dnslib 0.9.0

dnslib
------

A library to encode/decode DNS wire-format packets supporting both
Python 2.7 and Python 3.2+.

The library provides:

* Support for encoding/decoding DNS packets between wire format,
python objects, and Zone/DiG textual representation (dnslib.dns)

* A server framework allowing the simple creation of custom DNS
resolvers (dnslib.server) and a number of example servers
created using this frameowork

* A number of utilities for testing (dnslib.client, dnslib.proxy,
dnslib.intercept)

Python 3 support was added in Version 0.9.0 which represented a fairly
major update to the library - the key changes include:

* Python 2.7/3.2+ support (the last version supporting Python 2.6
or earlier was version 0.8.3)

* Support for encoding/decoding resource records in 'Zone' (BIND)
file format

* Support for encoding/decoding backets in 'DiG' format

* Server framework allowing (in most cases) custom resolvers to
be created by just subclassing the DNSResolver class and
overringing the 'resolve' method

* A lot of fixes to error detection/handling which should make
the library much more robust to invalid/unsupported data. The
library should now either return a valid DNSRecord instance
or raise DNSError (tested via fuzzing)

* Improved utilities (dnslib.client, dnslib.proxy, dnslib.intercept)

* Improvements to encoding/decoding tests including the ability
to generate test data automatically in test_decode.py (comparing
outputs against DiG)

* Ability to compare and diff DNSRecords

This is a large release and despite the testing there therefore are likely
to be some bugs. Once the 0.9 release is sufficiently stable I would expect
to release as 1.0.0 (and stabilise th api)

The key DNS packet handling classes are in dnslib.dns and map to the
standard DNS packet sections:

* DNSRecord - container for DNS packet. Contains:
- DNSHeader
- Question section containing zero or more DNSQuestion objects
- Answer section containing zero or more RR objects
- Authority section containing zero or more RR objects
- Additional section containing zero or more RR objects
* DNS RRs (resource records) contain an RR header and an RD object)
* Specific RD types are implemented as subclasses of RD
* DNS labels are represented by a DNSLabel class - in most cases
this handles conversion to/from textual representation however
does support arbitatry labels via a tuple of bytes objects)

Version 0.9 of the library was a major rewrite to support Python 3.2+
(retaining support for Python 2.7+). As part of the Py3 changes a
number of other significant changes were intrtoduced:

- Much better error handling (packet decoding errors should be
caught and DNSError raised)

Usage:
------

To decode a DNS packet:

>>> packet = binascii.unhexlify(b'd5ad818000010005000000000377777706676f6f676c6503636f6d0000010001c00c0005000100000005000803777777016cc010c02c0001000100000005000442f95b68c02c0001000100000005000442f95b63c02c0001000100000005000442f95b67c02c0001000100000005000442f95b93')
>>> d = DNSRecord.parse(packet)
>>> d
<DNS Header: id=0xd5ad type=RESPONSE opcode=QUERY flags=RD,RA rcode='NOERROR' q=1 a=5 ns=0 ar=0>
<DNS Question: 'www.google.com.' qtype=A qclass=IN>
<DNS RR: 'www.google.com.' rtype=CNAME rclass=IN ttl=5 rdata='www.l.google.com.'>
<DNS RR: 'www.l.google.com.' rtype=A rclass=IN ttl=5 rdata='66.249.91.104'>
<DNS RR: 'www.l.google.com.' rtype=A rclass=IN ttl=5 rdata='66.249.91.99'>
<DNS RR: 'www.l.google.com.' rtype=A rclass=IN ttl=5 rdata='66.249.91.103'>
<DNS RR: 'www.l.google.com.' rtype=A rclass=IN ttl=5 rdata='66.249.91.147'>

The default text representation of the DNSRecord is in zone file format:

>>> print(d)
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 54701
;; flags: qr rd ra; QUERY: 1, ANSWER: 5, AUTHORITY: 0, ADDITIONAL: 0
;; QUESTION SECTION:
;www.google.com. IN A
;; ANSWER SECTION:
www.google.com. 5 IN CNAME www.l.google.com.
www.l.google.com. 5 IN A 66.249.91.104
www.l.google.com. 5 IN A 66.249.91.99
www.l.google.com. 5 IN A 66.249.91.103
www.l.google.com. 5 IN A 66.249.91.147

To create a DNS Request Packet:

>>> d = DNSRecord.question("google.com")

(This is equivalent to: d = DNSRecord(q=DNSQuestion("google.com") )

>>> d
<DNS Header: id=... type=QUERY opcode=QUERY flags=RD rcode='NOERROR' q=1 a=0 ns=0 ar=0>
<DNS Question: 'google.com.' qtype=A qclass=IN>

>>> str(DNSRecord.parse(d.pack())) == str(d)
True

>>> print(d)
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: ...
;; flags: rd; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 0
;; QUESTION SECTION:
;google.com. IN A

>>> d = DNSRecord.question("google.com","MX")

(This is equivalent to: d = DNSRecord(q=DNSQuestion("google.com",QTYPE.MX) )

>>> str(DNSRecord.parse(d.pack())) == str(d)
True

>>> print(d)
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: ...
;; flags: rd; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 0
;; QUESTION SECTION:
;google.com. IN MX

To create a DNS Response Packet:

>>> d = DNSRecord(DNSHeader(qr=1,aa=1,ra=1),
... q=DNSQuestion("abc.com"),
... a=RR("abc.com",rdata=A("1.2.3.4")))
>>> d
<DNS Header: id=... type=RESPONSE opcode=QUERY flags=AA,RD,RA rcode='NOERROR' q=1 a=1 ns=0 ar=0>
<DNS Question: 'abc.com.' qtype=A qclass=IN>
<DNS RR: 'abc.com.' rtype=A rclass=IN ttl=0 rdata='1.2.3.4'>
>>> str(DNSRecord.parse(d.pack())) == str(d)
True

>>> print(d)
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: ...
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0
;; QUESTION SECTION:
;abc.com. IN A
;; ANSWER SECTION:
abc.com. 0 IN A 1.2.3.4

It is also possible to create RRs from a string in zone file format

>>> RR.fromZone("abc.com IN A 1.2.3.4")
[<DNS RR: 'abc.com.' rtype=A rclass=IN ttl=0 rdata='1.2.3.4'>]

(Note: this produces a list of RRs which should be unpacked if being
passed to add_answer/add_auth/add_ar etc)

>>> q = DNSRecord.question("abc.com")
>>> a = q.reply()
>>> a.add_answer(*RR.fromZone("abc.com 60 A 1.2.3.4"))
>>> print(a)
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: ...
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0
;; QUESTION SECTION:
;abc.com. IN A
;; ANSWER SECTION:
abc.com. 60 IN A 1.2.3.4

The zone file can contain multiple entries and supports most of the normal
format defined in RFC1035 (specifically not $INCLUDE)

>>> z = '''
... $TTL 300
... $ORIGIN abc.com
...
... @ IN MX 10 mail.abc.com.
... www IN A 1.2.3.4
... IN TXT "Some Text"
... mail IN CNAME www.abc.com.
... '''
>>> for rr in RR.fromZone(textwrap.dedent(z)):
... print(rr)
abc.com. 300 IN MX 10 mail.abc.com.
www.abc.com. 300 IN A 1.2.3.4
www.abc.com. 300 IN TXT "Some Text"
mail.abc.com. 300 IN CNAME www.abc.com.

To create a skeleton reply to a DNS query:

>>> q = DNSRecord(q=DNSQuestion("abc.com",QTYPE.ANY))
>>> a = q.reply()
>>> a.add_answer(RR("abc.com",QTYPE.A,rdata=A("1.2.3.4"),ttl=60))
>>> str(DNSRecord.parse(a.pack())) == str(a)
True
>>> print(a)
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: ...
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0
;; QUESTION SECTION:
;abc.com. IN ANY
;; ANSWER SECTION:
abc.com. 60 IN A 1.2.3.4

Add additional RRs:

>>> a.add_answer(RR("xxx.abc.com",QTYPE.A,rdata=A("1.2.3.4")))
>>> a.add_answer(RR("xxx.abc.com",QTYPE.AAAA,rdata=AAAA("1234:5678::1")))
>>> str(DNSRecord.parse(a.pack())) == str(a)
True
>>> print(a)
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: ...
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 3, AUTHORITY: 0, ADDITIONAL: 0
;; QUESTION SECTION:
;abc.com. IN ANY
;; ANSWER SECTION:
abc.com. 60 IN A 1.2.3.4
xxx.abc.com. 0 IN A 1.2.3.4
xxx.abc.com. 0 IN AAAA 1234:5678::1


It is also possible to create a reply from a string in zone file format:

>>> q = DNSRecord(q=DNSQuestion("abc.com",QTYPE.ANY))
>>> a = q.replyZone("abc.com 60 IN CNAME xxx.abc.com")
>>> print(a)
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: ...
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0
;; QUESTION SECTION:
;abc.com. IN ANY
;; ANSWER SECTION:
abc.com. 60 IN CNAME xxx.abc.com.

>>> str(DNSRecord.parse(a.pack())) == str(a)
True

>>> q = DNSRecord(q=DNSQuestion("abc.com",QTYPE.ANY))
>>> a = q.replyZone(textwrap.dedent(z))
>>> print(a)
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: ...
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 4, AUTHORITY: 0, ADDITIONAL: 0
;; QUESTION SECTION:
;abc.com. IN ANY
;; ANSWER SECTION:
abc.com. 300 IN MX 10 mail.abc.com.
www.abc.com. 300 IN A 1.2.3.4
www.abc.com. 300 IN TXT "Some Text"
mail.abc.com. 300 IN CNAME www.abc.com.


The library also includes a simple framework for generating custom DNS
resolvers in dnslib.server (see module docs). In post cases this just
requires implementing a custom 'resolve' method which receives a question
object and returns a response.

A number of sample resolvers are provided as examples (see CLI --help):

dnslib.fixedresolver - Respond to all requests with fixed response
dnslib.zoneresolver - Respond from Zone file
dnslib.shellresolver - Call shell script to generate response

The library includes a number of client utilities which can be run using:

DiG like client library
# python -m dnslib.client --help

DNS Proxy Server
# python -m dnslib.proxy --help

Intercepting DNS Proxy Server (replace proxy responses for specified domains)
# python -m dnslib.intercept --help


Changelog:
----------

* 0.1 2010-09-19 Initial Release
* 0.2 2010-09-22 Minor fixes
* 0.3 2010-10-02 Add DNSLabel class to support arbitrary labels (embedded '.')
* 0.4 2012-02-26 Merge with dbslib-circuits
* 0.5 2012-09-13 Add support for RFC2136 DDNS updates
Patch provided by Wesley Shields <wxs@FreeBSD.org> - thanks
* 0.6 2012-10-20 Basic AAAA support
* 0.7 2012-10-20 Add initial EDNS0 support (untested)
* 0.8 2012-11-04 Add support for NAPTR, Authority RR and additional RR
Patch provided by Stefan Andersson (https://bitbucket.org/norox) - thanks
* 0.8.1 2012-11-05 Added NAPTR test case and fixed logic error
Patch provided by Stefan Andersson (https://bitbucket.org/norox) - thanks
* 0.8.2 2012-11-11 Patch to fix IPv6 formatting
Patch provided by Torbjörn Lönnemark (https://bitbucket.org/tobbezz) - thanks
* 0.8.3 2013-04-27 Don't parse rdata if rdlength is 0
Patch provided by Wesley Shields <wxs@FreeBSD.org> - thanks
* 0.9.0 2014-05-05 Major update including Py3 support (see docs)

License:
--------

* BSD

Author:
-------

* Paul Chakravarti (paul.chakravarti@gmail.com)

Master Repository/Issues:
-------------------------

* https://bitbucket.org/paulc/dnslib
(Cloned on GitHub: https://github.com/paulchakravarti/dnslib)