Implement event filtering on measurements (#77)

lib/telemetry_metrics.ex

@@ -68,10 +68,12 @@ defmodule Telemetry.Metrics do
     * `:tag_values` - a function that receives the metadata and returns a map with
       the tags as keys and their respective values. Defaults to returning the
       metadata itself.
-    * `:keep` - a predicate function that evaluates the metadata to conditionally
-      record a given event. `:keep` and `:drop` cannot be combined. Defaults to `nil`.
-    * `:drop` - a predicate function that evaluates the metadata to conditionally
-      skip recording a given event. `:keep` and `:drop` cannot be combined. Defaults to `nil`.
+    * `:keep` - a predicate function that evaluates the metadata and measurement
+      to conditionally record a given event. `:keep` and `:drop` cannot be
+      combined. Defaults to `nil`.
+    * `:drop` - a predicate function that evaluates the metadata and measurement
+      to conditionally skip recording a given event. `:keep` and `:drop` cannot
+      be combined. Defaults to `nil`.
     * `:description` - human-readable description of the metric. Might be used by
       reporters for documentation purposes. Defaults to `nil`.
     * `:unit` - an atom describing the unit of selected measurement, typically in
@@ -408,7 +410,9 @@ defmodule Telemetry.Metrics do
   @type tag :: term()
   @type tags :: [tag()]
   @type tag_values :: (:telemetry.event_metadata() -> :telemetry.event_metadata())
-  @type keep :: (:telemetry.event_metadata() -> boolean())
+  @type keep ::
+          (:telemetry.event_metadata() -> boolean())
+          | (:telemetry.event_metadata(), :telemetry.event_measurements() -> boolean())
   @type drop :: (:telemetry.event_metadata() -> boolean())
   @type description :: nil | String.t()
   @type unit :: atom()
@@ -614,11 +618,11 @@ defmodule Telemetry.Metrics do
   end
 
   defp validate_recording_rule_fun!(nil), do: nil
-  defp validate_recording_rule_fun!(fun) when is_function(fun, 1), do: fun
+  defp validate_recording_rule_fun!(fun) when is_function(fun, 1) or is_function(fun, 2), do: fun
 
   defp validate_recording_rule_fun!(term) do
     raise ArgumentError,
-          "expected recording rule to be a function accepting metadata, got #{inspect(term)}"
+          "expected recording rule to be a function accepting either metadata or metadata and measurements, got #{inspect(term)}"
   end
 
   defp validate_recording_rule_fun_options!(keep, drop) when is_nil(keep) or is_nil(drop), do: :ok
@@ -629,8 +633,9 @@ defmodule Telemetry.Metrics do
   end
 
   defp keep_fun(nil, nil), do: nil
-  defp keep_fun(nil, drop), do: fn meta -> not drop.(meta) end
   defp keep_fun(keep, nil), do: keep
+  defp keep_fun(nil, drop) when is_function(drop, 1), do: &(not drop.(&1))
+  defp keep_fun(nil, drop) when is_function(drop, 2), do: &(not drop.(&1, &2))
 
   @spec fill_in_default_metric_options([metric_option()]) :: [metric_option()]
   defp fill_in_default_metric_options(options) do

lib/telemetry_metrics/console_reporter.ex

@@ -100,7 +100,7 @@ defmodule Telemetry.Metrics.ConsoleReporter do
                   Measurement value missing (metric skipped)
                   """
 
-                not keep?(metric, metadata) ->
+                not keep?(metric, metadata, measurements) ->
                   """
                   Event dropped
                   """
@@ -142,8 +142,13 @@ defmodule Telemetry.Metrics.ConsoleReporter do
     "#{inspect(measurement)} [via #{inspect(fun)}]"
   end
 
-  defp keep?(%{keep: nil}, _metadata), do: true
-  defp keep?(metric, metadata), do: metric.keep.(metadata)
+  defp keep?(metric, metadata, measurements) do
+    case metric do
+      %{keep: nil} -> true
+      %{keep: keep} when is_function(keep, 1) -> keep.(metadata)
+      %{keep: keep} when is_function(keep, 2) -> keep.(metadata, measurements)
+    end
+  end
 
   defp extract_measurement(metric, measurements, metadata) do
     case metric.measurement do

lib/telemetry_metrics/counter.ex

@@ -22,8 +22,8 @@ defmodule Telemetry.Metrics.Counter do
           event_name: :telemetry.event_name(),
           measurement: Metrics.measurement(),
           tags: Metrics.tags(),
-          tag_values: (:telemetry.event_metadata() -> :telemetry.event_metadata()),
-          keep: (:telemetry.event_metadata() -> boolean()),
+          tag_values: Metrics.tag_values(),
+          keep: Metrics.keep(),
           description: Metrics.description(),
           unit: Metrics.unit(),
           reporter_options: Metrics.reporter_options()

lib/telemetry_metrics/distribution.ex

@@ -22,8 +22,8 @@ defmodule Telemetry.Metrics.Distribution do
           event_name: :telemetry.event_name(),
           measurement: Metrics.measurement(),
           tags: Metrics.tags(),
-          tag_values: (:telemetry.event_metadata() -> :telemetry.event_metadata()),
-          keep: (:telemetry.event_metadata() -> boolean()),
+          tag_values: Metrics.tag_values(),
+          keep: Metrics.keep(),
           description: Metrics.description(),
           unit: Metrics.unit(),
           reporter_options: Metrics.reporter_options()

lib/telemetry_metrics/last_value.ex

@@ -22,8 +22,8 @@ defmodule Telemetry.Metrics.LastValue do
           event_name: :telemetry.event_name(),
           measurement: Metrics.measurement(),
           tags: Metrics.tags(),
-          tag_values: (:telemetry.event_metadata() -> :telemetry.event_metadata()),
-          keep: (:telemetry.event_metadata() -> boolean()),
+          tag_values: Metrics.tag_values(),
+          keep: Metrics.keep(),
           description: Metrics.description(),
           unit: Metrics.unit(),
           reporter_options: Metrics.reporter_options()

lib/telemetry_metrics/sum.ex

@@ -22,8 +22,8 @@ defmodule Telemetry.Metrics.Sum do
           event_name: :telemetry.event_name(),
           measurement: Metrics.measurement(),
           tags: Metrics.tags(),
-          tag_values: (:telemetry.event_metadata() -> :telemetry.event_metadata()),
-          keep: (:telemetry.event_metadata() -> boolean()),
+          tag_values: Metrics.tag_values(),
+          keep: Metrics.keep(),
           description: Metrics.description(),
           unit: Metrics.unit(),
           reporter_options: Metrics.reporter_options()

lib/telemetry_metrics/summary.ex

@@ -22,8 +22,8 @@ defmodule Telemetry.Metrics.Summary do
           event_name: :telemetry.event_name(),
           measurement: Metrics.measurement(),
           tags: Metrics.tags(),
-          tag_values: (:telemetry.event_metadata() -> :telemetry.event_metadata()),
-          keep: (:telemetry.event_metadata() -> boolean()),
+          tag_values: Metrics.tag_values(),
+          keep: Metrics.keep(),
           description: Metrics.description(),
           unit: Metrics.unit(),
           reporter_options: Metrics.reporter_options()

test/telemetry_metrics_test.exs

@@ -146,28 +146,31 @@ defmodule Telemetry.MetricsTest do
         keep_metric =
           apply(Metrics, unquote(metric_type), [
             "my.repo.query",
-            [
-              keep: &match?(%{repo: :my_app_read_only_repo}, &1)
-            ]
+            [keep: &match?(%{repo: :my_app_read_only_repo}, &1)]
           ])
 
         drop_metric =
           apply(Metrics, unquote(metric_type), [
             "my.repo.query",
-            [
-              drop: &match?(%{repo: :my_app_read_only_repo}, &1)
-            ]
+            [drop: &match?(%{repo: :my_app_read_only_repo}, &1)]
           ])
 
-        keep_filter_fun = keep_metric.keep
+        assert keep_metric.keep.(%{repo: :my_app_read_only_repo})
+        refute keep_metric.keep.(%{repo: :my_app_repo})
 
-        assert keep_filter_fun.(%{repo: :my_app_read_only_repo})
-        refute keep_filter_fun.(%{repo: :my_app_repo})
+        refute drop_metric.keep.(%{repo: :my_app_read_only_repo})
+        assert drop_metric.keep.(%{repo: :my_app_repo})
+      end
 
-        drop_filter_fun = drop_metric.keep
+      test "using event filter that evaluates both metadata and measurement" do
+        metric =
+          apply(Metrics, unquote(metric_type), [
+            "my.repo.query",
+            [keep: &(match?(%{repo: :my_app_read_only_repo}, &1) and &2 > 100)]
+          ])
 
-        refute drop_filter_fun.(%{repo: :my_app_read_only_repo})
-        assert drop_filter_fun.(%{repo: :my_app_repo})
+        assert metric.keep.(%{repo: :my_app_read_only_repo}, 200)
+        refute metric.keep.(%{repo: :my_app_read_only_repo}, 50)
       end
 
       test "setting both keep and drop options raises" do
@@ -314,7 +317,7 @@ defmodule Telemetry.MetricsTest do
         end
       end
 
-      test "raises when event filter is not a function with an arity of 2" do
+      test "raises when event filter is not a function with an arity of 1 or 2" do
         Enum.each([keep: fn -> true end, drop: fn -> true end], fn filter ->
           assert_raise ArgumentError, fn ->
             apply(Metrics, unquote(metric_type), [