Move Prometheus presentation logic to PrometheusText

+ Use NullMetrics to mock metrics when unused
+ Use method_missing in NullMetrics mocking
+ Update prometheus gem to version that correctly uses transitive dependencies
+ Ensure correct folders are used in Multiprocess prometheus client tests.
+ rename Sessions controller's metric

1 files changed, 38 insertions, 0 deletions

diff --git a/lib/gitlab/health_checks/prometheus_text.rb b/lib/gitlab/health_checks/prometheus_text.rb
new file mode 100644
index 00000000000..a01e6b2be1f
--- /dev/null
+++ b/lib/gitlab/health_checks/prometheus_text.rb
@@ -0,0 +1,38 @@
+module Gitlab::HealthChecks
+  class PrometheusText
+    def marshal(metrics)
+      metrics_with_type_declarations(metrics).join("\n")
+    end
+
+    private
+
+    def metrics_with_type_declarations(metrics)
+      type_declaration_added = {}
+
+      metrics.flat_map do |metric|
+        metric_lines = []
+
+        unless type_declaration_added.has_key?(metric.name)
+          type_declaration_added[metric.name] = true
+          metric_lines << metric_type_declaration(metric)
+        end
+
+        metric_lines << metric_text(metric)
+      end
+    end
+
+    def metric_type_declaration(metric)
+      "# TYPE #{metric.name} gauge"
+    end
+
+    def metric_text(metric)
+      labels = metric.labels&.map { |key, value| "#{key}=\"#{value}\"" }&.join(',') || ''
+
+      if labels.empty?
+        "#{metric.name} #{metric.value}"
+      else
+        "#{metric.name}{#{labels}} #{metric.value}"
+      end
+    end
+  end
+end