Exploring Go json v2 unmarshall in depth

Go encoding/json/v2 Unmarshall Stream

How to Efficiently unmarshall a stream of data ⁇

Old Ways with encoding/json

• Method 1
  • Read all the stream data with io.ReadAll
  • Unmarshall it to a custom type with json.Unmarshall

func OldJsonStreamUnmarshal(dataStream io.Reader, v interface{}) error {
	data, err := io.ReadAll(dataStream)
	if err != nil {
		return err
	}
	return json.Unmarshal(data, v)
}

• Method 2
  • use relatively modern NewDecoder to create a Decocer for the input stream io.Reader
  • Decode it to custom type with Decode

func OldJsonStreamUnmarshalWithDecoder(dataStream io.Reader, v interface{}) error {
	return json.NewDecoder(dataStream).Decode(v)
}

New Ways with encoding/json/v2

• Method 1

  • Read all the stream data with io.ReadAll
  • Unmarshall it to a custom type with jsonv2.Unmarshall
  • consider import as

• Import

import (
	"encoding/json"
	jsonv2 "encoding/json/v2"
	"io"
)

• Function

func NewJsonV2StreamUnmarshal(dataStream io.Reader, v interface{}) error {
	data, err := io.ReadAll(dataStream)
	if err != nil {
		return err
	}
	return jsonv2.Unmarshal(data, v)
}

• Method 2

  • using newer function UnmarshalRead from go1.27 -> encoding/json/v2
  • which handles Read stream data and Unmarshall to our Custom Type all in one step.
  • consider import as

• Import

import (
	"encoding/json"
	jsonv2 "encoding/json/v2"
	"io"
)

• Function

func NewJsonV2StreamUnmarshalWithDecoder(dataStream io.Reader, v interface{}) error {
	return jsonv2.UnmarshalRead(dataStream, v)
}

Comparision

• when ran each of these respective functions

• ref :- https://gist.github.com/Sandy10247/ded8c4bd81cde7e0cbeb45f40c968fad

Conclusion

• The main result is that NewJsonV2StreamUnmarshalWithDecoder is the best default for streaming JSON in this benchmark.

func NewJsonV2StreamUnmarshalWithDecoder(dataStream io.Reader, v interface{}) error {
	return jsonv2.UnmarshalRead(dataStream, v)
}

• ref :- https://gist.github.com/Sandy10247/ded8c4bd81cde7e0cbeb45f40c968fad#file-main-go

	// NewJsonV2StreamUnmarshalWithDecoder
	var person4 Person
	err = NewJsonV2StreamUnmarshalWithDecoder(getNewStream(), &person4)
	if err != nil {
		fmt.Println("Error unmarshalling JSON v2 with decoder:", err)
		return
	}
	fmt.Printf("New JSON v2 Unmarshal with Decoder: %+v\n", person4)

References

• https://pkg.go.dev/golang.org/x/perf/cmd/benchstat
• https://pkg.go.dev/encoding/json/v2

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