Add core modules (SSH args parser, cache, resolver, NetBox client) with tests

internal/resolver/management.go

@@ -0,0 +1,53 @@
+package resolver
+
+import (
+	"context"
+	"fmt"
+	"net"
+
+	"git.zb-server.de/Sebi/ssh-netbox-wrapper/internal/netbox"
+)
+
+// ManagementSubnetStrategy finds the first IP of a host that falls within
+// one of the configured management subnets.
+type ManagementSubnetStrategy struct {
+	subnets []*net.IPNet
+}
+
+func NewManagementSubnetStrategy(cidrs []string) (*ManagementSubnetStrategy, error) {
+	nets := make([]*net.IPNet, 0, len(cidrs))
+	for _, cidr := range cidrs {
+		_, ipNet, err := net.ParseCIDR(cidr)
+		if err != nil {
+			return nil, fmt.Errorf("invalid CIDR %q: %w", cidr, err)
+		}
+		nets = append(nets, ipNet)
+	}
+	return &ManagementSubnetStrategy{subnets: nets}, nil
+}
+
+func (s *ManagementSubnetStrategy) Name() string { return "management_subnet" }
+
+func (s *ManagementSubnetStrategy) Resolve(ctx context.Context, entry *netbox.HostEntry, client *netbox.Client) (string, error) {
+	if len(s.subnets) == 0 {
+		return "", ErrNoIP
+	}
+
+	ips, err := client.GetIPs(ctx, *entry)
+	if err != nil {
+		return "", fmt.Errorf("fetching IPs: %w", err)
+	}
+
+	for _, rawIP := range ips {
+		ip := net.ParseIP(rawIP)
+		if ip == nil {
+			continue
+		}
+		for _, subnet := range s.subnets {
+			if subnet.Contains(ip) {
+				return rawIP, nil
+			}
+		}
+	}
+	return "", ErrNoIP
+}