Fetching files and generate zip file

Here's a practical approach for downloading remote files and combining them into a compressed archive using Ruby on Rails.

Main Method

The generate_zip function handles the core logic:

def generate_zip
  filename = "filename.zip"
  temp_file = Tempfile.new(filename)
  files_to_zip = []

  # Initialize the temp file as a zip file
  Zip::OutputStream.open(temp_file) { |zos| }

  # Add files to the zip file as usual
  Zip::File.open(temp_file.path, Zip::File::CREATE) do |_zip|
    file_urls.each do |file_url|
      file_to_zip = get_document_for_zip(file_url)
      files_to_zip << file_to_zip
      _zip.add('some file name', file_to_zip)
    end
  end

  # Read the binary data from the file
  zip_data = File.open(temp_file.path)
  zip_data
rescue StandardError => e
  # do something
ensure
  temp_file.close
  temp_file.unlink
  files_to_zip.each do |file_to_zip|
    file_to_zip.close
    file_to_zip.unlink
  end
end

Helper Method

The get_document_for_zip method retrieves individual files from CDN:

def get_document_for_zip(file_url)
  file_to_zip = Tempfile.new('some file name')
  file_to_zip.binmode
  file_to_zip.write(HTTParty.get(file_url))
  file_to_zip.flush
  file_to_zip
end

Controller Integration

def export
  respond_to do |format|
    format.zip do
      send_data generate_zip, filename: "filename.zip", type: "application/zip"
    end
  end
end

The solution avoids sending temporary files directly to browsers because they may be deleted before Rails completes transmission. Instead, it reads binary data first, then streams it as an attachment.