logger

Overview ¶

Package logger provides structured logging with context extraction and Sentry integration.

This package extends the standard library's log/slog with two key capabilities: automatic context-based attribute injection and optional Sentry error reporting. It is designed for production applications that need consistent, enriched logs with minimal boilerplate.

Overview ¶

The package provides:

• Context extractors that automatically inject request-scoped values (e.g., request IDs, user IDs)
• A decorator pattern that wraps any slog.Handler to add extraction behavior
• Sentry integration for error tracking with graceful fallback when unconfigured
• Multi-handler support for routing logs to multiple destinations

Basic Usage ¶

Create a logger with context extractors:

// Define an extractor for request ID
requestIDExtractor := func(ctx context.Context) (slog.Attr, bool) {
	if reqID, ok := ctx.Value("request_id").(string); ok && reqID != "" {
		return slog.String("request_id", reqID), true
	}
	return slog.Attr{}, false
}

// Create logger with extractors
log := logger.New(requestIDExtractor)

// Use with context - request_id is automatically included
ctx := context.WithValue(context.Background(), "request_id", "abc-123")
log.InfoContext(ctx, "request processed", slog.Int("status", 200))
// Output: {"level":"INFO","msg":"request processed","status":200,"request_id":"abc-123"}

Sentry Integration ¶

For production error tracking, use NewWithSentry:

cfg := logger.SentryConfig{
	DSN:         os.Getenv("SENTRY_DSN"),
	Environment: "production",
	MinLevel:    slog.LevelWarn, // Send warnings and errors to Sentry
}

log := logger.NewWithSentry(cfg, requestIDExtractor)

// Errors create Issues in Sentry, warnings are stored for context
log.ErrorContext(ctx, "payment failed", slog.String("user_id", "user-456"))

If SENTRY_DSN is empty, the logger gracefully falls back to stdout-only logging, making it safe to use the same code path in development and production.

Context Extractors ¶

A ContextExtractor is a function that extracts a log attribute from context:

type ContextExtractor func(ctx context.Context) (slog.Attr, bool)

Extractors are called on every log call, ensuring fresh values for request-scoped data. Return false from the extractor to skip adding the attribute for that log entry.

Common extractors include:

• Request ID extractor for HTTP request tracing
• User ID extractor for authentication context
• Tenant ID extractor for multi-tenant applications

Handler Decoration ¶

The LogHandlerDecorator can wrap any slog.Handler to add context extraction:

// Wrap a custom handler
jsonHandler := slog.NewJSONHandler(os.Stdout, &slog.HandlerOptions{Level: slog.LevelDebug})
decorated := logger.NewLogHandlerDecorator(jsonHandler, extractors...)
log := slog.New(decorated)

This allows using context extractors with any handler implementation.

Architecture ¶

The package uses several design patterns:

Decorator Pattern: LogHandlerDecorator wraps any slog.Handler, intercepting Handle calls to inject extracted attributes before delegating to the underlying handler.

Multi-Handler Pattern: An internal multiHandler forwards logs to multiple destinations, enabling simultaneous stdout and Sentry logging.

Graceful Degradation: Sentry integration fails gracefully - if DSN is missing or initialization fails, logging continues to stdout without disruption.