RFC: add support for Service Request and Response type

[bwgjoseph]

Hi,

This PR would likely be a breaking change, so I am actually hoping to make it into dove instead of crow. I have most of the description written in this-repo that I created to showcase, but I will put some of key info here.

---

For the longest time, I have been wanting to have some ways to allow me to define a different set of request/response interface since it can be different (and it is for most cases that I have encounter). There have been some chats about this in slack as well, and I thought I can start making some changes and see if this can be accepted, and I'm sure can be further improved as well.

https://feathersjs.slack.com/archives/C52QSFK0A/p1594138177347400
https://feathersjs.slack.com/archives/C3M4SBWT0/p1600014049010600

Objective

Allow to declare a different set of interface for Request and Response which can also greatly improve dev-experience.

Example

// post.interface.ts
interface Base {
    readonly _id: string;
    createdAt: Date;
    updatedAt: Date;
}

/ Client facing interface
interface PostRequest {
    title: string;
    body: string;
    comments?: string[];
}

// Base fields generated at server side
interface ServerPostRequest extends PostRequest, Omit<Base, '_id'> {}

interface PostResponse extends Omit<PostRequest, 'comments'>, Base {}

// post.service.ts
declare module '../../declarations' {
  interface ServiceTypes {
    'post': Service<PostRequest, PostResponse> & Post;
  }
}

// if you choose not to have different request/response interface, you can still do this
// the response type will still be PostInterface
declare module '../../declarations' {
  interface ServiceTypes {
    'post': Service<PostInterface> & Post;
  }
}

Result

---

For more details, and example, please refer to feathers-request-response-demo

If there is a better way to do this, I would like to have your feedback. This should not affect any actual functionality of the application, it all just providing better typing's for typescript developers.

Thanks!

[bwgjoseph]

@daffl would this be considered for v5 seeing that the first pre-release is out. Thanks

[daffl]

This is a good suggestion. Since there already was a major refactoring in the works (PR via #2255) I included it there so we'll close this PR. Thank you for putting this up!

[bwgjoseph]

Thanks @daffl!

Will try it out after you have release a alpha/beta for it. The only thing that I noticed (now, with a quick look) is that you had the request at the 2nd arg, and response at the first. ServiceInterface<Response, Request = Response>. I guess it make sense if majority of the usage is without a different request, then there is no need to define the 2nd arg. 👍