expose the last_forwarded_ip/2 function for usage outside of Plug

README.md

@@ -48,6 +48,23 @@ end
 
 Note that, due to limitations in the [inet_cidr](https://github.com/Cobenian/inet_cidr) library used to parse them, `:proxies` **must** be written in full CIDR notation, even if specifying just a single IP. So instead of `"127.0.0.1"` and `"a:b::c:d"`, you would use `"127.0.0.1/32"` and `"a:b::c:d/128"`.
 
+### Without plug
+
+For usage outside of plug, there is the `RemoteIp.last_forwarded_ip/2` function, which can be used like so:
+
+```elixir
+RemoteIp.last_forwarded_ip([{"x-forwarded-for", "1.2.3.4"}]) => {1, 2, 3, 4}
+```
+
+The headers can also be customized like so:
+
+```elixir
+RemoteIp.last_forwarded_ip([{"x-foo", "1.2.3.4"}],
+  headers: ~w[x-foo x-bar x-baz],
+  proxies: ~w[1.2.0.0/16]
+) => {1, 2, 3, 4}
+
+
 ## Background
 
 ### Problem: Your app is behind a proxy and you want to know the original client's IP address.

lib/remote_ip.ex

@@ -1,7 +1,8 @@
 defmodule RemoteIp do
   @moduledoc """
   A plug to overwrite the `Plug.Conn`'s `remote_ip` based on headers such as
-  `X-Forwarded-For`.
+  `X-Forwarded-For`. The `last_forwarded_ip/2` function can be used directly
+  for usage outside of plug.
 
   To use, add the `RemoteIp` plug to your app's plug pipeline:
 
@@ -73,20 +74,24 @@ defmodule RemoteIp do
   end
 
   def call(conn, {headers, proxies}) do
-    case last_forwarded_ip(conn, headers, proxies) do
+    case last_forwarded_ip(conn.req_headers, headers: headers, proxies: proxies) do
       nil -> conn
       ip  -> %{conn | remote_ip: ip}
     end
   end
 
-  defp last_forwarded_ip(conn, headers, proxies) do
-    conn
-    |> ips_from(headers)
-    |> last_ip_forwarded_through(proxies)
-  end
+  @doc """
+  Given a list of headers, return the last ip address.
+  """
+  def last_forwarded_ip(req_headers, opts \\ []) do
+    headers =
+      Keyword.get(opts, :headers, @headers)
+      |> MapSet.new()
+    proxies = Keyword.get(opts, :proxies, @proxies) ++ @reserved
 
-  defp ips_from(%Plug.Conn{req_headers: headers}, allowed) do
-    RemoteIp.Headers.parse(headers, allowed)
+    req_headers
+    |> RemoteIp.Headers.parse(headers)
+    |> last_ip_forwarded_through(proxies)
   end
 
   defp last_ip_forwarded_through(ips, proxies) do

test/remote_ip_test.exs

@@ -24,6 +24,17 @@ defmodule RemoteIpTest do
   #
   @conn %Plug.Conn{remote_ip: :peer}
 
+  describe "last_forwarded_ip/2" do
+    test "using the default options" do
+      assert RemoteIp.last_forwarded_ip([]) == nil
+      assert RemoteIp.last_forwarded_ip([{"x-forwarded-for", "1.2.3.4"}]) == {1, 2, 3, 4}
+    end
+
+    test "using custom headers" do
+      assert RemoteIp.last_forwarded_ip([{"x-custom", "1.2.3.4"}], headers: ["x-custom"]) == {1, 2, 3, 4}
+    end
+  end
+
   test "zero hops (i.e., no forwarding headers)" do
     assert :peer == @conn |> remote_ip
     assert :peer == @conn |> remote_ip(headers: ~w[])