NetworkTool/server/internal/discovery/discovery_test.go

package discovery

import (
	"net"
	"testing"
)

func TestBestSourceIPForRemoteUsesMostSpecificMatchingSubnet(t *testing.T) {
	addresses := []net.Addr{
		mustIPNet(t, "169.254.101.3/16"),
		mustIPNet(t, "192.168.229.138/24"),
	}

	actual := bestSourceIPForRemote(addresses, net.ParseIP("192.168.229.1"))
	if actual == nil || actual.String() != "192.168.229.138" {
		t.Fatalf("expected source 192.168.229.138, got %v", actual)
	}
}

func TestBestSourceIPForRemoteUsesLinkLocalAddressForLinkLocalClient(t *testing.T) {
	addresses := []net.Addr{
		mustIPNet(t, "169.254.101.3/16"),
		mustIPNet(t, "192.168.229.138/24"),
	}

	actual := bestSourceIPForRemote(addresses, net.ParseIP("169.254.100.1"))
	if actual == nil || actual.String() != "169.254.101.3" {
		t.Fatalf("expected source 169.254.101.3, got %v", actual)
	}
}

func TestBestSourceIPForRemoteReturnsNilWithoutMatchingSubnet(t *testing.T) {
	addresses := []net.Addr{mustIPNet(t, "169.254.101.3/16")}
	if actual := bestSourceIPForRemote(addresses, net.ParseIP("192.168.229.1")); actual != nil {
		t.Fatalf("expected no matching source, got %v", actual)
	}
}

func TestBroadcastResponseTargetUsesRequesterPort(t *testing.T) {
	remote := &net.UDPAddr{IP: net.ParseIP("192.168.44.1"), Port: 55869}
	target := broadcastResponseTarget(remote)
	if !target.IP.Equal(net.IPv4bcast) || target.Port != remote.Port {
		t.Fatalf("expected 255.255.255.255:%d, got %s", remote.Port, target)
	}
}

func mustIPNet(t *testing.T, cidr string) *net.IPNet {
	t.Helper()
	ip, network, err := net.ParseCIDR(cidr)
	if err != nil {
		t.Fatal(err)
	}
	network.IP = ip
	return network
}