Gem::Source#fetch_spec

# File tmp/rubies/ruby-4.1.0-preview1/lib/rubygems/source.rb, line 126
def fetch_spec(name_tuple)
  fetcher = Gem::RemoteFetcher.fetcher

  spec_file_name = name_tuple.spec_name

  # The name tuple comes from a remote index and is not otherwise
  # validated, so refuse anything that would escape the spec cache
  # directory when used as a path component.
  if File.basename(spec_file_name) != spec_file_name
    raise Gem::Exception, "malformed spec name: #{spec_file_name.inspect}"
  end

  source_uri = enforce_trailing_slash(uri) + "#{Gem::MARSHAL_SPEC_DIR}#{spec_file_name}"

  cache_dir = cache_dir source_uri

  local_spec = File.join cache_dir, spec_file_name

  if File.exist? local_spec
    spec = Gem.read_binary local_spec
    Gem.load_safe_marshal
    spec = begin
             Gem::SafeMarshal.safe_load(spec)
           rescue StandardError
             nil
           end
    return spec if spec
  end

  source_uri.path << ".rz"

  spec = fetcher.fetch_path source_uri
  spec = Gem::Util.inflate spec

  if update_cache?
    require "fileutils"
    FileUtils.mkdir_p cache_dir

    File.open local_spec, "wb" do |io|
      io.write spec
    end
  end

  Gem.load_safe_marshal
  # TODO: Investigate setting Gem::Specification#loaded_from to a URI
  Gem::SafeMarshal.safe_load spec
end