Exclude empty telemetry metrics (#3421)

Author: Stephen Belanger

packages/dd-trace/src/telemetry/metrics.js

@@ -25,6 +25,10 @@ function mapToJsonArray (map) {
   return Array.from(map.values()).map(v => v.toJSON())
 }
 
+function hasPoints (metric) {
+  return metric.points.length > 0
+}
+
 class Metric {
   constructor (namespace, metric, common, tags) {
     this.namespace = namespace.toString()
@@ -172,10 +176,16 @@ class MetricsCollection extends Map {
 
   toJSON () {
     if (!this.size) return
+
+    const series = mapToJsonArray(this)
+      .filter(hasPoints)
+
+    if (!series.length) return
+
     const { namespace } = this
     return {
       namespace,
-      series: mapToJsonArray(this)
+      series
     }
   }
 }

packages/dd-trace/test/telemetry/metrics.spec.js

@@ -157,6 +157,33 @@ describe('metrics', () => {
           ]
         })
     })
+
+    it('should not send empty metrics', () => {
+      const manager = new metrics.NamespaceManager()
+
+      const ns = manager.namespace('test')
+
+      const metric = ns.count('metric', { bar: 'baz' })
+      metric.inc()
+      metric.reset()
+
+      const config = {
+        hostname: 'localhost',
+        port: 12345,
+        tags: {
+          'runtime-id': 'abc123'
+        }
+      }
+      const application = {
+        language_name: 'nodejs',
+        tracer_version: '1.2.3'
+      }
+      const host = {}
+
+      manager.send(config, application, host)
+
+      expect(sendData).to.not.have.been.called
+    })
   })
 
   describe('Namespace', () => {
@@ -249,6 +276,18 @@ describe('metrics', () => {
         }
       })
     })
+
+    it('should skip empty metrics', () => {
+      const ns = new metrics.Namespace('test')
+      const metric = ns.count('foo', { bar: 'baz' })
+      metric.inc()
+      metric.reset()
+
+      expect(ns.toJSON()).to.deep.equal({
+        distributions: undefined,
+        metrics: undefined
+      })
+    })
   })
 
   describe('CountMetric', () => {