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/v2 

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>