experimental: poll interceptor

package.json

@@ -1,6 +1,6 @@
 {
   "name": "@eppo/js-client-sdk-common",
-  "version": "4.15.1",
+  "version": "4.16.0-experimental.1",
   "description": "Common library for Eppo JavaScript SDKs (web, react native, and node)",
   "main": "dist/index.js",
   "files": [

src/client/eppo-client.ts

@@ -55,7 +55,7 @@ import {
 } from '../interfaces';
 import { getMD5Hash } from '../obfuscation';
 import { OverridePayload, OverrideValidator } from '../override-validator';
-import initPoller, { IPoller } from '../poller';
+import initPoller, { IPoller, PollInterceptor } from '../poller';
 import SdkTokenDecoder from '../sdk-token-decoder';
 import {
   Attributes,
@@ -89,6 +89,7 @@ export type FlagConfigurationRequestParameters = {
   pollAfterFailedInitialization?: boolean;
   throwOnFailedInitialization?: boolean;
   skipInitialPoll?: boolean;
+  pollWrapper?: PollInterceptor;
 };
 
 export interface IContainerExperiment<T> {
@@ -355,6 +356,7 @@ export default class EppoClient {
       pollAfterFailedStart: pollAfterFailedInitialization,
       errorOnFailedStart: throwOnFailedInitialization,
       skipInitialPoll: skipInitialPoll,
+      pollIntercept: this.configurationRequestParameters?.pollWrapper,
     });
 
     await this.requestPoller.start();

src/index.ts

@@ -67,6 +67,7 @@ import {
   Environment,
 } from './interfaces';
 import { buildStorageKeySuffix } from './obfuscation';
+import { PollInterceptor } from './poller';
 import {
   AttributeType,
   Attributes,
@@ -96,6 +97,7 @@ export {
   FlagConfigRequestor,
   HttpClient,
   validation,
+  PollInterceptor as PollWrapper,
 
   // Precomputed Client
   EppoPrecomputedClient,

src/poller.ts

@@ -10,6 +10,9 @@ export interface IPoller {
   start: () => Promise<void>;
   stop: () => void;
 }
+export type PollInterceptor = (pollAndProcess: () => Promise<void>) => Promise<void>;
+
+const defaultPollInterceptor: PollInterceptor = async (pollAndProcess) => pollAndProcess();
 
 // TODO: change this to a class with methods instead of something that returns a function
 
@@ -25,13 +28,15 @@ export default function initPoller(
     errorOnFailedStart?: boolean;
     pollAfterFailedStart?: boolean;
     skipInitialPoll?: boolean;
+    pollIntercept?: PollInterceptor;
   },
 ): IPoller {
   let stopped = false;
   let failedAttempts = 0;
   let nextPollMs = intervalMs;
   let previousPollFailed = false;
   let nextTimer: NodeJS.Timeout | undefined = undefined;
+  const pollIntercept = options?.pollIntercept ?? defaultPollInterceptor;
 
   const start = async () => {
     stopped = false;
@@ -106,38 +111,45 @@ export default function initPoller(
     if (stopped) {
       return;
     }
+    const workFunction = async () => {
+      try {
+        await callback();
+        // If no error, reset any retrying
+        failedAttempts = 0;
+        nextPollMs = intervalMs;
+        if (previousPollFailed) {
+          previousPollFailed = false;
+          logger.info('Eppo SDK poll successful; resuming normal polling');
+        }
+      } catch (error: any) {
+        previousPollFailed = true;
+        logger.warn(`Eppo SDK encountered an error polling configurations: ${error.message}`);
+        const maxTries = 1 + (options?.maxPollRetries ?? DEFAULT_POLL_CONFIG_REQUEST_RETRIES);
+        if (++failedAttempts < maxTries) {
+          const failureWaitMultiplier = Math.pow(2, failedAttempts);
+          const jitterMs = randomJitterMs(intervalMs);
+          nextPollMs = failureWaitMultiplier * intervalMs + jitterMs;
+          logger.warn(
+            `Eppo SDK will try polling again in ${nextPollMs} ms (${
+              maxTries - failedAttempts
+            } attempts remaining)`,
+          );
+        } else {
+          logger.error(
+            `Eppo SDK reached maximum of ${failedAttempts} failed polling attempts. Stopping polling`,
+          );
+          stop();
+        }
+      }
+    };
 
     try {
-      await callback();
-      // If no error, reset any retrying
-      failedAttempts = 0;
-      nextPollMs = intervalMs;
-      if (previousPollFailed) {
-        previousPollFailed = false;
-        logger.info('Eppo SDK poll successful; resuming normal polling');
-      }
-    } catch (error: any) {
-      previousPollFailed = true;
-      logger.warn(`Eppo SDK encountered an error polling configurations: ${error.message}`);
-      const maxTries = 1 + (options?.maxPollRetries ?? DEFAULT_POLL_CONFIG_REQUEST_RETRIES);
-      if (++failedAttempts < maxTries) {
-        const failureWaitMultiplier = Math.pow(2, failedAttempts);
-        const jitterMs = randomJitterMs(intervalMs);
-        nextPollMs = failureWaitMultiplier * intervalMs + jitterMs;
-        logger.warn(
-          `Eppo SDK will try polling again in ${nextPollMs} ms (${
-            maxTries - failedAttempts
-          } attempts remaining)`,
-        );
-      } else {
-        logger.error(
-          `Eppo SDK reached maximum of ${failedAttempts} failed polling attempts. Stopping polling`,
-        );
-        stop();
-      }
+      await pollIntercept(workFunction);
+    } catch (e: any) {
+      logger.error(`Eppo SDK encountered an error with the polling wrapper: ${e.message}`);
     }
 
-    setTimeout(poll, nextPollMs);
+    nextTimer = setTimeout(poll, nextPollMs);
   }
 
   return {