Support :all as an aggregation mode in DirectFileStore

We want to support exporting each process's individual value for gauges.
To enable this, DirectFileStore needs a new aggregation mode - :all.

Signed-off-by: Chris Sinjakli <chris@gocardless.com>

Author: Chris Sinjakli

lib/prometheus/client/data_stores/direct_file_store.rb

@@ -26,7 +26,7 @@ module DataStores
 
       class DirectFileStore
         class InvalidStoreSettingsError < StandardError; end
-        AGGREGATION_MODES = [MAX = :max, MIN = :min, SUM = :sum]
+        AGGREGATION_MODES = [MAX = :max, MIN = :min, SUM = :sum, ALL = :all]
         DEFAULT_METRIC_SETTINGS = { aggregation: SUM }
 
         def initialize(dir:)
@@ -120,16 +120,30 @@ def all_values
                     [k.to_sym, vs.first]
                   end.to_h
 
+                  if @values_aggregation_mode == ALL
+                    #  TODO: Can I do this in a less gross way?
+                    pid = /(\d+)\.bin$/.match(file_path)[1]
+                    label_set[:pid] = pid
+                  end
+
                   stores_data[label_set] << v
                 end
               ensure
                 store.close if store
               end
             end
 
-            # Aggregate all the different values for each label_set
-            stores_data.each_with_object({}) do |(label_set, values), acc|
-              acc[label_set] = aggregate_values(values)
+            if @values_aggregation_mode == ALL
+              stores_data.each do |label_set, values|
+                stores_data[label_set] = values.first
+              end
+
+              stores_data
+            else
+              # Aggregate all the different values for each label_set
+              stores_data.each_with_object({}) do |(label_set, values), acc|
+                acc[label_set] = aggregate_values(values)
+              end
             end
           end
 

spec/prometheus/client/data_stores/direct_file_store_spec.rb

@@ -150,6 +150,42 @@
     end
   end
 
+  context "with a metric that takes ALL instead of SUM" do
+    it "reports all the values from different processes" do
+      allow(Process).to receive(:pid).and_return(12345)
+      metric_store1 = subject.for_metric(
+        :metric_name,
+        metric_type: :gauge,
+        metric_settings: { aggregation: :all }
+      )
+      metric_store1.set(labels: { foo: "bar" }, val: 1)
+      metric_store1.set(labels: { foo: "baz" }, val: 7)
+      metric_store1.set(labels: { foo: "yyy" }, val: 3)
+
+      allow(Process).to receive(:pid).and_return(23456)
+      metric_store2 = subject.for_metric(
+        :metric_name,
+        metric_type: :gauge,
+        metric_settings: { aggregation: :all }
+      )
+      metric_store2.set(labels: { foo: "bar" }, val: 3)
+      metric_store2.set(labels: { foo: "baz" }, val: 2)
+      metric_store2.set(labels: { foo: "zzz" }, val: 1)
+
+      expect(metric_store1.all_values).to eq(
+        { foo: "bar", pid: "12345" } => 1.0,
+        { foo: "bar", pid: "23456" } => 3.0,
+        { foo: "baz", pid: "12345" } => 7.0,
+        { foo: "baz", pid: "23456" } => 2.0,
+        { foo: "yyy", pid: "12345" } => 3.0,
+        { foo: "zzz", pid: "23456" } => 1.0,
+      )
+
+      # Both processes should return the same value
+      expect(metric_store1.all_values).to eq(metric_store2.all_values)
+    end
+  end
+
   it "resizes the File if metrics get too big" do
      truncate_calls_count = 0
      allow_any_instance_of(Prometheus::Client::DataStores::DirectFileStore::FileMappedDict).