How to download images from AWS S3 (rails, carrierwave)

environment ruby2.6.5 rails5.2.4 gem 'carrierwave' gem 'fog-aws'

Step 1 Let's stop Japanese file names

If the posted file name contains Japanese, subsequent processing will be difficult. With gem'carrierwave', you can rename the file as officially stated, so let's start from there. In my case, I decided to save the filename as a random alphanumeric character. Don't use the current time when saving. When resizing, the time will be off and an error will occur.

`image_uploader.rb`



  def filename
    "#{secure_token}.#{file.extension}" if original_filename.present?
  end

  def secure_token
    var = :"@#{mounted_as}_secure_token"
    model.instance_variable_get(var) or model.instance_variable_set(var, SecureRandom.uuid)
  end

By writing in this way, the posted file name will be saved in random alphanumeric characters. Although the file name was changed with only filename, access to S3 did not work, but it was solved by adding def secure_token.

Step 2 Set the routing

`routes.rb`


  resources :posts do
    member do
      get :download
    end
  end

Step 3 Let's write the download method in the controller

`posts_controller.rb`



  def download
    url = URI.encode(@post.image.url)
    data_path = open(url)
    send_data data_path.read, disposition: 'attachment',
    type: @post.image_type
  end

Since my level is a beginner level, I think there is a waste in the description, but please forgive me.

Until the error and resolution encountered

When the file name first contained a Japanese name, there was nothing wrong with uploading. However, when I wrote the download method and tried to download it, 502 access denied was displayed. This 502 is awkward and at first I thought I didn't have access to AWS, but if I could upload it, I should have access. Further investigation reveals that 502 is displayed even if the URL is not found, Furthermore, it turned out that the cause was the Japanese notation. This is probably the reason why the files are often random alphanumeric files when downloaded on image posting sites.