YAML support for the Go language

Fork

This fork is an improved version of the go-yaml/yaml package, enhanced to inject __origin__ metadata into YAML mapping nodes during decoding, recording the file, line, and column of each key.

To enable origin tracking, call Origin on the decoder before decoding:

dec := yaml.NewDecoder(r)
dec.Origin(true, "myfile.yaml")

var v interface{}
dec.Decode(&v)
// Each decoded map now contains a synthetic "__origin__" key whose value is
// a compact []interface{} sequence:
//   [file, key_name, key_line, key_col, nf, f1_name, f1_delta, f1_col, ..., ns, s1_name, s1_count, (name, delta, col)×count, ...]
// where nf = number of scalar/sequence fields, ns = number of sequences with item locations,
// and deltas are line offsets from key_line.

Origin nodes are synthetic: their key node has Line == 0 (since real YAML lines are 1-based), which allows callers to detect and strip them. The oasdiff/yaml package uses this to build an OriginTree before JSON conversion, keeping __origin__ entirely out of the decoded struct.

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.

Installation and usage

The import path for the package is github.com/oasdiff/yaml3.

To install it, run:

go get github.com/oasdiff/yaml3

API documentation

• https://pkg.go.dev/github.com/oasdiff/yaml3

License

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

Example

package main

import (
        "fmt"
        "log"

        "github.com/oasdiff/yaml3"
)

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