Durable Object State

Description

The DurableObjectState interface is accessible as an instance property on the Durable Object class. This interface encapsulates methods that modify the state of a Durable Object, for example which WebSockets are attached to a Durable Object or how the runtime should handle concurrent Durable Object requests.

The DurableObjectState interface is different from the Storage API in that it does not have top-level methods which manipulate persistent application data. These methods are instead encapsulated in the DurableObjectStorage interface and accessed by DurableObjectState::storage.

JavaScript

import { DurableObject } from "cloudflare:workers";

// Durable Object
export class MyDurableObject extends DurableObject {
  // DurableObjectState is accessible via the ctx instance property
  constructor(ctx, env) {
    super(ctx, env);
  }
  ...
}

TypeScript

import { DurableObject } from "cloudflare:workers";

export interface Env {
  MY_DURABLE_OBJECT: DurableObjectNamespace<MyDurableObject>;
}

// Durable Object
export class MyDurableObject extends DurableObject {
  // DurableObjectState is accessible via the ctx instance property
  constructor(ctx: DurableObjectState, env: Env) {
    super(ctx, env);
  }
  ...
}

Methods

waitUntil

waitUntil waits until the promise which is passed as a parameter resolves and can extends an event context up to 30 seconds after the last client disconnects.

waitUntil is not necessary

The event context for a Durable Objects extends at least 60 seconds after the last client disconnects. So waitUntil is not necessary. It remains part of the DurableObjectState interface to remain compatible with Workers Runtime APIs.

Parameters

• A required promise of any type.

Return values

• None.

blockConcurrencyWhile

blockConcurrencyWhile executes an async callback while blocking any other events from being delivered to the Durable Object until the callback completes. This method guarantees ordering and prevents concurrent requests. All events that were not explicitly initiated as part of the callback itself will be blocked. Once the callback completes, all other events will be delivered.

blockConcurrencyWhile is commonly used within the constructor of the Durable Object class to enforce initialization to occur before any requests are delivered. Another use case is executing async operations based on the current state of the Durable Object and using blockConcurrencyWhile to prevent that state from changing while yielding the event loop.

If the callback throws an exception, the object will be terminated and reset. This ensures that the object cannot be left stuck in an uninitialized state if something fails unexpectedly. To avoid this behavior, enclose the body of your callback in a try...catch block to ensure it cannot throw an exception.

To help mitigate deadlocks there is a 30 second timeout applied when executing the callback. If this timeout is exceeded, the Durable Object will be reset. It is best practice to have the callback do as little work as possible to improve overall request throughput to the Durable Object.

// Durable Object
export class MyDurableObject extends DurableObject {
  initialized = false;

  constructor(ctx, env) {
    super(ctx, env);

    // blockConcurrencyWhile will ensure that initialized will always be true
    this.ctx.blockConcurrencyWhile(async () => {
      this.initialized = true;
    });
  }
  ...
}

Parameters

• A required callback which returns a Promise<T>.

Return values

• A Promise<T> returned by the callback.

acceptWebSocket

acceptWebSocket is part of the WebSocket Hibernation API, which allows a Durable Object to be removed from memory to save costs while keeping its WebSockets connected.

acceptWebSocket adds a WebSocket to the set of WebSockets attached to the Durable Object. Once called, any incoming messages will be delivered by calling the Durable Object’s webSocketMessage handler, and webSocketClose will be invoked upon disconnect. After calling acceptWebSocket, the WebSocket is accepted and its send and close methods can be used.

The WebSocket Hibernation API takes the place of the standard WebSockets API. Therefore, ws.accept must not have been called separately and ws.addEventListener method will not receive events as they will instead be delivered to the Durable Object.

The WebSocket Hibernation API permits a maximum of 32,768 WebSocket connections per Durable Object, but the CPU and memory usage of a given workload may further limit the practical number of simultaneous connections.

Parameters

• A required WebSocket with name ws.
• An optional Array<string> of associated tags. Tags can be used to retrieve WebSockets via DurableObjectState::getWebSockets. Each tag is a maximum of 256 characters and there can be at most 10 tags associated with a WebSocket.

Return values

• None.

getWebSockets

getWebSockets is part of the WebSocket Hibernation API, which allows a Durable Object to be removed from memory to save costs while keeping its WebSockets connected.

getWebSockets returns an Array<WebSocket> which is the set of WebSockets attached to the Durable Object. An optional tag argument can be used to filter the list according to tags supplied when calling DurableObjectState::acceptWebSocket.

waitUntil is not necessary

Disconnected WebSockets are not returned by this method, but getWebSockets may still return WebSockets even after ws.close has been called. For example, if the server-side WebSocket sends a close, but does not receive one back (and has not detected a disconnect from the client), then the connection is in the CLOSING ‘readyState’. The client might send more messages, so the WebSocket is technically not disconnected.

Parameters

• An optional tag of type string.

Return values

• An Array<WebSocket>.

setWebSocketAutoResponse

setWebSocketAutoResponse is part of the WebSocket Hibernation API, which allows a Durable Object to be removed from memory to save costs while keeping its WebSockets connected.

setWebSocketAutoResponse sets an automatic response, auto-response, for the request provided for all WebSockets attached to the Durable Object. If a request is received matching the provided request then the auto-response will be returned without waking WebSockets in hibernation and incurring billable duration charges.

setWebSocketAutoResponse is a common alternative to setting up a server for static ping/pong messages because this can be handled without waking hibernating WebSockets.

Parameters

• An optional WebSocketRequestResponsePair(request string, response string) enabling any WebSocket accepted via DurableObjectState::acceptWebSocket to automatically reply to the provided response when it receives the provided request. Both request and response are limited to 2,048 characters each. If the parameter is omitted, any previously set auto-response configuration will be removed. DurableObjectState::getWebSocketAutoResponseTimestamp will still reflect the last timestamp that an auto-response was sent.

Return values

• None.

getWebSocketAutoResponse

getWebSocketAutoResponse returns the WebSocketRequestResponsePair object last set by DurableObjectState::setWebSocketAutoResponse, or null if not auto-response has been set.

inspect WebSocketRequestResponsePair

WebSocketRequestResponsePair can be inspected further by calling getRequest and getResponse methods.

Parameters

• None.

Return values

• A WebSocketRequestResponsePair or null.

getWebSocketAutoResponseTimestamp

getWebSocketAutoResponseTimestamp is part of the WebSocket Hibernation API, which allows a Durable Object to be removed from memory to save costs while keeping its WebSockets connected.

getWebSocketAutoResponseTimestamp gets the most recent Date on which the given WebSocket sent an auto-response, or null if the given WebSocket never sent an auto-response.

Parameters

• A required WebSocket.

Return values

• A Date or null.

setHibernatableWebSocketEventTimeout

setHibernatableWebSocketEventTimeout is part of the WebSocket Hibernation API, which allows a Durable Object to be removed from memory to save costs while keeping its WebSockets connected.

setHibernatableWebSocketEventTimeout sets the maximum amount of time in milliseconds that a WebSocket event can run for.

If no parameter or a parameter of 0 is provided and a timeout has been previously set, then the timeout will be unset. The maximum value of timeout is 604,800,000 ms (7 days).

Parameters

• An optional number.

Return values

• None.

getHibernatableWebSocketEventTimeout

getHibernatableWebSocketEventTimeout is part of the WebSocket Hibernation API, which allows a Durable Object to be removed from memory to save costs while keeping its WebSockets connected.

getHibernatableWebSocketEventTimeout gets the currently set hibernatable WebSocket event timeout if one has been set via DurableObjectState::setHibernatableWebSocketEventTimeout.

Parameters

• None.

Return values

• A number, or null if the timeout has not been set.

getTags

getTags is part of the WebSocket Hibernation API, which allows a Durable Object to be removed from memory to save costs while keeping its WebSockets connected.

getTags returns tags associated with a given WebSocket. This method throws an exception if the WebSocket has not been associated with the Durable Object via DurableObjectState::acceptWebSocket.

Parameters

• A required WebSocket.

Return values

• An Array<string> of tags.

abort

abort is used to forcibly reset a Durable Object. A JavaScript Error with the message passed as a parameter will be logged. This error is not able to be caught within the application code.

// Durable Object
export class MyDurableObject extends DurableObject {
  constructor(ctx: DurableObjectState, env: Env) {
    super(ctx, env);
  }

  async sayHello() {
    // Error: Hello, World! will be logged
    this.ctx.abort("Hello, World!");
  }
}

Not available in local development

abort is not available in local development with the wrangler dev CLI command.

Parameters

• An optional string .

Return values

• None.

Properties

id

id is a readonly property of type DurableObjectId corresponding to the DurableObjectId of the Durable Object.

storage

storage is a readonly property of type DurableObjectStorage encapsulating the Storage API.

Related resources

• Durable Objects: Easy, Fast, Correct – Choose Three ↗.