discourse/spec/support/fake_s3.rb

# frozen_string_literal: true

class FakeS3
  attr_reader :s3_client

  def self.create
    s3 = self.new
    s3.stub_bucket(SiteSetting.s3_upload_bucket) if SiteSetting.s3_upload_bucket.present?
    s3.stub_bucket(File.join(SiteSetting.s3_backup_bucket, RailsMultisite::ConnectionManagement.current_db)) if SiteSetting.s3_backup_bucket.present?
    s3.stub_s3_helper
    s3
  end

  def initialize
    @buckets = {}
    @operations = []
    @s3_client = Aws::S3::Client.new(stub_responses: true, region: SiteSetting.s3_region)

    stub_methods
  end

  def bucket(bucket_name)
    bucket_name, _prefix = bucket_name.split("/", 2)
    @buckets[bucket_name]
  end

  def stub_bucket(full_bucket_name)
    bucket_name, _prefix = full_bucket_name.split("/", 2)

    s3_helper = S3Helper.new(
      full_bucket_name,
      Rails.configuration.multisite ? FileStore::S3Store.new.multisite_tombstone_prefix : FileStore::S3Store::TOMBSTONE_PREFIX,
      client: @s3_client
    )
    @buckets[bucket_name] = FakeS3Bucket.new(full_bucket_name, s3_helper)
  end

  def stub_s3_helper
    @buckets.each do |bucket_name, bucket|
      S3Helper.stubs(:new)
        .with { |b| b == bucket_name || b == bucket.name }
        .returns(bucket.s3_helper)
    end
  end

  def operation_called?(name)
    @operations.any? do |operation|
      operation[:name] == name && (block_given? ? yield(operation) : true)
    end
  end

  private

  def find_bucket(params)
    bucket(params[:bucket])
  end

  def find_object(params)
    bucket = find_bucket(params)
    bucket&.find_object(params[:key])
  end

  def log_operation(context)
    @operations << {
      name: context.operation_name,
      params: context.params.dup
    }
  end

  def calculate_etag(context)
    # simple, reproducible ETag calculation
    Digest::MD5.hexdigest(context.params.to_json)
  end

  def stub_methods
    @s3_client.stub_responses(:head_object, -> (context) do
      log_operation(context)

      if object = find_object(context.params)
        { content_length: object[:size], last_modified: object[:last_modified], metadata: object[:metadata] }
      else
        { status_code: 404, headers: {}, body: "" }
      end
    end)

    @s3_client.stub_responses(:get_object, -> (context) do
      log_operation(context)

      if object = find_object(context.params)
        { content_length: object[:size], body: "" }
      else
        { status_code: 404, headers: {}, body: "" }
      end
    end)

    @s3_client.stub_responses(:delete_object, -> (context) do
      log_operation(context)

      find_bucket(context.params)&.delete_object(context.params[:key])
      nil
    end)

    @s3_client.stub_responses(:copy_object, -> (context) do
      log_operation(context)

      source_bucket_name, source_key = context.params[:copy_source].split("/", 2)
      copy_source = { bucket: source_bucket_name, key: source_key }

      if context.params[:metadata_directive] == "REPLACE"
        attribute_overrides = context.params.except(:copy_source, :metadata_directive)
      else
        attribute_overrides = context.params.slice(:key, :bucket)
      end

      new_object = find_object(copy_source).dup.merge(attribute_overrides)
      find_bucket(new_object).put_object(new_object)

      { copy_object_result: { etag: calculate_etag(context) } }
    end)

    @s3_client.stub_responses(:create_multipart_upload, -> (context) do
      log_operation(context)

      find_bucket(context.params).put_object(context.params)
      { upload_id: SecureRandom.hex }
    end)

    @s3_client.stub_responses(:put_object, -> (context) do
      log_operation(context)

      find_bucket(context.params).put_object(context.params)
      { etag: calculate_etag(context) }
    end)
  end
end

class FakeS3Bucket
  attr_reader :name, :s3_helper

  def initialize(bucket_name, s3_helper)
    @name = bucket_name
    @s3_helper = s3_helper
    @objects = {}
  end

  def put_object(obj)
    @objects[obj[:key]] = obj
  end

  def delete_object(key)
    @objects.delete(key)
  end

  def find_object(key)
    @objects[key]
  end
end