ShawnMilo / logger

A simple Go JSON logger.

logger

A simple JSON logger for Go.

It uses a context.Context to store values which will then be logged along with each message.

It is possible to recover these values but this should not be used to pass arguments into functions. Do not use this to pass required arguments.

Using Error or Errorf will also log a stack trace to help you easily find the source of the error.

Usage

The API is very small.

1. Create a logger with logger.New()
2. (Optional) Call SetDebug(bool) to enable debug logging, or use the DEBUG environment variable
3. Log using Debug, Info, Error, Debugf, Infof, or Errorf
4. (Optional) As desired, use With to add a value to the loggers "tags"
5. (Optional) Recover a value from the tags using ValueString

package main

import (
	"context"
	"fmt"

	"github.com/ShawnMilo/logger"
)

func main() {
	lg := logger.New()
	lg.Info("first message")
	ctx := context.Background()
	ctx = lg.With(ctx, "user_id", "123")
	lg.Info("second message")
	stuff(ctx)
}

func stuff(ctx context.Context) {
	lg := logger.FromContext(ctx)
	ctx = lg.With(ctx, "function", "stuff")
	lg.Info("thing message")
	userID := lg.ValueString("user_id")
	fmt.Printf("user_id: %s\n", userID)
	crash(ctx)
}

func crash(ctx context.Context) {
	lg := logger.FromContext(ctx)
	lg.Error("broken")
}

Output:

{"level":"INFO","event_time":"2021-12-19T03:26:15Z","message":"first message"}
{"level":"INFO","event_time":"2021-12-19T03:26:15Z","message":"second message","tags":{"user_id":"123"}}
{"level":"INFO","event_time":"2021-12-19T03:26:15Z","message":"thing message","tags":{"function":"stuff","user_id":"123"}}
user_id: 123
{"level":"ERROR","event_time":"2021-12-19T03:26:15Z","message":"broken","trace":"main.go:main.crash:30, main.go:main.stuff:25, main.go:main.main:16, proc.go:runtime.main:255","tags":{"function":"stuff","user_id":"123"}}