From 879cfe327788e2e3c4a140840371868cfa62bcbc Mon Sep 17 00:00:00 2001
From: Tim Yiu <137842098+tyiuhc@users.noreply.github.com>
Date: Wed, 30 Oct 2024 10:44:25 -0700
Subject: [PATCH] fix: catch variant/flag fetch timeout error and log at
 debug-level (#135)

---
 .../src/experimentClient.ts                   | 30 ++++++++++++++-----
 .../experiment-browser/src/transport/http.ts  |  9 ++++--
 .../experiment-core/src/evaluation/error.ts   |  7 +++++
 packages/experiment-core/src/index.ts         |  2 +-
 4 files changed, 37 insertions(+), 11 deletions(-)

diff --git a/packages/experiment-browser/src/experimentClient.ts b/packages/experiment-browser/src/experimentClient.ts
index e4fd5bc4..0aabab8f 100644
--- a/packages/experiment-browser/src/experimentClient.ts
+++ b/packages/experiment-browser/src/experimentClient.ts
@@ -12,6 +12,7 @@ import {
   Poller,
   SdkEvaluationApi,
   SdkFlagApi,
+  TimeoutError,
   topologicalSort,
 } from '@amplitude/experiment-core';
 
@@ -255,7 +256,11 @@ export class ExperimentClient implements Client {
       );
     } catch (e) {
       if (this.config.debug) {
-        console.error(e);
+        if (e instanceof TimeoutError) {
+          console.debug(e);
+        } else {
+          console.error(e);
+        }
       }
     }
     return this;
@@ -697,13 +702,22 @@ export class ExperimentClient implements Client {
   }
 
   private async doFlags(): Promise<void> {
-    const flags = await this.flagApi.getFlags({
-      libraryName: 'experiment-js-client',
-      libraryVersion: PACKAGE_VERSION,
-      timeoutMillis: this.config.fetchTimeoutMillis,
-    });
-    this.flags.clear();
-    this.flags.putAll(flags);
+    try {
+      const flags = await this.flagApi.getFlags({
+        libraryName: 'experiment-js-client',
+        libraryVersion: PACKAGE_VERSION,
+        timeoutMillis: this.config.fetchTimeoutMillis,
+      });
+      this.flags.clear();
+      this.flags.putAll(flags);
+    } catch (e) {
+      if (this.config.debug && e instanceof TimeoutError) {
+        console.debug(e);
+      } else {
+        throw e;
+      }
+    }
+
     try {
       this.flags.store();
     } catch (e) {
diff --git a/packages/experiment-browser/src/transport/http.ts b/packages/experiment-browser/src/transport/http.ts
index b0b6f9e4..b87c3750 100644
--- a/packages/experiment-browser/src/transport/http.ts
+++ b/packages/experiment-browser/src/transport/http.ts
@@ -3,7 +3,7 @@
  * @internal
  */
 
-import { safeGlobal } from '@amplitude/experiment-core';
+import { safeGlobal, TimeoutError } from '@amplitude/experiment-core';
 import {
   HttpClient as CoreHttpClient,
   HttpRequest,
@@ -29,7 +29,11 @@ const timeout = (
   }
   return new Promise(function (resolve, reject) {
     safeGlobal.setTimeout(function () {
-      reject(Error('Request timeout after ' + timeoutMillis + ' milliseconds'));
+      reject(
+        new TimeoutError(
+          'Request timeout after ' + timeoutMillis + ' milliseconds',
+        ),
+      );
     }, timeoutMillis);
     promise.then(resolve, reject);
   });
@@ -63,6 +67,7 @@ const _request = (
  */
 export class WrapperClient implements CoreHttpClient {
   private readonly client: HttpClient;
+
   constructor(client: HttpClient) {
     this.client = client;
   }
diff --git a/packages/experiment-core/src/evaluation/error.ts b/packages/experiment-core/src/evaluation/error.ts
index b24e516d..c03b8a75 100644
--- a/packages/experiment-core/src/evaluation/error.ts
+++ b/packages/experiment-core/src/evaluation/error.ts
@@ -7,3 +7,10 @@ export class FetchError extends Error {
     Object.setPrototypeOf(this, FetchError.prototype);
   }
 }
+
+export class TimeoutError extends Error {
+  constructor(message: string) {
+    super(message);
+    Object.setPrototypeOf(this, TimeoutError.prototype);
+  }
+}
diff --git a/packages/experiment-core/src/index.ts b/packages/experiment-core/src/index.ts
index 09bd0b37..d5f1bb83 100644
--- a/packages/experiment-core/src/index.ts
+++ b/packages/experiment-core/src/index.ts
@@ -23,4 +23,4 @@ export {
   getGlobalScope,
   isLocalStorageAvailable,
 } from './util/global';
-export { FetchError } from './evaluation/error';
+export { FetchError, TimeoutError } from './evaluation/error';