fix: crashing error when active:false and agent.registerMetrics is called (#2290)

* fix: crashing error when active:false and agent.registerMetrics is called

Fixes: #1799

Author: astorm

CHANGELOG.asciidoc

@@ -43,6 +43,7 @@ Notes:
 * Ensure the internal HTTP(S) client requests made by the APM agent to APM
   server are not themselves traced. ({issues}1168[#1168], {issues}1136[#1136])
 
+* Fix crashing error with `agent.registerMetric` and `active:false` configuration. ({issues}1799[#1799], {pull}2290[#2290])
 
 [[release-notes-3.20.0]]
 ==== 3.20.0 2021/08/12

lib/metrics/index.js

@@ -42,6 +42,9 @@ class Metrics {
   }
 
   getOrCreateCounter (...args) {
+    if (!this[registrySymbol]) {
+      return
+    }
     return this[registrySymbol].getOrCreateCounter(...args)
   }
 
@@ -54,13 +57,19 @@ class Metrics {
   }
 
   getOrCreateGauge (...args) {
+    if (!this[registrySymbol]) {
+      return
+    }
     return this[registrySymbol].getOrCreateGauge(...args)
   }
 
   // factory function for creating a queue metrics collector
   //
   // called from instrumentation, only when the agent receives a queue message
   createQueueMetricsCollector (queueOrTopicName) {
+    if (!this[registrySymbol]) {
+      return
+    }
     const collector = createQueueMetrics(queueOrTopicName, this[registrySymbol])
     return collector
   }

test/metrics/index.test.js

@@ -211,6 +211,18 @@ test('noop counter when not active', function (t) {
   t.end()
 })
 
+test('Metrics objects do not throw/crash when not started', function (t) {
+  const metrics = new Metrics()
+
+  t.equals(metrics.stop(), undefined, 'unset registrySymbol does not crash metrics object')
+  t.equals(metrics.getOrCreateCounter('foo', {}, null), undefined, 'unset registrySymbol does not crash metrics object')
+  t.equals(metrics.incrementCounter('foo'), undefined, 'unset registrySymbol does not crash metrics object')
+  t.equals(metrics.getOrCreateGauge('foo', function () {}), undefined, 'unset registrySymbol does not crash metrics object')
+  t.equals(metrics.createQueueMetricsCollector('foo'), undefined, 'unset registrySymbol does not crash metrics object')
+
+  t.end()
+})
+
 function spinCPUFor (durationMs) {
   const start = Date.now()
   while (Date.now() - start < durationMs) {}