gojay

GoJay

GoJay is a performant JSON encoder/decoder for Golang (currently the most performant, see benchmarks).

It has a simple API and doesn't use reflection. It relies on small interfaces to decode/encode structures and slices.

Gojay also comes with powerful stream decoding features and an even faster Unsafe API.

There is also a code generation tool to make usage easier and faster.

Why another JSON parser?

I looked at other fast decoder/encoder and realised it was mostly hardly readable static code generation or a lot of reflection, poor streaming features, and not so fast in the end.

Also, I wanted to build a decoder that could consume an io.Reader of line or comma delimited JSON, in a JIT way. To consume a flow of JSON objects from a TCP connection for example or from a standard output. Same way I wanted to build an encoder that could encode a flow of data to a io.Writer.

This is how GoJay aims to be a very fast, JIT stream parser with 0 reflection, low allocation with a friendly API.

Get started

go get github.com/francoispqt/gojay

• Encoder
• Decoder
• Stream API
• Code Generation

Decoding

Decoding is done through two different API similar to standard encoding/json:

• Unmarshal
• Decode

Example of basic stucture decoding with Unmarshal:

…

with Decode:

func main() {
    u := &user{}
    dec := gojay.NewDecoder(bytes.NewReader([]byte(`{"id":1,"name":"gojay","email":"[email protected]"}`)))
    err := dec.DecodeObject(d, u)
    if err != nil {
        log.Fatal(err)
    }
}

Unmarshal API

Unmarshal API decodes a []byte to a given pointer with a single function.

Behind the doors, Unmarshal API borrows a *gojay.Decoder resets its settings and decodes the data to the given pointer and releases the *gojay.Decoder to the pool when it finishes, whether it encounters an error or not.

If it cannot find the right Decoding strategy for the type of the given pointer, it returns an InvalidUnmarshalError. You can test the error returned by doing if ok := err.(InvalidUnmarshalError); ok {}.

Unmarshal API comes with three functions:

• Unmarshal

func Unmarshal(data []byte, v interface{}) error

• UnmarshalJSONObject

func UnmarshalJSONObject(data []byte, v gojay.UnmarshalerJSONObject) error

• UnmarshalJSONArray

func UnmarshalJSONArray(data []byte, v gojay.UnmarshalerJSONArray) error

Decode API

Decode API decodes a []byte to a given pointer by creating or borrowing a *gojay.Decoder with an io.Reader and calling Decode methods.

Getting a *gojay.Decoder or Borrowing

You can either get a fresh *gojay.Decoder calling dec := gojay.NewDecoder(io.Reader) or borrow one from the pool by calling dec := gojay.BorrowDecoder(io.Reader).

After using a decoder, you can release it by calling dec.Release(). Beware, if you reuse the decoder after releasing it, it will panic with an error of type InvalidUsagePooledDecoderError. If you want to fully benefit from the pooling, you must release your decoders after using.

Example getting a fresh an releasing:

str := ""
dec := gojay.NewDecoder(strings.NewReader(`"test"`))
defer dec.Release()
if err := dec.Decode(&str); err != nil {
    log.Fatal(err)
}

Example borrowing a decoder and releasing:

str := ""
dec := gojay.BorrowDecoder(strings.NewReader(`"test"`))
defer dec.Release()
if err := dec.Decode(&str); err != nil {
    log.Fatal(err)
}

*gojay.Decoder has multiple methods to decode to specific types:

• Decode

func (dec *gojay.Decoder) Decode(v interface{}) error

• DecodeObject

func (dec *gojay.Decoder) DecodeObject(v gojay.UnmarshalerJSONObject) error

• DecodeArray

func (dec *gojay.Decoder) DecodeArray(v gojay.UnmarshalerJSONArray) error

• DecodeInt

func (dec *gojay.Decoder) DecodeInt(v *int) error

• DecodeBool

func (dec *gojay.Decoder) DecodeBool(v *bool) error

• DecodeString

func (dec *gojay.Decoder) DecodeString(v *string) error

All DecodeXxx methods are used to decode top level JSON values. If you are decoding keys or items of a JSON object or array, don't use the Decode methods.

Example:

reader := strings.NewReader(`"John Doe"`)
dec := NewDecoder(reader)

var str string
err := dec.DecodeString(&str)
if err != nil {
    log.Fatal(err)
}

fmt.Println(str) // John Doe

Structs and Maps

UnmarshalerJSONObject Interface

To unmarshal a JSON object to a structure, the structure must implement the UnmarshalerJSONObject interface:

type UnmarshalerJSONObject interface {
	UnmarshalJSONObject(*gojay.Decoder, string) error
	NKeys() int
}

UnmarshalJSONObject method takes two arguments, the first one is a pointer to the Decoder (*gojay.Decoder) and the second one is the string value of the current key being parsed. If the JSON data is not an object, the UnmarshalJSONObject method will never be called.

NKeys method must return the number of keys to Unmarshal in the JSON object or 0. If zero is returned, all keys will be parsed.

Example of implementation for a struct:

type user struct {
    id int
    name string
    email string
}
// implement UnmarshalerJSONObject
func (u *user) UnmarshalJSONObject(dec *gojay.Decoder, key string) error {
    switch key {
    case "id":
        return dec.Int(&u.id)
    case "name":
        return dec.String(&u.name)
    case "email":
        return dec.String(&u.email)
    }
    return nil
}
func (u *user) NKeys() int {
    return 3
}

Example of implementation for a map[string]string:

// define our custom map type implementing UnmarshalerJSONObject
type message map[string]string

// Implementing Unmarshaler
func (m message) UnmarshalJSONObject(dec *gojay.Decoder, k string) error {
	str := ""
	err := dec.String(&str)
	if err != nil {
		return err
	}
	m[k] = str
	return nil
}

// we return 0, it tells the Decoder to decode all keys
func (m message) NKeys() int {
	return 0
}

Arrays, Slices and Channels

To unmarshal a JSON object to a slice an array or a channel, it must implement the UnmarshalerJSONArray interface:

type UnmarshalerJSONArray interface {
	UnmarshalJSONArray(*gojay.Decoder) error
}

UnmarshalJSONArray method takes one argument, a pointer to the Decoder (*gojay.Decoder). If the JSON data is not an array, the Unmarshal method will never be called.

Example of implementation with a slice:

type testSlice []string
// implement UnmarshalerJSONArray
func (t *testSlice) UnmarshalJSONArray(dec *gojay.Decoder) error {
	str := ""
	if err := dec.String(&str); err != nil {
		return err
	}
	*t = append(*t, str)
	return nil
}

func main() {
	dec := gojay.BorrowDecoder(strings.NewReader(`["Tom", "Jim"]`))
	var slice testSlice
	err := dec.DecodeArray(&slice)
	if err != nil {
		log.Fatal(err)
	}
	fmt.Println(slice) // [Tom Jim]
	dec.Release()
}

Example of implementation with a channel:

type testChannel chan string
// implement UnmarshalerJSONArray
func (c testChannel) UnmarshalJSONArray(dec *gojay.Decoder) error {
	str := ""
	if err := dec.String(&str); err != nil {
		return err
	}
	c <- str
	return nil
}

func main() {
	dec := gojay.BorrowDecoder(strings.NewReader(`["Tom", "Jim"]`))
	c := make(testChannel, 2)
	err := dec.DecodeArray(c)
	if err != nil {
		log.Fatal(err)
	}
	for i := 0; i < 2; i++ {
		fmt.Println(<-c)
	}
	close(c)
	dec.Release()
}

Example of implementation with an array:

type testArray [3]string
// implement UnmarshalerJSONArray
func (a *testArray) UnmarshalJSONArray(dec *Decoder) error {
	var str string
	if err := dec.String(&str); err != nil {
		return err
	}
	a[dec.Index()] = str
	return nil
}

func main() {
	dec := gojay.BorrowDecoder(strings.NewReader(`["Tom", "Jim", "Bob"]`))
	var a testArray
	err := dec.DecodeArray(&a)
	fmt.Println(a) // [Tom Jim Bob]
	dec.Release()
}

Other types

To decode other types (string, int, int32, int64, uint32, uint64, float, booleans), you don't need to implement any interface.

Example of encoding strings:

func main() {
    json := []byte(`"Jay"`)
    var v string
    err := gojay.Unmarshal(json, &v)
    if err != nil {
        log.Fatal(err)
    }
    fmt.Println(v) // Jay
}

Decode values methods

When decoding a JSON object of a JSON array using UnmarshalerJSONObject or UnmarshalerJSONArray interface, the gojay.Decoder provides dozens of methods to Decode multiple types.

Non exhaustive list of methods available (to see all methods, check the godoc):

dec.Int
dec.Int8
dec.Int16
dec.Int32
dec.Int64
dec.Uint8
dec.Uint16
dec.Uint32
dec.Uint64
dec.String
dec.Time
dec.Bool
dec.SQLNullString
dec.SQLNullInt64

Encoding

Encoding is done through two different API similar to standard encoding/json:

• Marshal
• Encode

Example of basic structure encoding with Marshal:

import "github.com/francoispqt/gojay"

type user struct {
	id    int
	name  string
	email string
}

// implement MarshalerJSONObject
func (u *user) MarshalJSONObject(enc *gojay.Encoder) {
	enc.IntKey("id", u.id)
	enc.StringKey("name", u.name)
	enc.StringKey("email", u.email)
}
func (u *user) IsNil() bool {
	return u == nil
}

func main() {
	u := &user{1, "gojay", "[email protected]"}
	b, err := gojay.MarshalJSONObject(u)
	if err != nil {
		log.Fatal(err)
	}
	fmt.Println(string(b)) // {"id":1,"name":"gojay","email":"[email protected]"}
}

with Encode:

func main() {
	u := &user{1, "gojay", "[email protected]"}
	b := strings.Builder{}
	enc := gojay.NewEncoder(&b)
	if err := enc.Encode(u); err != nil {
		log.Fatal(err)
	}
	fmt.Println(b.String()) // {"id":1,"name":"gojay","email":"[email protected]"}
}

Marshal API

Marshal API encodes a value to a JSON []byte with a single function.

Behind the doors, Marshal API borrows a *gojay.Encoder resets its settings and encodes the data to an internal byte buffer and releases the *gojay.Encoder to the pool when it finishes, whether it encounters an error or not.

If it cannot find the right Encoding strategy for the type of the given value, it returns an InvalidMarshalError. You can test the error returned by doing if ok := err.(InvalidMarshalError); ok {}.

Marshal API comes with three functions:

• Marshal

func Marshal(v interface{}) ([]byte, error)

• MarshalJSONObject

func MarshalJSONObject(v gojay.MarshalerJSONObject) ([]byte, error)

• MarshalJSONArray

func MarshalJSONArray(v gojay.MarshalerJSONArray) ([]byte, error)

Encode API

Encode API decodes a value to JSON by creating or borrowing a *gojay.Encoder sending it to an io.Writer and calling Encode methods.

Getting a *gojay.Encoder or Borrowing

You can either get a fresh *gojay.Encoder calling enc := gojay.NewEncoder(io.Writer) or borrow one from the pool by calling enc := gojay.BorrowEncoder(io.Writer).

After using an encoder, you can release it by calling enc.Release(). Beware, if you reuse the encoder after releasing it, it will panic with an error of type InvalidUsagePooledEncoderError. If you want to fully benefit from the pooling, you must release your encoders after using.

Example getting a fresh encoder an releasing:

str := "test"
b := strings.Builder{}
enc := gojay.NewEncoder(&b)
defer enc.Release()
if err := enc.Encode(str); err != nil {
    log.Fatal(err)
}

Example borrowing an encoder and releasing:

str := "test"
b := strings.Builder{}
enc := gojay.BorrowEncoder(b)
defer enc.Release()
if err := enc.Encode(str); err != nil {
    log.Fatal(err)
}

*gojay.Encoder has multiple methods to encoder specific types to JSON:

• Encode

func (enc *gojay.Encoder) Encode(v interface{}) error

• EncodeObject

func (