Use RpcTarget class to handle Durable Object metadata

When working with Durable Objects, you will need to access the name that was used to create the Durable Object via idFromName(). This name is typically a meaningful identifier that represents what the Durable Object is responsible for (like a user ID, room name, or resource identifier).

However, there is a limitation in the current implementation: even though you can create a Durable Object with .idFromName(name), you cannot directly access this name inside the Durable Object via this.ctx.id.name.

The RpcTarget pattern shown below offers a solution by creating a communication layer that automatically carries the name with each method call. This keeps your API clean while ensuring the Durable Object has access to its own name.

Based on your needs, you can either store the metadata temporarily in the RpcTarget class, or use Durable Object storage to persist the metadata for the lifetime of the object.

This example does not persist the Durable Object metadata. It demonstrates how to:

Create an RpcTarget class
Set the Durable Object metadata (identifier in this example) in the RpcTarget class
Pass the metadata to a Durable Object method
Clean up the RpcTarget class after use

import { DurableObject, RpcTarget } from "cloudflare:workers";

//  * Create an RpcDO class that extends RpcTarget
//  * Use this class to set the Durable Object metadata
//  * Pass the metadata in the Durable Object methods
//  * @param mainDo - The main Durable Object class
//  * @param doIdentifier - The identifier of the Durable Object

export class RpcDO extends RpcTarget {
	constructor(
		private mainDo: MyDurableObject,
		private doIdentifier: string,
	) {
		super();
	}

	//  * Pass the user's name to the Durable Object method
	//  * @param userName - The user's name to pass to the Durable Object method

	async computeMessage(userName: string): Promise<string> {
		// Call the Durable Object method and pass the user's name and the Durable Object identifier
		return this.mainDo.computeMessage(userName, this.doIdentifier);
	}

	//  * Call the Durable Object method without using the Durable Object identifier
	//  * @param userName - The user's name to pass to the Durable Object method

	async simpleGreeting(userName: string) {
		return this.mainDo.simpleGreeting(userName);
	}
}

//  * Create a Durable Object class
//  * You can use the RpcDO class to set the Durable Object metadata

export class MyDurableObject extends DurableObject<Env> {
	constructor(ctx: DurableObjectState, env: Env) {
		super(ctx, env);
	}

	//  * Initialize the RpcDO class
	//  * You can set the Durable Object metadata here
	//  * It returns an instance of the RpcDO class
	//  * @param doIdentifier - The identifier of the Durable Object