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packet.py
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packet.py
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import ipaddress
import pprint
from dataclasses import asdict, dataclass
from enum import IntEnum
from typing import List, Union
from buffer import Buffer
class ResultCode(IntEnum):
NOERROR = 0
FORMERR = 1
SERVFAIL = 2
NXDOMAIN = 3
NOTIMP = 4
REFUSED = 5
class QueryType(IntEnum):
UNKNOWN = 0
A = 1
NS = 2
CNAME = 5
SOA = 6
PTR = 12
MX = 15
AAAA = 28
@dataclass
class DnsHeader:
id: int # 16 bits
recursion_desired: bool # 1 bit
truncated_message: bool # 1 bit
authoritative_answer: bool # 1 bit
opcode: int # 4 bits
response: bool # 1 bit
rescode: ResultCode # 4 bits
checking_disabled: bool # 1 bit
authed_data: bool # 1 bit
z: bool # 1 bit
recursion_available: bool # 1 bit
questions: int # 16 bits
answers: int # 16 bits
authoritative_entries: int # 16 bits
resource_entries: int # 16 bits
@classmethod
def default(cls):
return cls(
id=0,
recursion_desired=False,
truncated_message=False,
authoritative_answer=False,
opcode=0,
response=False,
rescode=ResultCode.NOERROR,
checking_disabled=False,
authed_data=False,
z=False,
recursion_available=False,
questions=0,
answers=0,
authoritative_entries=0,
resource_entries=0,
)
@classmethod
def parse(cls, buf: Buffer):
assert len(buf) >= 12, "Packet header must be atleast 12 bytes"
(id, flags, questions, answers, auth, res) = buf.unpack("!HHHHHH")
# a represents the first 8 bits of the flags
# b represents the last 8 bits of the flags
# flags is 16 bits long
a, b = flags >> 8, flags & 0xFF
recursion_desired = (a & (1 << 0)) > 0
truncated_message = (a & (1 << 1)) > 0
authoritative_answer = (a & (1 << 2)) > 0
opcode = (a >> 3) & 0x0F
response = (a & (1 << 7)) > 0
rescode = ResultCode(b & 0x0F)
checking_disabled = (b & (1 << 4)) > 0
authed_data = (b & (1 << 5)) > 0
z = (b & (1 << 6)) > 0
recursion_available = (b & (1 << 7)) > 0
return cls(
id=id,
recursion_desired=recursion_desired,
truncated_message=truncated_message,
authoritative_answer=authoritative_answer,
opcode=opcode,
response=response,
rescode=rescode,
checking_disabled=checking_disabled,
authed_data=authed_data,
z=z,
recursion_available=recursion_available,
questions=questions,
answers=answers,
authoritative_entries=auth,
resource_entries=res,
)
def __str__(self):
return f"DnsHeader {pprint.pformat(asdict(self))}"
def write(self, buf: Buffer):
buf.write("!H", self.id)
buf.write(
"!B",
(
(self.recursion_desired << 0)
| (self.truncated_message << 1)
| (self.authoritative_answer << 2)
| (self.opcode << 3)
| (self.response << 7)
),
)
buf.write(
"!B",
(
(self.rescode << 0)
| (self.checking_disabled << 4)
| (self.authed_data << 5)
| (self.z << 6)
| (self.recursion_available << 7)
),
)
buf.write(
"!HHHH",
self.questions,
self.answers,
self.authoritative_entries,
self.resource_entries,
)
@dataclass
class DnsQuestion:
name: str
qtype: QueryType
@classmethod
def parse(cls, buf: Buffer):
name = buf.read_qname()
(qtype, _) = buf.unpack("!HH")
return cls(name=name, qtype=QueryType(qtype))
def __str__(self):
return f"DnsQuestion {pprint.pformat(asdict(self))}"
def write(self, buf: Buffer):
buf.write_qname(self.name)
buf.write("!HH", self.qtype, 1)
@dataclass
class DnsRecordUnknown:
domain: str
qtype: int # 16 bits
length: int # 16 bits
ttl: int # 32 bits
def write(self, buf: Buffer):
print("Writing unknown record")
buf.write_qname(self.domain)
buf.write("!HHIH", self.qtype, 1, self.ttl, self.length)
@dataclass
class DnsRecordA:
domain: str
addr: ipaddress.IPv4Address
ttl: int # 32 bits
def write(self, buf: Buffer):
buf.write_qname(self.domain)
buf.write("!HHIH", QueryType.A, 1, self.ttl, 4)
buf.write("!I", int(self.addr))
@dataclass
class DnsRecordSOA:
domain: str
mname: str
rname: str
serial: int
refresh: int
retry: int
expire: int
minimum: int
ttl: int
@dataclass
class DnsRecordNS:
domain: str
ns_name: str
ttl: int
@dataclass
class DnsRecordAAAA:
domain: str
ipv6_addr: str
ttl: int
@dataclass
class DnsRecordCNAME:
domain: str
cname: str
ttl: int
DnsRecord = Union[DnsRecordUnknown, DnsRecordA]
@dataclass
class DnsRecord:
record: Union[DnsRecordUnknown, DnsRecordA]
@classmethod
def parse(cls, buf: Buffer):
data = None
domain = buf.read_qname()
(qtype,) = buf.unpack("!H")
try:
qtype = QueryType(qtype)
except ValueError:
pass
_ = buf.unpack("!H") # class
(ttl,) = buf.unpack("!I")
(length,) = buf.unpack("!H")
if qtype == QueryType.A:
(addr,) = buf.unpack("!I")
addr = ipaddress.ip_address(addr)
data = DnsRecordA(domain=domain, addr=addr, ttl=ttl)
elif qtype == QueryType.SOA:
mname = buf.read_qname()
rname = buf.read_qname()
(serial,) = buf.unpack("!I")
(refresh,) = buf.unpack("!I")
(retry,) = buf.unpack("!I")
(expire,) = buf.unpack("!I")
(minimum,) = buf.unpack("!I")
data = DnsRecordSOA(
domain=domain,
mname=mname,
rname=rname,
serial=serial,
refresh=refresh,
retry=retry,
expire=expire,
minimum=minimum,
ttl=ttl,
)
elif qtype == QueryType.NS:
ns_name = buf.read_qname()
data = DnsRecordNS(domain=domain, ns_name=ns_name, ttl=ttl)
elif qtype == QueryType.AAAA:
(ipv6_bytes,) = buf.unpack("!16s")
ipv6_addr = ipaddress.IPv6Address(ipv6_bytes).compressed
data = DnsRecordAAAA(domain=domain, ipv6_addr=ipv6_addr, ttl=ttl)
elif qtype == QueryType.CNAME:
cname = buf.read_qname()
data = DnsRecordCNAME(domain=domain, cname=cname, ttl=ttl)
else:
data = DnsRecordUnknown(domain=domain, qtype=qtype, length=length, ttl=ttl)
return cls(record=data)
def write(self, buf: Buffer):
self.record.write(buf)
@dataclass
class DnsPacket:
header: DnsHeader
questions: List[DnsQuestion]
answers: List[DnsRecord]
authoritative_entries: List[DnsRecord]
resource_entries: List[DnsRecord]
@classmethod
def default(cls):
return cls(
header=DnsHeader.default(),
questions=[],
answers=[],
authoritative_entries=[],
resource_entries=[],
)
@classmethod
def parse(cls, buf: Buffer):
questions = []
answers = []
authoritative_entries = []
resource_entries = []
header = DnsHeader.parse(buf)
for _ in range(header.questions):
questions.append(DnsQuestion.parse(buf))
for _ in range(header.answers):
# answers.append(parse_dns_record(buf))
answers.append(DnsRecord.parse(buf))
for _ in range(header.authoritative_entries):
# authoritative_entries.append(parse_dns_record(buf))
authoritative_entries.append(DnsRecord.parse(buf))
for _ in range(header.resource_entries):
# resource_entries.append(parse_dns_record(buf))
resource_entries.append(DnsRecord.parse(buf))
return cls(
header=header,
questions=questions,
answers=answers,
authoritative_entries=authoritative_entries,
resource_entries=resource_entries,
)
def write(self, buf: Buffer):
self.header.write(buf)
for question in self.questions:
question.write(buf)
for answer in self.answers:
answer.write(buf)
for auth in self.authoritative_entries:
auth.write(buf)
for resource in self.resource_entries:
resource.write(buf)
if __name__ == "__main__":
import sys
if len(sys.argv) == 1:
print("Usage: python3 packet.py <filename>")
sys.exit(1)
else:
filename = sys.argv[1]
with open(filename, "rb") as f:
buf = Buffer(f.read())
packet = DnsPacket.parse(buf)
pprint.pprint(packet)