YAML support for the Go language

Note

This is a fork of gopkg.in/yaml.v3 which provides more specific error types when using Unmarshal to decode documents (see example).

Introduction

The yaml package enables Go programs to comfortably encode and decode YAML values. It was developed within Canonical as part of the juju project, and is based on a pure Go port of the well-known libyaml C library to parse and generate YAML data quickly and reliably.

Compatibility

The yaml package supports most of YAML 1.2, but preserves some behavior from 1.1 for backwards compatibility.

Specifically, as of v3 of the yaml package:

• YAML 1.1 bools (yes/no, on/off) are supported as long as they are being decoded into a typed bool value. Otherwise they behave as a string. Booleans in YAML 1.2 are true/false only.
• Octals encode and decode as 0777 per YAML 1.1, rather than 0o777 as specified in YAML 1.2, because most parsers still use the old format. Octals in the 0o777 format are supported though, so new files work.
• Does not support base-60 floats. These are gone from YAML 1.2, and were actually never supported by this package as it's clearly a poor choice.

and offers backwards compatibility with YAML 1.1 in some cases. 1.2, including support for anchors, tags, map merging, etc. Multi-document unmarshalling is not yet implemented, and base-60 floats from YAML 1.1 are purposefully not supported since they're a poor design and are gone in YAML 1.2.

Installation and usage

The import path for the package is github.com/conduitio/yaml/v3.

To install it, run:

go get github.com/conduitio/yaml/v3

API documentation

API documentation is hosted on pkg.go.dev:

• https://pkg.go.dev/github.com/conduitio/yaml

API stability

The package API for yaml v3 will remain stable as described in gopkg.in.

License

The yaml package is licensed under the MIT and Apache License 2.0 licenses. Please see the LICENSE file for details.

Example (basic)

package main

import (
        "fmt"
        "log"

        "github.com/conduitio/yaml/v3"
)

var data = `
a: Easy!
b:
  c: 2
  d: [3, 4]
`

// Note: struct fields must be public in order for unmarshal to
// correctly populate the data.
type T struct {
        A string
        B struct {
                RenamedC int   `yaml:"c"`
                D        []int `yaml:",flow"`
        }
}

func main() {
        t := T{}
    
        err := yaml.Unmarshal([]byte(data), &t)
        if err != nil {
                log.Fatalf("error: %v", err)
        }
        fmt.Printf("--- t:\n%v\n\n", t)
    
        d, err := yaml.Marshal(&t)
        if err != nil {
                log.Fatalf("error: %v", err)
        }
        fmt.Printf("--- t dump:\n%s\n\n", string(d))
    
        m := make(map[interface{}]interface{})
    
        err = yaml.Unmarshal([]byte(data), &m)
        if err != nil {
                log.Fatalf("error: %v", err)
        }
        fmt.Printf("--- m:\n%v\n\n", m)
    
        d, err = yaml.Marshal(&m)
        if err != nil {
                log.Fatalf("error: %v", err)
        }
        fmt.Printf("--- m dump:\n%s\n\n", string(d))
}

This example will generate the following output:

--- t:
{Easy! {2 [3 4]}}

--- t dump:
a: Easy!
b:
  c: 2
  d: [3, 4]


--- m:
map[a:Easy! b:map[c:2 d:[3 4]]]

--- m dump:
a: Easy!
b:
  c: 2
  d:
  - 3
  - 4

Example (error types)

package main

import (
	"fmt"

	"github.com/conduitio/yaml/v3"
)


var data = `
a: Easy!
b:
  c: abc   # expected int
  d: [3, 4]
foo: unknown
bar:
  Duplicate: first
  Duplicate: again
`

type T struct {
	A string
	B struct {
		RenamedC int   `yaml:"c"`
		D        []int `yaml:",flow"`
	}
	Bar struct {
		Duplicate string
	}
}

func main() {
	var t T

	dec := yaml.NewDecoder(bytes.NewBufferString(data))
	dec.KnownFields(true) // enable *yaml.UnknownFieldError

	err := dec.Decode(&t)
	if err != nil {
		fmt.Println("oops, something went wrong")
		if terr, ok := err.(*yaml.TypeError); ok {
			for _,unmarshalErr := range terr.Errors {
				fmt.Printf("  %T: line %d col %d: %v\n", unmarshalErr, unmarshalErr.Line(), unmarshalErr.Column(), unmarshalErr.Error())
			}
		}
	}
	d, _ := yaml.Marshal(&t)
	fmt.Printf("--- t dump:\n%s\n\n", string(d))
}

Produces:

oops, something went wrong
  *yaml.InvalidTypeError: line 4 col 6: cannot unmarshal !!str `abc` into int
  *yaml.UnknownFieldError: line 6 col 1: field foo not found in type yaml_test.T
  *yaml.DuplicateMappingKeyError: line 9 col 3: mapping key "Duplicate" already defined at line 8
--- t dump:
a: Easy!
b:
    c: 0
    d: [3, 4]
bar:
    duplicate: ""