feat(core): Public custom service methods

[daffl]

This pull request implements tests and client side functionality for custom service methods outlined in and closes #1976.

On the server a custom service method is added like this:

class MyMessageService {
  async create (data, params) {}

  async findOne (data, params) {}

  async resendNotification (data, params) {}
}

app.use('/messages', new MyMessageService(), {
  methods: [ 'create', 'findOne', 'resendNotification' ]
});

It can be used via an HTTP and socket API directly as described in #1976.

On the Feathers client it is used like this:

const feathers = require('@feathersjs/feathers');
const socketio = require('@feathersjs/socketio-client');
const io = require('socket.io-client');

const socket = io('http://api.feathersjs.com');
const app = feathers();

// Set up Socket.io client with the socket
app.configure(socketio(socket));

// Since there is no introspection, custom methods need to be initialized on a service
app.service('messages').methods('customMethod', 'findOne');

const message = await app.service('messages').findOne({ userId: 1 });

TypeScript has a CustomMethod and client interface:

import { feathers, CustomMethod } from '@feathersjs/feathers';
import socketio, { SocketClient } from '@feathersjs/socketio-client';
import io from 'socket.io-client';

type ServiceTypes = {
  messages: SocketClient & CustomMethod<'customMethod'|'findOne'>
}

const socket = io('http://api.feathersjs.com');
const app = feathers<ServiceTypes>();

// Set up Socket.io client with the socket
app.configure(socketio(socket));

// Since there is no introspection, custom methods need to be initialized on a service
app.service('messages').methods('customMethod', 'findOne');

const message = await app.service('messages').findOne({ userId: 1 });

[bertho-zero]

Great ! The only thing that bothers me is that the arguments are not free.

The signature of a method must be [data, params] and I currently have custom methods that expect [id, params] or [id, data, params].

Maybe we can add flexibly if we give an array of argument to body? Which could be empty and to which we would concatenate params from the url.

[daffl]

Oh, I forgot to mention, that I added a middleware that should still allow to register any other kinds of custom methods:

const { createContext } = require('@feathersjs/feathers');
const { serviceMiddleware } = require('@feathersjs/express');

app.use('/myservice', myservice);

// With custom method handler
app.get('/myservice/:__feathersId/my-method', serviceMiddleware(async ({ req, res, options }) => {
  // options.id - __feathersId
  // options.params - Service params
  // options.data - body

  const { params, id } = options;

  return app.service('my-service').myCustomMethod(id, params);
}));

// With different params, using the body and returning the context (when using it with hooks)
app.post('/myservice/:myId/myMethod', serviceMiddleware(async ({ req, res, options }) => {
  const { myId } = req.params;
  const { params, data } = options;
  const context = createContext(service, method);

  return app.service('my-service').myCustomMethod(myId, data, params, context);
}));

It's not as declarative but I'm hoping it to be more flexible and explicit.