Is there a way to add a yaml node to an existing yaml document in golang?

I am reading a yaml file with goyaml lib. I intend to modify some of its entries and add an entry if the key to be added is not already present.

e.g.

original yaml

root:
  entry1: val1

1 mod and 1 add target yaml

root:
 entry1: valUpdated
 entry2: newkey added

I cannot find any yaml lib which can allow me to add a node to yaml.

thanks for your help

You can do this with go-yaml if you unmarshal to yaml.Node:

package main

import (
	"os"

	"gopkg.in/yaml.v3"
)

var input = []byte(`root:
  entry1: val1`)

func main() {
	var document yaml.Node
	if err := yaml.Unmarshal(input, &document); err != nil {
		panic(err)
	}
	data := document.Content[0]
	var rootVal *yaml.Node
	for i := 0; i < len(data.Content); i += 2 {
		node := data.Content[i]
		if node.Kind == yaml.ScalarNode && node.Value == "root" {
			rootVal = data.Content[i+1]
			break
		}
	}
	if rootVal == nil {
		panic("root key missing")
	}

	found := false
	for i := 0; i < len(rootVal.Content); i += 2 {
		node := rootVal.Content[i]
		if node.Kind != yaml.ScalarNode {
			continue
		}
		switch node.Value {
		case "entry1":
			rootVal.Content[i+1].SetString("valUpdated")
		case "entry2":
			found = true
		}
	}
	if !found {
		var key, value yaml.Node
		key.SetString("entry2")
		value.SetString("newkey added")
		rootVal.Content = append(rootVal.Content, &key, &value)
	}
	out, err := yaml.Marshal(data)
	if err != nil {
		panic(err)
	}
	os.Stdout.Write(out)
}

output:

root:
    entry1: valUpdated
    entry2: newkey added

Playground link

Unmarshal gets you a document node with the root node as sole content node. Marshal expects the root node as data, so you feed data instead of document into it. I am not really sure why the API is like that.