two methods for adding custom headers in ruby / rails

headers.rb

#
# If you wna to copy headers directly onto tags as spans, there's a short hand method
# that works via configuration.
#

Datadog.configure do |c|
  c.use :rack, headers: {
    request: [
      'x-customer-mobile-screen',
      'x-customer-mobile-userflow'
    ]
  }
end

# 
# If you want to map the headers to a more human readable names, use custom middleware like this.
#  Note: it has to be run _after_ our Standard Rack/Rails tracing middleware.  
#
class AddMobileHeaders
  def initialize(app)
    @app = app
  end

  def call(env)
    request = Rack::Request.new(env)

    span = Datadog.tracer.active_root_span
    if not span.nil?
      screen = request.headers["x-customer-mobile-screen"]
      userflow = request.headers["x-customer-mobile-userflow"]
  
      span.set_tag("mobile.screen", screen)
      span.set_tag("mobile.userflow", userflow)
    end
  
    return @app.call(env)
  end
end

YourRailsApp::Application.configure do
  config.middleware.use "AddMobileHeaders"
  # ...
end