class ActiveStorage::Blob

def compute_checksum_in_chunks(io)
  raise ArgumentError, "io must be rewindable" unless io.respond_to?(:rewind)
  OpenSSL::Digest::MD5.new.tap do |checksum|
    while chunk = io.read(5.megabytes)
      checksum << chunk
    end
    io.rewind
  end.base64digest
end