fix error in http2 plugin when it was enabled after request start (#3714

)

* fix error in http2 plugin when it was enabled after request start

packages/datadog-plugin-http2/src/client.js

@@ -73,6 +73,9 @@ class Http2ClientPlugin extends ClientPlugin {
   }
 
   bindAsyncStart ({ eventName, eventData, currentStore, parentStore }) {
+    // Plugin wasn't enabled when the request started.
+    if (!currentStore) return storage('legacy').getStore()
+
     switch (eventName) {
       case 'response':
         this._onResponse(currentStore, eventData)

packages/datadog-plugin-http2/test/client.spec.js

@@ -680,6 +680,52 @@ describe('Plugin', () => {
         })
       })
 
+      describe('with late plugin initialization and an external subscriber', () => {
+        let ch
+        let sub
+
+        beforeEach(() => {
+          return agent.load('http2', { server: false })
+            .then(() => {
+              ch = require('dc-polyfill').channel('apm:http2:client:request:start')
+              sub = () => {}
+              tracer = require('../../dd-trace')
+              http2 = require('http2')
+            })
+        })
+
+        afterEach(() => {
+          ch.unsubscribe(sub)
+        })
+
+        it('should not crash', done => {
+          const app = (stream, headers) => {
+            stream.respond({
+              ':status': 200
+            })
+            stream.end()
+          }
+
+          appListener = server(app, port => {
+            ch.subscribe(sub)
+
+            const client = http2
+              .connect(`${protocol}://localhost:${port}`)
+              .on('error', done)
+
+            tracer.use('http2', false)
+
+            const req = client.request({ ':path': '/user', ':method': 'GET' })
+            req.on('error', done)
+            req.on('response', () => done())
+
+            tracer.use('http2', true)
+
+            req.end()
+          })
+        })
+      })
+
       describe('with validateStatus configuration', () => {
         let config