fix errors caused by instrumentation when the tracer is disabled

src/instrumenter.js

@@ -14,6 +14,7 @@ shimmer({ logger: () => {} })
 class Instrumenter {
   constructor (tracer) {
     this._tracer = tracer
+    this._enabled = false
     this._names = new Set()
     this._plugins = new Map()
     this._instrumented = new Map()
@@ -55,6 +56,8 @@ class Instrumenter {
   }
 
   reload () {
+    if (!this._enabled) return
+
     const instrumentations = Array.from(this._plugins.keys())
       .reduce((prev, current) => prev.concat(current), [])
 
@@ -128,6 +131,10 @@ class Instrumenter {
     return moduleExports
   }
 
+  enable () {
+    this._enabled = true
+  }
+
   _set (plugin, meta) {
     this._plugins.set(plugin, Object.assign({ config: {} }, meta))
   }

src/proxy.js

@@ -57,6 +57,7 @@ class Tracer extends BaseTracer {
           platform.configure(config)
 
           this._tracer = new DatadogTracer(config)
+          this._instrumenter.enable()
           this._instrumenter.patch(config)
         }
       } catch (e) {

test/instrumenter.spec.js

@@ -7,13 +7,16 @@ describe('Instrumenter', () => {
   let instrumenter
   let integrations
   let tracer
+  let tracerConfig
   let shimmer
 
   beforeEach(() => {
     tracer = {
       _tracer: 'tracer'
     }
 
+    tracerConfig = { enabled: true }
+
     integrations = {
       http: {
         name: 'http',
@@ -60,14 +63,18 @@ describe('Instrumenter', () => {
       './plugins/mysql-mock': integrations.mysql
     })
 
-    instrumenter = new Instrumenter(tracer)
+    instrumenter = new Instrumenter(tracer, tracerConfig)
   })
 
   afterEach(() => {
     delete require.cache[require.resolve('mysql-mock')]
   })
 
   describe('with integrations enabled', () => {
+    beforeEach(() => {
+      instrumenter.enable()
+    })
+
     describe('use', () => {
       it('should allow configuring a plugin by name', () => {
         const config = { foo: 'bar' }
@@ -240,6 +247,10 @@ describe('Instrumenter', () => {
   })
 
   describe('with integrations disabled', () => {
+    beforeEach(() => {
+      instrumenter.enable()
+    })
+
     describe('use', () => {
       it('should still allow adding plugins manually by name', () => {
         instrumenter.use('express-mock')
@@ -261,4 +272,30 @@ describe('Instrumenter', () => {
       })
     })
   })
+
+  describe('with the instrumenter disabled', () => {
+    describe('use', () => {
+      it('should not patch modules when they are loaded when the tracer is disabled', () => {
+        tracerConfig.enabled = false
+
+        instrumenter.patch()
+
+        require('express-mock')
+
+        expect(integrations.express.patch).to.not.have.been.called
+      })
+    })
+
+    describe('patch', () => {
+      it('should not patch if the tracer is disabled', () => {
+        tracerConfig.enabled = false
+
+        instrumenter.use('express-mock')
+
+        require('express-mock')
+
+        expect(integrations.express.patch).to.not.have.been.called
+      })
+    })
+  })
 })

test/proxy.spec.js

@@ -35,6 +35,7 @@ describe('TracerProxy', () => {
     }
 
     instrumenter = {
+      enable: sinon.spy(),
       patch: sinon.spy(),
       use: sinon.spy()
     }
@@ -103,6 +104,7 @@ describe('TracerProxy', () => {
       it('should set up automatic instrumentation', () => {
         proxy.init()
 
+        expect(instrumenter.enable).to.have.been.called
         expect(instrumenter.patch).to.have.been.called
       })