feat: user service

user/internal/service/shared/observability.go

@@ -0,0 +1,73 @@
+package shared
+
+import (
+	"context"
+	"log/slog"
+
+	"galaxy/user/internal/logging"
+)
+
+// LogServiceOutcome writes one structured service-level outcome log with a
+// stable severity derived from err and with trace fields attached when ctx
+// carries an active span.
+func LogServiceOutcome(logger *slog.Logger, ctx context.Context, message string, err error, attrs ...any) {
+	if logger == nil {
+		logger = slog.Default()
+	}
+
+	attrs = append(attrs, logging.TraceAttrsFromContext(ctx)...)
+
+	switch {
+	case err == nil:
+		logger.InfoContext(ctx, message, attrs...)
+	case isExpectedServiceErrorCode(CodeOf(err)):
+		logger.WarnContext(ctx, message, append(attrs, "error", err.Error())...)
+	default:
+		logger.ErrorContext(ctx, message, append(attrs, "error", err.Error())...)
+	}
+}
+
+// MetricOutcome returns the stable low-cardinality outcome label derived from
+// err for service metrics.
+func MetricOutcome(err error) string {
+	if err == nil {
+		return "success"
+	}
+
+	code := CodeOf(err)
+	if code == "" {
+		return ErrorCodeInternalError
+	}
+
+	return code
+}
+
+// LogEventPublicationFailure writes one structured error log for an auxiliary
+// post-commit event publication failure.
+func LogEventPublicationFailure(logger *slog.Logger, ctx context.Context, eventType string, err error, attrs ...any) {
+	if err == nil {
+		return
+	}
+	if logger == nil {
+		logger = slog.Default()
+	}
+
+	attrs = append(attrs,
+		"event_type", eventType,
+		"error", err.Error(),
+	)
+	attrs = append(attrs, logging.TraceAttrsFromContext(ctx)...)
+
+	logger.ErrorContext(ctx, "auxiliary event publication failed", attrs...)
+}
+
+func isExpectedServiceErrorCode(code string) bool {
+	switch code {
+	case ErrorCodeInvalidRequest,
+		ErrorCodeConflict,
+		ErrorCodeSubjectNotFound:
+		return true
+	default:
+		return false
+	}
+}