func prepareBPF(fd int, name string) (int, error) {
if err := syscall.SetBpfInterface(fd, name); err != nil {
return 0, err
}
if err := syscall.CheckBpfVersion(fd); err != nil {
return 0, err
}
if err := syscall.SetBpfImmediate(fd, 1); err != nil {
return 0, err
}
if err := syscall.SetBpfPromisc(fd, 1); err != nil {
return 0, err
}
buflen, err := syscall.BpfBuflen(fd)
if err != nil {
return 0, err
}
if _, err = syscall.BpfHeadercmpl(fd); err != nil {
return 0, err
}
if err := syscall.SetBpfHeadercmpl(fd, 0); err != nil {
return 0, err
}
if _, err := syscall.BpfTimeout(fd); err != nil {
return 0, err
}
tv := syscall.Timeval{Usec: 10}
if err := syscall.SetBpfTimeout(fd, &tv); err != nil {
return 0, err
}
if err := syscall.SetBpf(fd, ipv6OverEthernet); err != nil {
return 0, nil
}
if err := syscall.FlushBpf(fd); err != nil {
return 0, err
}
return buflen, nil
}
// NewBPFSniffer is used to create BSD-only BPF ethernet sniffer
// iface is the network interface device name that you wish to sniff
// options can set to nil in order to utilize default values for everything.
// Each field of Options also have a default setting if left unspecified by
// the user's custome Options struct.
func NewBPFSniffer(iface string, options *Options) (*BPFSniffer, error) {
var err error
enable := 1
sniffer := BPFSniffer{
sniffDeviceName: iface,
}
if options == nil {
sniffer.options = &defaultOptions
} else {
sniffer.options = options
}
if sniffer.options.BPFDeviceName == "" {
sniffer.pickBpfDevice()
}
// setup our read buffer
if sniffer.options.ReadBufLen == 0 {
sniffer.options.ReadBufLen, err = syscall.BpfBuflen(sniffer.fd)
if err != nil {
return nil, err
}
} else {
sniffer.options.ReadBufLen, err = syscall.SetBpfBuflen(sniffer.fd, sniffer.options.ReadBufLen)
if err != nil {
return nil, err
}
}
sniffer.readBuffer = make([]byte, sniffer.options.ReadBufLen)
err = syscall.SetBpfInterface(sniffer.fd, sniffer.sniffDeviceName)
if err != nil {
return nil, err
}
if sniffer.options.Immediate {
// turn immediate mode on. This makes the snffer non-blocking.
err = syscall.SetBpfImmediate(sniffer.fd, enable)
if err != nil {
return nil, err
}
}
// the above call to syscall.SetBpfImmediate needs to be made
// before setting a timer otherwise the reads will block for the
// entire timer duration even if there are packets to return.
if sniffer.options.Timeout != nil {
err = syscall.SetBpfTimeout(sniffer.fd, sniffer.options.Timeout)
if err != nil {
return nil, err
}
}
if sniffer.options.PreserveLinkAddr {
// preserves the link level source address...
// higher level protocol analyzers will not need this
err = syscall.SetBpfHeadercmpl(sniffer.fd, enable)
if err != nil {
return nil, err
}
}
if sniffer.options.Promisc {
// forces the interface into promiscuous mode
err = syscall.SetBpfPromisc(sniffer.fd, enable)
if err != nil {
return nil, err
}
}
return &sniffer, nil
}