Logger
A lightweight, structured logging package for Go.
Features
- Simple API: Format strings and structured fields
- Global & Instance: Use default global logger or create custom instances
- Context Support: Extract trace_id from context automatically
- Multiple Formats: Text (default) and JSON
- Level Filtering: DEBUG, INFO, WARN, ERROR, FATAL, PANIC
- No Dependencies: Standard library only
Quick Start
import "gitea.loveuer.com/loveuer/upkg/logger"
// Global logger (default)
logger.Info("hello %s", "world")
logger.Error("failed: %v", err)
// With fields
logger.InfoField("user logged in",
"user_id", 123,
"action", "login",
)
// Context with trace_id
ctx := context.WithValue(ctx, "trace_id", "req-123")
logger.InfoCtx(ctx, "request processed")
Custom Logger
log := logger.New(
logger.WithLevel(logger.DEBUG),
logger.WithFormat(logger.JSON),
logger.WithOutput(logger.Stdout),
logger.WithCaller(true),
)
log.Info("custom logger")
log.InfoField("event", "key", "value")
API
Level Methods
log.Debug(format string, args ...)
log.Info(format string, args ...)
log.Warn(format string, args ...)
log.Error(format string, args ...)
log.Fatal(format string, args ...)
log.Panic(format string, args ...)
Context Methods
log.InfoCtx(ctx, format string, args ...)
// Automatically adds trace_id from ctx as a field
Field Methods
log.InfoField(message string, keyValues ...interface{})
// Example: log.InfoField("user created", "id", 123, "name", "john")
Configuration Options
logger.New(
WithLevel(INFO), // Minimum log level
WithFormat(TEXT), // TEXT or JSON
WithOutput(Stdout), // Stdout, Stderr, or use WithOutputFile
WithOutputFile("/path/to.log"), // Write to file
WithCaller(true), // Include file:line in output
WithFieldKey("trace_id"), // Context field key name
WithPrefix("myapp"), // Text format prefix
WithTimeFormat("2006-01-02"), // Custom time format
)
Text Format Output
2026-01-17 15:30:45 INFO hello world
2026-01-17 15:30:45 INFO user logged in user_id=123 action=login
JSON Format Output
{"time":"2026-01-17T15:30:45Z","level":"INFO","message":"hello world"}
{"time":"2026-01-17T15:30:45Z","level":"INFO","message":"user logged in","user_id":123,"action":"login"}
Global Functions
import "gitea.loveuer.com/loveuer/upkg/logger"
func Debug(format string, args ...)
func Info(format string, args ...)
func Warn(format string, args ...)
func Error(format string, args ...)
func Fatal(format string, args ...)
func Panic(format string, args ...)
func DebugCtx(ctx context.Context, format string, args ...)
func InfoCtx(ctx context.Context, format string, args ...)
func WarnCtx(ctx context.Context, format string, args ...)
func ErrorCtx(ctx context.Context, format string, args ...)
func FatalCtx(ctx context.Context, format string, args ...)
func PanicCtx(ctx context.Context, format string, args ...)
func DebugField(message string, keyValues ...interface{})
func InfoField(message string, keyValues ...interface{})
func WarnField(message string, keyValues ...interface{})
func ErrorField(message string, keyValues ...interface{})
func FatalField(message string, keyValues ...interface{})
func PanicField(message string, keyValues ...interface{})