romshark / jscan

High performance JSON iterator & validator for Go

jscan

jscan provides high-performance zero-allocation JSON iterator and validator for Go. This module doesn't provide Marshal/Unmarshal capabilities yet, instead it focuses on highly efficient iteration over JSON data with on-the-fly validation.

An experimental decoder with backward compatibility to encoding/json is WiP 🧪 and is expected to be introduced together with jscan v3.

jscan is tested against https://github.com/nst/JSONTestSuite, a comprehensive test suite for RFC 8259 compliant JSON parsers.

See jscan-benchmark for benchmark results 🏎️ 🏁.

Example

https://go.dev/play/p/moP3l9EkebF

package main

import (
	"fmt"

	"github.com/romshark/jscan/v2"
)

func main() {
	j := `{
		"s": "value",
		"t": true,
		"f": false,
		"0": null,
		"n": -9.123e3,
		"o0": {},
		"a0": [],
		"o": {
			"k": "\"v\"",
			"a": [
				true,
				null,
				"item",
				-67.02e9,
				["foo"]
			]
		},
		"a3": [
			0,
			{
				"a3.a3":8
			}
		]
	}`

	err := jscan.Scan(j, func(i *jscan.Iterator[string]) (err bool) {
		fmt.Printf("%q:\n", i.Pointer())
		fmt.Printf("├─ valueType:  %s\n", i.ValueType().String())
		if k := i.Key(); k != "" {
			fmt.Printf("├─ key:        %q\n", k[1:len(k)-1])
		}
		if ai := i.ArrayIndex(); ai != -1 {
			fmt.Printf("├─ arrayIndex: %d\n", ai)
		}
		if v := i.Value(); v != "" {
			fmt.Printf("├─ value:      %q\n", v)
		}
		fmt.Printf("└─ level:      %d\n", i.Level())
		return false // Resume scanning
	})

	if err.IsErr() {
		fmt.Printf("ERR: %s\n", err)
		return
	}
}