Do not use a singleton for EE (#1543) (#1544)

Co-authored-by: Tomas Della Vedova <delvedor@users.noreply.github.com>

lib/Transport.js

@@ -36,13 +36,13 @@ const {
 
 const noop = () => {}
 
-const productCheckEmitter = new EventEmitter()
 const clientVersion = require('../package.json').version
 const userAgent = `elasticsearch-js/${clientVersion} (${os.platform()} ${os.release()}-${os.arch()}; Node.js ${process.version})`
 const MAX_BUFFER_LENGTH = buffer.constants.MAX_LENGTH
 const MAX_STRING_LENGTH = buffer.constants.MAX_STRING_LENGTH
 const kProductCheck = Symbol('product check')
 const kApiVersioning = Symbol('api versioning')
+const kEventEmitter = Symbol('event emitter')
 
 class Transport {
   constructor (opts) {
@@ -71,6 +71,7 @@ class Transport {
     this.opaqueIdPrefix = opts.opaqueIdPrefix
     this[kProductCheck] = 0 // 0 = to be checked, 1 = checking, 2 = checked-ok, 3 checked-notok, 4 checked-nodefault
     this[kApiVersioning] = process.env.ELASTIC_CLIENT_APIVERSIONING === 'true'
+    this[kEventEmitter] = new EventEmitter()
 
     this.nodeFilter = opts.nodeFilter || defaultNodeFilter
     if (typeof opts.nodeSelector === 'function') {
@@ -460,7 +461,7 @@ class Transport {
         prepareRequest()
       } else {
         // wait for product check to finish
-        productCheckEmitter.once('product-check', (error, status) => {
+        this[kEventEmitter].once('product-check', (error, status) => {
           if (status === false) {
             const err = error || new ProductNotSupportedError(result)
             if (this[kProductCheck] === 4) {
@@ -564,48 +565,48 @@ class Transport {
             'The client is unable to verify that the server is Elasticsearch due to security privileges on the server side. Some functionality may not be compatible if the server is running an unsupported product.',
             'ProductNotSupportedSecurityError'
           )
-          productCheckEmitter.emit('product-check', null, true)
+          this[kEventEmitter].emit('product-check', null, true)
         } else {
           this[kProductCheck] = 0
-          productCheckEmitter.emit('product-check', err, false)
+          this[kEventEmitter].emit('product-check', err, false)
         }
       } else {
         debug('Checking elasticsearch version', result.body, result.headers)
         if (result.body.version == null || typeof result.body.version.number !== 'string') {
           debug('Can\'t access Elasticsearch version')
-          return productCheckEmitter.emit('product-check', null, false)
+          return this[kEventEmitter].emit('product-check', null, false)
         }
         const tagline = result.body.tagline
         const version = result.body.version.number.split('.')
         const major = Number(version[0])
         const minor = Number(version[1])
         if (major < 6) {
-          return productCheckEmitter.emit('product-check', null, false)
+          return this[kEventEmitter].emit('product-check', null, false)
         } else if (major >= 6 && major < 7) {
           if (tagline !== 'You Know, for Search') {
             debug('Bad tagline')
-            return productCheckEmitter.emit('product-check', null, false)
+            return this[kEventEmitter].emit('product-check', null, false)
           }
         } else if (major === 7 && minor < 14) {
           if (tagline !== 'You Know, for Search') {
             debug('Bad tagline')
-            return productCheckEmitter.emit('product-check', null, false)
+            return this[kEventEmitter].emit('product-check', null, false)
           }
 
           if (result.body.version.build_flavor !== 'default') {
             debug('Bad build_flavor')
             this[kProductCheck] = 4
-            return productCheckEmitter.emit('product-check', null, false)
+            return this[kEventEmitter].emit('product-check', null, false)
           }
         } else {
           if (result.headers['x-elastic-product'] !== 'Elasticsearch') {
             debug('x-elastic-product not recognized')
-            return productCheckEmitter.emit('product-check', null, false)
+            return this[kEventEmitter].emit('product-check', null, false)
           }
         }
         debug('Valid Elasticsearch distribution')
         this[kProductCheck] = 2
-        productCheckEmitter.emit('product-check', null, true)
+        this[kEventEmitter].emit('product-check', null, true)
       }
     })
   }