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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 "gvisor.googlesource.com/gvisor/pkg/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 = 2 + 2 + 1 + 1 + 2 + 2*6 + 2*4
)
// 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
func (a ARP) hardwareAddressSpace() uint16 { return uint16(a[0])<<8 | uint16(a[1]) }
func (a ARP) protocolAddressSpace() uint16 { return uint16(a[2])<<8 | uint16(a[3]) }
func (a ARP) hardwareAddressSize() int { return int(a[4]) }
func (a ARP) protocolAddressSize() int { return int(a[5]) }
// Op is the ARP opcode.
func (a ARP) Op() ARPOp { return ARPOp(a[6])<<8 | ARPOp(a[7]) }
// SetOp sets the ARP opcode.
func (a ARP) SetOp(op ARPOp) {
a[6] = uint8(op >> 8)
a[7] = uint8(op)
}
// SetIPv4OverEthernet configures the ARP packet for IPv4-over-Ethernet.
func (a ARP) SetIPv4OverEthernet() {
a[0], a[1] = 0, 1 // htypeEthernet
a[2], a[3] = 0x08, 0x00 // IPv4ProtocolNumber
a[4] = 6 // macSize
a[5] = 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 {
const s = 8
return a[s : s+6]
}
// 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 {
const s = 8 + 6
return a[s : s+4]
}
// 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 {
const s = 8 + 6 + 4
return a[s : s+6]
}
// 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 {
const s = 8 + 6 + 4 + 6
return a[s : s+4]
}
// IsValid reports whether this is an ARP packet for IPv4 over Ethernet.
func (a ARP) IsValid() bool {
if len(a) < ARPSize {
return false
}
const htypeEthernet = 1
const macSize = 6
return a.hardwareAddressSpace() == htypeEthernet &&
a.protocolAddressSpace() == uint16(IPv4ProtocolNumber) &&
a.hardwareAddressSize() == macSize &&
a.protocolAddressSize() == IPv4AddressSize
}
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