slogo

README

SLogo

SLogo is a lightweight, customizable formatter and handler for the Go standard library's log/slog package. It enhances logging capabilities by providing structured logging with custom formatters and multiple handler support.

Features

• Custom Formatters: Format struct fields, errors, and other complex data types in a human-readable format
• Multiple Handler Support: Route logs to multiple destinations using the slogmulti fanout capability
• Configurable Options: Easily customize logging behavior with functional options
• Enhanced Error Reporting: Capture error details including type and message
• Struct Field Handling: Control how struct fields are logged, including field redaction
• JSON Tag Support: Respects JSON field tags for naming consistency

Installation

go get github.com/naicoi92/slogo

Quick Start

package main

import (
    "errors"
    "log/slog"
    "os"
    
    "github.com/naicoi92/slogo"
)

func main() {
    // Create a new logger with default settings
    logger := slog.New(
        slogo.NewHandler(
            os.Stdout,
            &slog.HandlerOptions{
                Level:     slog.LevelInfo,
                AddSource: true,
            },
        ),
    )
    
    // Set as default logger
    slog.SetDefault(logger)
    
    // Log messages
    slog.Info("Hello from SLogo")
    
    // Log with attributes
    slog.Info("User login", "user_id", 12345, "action", "login")
    
    // Log structs
    type User struct {
        ID        int    `json:"id"`
        Username  string `json:"username"`
        Password  string `json:"password" slog:"restrict"` // This field will be redacted
        Email     string `json:"email"`
    }
    
    user := User{
        ID:       1,
        Username: "johndoe",
        Password: "secret123",
        Email:    "john@example.com",
    }
    
    slog.Info("User details", "user", user)
    
    // Log errors with type and message information
    if err := errors.New("an example error"); err != nil {
        slog.Error("Operation failed", "error", err)
    }
}

Complex Struct Example

SLogo excels at formatting complex nested structs:

type User struct {
    ID        int        `json:"id"`
    Username  string     `json:"username"`
    Password  string     `json:"password" slog:"restrict"` // This field will be redacted
    Email     string     `json:"email"`
    IpAddress netip.Addr `json:"ip_address"`
    Members   []*User    `json:"members"`
}

// Create a user with nested members
ip, _ := netip.ParseAddr("10.0.0.1")
user := User{
    ID:        1,
    Username:  "johndoe",
    Password:  "secret123",
    Email:     "john@example.com",
    IpAddress: ip,
    Members: []*User{
        {
            ID:       2,
            Username: "janedoe",
        },
        {
            ID:        3,
            Username:  "alice",
            IpAddress: ip,
        },
    },
}

slog.Info("User details", "user", user)

Configuration Options

SLogo provides several configuration options through functional options:

WithSlogor

Use the underlying slogor handler:

logger := slog.New(slogo.NewHandler(os.Stdout, &slog.HandlerOptions{
    Level: slog.LevelInfo,
}, slogo.WithSlogor()))

WithSlogHandler

Add a custom slog.Handler:

customHandler := // your custom handler
logger := slog.New(slogo.NewHandler(os.Stdout, &slog.HandlerOptions{}, 
    slogo.WithSlogHandler(customHandler)))

WithFormatter

Add a custom formatter:

customFormatter := // your custom formatter
logger := slog.New(slogo.NewHandler(os.Stdout, &slog.HandlerOptions{}, 
    slogo.WithFormatter(customFormatter)))

Built-in Formatters

FormatStruct

The FormatStruct formatter handles struct data types and provides special handling for struct fields:

• Uses JSON field tags for field names if available
• Recursively formats nested structs and slices
• Skips empty values
• Respects slog struct tags:
  • -: Skip this field entirely
  • restrict: Redact the field value (shows "[REDACTED]")

Example of formatting a struct with redacted fields:

[id=1, username=johndoe, password=[REDACTED], email=john@example.com, ip_address=10.0.0.1, members=[[id=2, username=janedoe], [id=3, username=alice, ip_address=10.0.0.1]]]

FormatError

The FormatError formatter enhances error logging by capturing:

• Error message
• Error type

Example of formatted error output:

[Message=an example error, Type=*errors.errorString]

Dependencies

SLogo depends on the following packages:

• github.com/samber/slog-formatter
• github.com/samber/slog-multi
• gitlab.com/greyxor/slogor

Complete Example

Check out the example directory for a complete working example of SLogo.

License

This project is licensed under the terms found in the LICENSE file.

Contributing

Contributions are welcome! Please feel free to submit a Pull Request.

1. Fork the repository
2. Create your feature branch (git checkout -b feature/amazing-feature)
3. Commit your changes (git commit -m 'Add some amazing feature')
4. Push to the branch (git push origin feature/amazing-feature)
5. Open a Pull Request

Documentation

Index

• func FormatError() slogformatter.Formatter
• func FormatStruct() slogformatter.Formatter
• func NewHandler(w io.Writer, opts *slog.HandlerOptions, options ...Option) slog.Handler
• type ErrorStruct
• type Option
  • func WithFormatter(formatter slogformatter.Formatter) Option
  • func WithSlogHandler(handler slog.Handler) Option
  • func WithSlogor() Option
• type SlogoHandler

Functions

func FormatError

func FormatError() slogformatter.Formatter

func FormatStruct

func FormatStruct() slogformatter.Formatter

func NewHandler

func NewHandler(w io.Writer, opts *slog.HandlerOptions, options ...Option) slog.Handler

Types

type ErrorStruct

type ErrorStruct struct {
	Type    string
	Message string
}

type Option

type Option func(*SlogoHandler)

func WithFormatter

func WithFormatter(formatter slogformatter.Formatter) Option

func WithSlogHandler

func WithSlogHandler(handler slog.Handler) Option

func WithSlogor

func WithSlogor() Option

type SlogoHandler

type SlogoHandler struct {
	// contains filtered or unexported fields
}