--- name: butterbase-ai/durable-objects source: https://app.decimal.ai/s/butterbase-ai-durable-objects@1/SKILL.md source_sha256: b64cea2d1e0f --- # Butterbase Durable Objects Durable Objects (DOs) are **stateful per-key actors** running on Cloudflare Workers. Each instance has its own in-memory state and a built-in transactional KV store. Use one when state must survive across requests for a single room/user/agent. For stateless work, use a serverless function instead (`butterbase-skills:function-dev`). One tool: **`manage_durable_objects`**. --- ## 1. The mental model ``` Class: ChatRoom (deployed once) │ ├── instance "lobby" ─► in-memory state + state.storage + WebSockets ├── instance "general" ─► separate state, separate sockets └── instance "user-123" ─► separate again Each URL https://.butterbase.dev/_do/chat-room/ gets routed to the instance with that id. State is isolated per id. ``` A class is shared code; an **instance** is a unique key (`/lobby`, `/general`, `/user-123`). Different ids = different state. There is no shared cross-instance state. --- ## 2. Constraints (read these first) - **One TypeScript file per class.** No npm imports. Only `import { ... } from 'cloudflare:workers'` is allowed. - **Exactly one exported class.** `export class Foo { ... }` — no extra exports, no helpers re-exported. - **PascalCase class name** in source; **kebab-case** for the URL name (e.g. `ChatRoom` ↔ `chat-room`). - File size: ≤ 5 MB. Total of all DO classes per app: ≤ 10 MB compressed. - ≤ 5 DO classes per app (v1). - **No service bindings yet.** Functions reach DOs over HTTP, not via env binding. - `state.storage` keys/values capped at 128 KB. Larger blobs → Butterbase Storage. - **Browser WebSockets need `access_mode: "public"`.** Browsers can't set custom headers on WS upgrade, and the `_do/` dispatcher reads auth *only* from `Authorization` — `?token=` and `Sec-WebSocket-Protocol` are silently ignored at the dispatcher (unlike the `/realtime` route, which does accept `?token=`). Set the DO public, then read the token from `?token=` (or `Sec-WebSocket-Protocol`) inside `fetch()` and verify it yourself before accepting the upgrade. Server-to-server callers can still use `authenticated`/`service_key`. --- ## 3. The class skeleton ```typescript export class ChatRoom { constructor(public state: DurableObjectState, public env: Env) {} async fetch(req: Request): Promise { if (req.headers.get("Upgrade") === "websocket") { const pair = new WebSocketPair(); this.state.acceptWebSocket(pair[1]); return new Response(null, { status: 101, webSocket: pair[0] }); } if (req.method === "POST") { // handle plain HTTP } return Response.json({ ok: true }); } // Optional WebSocket lifecycle hooks — called by the runtime async webSocketMessage(ws: WebSocket, msg: string | ArrayBuffer) { if (typeof msg !== "string") return; // guard binary for (const peer of this.state.getWebSockets()) { try { peer.send(msg); } catch {} } } async webSocketClose(ws: WebSocket, code: number, reason: string, wasClean: boolean) {} async webSocketError(ws: WebSocket, err: Error) {} } ``` Key APIs: | API | Purpose | |-----|---------| | `state.storage.get/put/delete/deleteAll/list` | Async transactional KV store | | `state.acceptWebSocket(ws)` | Hold a WS connection; runtime routes messages to `webSocketMessage` | | `state.getWebSockets()` | All active WS connections for this instance | | `new WebSocketPair()` | Returns `[client, server]` — return `client` to browser, accept `server` | | `this.env.KEY` | Read DO env vars (set via `set_env`) | --- ## 4. Deploy ```js manage_durable_objects({ app_id: "app_abc123", action: "deploy", name: "chat-room", // kebab-case URL name code: "", access_mode: "authenticated" // "public" | "authenticated" (default) | "service_key" }) // → { id, name, class_name, status: "READY", access_mode, last_deployed_at } ``` Re-deploying with the same `name` updates the class; old in-memory state is evicted on next request. Storage persists across redeploys (same instance id = same `state.storage`). ### Access modes | Mode | Auth required | |------|---------------| | `public` | None — validate tokens inside `fetch()` if you need any | | `authenticated` (default) | End-user JWT in `Authorization: Bearer ` | | `service_key` | Butterbase service key — backend-to-backend | > The dispatcher only checks header **shape**, not validity. For real auth on production DOs, validate the token inside `fetch()`. --- ## 5. Address an instance ``` https://.butterbase.dev/_do// ``` - `` = kebab-case DO name from deploy - `` = anything you choose (`/lobby`, `/user-123`, `/main`) Both HTTP and WebSocket upgrade work on the same URL. ```js // HTTP fetch("https://app.butterbase.dev/_do/chat-room/lobby", { method: "POST", body: JSON.stringify({ user: "alice", text: "hi" }) }); // WebSocket const ws = new WebSocket("wss://app.butterbase.dev/_do/chat-room/lobby"); ``` Different instance ids → completely separate state. There is no shared global view; if you need one, build it yourself (e.g. a `/registry` instance that other instances report into). --- ## 6. Env vars Env vars are app-wide across all DO classes. Setting one redeploys the DO Worker — existing in-memory state is evicted, active WS connections drop. ```js manage_durable_objects({ app_id, action: "list_env" }) // keys only, never values manage_durable_objects({ app_id, action: "set_env", key: "AI_API_KEY", value: "sk-..." }) manage_durable_objects({ app_id, action: "delete_env", key: "AI_API_KEY" }) ``` - Keys must match `^[A-Z_][A-Z0-9_]*$` (UPPER_SNAKE). - A key can't collide with a DO class binding (e.g. `chat-room` reserves `CHAT_ROOM`). - Read in code as `this.env.KEY_NAME`. --- ## 7. Lifecycle, listing, deletion ```js manage_durable_objects({ app_id, action: "list" }) manage_durable_objects({ app_id, action: "get", name: "chat-room" }) // includes full source + status + error_message manage_durable_objects({ app_id, action: "delete", name: "chat-room" }) // IRREVERSIBLE: purges all instances + storage manage_durable_objects({ app_id, action: "usage", name: "chat-room" }) // do_requests, do_cpu_ms (refreshed every 15 min) ``` Status transitions: `PENDING → BUILDING → READY` or `ERROR` (with `error_message`). --- ## 8. Patterns ### Chat room (broadcast) ```typescript export class ChatRoom { constructor(public state: DurableObjectState, public env: any) {} async fetch(req: Request): Promise { if (req.headers.get("Upgrade") === "websocket") { const pair = new WebSocketPair(); this.state.acceptWebSocket(pair[1]); const history = (await this.state.storage.get("messages")) ?? []; pair[1].send(JSON.stringify({ type: "init", messages: history })); return new Response(null, { status: 101, webSocket: pair[0] }); } return Response.json(await this.state.storage.get("messages") ?? []); } async webSocketMessage(ws: WebSocket, msg: string | ArrayBuffer) { if (typeof msg !== "string") return; const history: any[] = (await this.state.storage.get("messages")) ?? []; const parsed = JSON.parse(msg); history.push(parsed); await this.state.storage.put("messages", history.slice(-200)); for (const peer of this.state.getWebSockets()) { try { peer.send(msg); } catch {} } } } ``` ### Sliding-window rate limiter ```typescript export class RateLimiter { constructor(public state: DurableObjectState, public env: any) {} async fetch(req: Request): Promise { const now = Date.now(); const window = 60_000; const limit = 100; const requests: number[] = (await this.state.storage.get("requests")) ?? []; const recent = requests.filter(t => now - t < window); if (recent.length >= limit) return new Response("rate limit", { status: 429 }); recent.push(now); await this.state.storage.put("requests", recent); return Response.json({ ok: true, remaining: limit - recent.length }); } } ``` Address one instance per actor: `/_do/rate-limiter/` or `/_do/rate-limiter/`. ### Long-running AI agent ```typescript export class Agent { constructor(public state: DurableObjectState, public env: any) {} async fetch(req: Request): Promise { const { prompt } = await req.json(); const r = await fetch(this.env.AI_API_ENDPOINT, { method: "POST", headers: { Authorization: `Bearer ${this.env.AI_API_KEY}` }, body: JSON.stringify({ prompt }) }); const data = await r.json(); await this.state.storage.put("last_response", data); return Response.json(data); } } ``` One DO instance per conversation; storage holds the rolling history. ### Counter / leaderboard Each instance is its own counter. `/_do/leaderboard/main` and `/_do/leaderboard/season-2` have independent state — no coordination needed in v1. --- ## 9. Errors Build-time (rejected on deploy): | Code | Cause | |------|-------| | `NO_EXPORTED_CLASS` | Source doesn't export a class | | `MULTIPLE_EXPORTS` | More than one export, or export of non-class | | `INVALID_IMPORT` | Imported anything other than `cloudflare:workers` | | `CLASS_NAME_PARSE_ERROR` | TS AST couldn't extract the class name | | `NAME_REGEX_VIOLATION` | `name` doesn't match `^[a-z][a-z0-9]*(?:-[a-z0-9]+)*$` | | `QUOTA_DO_LIMIT` | Already 5 classes for this app | | `BUNDLE_SIZE_EXCEEDED` / `SOURCE_SIZE_EXCEEDED` | Over the 10 MB / 5 MB limits | Runtime / async-deploy: - Status `ERROR` after a deploy → check `manage_durable_objects` (`get`) `error_message`. - WebSocket message handler only fires if you called `state.acceptWebSocket(ws)` — easy to forget. - `webSocketMessage` receives `string | ArrayBuffer`. Always guard before `JSON.parse`. --- ## 10. Anti-patterns | Don't | Do | |-------|----| | Try to share state between instances directly | Pick a single "registry" instance and have others fetch into it | | Use a DO for stateless HTTP work | Use a function — DOs cost more and have stricter constraints | | Rely on dispatcher access_mode for real auth | Validate JWTs inside `fetch()` for production | | Use `access_mode: "authenticated"` for browser WebSockets | Use `public` + token-in-query-string + manual validation; browsers can't set headers | | Stuff > 128 KB blobs into `state.storage` | Use Butterbase Storage and store the `object_id` in DO state | | Update env vars in tight loops | Each `set_env` redeploys the Worker — drops connections | | Forget redeploy semantics | Code change or env change evicts all instances; storage survives but in-memory caches don't | --- If a `docs/butterbase/00-state.md` exists in the working directory, prefer invoking via `/butterbase-skills:journey-durable` so the journey orchestrator stays in sync.