TRPC Durable Objects

After playing around with Durable Objects for a while I realized that this conceptually really is an RPC setup, you create a stub and want to interact with a remote object. I had a look at (itty-durable)[https://github.com/kwhitley/itty-durable] which is a cool solution, but it doesn't provide strict typing. A few weeks ago I bumped into the (TRPC)[https://trpc.io/] framework that seems to be the perfect solution for doing typesafe RPC.

This package provides a factory for creating both the strictly typed stub and server for a durable object using a TRPC-router.

Usage

The first step is to create a TRPC router:

import { initTRPC } from '@trpc/server';
import { z } from 'zod';
import { Context } from '../../src/context';

const t = initTRPC.context<Context>().create();

const publicProcedure = t.procedure;

const router = t.router;

export const counterRouter = router({
  up: publicProcedure
    .input(z.string().nullish())
    .query(async ({ input, ctx }) => {
      const count: number | undefined = await ctx.state.storage.get('count');
      const newCount = (count || 0) + 1;

      await ctx.state.storage.put('count', newCount);
      return `Count: ${newCount}`;
    }),
  down: publicProcedure
    .input(z.string().nullish())
    .query(async ({ input, ctx }) => {
      const count: number | undefined = await ctx.state.storage.get('count');
      const newCount = (count || 0) - 1;

      await ctx.state.storage.put('count', newCount);
      return `Count: ${newCount}`;
    }),
});

export type CounterRouter = typeof counterRouter;

The router will be executed within a durable object but the types are exposed so the stub or proxy will be strictly typed.

The router is then passed to the factory method:

import { CounterRouter, counterRouter } from './Counter';
import { createProxy } from 'trpc-durable-object';

export const Counter = createProxy<CounterRouter>(counterRouter);

export default {
  async fetch(
    request: Request,
    env: Env,
    ctx: ExecutionContext,
  ): Promise<Response> {
    const counter = Counter.getInstance(env.COUNTER, 'dummy-id');

    // increase the counter value
    const body = await counter.up.query();

    ...
  },
};