FFM-7412 - Reduce complexity of SSE code (#70)

FFM-7412 - Reduce complexity of SSE code

What
Remove eventsource dependency to reduce code complexity and create an easier to maintain implementation

Why
We're seeing the eventsource/retry packages spin and cause a lot of retries to happen at once, causing an adverse effect on system resources.

Testing
Manual testing with custom proxies to simulate network failures.

Author: andybharness

package-lock.json

@@ -1,6 +1,6 @@
 {
   "name": "@harnessio/ff-nodejs-server-sdk",
-  "version": "1.2.15",
+  "version": "1.2.16",
   "description": "Feature flags SDK for NodeJS environments",
   "main": "dist/cjs/index.js",
   "module": "dist/esm/index.mjs",
@@ -41,8 +41,8 @@
     "versioning": "node -p \"'export const VERSION = ' + JSON.stringify(require('./package.json').version) + ';'\" > src/version.ts",
     "prebuild": "npm run clean; npm run versioning; npm run lint",
     "dts": "tsc ./src/index.ts --declaration --emitDeclarationOnly --esModuleInterop --downlevelIteration --outdir ./dist",
-    "build:esm": "esbuild ./src/index.ts --tsconfig=tsconfig.modules.json --minify --bundle --sourcemap --target=node12.22.5 --platform=node --format=esm --outfile=./dist/esm/index.mjs --external:keyv --external:keyv-file --external:eventsource --external:axios",
-    "build:cjs": "esbuild ./src/index.ts --tsconfig=tsconfig.release.json --minify --bundle --sourcemap --target=node12.22.5 --platform=node --format=cjs --outfile=./dist/cjs/index.js --external:keyv --external:keyv-file --external:eventsource --external:axios",
+    "build:esm": "esbuild ./src/index.ts --tsconfig=tsconfig.modules.json --minify --bundle --sourcemap --target=node12.22.5 --platform=node --format=esm --outfile=./dist/esm/index.mjs --external:keyv --external:keyv-file --external:axios",
+    "build:cjs": "esbuild ./src/index.ts --tsconfig=tsconfig.release.json --minify --bundle --sourcemap --target=node12.22.5 --platform=node --format=cjs --outfile=./dist/cjs/index.js --external:keyv --external:keyv-file --external:axios",
     "build": "npm run build:esm; npm run build:cjs; npm run dts",
     "build:watch": "tsc -w -p tsconfig.release.json",
     "prepare": "npm run build",
@@ -63,7 +63,6 @@
   "dependencies": {
     "axios": "^0.22.0",
     "axios-retry": "^3.2.0",
-    "@harnessio/eventsource": "^2.1.4",
     "jwt-decode": "^3.1.2",
     "keyv": "^4.0.3",
     "keyv-file": "^0.2.0",

package.json

@@ -6,8 +6,8 @@ jest.mock('../openapi/api');
 
 describe('Client', () => {
   beforeEach(() => {
-    jest.resetAllMocks()
-  })
+    jest.resetAllMocks();
+  });
 
   it('should close the client when the close method is called', async () => {
     // given
@@ -28,7 +28,7 @@ describe('Client', () => {
   });
 
   it('should warn if poll interval is set below the default', async () => {
-    jest.spyOn(PollingProcessor.prototype, 'start').mockReturnValue(undefined)
+    jest.spyOn(PollingProcessor.prototype, 'start').mockReturnValue(undefined);
     const warnSpy = jest.spyOn(console, 'warn').mockReturnValue(undefined);
 
     new Client('some key', {
@@ -55,7 +55,7 @@ describe('Client', () => {
   });
 
   it('should warn if events sync interval is set below the default', async () => {
-    jest.spyOn(PollingProcessor.prototype, 'start').mockReturnValue(undefined)
+    jest.spyOn(PollingProcessor.prototype, 'start').mockReturnValue(undefined);
     const warnSpy = jest.spyOn(console, 'warn');
 
     new Client('some key', {

src/__tests__/client.test.ts

@@ -61,12 +61,16 @@ export default class Client {
 
     if (options.pollInterval < defaultOptions.pollInterval) {
       this.options.pollInterval = defaultOptions.pollInterval;
-      this.log.warn(`Polling interval cannot be lower than ${defaultOptions.pollInterval} ms`);
+      this.log.warn(
+        `Polling interval cannot be lower than ${defaultOptions.pollInterval} ms`,
+      );
     }
 
     if (options.eventsSyncInterval < defaultOptions.eventsSyncInterval) {
       this.options.eventsSyncInterval = defaultOptions.eventsSyncInterval;
-      this.log.warn(`Events sync interval cannot be lower than ${defaultOptions.eventsSyncInterval} ms`);
+      this.log.warn(
+        `Events sync interval cannot be lower than ${defaultOptions.eventsSyncInterval} ms`,
+      );
     }
 
     this.configuration = new Configuration({
@@ -105,15 +109,19 @@ export default class Client {
 
     this.eventBus.on(StreamEvent.RETRYING, () => {
       this.failure = true;
-      this.log.error('Issue with streaming: falling back to polling while the SDK attempts to reconnect');
+      this.log.error(
+        'Issue with streaming: falling back to polling while the SDK attempts to reconnect',
+      );
       if (!this.closing) {
         this.pollProcessor.start();
       }
     });
 
     this.eventBus.on(StreamEvent.ERROR, () => {
       this.failure = true;
-      this.log.error('Unrecoverable issue with streaming: falling back to polling');
+      this.log.error(
+        'Unrecoverable issue with streaming: falling back to polling',
+      );
       if (!this.closing) {
         this.pollProcessor.start();
       }

src/client.ts

@@ -206,7 +206,7 @@ export class Evaluator {
     target: Target,
   ): Promise<boolean> {
     for (const clause of clauses) {
-      if ((await this.evaluateClause(clause, target))) {
+      if (await this.evaluateClause(clause, target)) {
         // If any clause returns true we return - rules being treated as OR rather than AND
         return true;
       }

src/evaluator.ts

@@ -20,6 +20,7 @@ export class PollingProcessor {
   private eventBus: EventEmitter;
   private timeout: NodeJS.Timeout;
   private log: ConsoleLog;
+  private lastPollTime = 0;
 
   constructor(
     environment: string,
@@ -52,6 +53,17 @@ export class PollingProcessor {
       this.timeout = setTimeout(() => this.poll(), sleepFor);
     };
 
+    if (this.lastPollTime > Date.now() - this.options.pollInterval) {
+      this.log.info(
+        `Last poll was ${Math.round(
+          (Date.now() - this.lastPollTime) / 1000,
+        )} seconds ago, skipping flag refresh`,
+      );
+      pollAgain();
+      return;
+    }
+
+    this.lastPollTime = Date.now();
     Promise.all([this.retrieveFlags(), this.retrieveSegments()])
       .then(() => {
         // when first fetch is successful then poller is ready