dynjson

Client-customizable JSON formats for dynamic APIs.

Introduction

dynjson allow APIs to return only fields selected by the API client:

GET https://api.example.com/v1/foos
[{"id":1,foo":1,"bar":2,"baz":3}]

GET https://api.example.com/v1/foos?select=foo
[{"foo":1}]

GET https://api.example.com/v1/foos/1?select=foo
{"foo":1}

dynjson mimicks the original struct using the original types and json tags. The field order is the same as the select parameters.

Installation

go get github.com/cocoonspace/dynjson

Examples

type APIResult struct {
    Foo int     `json:"foo"`
    Bar string  `json:"bar"`
}

f := dynjson.NewFormatter()

res := &APIResult{Foo:1, Bar:"bar"}
o, err := f.Format(res, dynjson.FieldsFromRequest(r))
if err != nil {
    // handle error
}
err = json.NewEncoder(w).Encode(o) // {"foo": 1}

With struct fields:

type APIResult struct {
    Foo int          `json:"foo"`
    Bar APIIncluded  `json:"bar"`
}

type APIIncluded struct {
    BarFoo int    `json:"barfoo"`
    BarBar string `json:"barbar"`
}

f := dynjson.NewFormatter()

res := &APIResult{Foo: 1, Bar: APIIncluded{BarFoo:1, BarBar: "bar"}}
o, err := f.Format(res, []string{"foo", "bar.barfoo"})
if err != nil {
    // handle error
}
err = json.NewEncoder(w).Encode(o) // {"foo": 1, "bar":{"barfoo": 1}}

With slices:

type APIResult struct {
    Foo int     `json:"foo"`
    Bar string  `json:"bar"`
}

f := dynjson.NewFormatter()

res := []APIResult{{Foo: 1, Bar: "bar"}}
o, err := f.Format(res, []string{"foo"})
if err != nil {
    // handle error
}
err = json.NewEncoder(w).Encode(o) // [{"foo": 1}]

type APIResult struct {
    Foo int        `json:"foo"`
    Bar []APIItem  `json:"bar"`
}

type APIItem struct {
    BarFoo int    `json:"barfoo"`
    BarBar string `json:"barbar"`
}

f := dynjson.NewFormatter()

res := &APIResult{Foo: 1, Bar: []APIItem{{BarFoo: 1, BarBar: "bar"}}}
o, err := f.Format(res, []string{"foo", "bar.barfoo"})
if err != nil {
    // handle error
}
err = json.NewEncoder(w).Encode(o) // {"foo": 1, "bar":[{"barfoo": 1}]}

Limitations

• Anonymous fields without a json tag (embedded by the Go JSON encoder in the enclosing struct) are not supported,
• Maps are copied as is, you cannot filter map contents using map_field_name.map_key.

Performance impact

BenchmarkFormat_Fields
BenchmarkFormat_Fields-8     	 2466639	       480 ns/op	     184 B/op	       7 allocs/op
BenchmarkFormat_NoFields
BenchmarkFormat_NoFields-8   	 5255031	       232 ns/op	      32 B/op	       1 allocs/op
BenchmarkRawJSON
BenchmarkRawJSON-8           	 5351313	       223 ns/op	      32 B/op	       1 allocs/op

Contribution guidelines

Contributions are welcome, as long as:

• unit tests & comments are included,
• no external package is used.

License

MIT - See LICENSE