Handle empty indexes for slices and arrays (eg. field[]=1&field[]=2)

[mfly]

Fixes Or Enhances

Related to: #60

This PR introduces support for parsing arrays with trailing square brackets (field[]=1&field[]=2).

This format is quite widespread and supported by numerous FE and BE frameworks.

Make sure that you've checked the boxes below before you submit PR:

• Tests exist or have been written that cover this particular change.

@go-playground/admins

[coveralls]

coverage: 99.817% (+0.003%) from 99.814%
when pulling fb76283 on mfly:mm-handle-empty-slice-index
into 8785d3c on go-playground:master.

[deankarn]

@mfly TY for the PR and I would like to support this.

I wonder if this can be abstracted away during parsing within parseMapData if possible though to keep the setFieldByType as simple as possible?

[mfly]

Hi @deankarn, thanks for expressing your interest in this. I've considered three options:

1. Preprocess the url.Values by merging keys ending with [] suffix with the respective keys without the suffix - pretty straightforward way to fix the issue, but breaks existing usages like this one
2. changes in parseMapData - I attempted that, but it seemed out of place and I encountered some problems with namespaces
3. the proposed approach - pretty simple, explicit and clean. Works with all the use cases I came up with

If you don't like the current approach I can revisit 2. at some point. Happy to take any suggestions you may have.

[brunoluiz]

From some quick tests I have done, this doesn't seem to handle a struct slice with empty index, such as the field FooSlice[].ID on the following struct

type Foo struct {
	ID string
}

// TestDecoder_ArrayIndexes fails to handle slices with structs
func TestDecoder_ArrayIndexes(t *testing.T) {
	type PostsRequest struct {
		FooSlice []Foo
	}
	in := url.Values{
		"FooSlice[].ID": []string{"0", "1", "2", "3"},
	}

	v := new(PostsRequest)
	d := NewDecoder()
	err := d.Decode(v, in)
	Equal(t, err, nil)
	Equal(t, len(v.FooSlice), 4)
	Equal(t, v.FooSlice[0].ID, "0")
	Equal(t, v.FooSlice[1].ID, "1")
	Equal(t, v.FooSlice[2].ID, "2")
	Equal(t, v.FooSlice[3].ID, "3")
}