# 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()