Cast from an async sanitizer

[getlarge]

It seems it is not yet possible to use an async sanitizer function inside cast, do i mistake ?

If not, would it be possible to add support for this ?

Example

Sanitizer

import { Result } from '@restless/sanitizers';

export const asCertificate = async (value, path: string) => {
  const errors = (await validate(value)) as any[];
  
  if (Object.keys(errors).length) {
    const resultError = flatten(
      Object.values(errors).map((error) => {
        return error.map((error) => ({
          path: `${path}${error.path}`,
          expected: error.expected || '',
        }));
      })
    );

    console.log(resultError);
    return Result.error(resultError);
  }
  return Result.ok(value as Certificate);
};

Cast

import {cast} from '@restless/sanitizers';
import {asCertificate} from './somewhere';

const certificate = {};
const value = cast(certificate, asCertificate);

[sz-piotr]

Yes that is correct. Currently there is no notion of an async sanitizer in the library, but a PR would be greatly appreciated. In the meantime all you really need to do is await the result of asCertificate and then unwrap it like so: https://github.com/EthWorks/restless/blob/master/sanitizers/src/cast.ts#L11-L16

[getlarge]

I'm ok to make a PR. Would that be fine to add an asyncCast function that takes a Promise<Sanitizer<T>> as input and returns Promise<T> ?

[sz-piotr]

That could also work, but it does not cover your use case. Your use case is a sanitizer that returns a promise, not a promise with a sanitizer.

[sz-piotr]

Hey @getlarge. I thought about your issue over the weekend and here is what I came up with:

import { Result, SanitizerFailure, CastError } from "@restless/sanitizers";

export type AsyncSanitizer<T> = (value: unknown, path: string) => Promise<Result<SanitizerFailure[], T>>

export async function asyncCast<T>(value: unknown, sanitizer: AsyncSanitizer<T>, message?: string): Promise<T> {
  const result = await sanitizer(value, '')
  if (Result.isOk(result)) {
    return result.ok
  } else {
    throw new CastError(result.error, message)
  }
}

You should be able to drop this code in your project and use it without issues.

If however you wanted a function that takes a Promise<Sanitizer<T> it becomes even easier:

import { Sanitizer, cast } from "@restless/sanitizers";

export async function asyncCast<T>(value: unknown, sanitizer: Promise<Sanitizer<T>>, message?: string): Promise<T> {
  return cast(value, await sanitizer, message)
}

[getlarge]

Hey @sz-piotr, sorry for the delay. You were right, the use case is a sanitizer that returns a promise.

Thanks a lot for your snippet and your feedback. Do you intend to add the AsyncSanitizer type and asyncCast function in restless ?

[getlarge]

In fact my question was more to know if you would prefer a cast function that could take an async | sync sanitizer as 2nd argument or to separate async and sync sanitizer with another function and type.

[sz-piotr]

Here is my line of thinking. If async sanitizers were to be supported by default by the library this should be a bigger change, where all the other higher-order sanitizers like asArray would take either a sync or async sanitizer. In this scenario it makes sense that cast serves a dual purpose being sync or async depending on what it receives.

However since there are currently no async sanitizers in the library code I believe keeping the asyncCast function as separate from both the cast and the library itself makes sense.

[getlarge]

But since a user can create an async sanitizer maybe we can add an example or test to illustrate that case ?

[sz-piotr]

Hmm might be indeed useful once we have the notion of AsyncSanitizers somewhere in the library. If in the future we add this it will definitely be described in the readme.