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Implemented a simple SQL based TTL cache (#140)
- Implemented a simple SQL based TTL cache. - Introduced `HttpApi.create()` to support async object creation pattern. - Fixed bug in PostgreSQL dialect instantiation. - 100% new code coverage.
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,123 @@ | ||
| import type { Dialect } from '@tbd54566975/dwn-sql-store'; | ||
| import { Kysely } from 'kysely'; | ||
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| /** | ||
| * The SqlTtlCache is responsible for storing and retrieving cache data with TTL (Time-to-Live). | ||
| */ | ||
| export class SqlTtlCache { | ||
| private static readonly cacheTableName = 'cacheEntries'; | ||
| private static readonly cleanupIntervalInSeconds = 60; | ||
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| private db: Kysely<CacheDatabase>; | ||
| private cleanupTimer: NodeJS.Timeout; | ||
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| private constructor(sqlDialect: Dialect) { | ||
| this.db = new Kysely<CacheDatabase>({ dialect: sqlDialect }); | ||
| } | ||
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| /** | ||
| * Creates a new SqlTtlCache instance. | ||
| */ | ||
| public static async create(sqlDialect: Dialect): Promise<SqlTtlCache> { | ||
| const cacheManager = new SqlTtlCache(sqlDialect); | ||
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| await cacheManager.initialize(); | ||
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| return cacheManager; | ||
| } | ||
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| private async initialize(): Promise<void> { | ||
| await this.db.schema | ||
| .createTable(SqlTtlCache.cacheTableName) | ||
| .ifNotExists() | ||
| // 512 chars to accommodate potentially large `state` in Web5 Connect flow | ||
| .addColumn('key', 'varchar(512)', (column) => column.primaryKey()) | ||
| .addColumn('value', 'text', (column) => column.notNull()) | ||
| .addColumn('expiry', 'integer', (column) => column.notNull()) | ||
| .execute(); | ||
|
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| // Start the cleanup timer | ||
| this.startCleanupTimer(); | ||
| } | ||
|
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| /** | ||
| * Starts a timer to periodically clean up expired cache entries. | ||
| */ | ||
| private startCleanupTimer(): void { | ||
| this.cleanupTimer = setInterval(async () => { | ||
| await this.cleanUpExpiredEntries(); | ||
| }, SqlTtlCache.cleanupIntervalInSeconds * 1000); | ||
| } | ||
|
|
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| /** | ||
| * Inserts a cache entry. | ||
| * @param ttl The time-to-live in seconds. | ||
| */ | ||
| public async insert(key: string, value: object, ttl: number): Promise<void> { | ||
| const expiry = Date.now() + (ttl * 1000); | ||
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| const objectString = JSON.stringify(value); | ||
|
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| await this.db | ||
| .insertInto(SqlTtlCache.cacheTableName) | ||
| .values({ key, value: objectString, expiry }) | ||
| .execute(); | ||
| } | ||
|
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||
| /** | ||
| * Retrieves a cache entry if it is not expired and cleans up expired entries. | ||
| */ | ||
| public async get(key: string): Promise<object | undefined> { | ||
| const result = await this.db | ||
| .selectFrom(SqlTtlCache.cacheTableName) | ||
| .select('key') | ||
| .select('value') | ||
| .select('expiry') | ||
| .where('key', '=', key) | ||
| .execute(); | ||
|
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| if (result.length === 0) { | ||
| return undefined; | ||
| } | ||
|
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| const entry = result[0]; | ||
|
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| // if the entry is expired, don't return it and delete it | ||
| if (Date.now() >= entry.expiry) { | ||
| this.delete(key); // no need to await | ||
| return undefined; | ||
| } | ||
|
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| return JSON.parse(entry.value); | ||
| } | ||
|
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| /** | ||
| * Deletes a cache entry. | ||
| */ | ||
| public async delete(key: string): Promise<void> { | ||
| await this.db | ||
| .deleteFrom(SqlTtlCache.cacheTableName) | ||
| .where('key', '=', key) | ||
| .execute(); | ||
| } | ||
|
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| /** | ||
| * Periodically clean up expired cache entries. | ||
| */ | ||
| public async cleanUpExpiredEntries(): Promise<void> { | ||
| await this.db | ||
| .deleteFrom(SqlTtlCache.cacheTableName) | ||
| .where('expiry', '<', Date.now()) | ||
| .execute(); | ||
| } | ||
| } | ||
|
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| interface CacheEntry { | ||
| key: string; | ||
| value: string; | ||
| expiry: number; | ||
| } | ||
|
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| interface CacheDatabase { | ||
| cacheEntries: CacheEntry; | ||
| } |
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