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greghuelsgreghuels
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feat: server overrides
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‎src/client/eppo-client-with-overrides.spec.ts‎

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@@ -0,0 +1,141 @@
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import { MemoryOnlyConfigurationStore } from '../configuration-store/memory.store';
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import { Flag, FormatEnum, ObfuscatedFlag, VariationType } from '../interfaces';
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import * as overrideValidatorModule from '../override-validator';
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import EppoClient from './eppo-client';
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describe('EppoClient', () => {
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const storage = new MemoryOnlyConfigurationStore<Flag | ObfuscatedFlag>();
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function setUnobfuscatedFlagEntries(
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entries: Record<string, Flag | ObfuscatedFlag>,
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): Promise<boolean> {
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storage.setFormat(FormatEnum.SERVER);
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return storage.setEntries(entries);
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}
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const flagKey = 'mock-flag';
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const variationA = {
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key: 'a',
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value: 'variation-a',
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};
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const variationB = {
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key: 'b',
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value: 'variation-b',
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};
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const mockFlag: Flag = {
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key: flagKey,
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enabled: true,
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variationType: VariationType.STRING,
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variations: { a: variationA, b: variationB },
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allocations: [
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{
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key: 'allocation-a',
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rules: [],
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splits: [
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{
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shards: [],
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variationKey: 'a',
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},
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],
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doLog: true,
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},
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],
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totalShards: 10000,
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};
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let client: EppoClient;
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let subjectKey: string;
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beforeEach(async () => {
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await setUnobfuscatedFlagEntries({ [flagKey]: mockFlag });
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subjectKey = 'subject-10';
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client = new EppoClient({ flagConfigurationStore: storage });
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});
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describe('parseOverrides', () => {
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it('should parse a valid payload', async () => {
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jest.spyOn(overrideValidatorModule, 'sendValidationRequest').mockResolvedValue(undefined);
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const result = await client.parseOverrides(
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JSON.stringify({
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browserExtensionKey: 'my-key',
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overrides: { [flagKey]: variationB },
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}),
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);
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expect(result).toEqual({ [flagKey]: variationB });
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});
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it('should throw an error if the key is missing', async () => {
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jest.spyOn(overrideValidatorModule, 'sendValidationRequest').mockResolvedValue(undefined);
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expect(() =>
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client.parseOverrides(
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JSON.stringify({
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overrides: { [flagKey]: variationB },
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}),
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),
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).rejects.toThrow();
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});
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it('should throw an error if the key is not a string', async () => {
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jest.spyOn(overrideValidatorModule, 'sendValidationRequest').mockResolvedValue(undefined);
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expect(() =>
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client.parseOverrides(
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JSON.stringify({
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browserExtensionKey: 123,
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overrides: { [flagKey]: variationB },
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}),
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),
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).rejects.toThrow();
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});
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it('should throw an error if the overrides are not parseable', async () => {
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jest.spyOn(overrideValidatorModule, 'sendValidationRequest').mockResolvedValue(undefined);
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expect(() =>
97+
client.parseOverrides(`{
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browserExtensionKey: 'my-key',
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overrides: { [flagKey]: ,
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}`),
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).rejects.toThrow();
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});
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it('should throw an error if overrides is not an object', async () => {
105+
jest.spyOn(overrideValidatorModule, 'sendValidationRequest').mockResolvedValue(undefined);
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expect(() =>
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client.parseOverrides(
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JSON.stringify({
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browserExtensionKey: 'my-key',
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overrides: false,
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}),
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),
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).rejects.toThrow();
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});
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it('should throw an error if an invalid key is supplied', async () => {
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jest.spyOn(overrideValidatorModule, 'sendValidationRequest').mockImplementation(async () => {
118+
throw new Error(`Unable to authorize key`);
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});
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expect(() =>
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client.parseOverrides(
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JSON.stringify({
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browserExtensionKey: 'my-key',
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overrides: { [flagKey]: variationB },
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}),
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),
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).rejects.toThrow();
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});
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});
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describe('withOverrides', () => {
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it('should create a new instance of EppoClient with specified overrides without affecting the original instance', () => {
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const clientWithOverrides = client.withOverrides({ [flagKey]: variationB });
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expect(client.getStringAssignment(flagKey, subjectKey, {}, 'default')).toBe('variation-a');
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expect(clientWithOverrides.getStringAssignment(flagKey, subjectKey, {}, 'default')).toBe(
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'variation-b',
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);
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});
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});
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});

‎src/client/eppo-client.ts‎

Lines changed: 33 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -16,6 +16,7 @@ import { NonExpiringInMemoryAssignmentCache } from '../cache/non-expiring-in-mem
1616
import { TLRUInMemoryAssignmentCache } from '../cache/tlru-in-memory-assignment-cache';
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import ConfigurationRequestor from '../configuration-requestor';
1818
import { IConfigurationStore, ISyncStore } from '../configuration-store/configuration-store';
19+
import { MemoryOnlyConfigurationStore } from '../configuration-store/memory.store';
1920
import {
2021
ConfigurationWireV1,
2122
IConfigurationWire,
@@ -53,6 +54,7 @@ import {
5354
VariationType,
5455
} from '../interfaces';
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import { getMD5Hash } from '../obfuscation';
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import { OverridePayload, OverrideValidator } from '../override-validator';
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import initPoller, { IPoller } from '../poller';
5759
import {
5860
Attributes,
@@ -63,6 +65,7 @@ import {
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FlagKey,
6466
ValueType,
6567
} from '../types';
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import { shallowClone } from '../util';
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import { validateNotBlank } from '../validation';
6770
import { LIB_VERSION } from '../version';
6871

@@ -134,6 +137,7 @@ export default class EppoClient {
134137
private requestPoller?: IPoller;
135138
private readonly evaluator = new Evaluator();
136139
private configurationRequestor?: ConfigurationRequestor;
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private readonly overrideValidator = new OverrideValidator();
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138142
constructor({
139143
eventDispatcher = new NoOpEventDispatcher(),
@@ -199,6 +203,35 @@ export default class EppoClient {
199203
return this.configObfuscatedCache;
200204
}
201205

206+
/**
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* Validates and parses x-eppo-overrides header sent by Eppo's Chrome extension
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*/
209+
async parseOverrides(
210+
overridePayload: string | undefined,
211+
): Promise<Record<FlagKey, Variation> | undefined> {
212+
if (!overridePayload) {
213+
return undefined;
214+
}
215+
const payload: OverridePayload = this.overrideValidator.parseOverridePayload(overridePayload);
216+
await this.overrideValidator.validateKey(payload.browserExtensionKey);
217+
return payload.overrides;
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}
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/**
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* Creates an EppoClient instance that has the specified overrides applied
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* to it without affecting the original EppoClient singleton. Useful for
223+
* applying overrides in a shared Node instance, such as a web server.
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*/
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withOverrides(overrides: Record<FlagKey, Variation>): EppoClient {
226+
if (overrides && Object.keys(overrides).length) {
227+
const copy = shallowClone(this);
228+
copy.overrideStore = new MemoryOnlyConfigurationStore<Variation>();
229+
copy.overrideStore.setEntries(overrides);
230+
return copy;
231+
}
232+
return this;
233+
}
234+
202235
setConfigurationRequestParameters(
203236
configurationRequestParameters: FlagConfigurationRequestParameters,
204237
) {

‎src/override-validator.ts‎

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import { TLRUCache } from './cache/tlru-cache';
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import { Variation } from './interfaces';
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import { FlagKey } from './types';
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const FIVE_MINUTES_IN_MS = 5 * 3600 * 1000;
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const KEY_VALIDATION_URL = 'https://eppo.cloud/api/flag-overrides/v1/validate-key';
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export interface OverridePayload {
9+
browserExtensionKey: string;
10+
overrides: Record<FlagKey, Variation>;
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}
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export const sendValidationRequest = async (browserExtensionKey: string) => {
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const response = await fetch(KEY_VALIDATION_URL, {
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method: 'POST',
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body: JSON.stringify({
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key: browserExtensionKey,
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}),
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headers: {
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'Content-Type': 'application/json',
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},
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});
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if (response.status !== 200) {
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throw new Error(`Unable to authorize key: ${response.statusText}`);
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}
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};
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export class OverrideValidator {
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private validKeyCache = new TLRUCache(100, FIVE_MINUTES_IN_MS);
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parseOverridePayload(overridePayload: string): OverridePayload {
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const errorMsg = (msg: string) => `Unable to parse overridePayload: ${msg}`;
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try {
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const parsed = JSON.parse(overridePayload);
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this.validateParsedOverridePayload(parsed);
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return parsed as OverridePayload;
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} catch (err: unknown) {
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const message: string = (err as any)?.message ?? 'unknown error';
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throw new Error(errorMsg(message));
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}
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}
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private validateParsedOverridePayload(parsed: any) {
44+
if (typeof parsed !== 'object') {
45+
throw new Error(`Expected object, but received ${typeof parsed}`);
46+
}
47+
const keys = Object.keys(parsed);
48+
if (!keys.includes('browserExtensionKey')) {
49+
throw new Error(`Missing required field: 'browserExtensionKey'`);
50+
}
51+
if (!keys.includes('overrides')) {
52+
throw new Error(`Missing required field: 'overrides'`);
53+
}
54+
if (typeof parsed['browserExtensionKey'] !== 'string') {
55+
throw new Error(
56+
`Invalid type for 'browserExtensionKey'. Expected string, but received ${typeof parsed['browserExtensionKey']}`,
57+
);
58+
}
59+
if (typeof parsed['overrides'] !== 'object') {
60+
throw new Error(
61+
`Invalid type for 'overrides'. Expected object, but received ${typeof parsed['overrides']}.`,
62+
);
63+
}
64+
}
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66+
async validateKey(browserExtensionKey: string) {
67+
if (this.validKeyCache.get(browserExtensionKey) === 'true') {
68+
return true;
69+
}
70+
await sendValidationRequest(browserExtensionKey);
71+
this.validKeyCache.set(browserExtensionKey, 'true');
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}
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}

‎src/util.ts‎

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Original file line numberDiff line numberDiff line change
@@ -2,3 +2,7 @@
22
export async function waitForMs(ms: number) {
33
await new Promise((resolve) => setTimeout(resolve, ms));
44
}
5+
6+
export function shallowClone<T>(original: T): T {
7+
return Object.assign(Object.create(Object.getPrototypeOf(original)), original);
8+
}

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