From: Massimiliano Mirra <list@...>
Date: 2002-07-09T22:41:24+09:00
Subject: Re: SV: SV: [ANN] Archive 0.2

On Mon, Jul 08, 2002 at 08:41:41PM +0900, Thomas S�ndergaard wrote:
> > Do you think it would be possible to add a set of proxies that adapt
> > rubyzip interface to Archive's?  After all, the whole Archive thing is
> > just a matter of convenience (learn to deal with archives once, apply
> > the knowledge on all formats).
> 
> I don't see why not, and I'd even like to do it. Are the interfaces
> that rubyzip would have to implement apparent from the archive
> module code? If not, do you have some documentation.

Here is the skeleton of Archive::(Reader|Writer|Modifier|Entry)::Ar.
As you can see, most of the work is done in Entry::Ar.

module Archive
	module Modifier
		class Ar < Generic
			# nothing to do here, taken care in Generic
		end
	end


	module Reader
		class Ar < Generic
			def initialize(io)
				# mostly nothing to do here
			end
		end
	end


	module Writer
		class Ar < Generic
			# nothing to do here, taken care in Generic
		end
	end


	module Entry
		class Ar < Generic
			def initialize(io)
				# creates two parts and extracts an
				# entry from the io stream
				
				super(io, :header, :data)
				parse
			end

			def parse 
				@parts[:header] = EntryPart.new(Header) do
					start = @io.pos
					raw = @io.read(Header::LEN)
					[start...@io.pos, raw]
				end

				@parts[:data] = EntryPart.new(String) do
					start = @io.pos
					raw = @io.read(@parts[:header].parsed.size)
					[start...@io.pos, raw]
				end

				# ...
			end

			def update 
				@parts[:header].parsed.size = @parts[:data].raw.length
			end

			def to_arc_format 
				# ...
				update
				dump = header.parsed.to_arc_format + data.raw
				return dump
			end
			
			class Header
				# various constants such as header
				# length defined here

				def initialize(header_raw)
					# takes raw header and parses it
					# to initialize itself
				end

				def to_arc_format 
					# ...
				end
			end 
		end
	end
end 


Basically, you need an Archive::Entry::Zip < Archive::Entry::Generic
that, given a io stream passed to initialize, reads and parses an
archive entry, and leaves the io cursor at the beginning of the next
one.  If it can also output itself in Zip format again, you will be
able to pass entries to Archive::Writer for writing.

Each Entry::XYZ has `parts': a Zip entry will most likely have a
`data' and a `header' part.  Each part, in turn, has a `raw' and a
`parsed' attribute: `raw' points to the raw stuff as read from the
stream, `parsed' to a structure modifiable from code.  You will
probably create an Archive::Entry::Zip::Header object that takes care
of receiving the Zip raw header, parse it, and initialize itself.  The
data part will usually remain unparsed.

One nice thing of this design is that a mbox Entry can, for example,
implement a to_zip method.  Then you could do something like this:

in = File.open("/var/mail/joe")
out = File.open("/home/joe/mails.zip")

mbox = Archive::Reader::Mbox.new(in)
zip = Archive::Writer::Zip.new(out)

mbox.scan do |entry|
	zip.add(entry)
end

The `add' method from Archive::Writer will see that we're trying to
write on a zip and that we have a Mbox::Entry#to_zip method, so will
use that, and we'll have converted from Mbox to Zip on the fly.

(This is not in Archive::Writer::Generic yet, because I have written
no to_xyz methods so far.)

If you have any questions, just ask.


Massimiliano

  
p.s.: Sorry to ask, isn't there some way to have your mail client set
correct References: or at least not modify the subject?