Carrierwave preloading

README.md

• How to preload file via Carrierwave for api?
• How to preload huge file before sending all form?

Carrierwave doesn't give approach for preloading file, so there is simple implementation.

carrierwave.rb

# config/initializers/carrierwave.rb

ActiveRecord::Base.extend Carrierwave::PreloadAdapter

document.rb

# app/models/document.rb

class Document < ApplicationRecord
  mount_preload_uploader :file, FileUploader
  mount_preload_uploaders :files, FileUploader
end

preload_adapter.rb

# lib/carrierwave/preload_adapter.rb

module Carrierwave
  module PreloadAdapter
    def mount_preload_uploader(attribute, uploader_class, **options)
      mount_uploader attribute, uploader_class, options

      define_method "#{attribute}=" do |data|
        uploader = PreloadUploader.build_preloaded(data)
        return super(data) if uploader.blank?

        @preload_uploaders ||= []
        @preload_uploaders << uploader
        super(uploader.file)
      end

      after_save { [*@preload_uploaders].compact.each(&:remove!) }
    end

    def mount_preload_uploaders(attribute, uploader_class, **options)
      mount_uploaders attribute, uploader_class, options

      define_method "#{attribute}=" do |data|
        uploaders = data.map { |el| PreloadUploader.build_preloaded(el) }.compact
        return super(data) if uploaders.blank?

        @preload_uploaders ||= []
        @preload_uploaders += uploaders
        super(uploaders.map(&:file))
      end

      after_save { [*@preload_uploaders].compact.each(&:remove!) }
    end
  end
end

preload_uploader.rb

# app/uploaders/preload_uploader.rb

class PreloadUploader < CarrierWave::Uploader::Base
  OUTCOME_PREFIX = 'preload'.freeze
  TIMESTAMP_FORMAT = '%Y%m%d-%H%M%-s'.freeze
  storage :file

  def self.build_preloaded(data)
    return unless data =~ %r{#{OUTCOME_PREFIX}:(\d{8}-\d{14})/(.*)}

    folder_name = Regexp.last_match[1]
    file_name = Regexp.last_match[2]
    instance = new(folder_name)
    instance.retrieve_from_store!(file_name)
    instance
  end

  def initialize(folder_name = Time.current.strftime(TIMESTAMP_FORMAT))
    @folder_name = folder_name
  end

  def store_dir
    "preloading/#{@folder_name}"
  end

  def move_to_cache
    false
  end

  def outcome
    "#{OUTCOME_PREFIX}:#{@folder_name}/#{filename}"
  end
end

routes.rb

Rails.application.routes.draw do
  resources :uploads do
    post :preload, on: :collection
  end
end

uploads_controller.rb

# app/controllers/uploads_controller.rb

class UploadsController < ApplicationController
  def preload
    uploader = PreloadUploader.new
    uploader.store!(params[:file])
    if uploader.file.present?
      render json: { code: :ok, result: uploader.outcome }
    else
      render json: { code: :error }, status: :unprocessable_entity
    end
  end
end