Stubbing the AWS SDK S3 (bucket.object, bucket.object.exists? methods and bucket.object.exists? responses)

0_Gemfile

# Gemfile
gem 'aws-sdk-s3'

1_aws.rb

# config/initializers/aws.rb

credentials = Aws::Credentials.new(
  Boyutluseyler.config[:direct_upload_access_key_id],
  Boyutluseyler.config[:direct_upload_secret_access_key]
)

# https://docs.aws.amazon.com/sdk-for-ruby/v3/api/Aws/S3/Resource.html
DIRECT_UPLOAD_RESOURCE = Aws::S3::Resource.new(
  stub_responses: Rails.env.test?,
  region: Boyutluseyler.config[:direct_upload_region],
  credentials: credentials
)

DIRECT_UPLOAD_BUCKET = DIRECT_UPLOAD_RESOURCE.bucket(Boyutluseyler.config[:direct_upload_bucket_name])

2_stub_aws_responses.rb

# spec/support/helpers/stub_aws_responses.rb

# https://docs.aws.amazon.com/sdk-for-ruby/v3/api/Aws/S3/Resource.html
# https://docs.aws.amazon.com/sdk-for-ruby/v3/api/Aws/S3/Client.html

# Stubbing the AWS SDK
# https://docs.aws.amazon.com/sdk-for-ruby/v3/developer-guide/stubbing.html
# https://docs.aws.amazon.com/sdk-for-ruby/v3/api/Aws/ClientStubs.html
# https://aws.amazon.com/blogs/developer/advanced-client-stubbing-in-the-aws-sdk-for-ruby-version-3/
# https://stelligent.com/2016/04/14/using-stubs-for-the-aws-sdk-for-ruby-2/
# https://semaphoreci.com/community/tutorials/stubbing-the-aws-sdk

module StubAWSResponses
  def stub_direct_upload_bucket_object_is_not_exist
    DIRECT_UPLOAD_RESOURCE.client.stub_responses(:head_object,
                                                 status_code: 404,
                                                 headers: {},
                                                 body: '')
  end

  def stub_direct_upload_bucket_object_exists
    DIRECT_UPLOAD_RESOURCE.client.stub_responses(:head_object,
                                                 status_code: 200,
                                                 headers: {},
                                                 body: '')
  end
end

3_spec_helper.rb

# spec/spec_helper.rb

RSpec.configure do |config|
  config.include StubAWSResponses
end

4_build_service.rb

# app/services/blueprints/build_service.rb

# frozen_string_literal: true

module Blueprints
  class BuildService < Blueprints::BaseService
    prepend ValidatesRemoteObject

    def execute
      validate!

      Blueprint.new.tap do |b|
        b.url = remote_object.public_url
        b.url_path = remote_object.key
        b.size = remote_object.size
        b.content_type = remote_object.content_type
        b.thumb_url = ''
      end
    end

    private

    def validate!
      raise ValidationError, 'File not found' unless remote_object_exists?
    end

    def bucket
      ObjectStorage::DirectUpload::Bucket
    end
  end
end

5_validates_remote_object.rb

# app/services/concerns/validates_remote_object.rb

# frozen_string_literal: true

module ValidatesRemoteObject
  # https://docs.aws.amazon.com/sdk-for-ruby/v3/api/Aws/S3/Object.html#exists%3F-instance_method
  delegate :exists?, to: :remote_object, prefix: true

  def remote_object
    @remote_object ||= bucket.object(key)
  end

  def bucket
    super || (raise NotImplementedError,
                    '"bucket" must be implemented and return an Aws::S3::Bucket')
  end

  def key
    params[:key] || (raise ArgumentError, 'Key needs to be specified')
  end
end

6_bucket.rb

# lib/object_storage/direct_upload/bucket.rb

# frozen_string_literal: true

# Wrapper class for AWS::S3::Bucket

require_relative 'presigned_post'

module ObjectStorage
  module DirectUpload
    class Bucket
      class << self
        delegate :object, to: :bucket

        def bucket
          @bucket ||= DIRECT_UPLOAD_BUCKET
        end

        def presigned_post(policy)
          PresignedPost.new(bucket, policy).create
        end
      end
    end
  end
end

7_build_service_spec.rb

# spec/services/blueprints/build_service_spec.rb

# frozen_string_literal: true

require 'spec_helper'

RSpec.describe Blueprints::BuildService do
  describe 'modules' do
    it { is_expected.to include_module(ValidatesRemoteObject) }
  end

  describe '#execute' do
    subject(:service) { described_class.new(user, params) }

    let(:user) { build_stubbed(:user) }
    let(:params) { { key: 'model.stl' } }
    let(:validation_error) { described_class::ValidationError }

    context 'when the remote object is not exist' do
      before do
        stub_direct_upload_bucket_object_is_not_exist
      end

      after do
        stub_direct_upload_bucket_object_exists # default stub behavior
      end

      it 'raises a file not found error' do
        expect { service.execute }.to raise_error(validation_error, 'File not found')
      end
    end

    context 'when the remote object exists' do
      it 'builds a blueprint without saving it' do
        direct_upload_bucket = class_double(ObjectStorage::DirectUpload::Bucket).as_stubbed_const
        # stubbing Aws::S3::Object
        remote_object = double(key: 'model.stl', size: 1, content_type: 'model/stl',
                               public_url: 'http://foo.com/model.stl', exists?: true)
        allow(direct_upload_bucket).to receive(:object).and_return(remote_object)

        result = service.execute

        expect(result).to be_valid
        expect(result).not_to be_persisted
      end
    end
  end
end