1 files changed, 136 insertions, 0 deletions
diff --git a/logging/log.go b/logging/log.go
new file mode 100644
index 0000000..8dc8017
--- /dev/null
+++ b/logging/log.go
@@ -0,0 +1,136 @@
+// Package logging provides helpers for context-aware logging using Go's slog package.
+//
+// It allows attaching loggers to context.Context for structured logging,
+// recovering and logging panics with stack traces,
+// and provides a simple package-level logger setup function.
+package logging
+
+import (
+	"context"
+	"fmt"
+	"io"
+	"log/slog"
+	"os"
+	"runtime"
+	"strings"
+)
+
+type ctxLoggerKeyType struct{}
+
+var ctxLoggerKey = ctxLoggerKeyType{}
+
+// WithLogger returns a new context derived from ctx that carries the provided slog.Logger.
+//
+// Typical usage:
+//
+//	ctx = logging.WithLogger(ctx, logger)
+func WithLogger(ctx context.Context, logger *slog.Logger) context.Context {
+	return context.WithValue(ctx, ctxLoggerKey, logger)
+}
+
+// FromContext retrieves the slog.Logger stored in ctx if any.
+// If no logger is attached to the context, returns slog.Default().
+func FromContext(ctx context.Context) *slog.Logger {
+	if logger, ok := ctx.Value(ctxLoggerKey).(*slog.Logger); ok {
+		return logger
+	}
+	return slog.Default()
+}
+
+// With returns a new slog.Logger augmented with the passed key-value pairs,
+// and a new context holding this logger.
+//
+// Typical usage:
+//
+//	logger, ctx := logging.With(ctx, "user_id", userID)
+func With(ctx context.Context, args ...any) (*slog.Logger, context.Context) {
+	logger := FromContext(ctx)
+	logger = logger.With(args...)
+	ctx = WithLogger(ctx, logger)
+	return logger, ctx
+}
+
+// WithGroup returns a new slog.Logger grouped under name,
+// and a new context holding this logger.
+//
+// Typical usage:
+//
+//	logger, ctx := logging.WithGroup(ctx, "http")
+func WithGroup(ctx context.Context, name string) (*slog.Logger, context.Context) {
+	logger := FromContext(ctx)
+	logger = logger.WithGroup(name)
+	ctx = WithLogger(ctx, logger)
+	return logger, ctx
+}
+
+// RecoverAndLog logs a recovered panic or error with a stack trace using the logger from ctx.
+//
+// Typically used in a deferred recover block:
+//
+//	defer func() {
+//	  if err := recover(); err != nil {
+//	    logging.RecoverAndLog(ctx, "Panic recovered", err)
+//	    os.Exit(1)
+//	  }
+//	}()
+func RecoverAndLog(ctx context.Context, msg string, err any) {
+	const size = 64 << 10 // 64 KB stack trace buffer
+	buf := make([]byte, size)
+	buf = buf[:runtime.Stack(buf, false)]
+	logger := FromContext(ctx)
+	logger.ErrorContext(ctx, msg, "Error", err, "stack", string(buf))
+}
+
+type LogSink string
+
+const (
+	SinkStdout LogSink = "stdout"
+	SinkStderr LogSink = "stderr"
+	SinkFile   LogSink = "file"
+)
+
+type LogConfig struct {
+	Level  slog.Level `toml:"level"`
+	Sink   LogSink    `toml:"sink"`
+	Format string     `toml:"format"`
+	File   string     `toml:"file"`
+}
+
+func Setup(cfg LogConfig) error {
+	var w io.Writer
+
+	switch cfg.Sink {
+	case SinkStdout, "":
+		w = os.Stdout
+	case SinkStderr:
+		w = os.Stderr
+	case SinkFile:
+		if cfg.File == "" {
+			return fmt.Errorf("log sink set to 'file' but no file path provided")
+		}
+		f, err := os.OpenFile(cfg.File, os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0644)
+		if err != nil {
+			return fmt.Errorf("failed to open log file: %w", err)
+		}
+		w = f
+	default:
+		return fmt.Errorf("unsupported log sink: %s", cfg.Sink)
+	}
+
+	var handler slog.Handler
+	opts := &slog.HandlerOptions{
+		Level: cfg.Level,
+	}
+
+	switch strings.ToLower(cfg.Format) {
+	case "text":
+		handler = slog.NewTextHandler(w, opts)
+	case "json", "":
+		handler = slog.NewJSONHandler(w, opts)
+	default:
+		return fmt.Errorf("unsupported log format: %s", cfg.Format)
+	}
+
+	slog.SetDefault(slog.New(handler))
+	return nil
+}