Initial commit: IT Nexus Web-App

nexus-scanner/internal/modules/dnsreverse/dnsreverse.go

@@ -0,0 +1,94 @@
+// Package dnsreverse implements the dns_reverse module.
+// It enriches already-known hosts by performing reverse-DNS lookups
+// for every host that has no hostname recorded yet.
+package dnsreverse
+
+import (
+	"context"
+	"fmt"
+	"log/slog"
+	"net"
+	"strings"
+	"time"
+
+	"github.com/cereda-systems/nexus-scanner/internal/db"
+)
+
+// Module enriches hosts in the database with reverse-DNS hostnames.
+type Module struct {
+	site  string
+	store *db.Store
+	log   *slog.Logger
+}
+
+// New returns a new dns_reverse module.
+func New(site string, store *db.Store) *Module {
+	return &Module{
+		site:  site,
+		store: store,
+		log:   slog.With("module", "dns_reverse"),
+	}
+}
+
+func (m *Module) Name() string            { return "dns_reverse" }
+func (m *Module) Interval() time.Duration { return 10 * time.Minute }
+
+// Run looks up hostnames for all hosts that have none recorded yet.
+func (m *Module) Run(ctx context.Context) error {
+	scanID, err := m.store.BeginScan(m.Name())
+	if err != nil {
+		return fmt.Errorf("begin scan: %w", err)
+	}
+
+	scanErr := m.scan(ctx)
+	if endErr := m.store.EndScan(scanID, scanErr); endErr != nil {
+		m.log.Error("record scan end", "err", endErr)
+	}
+	return scanErr
+}
+
+func (m *Module) scan(ctx context.Context) error {
+	hosts, err := m.store.ListHosts("")
+	if err != nil {
+		return fmt.Errorf("list hosts: %w", err)
+	}
+
+	resolved := 0
+	for _, h := range hosts {
+		// Skip hosts that already have a hostname.
+		if h.Hostname != "" {
+			continue
+		}
+
+		select {
+		case <-ctx.Done():
+			return ctx.Err()
+		default:
+		}
+
+		names, err := net.DefaultResolver.LookupAddr(ctx, h.IP)
+		if err != nil {
+			// A lookup failure is not fatal — continue with the next host.
+			m.log.Debug("reverse lookup failed", "ip", h.IP, "err", err)
+			continue
+		}
+		if len(names) == 0 {
+			continue
+		}
+
+		// LookupAddr returns FQDNs with a trailing dot — strip it.
+		hostname := strings.TrimSuffix(names[0], ".")
+
+		h.Hostname = hostname
+		if err := m.store.UpsertHost(h); err != nil {
+			m.log.Error("upsert host", "ip", h.IP, "err", err)
+			continue
+		}
+
+		m.log.Info("hostname resolved", "ip", h.IP, "hostname", hostname)
+		resolved++
+	}
+
+	m.log.Info("scan complete", "checked", len(hosts), "resolved", resolved)
+	return nil
+}