parser-go-json

Parser for JSON in Go, which tries to not allocate any memory.

We can parse json without unmarshaling it into a Go struct using the Parser interface:

import "github.com/katydid/parser-go-json/json"

func main() {
    jsonString := `{"otherfield": 123, "myfield": "myvalue"}`
    jsonParser := json.NewJsonParser()
    if err := jsonParser.Init([]byte(jsonString)); err != nil {
        panic(err)
    }
    myvalue, err := GetMyField(jsonParser)
    if err != nil {
        panic(err)
    }
    println(value)
}

We can then use the parser to decode only myfield and skip over other fields and return "myvalue":

func GetMyField(p parser.Interface) (string, error) {
	for {
		if err := p.Next(); err != nil {
			if err == io.EOF {
				break
			} else {
				return "", err
			}
		}
		fieldName, err := p.String()
		if err != nil {
			return "", err
		}
		if fieldName != "myfield" {
			continue
		}
		p.Down()
		if err := p.Next(); err != nil {
			if err == io.EOF {
				break
			} else {
				return "", err
			}
		}
		return p.String()
	}
	return "", nil
}

Special Considerations

• The parser uses a buffer pool, which will allocate memory until it is warmed up.
• Buffers are reused and pooled. This means that the String and Bytes methods, returns a string and []byte respectively that should be copied if it is needed again before calling Next, Up or Down.
• Arrays are indexed, which means that ["a","b","c"] will be parsed into something that looks like an integer indexed map: {O: "a", 1: "b", 2: "c"}.

Thank you

Thanks to the following people for consulting on the project:

• Jacques Marais
• Johan Brandhorst-Satzkorn

I still made all the bad design decisions, so don't blame them. They only made the project better than it would have been without their advice.