Re: [Boost-users] [iostreams] experience with automatically decompressing with gzip or bzip2

From: Jonathan Turkanis (technews_at_[hidden])
Date: 2005-09-18 14:45:49

Marcus Alanen wrote:
> Hello, I've recently used iostreams for easier gziping and bzip2ing of
> output streams. However, I'd also like to be able to read any file
> compressed with either gzip or bzip2, by analyzing the input stream
> and deducing which decompressor to use.
>
> I don't want to open the file twice or to seek in the stream, as this
> might not be possible due to e.g. reading from the network. My
> solution
> is to create a custom streambuf, which is told to read and retain the
> first few bytes to determine which decompressor to push onto the
> boost::iostreams::filtering_streambuf. Then the actual reading can
> take place, and the custom streambuf first returns the retained
> bytes, then just streams the rest of the actual input streambuf.

This is a nice idea. IMO, the best way to implement it would be as a filter -- 
perhaps you could call it a stream_signature_filter. You might use it as
follows:

   stream_signature_filter f;
   f.push("GZIP", gzip_decompressor());
   f.push("BZh", bzip2_decompressor());
   filtering_istreambuf in(f);
   in.push(file("archive.tar.gz"));

You could then define filters derived from stream_signature_filter that have
preset mappings from signatures to filters.

I'll add this to my list of ideas of 1.34.

Thanks!

>
> Regards,
> Marcus

Jonathan