func openTcpdump() (io.Writer, error) {
tcpdump := exec.Command("tcpdump", "-U", "-r", "-")
pipe, err := tcpdump.StdinPipe()
if err != nil {
return nil, err
}
tcpdump.Stdout = os.Stdout
tcpdump.Stderr = os.Stderr
err = tcpdump.Start()
if err != nil {
return nil, err
}
header := odp.MakeAlignedByteSlice(int(unsafe.Sizeof(pcapHeader{})))
*(*pcapHeader)(unsafe.Pointer(&header[0])) = pcapHeader{
magicNumber: 0xa1b23c4d, // nanosecond times
versionMajor: 2,
versionMinor: 4,
thisZone: 0,
sigFigs: 0,
snapLen: 65535,
network: 1, // ethernet frames
}
_, err = pipe.Write(header)
return pipe, err
}
func writeTcpdumpPacket(pipe io.Writer, t time.Time, data []byte) error {
header := odp.MakeAlignedByteSlice(int(unsafe.Sizeof(pcapPacketHeader{})))
*(*pcapPacketHeader)(unsafe.Pointer(&header[0])) = pcapPacketHeader{
sec: uint32(t.Unix()),
usec: uint32(t.Nanosecond()), // nanosecond field despite name
inclLen: uint32(len(data)),
origLen: uint32(len(data)),
}
_, err := pipe.Write(header)
if err != nil {
return err
}
_, err = pipe.Write(data)
return err
}