From c11504f5ad70253be375222236d96d27fbd49f30 Mon Sep 17 00:00:00 2001
From: Tim Blakely <tim.blakely@gmail.com>
Date: Mon, 5 Feb 2018 17:55:19 -0800
Subject: [PATCH] fix(StoreDevtools): Do not send full liftedState for
 application actions (#790)

---
 modules/store-devtools/src/extension.ts | 35 ++++++++++++++++++++++---
 1 file changed, 31 insertions(+), 4 deletions(-)

diff --git a/modules/store-devtools/src/extension.ts b/modules/store-devtools/src/extension.ts
index 088e1d795c..7394673768 100644
--- a/modules/store-devtools/src/extension.ts
+++ b/modules/store-devtools/src/extension.ts
@@ -10,6 +10,7 @@ import { takeUntil } from 'rxjs/operator/takeUntil';
 
 import { STORE_DEVTOOLS_CONFIG, StoreDevtoolsConfig } from './config';
 import { LiftedState } from './reducer';
+import { PerformAction } from './actions';
 import { applyOperators } from './utils';
 
 export const ExtensionActionTypes = {
@@ -28,11 +29,13 @@ export interface ReduxDevtoolsExtensionConnection {
   unsubscribe(): void;
   send(action: any, state: any): void;
   init(state?: any): void;
+  error(any: any): void;
 }
 export interface ReduxDevtoolsExtensionConfig {
   features?: object | boolean;
   name: string | undefined;
   instanceId: string;
+  maxAge?: number;
 }
 
 export interface ReduxDevtoolsExtension {
@@ -51,6 +54,7 @@ export interface ReduxDevtoolsExtension {
 export class DevtoolsExtension {
   private instanceId = `ngrx-store-${Date.now()}`;
   private devtoolsExtension: ReduxDevtoolsExtension;
+  private extensionConnection: ReduxDevtoolsExtensionConnection;
 
   liftedActions$: Observable<any>;
   actions$: Observable<any>;
@@ -68,7 +72,26 @@ export class DevtoolsExtension {
       return;
     }
 
-    this.devtoolsExtension.send(null, state, this.config, this.instanceId);
+    // Check to see if the action requires a full update of the liftedState.
+    // If it is a simple action generated by the user's app, only send the
+    // action and the current state (fast).
+    //
+    // A full liftedState update (slow: serializes the entire liftedState) is
+    // only required when:
+    //   a) redux-devtools-extension fires the @@Init action (ignored by
+    //      @ngrx/store-devtools)
+    //   b) an action is generated by an @ngrx module (e.g. @ngrx/effects/init
+    //      or @ngrx/store/update-reducers)
+    //   c) the state has been recomputed due to time-traveling
+    //   d) any action that is not a PerformAction to err on the side of
+    //      caution.
+    if (action instanceof PerformAction) {
+      const currentState = state.computedStates[state.currentStateIndex].state;
+      this.extensionConnection.send(action.action, currentState);
+    } else {
+      // Requires full state update;
+      this.devtoolsExtension.send(null, state, this.config, this.instanceId);
+    }
   }
 
   private createChangesObservable(): Observable<any> {
@@ -77,15 +100,19 @@ export class DevtoolsExtension {
     }
 
     return new Observable(subscriber => {
-      const connection = this.devtoolsExtension.connect({
+      let extensionOptions: ReduxDevtoolsExtensionConfig = {
         instanceId: this.instanceId,
         name: this.config.name,
         features: this.config.features,
-      });
+      };
+      if (this.config.maxAge !== false /* support === 0 */) {
+        extensionOptions.maxAge = this.config.maxAge;
+      }
+      const connection = this.devtoolsExtension.connect(extensionOptions);
+      this.extensionConnection = connection;
       connection.init();
 
       connection.subscribe((change: any) => subscriber.next(change));
-
       return connection.unsubscribe;
     });
   }