chore(events): Enforce max event length (#210)

Author: felipecsl

.gitignore

@@ -13,3 +13,4 @@ test/data
 .idea
 
 .DS_Store
+.vscode

.vscode/settings.json

@@ -60,6 +60,7 @@
     "jest-environment-jsdom": "^29.7.0",
     "lodash": "^4.17.21",
     "prettier": "^3.4.2",
+    "prettier-eslint": "^16.3.0",
     "terser-webpack-plugin": "^5.3.3",
     "testdouble": "^3.20.1",
     "ts-jest": "^29.1.1",

package.json

@@ -1004,7 +1004,6 @@ export default class EppoClient {
 
   /**
    * Enqueues an arbitrary event. Events must have a type and a payload.
-   * TODO: enforce max message size
    */
   track(type: string, payload: Record<string, unknown>) {
     this.eventDispatcher.dispatch({
@@ -1030,7 +1029,9 @@ export default class EppoClient {
     return {
       configFetchedAt: this.flagConfigurationStore.getConfigFetchedAt() ?? '',
       configPublishedAt: this.flagConfigurationStore.getConfigPublishedAt() ?? '',
-      configEnvironment: this.flagConfigurationStore.getEnvironment() ?? { name: '' },
+      configEnvironment: this.flagConfigurationStore.getEnvironment() ?? {
+        name: '',
+      },
       configFormat: this.flagConfigurationStore.getFormat() ?? '',
     };
   }

src/client/eppo-client.ts

@@ -318,4 +318,35 @@ describe('DefaultEventDispatcher', () => {
       expect(dispatcher).toBeInstanceOf(DefaultEventDispatcher);
     });
   });
+
+  describe('validation', () => {
+    it('should throw an error if the serialized event is too long', () => {
+      const { dispatcher } = createDispatcher();
+      // craft a payload that is over the limit
+      const payload = 'a'.repeat(5000);
+      expect(() =>
+        dispatcher.dispatch({
+          uuid: 'foo-1',
+          payload: { foo: payload },
+          timestamp: new Date().getTime(),
+          type: 'foo',
+        }),
+      ).toThrow();
+    });
+
+    it('should not throw an error if the serialized event is within the limit', () => {
+      const { dispatcher } = createDispatcher();
+      const payload = 'a'.repeat(4000);
+      const fetch = global.fetch as jest.Mock;
+      fetch.mockResolvedValue({ ok: true, json: () => Promise.resolve([]) });
+      expect(() =>
+        dispatcher.dispatch({
+          uuid: 'foo-1',
+          payload: { foo: payload },
+          timestamp: new Date().getTime(),
+          type: 'foo',
+        }),
+      ).not.toThrow();
+    });
+  });
 });

src/events/default-event-dispatcher.spec.ts

@@ -25,6 +25,7 @@ export type EventDispatcherConfig = {
   maxRetries?: number;
 };
 
+export const MAX_EVENT_SERIALIZED_LENGTH = 4096;
 export const DEFAULT_EVENT_DISPATCHER_BATCH_SIZE = 1_000;
 export const DEFAULT_EVENT_DISPATCHER_CONFIG: Omit<
   EventDispatcherConfig,
@@ -75,10 +76,17 @@ export default class DefaultEventDispatcher implements EventDispatcher {
   }
 
   dispatch(event: Event) {
+    this.ensureValidEvent(event);
     this.batchProcessor.push(event);
     this.maybeScheduleNextDelivery();
   }
 
+  private ensureValidEvent(event: Event) {
+    if (JSON.stringify(event).length > MAX_EVENT_SERIALIZED_LENGTH) {
+      throw new Error('Event serialized length exceeds maximum allowed length of 4096');
+    }
+  }
+
   private async deliverNextBatch() {
     if (this.isOffline) {
       logger.warn('[EventDispatcher] Skipping delivery; network status is offline.');