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# frozen_string_literal: true
require_relative 'constants'
module Rack
# Rack::Cascade tries a request on several apps, and returns the
# first response that is not 404 or 405 (or in a list of configured
# status codes). If all applications tried return one of the configured
# status codes, return the last response.
class Cascade
# An array of applications to try in order.
attr_reader :apps
# Set the apps to send requests to, and what statuses result in
# cascading. Arguments:
#
# apps: An enumerable of rack applications.
# cascade_for: The statuses to use cascading for. If a response is received
# from an app, the next app is tried.
def initialize(apps, cascade_for = [404, 405])
@apps = []
apps.each { |app| add app }
@cascade_for = {}
[*cascade_for].each { |status| @cascade_for[status] = true }
end
# Call each app in order. If the responses uses a status that requires
# cascading, try the next app. If all responses require cascading,
# return the response from the last app.
def call(env)
return [404, { CONTENT_TYPE => "text/plain" }, []] if @apps.empty?
result = nil
last_body = nil
@apps.each do |app|
# The SPEC says that the body must be closed after it has been iterated
# by the server, or if it is replaced by a middleware action. Cascade
# replaces the body each time a cascade happens. It is assumed that nil
# does not respond to close, otherwise the previous application body
# will be closed. The final application body will not be closed, as it
# will be passed to the server as a result.
last_body.close if last_body.respond_to? :close
result = app.call(env)
return result unless @cascade_for.include?(result[0].to_i)
last_body = result[2]
end
result
end
# Append an app to the list of apps to cascade. This app will
# be tried last.
def add(app)
@apps << app
end
# Whether the given app is one of the apps to cascade to.
def include?(app)
@apps.include?(app)
end
alias_method :<<, :add
end
end
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