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# Copyright (C) 2015 Nippon Telegraph and Telephone Corporation.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
# implied.
# See the License for the specific language governing permissions and
# limitations under the License.
"""
Parsing libpcap and reading/writing PCAP file.
Reference source: http://wiki.wireshark.org/Development/LibpcapFileFormat
Libpcap File Format
+---------------------+
| |
| Global Header |
| |
+---------------------+
| Packet Header |
+---------------------+
| Packet Data |
+---------------------+
| Packet Header |
+---------------------+
| Packet Data |
+---------------------+
| ... |
+---------------------+
"""
import struct
import sys
import time
class PcapFileHdr(object):
"""
Global Header
typedef struct pcap_hdr_s {
guint32 magic_number; /* magic number */
guint16 version_major; /* major version number */
guint16 version_minor; /* minor version number */
gint32 thiszone; /* GMT to local correction */
guint32 sigfigs; /* accuracy of timestamps */
guint32 snaplen; /* max length of captured packets,
in octets */
guint32 network; /* data link type */
} pcap_hdr_t;
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Magic Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Version Major | Version Minor |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Thiszone |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sigfigs |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Snaplen |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Network |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
File Format
"""
_FILE_HDR_FMT = '4sHHIIII'
_FILE_HDR_FMT_BIG_ENDIAN = '>' + _FILE_HDR_FMT
_FILE_HDR_FMT_LITTLE_ENDIAN = '<' + _FILE_HDR_FMT
FILE_HDR_SIZE = struct.calcsize(_FILE_HDR_FMT)
# Magic Number field is used to detect the file format itself and
# the byte ordering.
MAGIC_NUMBER_IDENTICAL = b'\xa1\xb2\xc3\xd4' # Big Endian
MAGIC_NUMBER_SWAPPED = b'\xd4\xc3\xb2\xa1' # Little Endian
def __init__(self, magic=MAGIC_NUMBER_SWAPPED, version_major=2,
version_minor=4, thiszone=0, sigfigs=0, snaplen=0,
network=0):
self.magic = magic
self.version_major = version_major
self.version_minor = version_minor
self.thiszone = thiszone
self.sigfigs = sigfigs
self.snaplen = snaplen
self.network = network
@classmethod
def parser(cls, buf):
magic_buf = buf[:4]
if magic_buf == cls.MAGIC_NUMBER_IDENTICAL:
# Big Endian
fmt = cls._FILE_HDR_FMT_BIG_ENDIAN
byteorder = 'big'
elif magic_buf == cls.MAGIC_NUMBER_SWAPPED:
# Little Endian
fmt = cls._FILE_HDR_FMT_LITTLE_ENDIAN
byteorder = 'little'
else:
raise struct.error('Invalid byte ordered pcap file.')
return cls(*struct.unpack_from(fmt, buf)), byteorder
def serialize(self):
if sys.byteorder == 'big':
# Big Endian
fmt = self._FILE_HDR_FMT_BIG_ENDIAN
self.magic = self.MAGIC_NUMBER_IDENTICAL
else:
# Little Endian
fmt = self._FILE_HDR_FMT_LITTLE_ENDIAN
self.magic = self.MAGIC_NUMBER_SWAPPED
return struct.pack(fmt, self.magic, self.version_major,
self.version_minor, self.thiszone,
self.sigfigs, self.snaplen, self.network)
class PcapPktHdr(object):
"""
Record (Packet) Header
typedef struct pcaprec_hdr_s {
guint32 ts_sec; /* timestamp seconds */
guint32 ts_usec; /* timestamp microseconds */
guint32 incl_len; /* number of octets of packet
saved in file */
guint32 orig_len; /* actual length of packet */
} pcaprec_hdr_t;
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Timestamp Seconds |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Timestamp Microseconds |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Number of octets of saved in file |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Actual length of packet |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Record (Packet) Header Format
"""
_PKT_HDR_FMT = 'IIII'
_PKT_HDR_FMT_BIG_ENDIAN = '>' + _PKT_HDR_FMT
_PKT_HDR_FMT_LITTLE_ENDIAN = '<' + _PKT_HDR_FMT
PKT_HDR_SIZE = struct.calcsize(_PKT_HDR_FMT)
def __init__(self, ts_sec=0, ts_usec=0, incl_len=0, orig_len=0):
self.ts_sec = ts_sec
self.ts_usec = ts_usec
self.incl_len = incl_len
self.orig_len = orig_len
@classmethod
def parser(cls, buf, byteorder='little'):
if not buf:
raise IndexError('No data')
if byteorder == 'big':
# Big Endian
fmt = cls._PKT_HDR_FMT_BIG_ENDIAN
else:
# Little Endian
fmt = cls._PKT_HDR_FMT_LITTLE_ENDIAN
(ts_sec, ts_usec, incl_len, orig_len) = struct.unpack_from(fmt, buf)
hdr = cls(ts_sec, ts_usec, incl_len, orig_len)
return hdr, buf[cls.PKT_HDR_SIZE:cls.PKT_HDR_SIZE + incl_len]
def serialize(self):
if sys.byteorder == 'big':
# Big Endian
fmt = self._PKT_HDR_FMT_BIG_ENDIAN
else:
# Little Endian
fmt = self._PKT_HDR_FMT_LITTLE_ENDIAN
return struct.pack(fmt, self.ts_sec, self.ts_usec,
self.incl_len, self.orig_len)
class Reader(object):
"""
PCAP file reader
================ ===================================
Argument Description
================ ===================================
file_obj File object which reading PCAP file
in binary mode
================ ===================================
Example of usage::
from os_ken.lib import pcaplib
from os_ken.lib.packet import packet
frame_count = 0
# iterate pcaplib.Reader that yields (timestamp, packet_data)
# in the PCAP file
for ts, buf in pcaplib.Reader(open('test.pcap', 'rb')):
frame_count += 1
pkt = packet.Packet(buf)
print("%d, %f, %s" % (frame_count, ts, pkt))
"""
def __init__(self, file_obj):
self._fp = file_obj
buf = self._fp.read(PcapFileHdr.FILE_HDR_SIZE)
# Read only pcap file header
self.pcap_header, self._file_byteorder = PcapFileHdr.parser(buf)
# Read pcap data with out header
self._pcap_body = self._fp.read()
self._fp.close()
self._next_pos = 0
def __iter__(self):
return self
def next(self):
try:
pkt_hdr, pkt_data = PcapPktHdr.parser(
self._pcap_body[self._next_pos:], self._file_byteorder)
self._next_pos += pkt_hdr.incl_len + PcapPktHdr.PKT_HDR_SIZE
except IndexError:
raise StopIteration()
return pkt_hdr.ts_sec + (pkt_hdr.ts_usec / 1e6), pkt_data
# for Python 3 compatible
__next__ = next
class Writer(object):
"""
PCAP file writer
========== ==================================================
Argument Description
========== ==================================================
file_obj File object which writing PCAP file in binary mode
snaplen Max length of captured packets (in octets)
network Data link type. (e.g. 1 for Ethernet,
see `tcpdump.org`_ for details)
========== ==================================================
.. _tcpdump.org: http://www.tcpdump.org/linktypes.html
Example of usage::
...
from os_ken.lib import pcaplib
class SimpleSwitch13(app_manager.OSKenApp):
OFP_VERSIONS = [ofproto_v1_3.OFP_VERSION]
def __init__(self, *args, **kwargs):
super(SimpleSwitch13, self).__init__(*args, **kwargs)
self.mac_to_port = {}
# Create pcaplib.Writer instance with a file object
# for the PCAP file
self.pcap_writer = pcaplib.Writer(open('mypcap.pcap', 'wb'))
...
@set_ev_cls(ofp_event.EventOFPPacketIn, MAIN_DISPATCHER)
def _packet_in_handler(self, ev):
# Dump the packet data into PCAP file
self.pcap_writer.write_pkt(ev.msg.data)
...
"""
def __init__(self, file_obj, snaplen=65535, network=1):
self._f = file_obj
self.snaplen = snaplen
self.network = network
self._write_pcap_file_hdr()
def _write_pcap_file_hdr(self):
pcap_file_hdr = PcapFileHdr(snaplen=self.snaplen,
network=self.network)
self._f.write(pcap_file_hdr.serialize())
def _write_pkt_hdr(self, ts, buf_len):
sec = int(ts)
usec = int(round(ts % 1, 6) * 1e6) if sec != 0 else 0
pc_pkt_hdr = PcapPktHdr(ts_sec=sec, ts_usec=usec,
incl_len=buf_len, orig_len=buf_len)
self._f.write(pc_pkt_hdr.serialize())
def write_pkt(self, buf, ts=None):
ts = time.time() if ts is None else ts
# Check the max length of captured packets
buf_len = len(buf)
if buf_len > self.snaplen:
buf_len = self.snaplen
buf = buf[:self.snaplen]
self._write_pkt_hdr(ts, buf_len)
self._f.write(buf)
def __del__(self):
self._f.close()
|
