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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.

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Class Public methods
new(env, middleware)
# File actionpack/lib/action_dispatch/middleware/remote_ip.rb, line 85
def initialize(env, middleware)
  @env      = env
  @check_ip = middleware.check_ip
  @proxies  = middleware.proxies
end
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 “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.

# File actionpack/lib/action_dispatch/middleware/remote_ip.rb, line 109
def calculate_ip
  # Set by the Rack web server, this is a single value.
  remote_addr = ips_from('REMOTE_ADDR').last

  # Could be a CSV list and/or repeated headers that were concatenated.
  client_ips    = ips_from('HTTP_CLIENT_IP').reverse
  forwarded_ips = ips_from('HTTP_X_FORWARDED_FOR').reverse

  # +Client-Ip+ and +X-Forwarded-For+ should not, generally, both be set.
  # If they are both set, it means that this request passed through two
  # proxies with incompatible IP header conventions, and there is no way
  # for us to determine which header is the right one after the fact.
  # Since we have no idea, we give up and explode.
  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=#{@env['HTTP_CLIENT_IP'].inspect} " +
      "HTTP_X_FORWARDED_FOR=#{@env['HTTP_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, remote_addr].flatten.compact

  # If every single IP option is in the trusted list, just return REMOTE_ADDR
  filter_proxies(ips).first || remote_addr
end
to_s()

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

# File actionpack/lib/action_dispatch/middleware/remote_ip.rb, line 143
def to_s
  @ip ||= calculate_ip
end
Instance Protected methods
filter_proxies(ips)
# File actionpack/lib/action_dispatch/middleware/remote_ip.rb, line 164
def filter_proxies(ips)
  ips.reject do |ip|
    @proxies.any? { |proxy| proxy === ip }
  end
end
ips_from(header)
# File actionpack/lib/action_dispatch/middleware/remote_ip.rb, line 149
def ips_from(header)
  # Split the comma-separated list into an array of strings
  ips = @env[header] ? @env[header].strip.split(/[,\s]+/) : []
  ips.select do |ip|
    begin
      # 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, IPAddr::InvalidAddressError
      nil
    end
  end
end