use golang net lib to parse google json param [ecs]

[sanyo0714]

use net.ParseCIDR to parse edns_client_subnet.

[m13253]

Thank you for your contribution!

I remember I once used net.ParseCIDR for this, but later I rewrote it without net.ParseCIDR.
I forget the exact reason why net.ParseCIDR did not work. Perhaps it's because it couldn't handle IPv4-mapped-IPv6 well, or any other security or functional problems.

Perhaps the problem which prevented me from using net.ParseCIDR has already been fixed by Golang.
So would you please check whether the new code can handle any strange inputs you can come up with?

Thank you again!

[sanyo0714]

test for net.ParseCIDR

func TestParseCIDR(t *testing.T) {
	parseIp("2001:db8::/0")
	parseIp("2001:db8::/56")
	parseIp("2001:db8::/129")
	parseIp("2001:db8::")

	parseIp("127.0.0.1/0")
	parseIp("127.0.0.1/24")
	parseIp("127.0.0.1/33")
	parseIp("127.0.0.1")

	parseIp("test")
	parseIp("test/0")
	parseIp("test/24")
	parseIp("test/34")
	parseIp("test/56")
	parseIp("test/129")
}

func parseIp(ednsClientSubnet string) {
	ip, ipNet, err := net.ParseCIDR(ednsClientSubnet)

	if err != nil {
		log.Println(fmt.Sprintf("[error] ecs:%s ip:[%v]  ipNet:[%v]  err:[%v]\n", ednsClientSubnet, ip, ipNet, err))
		return
	}

	netmask, ipLen := ipNet.Mask.Size()
	log.Println(fmt.Sprintf("[info ] ecs:%s ip:[%v]  ipNet:[%v]  netmask:[%v]  ipLen:[%v]   err:[%v]\n", ednsClientSubnet, ip, ipNet, netmask, ipLen, err))
}

The results of

=== RUN   TestParseCIDR
2020/07/30 10:06:11 [info ] ecs:2001:db8::/0 ip:[2001:db8::]  ipNet:[::/0]  netmask:[0]  ipLen:[128]   err:[<nil>]
2020/07/30 10:06:11 [info ] ecs:2001:db8::/56 ip:[2001:db8::]  ipNet:[2001:db8::/56]  netmask:[56]  ipLen:[128]   err:[<nil>]
2020/07/30 10:06:11 [error] ecs:2001:db8::/129 ip:[<nil>]  ipNet:[<nil>]  err:[invalid CIDR address: 2001:db8::/129]
2020/07/30 10:06:11 [error] ecs:2001:db8:: ip:[<nil>]  ipNet:[<nil>]  err:[invalid CIDR address: 2001:db8::]
2020/07/30 10:06:11 [info ] ecs:127.0.0.1/0 ip:[127.0.0.1]  ipNet:[0.0.0.0/0]  netmask:[0]  ipLen:[32]   err:[<nil>]
2020/07/30 10:06:11 [info ] ecs:127.0.0.1/24 ip:[127.0.0.1]  ipNet:[127.0.0.0/24]  netmask:[24]  ipLen:[32]   err:[<nil>]
2020/07/30 10:06:11 [error] ecs:127.0.0.1/33 ip:[<nil>]  ipNet:[<nil>]  err:[invalid CIDR address: 127.0.0.1/33]
2020/07/30 10:06:11 [error] ecs:127.0.0.1 ip:[<nil>]  ipNet:[<nil>]  err:[invalid CIDR address: 127.0.0.1]
2020/07/30 10:06:11 [error] ecs:test ip:[<nil>]  ipNet:[<nil>]  err:[invalid CIDR address: test]
2020/07/30 10:06:11 [error] ecs:test/0 ip:[<nil>]  ipNet:[<nil>]  err:[invalid CIDR address: test/0]
2020/07/30 10:06:11 [error] ecs:test/24 ip:[<nil>]  ipNet:[<nil>]  err:[invalid CIDR address: test/24]
2020/07/30 10:06:11 [error] ecs:test/34 ip:[<nil>]  ipNet:[<nil>]  err:[invalid CIDR address: test/34]
2020/07/30 10:06:11 [error] ecs:test/56 ip:[<nil>]  ipNet:[<nil>]  err:[invalid CIDR address: test/56]
2020/07/30 10:06:11 [error] ecs:test/129 ip:[<nil>]  ipNet:[<nil>]  err:[invalid CIDR address: test/129]
--- PASS: TestParseCIDR (0.00s)
PASS

[m13253]

The test fails with IPv4-mapped-IPv6 addresses:

parseIp("::ffff:7f00:1/0")
parseIp("::ffff:7f00:1/120")
parseIp("::ffff:7f00:1")
parseIp("127.0.0.1/0")
parseIp("127.0.0.1/24")
parseIp("127.0.0.1")

net.ParseCIDR cannot distinguish between these two cases. And if we write additional logic to address this issue, we might write more code than the original split-then-parse version.

[sanyo0714]

func TestEdns0SubnetParseCIDR(t *testing.T) {
	// init dns Msg
	msg := new(dns.Msg)
	msg.Id = dns.Id()
	msg.SetQuestion(dns.Fqdn("example.com"), 1)

	// init edns0Subnet
	edns0Subnet := new(dns.EDNS0_SUBNET)
	edns0Subnet.Code = dns.EDNS0SUBNET
	edns0Subnet.SourceScope = 0

	// init opt
	opt := new(dns.OPT)
	opt.Hdr.Name = "."
	opt.Hdr.Rrtype = dns.TypeOPT
	opt.SetUDPSize(dns.DefaultMsgSize)

	opt.Option = append(opt.Option, edns0Subnet)
	msg.Extra = append(msg.Extra, opt)

	// ------------------------------------------
	var ipLen int
	//edns0Subnet.Address, edns0Subnet.SourceNetmask, ipLen = parseSubnet("::ffff:7f00:1/120")
	edns0Subnet.Address, edns0Subnet.SourceNetmask, ipLen = parseSubnet("127.0.0.1/24")

	switch ipLen {
	case 128: // ipv6
		edns0Subnet.Family = 2
	case 32: // ipv4
		edns0Subnet.Family = 1
	default:

	}
	log.Println(msg.Pack())

	// ------127.0.0.1/24-----
	// [143 29 1 0 0 1 0 0 0 0 0 1 7 101 120 97 109 112 108 101 3 99 111 109 0 0 1 0 1 0
	// opt start   0 41 16 0 0 0 0 0 0 11
	// subnet start 0 8 0 7 0 1 24 0
	// client subnet start 127 0 0]


	// -----::ffff:7f00:1/120----
	// [111 113 1 0 0 1 0 0 0 0 0 1 7 101 120 97 109 112 108 101 3 99 111 109 0 0 1 0 1 0
	// opt start  0 41 16 0 0 0 0 0 0 23
	// subnet start  0 8 0 19 0 2 120 0
	// client subnet start 0 0 0 0 0 0 0 0 0 0 255 255 127 0 0]

}

func parseSubnet(ednsClientSubnet string) (net.IP, uint8, int) {
	ip, ipNet, err := net.ParseCIDR(ednsClientSubnet)

	if err != nil {
		return nil, 0, 0
	}

	netmask, ipLen := ipNet.Mask.Size()
	return ip, uint8(netmask), ipLen
}

The result of msg.Pack() is ok~

// ------127.0.0.1/24-----
// [143 29 1 0 0 1 0 0 0 0 0 1 7 101 120 97 109 112 108 101 3 99 111 109 0 0 1 0 1 0
// opt start   0 41 16 0 0 0 0 0 0 11
// subnet start 0 8 0 7 0 1 24 0
// client subnet start 127 0 0]


// -----::ffff:7f00:1/120----
// [111 113 1 0 0 1 0 0 0 0 0 1 7 101 120 97 109 112 108 101 3 99 111 109 0 0 1 0 1 0
// opt start  0 41 16 0 0 0 0 0 0 23
// subnet start  0 8 0 19 0 2 120 0
// client subnet start 0 0 0 0 0 0 0 0 0 0 255 255 127 0 0]

[m13253]

The result of msg.Pack() is ok~

A recent pull does not pass the test.
Please update your code to fix the problem.