ActiveStorage File Attachment Validation

Question

Is there a way to validate attachments with ActiveStorage? For example, if I want to validate the content type or the file size?

Something like Paperclip's approach would be great!

  validates_attachment_content_type :logo, content_type: /\Aimage\/.*\Z/
  validates_attachment_size :logo, less_than: 1.megabytes

Answer 1

Well, it ain't pretty, but this may be necessary until they bake in some validation:

  validate :logo_validation

  def logo_validation
    if logo.attached?
      if logo.blob.byte_size > 1000000
        logo.purge
        errors[:base] << 'Too big'
      elsif !logo.blob.content_type.starts_with?('image/')
        logo.purge
        errors[:base] << 'Wrong format'
      end
    end
  end

Answer 2

ActiveStorage doesn't support validations right now. According to https://github.com/rails/rails/issues/31656.

---

Update:

Rails 6 will support ActiveStorage validations.

https://github.com/rails/rails/commit/e8682c5bf051517b0b265e446aa1a7eccfd47bf7

Uploaded files assigned to a record are persisted to storage when the record
is saved instead of immediately.
In Rails 5.2, the following causes an uploaded file in `params[:avatar]` to
be stored:
```ruby
@user.avatar = params[:avatar]
```
In Rails 6, the uploaded file is stored when `@user` is successfully saved.

Answer 3

Came across this gem: https://github.com/igorkasyanchuk/active_storage_validations

    class User < ApplicationRecord
      has_one_attached :avatar
      has_many_attached :photos
    
      validates :name, presence: true
    
      validates :avatar, attached: true, content_type: 'image/png',
                                         dimension: { width: 200, height: 200 }
      validates :photos, attached: true, content_type: ['image/png', 'image/jpg', 'image/jpeg'],
                                         dimension: { width: { min: 800, max: 2400 },
                                                      height: { min: 600, max: 1800 }, message: 'is not given between dimension' }
    end

Answer 4

You can use awesome https://github.com/musaffa/file_validators gem

class Profile < ActiveRecord::Base
  has_one_attached :avatar
  validates :avatar, file_size: { less_than_or_equal_to: 100.kilobytes },
    file_content_type: { allow: ['image/jpeg', 'image/png'] }
end

I'm using it with form object so I'm not 100% sure it is working directly with AR but it should...

Answer 5

Here is my solution to validate content types in Rails 5.2, that as you may know it has the pitfall that attachments are saved as soon as they are assigned to a model. It may also work for Rails 6. What I did is monkey-patch ActiveStorage::Attachment to include validations:

config/initializers/active_storage_attachment_validations.rb:

Rails.configuration.to_prepare do
  ActiveStorage::Attachment.class_eval do
    ALLOWED_CONTENT_TYPES = %w[image/png image/jpg image/jpeg].freeze

    validates :content_type, content_type: { in: ALLOWED_CONTENT_TYPES, message: 'of attached files is not valid' }
  end
end

app/validators/content_type_validator.rb:

class ContentTypeValidator < ActiveModel::EachValidator
  def validate_each(record, attribute, _value)
    return true if types.empty?
    return true if content_type_valid?(record)

    errors_options = { authorized_types: types.join(', ') }
    errors_options[:message] = options[:message] if options[:message].present?
    errors_options[:content_type] = record.blob&.content_type
    record.errors.add(attribute, :content_type_invalid, errors_options)
  end

  private

  def content_type_valid?(record)
    record.blob&.content_type.in?(types)
  end

  def types
    Array.wrap(options[:with]) + Array.wrap(options[:in])
  end
end

Due to the implementation of the attach method in Rails 5:

    def attach(*attachables)
      attachables.flatten.collect do |attachable|
        if record.new_record?
          attachments.build(record: record, blob: create_blob_from(attachable))
        else
          attachments.create!(record: record, blob: create_blob_from(attachable))
        end
      end
    end

The create! method raises an ActiveRecord::RecordInvalid exception when validations fail, but it just needs to be rescued and that's all.

Answer 6

Copy contents of the ActiveStorage's DirectUploadsController in the app/controllers/active_storage/direct_uploads_controller.rb file and modify the create method. You can add authentication to this controller, add general validations on the file size or mime type, because create method of this controller creates the url for the file to be uploaded. So you can prevent any file upload by controlling size and mime type in this controller.

A simple validation could be:

# ...
def create
  raise SomeError if blob_args[:byte_size] > 10240 # 10 megabytes
  blob = ActiveStorage::Blob.create_before_direct_upload!(blob_args)
  render json: direct_upload_json(blob)
end
# ...

Answer 7

I found a way to validate and delete attachments with callback before_save. This is a useful approach because if you validate file during the transaction (and you want to purge it), after adding error and it will rollback deleting the attachment.

before_save :check_logo_file, on: %i[create update]

def check_favicon_content_type
    PartnerValidators::CustomPartnerFaviconValidator.new.validate(self)
end

module PartnerValidators
    class CustomPartnerFaviconValidator < ActiveModel::Validator
        ALLOWED_MIME_TYPES = %w(image/vnd.microsoft.icon image/x-icon image/png).freeze
        private_constant :ALLOWED_MIME_TYPES

        def validate(partner)
            if partner.favicon.attached? && invalid_content_type?(partner)
                partner.errors.add(:favicon, I18n.t("active_admin.errors.favicon"))
                partner.favicon.purge
            end
        end

        private

        def invalid_content_type?(partner)
            !partner.favicon.blob.content_type.in?(ALLOWED_MIME_TYPES)
        end
    end
end