Uploading images to a Rails API using Paperclip (via either base64 string-encoded image or a public HTTP image URL)

image_uploadable.rb

module ImageUploadable
  extend ActiveSupport::Concern

  private

  def set_image_by_params_for(model, params)
    image_uri    = params[:image_uri]
    image_base64 = params[:image_base64]

    set_image_from_uri_for(model, image_uri)       if image_uri.present?
    set_image_from_base64_for(model, image_base64) if image_base64.present?
  end

  def set_image_from_uri_for(model, image_uri)
    model.image = URI.parse(image_uri)
  end

  def set_image_from_base64_for(model, image_base64)
    tempfile = Tempfile.new(tempfile_name_for(model))

    tempfile.binmode
    tempfile.write(Base64.decode64(image_base64))
    tempfile.rewind

    model.image = tempfile
  ensure
    tempfile.close
    tempfile.unlink
  end

  def tempfile_name_for(model)
    @image_tempfile_name ||= begin
      millisecond_timestamp = (Time.now.to_f * 10000).to_i
      "#{model.class.name}_image_#{millisecond_timestamp}"
    end
  end
end

users_controller.rb

# example usage

class UsersController < ApiController
  include ImageUploadable
  
  def update
    user = User.find(params[:id])
    user.assign_attributes(user_params)
    set_image_by_params_for(user, params[:user])
    
    if user.save
      render json: user, status: :ok
    else
      render json: { errors: user.errors }, status: :unprocessable_entity
    end
  end
  
  private
  
  def user_params
    params.require(:user).permit(:email, :name)
  end
end