dhcpv6: Implement RelayPort option

This is a simple 1-value option used in relay messages for RFC8357, specifying
the UDP port on which messages should be sent to the relay

Signed-off-by: Anatole Denis <natolumin@unverle.fr>

3 files changed, 62 insertions, 0 deletions

diff --git a/dhcpv6/option_relayport.go b/dhcpv6/option_relayport.go
new file mode 100644
index 0000000..fd51948
--- /dev/null
+++ b/dhcpv6/option_relayport.go
@@ -0,0 +1,42 @@
+// This module defines the optRelayPort structure.
+// https://www.ietf.org/rfc/rfc8357.txt
+
+package dhcpv6
+
+import (
+	"fmt"
+
+	"github.com/u-root/uio/uio"
+)
+
+// OptRelayPort specifies an UDP port to use for the downstream relay
+func OptRelayPort(port uint16) Option {
+	return &optRelayPort{DownstreamSourcePort: port}
+}
+
+type optRelayPort struct {
+	DownstreamSourcePort uint16
+}
+
+func (op *optRelayPort) Code() OptionCode {
+	return OptionRelayPort
+}
+
+func (op *optRelayPort) ToBytes() []byte {
+	buf := uio.NewBigEndianBuffer(nil)
+	buf.Write16(op.DownstreamSourcePort)
+	return buf.Data()
+}
+
+func (op *optRelayPort) String() string {
+	return fmt.Sprintf("RelayPort: %d", op.DownstreamSourcePort)
+}
+
+// build an optRelayPort structure from a sequence of bytes.
+// The input data does not include option code and length bytes.
+func parseOptRelayPort(data []byte) (*optRelayPort, error) {
+	var opt optRelayPort
+	buf := uio.NewBigEndianBuffer(data)
+	opt.DownstreamSourcePort = buf.Read16()
+	return &opt, buf.FinError()
+}
diff --git a/dhcpv6/option_relayport_test.go b/dhcpv6/option_relayport_test.go
new file mode 100644
index 0000000..124af62
--- /dev/null
+++ b/dhcpv6/option_relayport_test.go
@@ -0,0 +1,18 @@
+package dhcpv6
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestParseRelayPort(t *testing.T) {
+	opt, err := parseOptRelayPort([]byte{0x12, 0x32})
+	require.NoError(t, err)
+	require.Equal(t, &optRelayPort{DownstreamSourcePort: 0x1232}, opt)
+}
+
+func TestRelayPortToBytes(t *testing.T) {
+	op := OptRelayPort(0x3845)
+	require.Equal(t, []byte{0x38, 0x45}, op.ToBytes())
+}
diff --git a/dhcpv6/options.go b/dhcpv6/options.go
index 06a1028..f8445bb 100644
--- a/dhcpv6/options.go
+++ b/dhcpv6/options.go
@@ -105,6 +105,8 @@ func ParseOption(code OptionCode, optData []byte) (Option, error) {
 		opt, err = ParseOpt4RDMapRule(optData)
 	case Option4RDNonMapRule:
 		opt, err = ParseOpt4RDNonMapRule(optData)
+	case OptionRelayPort:
+		opt, err = parseOptRelayPort(optData)
 	default:
 		opt = &OptionGeneric{OptionCode: code, OptionData: optData}
 	}