new

# File actionpack/lib/action_dispatch/middleware/remote_ip.rb, line 61
    def initialize(app, ip_spoofing_check = true, custom_proxies = nil)
      @app = app
      @check_ip = ip_spoofing_check
      @proxies = if custom_proxies.blank?
        TRUSTED_PROXIES
      elsif custom_proxies.respond_to?(:any?)
        custom_proxies
      else
        raise(ArgumentError, <<~EOM)
          Setting config.action_dispatch.trusted_proxies to a single value isn't
          supported. Please set this to an enumerable instead. For
          example, instead of:

          config.action_dispatch.trusted_proxies = IPAddr.new("10.0.0.0/8")

          Wrap the value in an Array:

          config.action_dispatch.trusted_proxies = [IPAddr.new("10.0.0.0/8")]

          Note that passing an enumerable will *replace* the default set of trusted proxies.
        EOM
      end
    end

    # Since the IP address may not be needed, we store the object here
    # without calculating the IP to keep from slowing down the majority of
    # requests. For those requests that do need to know the IP, the
    # GetIp#calculate_ip method will calculate the memoized client IP address.
    def call(env)
      req = ActionDispatch::Request.new env
      req.remote_ip = GetIp.new(req, check_ip, proxies)
      @app.call(req.env)
    end

    # The GetIp class exists as a way to defer processing of the request data
    # into an actual IP address. If the ActionDispatch::Request#remote_ip method
    # is called, this class will calculate the value and then memoize it.
    class GetIp
      def initialize(req, check_ip, proxies)
        @req      = req
        @check_ip = check_ip
        @proxies  = proxies
      end

      # Sort through the various IP address headers, looking for the IP most
      # likely to be the address of the actual remote client making this
      # request.
      #
      # REMOTE_ADDR will be correct if the request is made directly against the
      # Ruby process, on e.g. Heroku. When the request is proxied by another
      # server like HAProxy or NGINX, the IP address that made the original
      # request will be put in an +X-Forwarded-For+ header. If there are multiple
      # proxies, that header may contain a list of IPs. Other proxy services
      # set the +Client-Ip+ header instead, so we check that too.
      #
      # As discussed in {this post about Rails IP Spoofing}[https://web.archive.org/web/20170626095448/https://blog.gingerlime.com/2012/rails-ip-spoofing-vulnerabilities-and-protection/],
      # while the first IP in the list is likely to be the "originating" IP,
      # it could also have been set by the client maliciously.
      #
      # In order to find the first address that is (probably) accurate, we
      # take the list of IPs, remove known and trusted proxies, and then take
      # the last address left, which was presumably set by one of those proxies.
      def calculate_ip
        # Set by the Rack web server, this is a single value.
        remote_addr = ips_from(@req.remote_addr).last

        # Could be a CSV list and/or repeated headers that were concatenated.
        client_ips    = ips_from(@req.client_ip).reverse!
        forwarded_ips = ips_from(@req.x_forwarded_for).reverse!

        # +Client-Ip+ and +X-Forwarded-For+ should not, generally, both be set.
        # If they are both set, it means that either:
        #
        # 1) This request passed through two proxies with incompatible IP header
        #    conventions.
        # 2) The client passed one of +Client-Ip+ or +X-Forwarded-For+
        #    (whichever the proxy servers weren't using) themselves.
        #
        # Either way, there is no way for us to determine which header is the
        # right one after the fact. Since we have no idea, if we are concerned
        # about IP spoofing we need to give up and explode. (If you're not
        # concerned about IP spoofing you can turn the +ip_spoofing_check+
        # option off.)
        should_check_ip = @check_ip && client_ips.last && forwarded_ips.last
        if should_check_ip && !forwarded_ips.include?(client_ips.last)
          # We don't know which came from the proxy, and which from the user
          raise IpSpoofAttackError, "IP spoofing attack?! "              "HTTP_CLIENT_IP=#{@req.client_ip.inspect} "              "HTTP_X_FORWARDED_FOR=#{@req.x_forwarded_for.inspect}"
        end

        # We assume these things about the IP headers:
        #
        #   - X-Forwarded-For will be a list of IPs, one per proxy, or blank
        #   - Client-Ip is propagated from the outermost proxy, or is blank
        #   - REMOTE_ADDR will be the IP that made the request to Rack
        ips = forwarded_ips + client_ips
        ips.compact!

        # If every single IP option is in the trusted list, return the IP
        # that's furthest away
        filter_proxies(ips + [remote_addr]).first || ips.last || remote_addr
      end

      # Memoizes the value returned by #calculate_ip and returns it for
      # ActionDispatch::Request to use.
      def to_s
        @ip ||= calculate_ip
      end

    private
      def ips_from(header) # :doc:
        return [] unless header
        # Split the comma-separated list into an array of strings.
        ips = header.strip.split(/[,\s]+/)
        ips.select! do |ip|
          # Only return IPs that are valid according to the IPAddr#new method.
          range = IPAddr.new(ip).to_range
          # We want to make sure nobody is sneaking a netmask in.
          range.begin == range.end
        rescue ArgumentError
          nil
        end
        ips
      end

      def filter_proxies(ips) # :doc:
        ips.reject do |ip|
          @proxies.any? { |proxy| proxy === ip }
        end
      end
    end