import "github.com/google/gopacket/pcap"
Package pcap allows users of gopacket to read packets off the wire or from pcap files.
This package is meant to be used with its parent, http://github.com/google/gopacket, although it can also be used independently if you just want to get packet data from the wire.
The following code can be used to read in data from a pcap file.
if handle, err := pcap.OpenOffline("/path/to/my/file"); err != nil {
panic(err)
} else {
packetSource := gopacket.NewPacketSource(handle, handle.LinkType())
for packet := range packetSource.Packets() {
handlePacket(packet) // Do something with a packet here.
}
}
The following code can be used to read in data from a live device, in this case "eth0".
if handle, err := pcap.OpenLive("eth0", 1600, true, pcap.BlockForever); err != nil {
panic(err)
} else if err := handle.SetBPFFilter("tcp and port 80"); err != nil { // optional
panic(err)
} else {
packetSource := gopacket.NewPacketSource(handle, handle.LinkType())
for packet := range packetSource.Packets() {
handlePacket(packet) // Do something with a packet here.
}
}
Newer PCAP functionality requires the concept of an 'inactive' PCAP handle. Instead of constantly adding new arguments to pcap_open_live, users now call pcap_create to create a handle, set it up with a bunch of optional function calls, then call pcap_activate to activate it. This library mirrors that mechanism, for those that want to expose/use these new features:
inactive, err := pcap.NewInactiveHandle(deviceName)
if err != nil {
log.Fatal(err)
}
defer inactive.CleanUp()
// Call various functions on inactive to set it up the way you'd like:
if err = inactive.SetTimeout(time.Minute); err != nil {
log.Fatal(err)
} else if err = inactive.SetTimestampSource("foo"); err != nil {
log.Fatal(err)
}
// Finally, create the actual handle by calling Activate:
handle, err := inactive.Activate() // after this, inactive is no longer valid
if err != nil {
log.Fatal(err)
}
defer handle.Close()
// Now use your handle as you see fit.
pcap.OpenLive and pcap.SetTimeout both take timeouts. If you don't care about timeouts, just pass in BlockForever, which should do what you expect with minimal fuss.
A timeout of 0 is not recommended. Some platforms, like Macs (http://www.manpages.info/macosx/pcap.3.html) say:
The read timeout is used to arrange that the read not necessarily return immediately when a packet is seen, but that it wait for some amount of time to allow more packets to arrive and to read multiple packets from the OS kernel in one operation.
This means that if you only capture one packet, the kernel might decide to wait 'timeout' for more packets to batch with it before returning. A timeout of 0, then, means 'wait forever for more packets', which is... not good.
To get around this, we've introduced the following behavior: if a negative timeout is passed in, we set the positive timeout in the handle, then loop internally in ReadPacketData/ZeroCopyReadPacketData when we see timeout errors.
This package does not implement PCAP file writing. However, gopacket/pcapgo does! Look there if you'd like to write PCAP files.
If you're trying to use 64-bit winpcap on Windows 10, you might have to do the crazy hijinks detailed at http://stackoverflow.com/questions/38047858/compile-gopacket-on-windows-64bit
const BlockForever = -time.Millisecond * 10
BlockForever causes it to block forever waiting for packets, when passed into SetTimeout or OpenLive, while still returning incoming packets to userland relatively quickly.
ErrNotActive is returned if handle is not activated
const MaxBpfInstructions = 4096MaxBpfInstructions is the maximum number of BPF instructions supported (BPF_MAXINSNS), taken from Linux kernel: include/uapi/linux/bpf_common.h
https://github.com/torvalds/linux/blob/master/include/uapi/linux/bpf_common.h
CannotSetRFMon is returned by SetRFMon if the handle does not allow setting RFMon because pcap_can_set_rfmon returns 0.
DatalinkNameToVal returns pcap_datalink_name_to_val as int
DatalinkValToDescription returns pcap_datalink_val_to_description as string
DatalinkValToName returns pcap_datalink_val_to_name as string
Version returns pcap_lib_version.
type BPF struct {
// contains filtered or unexported fields
}BPF is a compiled filter program, useful for offline packet matching.
Code:
handle, err := OpenOffline("test_ethernet.pcap")
if err != nil {
log.Fatal(err)
}
synack, err := handle.NewBPF("tcp[tcpflags] & (tcp-syn|tcp-ack) == (tcp-syn|tcp-ack)")
if err != nil {
log.Fatal(err)
}
syn, err := handle.NewBPF("tcp[tcpflags] & (tcp-syn|tcp-ack) == tcp-syn")
if err != nil {
log.Fatal(err)
}
for {
data, ci, err := handle.ReadPacketData()
switch {
case err == io.EOF:
return
case err != nil:
log.Fatal(err)
case synack.Matches(ci, data):
fmt.Println("SYN/ACK packet")
case syn.Matches(ci, data):
fmt.Println("SYN packet")
default:
fmt.Println("SYN flag not set")
}
}
Output:
SYN packet SYN/ACK packet SYN flag not set SYN flag not set SYN flag not set SYN flag not set SYN flag not set SYN flag not set SYN flag not set SYN flag not set
Matches returns true if the given packet data matches this filter.
String returns the original string this BPF filter was compiled from.
BPFInstruction is a byte encoded structure holding a BPF instruction
func CompileBPFFilter(linkType layers.LinkType, captureLength int, expr string) ([]BPFInstruction, error)
CompileBPFFilter compiles and returns a BPF filter with given a link type and capture length.
Datalink describes the datalink
Direction is used by Handle.SetDirection.
const (
DirectionIn Direction = C.PCAP_D_IN
DirectionOut Direction = C.PCAP_D_OUT
DirectionInOut Direction = C.PCAP_D_INOUT
)Direction values for Handle.SetDirection.
type Handle struct {
// contains filtered or unexported fields
}Handle provides a connection to a pcap handle, allowing users to read packets off the wire (Next), inject packets onto the wire (Inject), and perform a number of other functions to affect and understand packet output.
Handles are already pcap_activate'd
func OpenLive(device string, snaplen int32, promisc bool, timeout time.Duration) (handle *Handle, _ error)
OpenLive opens a device and returns a *Handle. It takes as arguments the name of the device ("eth0"), the maximum size to read for each packet (snaplen), whether to put the interface in promiscuous mode, and a timeout.
See the package documentation for important details regarding 'timeout'.
OpenOffline opens a file and returns its contents as a *Handle.
OpenOfflineFile returns contents of input file as a *Handle.
Close closes the underlying pcap handle.
func (p *Handle) CompileBPFFilter(expr string) ([]BPFInstruction, error)
CompileBPFFilter compiles and returns a BPF filter for the pcap handle.
Error returns the current error associated with a pcap handle (pcap_geterr).
LinkType returns pcap_datalink, as a layers.LinkType.
ListDataLinks obtains a list of all possible data link types supported for an interface.
NewBPF compiles the given string into a new filter program.
BPF filters need to be created from activated handles, because they need to know the underlying link type to correctly compile their offsets.
func (p *Handle) NewBPFInstructionFilter(bpfInstructions []BPFInstruction) (*BPF, error)
NewBPFInstructionFilter sets the given BPFInstructions as new filter program.
BPF filters need to be created from activated handles, because they need to know the underlying link type to correctly compile their offsets.
ReadPacketData returns the next packet read from the pcap handle, along with an error code associated with that packet. If the packet is read successfully, the returned error is nil.
SetBPFFilter compiles and sets a BPF filter for the pcap handle.
func (p *Handle) SetBPFInstructionFilter(bpfInstructions []BPFInstruction) (err error)
SetBPFInstructionFilter may be used to apply a filter in BPF asm byte code format.
Simplest way to generate BPF asm byte code is with tcpdump:
tcpdump -dd 'udp'
The output may be used directly to add a filter, e.g.:
bpfInstructions := []pcap.BpfInstruction{
{0x28, 0, 0, 0x0000000c},
{0x15, 0, 9, 0x00000800},
{0x30, 0, 0, 0x00000017},
{0x15, 0, 7, 0x00000006},
{0x28, 0, 0, 0x00000014},
{0x45, 5, 0, 0x00001fff},
{0xb1, 0, 0, 0x0000000e},
{0x50, 0, 0, 0x0000001b},
{0x54, 0, 0, 0x00000012},
{0x15, 0, 1, 0x00000012},
{0x6, 0, 0, 0x0000ffff},
{0x6, 0, 0, 0x00000000},
}
An other posibility is to write the bpf code in bpf asm. Documentation: https://www.kernel.org/doc/Documentation/networking/filter.txt
To compile the code use bpf_asm from https://github.com/torvalds/linux/tree/master/tools/net
The following command may be used to convert bpf_asm output to c/go struct, usable for SetBPFFilterByte: bpf_asm -c tcp.bpf
SetDirection sets the direction for which packets will be captured.
SetLinkType calls pcap_set_datalink on the pcap handle.
SnapLen returns the snapshot length
Stats returns statistics on the underlying pcap handle.
WritePacketData calls pcap_sendpacket, injecting the given data into the pcap handle.
ZeroCopyReadPacketData reads the next packet off the wire, and returns its data. The slice returned by ZeroCopyReadPacketData points to bytes owned by the the Handle. Each call to ZeroCopyReadPacketData invalidates any data previously returned by ZeroCopyReadPacketData. Care must be taken not to keep pointers to old bytes when using ZeroCopyReadPacketData... if you need to keep data past the next time you call ZeroCopyReadPacketData, use ReadPacketData, which copies the bytes into a new buffer for you.
data1, _, _ := handle.ZeroCopyReadPacketData() // do everything you want with data1 here, copying bytes out of it if you'd like to keep them around. data2, _, _ := handle.ZeroCopyReadPacketData() // invalidates bytes in data1
type InactiveHandle struct {
// contains filtered or unexported fields
}InactiveHandle allows you to call pre-pcap_activate functions on your pcap handle to set it up just the way you'd like.
func NewInactiveHandle(device string) (*InactiveHandle, error)
NewInactiveHandle creates a new InactiveHandle, which wraps an un-activated PCAP handle. Callers of NewInactiveHandle should immediately defer 'CleanUp', as in:
inactive := NewInactiveHandle("eth0")
defer inactive.CleanUp()
func (p *InactiveHandle) Activate() (*Handle, error)
Activate activates the handle. The current InactiveHandle becomes invalid and all future function calls on it will fail.
func (p *InactiveHandle) CleanUp()
CleanUp cleans up any stuff left over from a successful or failed building of a handle.
func (p *InactiveHandle) Error() error
Error returns the current error associated with a pcap handle (pcap_geterr).
func (p *InactiveHandle) SetBufferSize(bufferSize int) error
SetBufferSize sets the buffer size (in bytes) of the handle.
func (p *InactiveHandle) SetImmediateMode(mode bool) error
SetImmediateMode sets (or unsets) the immediate mode of the handle. In immediate mode, packets are delivered to the application as soon as they arrive. In other words, this overrides SetTimeout.
func (p *InactiveHandle) SetPromisc(promisc bool) error
SetPromisc sets the handle to either be promiscuous (capture packets unrelated to this host) or not.
func (p *InactiveHandle) SetRFMon(monitor bool) error
SetRFMon turns on radio monitoring mode, similar to promiscuous mode but for wireless networks. If this mode is enabled, the interface will not need to associate with an access point before it can receive traffic.
func (p *InactiveHandle) SetSnapLen(snaplen int) error
SetSnapLen sets the snap length (max bytes per packet to capture).
func (p *InactiveHandle) SetTimeout(timeout time.Duration) error
SetTimeout sets the read timeout for the handle.
See the package documentation for important details regarding 'timeout'.
func (p *InactiveHandle) SetTimestampSource(t TimestampSource) error
SetTimestampSource sets the type of timestamp generator PCAP uses when attaching timestamps to packets.
func (p *InactiveHandle) SupportedTimestamps() (out []TimestampSource)
SupportedTimestamps returns a list of supported timstamp types for this handle.
type Interface struct {
Name string
Description string
Flags uint32
Addresses []InterfaceAddress
}Interface describes a single network interface on a machine.
FindAllDevs attempts to enumerate all interfaces on the current machine.
type InterfaceAddress struct {
IP net.IP
Netmask net.IPMask // Netmask may be nil if we were unable to retrieve it.
Broadaddr net.IP // Broadcast address for this IP may be nil
P2P net.IP // P2P destination address for this IP may be nil
}InterfaceAddress describes an address associated with an Interface. Currently, it's IPv4/6 specific.
NextError is the return code from a call to Next.
const (
NextErrorOk NextError = 1
NextErrorTimeoutExpired NextError = 0
NextErrorReadError NextError = -1
// NextErrorNoMorePackets is returned when reading from a file (OpenOffline) and
// EOF is reached. When this happens, Next() returns io.EOF instead of this.
NextErrorNoMorePackets NextError = -2
NextErrorNotActivated NextError = -3
)NextError values.
NextError implements the error interface.
Stats contains statistics on how many packets were handled by a pcap handle, and what was done with those packets.
TimestampSource tells PCAP which type of timestamp to use for packets.
func TimestampSourceFromString(s string) (TimestampSource, error)
TimestampSourceFromString translates a string into a timestamp type, case insensitive.
func (t TimestampSource) String() string
String returns the timestamp type as a human-readable string.
| Path | Synopsis |
|---|---|
| gopacket_benchmark | This benchmark reads in file <tempdir>/gopacket_benchmark.pcap and measures the time it takes to decode all packets from that file. |
Package pcap imports 16 packages (graph) and is imported by 123 packages. Updated 2018-04-24. Refresh now. Tools for package owners.