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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 (
"reflect"
"time"
"unsafe"
)
// #include <linux/if_packet.h>
import "C"
// Our model of handling all TPacket versions is a little hacky, to say the
// least. We use the header interface to handle interactions with the
// tpacket1/tpacket2 packet header AND the tpacket3 block header. The big
// difference is that tpacket3's block header implements the next() call to get
// the next packet within the block, while v1/v2 just always return false.
type header interface {
// getStatus returns the TPacket status of the current header.
getStatus() int
// clearStatus clears the status of the current header, releasing its
// underlying data back to the kernel for future use with new packets.
// Using the header after calling clearStatus is an error. clearStatus
// should only be called after next() returns false.
clearStatus()
// getTime returns the timestamp for the current packet pointed to by
// the header.
getTime() time.Time
// getData returns the packet data pointed to by the current header.
getData() []byte
// getLength returns the total length of the packet.
getLength() int
// getIfaceIndex returns the index of the network interface
// where the packet was seen. The index can later be translated to a name.
getIfaceIndex() int
// next moves this header to point to the next packet it contains,
// returning true on success (in which case getTime and getData will
// return values for the new packet) or false if there are no more
// packets (in which case clearStatus should be called).
next() bool
}
func tpAlign(x int) int {
return int((uint(x) + tpacketAlignment - 1) &^ (tpacketAlignment - 1))
}
type v1header C.struct_tpacket_hdr
type v2header C.struct_tpacket2_hdr
func makeSlice(start uintptr, length int) (data []byte) {
slice := (*reflect.SliceHeader)(unsafe.Pointer(&data))
slice.Data = start
slice.Len = length
slice.Cap = length
return
}
func (h *v1header) getStatus() int {
return int(h.tp_status)
}
func (h *v1header) clearStatus() {
h.tp_status = 0
}
func (h *v1header) getTime() time.Time {
return time.Unix(int64(h.tp_sec), int64(h.tp_usec)*1000)
}
func (h *v1header) getData() []byte {
return makeSlice(uintptr(unsafe.Pointer(h))+uintptr(h.tp_mac), int(h.tp_snaplen))
}
func (h *v1header) getLength() int {
return int(h.tp_len)
}
func (h *v1header) getIfaceIndex() int {
ll := (*C.struct_sockaddr_ll)(unsafe.Pointer(uintptr(unsafe.Pointer(h)) + uintptr(tpAlign(int(C.sizeof_struct_tpacket_hdr)))))
return int(ll.sll_ifindex)
}
func (h *v1header) next() bool {
return false
}
func (h *v2header) getStatus() int {
return int(h.tp_status)
}
func (h *v2header) clearStatus() {
h.tp_status = 0
}
func (h *v2header) getTime() time.Time {
return time.Unix(int64(h.tp_sec), int64(h.tp_nsec))
}
func (h *v2header) getData() []byte {
return makeSlice(uintptr(unsafe.Pointer(h))+uintptr(h.tp_mac), int(h.tp_snaplen))
}
func (h *v2header) getLength() int {
return int(h.tp_len)
}
func (h *v2header) getIfaceIndex() int {
ll := (*C.struct_sockaddr_ll)(unsafe.Pointer(uintptr(unsafe.Pointer(h)) + uintptr(tpAlign(int(C.sizeof_struct_tpacket2_hdr)))))
return int(ll.sll_ifindex)
}
func (h *v2header) next() bool {
return false
}
type v3wrapper struct {
block *C.struct_tpacket_block_desc
blockhdr *C.struct_tpacket_hdr_v1
packet *C.struct_tpacket3_hdr
used C.__u32
}
func initV3Wrapper(block unsafe.Pointer) (w v3wrapper) {
w.block = (*C.struct_tpacket_block_desc)(block)
w.blockhdr = (*C.struct_tpacket_hdr_v1)(unsafe.Pointer(&w.block.hdr[0]))
w.packet = (*C.struct_tpacket3_hdr)(unsafe.Pointer(uintptr(block) + uintptr(w.blockhdr.offset_to_first_pkt)))
return
}
func (w *v3wrapper) getStatus() int {
return int(w.blockhdr.block_status)
}
func (w *v3wrapper) clearStatus() {
w.blockhdr.block_status = 0
}
func (w *v3wrapper) getTime() time.Time {
return time.Unix(int64(w.packet.tp_sec), int64(w.packet.tp_nsec))
}
func (w *v3wrapper) getData() []byte {
return makeSlice(uintptr(unsafe.Pointer(w.packet))+uintptr(w.packet.tp_mac), int(w.packet.tp_snaplen))
}
func (w *v3wrapper) getLength() int {
return int(w.packet.tp_len)
}
func (w *v3wrapper) getIfaceIndex() int {
ll := (*C.struct_sockaddr_ll)(unsafe.Pointer(uintptr(unsafe.Pointer(w.packet)) + uintptr(tpAlign(int(C.sizeof_struct_tpacket3_hdr)))))
return int(ll.sll_ifindex)
}
func (w *v3wrapper) next() bool {
w.used++
if w.used >= w.blockhdr.num_pkts {
return false
}
next := uintptr(unsafe.Pointer(w.packet))
if w.packet.tp_next_offset != 0 {
next += uintptr(w.packet.tp_next_offset)
} else {
next += uintptr(tpacketAlign(int(w.packet.tp_snaplen) + int(w.packet.tp_mac)))
}
w.packet = (*C.struct_tpacket3_hdr)(unsafe.Pointer(next))
return true
}
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