Improve log around the request handlers

Author: bigmontz

src/internal/bolt/response-handler.js

@@ -35,6 +35,7 @@ const NO_OP_OBSERVER = {
   onCompleted: NO_OP,
   onError: NO_OP
 }
+let requestHandlerNextId = 0
 
 /**
  * Treat the protocol responses and notify the observers
@@ -73,6 +74,8 @@ export default class ResponseHandler {
    * @param {ResponseHandler~Observer} observer Object which will be notified about errors
    */
   constructor ({ transformMetadata, log, observer } = {}) {
+    this._lastUpdateCurrentObserverCall = {}
+    this._lastQueueObserverCall = {}
     this._pendingObservers = []
     this._log = log
     this._transformMetadata = transformMetadata || NO_OP_IDENTITY
@@ -84,6 +87,7 @@ export default class ResponseHandler {
       },
       observer
     )
+    this._requestHandlerId = requestHandlerNextId++
   }
 
   handleResponse (msg) {
@@ -102,6 +106,13 @@ export default class ResponseHandler {
         }
         try {
           const metadata = this._transformMetadata(payload)
+          if (!this._currentObserver) {
+            this._log.trace(
+              `${this._requestHandlerId}.handleResponse(SUCCESS) current observer is undefined`,
+              this._lastQueueObserverCall,
+              this._lastUpdateCurrentObserverCall
+            )
+          }
           this._currentObserver.onCompleted(metadata)
         } finally {
           this._updateCurrentObserver()
@@ -151,23 +162,41 @@ export default class ResponseHandler {
    * @protected
    */
   _updateCurrentObserver () {
+    const previousObserver = this._currentObserver
     this._currentObserver = this._pendingObservers.shift()
+    this._lastUpdateCurrentObserverCall = {
+      previousObserver,
+      currentObserver: this._currentObserver,
+      stacktrace: new Error().stack
+    }
   }
 
   _queueObserver (observer) {
     observer = observer || NO_OP_OBSERVER
     observer.onCompleted = observer.onCompleted || NO_OP
     observer.onError = observer.onError || NO_OP
     observer.onNext = observer.onNext || NO_OP
+    const previousObserver = this._currentObserver
     if (this._currentObserver === undefined) {
       this._currentObserver = observer
     } else {
       this._pendingObservers.push(observer)
     }
+    this._lastQueueObserverCall = {
+      previousObserver,
+      observer,
+      currentObserver: this._currentObserver,
+      stacktrace: new Error().stack
+    }
     return true
   }
 
   _notifyErrorToObservers (error) {
+    console.trace(
+      `${this._requestHandlerId}._notifyErrorToObservers, this._currentObserver=`,
+      this._currentObserver,
+      error
+    )
     if (this._currentObserver && this._currentObserver.onError) {
       this._currentObserver.onError(error)
     }