class Bundler::CompactIndexClient::Updater

def update(local_path, remote_path, retrying = nil)
  headers = {}
  local_temp_path = local_path.sub(/$/, ".#{$$}")
  local_temp_path = local_temp_path.sub(/$/, ".retrying") if retrying
  local_temp_path = local_temp_path.sub(/$/, ".tmp")
  # first try to fetch any new bytes on the existing file
  if retrying.nil? && local_path.file?
    copy_file local_path, local_temp_path
    headers["If-None-Match"] = etag_for(local_temp_path)
    headers["Range"] =
      if local_temp_path.size.nonzero?
        # Subtract a byte to ensure the range won't be empty.
        # Avoids 416 (Range Not Satisfiable) responses.
        "bytes=#{local_temp_path.size - 1}-"
      else
        "bytes=#{local_temp_path.size}-"
      end
  end
  response = @fetcher.call(remote_path, headers)
  return nil if response.is_a?(Net::HTTPNotModified)
  content = response.body
  etag = (response["ETag"] || "").gsub(%r{\AW/}, "")
  correct_response = SharedHelpers.filesystem_access(local_temp_path) do
    if response.is_a?(Net::HTTPPartialContent) && local_temp_path.size.nonzero?
      local_temp_path.open("a") {|f| f << slice_body(content, 1..-1) }
      etag_for(local_temp_path) == etag
    else
      local_temp_path.open("wb") {|f| f << content }
      etag.length.zero? || etag_for(local_temp_path) == etag
    end
  end
  if correct_response
    SharedHelpers.filesystem_access(local_path) do
      FileUtils.mv(local_temp_path, local_path)
    end
    return nil
  end
  if retrying
    raise MisMatchedChecksumError.new(remote_path, etag, etag_for(local_temp_path))
  end
  update(local_path, remote_path, :retrying)
rescue Zlib::GzipFile::Error
  raise Bundler::HTTPError
ensure
  FileUtils.remove_file(local_temp_path) if File.exist?(local_temp_path)
end