The format class knows the guts of the ancient .gem file format and provides the capability to read such ancient gems.

Please pretend this doesn't exist.

Methods
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Class Public methods
new(gem)

Creates a new old-format package reader for gem. Old-format packages cannot be written.

Source: show | on GitHub 

# File lib/rubygems/package/old.rb, line 21
def initialize gem
  require 'fileutils'
  require 'zlib'
  Gem.load_yaml

  @contents        = nil
  @gem             = gem
  @security_policy = nil
  @spec            = nil
end
Instance Public methods
contents()

A list of file names contained in this gem

Source: show | on GitHub 

# File lib/rubygems/package/old.rb, line 35
def contents
  verify

  return @contents if @contents

  open @gem, 'rb' do |io|
    read_until_dashes io # spec
    header = file_list io

    @contents = header.map { |file| file['path'] }
  end
end
extract_files(destination_dir)

Extracts the files in this package into destination_dir

Source: show | on GitHub 

# File lib/rubygems/package/old.rb, line 51
def extract_files destination_dir
  verify

  errstr = "Error reading files from gem"

  open @gem, 'rb' do |io|
    read_until_dashes io # spec
    header = file_list io
    raise Gem::Exception, errstr unless header

    header.each do |entry|
      full_name = entry['path']

      destination = install_location full_name, destination_dir

      file_data = ''

      read_until_dashes io do |line|
        file_data << line
      end

      file_data = file_data.strip.unpack("m")[0]
      file_data = Zlib::Inflate.inflate file_data

      raise Gem::Package::FormatError, "#{full_name} in #{@gem} is corrupt" if
        file_data.length != entry['size'].to_i

      FileUtils.rm_rf destination

      FileUtils.mkdir_p File.dirname destination

      open destination, 'wb', entry['mode'] do |out|
        out.write file_data
      end

      say destination if Gem.configuration.really_verbose
    end
  end
rescue Zlib::DataError
  raise Gem::Exception, errstr
end
spec()

The specification for this gem

Source: show | on GitHub 

# File lib/rubygems/package/old.rb, line 132
def spec
  verify

  return @spec if @spec

  yaml = ''

  open @gem, 'rb' do |io|
    skip_ruby io
    read_until_dashes io do |line|
      yaml << line
    end
  end

  yaml_error = if RUBY_VERSION < '1.9' then
                 YAML::ParseError
               elsif YAML::ENGINE.yamler == 'syck' then
                 YAML::ParseError
               else
                 YAML::SyntaxError
               end

  begin
    @spec = Gem::Specification.from_yaml yaml
  rescue yaml_error => e
    raise Gem::Exception, "Failed to parse gem specification out of gem file"
  end
rescue ArgumentError => e
  raise Gem::Exception, "Failed to parse gem specification out of gem file"
end
verify()

Raises an exception if a security policy that verifies data is active. Old format gems cannot be verified as signed.

Source: show | on GitHub 

# File lib/rubygems/package/old.rb, line 167
def verify
  return true unless @security_policy

  raise Gem::Security::Exception,
        'old format gems do not contain signatures and cannot be verified' if
    @security_policy.verify_data

  true
end