WeezyEzo•6mo ago

Ability to mutate/extend `input` from middlewares

Hi I have a global middleware that should run for every route. This middleware simply coerces '' (empty string) to undefined for the whole input object. Here is my setup:

export const defaultProcedure = t.procedure.use(async ({ next, getRawInput }) => {
  const input = await getRawInput()
  const newInput = coerceEmptyStringsToUndefined(input)
  return next({
    input: newInput,
  })
})

export const defaultProcedure = t.procedure.use(async ({ next, getRawInput }) => {
  const input = await getRawInput()
  const newInput = coerceEmptyStringsToUndefined(input)
  return next({
    input: newInput,
  })
})

the function coerceEmptyStringsToUndefined is guarnteed to work as expected. Here is the implementation btw:

import mapValues from 'lodash.mapvalues'

// Note: not working with arrays
export function coerceEmptyStringsToUndefined(o: unknown): any {
  if (typeof o === 'object' && o !== null) {
    if (Array.isArray(o)) {
      // return something here if you want it to work with arrays
    } else {
      return mapValues(o, coerceEmptyStringsToUndefined)
    }
  }
  return o === '' ? undefined : o
}

import mapValues from 'lodash.mapvalues'

// Note: not working with arrays
export function coerceEmptyStringsToUndefined(o: unknown): any {
  if (typeof o === 'object' && o !== null) {
    if (Array.isArray(o)) {
      // return something here if you want it to work with arrays
    } else {
      return mapValues(o, coerceEmptyStringsToUndefined)
    }
  }
  return o === '' ? undefined : o
}

The problem: this code throws a validation error

const testRouter = createTRPCRouter({
  test: defaultProcedure
    .input(
      z.object({
        a: z.number().optional(),
      })
    )
    .query(async ({ input }) => {
      console.log(input)
    }),
})

const testRouter = createTRPCRouter({
  test: defaultProcedure
    .input(
      z.object({
        a: z.number().optional(),
      })
    )
    .query(async ({ input }) => {
      console.log(input)
    }),
})

The error is from zod which is: {received: '""', expected: 'number'}.

11 Replies

Nick•6mo ago

This sounds like a hack Why not just fix the data being sent to the API? And what’s wrong with defining your inputs in each procedure? Much easier to maintain if you don’t have global behaviour Zod has coerce by the way, might also be a fix for your actual types

WeezyEzo•6mo ago

This would be an overhead. In my application, empty strings are considered as undefined. Using something like sendDataToTrpcRoute({ a: a === '' ? undefined: a}) for every piece of data is not a good solution for me

Nick•6mo ago

Well Zod has tools to let you manipulate stuff. Coerce and Preprocess are likely what you want. Maybe refine/suoerRefine/transform too You could define some custom string type that you use instead of z.string()

WeezyEzo•6mo ago

I still think that mutating input is the responsibility of trpc. A lot of web frameworks allow you to mutate the input passed. Trpc itself lets you extend the context. Implementing it for input would be convenient as well. This idea will introduce the same overhead, that is, I have to change every schema to transform to coerce empty strings to undefined.

Nick•6mo ago

Well I think you can already do this, it’s just a bad idea

WeezyEzo•6mo ago

I have to mention that I like TRPC and since I have used I didn't use any other approach for backend routes. Just to be clear.

Nick•6mo ago

Pretty sure you can chain input calls

WeezyEzo•6mo ago

It would be nice if you can provide a sample code that works for my case

Nick•6mo ago

Have a look at how our input parser works internally, it’s just a middleware to begin with .input() isn’t real

WeezyEzo•6mo ago

So here is what i found. tldr: none of the functions are exported for external use. There is a function called createNewBuilder It does what i want, but it is not exported for external use. There are some other functions that could help (for example, createResolver to create a custom reoslver with my middlewares applied), but I was not able to import them.

GitHub

trpc/packages/server/src/unstable-core-do-not-import/procedureBuild...

🧙‍♀️ Move Fast and Break Nothing. End-to-end typesafe APIs made easy. - trpc/trpc

WeezyEzo•6mo ago

Currently, there is no way to implement this functionality outside @trpc/server package. I do not have time to work on this. But if you have a working approach I would be more than happy. For now, i will fix the data before sending it to trpc Is there any hope that this will be a feature request or something? I would appreciate this