fix(rtdb): Fixing a token refresh livelock in Cloud Functions (#1234)

Author: hiranya911

src/database/database-internal.ts

@@ -116,18 +116,15 @@ export class DatabaseService {
 
   // eslint-disable-next-line @typescript-eslint/no-unused-vars
   private onTokenChange(_: string): void {
-    this.appInternal.INTERNAL.getToken()
-      .then((token) => {
-        const delayMillis = token.expirationTime - TOKEN_REFRESH_THRESHOLD_MILLIS - Date.now();
-        // If the new token is set to expire soon (unlikely), do nothing. Somebody will eventually
-        // notice and refresh the token, at which point this callback will fire again.
-        if (delayMillis > 0) {
-          this.scheduleTokenRefresh(delayMillis);
-        }
-      })
-      .catch((err) => {
-        console.error('Unexpected error while attempting to schedule a token refresh:', err);
-      });
+    const token = this.appInternal.INTERNAL.getCachedToken();
+    if (token) {
+      const delayMillis = token.expirationTime - TOKEN_REFRESH_THRESHOLD_MILLIS - Date.now();
+      // If the new token is set to expire soon (unlikely), do nothing. Somebody will eventually
+      // notice and refresh the token, at which point this callback will fire again.
+      if (delayMillis > 0) {
+        this.scheduleTokenRefresh(delayMillis);
+      }
+    }
   }
 
   private scheduleTokenRefresh(delayMillis: number): void {

src/firebase-app.ts

@@ -74,6 +74,10 @@ export class FirebaseAppInternals {
     return Promise.resolve(this.cachedToken_);
   }
 
+  public getCachedToken(): FirebaseAccessToken | null {
+    return this.cachedToken_ || null;
+  }
+
   private refreshToken(): Promise<FirebaseAccessToken> {
     return Promise.resolve(this.credential_.getAccessToken())
       .then((result) => {
@@ -97,6 +101,8 @@ export class FirebaseAppInternals {
         if (!this.cachedToken_
           || this.cachedToken_.accessToken !== token.accessToken
           || this.cachedToken_.expirationTime !== token.expirationTime) {
+          // Update the cache before firing listeners. Listeners may directly query the
+          // cached token state.
           this.cachedToken_ = token;
           this.tokenListeners_.forEach((listener) => {
             listener(token.accessToken);

test/unit/database/database.spec.ts

@@ -211,9 +211,7 @@ describe('Database', () => {
         });
     });
 
-    // Currently doesn't work as expected since onTokenChange() can force a token refresh
-    // by calling getToken(). Skipping for now.
-    xit('should not reschedule when the token is about to expire in 5 minutes', () => {
+    it('should not reschedule when the token is about to expire in 5 minutes', () => {
       database.getDatabase();
       return mockApp.INTERNAL.getToken()
         .then((token1) => {