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[Christian Grabowski <mp+441702@xxxxxxxxxxxxxxxxxx>]

Diff comments:

> diff --git a/src/maasagent/internal/arp/ethernet.go b/src/maasagent/internal/arp/ethernet.go
> new file mode 100644
> index 0000000..0d3e7d3
> --- /dev/null
> +++ b/src/maasagent/internal/arp/ethernet.go
> @@ -0,0 +1,133 @@
> +package arp
> +
> +/*
> +	Copyright 2023 Canonical Ltd.  This software is licensed under the
> +	GNU Affero General Public License version 3 (see the file LICENSE).
> +*/
> +
> +import (
> +	"encoding/binary"
> +	"errors"
> +	"io"
> +	"net"
> +)
> +
> +const (
> +	minEthernetLen = 14
> +)
> +
> +const (
> +	// EthernetTypeLLC is a special ethernet type, if found the frame is truncated
> +	EthernetTypeLLC uint16 = 0
> +	// EthernetTypeIPv4 is the ethernet type for a frame containing an IPv4 packet
> +	EthernetTypeIPv4 uint16 = 0x0800
> +	// EthernetTypeARP is the ethernet type for a frame containing an ARP packet
> +	EthernetTypeARP uint16 = 0x0806
> +	// EthernetTypeIPv6 is the ethernet type for a frame containing an IPv6 packet
> +	EthernetTypeIPv6 uint16 = 0x86dd
> +	// EthernetTypeVLAN is the ethernet type for a frame containing a VLAN tag,
> +	// the VLAN tag bytes will indicate the actual type of packet the frame contains
> +	EthernetTypeVLAN uint16 = 0x8100
> +
> +	// NonStdLenEthernetTypes is a magic number to find any non-standard types
> +	// and mark them as EthernetTypeLLC
> +	NonStdLenEthernetTypes uint16 = 0x600
> +)
> +
> +var (
> +	// ErrNotVLAN is an error returned when calling EthernetFrame.ExtractVLAN
> +	// if the frame is not of type EthernetTypeVLAN
> +	ErrNotVLAN = errors.New("ethernet frame not of type VLAN")
> +	// ErrMalformedVLAN is an error returned when parsing a VLAN tag
> +	// that is malformed
> +	ErrMalformedVLAN = errors.New("VLAN tag is malformed")
> +)
> +
> +// VLAN represents a VLAN tag within an ethernet frame
> +type VLAN struct {
> +	Priority     uint8
> +	DropEligible bool
> +	ID           uint16
> +	EthernetType uint16
> +}
> +
> +// UnmarshalBinary will take the ethernet frame's payload
> +// and extract a VLAN tag if one is present
> +func (v *VLAN) UnmarshalBinary(buf []byte) error {
> +	if len(buf) < 4 {
> +		return ErrMalformedVLAN
> +	}
> +
> +	// extract the first 3 bits
> +	v.Priority = (buf[0] & 0xe0) >> 5
> +	// extract the next bit and turn it into a bool
> +	v.DropEligible = buf[0]&0x10 != 0
> +	// extract the next 12 bits for an ID
> +	v.ID = binary.BigEndian.Uint16(buf[:2]) & 0x0fff
> +	// last 2 bytes are ethernet type
> +	v.EthernetType = binary.BigEndian.Uint16(buf[2:])
> +	return nil
> +}
> +
> +// EthernetFrame represents an ethernet frame
> +type EthernetFrame struct {
> +	SrcMAC       net.HardwareAddr
> +	DstMAC       net.HardwareAddr
> +	EthernetType uint16
> +	Len          uint16
> +	Payload      []byte
> +}
> +
> +// ExtractARPPacket will extract an ARP packet from the ethernet frame's
> +// payload
> +func (e *EthernetFrame) ExtractARPPacket() (*Packet, error) {
> +	var buf []byte

actually after looking more closely, `sync.Pool` shouldn't make a difference here, as `var buf []byte` is set to an existing slice that is coming from the ethernet frame's payload, so we can't really use `sync.Pool` here, nor would it prevent allocation.

> +	if e.EthernetType == EthernetTypeVLAN {
> +		buf = e.Payload[4:]
> +	} else {
> +		buf = e.Payload
> +	}
> +	a := &Packet{}
> +	err := a.UnmarshalBinary(buf)
> +	if err != nil {
> +		return nil, err
> +	}
> +	return a, nil
> +}
> +
> +// ExtractVLAN will extract the VLAN tag from the ethernet frame's
> +// payload if one is present and return ErrNotVLAN if not
> +func (e *EthernetFrame) ExtractVLAN() (*VLAN, error) {
> +	if e.EthernetType != EthernetTypeVLAN {
> +		return nil, ErrNotVLAN
> +	}
> +	v := &VLAN{}
> +	err := v.UnmarshalBinary(e.Payload[0:4])
> +	if err != nil {
> +		return nil, err
> +	}
> +	return v, nil
> +}
> +
> +// UnmarshalBinary parses ethernet frame bytes into an EthernetFrame
> +func (eth *EthernetFrame) UnmarshalBinary(buf []byte) error {
> +	if len(buf) < minEthernetLen {
> +		return io.ErrUnexpectedEOF
> +	}
> +
> +	eth.DstMAC = buf[0:6]
> +	eth.SrcMAC = buf[6:12]
> +	eth.EthernetType = binary.BigEndian.Uint16(buf[12:14])
> +	eth.Payload = buf[14:]
> +	if eth.EthernetType < NonStdLenEthernetTypes {
> +		eth.Len = eth.EthernetType
> +		eth.EthernetType = EthernetTypeLLC
> +		cmp := len(eth.Payload) - int(eth.Len)
> +		if cmp < 0 {
> +			return io.ErrUnexpectedEOF
> +		} else if cmp > 0 {
> +			eth.Payload = eth.Payload[:len(eth.Payload)-cmp]
> +		}
> +	}
> +	return nil
> +}


-- 
https://code.launchpad.net/~cgrabowski/maas/+git/maas/+merge/441702
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