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// Copyright 2018 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"
"inet.af/netstack/tcpip"
)
const (
// ARPProtocolNumber is the ARP network protocol number.
ARPProtocolNumber tcpip.NetworkProtocolNumber = 0x0806
// ARPSize is the size of an IPv4-over-Ethernet ARP packet.
ARPSize = 28
)
// ARPHardwareType is the hardware type for LinkEndpoint in an ARP header.
type ARPHardwareType uint16
// Typical ARP HardwareType values. Some of the constants have to be specific
// values as they are egressed on the wire in the HTYPE field of an ARP header.
const (
ARPHardwareNone ARPHardwareType = 0
// ARPHardwareEther specifically is the HTYPE for Ethernet as specified
// in the IANA list here:
//
// https://www.iana.org/assignments/arp-parameters/arp-parameters.xhtml#arp-parameters-2
ARPHardwareEther ARPHardwareType = 1
ARPHardwareLoopback ARPHardwareType = 2
)
// ARPOp is an ARP opcode.
type ARPOp uint16
// Typical ARP opcodes defined in RFC 826.
const (
ARPRequest ARPOp = 1
ARPReply ARPOp = 2
)
// ARP is an ARP packet stored in a byte array as described in RFC 826.
type ARP []byte
const (
hTypeOffset = 0
protocolOffset = 2
haAddressSizeOffset = 4
protoAddressSizeOffset = 5
opCodeOffset = 6
senderHAAddressOffset = 8
senderProtocolAddressOffset = senderHAAddressOffset + EthernetAddressSize
targetHAAddressOffset = senderProtocolAddressOffset + IPv4AddressSize
targetProtocolAddressOffset = targetHAAddressOffset + EthernetAddressSize
)
func (a ARP) hardwareAddressType() ARPHardwareType {
return ARPHardwareType(binary.BigEndian.Uint16(a[hTypeOffset:]))
}
func (a ARP) protocolAddressSpace() uint16 { return binary.BigEndian.Uint16(a[protocolOffset:]) }
func (a ARP) hardwareAddressSize() int { return int(a[haAddressSizeOffset]) }
func (a ARP) protocolAddressSize() int { return int(a[protoAddressSizeOffset]) }
// Op is the ARP opcode.
func (a ARP) Op() ARPOp { return ARPOp(binary.BigEndian.Uint16(a[opCodeOffset:])) }
// SetOp sets the ARP opcode.
func (a ARP) SetOp(op ARPOp) {
binary.BigEndian.PutUint16(a[opCodeOffset:], uint16(op))
}
// SetIPv4OverEthernet configures the ARP packet for IPv4-over-Ethernet.
func (a ARP) SetIPv4OverEthernet() {
binary.BigEndian.PutUint16(a[hTypeOffset:], uint16(ARPHardwareEther))
binary.BigEndian.PutUint16(a[protocolOffset:], uint16(IPv4ProtocolNumber))
a[haAddressSizeOffset] = EthernetAddressSize
a[protoAddressSizeOffset] = uint8(IPv4AddressSize)
}
// HardwareAddressSender is the link address of the sender.
// It is a view on to the ARP packet so it can be used to set the value.
func (a ARP) HardwareAddressSender() []byte {
return a[senderHAAddressOffset : senderHAAddressOffset+EthernetAddressSize]
}
// ProtocolAddressSender is the protocol address of the sender.
// It is a view on to the ARP packet so it can be used to set the value.
func (a ARP) ProtocolAddressSender() []byte {
return a[senderProtocolAddressOffset : senderProtocolAddressOffset+IPv4AddressSize]
}
// HardwareAddressTarget is the link address of the target.
// It is a view on to the ARP packet so it can be used to set the value.
func (a ARP) HardwareAddressTarget() []byte {
return a[targetHAAddressOffset : targetHAAddressOffset+EthernetAddressSize]
}
// ProtocolAddressTarget is the protocol address of the target.
// It is a view on to the ARP packet so it can be used to set the value.
func (a ARP) ProtocolAddressTarget() []byte {
return a[targetProtocolAddressOffset : targetProtocolAddressOffset+IPv4AddressSize]
}
// IsValid reports whether this is an ARP packet for IPv4 over Ethernet.
func (a ARP) IsValid() bool {
if len(a) < ARPSize {
return false
}
return a.hardwareAddressType() == ARPHardwareEther &&
a.protocolAddressSpace() == uint16(IPv4ProtocolNumber) &&
a.hardwareAddressSize() == EthernetAddressSize &&
a.protocolAddressSize() == IPv4AddressSize
}
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