yaml

YAML 1.2 marshaling and unmarshaling support for Go

A simple package to marshal and unmarshal YAML 1.2 in Go.

⚙️ Installation

go get -u czechia.dev/yaml

📝 Introduction

This package is a rewrite of github.com/ghodss/yaml using the new yaml.Node API in yaml.v3. The API of this package is the same as ghodss/yaml so you can use it as a drop-in replacement wherever ghodss/yaml is used.

The original library was designed to enable a better way of handling YAML when marshaling to and from structs.

This library first converts YAML to JSON using yaml.v3 and then uses json.Unmarshal to convert to the desired struct. This means that it uses the same JSON struct tags as well as the custom JSON methods MarshalJSON and UnmarshalJSON.

For a detailed overview of the reasoning behind this method, see this archived blog post.

👍 Compatibility

This package uses yaml.v3 and therefore supports everything yaml.v3 supports.

The most noticable difference between yaml.v2 and yaml.v3 (or rather the YAML 1.1 and YAML 1.2 specifications) is around booleans. Specifically only variants of true and false are booleans, so y is now treated as a string.

⛔️ Caveats

Caveat #1: When using yaml.Marshal and yaml.Unmarshal, binary data should NOT be preceded with the !!binary YAML tag. If you do, yaml.v3 will convert the binary data from base64 to native binary data, which is not compatible with JSON. You can still use binary in your YAML files - just store them without the !!binary tag and decode the base64 in your code (e.g. in the custom JSON methods MarshalJSON and UnmarshalJSON). This has the benefit that binary data will be decoded exactly the same way for both YAML and JSON.

Caveat #2: When using YAMLToJSON directly, maps with keys that are maps will result in an error since this is not supported by JSON. This error will occur in Unmarshal as well since you can't unmarshal map keys anyways since struct fields can't be keys.

💻 Usage

Import using:

import "czechia.dev/yaml"

Usage is very similar to the JSON library:

package main

import (
	"fmt"

	"czechia.dev/yaml"
)

type Person struct {
	Name string `json:"name"` // Affects YAML field names too.
	Age  int    `json:"age"`
}

func main() {
	// Marshal a Person struct to YAML.
	p := Person{"John", 30}
	y, err := yaml.Marshal(p)
	if err != nil {
		fmt.Printf("err: %v\n", err)
		return
	}
	fmt.Println(string(y))
	/* Output:
	name: John
	age: 30
	*/

	// Unmarshal the YAML back into a Person struct.
	var p2 Person
	err = yaml.Unmarshal(y, &p2)
	if err != nil {
		fmt.Printf("err: %v\n", err)
		return
	}
	fmt.Println(p2)
	/* Output:
	{John 30}
	*/
}

The intermediate yaml.YAMLToJSON and yaml.JSONToYAML methods are also available:

package main

import (
	"fmt"

	"czechia.dev/yaml"
)

func main() {
	j := []byte(`{"name": "John", "age": 30}`)
	y, err := yaml.JSONToYAML(j)
	if err != nil {
		fmt.Printf("err: %v\n", err)
		return
	}
	fmt.Println(string(y))
	/* Output:
	age: 30
	name: John
	*/

	j2, err := yaml.YAMLToJSON(y)
	if err != nil {
		fmt.Printf("err: %v\n", err)
		return
	}
	fmt.Println(string(j2))
	/* Output:
	{"age":30,"name":"John"}
	*/
}