Add support for "metadata_filter".

README.md

@@ -8,14 +8,15 @@ Configuration
 
 This logger backend provides follow options:
 
-| name          | description |
-| ------------- | ----------- |
-| path          | log file path. this option is "MUST" |
-| level         | minimum logging level. default is `:info` |
-| metadata      | included metadata keys list. detault is empty list |
+| name              | description |
+| ----------------- | ----------- |
+| path              | log file path. this option is "MUST" |
+| level             | minimum logging level. default is `:info` |
+| metadata          | included metadata keys list. detault is empty list |
+| metadata_filter   | metadata terms which must be present in order to log, for example: [status: 404]. detault is empty list |
 | metadata\_triming | if false, ignoring previous metadata options and all metadata are output. default is true. It is recommended true in production environment. |
-| json\_encoder | using json encoder. default [jason](https://github.com/michalmuskala/jason) |
-| uuid          | If true, add uuid field to record. Default is false. |
+| json\_encoder     | using json encoder. default [jason](https://github.com/michalmuskala/jason) |
+| uuid              | If true, add uuid field to record. Default is false. |
 
 You need to add logger backend setting
 
@@ -27,6 +28,7 @@ config :logger, :log_name,
   path: "/var/log/my_app/app.log",
   level: :info,
   metadata: [:request_id, :user_id, :method, :path, :req_params],
+  metadata_filter: [status: 404],
   json_encoder: Poison, # default is Jason
   uuid: true
 ```
@@ -36,10 +38,23 @@ Use case
 
 This module is assumed to be used with a custom plug logger.
 
+Example 1:
+
 ```elixir
 Logger.info("request", [
   method:     conn.method,
   path:       conn.request_path,
   req_params: conn.params,
 ])
 ```
+
+Example 2:
+
+```elixir
+Logger.error("not found", [
+  method:     conn.method,
+  path:       conn.request_path,
+  req_params: conn.params,
+  status:     404
+])
+```

lib/logger_json_file_backend.ex

@@ -20,8 +20,8 @@ defmodule LoggerJSONFileBackend do
   end
 
   @impl :gen_event
-  def handle_event({level, _gl, {Logger, msg, ts, md}}, %{level: min_level}=state) do
-    if is_nil(min_level) or Logger.compare_levels(level, min_level) != :lt do
+  def handle_event({level, _gl, {Logger, msg, ts, md}}, %{level: min_level, metadata_filter: metadata_filter}=state) do
+    if (is_nil(min_level) or Logger.compare_levels(level, min_level) != :lt) and metadata_matches?(md, metadata_filter) do
       log_event(level, msg, ts, md, state)
     else
       {:ok, state}
@@ -116,8 +116,20 @@ defmodule LoggerJSONFileBackend do
     end
   end
 
+  @doc false
+  @spec metadata_matches?(Keyword.t, nil|Keyword.t) :: true|false
+  def metadata_matches?(_md, nil), do: true
+  def metadata_matches?(_md, []), do: true # all of the filter keys are present
+  def metadata_matches?(md, [{key, val}|rest]) do
+    case Keyword.fetch(md, key) do
+      {:ok, ^val} ->
+        metadata_matches?(md, rest)
+      _ -> false #fail on first mismatch
+    end
+  end
+
   defp configure(name, opts) do
-    state = %{name: nil, path: nil, io_device: nil, inode: nil, level: nil, metadata: nil, json_encoder: nil, triming: false, uuid: false}
+    state = %{name: nil, path: nil, io_device: nil, inode: nil, level: nil, metadata: nil, metadata_filter: nil, json_encoder: nil, triming: false, uuid: false}
     configure(name, opts, state)
   end
 
@@ -126,13 +138,14 @@ defmodule LoggerJSONFileBackend do
     opts = Keyword.merge(env, opts)
     Application.put_env(:logger, name, opts)
 
-    level        = Keyword.get(opts, :level, :info)
-    metadata     = Keyword.get(opts, :metadata, [])
-    path         = Keyword.get(opts, :path)
-    json_encoder = Keyword.get(opts, :json_encoder, Jason)
-    triming      = Keyword.get(opts, :metadata_triming, true)
-    uuid         = Keyword.get(opts, :uuid, false)
+    level           = Keyword.get(opts, :level, :info)
+    metadata        = Keyword.get(opts, :metadata, [])
+    metadata_filter = Keyword.get(opts, :metadata_filter)
+    path            = Keyword.get(opts, :path)
+    json_encoder    = Keyword.get(opts, :json_encoder, Jason)
+    triming         = Keyword.get(opts, :metadata_triming, true)
+    uuid            = Keyword.get(opts, :uuid, false)
 
-    %{state | name: name, path: path, level: level, metadata: metadata, json_encoder: json_encoder, triming: triming, uuid: uuid}
+    %{state | name: name, path: path, level: level, metadata: metadata, metadata_filter: metadata_filter, json_encoder: json_encoder, triming: triming, uuid: uuid}
   end
 end

mix.lock

@@ -1,8 +1,8 @@
 %{
-  "earmark": {:hex, :earmark, "1.0.3", "89bdbaf2aca8bbb5c97d8b3b55c5dd0cff517ecc78d417e87f1d0982e514557b", [:mix], [], "hexpm"},
-  "ex_doc": {:hex, :ex_doc, "0.14.3", "e61cec6cf9731d7d23d254266ab06ac1decbb7651c3d1568402ec535d387b6f7", [:mix], [{:earmark, "~> 1.0", [hex: :earmark, repo: "hexpm", optional: false]}], "hexpm"},
-  "jason": {:hex, :jason, "1.1.2", "b03dedea67a99223a2eaf9f1264ce37154564de899fd3d8b9a21b1a6fd64afe7", [:mix], [{:decimal, "~> 1.0", [hex: :decimal, repo: "hexpm", optional: true]}], "hexpm"},
+  "earmark": {:hex, :earmark, "1.0.3", "89bdbaf2aca8bbb5c97d8b3b55c5dd0cff517ecc78d417e87f1d0982e514557b", [:mix], [], "hexpm", "0fdcd651f9689e81cda24c8e5d06947c5aca69dbd8ce3d836b02bcd0c6004592"},
+  "ex_doc": {:hex, :ex_doc, "0.14.3", "e61cec6cf9731d7d23d254266ab06ac1decbb7651c3d1568402ec535d387b6f7", [:mix], [{:earmark, "~> 1.0", [hex: :earmark, repo: "hexpm", optional: false]}], "hexpm", "6bf36498c4c67fdbe6d4ad73a112098cbcc09b147b859219b023fc2636729bf6"},
+  "jason": {:hex, :jason, "1.1.2", "b03dedea67a99223a2eaf9f1264ce37154564de899fd3d8b9a21b1a6fd64afe7", [:mix], [{:decimal, "~> 1.0", [hex: :decimal, repo: "hexpm", optional: true]}], "hexpm", "fdf843bca858203ae1de16da2ee206f53416bbda5dc8c9e78f43243de4bc3afe"},
   "json": {:hex, :json, "0.3.3", "373eb4f7321f898ad6772999f30daf65f9f38e1d3dd4d798d7a82d3b123fe1d3", [:mix], [], "hexpm"},
-  "poison": {:hex, :poison, "3.1.0", "d9eb636610e096f86f25d9a46f35a9facac35609a7591b3be3326e99a0484665", [:mix], [], "hexpm"},
-  "uuid": {:hex, :uuid, "1.1.7", "007afd58273bc0bc7f849c3bdc763e2f8124e83b957e515368c498b641f7ab69", [:mix], [], "hexpm"},
+  "poison": {:hex, :poison, "3.1.0", "d9eb636610e096f86f25d9a46f35a9facac35609a7591b3be3326e99a0484665", [:mix], [], "hexpm", "fec8660eb7733ee4117b85f55799fd3833eb769a6df71ccf8903e8dc5447cfce"},
+  "uuid": {:hex, :uuid, "1.1.7", "007afd58273bc0bc7f849c3bdc763e2f8124e83b957e515368c498b641f7ab69", [:mix], [], "hexpm", "5c4eba9164d3567732280e6bc4edb115a82d5809c33f862098938b608a82caff"},
 }

test/logger_json_file_backend_test.exs

@@ -26,6 +26,30 @@ defmodule LoggerJSONFileBackendTest do
     assert not Map.has_key?(json_log, "uuid")
   end
 
+  test "test metadata_filter" do
+    refute File.exists?(path())
+    config [path: "test/logs/test.log", level: :info, metadata: [:foo, :pid], metadata_filter: [status: 404], metadata_triming: true, json_encoder: Jason, uuid: false]
+    #
+    Logger.error("Not found", [foo: "bar", status: 404])
+    assert File.exists?(path())
+    json_log = Jason.decode! log()
+    assert json_log["level"] == "error"
+    assert json_log["message"] == "Not found"
+    path() && File.rm_rf!(Path.dirname(path()))
+    #
+    Logger.info("OK")
+    refute File.exists?(path())
+    #
+    Logger.info("OK", [status: 200])
+    refute File.exists?(path())
+    #
+    Logger.error("Not found again", [status: 404])
+    assert File.exists?(path())
+    json_log = Jason.decode! log()
+    assert json_log["level"] == "error"
+    assert json_log["message"] == "Not found again"
+  end
+
   test "can log structured object" do
     Logger.info("msg body", [foo: %{bar: [:baz]}])
     json_log = Jason.decode! log()