class Bundler::CompactIndexClient::Updater

def update(local_path, remote_path, retrying = nil)
  headers = {}
  Dir.mktmpdir("bundler-compact-index-") do |local_temp_dir|
    local_temp_path = Pathname.new(local_temp_dir).join(local_path.basename)
    # first try to fetch any new bytes on the existing file
    if retrying.nil? && local_path.file?
      FileUtils.cp local_path, local_temp_path
      headers["If-None-Match"] = etag_for(local_temp_path)
      headers["Range"] = "bytes=#{local_temp_path.size}-"
    else
      # Fastly ignores Range when Accept-Encoding: gzip is set
      headers["Accept-Encoding"] = "gzip"
    end
    response = @fetcher.call(remote_path, headers)
    return nil if response.is_a?(Net::HTTPNotModified)
    content = response.body
    if response["Content-Encoding"] == "gzip"
      content = Zlib::GzipReader.new(StringIO.new(content)).read
    end
    mode = response.is_a?(Net::HTTPPartialContent) ? "a" : "w"
    SharedHelpers.filesystem_access(local_temp_path) do
      local_temp_path.open(mode) {|f| f << content }
    end
    response_etag = (response["ETag"] || "").gsub(%r{\AW/}, "")
    if etag_for(local_temp_path) == response_etag
      SharedHelpers.filesystem_access(local_path) do
        FileUtils.mv(local_temp_path, local_path)
      end
      return nil
    end
    if retrying
      raise MisMatchedChecksumError.new(remote_path, response_etag, etag_for(local_temp_path))
    end
    update(local_path, remote_path, :retrying)
  end
end