Restrict metrics access and add optional dedicated metrics listener

README.md

@@ -6,6 +6,7 @@ It exposes:
 - a WebSocket relay endpoint at `/relay`
 - NIP-11 relay info on `GET /relay` with `Accept: application/nostr+json`
 - operational HTTP endpoints (`/health`, `/ready`, `/metrics`)
+  - `/metrics` is restricted by default to private/loopback source IPs
 - a NIP-86-style management API at `POST /management` (NIP-98 auth)
 
 ## Supported NIPs
@@ -56,7 +57,7 @@ ws://localhost:4000/relay
 
 - `GET /health` -> `ok`
 - `GET /ready` -> readiness status
-- `GET /metrics` -> Prometheus metrics
+- `GET /metrics` -> Prometheus metrics (private/loopback source IPs by default)
 - `GET /relay` + `Accept: application/nostr+json` -> NIP-11 document
 - `POST /management` -> management API (requires NIP-98 auth)
 
@@ -81,7 +82,20 @@ config :parrhesia, Parrhesia.Web.Endpoint,
   ip: {0, 0, 0, 0},
   port: 4000
 
+# Optional dedicated metrics listener (keep this internal)
+config :parrhesia, Parrhesia.Web.MetricsEndpoint,
+  enabled: true,
+  ip: {127, 0, 0, 1},
+  port: 9568
+
 config :parrhesia,
+  metrics: [
+    enabled_on_main_endpoint: false,
+    public: false,
+    private_networks_only: true,
+    allowed_cidrs: [],
+    auth_token: nil
+  ],
   limits: [
     max_frame_bytes: 1_048_576,
     max_event_bytes: 262_144,

config/config.exs

@@ -47,6 +47,13 @@ config :parrhesia,
     marmot_push_max_server_recipients: 1,
     management_auth_required: true
   ],
+  metrics: [
+    enabled_on_main_endpoint: true,
+    public: false,
+    private_networks_only: true,
+    allowed_cidrs: [],
+    auth_token: nil
+  ],
   features: [
     verify_event_signatures: true,
     nip_45_count: true,
@@ -63,6 +70,11 @@ config :parrhesia,
 
 config :parrhesia, Parrhesia.Web.Endpoint, port: 4000
 
+config :parrhesia, Parrhesia.Web.MetricsEndpoint,
+  enabled: false,
+  ip: {127, 0, 0, 1},
+  port: 9568
+
 config :parrhesia, ecto_repos: [Parrhesia.Repo]
 
 import_config "#{config_env()}.exs"

lib/parrhesia/application.ex

@@ -13,6 +13,7 @@ defmodule Parrhesia.Application do
       Parrhesia.Auth.Supervisor,
       Parrhesia.Policy.Supervisor,
       Parrhesia.Web.Endpoint,
+      Parrhesia.Web.MetricsEndpoint,
       Parrhesia.Tasks.Supervisor
     ]
 

lib/parrhesia/web/metrics.ex

@@ -0,0 +1,28 @@
+defmodule Parrhesia.Web.Metrics do
+  @moduledoc false
+
+  import Plug.Conn
+
+  alias Parrhesia.Telemetry
+  alias Parrhesia.Web.MetricsAccess
+
+  @spec enabled_on_main_endpoint?() :: boolean()
+  def enabled_on_main_endpoint? do
+    :parrhesia
+    |> Application.get_env(:metrics, [])
+    |> Keyword.get(:enabled_on_main_endpoint, true)
+  end
+
+  @spec handle(Plug.Conn.t()) :: Plug.Conn.t()
+  def handle(conn) do
+    if MetricsAccess.allowed?(conn) do
+      body = TelemetryMetricsPrometheus.Core.scrape(Telemetry.prometheus_reporter())
+
+      conn
+      |> put_resp_content_type("text/plain")
+      |> send_resp(200, body)
+    else
+      send_resp(conn, 403, "forbidden")
+    end
+  end
+end

lib/parrhesia/web/metrics_access.ex

@@ -0,0 +1,138 @@
+defmodule Parrhesia.Web.MetricsAccess do
+  @moduledoc false
+
+  import Plug.Conn
+  import Bitwise
+
+  @private_cidrs [
+    "127.0.0.0/8",
+    "10.0.0.0/8",
+    "172.16.0.0/12",
+    "192.168.0.0/16",
+    "169.254.0.0/16",
+    "::1/128",
+    "fc00::/7",
+    "fe80::/10"
+  ]
+
+  @spec allowed?(Plug.Conn.t()) :: boolean()
+  def allowed?(conn) do
+    if metrics_public?() do
+      true
+    else
+      token_allowed?(conn) and network_allowed?(conn)
+    end
+  end
+
+  defp token_allowed?(conn) do
+    case configured_auth_token() do
+      nil ->
+        true
+
+      token ->
+        provided_token(conn) == token
+    end
+  end
+
+  defp provided_token(conn) do
+    conn
+    |> get_req_header("authorization")
+    |> List.first()
+    |> normalize_authorization_header()
+  end
+
+  defp normalize_authorization_header("Bearer " <> token), do: token
+  defp normalize_authorization_header(token) when is_binary(token), do: token
+  defp normalize_authorization_header(_header), do: nil
+
+  defp network_allowed?(conn) do
+    remote_ip = conn.remote_ip
+
+    cond do
+      configured_allowed_cidrs() != [] ->
+        Enum.any?(configured_allowed_cidrs(), &ip_in_cidr?(remote_ip, &1))
+
+      metrics_private_networks_only?() ->
+        Enum.any?(@private_cidrs, &ip_in_cidr?(remote_ip, &1))
+
+      true ->
+        true
+    end
+  end
+
+  defp ip_in_cidr?(ip, cidr) do
+    with {network, prefix_len} <- parse_cidr(cidr),
+         {:ok, ip_size, ip_value} <- ip_to_int(ip),
+         {:ok, network_size, network_value} <- ip_to_int(network),
+         true <- ip_size == network_size,
+         true <- prefix_len >= 0,
+         true <- prefix_len <= ip_size do
+      mask = network_mask(ip_size, prefix_len)
+      (ip_value &&& mask) == (network_value &&& mask)
+    else
+      _other -> false
+    end
+  end
+
+  defp parse_cidr(cidr) when is_binary(cidr) do
+    case String.split(cidr, "/", parts: 2) do
+      [address, prefix_str] ->
+        with {prefix_len, ""} <- Integer.parse(prefix_str),
+             {:ok, ip} <- :inet.parse_address(String.to_charlist(address)) do
+          {ip, prefix_len}
+        else
+          _other -> :error
+        end
+
+      _other ->
+        :error
+    end
+  end
+
+  defp parse_cidr(_cidr), do: :error
+
+  defp ip_to_int({a, b, c, d}) do
+    {:ok, 32, (a <<< 24) + (b <<< 16) + (c <<< 8) + d}
+  end
+
+  defp ip_to_int({a, b, c, d, e, f, g, h}) do
+    {:ok, 128,
+     (a <<< 112) + (b <<< 96) + (c <<< 80) + (d <<< 64) + (e <<< 48) + (f <<< 32) + (g <<< 16) +
+       h}
+  end
+
+  defp ip_to_int(_ip), do: :error
+
+  defp network_mask(_size, 0), do: 0
+
+  defp network_mask(size, prefix_len) do
+    all_ones = (1 <<< size) - 1
+    all_ones <<< (size - prefix_len)
+  end
+
+  defp configured_allowed_cidrs do
+    :parrhesia
+    |> Application.get_env(:metrics, [])
+    |> Keyword.get(:allowed_cidrs, [])
+    |> Enum.filter(&is_binary/1)
+  end
+
+  defp configured_auth_token do
+    case :parrhesia |> Application.get_env(:metrics, []) |> Keyword.get(:auth_token) do
+      token when is_binary(token) and token != "" -> token
+      _other -> nil
+    end
+  end
+
+  defp metrics_public? do
+    :parrhesia
+    |> Application.get_env(:metrics, [])
+    |> Keyword.get(:public, false)
+  end
+
+  defp metrics_private_networks_only? do
+    :parrhesia
+    |> Application.get_env(:metrics, [])
+    |> Keyword.get(:private_networks_only, true)
+  end
+end

lib/parrhesia/web/metrics_endpoint.ex

@@ -0,0 +1,34 @@
+defmodule Parrhesia.Web.MetricsEndpoint do
+  @moduledoc """
+  Optional dedicated HTTP listener for Prometheus metrics scraping.
+  """
+
+  use Supervisor
+
+  def start_link(init_arg \\ []) do
+    Supervisor.start_link(__MODULE__, init_arg, name: __MODULE__)
+  end
+
+  @impl true
+  def init(init_arg) do
+    options = bandit_options(init_arg)
+
+    children =
+      if Keyword.get(options, :enabled, false) do
+        [{Bandit, Keyword.delete(options, :enabled)}]
+      else
+        []
+      end
+
+    Supervisor.init(children, strategy: :one_for_one)
+  end
+
+  defp bandit_options(overrides) do
+    configured = Application.get_env(:parrhesia, __MODULE__, [])
+
+    configured
+    |> Keyword.merge(overrides)
+    |> Keyword.put_new(:scheme, :http)
+    |> Keyword.put_new(:plug, Parrhesia.Web.MetricsRouter)
+  end
+end

lib/parrhesia/web/metrics_router.ex

@@ -0,0 +1,18 @@
+defmodule Parrhesia.Web.MetricsRouter do
+  @moduledoc false
+
+  use Plug.Router
+
+  alias Parrhesia.Web.Metrics
+
+  plug(:match)
+  plug(:dispatch)
+
+  get "/metrics" do
+    Metrics.handle(conn)
+  end
+
+  match _ do
+    send_resp(conn, 404, "not found")
+  end
+end

lib/parrhesia/web/router.ex

@@ -3,8 +3,8 @@ defmodule Parrhesia.Web.Router do
 
   use Plug.Router
 
-  alias Parrhesia.Telemetry
   alias Parrhesia.Web.Management
+  alias Parrhesia.Web.Metrics
   alias Parrhesia.Web.Readiness
   alias Parrhesia.Web.RelayInfo
 
@@ -30,11 +30,11 @@ defmodule Parrhesia.Web.Router do
   end
 
   get "/metrics" do
-    body = TelemetryMetricsPrometheus.Core.scrape(Telemetry.prometheus_reporter())
-
-    conn
-    |> put_resp_content_type("text/plain")
-    |> send_resp(200, body)
+    if Metrics.enabled_on_main_endpoint?() do
+      Metrics.handle(conn)
+    else
+      send_resp(conn, 404, "not found")
+    end
   end
 
   post "/management" do

test/parrhesia/application_test.exs

@@ -10,6 +10,7 @@ defmodule Parrhesia.ApplicationTest do
     assert is_pid(Process.whereis(Parrhesia.Auth.Supervisor))
     assert is_pid(Process.whereis(Parrhesia.Policy.Supervisor))
     assert is_pid(Process.whereis(Parrhesia.Web.Endpoint))
+    assert is_pid(Process.whereis(Parrhesia.Web.MetricsEndpoint))
     assert is_pid(Process.whereis(Parrhesia.Tasks.Supervisor))
 
     assert Enum.any?(Supervisor.which_children(Parrhesia.Web.Endpoint), fn {_id, pid, _type,

test/parrhesia/web/router_test.exs

@@ -43,13 +43,68 @@ defmodule Parrhesia.Web.RouterTest do
     assert 11 in body["supported_nips"]
   end
 
-  test "GET /metrics returns prometheus payload" do
+  test "GET /metrics returns prometheus payload for private-network clients" do
     conn = conn(:get, "/metrics") |> Router.call([])
 
     assert conn.status == 200
     assert get_resp_header(conn, "content-type") == ["text/plain; charset=utf-8"]
   end
 
+  test "GET /metrics denies public-network clients by default" do
+    conn = conn(:get, "/metrics")
+    conn = %{conn | remote_ip: {8, 8, 8, 8}}
+    conn = Router.call(conn, [])
+
+    assert conn.status == 403
+    assert conn.resp_body == "forbidden"
+  end
+
+  test "GET /metrics can be disabled on the main endpoint" do
+    previous_metrics = Application.get_env(:parrhesia, :metrics, [])
+
+    Application.put_env(
+      :parrhesia,
+      :metrics,
+      Keyword.put(previous_metrics, :enabled_on_main_endpoint, false)
+    )
+
+    on_exit(fn ->
+      Application.put_env(:parrhesia, :metrics, previous_metrics)
+    end)
+
+    conn = conn(:get, "/metrics") |> Router.call([])
+
+    assert conn.status == 404
+    assert conn.resp_body == "not found"
+  end
+
+  test "GET /metrics accepts bearer auth when configured" do
+    previous_metrics = Application.get_env(:parrhesia, :metrics, [])
+
+    Application.put_env(
+      :parrhesia,
+      :metrics,
+      previous_metrics
+      |> Keyword.put(:private_networks_only, false)
+      |> Keyword.put(:auth_token, "secret-token")
+    )
+
+    on_exit(fn ->
+      Application.put_env(:parrhesia, :metrics, previous_metrics)
+    end)
+
+    denied_conn = conn(:get, "/metrics") |> Router.call([])
+
+    assert denied_conn.status == 403
+
+    allowed_conn =
+      conn(:get, "/metrics")
+      |> put_req_header("authorization", "Bearer secret-token")
+      |> Router.call([])
+
+    assert allowed_conn.status == 200
+  end
+
   test "POST /management requires authorization" do
     conn =
       conn(:post, "/management", JSON.encode!(%{"method" => "ping", "params" => %{}}))