Making plug completely optional

lib/prom_ex/config.ex

@@ -199,7 +199,8 @@ defmodule PromEx.Config do
 
   * `:metrics_server` - This key contains the configuration information needed to run a standalone
     HTTP server powered by Cowboy. This server provides a lightweight solution to serving up PromEx
-    metrics. Its configuration options are:
+    metrics. In order to use this standalone metrics server plug you need to have `:plug` and `:plug_cowboy`
+    as dependencies in your project. Its configuration options are:
 
     * `:port` - The port that the Cowboy HTTP server should run on.
 

lib/prom_ex/metrics_server/plug.ex

@@ -1,81 +1,86 @@
-defmodule PromEx.MetricsServer.Plug do
-  @moduledoc """
-  This plug is used to serve metrics when PromEx is run in a
-  standalone server configuration. This plug supports the
-  following options:
+if Code.ensure_loaded?(Plug) do
+  defmodule PromEx.MetricsServer.Plug do
+    @moduledoc """
+    This plug is used to serve metrics when PromEx is run in a
+    standalone server configuration. This plug supports the
+    following options:
 
-  * `:path` - The route that should expose the metrics (default is "/metrics")
-  * `:prom_ex_module` - The PromEx module that this plug will expose
-  """
+    * `:path` - The route that should expose the metrics (default is "/metrics")
+    * `:prom_ex_module` - The PromEx module that this plug will expose
 
-  @behaviour Plug
+    In order to use this standalone metrics server plug you need to have `:plug` and `:plug_cowboy`
+    as dependencies in your project.
+    """
 
-  require Logger
+    @behaviour Plug
 
-  import Plug.Conn
+    require Logger
 
-  alias Plug.Conn
+    import Plug.Conn
 
-  @impl true
-  def init(opts) do
-    Map.pop(opts, :auth_strategy, :none)
-  end
+    alias Plug.Conn
+
+    @impl true
+    def init(opts) do
+      Map.pop(opts, :auth_strategy, :none)
+    end
 
-  @impl true
-  def call(%Conn{request_path: path} = conn, {:none, %{path: path, prom_ex_module: prom_ex_module}}) do
-    case PromEx.get_metrics(prom_ex_module) do
-      :prom_ex_down ->
-        Logger.warning("Attempted to fetch metrics from #{prom_ex_module}, but the module has not been initialized")
+    @impl true
+    def call(%Conn{request_path: path} = conn, {:none, %{path: path, prom_ex_module: prom_ex_module}}) do
+      case PromEx.get_metrics(prom_ex_module) do
+        :prom_ex_down ->
+          Logger.warning("Attempted to fetch metrics from #{prom_ex_module}, but the module has not been initialized")
 
-        conn
-        |> put_resp_content_type("text/plain")
-        |> send_resp(503, "Service Unavailable")
+          conn
+          |> put_resp_content_type("text/plain")
+          |> send_resp(503, "Service Unavailable")
 
-      metrics ->
-        PromEx.ETSCronFlusher.defer_ets_flush(prom_ex_module.__ets_cron_flusher_name__())
+        metrics ->
+          PromEx.ETSCronFlusher.defer_ets_flush(prom_ex_module.__ets_cron_flusher_name__())
 
-        conn
-        |> put_resp_content_type("text/plain")
-        |> send_resp(200, metrics)
+          conn
+          |> put_resp_content_type("text/plain")
+          |> send_resp(200, metrics)
+      end
     end
-  end
 
-  def call(
-        %Conn{request_path: path} = conn,
-        {:bearer, %{auth_token: auth_token, path: path} = plug_opts}
-      ) do
-    with ["Bearer " <> req_auth_token] <- get_req_header(conn, "authorization"),
-         true <- req_auth_token == auth_token do
-      call(conn, {:none, plug_opts})
-    else
-      _ ->
-        conn
-        |> put_resp_content_type("text/plain")
-        |> send_resp(401, "Unauthorized")
+    def call(
+          %Conn{request_path: path} = conn,
+          {:bearer, %{auth_token: auth_token, path: path} = plug_opts}
+        ) do
+      with ["Bearer " <> req_auth_token] <- get_req_header(conn, "authorization"),
+           true <- req_auth_token == auth_token do
+        call(conn, {:none, plug_opts})
+      else
+        _ ->
+          conn
+          |> put_resp_content_type("text/plain")
+          |> send_resp(401, "Unauthorized")
+      end
     end
-  end
 
-  def call(
-        %Conn{request_path: path} = conn,
-        {:basic, %{auth_user: auth_user, auth_password: auth_password, path: path} = plug_opts}
-      ) do
-    with ["Basic " <> req_auth_user_pass] <- get_req_header(conn, "authorization"),
-         {:ok, user_and_pass} <- Base.decode64(req_auth_user_pass),
-         [req_user, req_pass] <- String.split(user_and_pass, ":", parts: 2),
-         true <- req_user == auth_user,
-         true <- req_pass == auth_password do
-      call(conn, {:none, plug_opts})
-    else
-      _ ->
-        conn
-        |> put_resp_content_type("text/plain")
-        |> send_resp(401, "Unauthorized")
+    def call(
+          %Conn{request_path: path} = conn,
+          {:basic, %{auth_user: auth_user, auth_password: auth_password, path: path} = plug_opts}
+        ) do
+      with ["Basic " <> req_auth_user_pass] <- get_req_header(conn, "authorization"),
+           {:ok, user_and_pass} <- Base.decode64(req_auth_user_pass),
+           [req_user, req_pass] <- String.split(user_and_pass, ":", parts: 2),
+           true <- req_user == auth_user,
+           true <- req_pass == auth_password do
+        call(conn, {:none, plug_opts})
+      else
+        _ ->
+          conn
+          |> put_resp_content_type("text/plain")
+          |> send_resp(401, "Unauthorized")
+      end
     end
-  end
 
-  def call(conn, _opts) do
-    conn
-    |> put_resp_content_type("text/plain")
-    |> send_resp(404, "Not Found")
+    def call(conn, _opts) do
+      conn
+      |> put_resp_content_type("text/plain")
+      |> send_resp(404, "Not Found")
+    end
   end
 end