latch-store

latch-store is a Node/Bun middleware library that makes any mutating endpoint idempotent with one line of code. It provides:

• Two framework-specific entry points: idempotent.express() and idempotent.hono().
• A pluggable store interface with two built-in adapters: memoryStore() (dev/test) and redisStore() (production).
• Correctness guarantees under concurrent duplicate requests via atomic store operations and polling.
• Body-hash mismatch detection to reject key reuse with different payloads.
• A callback-based event system for observability.
• Graceful degradation when the store is unavailable.

Quick Start

npm install latch-store
# or
bun add latch-store
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Express

import { idempotent, memoryStore } from 'latch-store'

const store = memoryStore()
const app = express()

app.post('/charge', idempotent.express({ store }), async (req, res) => {
  // This handler runs at most once per unique Idempotency-Key
  res.json({ status: 'charged' })
})
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Hono

import { idempotent, memoryStore } from 'latch-store'

const store = memoryStore()
const app = new Hono()

app.post('/charge', idempotent.hono({ store }), async (c) => {
  return c.json({ status: 'charged' })
})
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API

See the generated documentation for the full API reference.

Store Adapters

Custom Adapter

Implement the Store interface (4 methods):

import type { Store } from 'latch-store'

class MyStore implements Store {
  async setIfAbsent(key, value, ttlMs) { /* ... */ }
  async set(key, value, ttlMs) { /* ... */ }
  async get(key) { /* ... */ }
  async del(key) { /* ... */ }
}
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Development

bun install
bun test          # run tests
bun run typecheck # type-check all source files
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License

MIT