looks like disposable script, but I think this reusable...

stringioextend.rb

require 'stringio'

module IOExtend
	def readq; self.read(8).unpack("Q")[0]; end
	def readd; self.read(4).unpack("V")[0]; end
	def readw; self.read(2).unpack("v")[0]; end
end

class IO; include IOExtend; end
class StringIO; include IOExtend; end

class String
	include IOExtend;

	# IO compat layer (incomplete)
	def read(n); io().read(n); end
	def eof(); io().eof(); end

	# Transparent IO layer
	def io(&block); @io ||= StringIO.open(self, "rb", &block); end
	def close(); if @io; @io.close; @io = nil; end; end
end

### example

# prepare file by...
# ruby -rzlib -e "d=['Hello','World-','Bye!'].map{|e|[e.size,e].pack('Va*')}.join;d=Zlib::Deflate.deflate d;$>.binmode.write [d.size,d].pack('Va*')" > test.bin

require 'zlib'
open("test.bin", "rb") do |f|
	len = f.readd
	dat = Zlib::Inflate.inflate(f.read(len))

	# usable type
	while !dat.eof
		dlen = dat.readd
		ddat = dat.read(dlen)

		puts "data = #{ddat}"
	end

	# another type
	dat.close	# reset...
	dat.io { |f|
		while !f.eof
			dlen = f.readd
			ddat = f.read(dlen)

			puts "data = #{ddat}"
		end
	}
end