def test_spb_snap_lengths():
"""
Simple Packet Blocks present a unique challenge in parsing. The packet does not
contain an explicit "captured length" indicator, only the original observed
packet length; one must consult the capturing network interface's snap length
in order to determine whether the packet may have been truncated.
The block interface was designed to take care of most of this for the developer,
both for reading and writing. For reading, the :py:method:`captured_len` is
a property that works out its value from the capturing interface and the original
packet length. For writing, packet data will be truncated to the capturing
interface's snap length if it would be too big.
"""
# Binary data to write/test
data = bytes(range(0, 256))
# First session: no snap length
o_shb = blocks.SectionHeader()
o_idb = o_shb.new_member(blocks.InterfaceDescription) # noqa: F841
o_blk1 = o_shb.new_member(blocks.SimplePacket, packet_data=data)
fake_file = io.BytesIO()
writer = FileWriter(fake_file, o_shb)
writer.write_block(o_blk1)
fake_file.seek(0)
(i_shb, i_idb, i_blk1) = list(FileScanner(fake_file))
assert i_blk1.captured_len == len(data)
assert i_blk1.packet_len == len(data)
assert i_blk1.packet_data == data
# Second session: with snap length
o_shb = blocks.SectionHeader()
o_idb = o_shb.new_member(blocks.InterfaceDescription,
snaplen=32) # noqa: F841
o_blk1 = o_shb.new_member(blocks.SimplePacket, packet_data=data[:16])
o_blk2 = o_shb.new_member(blocks.SimplePacket, packet_data=data[:32])
o_blk3 = o_shb.new_member(blocks.SimplePacket, packet_data=data[:33])
fake_file = io.BytesIO()
writer = FileWriter(fake_file, o_shb)
writer.write_block(o_blk1)
writer.write_block(o_blk2)
writer.write_block(o_blk3)
fake_file.seek(0)
(i_shb, i_idb, i_blk1, i_blk2, i_blk3) = list(FileScanner(fake_file))
assert i_blk1.captured_len == 16
assert i_blk1.packet_len == 16
assert i_blk1.packet_data == data[:16]
assert i_blk2.captured_len == 32
assert i_blk2.packet_len == 32
assert i_blk2.packet_data == data[:32]
assert i_blk3.captured_len == 32
assert i_blk3.packet_len == 33
assert i_blk3.packet_data == data[:32]
def _read_section_header(self):
"""
Section information headers are special blocks in that they
modify the state of the FileScanner instance (to change current
section / endianness)
"""
section_info = read_section_header(self.stream)
self.endianness = section_info["endianness"] # todo: use property?
# todo: make this use the standard schema facilities as well!
return blocks.SectionHeader(raw=section_info["data"],
endianness=section_info["endianness"])
def test_write_read_all_blocks(endianness):
# Track the blocks we're writing
out_blocks = []
# Build our original/output session
o_shb = blocks.SectionHeader(
endianness=endianness,
options={
"shb_hardware": "pytest",
"shb_os": "python",
"shb_userappl": "python-pcapng",
},
)
out_blocks.append(o_shb)
o_idb = o_shb.new_member(
blocks.InterfaceDescription,
link_type=1,
snaplen=65535,
options={
"if_name": "Interface Zero",
"if_description": "Test interface",
"if_os": "python",
"if_hardware": "whatever",
"if_filter": [(0, b"tcp port 23 and host 192.0.2.5")],
},
)
out_blocks.append(o_idb)
# The SHB and IDBs will be written right away here.
fake_file = io.BytesIO()
writer = FileWriter(fake_file, o_shb)
# Add blocks to the output
# epb
blk = o_shb.new_member(blocks.EnhancedPacket)
blk.packet_data = b"Test data 123 XYZ"
writer.write_block(blk)
out_blocks.append(blk)
# spb
blk = o_shb.new_member(blocks.SimplePacket)
blk.packet_data = b"Test data 123 XYZ"
writer.write_block(blk)
out_blocks.append(blk)
# pb (which is obsolete)
set_strictness(Strictness.FORBID)
blk = o_shb.new_member(blocks.ObsoletePacket)
blk.packet_data = b"Test data 123 XYZ"
with pytest.raises(PcapngStrictnessError, match="obsolete"):
# Should prevent writing by default
writer.write_block(blk)
# Set to warning mode and try again
set_strictness(Strictness.WARN)
with pytest.warns(PcapngStrictnessWarning, match="obsolete"):
# Should write the obsolete block now
writer.write_block(blk)
out_blocks.append(blk)
# Set to fix mode and try again
set_strictness(Strictness.FIX)
with pytest.warns(PcapngStrictnessWarning, match="obsolete"):
# Should write an enhanced block now
writer.write_block(blk)
out_blocks.append(blk.enhanced())
set_strictness(Strictness.FORBID)
# nrb
blk = o_shb.new_member(
blocks.NameResolution,
records=[
{
"type": 1,
"address": "127.0.0.1",
"names": ["localhost", "localhost.localdomain"],
},
{
"type": 2,
"address": "::1",
"names": ["localhost", "localhost.localdomain"],
},
],
)
writer.write_block(blk)
out_blocks.append(blk)
# isb
blk = o_shb.new_member(
blocks.InterfaceStatistics,
interface_id=0,
timestamp_high=0x01234567,
timestamp_low=0x89ABCDEF,
options={
"isb_starttime": 0x0123456789ABCD00,
"isb_endtime": 0x0123456789ABCDEF,
"isb_usrdeliv": 50,
},
)
writer.write_block(blk)
out_blocks.append(blk)
# Done writing blocks.
# Now get back what we wrote and see if things line up.
fake_file.seek(0)
in_blocks = list(FileScanner(fake_file))
compare_blocklists(in_blocks, out_blocks)
#!/usr/bin/env python
import argparse
import pcapng.blocks as blocks
from pcapng import FileWriter
parser = argparse.ArgumentParser()
parser.add_argument("outfile", type=argparse.FileType("wb"))
args = parser.parse_args()
shb = blocks.SectionHeader(
options={
"shb_hardware": "artificial",
"shb_os": "python",
"shb_userappl": "python-pcapng",
})
idb = shb.new_member(
blocks.InterfaceDescription,
link_type=1,
options={
"if_description": "Hand-rolled",
"if_os": "Python",
"if_filter": [(0, b"tcp port 23 and host 192.0.2.5")],
},
)
# FileWriter() immediately writes the SHB and any IDBs you've added to it
writer = FileWriter(args.outfile, shb)
# fmt: off
#!/usr/bin/env python
import pcapng
import pcapng.blocks as blocks
import argparse
parser = argparse.ArgumentParser()
parser.add_argument('outfile', type=argparse.FileType('wb'))
args = parser.parse_args()
shb = blocks.SectionHeader(
options={
'shb_hardware': 'artificial',
'shb_os': 'python',
'shb_userappl': 'python-pcapng'
})
shb.write(args.outfile)
idb = shb.new_member(blocks.InterfaceDescription,
link_type=1,
options={
"if_description": "Hand-rolled",
"if_os": "Python"
})
idb.write(args.outfile)
test_pl = (
0xff,
0xff,
0xff,
0xff,
0xff,
