checker: split monolithic rule into per-concern rules

checker/rules_resolution.go

@@ -0,0 +1,48 @@
+package checker
+
+import (
+	"context"
+	"fmt"
+
+	sdk "git.happydns.org/checker-sdk-go/checker"
+)
+
+// resolutionRule flags nameservers whose host names could not be resolved
+// to any IP address. An unresolvable NS is effectively dead weight in the
+// delegation and is its own concern (distinct from any answer-posture check).
+type resolutionRule struct{}
+
+func (r *resolutionRule) Name() string { return "ns_resolution" }
+func (r *resolutionRule) Description() string {
+	return "Verifies that every nameserver host name declared in the delegation resolves to at least one IP address"
+}
+
+func (r *resolutionRule) Evaluate(ctx context.Context, obs sdk.ObservationGetter, _ sdk.CheckerOptions) []sdk.CheckState {
+	report, errSt := loadReport(ctx, obs, "ns_resolution_error")
+	if errSt != nil {
+		return []sdk.CheckState{*errSt}
+	}
+
+	var out []sdk.CheckState
+	for _, srv := range report.Servers {
+		if srv.ResolutionError == "" {
+			continue
+		}
+		out = append(out, sdk.CheckState{
+			Status:  sdk.StatusCrit,
+			Message: fmt.Sprintf("DNS resolution failed: %s", srv.ResolutionError),
+			Code:    "ns_resolution_failed",
+			Subject: srv.Name,
+			Meta:    map[string]any{"name": srv.Name},
+		})
+	}
+
+	if len(out) == 0 {
+		return []sdk.CheckState{{
+			Status:  sdk.StatusOK,
+			Message: "every nameserver host name resolves to at least one IP address",
+			Code:    "ns_resolution_ok",
+		}}
+	}
+	return out
+}