jx 
Package jx implements encoding and decoding of json [RFC 7159]. Lightweight fork of jsoniter.
go get github.com/go-faster/jx
Features
- Directly encode and decode json values
- No reflect or
interface{} - Pools and direct buffer access for less (or none) allocations
- Multi-pass decoding
- Validation
See usage for examples. Mostly suitable for fast low-level json manipulation with high control. Used in ogen project for json (un)marshaling code generation based on json and OpenAPI schemas.
Why
Most of jsoniter issues are caused by necessity to be drop-in replacement for standard encoding/json. Removing such constrains greatly simplified implementation and reduced scope, allowing to focus on json stream processing.
- Commas are handled automatically while encoding
- Raw json, Number and Base64 support
- Reduced scope
- No reflection
- No
encoding/jsonadapter - 3.5x less code (8.5K to 2.4K SLOC)
- Fuzzing, improved test coverage
- Drastically refactored and simplified
- Explicit error returns
- No
ConfigorAPI
Usage
Decode
Use jx.Decoder. Zero value is valid, but constructors are available for convenience:
- jx.Decode(reader io.Reader, bufSize int) for
io.Reader - jx.DecodeBytes([]byte) for byte slices
- jx.DecodeStr(string) for strings
To reuse decoders and their buffers, use jx.GetDecoder and jx.PutDecoder alongside with reset functions:
- jx.Decoder.Reset(io.Reader) to reset to new
io.Reader - jx.Decoder.ResetBytes([]byte) to decode another byte slice
Decoder is reset on PutDecoder.
d := jx.DecodeStr(`{"values":[4,8,15,16,23,42]}`)
// Save all integers from "values" array to slice.
var values []int
// Iterate over each object field.
if err := d.Obj(func(d *jx.Decoder, key string) error {
switch key {
case "values":
// Iterate over each array element.
return d.Arr(func(d *jx.Decoder) error {
v, err := d.Int()
if err != nil {
return err
}
values = append(values, v)
return nil
})
default:
// Skip unknown fields if any.
return d.Skip()
}
}); err != nil {
panic(err)
}
fmt.Println(values)
// Output: [4 8 15 16 23 42]
Encode
Use jx.Encoder. Zero value is valid, reuse with jx.GetEncoder, jx.PutEncoder and jx.Encoder.Reset(). Encoder is reset on PutEncoder.
var e jx.Encoder
e.ObjStart() // {
e.FieldStart("values") // "values":
e.ArrStart() // [
for _, v := range []int{4, 8, 15, 16, 23, 42} {
e.Int(v)
}
e.ArrEnd() // ]
e.ObjEnd() // }
fmt.Println(e)
fmt.Println("Buffer len:", len(e.Bytes()))
// Output: {"values":[4,8,15,16,23,42]}
// Buffer len: 28
Raw
Use jx.Decoder.Raw to read raw json values, similar to json.RawMessage.
d := jx.DecodeStr(`{"foo": [1, 2, 3]}`)
var raw jx.Raw
if err := d.Obj(func(d *jx.Decoder, key string) error {
v, err := d.Raw()
if err != nil {
return err
}
raw = v
return nil
}); err != nil {
panic(err)
}
fmt.Println(raw.Type(), raw)
// Output:
// array [1, 2, 3]
Number
Use jx.Decoder.Num to read numbers, similar to json.Number. Also supports number strings, like "12345", which is common compatible way to represent uint64.
d := jx.DecodeStr(`{"foo": "10531.0"}`)
var n jx.Num
if err := d.Obj(func(d *jx.Decoder, key string) error {
v, err := d.Num()
if err != nil {
return err
}
n = v
return nil
}); err != nil {
panic(err)
}
fmt.Println(n)
fmt.Println("positive:", n.Positive())
// Can decode floats with zero fractional part as integers:
v, err := n.Int64()
if err != nil {
panic(err)
}
fmt.Println("int64:", v)
// Output:
// "10531.0"
// positive: true
// int64: 10531
Base64
Use jx.Encoder.Base64 and jx.Decoder.Base64 or jx.Decoder.Base64Append.
Same as encoding/json, base64.StdEncoding or [RFC 4648].
var e jx.Encoder
e.Base64([]byte("Hello"))
fmt.Println(e)
data, _ := jx.DecodeBytes(e.Bytes()).Base64()
fmt.Printf("%s", data)
// Output:
// "SGVsbG8="
// Hello
Validate
Check that byte slice is valid json with jx.Valid:
fmt.Println(jx.Valid([]byte(`{"field": "value"}`))) // true
fmt.Println(jx.Valid([]byte(`"Hello, world!"`))) // true
fmt.Println(jx.Valid([]byte(`["foo"}`))) // false
Capture
The jx.Decoder.Capture method allows to unread everything is read in callback. Useful for multi-pass parsing:
d := jx.DecodeStr(`["foo", "bar", "baz"]`)
var elems int
// NB: Currently Capture does not support io.Reader, only buffers.
if err := d.Capture(func(d *jx.Decoder) error {
// Everything decoded in this callback will be rolled back.
return d.Arr(func(d *jx.Decoder) error {
elems++
return d.Skip()
})
}); err != nil {
panic(err)
}
// Decoder is rolled back to state before "Capture" call.
fmt.Println("Read", elems, "elements on first pass")
fmt.Println("Next element is", d.Next(), "again")
// Output:
// Read 3 elements on first pass
// Next element is array again
ObjBytes
The Decoder.ObjBytes method tries not to allocate memory for keys, reusing existing buffer.
d := DecodeStr(`{"id":1,"randomNumber":10}`)
d.ObjBytes(func(d *Decoder, key []byte) error {
switch string(key) {
case "id":
case "randomNumber":
}
return d.Skip()
})
Roadmap
- Rework and export
Any - Support
Rawfor io.Reader - Support
Capturefor io.Reader - Improve Num
- Better validation on decoding
- Support BigFloat and BigInt
- Support equivalence check, like
eq(1.0, 1) == true
- Add non-callback decoding of objects
Non-goals
- Code generation for decoding or encoding
- Replacement for
encoding/json - Reflection or
interface{}based encoding or decoding - Support for json path or similar
This package should be kept as simple as possible and be used as low-level foundation for high-level projects like code generator.
License
MIT, same as jsoniter
