You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: cross_region_copying.rb
    path of file: ./repos/aws-sdk-ruby/gems/aws-sdk-docdb/lib/aws-sdk-docdb/plugins
    
    the code of the file until where you have to start completion: # frozen_string_literal: true

require 'aws-sigv4'

module Aws
  module DocDB
    module Plugins
      # This plugin populates the `:pre_signed_url` request param for APIs
      # that support cross region copying.
      #
      # This parameter is required by RDS when copying an encrypted snapshot
      # across regions. This plugin will be skipped if the `:pre_signed_url`
      # parameter is provided by the user.
      class CrossRegionCopying < Seahorse::Client::Plugin
        # @api private
        class Handler < Seahorse::Client::Handler
          def call(context)
            params = context.params
            if params.is_a?(Hash) &&
               params[:source_region] && !params[:pre_signed_url]
              params[:pre_signed_url] = presigned_url(context, params)
            end
            @handler.call(context)
          end

          private

          def presigned_url(context, params)
            # :source_region is not modeled in the api
            
    
          def presigned_url(context, params)
            # :source_region is not modeled in the api
            source_region = params.delete(:source_region)
            param_list = Aws::Query::ParamList.new
            param_list.set('Action', context.operation.name)
            param_list.set('DestinationRegion', context.config.region)
            param_list.set('Version', context.config.api.version)
            Aws::Query::ParamBuilder.new(param_list).apply(
              context.operation.input,
              params
            )

            endpoint_params = Aws::DocDB::EndpointParameters.new(
              region: source_region,
              use_dual_stack: context.config.use_dualstack_endpoint,
              use_fips: context.config.use_fips_endpoint
            )
            endpoint = context.config.endpoint_provider
                              .resolve_endpoint(endpoint_params)
            auth_scheme = Aws::Endpoints.resolve_auth_scheme(context, endpoint)

            signer = Aws::Plugins::Sign.signer_for(
              auth_scheme, context.config, source_region
            )

            signer.presign_url(
              http_method: 'GET',
              url: "#{endpoint.url}?#{param_list}",
              expires_in: 3600
            ).to_s
          end