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// +build linux
package raw
import (
var (
// Must implement net.PacketConn at compile-time.
_ net.PacketConn = &packetConn{}
// packetConn is the Linux-specific implementation of net.PacketConn for this
// package.
type packetConn struct {
ifi *net.Interface
s socket
pbe uint16
// Should timeouts be set at all?
noTimeouts bool
// Should stats be accumulated instead of reset on each call?
noCumulativeStats bool
// Internal storage for cumulative stats.
stats Stats
// Timeouts set via Set{Read,}Deadline, guarded by mutex.
timeoutMu sync.RWMutex
rtimeout time.Time
// socket is an interface which enables swapping out socket syscalls for
// testing.
type socket interface {
Bind(syscall.Sockaddr) error
Close() error
FD() int
GetSockopt(level, name int, v unsafe.Pointer, l uintptr) error
Recvfrom([]byte, int) (int, syscall.Sockaddr, error)
Sendto([]byte, int, syscall.Sockaddr) error
SetSockopt(level, name int, v unsafe.Pointer, l uint32) error
SetTimeout(time.Duration) error
// listenPacket creates a net.PacketConn which can be used to send and receive
// data at the device driver level.
func listenPacket(ifi *net.Interface, proto uint16, cfg Config) (*packetConn, error) {
// Convert proto to big endian.
pbe := htons(proto)
// Enabling overriding the socket type via config.
typ := syscall.SOCK_RAW
if cfg.LinuxSockDGRAM {
typ = syscall.SOCK_DGRAM
// Open a packet socket using specified socket and protocol types.
sock, err := syscall.Socket(syscall.AF_PACKET, typ, int(pbe))
if err != nil {
return nil, err
// Wrap raw socket in socket interface.
pc, err := newPacketConn(ifi, &sysSocket{fd: sock}, pbe)
if err != nil {
return nil, err
pc.noTimeouts = cfg.NoTimeouts
pc.noCumulativeStats = cfg.NoCumulativeStats
return pc, nil
// newPacketConn creates a net.PacketConn using the specified network
// interface, wrapped socket and big endian protocol number.
// It is the entry point for tests in this package.
func newPacketConn(ifi *net.Interface, s socket, pbe uint16) (*packetConn, error) {
// Bind the packet socket to the interface specified by ifi
// packet(7):
// Only the sll_protocol and the sll_ifindex address fields are used for
// purposes of binding.
err := s.Bind(&syscall.SockaddrLinklayer{
Protocol: pbe,
Ifindex: ifi.Index,
if err != nil {
return nil, err
return &packetConn{
ifi: ifi,
s: s,
pbe: pbe,
}, nil
// ReadFrom implements the net.PacketConn.ReadFrom method.
func (p *packetConn) ReadFrom(b []byte) (int, net.Addr, error) {
deadline := p.rtimeout
var (
// Information returned by syscall.Recvfrom.
n int
addr syscall.Sockaddr
err error
// Timeout for a single loop iteration.
timeout = readTimeout
for {
if !deadline.IsZero() {
timeout = deadline.Sub(time.Now())
if timeout > readTimeout {
timeout = readTimeout
// Set a timeout for this iteration if configured to do so.
if !p.noTimeouts {
if err := p.s.SetTimeout(timeout); err != nil {
return 0, nil, err
// Attempt to receive on socket
// The recvfrom sycall will NOT be interrupted by closing of the socket
n, addr, err = p.s.Recvfrom(b, 0)
switch err {
case nil:
// Got data, break this loop shortly.
case syscall.EAGAIN:
// Hit a timeout, keep looping.
// Return on any other error.
return n, nil, err
// Got data, exit the loop.
// Retrieve hardware address and other information from addr.
sa, ok := addr.(*syscall.SockaddrLinklayer)
if !ok || sa.Halen < 6 {
return n, nil, syscall.EINVAL
// Use length specified to convert byte array into a hardware address slice.
mac := make(net.HardwareAddr, sa.Halen)
copy(mac, sa.Addr[:])
// packet(7):
// sll_hatype and sll_pkttype are set on received packets for your
// information.
// TODO(mdlayher): determine if similar fields exist and are useful on
// non-Linux platforms
return n, &Addr{
HardwareAddr: mac,
}, nil
// WriteTo implements the net.PacketConn.WriteTo method.
func (p *packetConn) WriteTo(b []byte, addr net.Addr) (int, error) {
// Ensure correct Addr type.
a, ok := addr.(*Addr)
if !ok || a.HardwareAddr == nil || len(a.HardwareAddr) < 6 {
return 0, syscall.EINVAL
// Convert hardware address back to byte array form.
var baddr [8]byte
copy(baddr[:], a.HardwareAddr)
// Send message on socket to the specified hardware address from addr
// packet(7):
// When you send packets it is enough to specify sll_family, sll_addr,
// sll_halen, sll_ifindex, and sll_protocol. The other fields should
// be 0.
// In this case, sll_family is taken care of automatically by syscall.
err := p.s.Sendto(b, 0, &syscall.SockaddrLinklayer{
Ifindex: p.ifi.Index,
Halen: uint8(len(a.HardwareAddr)),
Addr: baddr,
Protocol: p.pbe,
return len(b), err
// Close closes the connection.
func (p *packetConn) Close() error {
return p.s.Close()
// LocalAddr returns the local network address.
func (p *packetConn) LocalAddr() net.Addr {
return &Addr{
HardwareAddr: p.ifi.HardwareAddr,
// SetDeadline implements the net.PacketConn.SetDeadline method.
func (p *packetConn) SetDeadline(t time.Time) error {
return p.SetReadDeadline(t)
// SetReadDeadline implements the net.PacketConn.SetReadDeadline method.
func (p *packetConn) SetReadDeadline(t time.Time) error {
p.rtimeout = t
return nil
// SetWriteDeadline implements the net.PacketConn.SetWriteDeadline method.
func (p *packetConn) SetWriteDeadline(t time.Time) error {
return nil
// SetBPF attaches an assembled BPF program to a raw net.PacketConn.
func (p *packetConn) SetBPF(filter []bpf.RawInstruction) error {
prog := syscall.SockFprog{
Len: uint16(len(filter)),
Filter: (*syscall.SockFilter)(unsafe.Pointer(&filter[0])),
err := p.s.SetSockopt(
if err != nil {
return os.NewSyscallError("setsockopt", err)
return nil
// SetPromiscuous enables or disables promiscuous mode on the interface, allowing it
// to receive traffic that is not addressed to the interface.
func (p *packetConn) SetPromiscuous(b bool) error {
mreq := unix.PacketMreq{
Ifindex: int32(p.ifi.Index),
membership := unix.PACKET_ADD_MEMBERSHIP
if !b {
membership = unix.PACKET_DROP_MEMBERSHIP
return p.s.SetSockopt(unix.SOL_PACKET, membership, unsafe.Pointer(&mreq), unix.SizeofPacketMreq)
// Stats retrieves statistics from the Conn.
func (p *packetConn) Stats() (*Stats, error) {
var s unix.TpacketStats
if err := p.s.GetSockopt(unix.SOL_PACKET, unix.PACKET_STATISTICS, unsafe.Pointer(&s), unsafe.Sizeof(s)); err != nil {
return nil, err
return p.handleStats(s), nil
// handleStats handles creation of Stats structures from raw packet socket stats.
func (p *packetConn) handleStats(s unix.TpacketStats) *Stats {
// Does the caller want instantaneous stats as provided by Linux? If so,
// return the structure directly.
if p.noCumulativeStats {
return &Stats{
Packets: uint64(s.Packets),
Drops: uint64(s.Drops),
// The caller wants cumulative stats. Add stats with the internal stats
// structure and return a copy of the resulting stats.
packets := atomic.AddUint64(&p.stats.Packets, uint64(s.Packets))
drops := atomic.AddUint64(&p.stats.Drops, uint64(s.Drops))
return &Stats{
Packets: packets,
Drops: drops,
// sysSocket is the default socket implementation. It makes use of
// Linux-specific system calls to handle raw socket functionality.
type sysSocket struct {
fd int
// Method implementations simply invoke the syscall of the same name, but pass
// the file descriptor stored in the sysSocket as the socket to use.
func (s *sysSocket) Bind(sa syscall.Sockaddr) error { return syscall.Bind(s.fd, sa) }
func (s *sysSocket) Close() error { return syscall.Close(s.fd) }
func (s *sysSocket) FD() int { return s.fd }
func (s *sysSocket) GetSockopt(level, name int, v unsafe.Pointer, l uintptr) error {
_, _, err := syscall.Syscall6(syscall.SYS_GETSOCKOPT, uintptr(s.fd), uintptr(level), uintptr(name), uintptr(v), uintptr(unsafe.Pointer(&l)), 0)
if err != 0 {
return syscall.Errno(err)
return nil
func (s *sysSocket) Recvfrom(p []byte, flags int) (int, syscall.Sockaddr, error) {
return syscall.Recvfrom(s.fd, p, flags)
func (s *sysSocket) Sendto(p []byte, flags int, to syscall.Sockaddr) error {
return syscall.Sendto(s.fd, p, flags, to)
func (s *sysSocket) SetSockopt(level, name int, v unsafe.Pointer, l uint32) error {
_, _, err := syscall.Syscall6(syscall.SYS_SETSOCKOPT, uintptr(s.fd), uintptr(level), uintptr(name), uintptr(v), uintptr(l), 0)
if err != 0 {
return syscall.Errno(err)
return nil
func (s *sysSocket) SetTimeout(timeout time.Duration) error {
tv, err := newTimeval(timeout)
if err != nil {
return err
return syscall.SetsockoptTimeval(s.fd, syscall.SOL_SOCKET, syscall.SO_RCVTIMEO, tv)