How to Parse Dynamic Keys in YAML with Go?

Dynamic Key Parsing in YAML with Go

When working with YAML files in Go, you may encounter scenarios where the key names within the file vary. This is often used for API versioning or dynamic configuration purposes. To effectively parse such YAML structures, you'll need to employ custom parsing strategies.

Issue Summary

In the context of API versioning, it's possible to have a YAML file with keys representing different versions, such as "V1", "V2", "V3", and so on. The catch is that these versions might not always be present in the file, and their order may be inconsistent.

Custom Unmarshaler Approach

To resolve this issue, consider implementing a custom Unmarshaler for the corresponding data structure. This allows you to control the unmarshalling process and handle dynamic key values.

<code class="go">package main

import (
    "fmt"

    "gopkg.in/yaml.v2"
)

type MajorVersion struct {
    Current                string   `yaml:"current"`
    MimeTypes              []string `yaml:"mime_types"`
    SkipVersionValidation  bool     `yaml:"skip-version-validation"`
    SkipMimeTypeValidation bool     `yaml:"skip-mime-type-validation"`
}

type Environment struct {
    SkipHeaderValidation bool
    Versions             map[string]MajorVersion
}

func (e *Environment) UnmarshalYAML(unmarshal func(interface{}) error) error {
    var params struct {
        SkipHeaderValidation bool `yaml:"skip-header-validation"`
    }
    if err := unmarshal(&amp;params); err != nil {
        return err
    }
    var versions map[string]MajorVersion
    if err := unmarshal(&amp;versions); err != nil {
        // Here we expect an error because a boolean cannot be converted to a MajorVersion
        if _, ok := err.(*yaml.TypeError); !ok {
            return err
        }
    }
    e.SkipHeaderValidation = params.SkipHeaderValidation
    e.Versions = versions
    return nil
}

func main() {
    var e map[string]Environment
    if err := yaml.Unmarshal([]byte(data), &amp;e); err != nil {
        fmt.Println(err.Error())
    }
    fmt.Printf("%#v\n", e)
}</code>

By defining a custom Unmarshaler for the Environment struct, you can effectively handle both boolean and nested structures within your YAML file.

Conclusion

Custom Unmarshalers offer a powerful way to parse complex and dynamic YAML structures in Golang. By implementing customized unmarshaling logic, you can adapt your data structures to varying key formats, making it easier to work with YAML files in situations where the structure might change over time.

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