams 
which use gzip and bzip2 (i didn't write the gzip support, and bzip2 
was simply a copy/paste plus a one-line change). These should be fairly 
trivial to port to FileStream subclasses. In fact, since they're 
already std::i/ostream[buffers], they may be usable as-is in P, after 
renaming them for P convensions.



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