sharing_data_downstream.md

Sharing data downstream

Usually, you'll find the need to prepare some data in one operation with the intention for it to be consumed by another downstream operation. The connection struct has a #bag attribute which is helpful for this purpose.

WebPipe::Conn#bag is a Hash with Symbol keys where the values can be anything you need to share. To help with the process, we have the following methods:

• #add(key, value): Assigns a value to a key.
• #fetch(key), #fetch(key, default): Retrieves the value associated to a given key. If it is not found, default is returned when provided.

This is a simple example of a web application that reads a name parameter and normalizes it before using it in the response body.

# config.ru
require 'web_pipe'

WebPipe.load_extensions(:params)

class NormalizeNameApp
  include WebPipe
  
  plug :normalize_name
  plug :respond
  
  private
  
  def normalize_name(conn)
    conn.add(
      :name, conn.params[:name].downcase.capitalize
    )
  end
  
  def respond(conn)
    conn.set_response_body(
      conn.fetch(:name)
    )
  end
end

run NormalizeNameApp.new