Usage

This page will explain how to construct a parser and how to use that parser.

Currently Katydid supports several parsers:

protobuf
json      
reflected go structures
xml

Constructing a Parser

A parser parses a specific serialization format or other parsable text or bytes. We need to put our unparsed text, bytes or other structure into a parser so that it can be validated by katydid.

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

func main() {
    jsonString := `{"a": "abc"}`
    jsonParser := json.NewJsonParser()
    if err := jsonParser.Init([]byte(jsonString)); err != nil {
        panic(err)
    }
}

We can also construct a protocol buffer parser.

import protoparser "github.com/katydid/katydid/parser/proto"
import "github.com/gogo/protobuf/proto"

func main() {
    protoParser := protoparser.NewProtoNameParser("mypackage","mymessage", &Mymessage{}.Description())
    msg := &Mymessage{A: "abc"}
    data, err := proto.Marshal(msg)
    if err != nil {
        panic(err)
    }
    if err := protoParser.Init(data); err != nil {
        panic(err)
    }
}

We can even construct a parser for a reflected go structure.

import reflectparser "github.com/katydid/katydid/parser/reflect"
import "reflect"

func main() {
    reflectParser := reflectparser.NewReflectParser()
    s := &MyStruct{A: "abc"}
    v := reflect.ValueOf(s)
    reflectParser.Init(v)
}

Walking the Tree

If you want to use a parser for you own use case, here is a simple walk function.

func walk(p parser.Interface) {
    for {
        if err := p.Next(); err != nil {
            if err == io.EOF {
                break
            } else {
                panic(err)
            }
        }
        value := print(p.(parser.Value))
        if !p.IsLeaf() {
            p.Down()
            walk(p)
            p.Up()
        }
    }
    return
}

We should always first call the Next method and check the error, to see if we have reached the end of the list of fields. Then we can retrieve a field value or field name, which can be of type int, double, uint, string, bytes or a bool. Lastly we can check whether the current position is a terminating leaf in the tree or if we can go down the tree and finally come back up. Please see the godoc for the parser.Interface and parser.Value.

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