module ActionController::Redirecting

:nodoc:

def _compute_redirect_to_location(request, options) #:nodoc:
  case options
  # The scheme name consist of a letter followed by any combination of
  # letters, digits, and the plus ("+"), period ("."), or hyphen ("-")
  # characters; and is terminated by a colon (":").
  # See http://tools.ietf.org/html/rfc3986#section-3.1
  # The protocol relative scheme starts with a double slash "//".
  when /\A([a-z][a-z\d\-+\.]*:|\/\/).*/i
    options
  when String
    request.protocol + request.host_with_port + options
  when :back
    ActiveSupport::Deprecation.warn(<<-MESSAGE.squish)
      `redirect_to :back` is deprecated and will be removed from Rails 5.1.
      Please use `redirect_back(fallback_location: fallback_location)` where
      `fallback_location` represents the location to use if the request has
      no HTTP referer information.
    MESSAGE
    request.headers["Referer"] or raise RedirectBackError
  when Proc
    _compute_redirect_to_location request, options.call
  else
    url_for(options)
  end.delete("\0\r\n")
end

def _extract_redirect_to_status(options, response_status)
  if options.is_a?(Hash) && options.key?(:status)
    Rack::Utils.status_code(options.delete(:status))
  elsif response_status.key?(:status)
    Rack::Utils.status_code(response_status[:status])
  else
    302
  end
end

options and the behavior is identical.
All options that can be passed to redirect_to are accepted as

redirect_back fallback_location: proc { edit_post_url(@post) }
redirect_back fallback_location: articles_url
redirect_back fallback_location: "/images/screenshot.jpg"
redirect_back fallback_location: "http://www.rubyonrails.org"
redirect_back fallback_location: post
redirect_back fallback_location: { action: "show", id: 5 }

is missing this header, the fallback_location will be used.
subject to browser security settings and user preferences. If the request
the request. This is an optional header and its presence on the request is
The referrer information is pulled from the HTTP `Referer` (sic) header on

location.
if possible, otherwise redirects to the provided default fallback
Redirects the browser to the page that issued the request (the referrer)

def redirect_back(fallback_location:, **args)
  if referer = request.headers["Referer"]
    redirect_to referer, **args
  else
    redirect_to fallback_location, **args
  end
end

:doc:

redirect_to({ action: 'atom' }, alert: "Something serious happened")
redirect_to post_url(@post), status: 301, flash: { updated_post_id: @post.id }
redirect_to post_url(@post), status: :found, notice: "Pay attention to the road"
redirect_to post_url(@post), alert: "Watch it, mister!"

+alert+ and +notice+ as well as a general purpose +flash+ bucket.
It is also possible to assign a flash message as part of the redirection. There are two special accessors for the commonly used flash names

redirect_to action: 'index', status: 303
redirect_to posts_url, status: :see_other

followed using a GET request.
around this you can return a 303 See Other status code which will be
method. This may lead to undesirable behavior such as a double DELETE. To work
request then some browsers will follow the redirect using the original request
If you are using XHR requests other than GET or POST and redirecting after the

Note that the status code must be a 3xx HTTP code, or redirection will not occur.
integer, or a symbol representing the downcased, underscored and symbolized description.
The status code can either be a standard {HTTP Status code}[http://www.iana.org/assignments/http-status-codes] as an

redirect_to action: 'atom', status: 302
redirect_to post_url(@post), status: 301
redirect_to action: 'atom', status: :moved_permanently
redirect_to post_url(@post), status: :found

The redirection happens as a "302 Found" header unless otherwise specified using the :status option:

redirect_to proc { edit_post_url(@post) }
redirect_to articles_url
redirect_to "/images/screenshot.jpg"
redirect_to "http://www.rubyonrails.org"
redirect_to post
redirect_to action: "show", id: 5

=== Examples:

* Proc - A block that will be executed in the controller's context. Should return any option accepted by +redirect_to+.
* String not containing a protocol - The current protocol and host is prepended to the string.
* String starting with protocol:// (like http://) or a protocol relative reference (like //) - Is passed straight through as the target for redirection.
* Record - The URL will be generated by calling url_for with the +options+, which will reference a named URL for that record.
* Hash - The URL will be generated by calling url_for with the +options+.

Redirects the browser to the target specified in +options+. This parameter can be any one of:

def redirect_to(options = {}, response_status = {}) #:doc:
  raise ActionControllerError.new("Cannot redirect to nil!") unless options
  raise AbstractController::DoubleRenderError if response_body
  self.status        = _extract_redirect_to_status(options, response_status)
  self.location      = _compute_redirect_to_location(request, options)
  self.response_body = "<html><body>You are being <a href=\"#{ERB::Util.unwrapped_html_escape(location)}\">redirected</a>.</body></html>"
end