rack middleware, best way to replace request body?

[Stephen Bannasch <stephen.bannasch@deanbrook.org>]

I like to create a rack middleware filter that will automatically 
decompress a request with a content encoding of 'b64gzip' before 
passing it on.

What's the best way for a rack middleware filter to replace the 
request bosy with an uncompressed version?

FYI, this is what my code looks like now -- it works except for the 
part of actualyy replacing the request body ;-)

module Rack

   class ExpandB64Gzip
     def initialize(app)
       @app = app
     end

     def call(env)
       @compressed = env['HTTP_CONTENT_ENCODING'] == "b64gzip"
       @app.call(env)
     end

     def each(&block)
       if @compressed
         req = Rack::Request.new(env)
         decompressed_body = b64gzip_decompress_body(req.body)
         debugger
         req.body = decompressed_body
       end

     end

     def b64gzip_decompress_body(body)
       Zlib::GzipReader.new(StringIO.new(B64::B64.decode(body.read))).read
     end
   end
end

module B64
   class B64
     def self.folding_encode(str, eol = "\n", limit = 60)
       [str].pack('m')
     end

     def self.encode(str)
       [str].pack('m').tr( "\r\n", '')
     end

     def self.decode(str, strict = false)
       str.unpack('m').first
     end
   end
end