Avoid compiling Peep.Plug when Plug module is not present.

lib/plug.ex

@@ -1,109 +1,111 @@
-defmodule Peep.Plug do
-  @moduledoc """
-  Use this plug to expose your metrics on an endpoint for scraping. This is useful if you are using Prometheus.
+if Code.ensure_loaded?(Plug) do
+  defmodule Peep.Plug do
+    @moduledoc """
+    Use this plug to expose your metrics on an endpoint for scraping. This is useful if you are using Prometheus.
+
+    This plug accepts the following options:
+
+    * `:peep_worker` - The name of the Peep worker to use. This is required.
+    * `:path` - The path to expose the metrics on. Defaults to `"/metrics"`.
+    * `:on_unmatched_path` - The intended behavior of this plug when handling a
+      request to a different path. There are two possible values:
+        - `:continue` (default) - This allows for subsequent Plugs in a router to
+          be executed. This option is useful when Peep.Plug is part of a router
+          for a Phoenix application, or a router that matches other paths after
+          Peep.Plug.
+
+        - `:halt` - Responds to requests with 404. This option is useful when
+          Peep.Plug is used for serving metrics on a separate port, which is a
+          practice that is encouraged by other libraries that export Prometheus
+          metrics.
+
+    ## Usage
+
+    You can use this plug in your Phoenix endpoint like this:
+
+      ```elixir
+      plug Peep.Plug, peep_worker: :my_peep_worker
+      ```
+
+    Or if you'd rather use a different path:
+
+      ```elixir
+      plug Peep.Plug, path: "/my-metrics"
+      ```
+
+    If you are not using Phoenix, you can use it directly with Cowboy by adding this to your applications's supervision tree:
+
+      ```elixir
+      {Plug.Cowboy, scheme: :http, plug: Peep.Plug, options: [port: 9000]}
+      ```
+
+    Similarly, if you are using Bandit, you can use it like so:
+
+      ```elixir
+      {Bandit, [
+        scheme: :http,
+        plug: {Peep.Plug, peep_worker: :my_app},
+        port: 9000
+      ]}
+      ```
+    """
+
+    @behaviour Plug
+
+    import Plug.Conn
+    alias Plug.Conn
+    require Logger
+
+    @default_metrics_path "/metrics"
+
+    @impl Plug
+    def init(opts) do
+      %{
+        metrics_path: Keyword.get(opts, :path, @default_metrics_path),
+        peep_worker: Keyword.fetch!(opts, :peep_worker),
+        on_unmatched_path: Keyword.get(opts, :on_unmatched_path, :continue)
+      }
+    end
+
+    @impl Plug
+    def call(%Conn{request_path: metrics_path, method: "GET"} = conn, %{
+          metrics_path: metrics_path,
+          peep_worker: peep_worker
+        }) do
+      metrics =
+        Peep.get_all_metrics(peep_worker)
+        |> Peep.Prometheus.export()
 
-  This plug accepts the following options:
-
-  * `:peep_worker` - The name of the Peep worker to use. This is required.
-  * `:path` - The path to expose the metrics on. Defaults to `"/metrics"`.
-  * `:on_unmatched_path` - The intended behavior of this plug when handling a
-    request to a different path. There are two possible values:
-      - `:continue` (default) - This allows for subsequent Plugs in a router to
-        be executed. This option is useful when Peep.Plug is part of a router
-        for a Phoenix application, or a router that matches other paths after
-        Peep.Plug.
-
-      - `:halt` - Responds to requests with 404. This option is useful when
-        Peep.Plug is used for serving metrics on a separate port, which is a
-        practice that is encouraged by other libraries that export Prometheus
-        metrics.
-
-  ## Usage
-
-  You can use this plug in your Phoenix endpoint like this:
-
-    ```elixir
-    plug Peep.Plug, peep_worker: :my_peep_worker
-    ```
-
-  Or if you'd rather use a different path:
-
-    ```elixir
-    plug Peep.Plug, path: "/my-metrics"
-    ```
-
-  If you are not using Phoenix, you can use it directly with Cowboy by adding this to your applications's supervision tree:
-
-    ```elixir
-    {Plug.Cowboy, scheme: :http, plug: Peep.Plug, options: [port: 9000]}
-    ```
-
-  Similarly, if you are using Bandit, you can use it like so:
-
-    ```elixir
-    {Bandit, [
-      scheme: :http,
-      plug: {Peep.Plug, peep_worker: :my_app},
-      port: 9000
-    ]}
-    ```
-  """
-
-  @behaviour Plug
-
-  import Plug.Conn
-  alias Plug.Conn
-  require Logger
-
-  @default_metrics_path "/metrics"
-
-  @impl Plug
-  def init(opts) do
-    %{
-      metrics_path: Keyword.get(opts, :path, @default_metrics_path),
-      peep_worker: Keyword.fetch!(opts, :peep_worker),
-      on_unmatched_path: Keyword.get(opts, :on_unmatched_path, :continue)
-    }
-  end
+      conn
+      |> put_resp_content_type("text/plain")
+      |> send_resp(200, metrics)
+      |> halt()
+    rescue
+      error ->
+        Logger.error(Exception.format(:error, error, __STACKTRACE__))
 
-  @impl Plug
-  def call(%Conn{request_path: metrics_path, method: "GET"} = conn, %{
-        metrics_path: metrics_path,
-        peep_worker: peep_worker
-      }) do
-    metrics =
-      Peep.get_all_metrics(peep_worker)
-      |> Peep.Prometheus.export()
-
-    conn
-    |> put_resp_content_type("text/plain")
-    |> send_resp(200, metrics)
-    |> halt()
-  rescue
-    error ->
-      Logger.error(Exception.format(:error, error, __STACKTRACE__))
+        conn
+        |> put_resp_content_type("text/plain")
+        |> send_resp(503, "Service Unavailable")
+        |> halt()
+    end
 
+    def call(%Conn{request_path: metrics_path} = conn, %{metrics_path: metrics_path}) do
       conn
       |> put_resp_content_type("text/plain")
-      |> send_resp(503, "Service Unavailable")
+      |> send_resp(400, "Invalid Request")
       |> halt()
-  end
+    end
 
-  def call(%Conn{request_path: metrics_path} = conn, %{metrics_path: metrics_path}) do
-    conn
-    |> put_resp_content_type("text/plain")
-    |> send_resp(400, "Invalid Request")
-    |> halt()
-  end
-
-  def call(%Conn{} = conn, %{on_unmatched_path: :continue}) do
-    conn
-  end
+    def call(%Conn{} = conn, %{on_unmatched_path: :continue}) do
+      conn
+    end
 
-  def call(%Conn{} = conn, %{on_unmatched_path: :halt}) do
-    conn
-    |> put_resp_content_type("text/plain")
-    |> send_resp(404, "Not Found")
-    |> halt()
+    def call(%Conn{} = conn, %{on_unmatched_path: :halt}) do
+      conn
+      |> put_resp_content_type("text/plain")
+      |> send_resp(404, "Not Found")
+      |> halt()
+    end
   end
 end