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// 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))
}
}
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