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#!/usr/bin/env python2
""" A DNS resource record
This class contains classes for DNS resource records and record data. This
module is fully implemented. You will have this module in the implementation
of your resolver and server.
"""
import socket
import struct
from dns.classes import Class
from dns.types import Type
class ResourceRecord(object):
""" DNS resource record """
def __init__(self, name, type_, class_, ttl, rdata):
""" Create a new resource record
Args:
name (str): domain name
type_ (Type): the type
class_ (Class): the class
rdata (RecordData): the record data
"""
self.name = name
self.type_ = type_
self.class_ = class_
self.ttl = ttl
self.rdata = rdata
def to_bytes(self, offset, composer):
""" Convert ResourceRecord to bytes """
name = composer.to_bytes(offset, [self.name])
offset += len(name)
rdata = self.rdata.to_bytes(offset, composer)
return (name +
struct.pack("!HHIH",
self.type_,
self.class_,
self.ttl,
len(rdata)) +
rdata)
@classmethod
def from_bytes(cls, packet, offset, parser):
""" Convert ResourceRecord from bytes """
names, offset = parser.from_bytes(packet, offset, 1)
name = names[0]
type_, class_, ttl, rdlength = struct.unpack_from("!HHIH", packet, offset)
offset += 10
rdata = RecordData.from_bytes(type_, packet, offset, rdlength, parser)
offset += rdlength
return cls(name, type_, class_, ttl, rdata), offset
class RecordData(object):
""" Record Data """
def __init__(self, data):
""" Initialize the record data
Args:
data (str): data
"""
self.data = data
@staticmethod
def create(type_, data):
""" Create a RecordData object from bytes
Args:
type_ (Type): type
packet (bytes): packet
offset (int): offset in message
rdlength (int): length of rdata
parser (int): domain name parser
"""
classdict = {
Type.A: ARecordData,
Type.CNAME: CNAMERecordData,
Type.NS: NSRecordData,
Type.AAAA: AAAARecordData
}
if type_ in classdict:
return classdict[type_](data)
else:
return GenericRecordData(data)
@staticmethod
def from_bytes(type_, packet, offset, rdlength, parser):
""" Create a RecordData object from bytes
Args:
type_ (Type): type
packet (bytes): packet
offset (int): offset in message
rdlength (int): length of rdata
parser (int): domain name parser
"""
classdict = {
Type.A: ARecordData,
Type.CNAME: CNAMERecordData,
Type.NS: NSRecordData,
Type.AAAA: AAAARecordData
}
if type_ in classdict:
return classdict[type_].from_bytes(
packet, offset, rdlength, parser)
else:
return GenericRecordData.from_bytes(
packet, offset, rdlength, parser)
class ARecordData(RecordData):
def to_bytes(self, offset, composer):
""" Convert to bytes
Args:
offset (int): offset in message
composer (Composer): domain name composer
"""
return socket.inet_aton(self.data)
@classmethod
def from_bytes(cls, packet, offset, rdlength, parser):
""" Create a RecordData object from bytes
Args:
packet (bytes): packet
offset (int): offset in message
rdlength (int): length of rdata
parser (int): domain name parser
"""
data = socket.inet_ntoa(packet[offset:offset+4])
return cls(data)
class CNAMERecordData(RecordData):
def to_bytes(self, offset, composer):
""" Convert to bytes
Args:
offset (int): offset in message
composer (Composer): domain name composer
"""
return composer.to_bytes(offset, [self.data])
@classmethod
def from_bytes(cls, packet, offset, rdlength, parser):
""" Create a RecordData object from bytes
Args:
packet (bytes): packet
offset (int): offset in message
rdlength (int): length of rdata
parser (int): domain name parser
"""
names, offset = parser.from_bytes(packet, offset, 1)
data = names[0]
return cls(data)
class NSRecordData(RecordData):
def to_bytes(self, offset, composer):
""" Convert to bytes
Args:
offset (int): offset in message
composer (Composer): domain name composer
"""
return composer.to_bytes(offset, [self.data])
@classmethod
def from_bytes(cls, packet, offset, rdlength, parser):
""" Create a RecordData object from bytes
Args:
packet (bytes): packet
offset (int): offset in message
rdlength (int): length of rdata
parser (int): domain name parser
"""
names, offset = parser.from_bytes(packet, offset, 1)
data = names[0]
return cls(data)
class AAAARecordData(RecordData):
def to_bytes(self, offset, composer):
""" Convert to bytes
Args:
offset (int): offset in message
composer (Composer): domain name composer
"""
return socket.inet_pton(socket.AF_INET6, self.data)
@classmethod
def from_bytes(packet, offset, rdlength, parser):
""" Create a RecordData object from bytes
Args:
packet (bytes): packet
offset (int): offset in message
rdlength (int): length of rdata
parser (int): domain name parser
"""
data = socket.inet_ntop(socket.AF_INET6, packet[offset:offset+16])
return cls(data)
class GenericRecordData(RecordData):
def to_bytes(self, offset, composer):
""" Convert to bytes
Args:
offset (int): offset in message
composer (Composer): domain name composer
"""
return self.data
@classmethod
def from_bytes(packet, offset, rdlength, parser):
""" Create a RecordData object from bytes
Args:
packet (bytes): packet
offset (int): offset in message
rdlength (int): length of rdata
parser (int): domain name parser
"""
data = packet[offset:offset+rdlength]
return cls(data)
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