yadu - a human readable yaml based slog.Handler

Introduction

Package yadu provides a handler for the log/slog logging framework.

It generates a mixture of text lines containing the timestamp and log message and a YAML dump of the provided attibutes.

Log format

The log format generated by yadu looks like this:

2023-04-02T10:50.09 EDT LEVEL Message text
    foo: value
    bar: 12345

Example

logger := slog.New(yadu.NewHandler(os.Stdout, nil))

type body string

type Ammo struct {
        Forweapon string
        Impact    int
        Cost      int
        Range     int
}

type Enemy struct {
    Alive  bool
    Health int
    Name   string
    Body   body `yaml:"-"` // not printed
    Ammo   []Ammo
}

e := &Enemy{Alive: true, Health: 10, Name: "Bodo", Body: "body\nbody\n",
    Ammo: []Ammo{{Forweapon: "Railgun", Range: 400, Impact: 100, Cost: 100000}},
}

slog.Info("info", "enemy", e, "spawn", 199)

Output:

2024-01-18T02:57.41 CET INFO: info 
    enemy:
        alive: true
        health: 10
        name: Bodo
        ammo:
            - forweapon: Railgun
              impact: 100
              cost: 100000
              range: 400
    spawn: 199

See example/example.go for usage.

Installation

Execute this to add the module to your project:

go get github.com/tlinden/yadu

Configuration

You can tweak the behavior of the handler as any other handler by using the Options struct:

func removeTime(_ []string, a slog.Attr) slog.Attr {
        if a.Key == slog.TimeKey {
                return slog.Attr{}
        }
        return a
}

opts := &yadu.Options{
           Level: slog.LevelDebug,
           ReplaceAttr: removeTime,
        }

Pass this object to yadu.NewHandler().

Because you can pass whole structs to the logger which will be dumped using YAML, there's also a way to exclude fields from being printed:

type User struct {
  Id int
  User string
  Pass string `yaml:"-"`
}

If you're already using YAML tags for other purposes you can also just add a LogValue() method to your struct, which will be called by slog. Refer to the slog documentation how to use it.

You can also modify the time format using yadu.Options.TimeFormat.

Acknowledgements

I wrote most of the code with the help of the humane slog handler. Also helpfull was the guide to writing slog handlers.

• humane slog handler
• A Guide to Writing slog Handlers
• A Comprehensive Guide to Structured Logging in Go

LICENSE

This module is published under the terms of the BSD 3-Clause License. Please read the file LICENSE for details.

Author

Thomas von Dein <git |AT| daemon.de>