the reason of ruby_core_source.rb:57 'initilize': not in gzip format (Zlib::GzipFile::Error)

ruby_core_source.rb

#
# the problem was
# this file was TAR compressed but not TAR.GZ
#
  uri_path = "http://ftp.ruby-lang.org/pub/ruby/1.9/" + ruby_dir + ".tar.gz"


  Tempfile.open("ruby-src") { |temp|

    temp.binmode
    uri = URI.parse(uri_path)
    uri.download(temp)

    tgz = Zlib::GzipReader.new(File.open(temp, "rb"))

    FileUtils.mkdir_p(dest_dir)
    Dir.mktmpdir { |dir|
      inc_dir = dir + "/" + ruby_dir + "/*.inc"
      hdr_dir = dir + "/" + ruby_dir + "/*.h"
      Archive::Tar::Minitar.unpack(tgz, dir)
      FileUtils.cp(Dir.glob([ inc_dir, hdr_dir ]), dest_dir)
    }
  }

workaround.rb

#    just a temp workaround when the ruby source format is TAR, but not TAR.GZ
#
#    tgz = Zlib::GzipReader.new(File.open(temp, "rb"))
    tgz = File.open(temp, "rb")