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.

Methods

Class Public methods

new(req, check_ip, proxies)

πŸ“ Source code 
# File actionpack/lib/action_dispatch/middleware/remote_ip.rb, line 88
      def initialize(req, check_ip, proxies)
        @req      = req
        @check_ip = check_ip
        @proxies  = proxies
      end
πŸ”Ž See on GitHub

Instance Public methods

calculate_ip()

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, while the first IP in the list is likely to be the β€œoriginating” 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.

πŸ“ Source code 
# File actionpack/lib/action_dispatch/middleware/remote_ip.rb, line 112
      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].flatten.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
πŸ”Ž See on GitHub

to_s()

Memoizes the value returned by calculate_ip and returns it for ActionDispatch::Request to use.

πŸ“ Source code 
# File actionpack/lib/action_dispatch/middleware/remote_ip.rb, line 155
      def to_s
        @ip ||= calculate_ip
      end
πŸ”Ž See on GitHub

Instance Private methods

filter_proxies(ips)

πŸ“ Source code 
# File actionpack/lib/action_dispatch/middleware/remote_ip.rb, line 174
      def filter_proxies(ips) # :doc:
        ips.reject do |ip|
          @proxies.any? { |proxy| proxy === ip }
        end
      end
πŸ”Ž See on GitHub

ips_from(header)

πŸ“ Source code 
# File actionpack/lib/action_dispatch/middleware/remote_ip.rb, line 160
      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
      end
πŸ”Ž See on GitHub