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// Copyright 2012 Google, Inc. All rights reserved.
// Use of this source code is governed by a BSD-style license
// that can be found in the LICENSE file in the root of the source
// tree.
// +build linux
package afpacket
import (
// OptTPacketVersion is the version of TPacket to use.
// It can be passed into NewTPacket.
type OptTPacketVersion int
// String returns a string representation of the version, generally of the form V#.
func (t OptTPacketVersion) String() string {
switch t {
case TPacketVersion1:
return "V1"
case TPacketVersion2:
return "V2"
case TPacketVersion3:
return "V3"
case TPacketVersionHighestAvailable:
return "HighestAvailable"
return "InvalidVersion"
// OptSocketType is the socket type used to open the TPacket socket.
type OptSocketType int
func (t OptSocketType) String() string {
switch t {
case SocketRaw:
return "SOCK_RAW"
case SocketDgram:
return "SOCK_DGRAM"
return "UnknownSocketType"
// TPacket version numbers for use with NewHandle.
const (
// TPacketVersionHighestAvailable tells NewHandle to use the highest available version of tpacket the kernel has available.
// This is the default, should a version number not be given in NewHandle's options.
TPacketVersionHighestAvailable = OptTPacketVersion(-1)
TPacketVersion1 = OptTPacketVersion(unix.TPACKET_V1)
TPacketVersion2 = OptTPacketVersion(unix.TPACKET_V2)
TPacketVersion3 = OptTPacketVersion(unix.TPACKET_V3)
tpacketVersionMax = TPacketVersion3
tpacketVersionMin = -1
// SocketRaw is the default socket type. It returns packet data
// including the link layer (ethernet headers, etc).
SocketRaw = OptSocketType(unix.SOCK_RAW)
// SocketDgram strips off the link layer when reading packets, and adds
// the link layer back automatically on packet writes (coming soon...)
SocketDgram = OptSocketType(unix.SOCK_DGRAM)
// OptInterface is the specific interface to bind to.
// It can be passed into NewTPacket.
type OptInterface string
// OptFrameSize is TPacket's tp_frame_size
// It can be passed into NewTPacket.
type OptFrameSize int
// OptBlockSize is TPacket's tp_block_size
// It can be passed into NewTPacket.
type OptBlockSize int
// OptNumBlocks is TPacket's tp_block_nr
// It can be passed into NewTPacket.
type OptNumBlocks int
// OptBlockTimeout is TPacket v3's tp_retire_blk_tov. Note that it has only millisecond granularity, so must be >= 1 ms.
// It can be passed into NewTPacket.
type OptBlockTimeout time.Duration
// OptPollTimeout is the number of milliseconds that poll() should block waiting for a file
// descriptor to become ready. Specifying a negative value in time‐out means an infinite timeout.
type OptPollTimeout time.Duration
// OptAddVLANHeader modifies the packet data that comes back from the
// kernel by adding in the VLAN header that the NIC stripped. AF_PACKET by
// default uses VLAN offloading, in which the NIC strips the VLAN header off of
// the packet before handing it to the kernel. This means that, even if a
// packet has an 802.1q header on the wire, it'll show up without one by the
// time it goes through AF_PACKET. If this option is true, the VLAN header is
// added back in before the packet is returned. Note that this potentially has
// a large performance hit, especially in otherwise zero-copy operation.
// Note that if you do not need to have a "real" VLAN layer, it may be
// preferable to use the VLAN ID provided by the AncillaryVLAN struct
// in CaptureInfo.AncillaryData, which is populated out-of-band and has
// negligible performance impact. Such ancillary data will automatically
// be provided if available.
type OptAddVLANHeader bool
// Default constants used by options.
const (
DefaultFrameSize = 4096 // Default value for OptFrameSize.
DefaultBlockSize = DefaultFrameSize * 128 // Default value for OptBlockSize.
DefaultNumBlocks = 128 // Default value for OptNumBlocks.
DefaultBlockTimeout = 64 * time.Millisecond // Default value for OptBlockTimeout.
DefaultPollTimeout = -1 * time.Millisecond // Default value for OptPollTimeout. This blocks forever.
type options struct {
frameSize int
framesPerBlock int
blockSize int
numBlocks int
addVLANHeader bool
blockTimeout time.Duration
pollTimeout time.Duration
version OptTPacketVersion
socktype OptSocketType
iface string
var defaultOpts = options{
frameSize: DefaultFrameSize,
blockSize: DefaultBlockSize,
numBlocks: DefaultNumBlocks,
blockTimeout: DefaultBlockTimeout,
pollTimeout: DefaultPollTimeout,
version: TPacketVersionHighestAvailable,
socktype: SocketRaw,
func parseOptions(opts ...interface{}) (ret options, err error) {
ret = defaultOpts
for _, opt := range opts {
switch v := opt.(type) {
case OptFrameSize:
ret.frameSize = int(v)
case OptBlockSize:
ret.blockSize = int(v)
case OptNumBlocks:
ret.numBlocks = int(v)
case OptBlockTimeout:
ret.blockTimeout = time.Duration(v)
case OptPollTimeout:
ret.pollTimeout = time.Duration(v)
case OptTPacketVersion:
ret.version = v
case OptInterface:
ret.iface = string(v)
case OptSocketType:
ret.socktype = v
case OptAddVLANHeader:
ret.addVLANHeader = bool(v)
err = errors.New("unknown type in options")
if err = ret.check(); err != nil {
ret.framesPerBlock = ret.blockSize / ret.frameSize
func (o options) check() error {
switch {
case o.blockSize%pageSize != 0:
return fmt.Errorf("block size %d must be divisible by page size %d", o.blockSize, pageSize)
case o.blockSize%o.frameSize != 0:
return fmt.Errorf("block size %d must be divisible by frame size %d", o.blockSize, o.frameSize)
case o.numBlocks < 1:
return fmt.Errorf("num blocks %d must be >= 1", o.numBlocks)
case o.blockTimeout < time.Millisecond:
return fmt.Errorf("block timeout %v must be > %v", o.blockTimeout, time.Millisecond)
case o.version < tpacketVersionMin || o.version > tpacketVersionMax:
return fmt.Errorf("tpacket version %v is invalid", o.version)
return nil
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