Logging with Go's slog

This Go package provides a customizable logger based on Go's standard slog package. It supports two output modes:

• JSON Output: Uses the built-in slog.JSONHandler for structured log output.
• Console Output: Uses a colorized, pretty-printed output via a custom ConsoleHandler. Ideal for human-friendly logging during development.

Features

• Log Levels:
  Controls verbosity using log levels in each logger (ERROR, WARN, INFO, DEBUG). You can configure the logger's verbosity by setting a level counter.

• Custom Handlers:
  Depending on the provided handler type ("default" or "console"), the logger either outputs JSON or pretty, colored log messages.

• Structured Logging:
  Support for structured key/value logging that can be extended with additional context or grouped attributes.

• Colorized Console Output:
  The ConsoleHandler formats time, level, and messages with ANSI color codes. Attributes and groups are printed with an appropriate indentation level, their contents prints as pretty JSON.

ConsoleHandler screenshot

Installation

To use this package in your project, simply install it using Go modules. For example:

go get github.com/voler88/logging

Usage

Below is a basic example of how to create and use the logger:

package main

import (
    "os"

    "github.com/voler88/logging"
)

func main() {
    // Create a new logger that writes to stdout.
    // Use "default" for JSON logging or "console" for pretty console output.
    logger := logging.New(os.Stdout, "console")

    // Set the desired verbosity level (0=ERROR, 1=WARN, 2=INFO, 3 or higher=DEBUG).
    if err := logger.SetLevel(logging.LevelDebug); err != nil {
        panic(err)
    }

    // Log messages at various levels.
    logger.Error("An error occurred", "code", 123)
    logger.Warn("This is a warning", "file", "server.go")
    logger.Info("Server started", "port", 8080)
    logger.Debug("Debug info", "config", map[string]string{"env": "dev"})
}

Testing

Unit tests are provided in the package and can be run using:

go test ./...
go test -bench=. ./...

Tests cover:

• Handler selection and output format.
• Log level filtering via SetLevel.
• Benchmark for default (JSON) and Console handlers.

Contributing

Feel free to open issues or pull requests if you have improvements or bug fixes.

License

This project is licensed under the MIT License.