Required metadata fields in middleware

[rhinodavid]

In the docs the metadata example uses a type with an optional key:

interface ORPCMetadata {
  cache?: boolean
}

I'm trying to use this with a contract implementation (I don't know if that detail matters) but when I make the key required I get a type error. Not sure if making this required just isn't possible or if I'm doing something wrong.

import { oc } from "@orpc/contract";
import { implement, os as orpcOs } from "@orpc/server";
import z from "zod";

export const contract = {
  echo: oc
    .meta({ cache: true })
    .input(z.object({ msg: z.string() }))
};

const cacheMiddleware = orpcOs.$meta<{ cache: boolean }>({ cache: false })
  .middleware(async (opts) => {
    const meta = opts.procedure["~orpc"].meta;

    if (meta.cache) {
      // Check cache logic here
      console.log("Caching enabled for this endpoint");
    }

    return opts.next();
  });

const os = implement(contract)
  .use(cacheMiddleware); // ⚠️  Type 'Record<never, never>' is not assignable to type '{ cache: boolean; } & Record<never, never>'

const _router = os.router({
  echo: os.echo.handler(({ input }) => ({ echo: input.msg })),
});

[unnoq]

Because you define .meta in completely wrong way:

You must use .$meta with default meta first, and .meta later for override or expend. Because we only infer meta type of .$meta that why you see your meta typed as Record<never, never>

export const contract = {
  echo: oc
    .$meta({ cache: true })
    .input(z.object({ msg: z.string() }))
};

[rhinodavid]

Thanks so much for the quick response.

I'm still confused about the middleware portion. Is there a way to define "dependent middleware" like we define a dependent context?

It seems like I have to overwrite it when I set up the middleware (if the meta key is required).

const cacheMiddleware = orpcOs.$meta<{ cache: boolean }>({ /* what goes here ??*/})
  .middleware(async (opts) => {
    const meta = opts.procedure["~orpc"].meta;

    if (meta.cache) {
      // Check cache logic here
      console.log("Caching enabled for this endpoint");
    }

    return opts.next();
  });

[unnoq]

.$meta like .$context help you define "dependant metadata", except you must define initial meta (middleware will ignore this) - so I recommend you make metadata optional.

[rhinodavid]

I think part of my goal with the $meta type would be to statically verify all procedures going into the router have the correct meta defined.

So it sounds like my choices would be to do this, and here I think you're saying the {cache: false} initial value doesn't do anything:

const cacheMiddleware = orpcOs.$meta<{ cache: boolean }>({ cache: false })
  .middleware(async (opts) => {});

or I do this but now i have no type-level guarantee the procedures have $meta defined.

const cacheMiddleware = orpcOs.$meta<{ cache?: boolean }>({ })
 .middleware(async (opts) => {});