Add types to parse MLD messages

Preparing for upcoming CLs that add MLD functionality.

Bug #4861

Test: header.TestMLD
PiperOrigin-RevId: 343391556

1 files changed, 96 insertions, 0 deletions

diff --git a/pkg/tcpip/header/mld.go b/pkg/tcpip/header/mld.go
new file mode 100644
index 000000000..f70623092
--- /dev/null
+++ b/pkg/tcpip/header/mld.go
@@ -0,0 +1,96 @@
+// Copyright 2020 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package header
+
+import (
+	"encoding/binary"
+	"fmt"
+	"time"
+
+	"gvisor.dev/gvisor/pkg/tcpip"
+)
+
+const (
+	// mldMaximumResponseDelayOffset is the offset to the Maximum Response Delay
+	// field within MLD.
+	mldMaximumResponseDelayOffset = 0
+
+	// mldMulticastAddressOffset is the offset to the Multicast Address field
+	// within MLD.
+	mldMulticastAddressOffset = 4
+)
+
+// MLD is a Multicast Listener Discovery message in an ICMPv6 packet.
+//
+// MLD will only contain the body of an ICMPv6 packet.
+//
+// As per RFC 2710 section 3, MLD messages have the following format (MLD only
+// holds the bytes after the first four bytes in the diagram below):
+//
+//    0                   1                   2                   3
+//    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+//   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+//   |     Type      |     Code      |          Checksum             |
+//   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+//   |     Maximum Response Delay    |          Reserved             |
+//   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+//   |                                                               |
+//   +                                                               +
+//   |                                                               |
+//   +                       Multicast Address                       +
+//   |                                                               |
+//   +                                                               +
+//   |                                                               |
+//   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+type MLD []byte
+
+// MaximumResponseDelay returns the Maximum Response Delay.
+func (m MLD) MaximumResponseDelay() time.Duration {
+	// As per RFC 2710 section 3.4:
+	//
+	//   The Maximum Response Delay field is meaningful only in Query
+	//   messages, and specifies the maximum allowed delay before sending a
+	//   responding Report, in units of milliseconds. In all other messages,
+	//   it is set to zero by the sender and ignored by receivers.
+	return time.Duration(binary.BigEndian.Uint16(m[mldMaximumResponseDelayOffset:])) * time.Millisecond
+}
+
+// SetMaximumResponseDelay sets the Maximum Response Delay field.
+//
+// maxRespDelayMS is the value in milliseconds.
+func (m MLD) SetMaximumResponseDelay(maxRespDelayMS uint16) {
+	binary.BigEndian.PutUint16(m[mldMaximumResponseDelayOffset:], maxRespDelayMS)
+}
+
+// MulticastAddress returns the Multicast Address.
+func (m MLD) MulticastAddress() tcpip.Address {
+	// As per RFC 2710 section 3.5:
+	//
+	//   In a Query message, the Multicast Address field is set to zero when
+	//   sending a General Query, and set to a specific IPv6 multicast address
+	//   when sending a Multicast-Address-Specific Query.
+	//
+	//   In a Report or Done message, the Multicast Address field holds a
+	//   specific IPv6 multicast address to which the message sender is
+	//   listening or is ceasing to listen, respectively.
+	return tcpip.Address(m[mldMulticastAddressOffset:][:IPv6AddressSize])
+}
+
+// SetMulticastAddress sets the Multicast Address field.
+func (m MLD) SetMulticastAddress(multicastAddress tcpip.Address) {
+	if n := copy(m[mldMulticastAddressOffset:], multicastAddress); n != IPv6AddressSize {
+		panic(fmt.Sprintf("copied %d bytes, expected to copy %d bytes", n, IPv6AddressSize))
+	}
+}