Introduce option for behavior of Peep.Plug for paths that don't match the metrics path

lib/plug.ex

@@ -6,6 +6,17 @@ defmodule Peep.Plug do
 
   * `: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
 
@@ -46,7 +57,8 @@ defmodule Peep.Plug do
   def init(opts) do
     %{
       metrics_path: Keyword.get(opts, :path, @default_metrics_path),
-      peep_worker: Keyword.fetch!(opts, :peep_worker)
+      peep_worker: Keyword.fetch!(opts, :peep_worker),
+      on_unmatched_path: Keyword.get(opts, :on_unmatched_path, :continue)
     }
   end
 
@@ -80,7 +92,11 @@ defmodule Peep.Plug do
     |> halt()
   end
 
-  def call(%Conn{} = conn, _opts) do
+  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")

mix.exs

@@ -40,11 +40,13 @@ defmodule Peep.MixProject do
       {:nimble_options, "~> 1.1"},
       {:telemetry_metrics, "~> 1.0"},
       # testing, docs, & linting
+      {:bandit, "~> 1.6", only: [:test], runtime: false},
       {:credo, "~> 1.7", only: [:dev, :test], runtime: false},
       {:dialyxir, "~> 1.4", only: [:dev, :test], runtime: false},
       {:inch_ex, "~> 2.0", only: [:dev, :test], runtime: false},
       {:ex_doc, "~> 0.34", only: [:dev], runtime: false},
       {:nimble_parsec, "~> 1.4", only: [:dev, :test], runtime: false},
+      {:plug_cowboy, "~> 2.7", only: [:test]},
 
       # Optional dependencies
       {:plug, "~> 1.16", optional: true}

mix.lock

@@ -1,11 +1,16 @@
 %{
+  "bandit": {:hex, :bandit, "1.6.0", "9cb6c67c27cecab2d0c93968cb957fa8decccb7275193c8bf33f97397b3ac25d", [:mix], [{:hpax, "~> 1.0", [hex: :hpax, repo: "hexpm", optional: false]}, {:plug, "~> 1.14", [hex: :plug, repo: "hexpm", optional: false]}, {:telemetry, "~> 0.4 or ~> 1.0", [hex: :telemetry, repo: "hexpm", optional: false]}, {:thousand_island, "~> 1.0", [hex: :thousand_island, repo: "hexpm", optional: false]}, {:websock, "~> 0.5", [hex: :websock, repo: "hexpm", optional: false]}], "hexpm", "fd2491e564a7c5e11ff8496ebf530c342c742452c59de17ac0fb1f814a0ab01a"},
   "bunt": {:hex, :bunt, "0.2.1", "e2d4792f7bc0ced7583ab54922808919518d0e57ee162901a16a1b6664ef3b14", [:mix], [], "hexpm", "a330bfb4245239787b15005e66ae6845c9cd524a288f0d141c148b02603777a5"},
+  "cowboy": {:hex, :cowboy, "2.12.0", "f276d521a1ff88b2b9b4c54d0e753da6c66dd7be6c9fca3d9418b561828a3731", [:make, :rebar3], [{:cowlib, "2.13.0", [hex: :cowlib, repo: "hexpm", optional: false]}, {:ranch, "1.8.0", [hex: :ranch, repo: "hexpm", optional: false]}], "hexpm", "8a7abe6d183372ceb21caa2709bec928ab2b72e18a3911aa1771639bef82651e"},
+  "cowboy_telemetry": {:hex, :cowboy_telemetry, "0.4.0", "f239f68b588efa7707abce16a84d0d2acf3a0f50571f8bb7f56a15865aae820c", [:rebar3], [{:cowboy, "~> 2.7", [hex: :cowboy, repo: "hexpm", optional: false]}, {:telemetry, "~> 1.0", [hex: :telemetry, repo: "hexpm", optional: false]}], "hexpm", "7d98bac1ee4565d31b62d59f8823dfd8356a169e7fcbb83831b8a5397404c9de"},
+  "cowlib": {:hex, :cowlib, "2.13.0", "db8f7505d8332d98ef50a3ef34b34c1afddec7506e4ee4dd4a3a266285d282ca", [:make, :rebar3], [], "hexpm", "e1e1284dc3fc030a64b1ad0d8382ae7e99da46c3246b815318a4b848873800a4"},
   "credo": {:hex, :credo, "1.7.7", "771445037228f763f9b2afd612b6aa2fd8e28432a95dbbc60d8e03ce71ba4446", [:mix], [{:bunt, "~> 0.2.1 or ~> 1.0", [hex: :bunt, repo: "hexpm", optional: false]}, {:file_system, "~> 0.2 or ~> 1.0", [hex: :file_system, repo: "hexpm", optional: false]}, {:jason, "~> 1.0", [hex: :jason, repo: "hexpm", optional: false]}], "hexpm", "8bc87496c9aaacdc3f90f01b7b0582467b69b4bd2441fe8aae3109d843cc2f2e"},
   "dialyxir": {:hex, :dialyxir, "1.4.3", "edd0124f358f0b9e95bfe53a9fcf806d615d8f838e2202a9f430d59566b6b53b", [:mix], [{:erlex, ">= 0.2.6", [hex: :erlex, repo: "hexpm", optional: false]}], "hexpm", "bf2cfb75cd5c5006bec30141b131663299c661a864ec7fbbc72dfa557487a986"},
   "earmark_parser": {:hex, :earmark_parser, "1.4.41", "ab34711c9dc6212dda44fcd20ecb87ac3f3fce6f0ca2f28d4a00e4154f8cd599", [:mix], [], "hexpm", "a81a04c7e34b6617c2792e291b5a2e57ab316365c2644ddc553bb9ed863ebefa"},
   "erlex": {:hex, :erlex, "0.2.7", "810e8725f96ab74d17aac676e748627a07bc87eb950d2b83acd29dc047a30595", [:mix], [], "hexpm", "3ed95f79d1a844c3f6bf0cea61e0d5612a42ce56da9c03f01df538685365efb0"},
   "ex_doc": {:hex, :ex_doc, "0.34.2", "13eedf3844ccdce25cfd837b99bea9ad92c4e511233199440488d217c92571e8", [:mix], [{:earmark_parser, "~> 1.4.39", [hex: :earmark_parser, repo: "hexpm", optional: false]}, {:makeup_c, ">= 0.1.0", [hex: :makeup_c, repo: "hexpm", optional: true]}, {:makeup_elixir, "~> 0.14 or ~> 1.0", [hex: :makeup_elixir, repo: "hexpm", optional: false]}, {:makeup_erlang, "~> 0.1 or ~> 1.0", [hex: :makeup_erlang, repo: "hexpm", optional: false]}, {:makeup_html, ">= 0.1.0", [hex: :makeup_html, repo: "hexpm", optional: true]}], "hexpm", "5ce5f16b41208a50106afed3de6a2ed34f4acfd65715b82a0b84b49d995f95c1"},
   "file_system": {:hex, :file_system, "1.0.0", "b689cc7dcee665f774de94b5a832e578bd7963c8e637ef940cd44327db7de2cd", [:mix], [], "hexpm", "6752092d66aec5a10e662aefeed8ddb9531d79db0bc145bb8c40325ca1d8536d"},
+  "hpax": {:hex, :hpax, "1.0.0", "28dcf54509fe2152a3d040e4e3df5b265dcb6cb532029ecbacf4ce52caea3fd2", [:mix], [], "hexpm", "7f1314731d711e2ca5fdc7fd361296593fc2542570b3105595bb0bc6d0fad601"},
   "inch_ex": {:hex, :inch_ex, "2.0.0", "24268a9284a1751f2ceda569cd978e1fa394c977c45c331bb52a405de544f4de", [:mix], [{:bunt, "~> 0.2", [hex: :bunt, repo: "hexpm", optional: false]}, {:jason, "~> 1.0", [hex: :jason, repo: "hexpm", optional: false]}], "hexpm", "96d0ec5ecac8cf63142d02f16b7ab7152cf0f0f1a185a80161b758383c9399a8"},
   "jason": {:hex, :jason, "1.4.3", "d3f984eeb96fe53b85d20e0b049f03e57d075b5acda3ac8d465c969a2536c17b", [:mix], [{:decimal, "~> 1.0 or ~> 2.0", [hex: :decimal, repo: "hexpm", optional: true]}], "hexpm", "9a90e868927f7c777689baa16d86f4d0e086d968db5c05d917ccff6d443e58a3"},
   "makeup": {:hex, :makeup, "1.1.2", "9ba8837913bdf757787e71c1581c21f9d2455f4dd04cfca785c70bbfff1a76a3", [:mix], [{:nimble_parsec, "~> 1.2.2 or ~> 1.3", [hex: :nimble_parsec, repo: "hexpm", optional: false]}], "hexpm", "cce1566b81fbcbd21eca8ffe808f33b221f9eee2cbc7a1706fc3da9ff18e6cac"},
@@ -15,7 +20,11 @@
   "nimble_options": {:hex, :nimble_options, "1.1.1", "e3a492d54d85fc3fd7c5baf411d9d2852922f66e69476317787a7b2bb000a61b", [:mix], [], "hexpm", "821b2470ca9442c4b6984882fe9bb0389371b8ddec4d45a9504f00a66f650b44"},
   "nimble_parsec": {:hex, :nimble_parsec, "1.4.0", "51f9b613ea62cfa97b25ccc2c1b4216e81df970acd8e16e8d1bdc58fef21370d", [:mix], [], "hexpm", "9c565862810fb383e9838c1dd2d7d2c437b3d13b267414ba6af33e50d2d1cf28"},
   "plug": {:hex, :plug, "1.16.1", "40c74619c12f82736d2214557dedec2e9762029b2438d6d175c5074c933edc9d", [:mix], [{:mime, "~> 1.0 or ~> 2.0", [hex: :mime, repo: "hexpm", optional: false]}, {:plug_crypto, "~> 1.1.1 or ~> 1.2 or ~> 2.0", [hex: :plug_crypto, repo: "hexpm", optional: false]}, {:telemetry, "~> 0.4.3 or ~> 1.0", [hex: :telemetry, repo: "hexpm", optional: false]}], "hexpm", "a13ff6b9006b03d7e33874945b2755253841b238c34071ed85b0e86057f8cddc"},
+  "plug_cowboy": {:hex, :plug_cowboy, "2.7.2", "fdadb973799ae691bf9ecad99125b16625b1c6039999da5fe544d99218e662e4", [:mix], [{:cowboy, "~> 2.7", [hex: :cowboy, repo: "hexpm", optional: false]}, {:cowboy_telemetry, "~> 0.3", [hex: :cowboy_telemetry, repo: "hexpm", optional: false]}, {:plug, "~> 1.14", [hex: :plug, repo: "hexpm", optional: false]}], "hexpm", "245d8a11ee2306094840c000e8816f0cbed69a23fc0ac2bcf8d7835ae019bb2f"},
   "plug_crypto": {:hex, :plug_crypto, "2.1.0", "f44309c2b06d249c27c8d3f65cfe08158ade08418cf540fd4f72d4d6863abb7b", [:mix], [], "hexpm", "131216a4b030b8f8ce0f26038bc4421ae60e4bb95c5cf5395e1421437824c4fa"},
+  "ranch": {:hex, :ranch, "1.8.0", "8c7a100a139fd57f17327b6413e4167ac559fbc04ca7448e9be9057311597a1d", [:make, :rebar3], [], "hexpm", "49fbcfd3682fab1f5d109351b61257676da1a2fdbe295904176d5e521a2ddfe5"},
   "telemetry": {:hex, :telemetry, "1.2.1", "68fdfe8d8f05a8428483a97d7aab2f268aaff24b49e0f599faa091f1d4e7f61c", [:rebar3], [], "hexpm", "dad9ce9d8effc621708f99eac538ef1cbe05d6a874dd741de2e689c47feafed5"},
   "telemetry_metrics": {:hex, :telemetry_metrics, "1.0.0", "29f5f84991ca98b8eb02fc208b2e6de7c95f8bb2294ef244a176675adc7775df", [:mix], [{:telemetry, "~> 0.4 or ~> 1.0", [hex: :telemetry, repo: "hexpm", optional: false]}], "hexpm", "f23713b3847286a534e005126d4c959ebcca68ae9582118ce436b521d1d47d5d"},
+  "thousand_island": {:hex, :thousand_island, "1.3.6", "835a626a8a6f6a1e681b63e1132a8427e87ce443aaf4888fbf63b2df77539b97", [:mix], [{:telemetry, "~> 0.4 or ~> 1.0", [hex: :telemetry, repo: "hexpm", optional: false]}], "hexpm", "0ed8798084c8c49a223840b20598b022e4eb8c9f390fb6701864c307fc9aa2cd"},
+  "websock": {:hex, :websock, "0.5.3", "2f69a6ebe810328555b6fe5c831a851f485e303a7c8ce6c5f675abeb20ebdadc", [:mix], [], "hexpm", "6105453d7fac22c712ad66fab1d45abdf049868f253cf719b625151460b8b453"},
 }

test/plug_test.exs

@@ -66,12 +66,49 @@ defmodule PlugTest do
     end
 
     test "returns 404 for non-metrics paths" do
-      opts = Peep.Plug.init(peep_worker: @peep_worker)
+      opts = Peep.Plug.init(peep_worker: @peep_worker, on_unmatched_path: :halt)
       conn = conn(:get, "/not-metrics")
       response = Peep.Plug.call(conn, opts)
 
       assert response.status == 404
     end
+
+    test "does not halt for non-metrics paths by default" do
+      opts = Peep.Plug.init(peep_worker: @peep_worker)
+      conn = conn(:get, "/not-metrics")
+      response = Peep.Plug.call(conn, opts)
+
+      refute response.halted
+    end
+  end
+
+  describe "servers" do
+    test "Bandit" do
+      name = :bandit_peep
+      metrics = [last_value("vm.memory.total", unit: :byte)]
+      _peep = start_supervised!({Peep, name: name, metrics: metrics})
+      plug = {Peep.Plug, peep_worker: name}
+      port = 9001
+
+      {:ok, _pid} = start_supervised({Bandit, plug: plug, port: port})
+
+      assert {:ok, {{~c"HTTP/1.1", 200, ~c"OK"}, _, _}} =
+               :httpc.request("http://localhost:#{port}/metrics")
+    end
+
+    test "Plug.Cowboy" do
+      name = :cowboy_peep
+      metrics = [last_value("vm.memory.total", unit: :byte)]
+      _peep = start_supervised!({Peep, name: name, metrics: metrics})
+      plug = {Peep.Plug, peep_worker: name}
+      port = 9002
+
+      {:ok, _pid} =
+        start_supervised({Plug.Cowboy, scheme: :http, plug: plug, options: [port: port]})
+
+      assert {:ok, {{~c"HTTP/1.1", 200, ~c"OK"}, _, _}} =
+               :httpc.request("http://localhost:#{port}/metrics")
+    end
   end
 
   def setup_peep_worker(context) do