fix: Improve remote evaluation fetch retry logic (#37)

Author: tyiuhc

__tests__/client.test.ts

@@ -1,4 +1,5 @@
 import { AnalyticsConnector } from '@amplitude/analytics-connector';
+import { FetchError } from '@amplitude/experiment-core';
 import AsyncStorage from '@react-native-async-storage/async-storage';
 
 import { Exposure } from '../lib/typescript';
@@ -61,6 +62,7 @@ class TestHttpClient implements HttpClient {
     return { status: this.status, body: this.body } as SimpleResponse;
   }
 }
+
 /**
  * Basic test that fetching variants for a user succeeds.
  */
@@ -957,3 +959,45 @@ describe('start', () => {
     expect(fetchSpy).toBeCalledTimes(0);
   });
 });
+
+describe('fetch retry with different response codes', () => {
+  beforeEach(() => {
+    jest.clearAllMocks();
+  });
+  test.each([
+    [300, 'Fetch Exception 300', 1],
+    [400, 'Fetch Exception 400', 0],
+    [429, 'Fetch Exception 429', 1],
+    [500, 'Fetch Exception 500', 1],
+    [0, 'Other Exception', 1],
+  ])(
+    'responseCode=%p, errorMessage=%p, retryCalled=%p',
+    async (responseCode, errorMessage, retryCalled) => {
+      const client = new ExperimentClient(API_KEY, {
+        retryFetchOnFailure: true,
+      });
+
+      jest
+        .spyOn(ExperimentClient.prototype as any, 'doFetch')
+        .mockImplementation(async () => {
+          return new Promise<ExperimentClient>((_resolve, reject) => {
+            if (responseCode === 0) {
+              reject(new Error(errorMessage));
+            } else {
+              reject(new FetchError(responseCode, errorMessage));
+            }
+          });
+        });
+      const retryMock = jest.spyOn(
+        ExperimentClient.prototype as any,
+        'startRetries',
+      );
+      try {
+        await client.fetch({ user_id: 'test_user' });
+      } catch (e) {
+        // catch error
+      }
+      expect(retryMock).toHaveBeenCalledTimes(retryCalled);
+    },
+  );
+});

package.json

@@ -48,7 +48,7 @@
   },
   "dependencies": {
     "@amplitude/analytics-connector": "^1.4.7",
-    "@amplitude/experiment-core": "^0.7.0",
+    "@amplitude/experiment-core": "^0.7.2",
     "@react-native-async-storage/async-storage": "^1.17.6",
     "unfetch": "^4.2.0"
   },

src/experimentClient.ts

@@ -8,6 +8,7 @@ import {
   EvaluationApi,
   EvaluationEngine,
   EvaluationFlag,
+  FetchError,
   FlagApi,
   Poller,
   SdkFlagApi,
@@ -607,7 +608,7 @@ export class ExperimentClient implements Client {
 
     this.debug(`[Experiment] Fetch all: retry=${retry}`);
 
-    // Proactively cancel retries if active in order to avoid unecessary API
+    // Proactively cancel retries if active in order to avoid unnecessary API
     // requests. A new failure will restart the retries.
     if (retry) {
       this.stopRetries();
@@ -618,7 +619,7 @@ export class ExperimentClient implements Client {
       await this.storeVariants(variants, options);
       return variants;
     } catch (e) {
-      if (retry) {
+      if (retry && this.shouldRetryFetch(e)) {
         this.startRetries(user, options);
       }
       throw e;
@@ -780,6 +781,13 @@ export class ExperimentClient implements Client {
       console.debug(message, ...optionalParams);
     }
   }
+
+  private shouldRetryFetch(e: Error): boolean {
+    if (e instanceof FetchError) {
+      return e.statusCode < 400 || e.statusCode >= 500 || e.statusCode === 429;
+    }
+    return true;
+  }
 }
 
 type SourceVariant = {

yarn.lock

@@ -14,10 +14,10 @@
   dependencies:
     "@amplitude/ua-parser-js" "^0.7.31"
 
-"@amplitude/experiment-core@^0.7.0":
-  version "0.7.0"
-  resolved "https://registry.yarnpkg.com/@amplitude/experiment-core/-/experiment-core-0.7.0.tgz#258d95d691461acf3b6d1bea430f5ba231986342"
-  integrity sha512-/W+BFGc2qix4aZ9V4VEYDcot8Vk/YirRcqY9Y0hlB27NPnhke0Id5mgPl/puKy7wqbXC6yTuda7rVpAtGBFMOA==
+"@amplitude/experiment-core@^0.7.2":
+  version "0.7.2"
+  resolved "https://registry.yarnpkg.com/@amplitude/experiment-core/-/experiment-core-0.7.2.tgz#f94219d68d86322e8d580c8fbe0672dcd29f86bb"
+  integrity sha512-Wc2NWvgQ+bLJLeF0A9wBSPIaw0XuqqgkPKsoNFQrmS7r5Djd56um75In05tqmVntPJZRvGKU46pAp8o5tdf4mA==
   dependencies:
     js-base64 "^3.7.5"