ActiveStorageDownloader

active_storage_downloader.rb

# frozen_string_literal: true

module ActiveStorageDownloader
  refine ActiveStorage::Blob do
    def download_to(tempdir: nil, &block)
      DownloadTo.new(self, tempdir: tempdir).download_blob_to_tempfile(&block)
    end
  end

  using self

  def self.download(name = :disk)
    STDOUT.puts "#{ActiveStorage::Blob.count} Blobs to go..."
    STDOUT.puts "max: #{ActiveStorage::Blob.maximum(:id)}"
    configs = Rails.configuration.active_storage.service_configurations
    to_service = ActiveStorage::Service.configure(name, configs)
    ActiveStorage::Blob.find_each do |blob|
      blob.download_to do |tf|
        to_service.upload(blob.key, tf, checksum: blob.checksum)
      end
      STDOUT.print "##{blob.id}\n"
    end
  end

  class DownloadTo
    def initialize(blob, tempdir: nil)
      @blob    = blob
      @tempdir = tempdir
    end

    def download_blob_to_tempfile
      open_tempfile do |file|
        download_blob_to file
        verify_integrity_of file
        yield file
      end
    rescue Aws::S3::Errors::NotFound
      blob.delete
    end

    private

    attr_reader :blob, :tempdir

    def open_tempfile
      file = Tempfile.open(["ActiveStorage-#{blob.id}-", blob.filename.extension_with_delimiter], tempdir)

      begin
        yield file
      ensure
        file.close!
      end
    end

    def download_blob_to(file)
      file.binmode
      blob.download { |chunk| file.write(chunk) }
      file.flush
      file.rewind
    end

    def verify_integrity_of(file)
      fail ActiveStorage::IntegrityError unless Digest::MD5.file(file).base64digest == blob.checksum
    end
  end
end