Open hook workflow to custom methods

[bertho-zero]

This PR allows you to add converters to your custom methods, which allows to create the hook corresponding to your arguments and finally to fully use the hook workflow.

I would have liked to use a Symbol but feathersjs/feathers#863.

Example:

const app = feathers().use('/dummy', {
  methods: {
    custom: ['id', 'data', 'params']
  },
  get() {},
  // ...
  custom(id, data, params) {
    return Promise.resolve([id, data, params]);
  }
});

app.service('dummy').hooks({
  before: {
    all: [/**/],
    custom: [/**/]
  },
  after: {
    all: [/**/],
    custom: [/**/]
  }
});

app.service('dummy').custom(28, { bar: 'foo' }, { provider: 'rest' });

[daffl]

This is great, thank you! I was actually thinking about doing the same thing for #853. I'm not sure if the converters are needed. I was going to put the arguments array for unknown methods into hook.arguments.

[bertho-zero]

I chose the simplest solution, the one used internally but it's true that converters can easily be translated from ['id', 'data', 'params'].

I do not know where exactly you would like to declare hook.arguments?

[bertho-zero]

Do you think of something like this?

const app = feathers().use('/dummy', {
  methods: {
    custom: ['id', 'data', 'params']
  },
  get() {},
  // ...
  custom(id, data, params) {
    return Promise.resolve([id, data, params]);
  }
});

app.service('dummy').hooks({
  before: {
    all: [/**/],
    custom: [/**/]
  },
  after: {
    all: [/**/],
    custom: [/**/]
  }
});

return app.service('dummy').custom(28, { bar: 'foo' }, { provider: 'rest' });

or

const app = feathers().use('/dummy', {
  methods: ['custom'],
  get() {},
  // ...
  custom(id, data, params) {
    return Promise.resolve([id, data, params]);
  }
});

app.service('dummy').hooks({
  arguments: {
    custom: ['id', 'data', 'params']
  }
  before: {
    all: [/**/],
    custom: [/**/]
  },
  after: {
    all: [/**/],
    custom: [/**/]
  }
});

return app.service('dummy').custom(28, { bar: 'foo' }, { provider: 'rest' });

[bertho-zero]

I have updated the first example.

[daffl]

What I mean is that context.arguments should contain the actual method arguments because I don't think we need a separate mechanism to convert non-standard method arguments since that can be done already in a hook if needed:

app.hooks({
  before: {
    myMethod(context) {
      const [ id, data, something ] = context.arguments;

      return Object.assign(context, {
        id, data, something
      });
    }
  }
});

In fact, I just realized that we might not need converters at all since the same can totally be done in the already existing argument validation hook (https://github.com/feathersjs/feathers/blob/master/lib/hooks.js#L47) for the normal service methods.

[bertho-zero]

I do not see exactly what changes I should make based on your comment, can you point me?

[daffl]

I'll merge this one and then will update it accordingly.

[bertho-zero]

I have updated this and feathersjs/feathers#864.

[bertho-zero]

I deleted converters, it's a hook that is just after validateHook that adds arguments for each method.
And I also modified validateArguments to validate all methods.

[daffl]

This looks great, thank you! I'll get this one in and then verify it against feathersjs/feathers#864