Add RemoteIp plug to show real client IP in K8s logs

Extracts client IP from CF-Connecting-IP or X-Forwarded-For headers
and sets conn.remote_ip before request logging, so K8s logs show the
actual client address instead of the internal cluster/ingress IP.

lib/aprsme_web/endpoint.ex

@@ -48,6 +48,7 @@ defmodule AprsmeWeb.Endpoint do
     param_key: "request_logger",
     cookie_key: "request_logger"
 
+  plug AprsmeWeb.Plugs.RemoteIp
   plug Plug.RequestId
   plug Plug.Telemetry, event_prefix: [:phoenix, :endpoint], log: {AprsmeWeb.Plugs.LogFilter, :log_level, []}
 

lib/aprsme_web/plugs/remote_ip.ex

@@ -0,0 +1,57 @@
+defmodule AprsmeWeb.Plugs.RemoteIp do
+  @moduledoc """
+  Plug that extracts the real client IP from Cloudflare or proxy headers
+  and sets `conn.remote_ip` so downstream logging shows the actual client address.
+
+  Header priority:
+  1. `CF-Connecting-IP` (Cloudflare)
+  2. `X-Forwarded-For` (first IP in the chain)
+  """
+  @behaviour Plug
+
+  import Plug.Conn
+
+  @impl true
+  def init(opts), do: opts
+
+  @impl true
+  def call(conn, _opts) do
+    case get_client_ip(conn) do
+      {:ok, ip} -> %{conn | remote_ip: ip}
+      :error -> conn
+    end
+  end
+
+  defp get_client_ip(conn) do
+    with :error <- parse_cf_header(conn) do
+      parse_forwarded_for(conn)
+    end
+  end
+
+  defp parse_cf_header(conn) do
+    case get_req_header(conn, "cf-connecting-ip") do
+      [ip_str | _] -> parse_ip(ip_str)
+      [] -> :error
+    end
+  end
+
+  defp parse_forwarded_for(conn) do
+    case get_req_header(conn, "x-forwarded-for") do
+      [value | _] ->
+        value
+        |> String.split(",")
+        |> List.first()
+        |> parse_ip()
+
+      [] ->
+        :error
+    end
+  end
+
+  defp parse_ip(ip_str) do
+    case ip_str |> String.trim() |> String.to_charlist() |> :inet.parse_address() do
+      {:ok, ip} -> {:ok, ip}
+      {:error, _} -> :error
+    end
+  end
+end

test/aprsme_web/plugs/remote_ip_test.exs

@@ -0,0 +1,81 @@
+defmodule AprsmeWeb.Plugs.RemoteIpTest do
+  use AprsmeWeb.ConnCase
+
+  alias AprsmeWeb.Plugs.RemoteIp
+
+  describe "call/2" do
+    test "sets remote_ip from CF-Connecting-IP header", %{conn: conn} do
+      conn =
+        conn
+        |> put_req_header("cf-connecting-ip", "203.0.113.50")
+        |> RemoteIp.call([])
+
+      assert conn.remote_ip == {203, 0, 113, 50}
+    end
+
+    test "sets remote_ip from X-Forwarded-For when CF header missing", %{conn: conn} do
+      conn =
+        conn
+        |> put_req_header("x-forwarded-for", "198.51.100.25, 10.0.0.1")
+        |> RemoteIp.call([])
+
+      assert conn.remote_ip == {198, 51, 100, 25}
+    end
+
+    test "prefers CF-Connecting-IP over X-Forwarded-For", %{conn: conn} do
+      conn =
+        conn
+        |> put_req_header("cf-connecting-ip", "203.0.113.50")
+        |> put_req_header("x-forwarded-for", "198.51.100.25")
+        |> RemoteIp.call([])
+
+      assert conn.remote_ip == {203, 0, 113, 50}
+    end
+
+    test "handles IPv6 addresses", %{conn: conn} do
+      conn =
+        conn
+        |> put_req_header("cf-connecting-ip", "2001:db8::1")
+        |> RemoteIp.call([])
+
+      assert conn.remote_ip == {8193, 3512, 0, 0, 0, 0, 0, 1}
+    end
+
+    test "leaves remote_ip unchanged when no proxy headers present", %{conn: conn} do
+      original_ip = conn.remote_ip
+
+      conn = RemoteIp.call(conn, [])
+
+      assert conn.remote_ip == original_ip
+    end
+
+    test "leaves remote_ip unchanged when header contains invalid IP", %{conn: conn} do
+      original_ip = conn.remote_ip
+
+      conn =
+        conn
+        |> put_req_header("cf-connecting-ip", "not-an-ip")
+        |> RemoteIp.call([])
+
+      assert conn.remote_ip == original_ip
+    end
+
+    test "trims whitespace from IP addresses", %{conn: conn} do
+      conn =
+        conn
+        |> put_req_header("cf-connecting-ip", " 203.0.113.50 ")
+        |> RemoteIp.call([])
+
+      assert conn.remote_ip == {203, 0, 113, 50}
+    end
+
+    test "takes first IP from X-Forwarded-For chain", %{conn: conn} do
+      conn =
+        conn
+        |> put_req_header("x-forwarded-for", "203.0.113.50, 10.0.0.1, 172.16.0.1")
+        |> RemoteIp.call([])
+
+      assert conn.remote_ip == {203, 0, 113, 50}
+    end
+  end
+end