tracing: fix child process bug when used with bluebird promises (#6002)

* fix bug

Author: wconti27

packages/datadog-instrumentations/src/child_process.js

@@ -179,7 +179,7 @@ function wrapChildProcessCustomPromisifyMethod (customPromisifyMethod, shell) {
       return result
     }
 
-    return Promise.prototype.then.call(result, resolve, reject)
+    return Promise.resolve(result).then(resolve, reject)
   }
 }
 

packages/datadog-plugin-child_process/test/index.spec.js

@@ -364,6 +364,114 @@ describe('Child process plugin', () => {
     })
   })
 
+  describe('Bluebird Promise Compatibility', () => {
+    // BLUEBIRD REGRESSION TEST - Prevents "this._then is not a function" bug
+
+    let childProcess, tracer, util
+    let originalPromise
+    let Bluebird
+
+    beforeEach(() => {
+      return agent.load('child_process', undefined, { flushInterval: 1 }).then(() => {
+        tracer = require('../../dd-trace')
+        childProcess = require('child_process')
+        util = require('util')
+        tracer.use('child_process', { enabled: true })
+        Bluebird = require('../../../versions/bluebird').get()
+
+        originalPromise = global.Promise
+        global.Promise = Bluebird
+      })
+    })
+
+    afterEach(() => {
+      global.Promise = originalPromise
+      return agent.close({ ritmReset: false })
+    })
+
+    it('should not crash with "this._then is not a function" when using Bluebird promises', async () => {
+      const execFileAsync = util.promisify(childProcess.execFile)
+
+      expect(global.Promise).to.equal(Bluebird)
+      expect(global.Promise.version).to.exist
+
+      const expectedPromise = expectSomeSpan(agent, {
+        type: 'system',
+        name: 'command_execution',
+        error: 0,
+        meta: {
+          component: 'subprocess',
+          'cmd.exec': '["echo","bluebird-test"]',
+        }
+      })
+
+      const result = await execFileAsync('echo', ['bluebird-test'])
+      expect(result).to.exist
+      expect(result.stdout).to.contain('bluebird-test')
+
+      return expectedPromise
+    })
+
+    it('should work with concurrent Bluebird promise calls', async () => {
+      const execFileAsync = util.promisify(childProcess.execFile)
+
+      const promises = []
+      for (let i = 0; i < 5; i++) {
+        promises.push(
+          execFileAsync('echo', [`concurrent-test-${i}`])
+            .then(result => {
+              expect(result.stdout).to.contain(`concurrent-test-${i}`)
+              return result
+            })
+        )
+      }
+
+      const results = await Promise.all(promises)
+      expect(results).to.have.length(5)
+    })
+
+    it('should handle Bluebird promise rejection properly', async () => {
+      global.Promise = Bluebird
+
+      const execFileAsync = util.promisify(childProcess.execFile)
+
+      const expectedPromise = expectSomeSpan(agent, {
+        type: 'system',
+        name: 'command_execution',
+        error: 1,
+        meta: {
+          component: 'subprocess',
+          'cmd.exec': '["node","-invalidFlag"]'
+        }
+      })
+
+      try {
+        await execFileAsync('node', ['-invalidFlag'], { stdio: 'pipe' })
+        throw new Error('Expected command to fail')
+      } catch (error) {
+        expect(error).to.exist
+        expect(error.code).to.exist
+      }
+
+      return expectedPromise
+    })
+
+    it('should work with util.promisify when global Promise is Bluebird', async () => {
+      // Re-require util to get Bluebird-aware promisify
+      delete require.cache[require.resolve('util')]
+      const utilWithBluebird = require('util')
+
+      const execFileAsync = utilWithBluebird.promisify(childProcess.execFile)
+
+      const promise = execFileAsync('echo', ['util-promisify-test'])
+      expect(promise.constructor).to.equal(Bluebird)
+      expect(promise.constructor.version).to.exist
+
+      const result = await promise
+      expect(result.stdout).to.contain('util-promisify-test')
+    })
+  })
+
   describe('Integration', () => {
     describe('Methods which spawn a shell by default', () => {
       const execAsyncMethods = ['exec']

packages/dd-trace/test/plugins/externals.json

@@ -61,6 +61,12 @@
       "versions": ["^4"]
     }
   ],
+  "child_process": [
+    {
+      "name": "bluebird",
+      "versions": ["^3"]
+    }
+  ],
   "cookie-parser": [
     {
       "name": "express",