From: "Berger, Daniel" <Daniel.Berger@...>
Date: 2006-04-07T05:03:24+09:00
Subject: Re: Archive::Tar uncompress question

> -----Original Message-----
> From: Dimitri Aivaliotis [mailto:aglarond@gmail.com] 
> Sent: Thursday, April 06, 2006 1:06 PM
> To: ruby-talk ML
> Subject: Archive::Tar uncompress question
> 
> 
> Hi,
> 
> I needed to use Archive::Tar today, and was bit by what I 
> guess was an unforseen use.  I need to simply unpack an 
> archive, optionally decompressing it first.  So, I have code 
> like this:
> 
>     def expand
>       t = Archive::Tar.new( @name )
>       case @name
>       when /\.tar\.bz2/
>         t.expand
>       when /\.bz2/
>         t.uncompress("bunzip2")
>       when /\.t(ar\.)?gz/
>         t.expand
>       when /\.gz/
>         t.uncompress("gunzip")
>       when /\.zip/
>         t.uncompress("unzip")
>       else
>         raise UnknownArchiveError
>       end
>     end
> 
> which works fine for what I need *if* I redefine 
> uncompress_archive like so:
> 
> <pseudo-patch>
> -         unless @compressed_archive_name
> -            raise CompressError, "no compressed file found"
> -         end
> +       unless @compressed_archive_name
> +         @compressed_archive_name = @archive_name
> +       end
> </pseudo-patch>
> 
> It seems that @compressed_archive_name can only be set if one 
> first compresses an archive.  I don't need to do that here - 
> I just need to uncompress an already-existing archive.
> 
> Should I be redefining this method or should the package be 
> changed to the (my) expected behavior?  Or have I just 
> totally missed the usage here?  Has anyone else run up against this?
> 
> - Dimitri

Hi Dimitri,

It basically boils down to a case of unexpected usage.  The assumption
is that you're creating (or going to create) an archive when you use
Archive::Tar.new.

You are, of course, free to redefine uncompress_archive, but rather than
patching the lib itself, I recommend taking advantage of Ruby's open
classes:

# Somewhere in your code:
module Archive
   class Tar
      def uncompress_archive(program="gunzip")
         @compressed_archive_name = @archive_name unless
@compressed_archive_name
            
         cmd = "#{program} #{@compressed_archive_name}"

         Open3.popen3(cmd){ |prog_in, prog_out, prog_err|
            err = prog_err.gets
            if err
               raise CompressError, err.chomp
            end
            @compressed_archive_name = nil
         }
         self
      end
   end
end

I suppose I could add class methods that would do the sort of thing
you're trying to do.  Or, you could add your own class method.

Also note that I'll probably be changing the name to
Archive::Tar::External in the future.

Regards,

Dan