loggie

README

loggie 🧠⚡️ — Context-Aware Logger for Go

Context-aware, pluggable logger for Go web applications.
No more passing logger through every function — just use context.Context.

---

🚀 What is loggie?

loggie helps you embed a structured logger inside context.Context, so you can log from any layer — service, repository, or handler — with a consistent trace_id, user_id, or any custom field.

It supports Zap, Logrus, OpenTelemetry, and works with any web framework.

---

✨ Features

✅ Structured logging via context.Context
✅ Auto-generated trace_id per request
✅ OTEL-compatible (extracts trace_id from spans)
✅ Custom fields via loggie.WithCustomField()
✅ Framework-agnostic logger injection
✅ Zap / Logrus support
✅ No-op fallback logger
✅ Fx lifecycle and context cancellation compatible

---

📦 Installation

go get github.com/ditthkr/loggie

---

🧠 Injecting Logger in Middleware

Use loggie.Injection(ctx, logger) inside any middleware, from any web framework.

ctx, traceId := loggie.Injection(req.Context(), logger)

✅ Fiber

app.Use(func(c *fiber.Ctx) error {
	ctx, traceId := loggie.Injection(c.UserContext(), logger)
	c.SetUserContext(ctx)
	c.Set("X-Trace-Id", traceId)
	return c.Next()
})

✅ Gin

r.Use(func(c *gin.Context) {
	ctx, traceId := loggie.Injection(c.Request.Context(), logger)
	c.Request = c.Request.WithContext(ctx)
	c.Writer.Header().Set("X-Trace-Id", traceId)
	c.Next()
})

✅ Echo

e.Use(func(next echo.HandlerFunc) echo.HandlerFunc {
	return func(c echo.Context) error {
		ctx, traceId := loggie.Injection(c.Request().Context(), logger)
		req := c.Request().WithContext(ctx)
		c.SetRequest(req)
		c.Response().Header().Set("X-Trace-Id", traceId)
		return next(c)
	}
})

---

🔌 Logger Interface

type Logger interface {
    Info(msg string, fields ...any)
    Error(msg string, fields ...any)
    With(fields ...any) Logger
}

✅ Supported Adapters

Logger	Package
Zap	loggie.ZapLogger
Logrus	loggie/logruslogger

---

📄 Usage Example

log := loggie.FromContext(ctx)
log.Info("Order created", "user_id", 123)

📤 Output (Zap or Logrus):

{
  "msg": "Order created",
  "trace_id": "...",
  "user_id": 123
}

---

🧰 Utilities

Function	Description
Injection(ctx, logger)	Inject logger + trace_id into ctx
FromContext(ctx)	Get logger with fields from ctx
WithTraceId(ctx)	Add trace_id manually
TraceId(ctx)	Get trace_id (auto or OTEL)
WithLogger(ctx, logger)	Attach logger
WithCustomField(ctx, key, val)	Add any key-value field
DefaultLogger()	Get fallback no-op logger

---

🌐 OpenTelemetry Support

If a context already contains an OTEL span, loggie will extract its trace_id:

span := trace.SpanFromContext(ctx)
traceId := span.SpanContext().TraceId().String()

You don’t need to do anything extra — TraceId(ctx) handles it automatically.

---

📃 License

MIT © 2025 @ditthkr

Documentation

Index

• func Injection(ctx context.Context, logger Logger) (context.Context, string)
• func TraceId(ctx context.Context) string
• func WithCustomField(ctx context.Context, key string, value any) context.Context
• func WithLogger(ctx context.Context, logger Logger) context.Context
• func WithTraceId(ctx context.Context) (context.Context, string)
• type Logger
  • func DefaultLogger() Logger
  • func FromContext(ctx context.Context) Logger
• type LogrusLogger
  • func (l *LogrusLogger) Error(msg string, fields ...any)
  • func (l *LogrusLogger) Info(msg string, fields ...any)
  • func (l *LogrusLogger) With(fields ...any) Logger
• type ZapLogger
  • func (r *ZapLogger) Error(msg string, fields ...any)
  • func (r *ZapLogger) Info(msg string, fields ...any)
  • func (r *ZapLogger) With(fields ...any) Logger

Functions

func Injection

func Injection(ctx context.Context, logger Logger) (context.Context, string)

Injection injects logger and trace_id into a context. Use it inside any web framework middleware.

func TraceId

func TraceId(ctx context.Context) string

TraceId returns the current trace Id from the context.

It checks the following, in order:

1. If an OpenTelemetry span exists in the context and has a valid TraceId, it is returned.
2. If a local trace Id was previously stored in context via WithTraceId(), it is returned.
3. Otherwise, a new UUId is generated and returned.

func WithCustomField

func WithCustomField(ctx context.Context, key string, value any) context.Context

WithCustomField adds a custom key-value pair to the context. These fields will be automatically injected into log output.

func WithLogger

func WithLogger(ctx context.Context, logger Logger) context.Context

WithLogger stores the given logger inside the context. It can be retrieved later using FromContext.

func WithTraceId

func WithTraceId(ctx context.Context) (context.Context, string)

WithTraceId returns a new context with a generated or existing trace Id, and the trace Id itself as a string.

It first checks if a trace Id exists in the context, otherwise it generates a new UUId. This function is compatible with both OpenTelemetry-based contexts and local fallback mode.

Types

type Logger

type Logger interface {
	Info(msg string, fields ...any)
	Error(msg string, fields ...any)
	With(fields ...any) Logger
}

Logger is the main interface used for logging. It mimics a simplified version of structured loggers like Zap or Logrus.

func DefaultLogger

func DefaultLogger() Logger

DefaultLogger returns the internal fallback logger used when no logger is found. This logger does nothing and is safe to call anywhere.

func FromContext

func FromContext(ctx context.Context) Logger

FromContext retrieves the logger from context. If no logger is found, it returns a default no-op logger.

type LogrusLogger

type LogrusLogger struct {
	L *logrus.Entry
}

func (*LogrusLogger) Error

func (l *LogrusLogger) Error(msg string, fields ...any)

func (*LogrusLogger) Info

func (l *LogrusLogger) Info(msg string, fields ...any)

func (*LogrusLogger) With

func (l *LogrusLogger) With(fields ...any) Logger

type ZapLogger

type ZapLogger struct {
	L *zap.Logger
}

func (*ZapLogger) Error

func (r *ZapLogger) Error(msg string, fields ...any)

func (*ZapLogger) Info

func (r *ZapLogger) Info(msg string, fields ...any)

func (*ZapLogger) With

func (r *ZapLogger) With(fields ...any) Logger