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ff-serv provides a powerful caching system built on Effect’s Cache with support for:
  • Stale-While-Revalidate (SWR): Serve stale data while refreshing in the background
  • TTL per entry: Override TTL on a per-key basis
  • Pluggable adapters: Memory, Redis (ioredis/bun-redis), or tiered caching
  • Type-safe: Full TypeScript inference

​
Installation

bun add ff-serv effect

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Basic Usage

import { Cache } from 'ff-serv/cache'
import { Effect, Duration } from 'effect'

const program = Effect.gen(function* () {
  const cache = yield* Cache.make({
    ttl: Duration.minutes(5),
    lookup: (userId: number) => 
      Effect.gen(function* () {
        // Fetch from database
        const user = yield* fetchUser(userId)
        return user
      }),
  })

  const user = yield* cache.get(1)
  yield* Effect.log(user)
})

​
Cache Options

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TTL (Time to Live)

How long cached values remain fresh: 
Cache.make({
  ttl: Duration.seconds(30),
  lookup: (key: string) => Effect.succeed(`value-${key}`),
})

​
SWR (Stale-While-Revalidate)

After TTL expires, serve stale data while refreshing in the background: 
Cache.make({
  ttl: Duration.minutes(5),
  swr: Duration.minutes(10), // Total window: 15 minutes
  lookup: (key: string) => fetchFromDatabase(key),
})
Behavior:
  • 0-5 min: Fresh value served
  • 5-15 min: Stale value served, background refresh triggered
  • 15+ min: Wait for fresh value (cache expired)

​
Lookup Function

The function that fetches values on cache miss: 
Cache.make({
  ttl: Duration.minutes(5),
  lookup: (key: string) => 
    Effect.gen(function* () {
      const response = yield* HttpClient.get(`https://api.example.com/data/${key}`)
      return yield* response.json
    }),
})
Return type can be:
  • The value directly: Value
  • A cache entry with custom TTL: Cache.entry(value, { ttl, swr })

​
Cache Instance API

​
get(key)

Retrieve a value from the cache: 
const user = yield* cache.get(123)
On cache miss, calls lookup(key) and stores the result.

​
invalidate(key)

Remove a single key: 
yield* cache.invalidate(123)

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invalidateAll

Clear all cached entries: 
yield* cache.invalidateAll

​
Per-Entry TTL

Override TTL and SWR for specific entries: 
import { Cache } from 'ff-serv/cache'
import { Duration } from 'effect'

const cache = yield* Cache.make({
  ttl: Duration.minutes(5),
  lookup: (type: string) => {
    if (type === 'config') {
      // Config cached for 1 hour
      return Effect.succeed(
        Cache.entry({ setting: 'value' }, {
          ttl: Duration.hours(1),
        })
      )
    }
    // Default TTL (5 minutes)
    return Effect.succeed({ data: 'default' })
  },
})

​
SWR Example

import { Cache } from 'ff-serv/cache'
import { Effect, Duration, Ref, TestClock } from 'effect'

const program = Effect.gen(function* () {
  const callCount = yield* Ref.make(0)

  const cache = yield* Cache.make({
    ttl: Duration.minutes(5),
    swr: Duration.minutes(10),
    lookup: (id: number) => 
      Effect.gen(function* () {
        const count = yield* Ref.updateAndGet(callCount, n => n + 1)
        return `user-${id}-v${count}`
      }),
  })

  // First call: cache miss
  const v1 = yield* cache.get(1)
  yield* Effect.log(v1) // "user-1-v1"

  // Simulate 7 minutes passing (past TTL, within SWR)
  yield* TestClock.adjust(Duration.minutes(7))

  // Second call: returns stale value immediately
  const v2 = yield* cache.get(1)
  yield* Effect.log(v2) // "user-1-v1" (stale)

  // Background refresh completes
  yield* Effect.yieldNow()

  // Third call: returns fresh value
  const v3 = yield* cache.get(1)
  yield* Effect.log(v3) // "user-1-v2" (refreshed)
})

​
Cache Adapters

By default, Cache.make() uses in-memory storage. Add persistence with adapters:

​
Memory Adapter (Default)

import { Cache, CacheAdapter } from 'ff-serv/cache'

const cache = yield* Cache.make({
  ttl: Duration.minutes(5),
  lookup: (key: string) => Effect.succeed(key),
  adapter: CacheAdapter.memory({ capacity: 1000 }),
})

​
Redis Adapter

See Cache with ioredis or Cache with bun-redis. 
import { CacheAdapter } from 'ff-serv/cache'
import { ioredis } from 'ff-serv/cache/ioredis'
import Redis from 'ioredis'

const redis = new Redis()
const client = ioredis(redis)

const cache = yield* Cache.make({
  ttl: Duration.minutes(5),
  lookup: (key: string) => fetchData(key),
  adapter: CacheAdapter.redis({
    client,
    keyPrefix: 'myapp',
  }),
})

​
Tiered Adapter

Combine L1 (memory) and L2 (Redis) for optimal performance: 
const l1 = CacheAdapter.memory({ capacity: 100 })
const l2 = CacheAdapter.redis({ client, keyPrefix: 'app' })

const cache = yield* Cache.make({
  ttl: Duration.minutes(5),
  lookup: (key: string) => fetchData(key),
  adapter: CacheAdapter.tiered(l1, l2),
})
How it works:
  1. Check L1 (memory) first
  2. If miss, check L2 (Redis)
  3. On write, update both L1 and L2

​
Error Propagation

Lookup errors are propagated to the caller: 
const cache = yield* Cache.make({
  ttl: Duration.minutes(5),
  lookup: (key: string) => Effect.fail('Database error'),
})

const result = yield* cache.get('key').pipe(Effect.either)

if (result._tag === 'Left') {
  yield* Effect.log('Cache lookup failed:', result.left)
}

​
Complete Example

import { Cache, CacheAdapter } from 'ff-serv/cache'
import { Effect, Duration, Context } from 'effect'
import { HttpClient } from '@effect/platform'

class Database extends Context.Tag('Database')<
  Database,
  { query: (sql: string) => Effect.Effect<unknown[]> }
>() {}

const program = Effect.gen(function* () {
  const db = yield* Database

  const userCache = yield* Cache.make({
    ttl: Duration.minutes(5),
    swr: Duration.minutes(5),
    lookup: (userId: number) =>
      Effect.gen(function* () {
        yield* Effect.log(`Fetching user ${userId} from database`)
        const rows = yield* db.query(`SELECT * FROM users WHERE id = ${userId}`)
        return rows[0]
      }),
    adapter: CacheAdapter.memory({ capacity: 1000 }),
  })

  // First call: cache miss, fetches from DB
  const user1 = yield* userCache.get(1)
  yield* Effect.log('First call:', user1)

  // Second call: cache hit, no DB query
  const user2 = yield* userCache.get(1)
  yield* Effect.log('Second call:', user2)

  // Invalidate
  yield* userCache.invalidate(1)

  // Third call: cache miss again
  const user3 = yield* userCache.get(1)
  yield* Effect.log('Third call:', user3)
})

Effect.runPromise(
  program.pipe(
    Effect.provideService(Database, {
      query: (sql) => Effect.succeed([{ id: 1, name: 'Alice' }]),
    })
  )
)

​
Type Signature

namespace Cache {
  function make<Key, Value, Error = never, R = never>(opts: {
    ttl: Duration.DurationInput
    swr?: Duration.DurationInput
    lookup: (key: Key) => Effect.Effect<LookupResult<Value>, Error, R>
    adapter?: CacheAdapter<Key, Value>
  }): Effect.Effect<CacheInstance<Key, Value, Error>, never, R>

  type LookupResult<Value> = Value | Entry<Value>

  function entry<Value>(
    value: Value,
    opts: { ttl: Duration.DurationInput; swr?: Duration.DurationInput }
  ): Entry<Value>
}

type CacheInstance<Key, Value, Error> = {
  readonly get: (key: Key) => Effect.Effect<Value, Error>
  readonly invalidate: (key: Key) => Effect.Effect<void>
  readonly invalidateAll: Effect.Effect<void>
}

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