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A Python library to encode/decode DNS wire-format packets
Home Page: https://github.com/paulc/dnslib
License: BSD 2-Clause "Simplified" License
This project forked from paulc/dnslib
A Python library to encode/decode DNS wire-format packets
Home Page: https://github.com/paulc/dnslib
License: BSD 2-Clause "Simplified" License
## From Version 0.9.12 the master repository for _dnslib_ has been moved to GitHub (https://github.com/paulc/dnslib). Please update any links to the original BitBucket repository as this will no longer be maintained. 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 framework * 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) * The 'Bimap' interface was changed significantly to explicitly split forward (value->text) lookups via __getitem__ and reverse (text->value) lookups via __getattr__. Applications using the old interface will need to be updated. * Hostnames are now returned with a trailing dot by default (in line with RFC) * Most object attributes are now typed in line with the record definitions to make it harder to generate invalid packets * Support for encoding/decoding resource records in 'Zone' (BIND) file format * Support for encoding/decoding packets in 'DiG' format * Server framework allowing (in most cases) custom resolvers to be created by just subclassing the DNSResolver class and overriding 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 when parsing a packet 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 Classes ------- 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 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. To send a DNSSEC request (EDNS OPT record with DO flag & header AD flag): >>> q = DNSRecord(q=DNSQuestion("abc.com",QTYPE.A)) >>> q.add_ar(EDNS0(flags="do",udp_len=4096)) >>> q.header.ad = 1 >>> print(q) ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: ... ;; flags: rd ad; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 1 ;; QUESTION SECTION: ;abc.com. IN A ;; ADDITIONAL SECTION: ;; OPT PSEUDOSECTION ; EDNS: version: 0, flags: do; udp: 4096 Note that when using the library you should always validate the received TXID q = DNSRecord.question("abc.com") a_pkt = q.send(address,port,tcp=args.tcp) a = DNSRecord.parse(a_pkt) if q.header.id != a.header.id: raise DNSError('Response transaction id does not match query transaction id') The library also includes a simple framework for generating custom DNS resolvers in dnslib.server (see module docs). In most 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: * 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 <[email protected]> - 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 Torbjorn Lonnemark (https://bitbucket.org/tobbezz) - thanks * 0.8.3 2013-04-27 Don't parse rdata if rdlength is 0 Patch provided by Wesley Shields <[email protected]> - thanks * 0.9.0 2014-05-05 Major update including Py3 support (see docs) * 0.9.1 2014-05-05 Minor fixes * 0.9.2 2014-08-26 Fix Bimap handling of unknown mappings to avoid exception in printing Add typed attributes to classes Misc fixes from James Mills - thanks * 0.9.3 2014-08-26 Workaround for argparse bug which raises AssertionError if [] is present in option text (really?) * 0.9.4 2015-04-10 Fix to support multiple strings in TXT record Patch provided by James Cherry (https://bitbucket.org/james_cherry) - thanks NOTE: For consistency this patch changes the 'repr' output for TXT records to always be quoted * 0.9.5 2015-10-27 Add threading & timeout handling to DNSServer * 0.9.6 2015-10-28 Replace strftime in RRSIG formatting to avoid possible locale issues Identified by Bryan Everly - thanks * 0.9.7 2017-01-15 Sort out CAA/TYPE257 DiG parsing mismatch * 0.9.8 2019-02-25 Force DNSKEY key to be bytes object Catch Bimap __wrapped__ attr (used by inspect module in 3.7) * 0.9.9 2019-03-19 Add support for DNSSEC flag getters/setters (from <[email protected]> - thanks) Added --dnssec flags to dnslib.client & dnslib.test_decode (sets EDNS0 DO flag) Added EDNS0 support to dnslib.digparser * 0.9.10 2019-03-24 Fixes to DNSSEC support Add NSEC RR support Add --dnssec flag to dnslib.client & dnslib.test_decode Quote/unquote non-printable characters in DNS labels Update test data (Thanks to <[email protected]> for help) * 0.9.11 2019-12-17 Encode NOTIFY Opcode (Issue #26) * 0.9.12 2019-12-17 Transition master repository to Github (Bitbucket shutting down hg) * 0.9.13 2020-06-01 Handle truncated requests in server.py (Issue #9) Replace thred.isAlive with thread.is_alive (Deprecated in Py3.9) Merged Pull Request #4 (Extra options for intercept.py) - thanks to @nolanl * 0.9.14 2020-06-09 Merged Pull Request #10 (Return doctest status via exit code) Thanks to @mgorny * 0.9.15 2021-05-07 DNSServer fixes - support IPv6 (from Pull Request #21) - thanks to @mikma - deamon threads (Pull Request #19) - thanks to @wojons Add unsupported RR types (Issue #27) * 0.9.16 2021-05-07 Merge pull request #23 from Tugzrida/patch-1 Add support for all RR types to NSEC type bitmap Merge pull request #17 from sunds/issue_16 Issue 16: uncaught exceptions leak open sockets * 0.9.18 2022-01-09 Validate TXID in client.py (Issue #30 - thanks to @daniel4x) * 0.9.19 2022-01-09 Allow custom log function (logf) in DNSLogger (Issue #31 - thanks to @DmitryFrolovTri) * 0.9.20 2022-07-17 Fix DeprecationWarnings about invalid escape sequences (Pull-Request #39 - thanks to @brianmaissy) Make DNSLabel matchSuffix and stripSuffix case-insensitive (Pull-Request #37 - thanks to @NiKiZe) Add support for HTTPS RR (Pull-Request #35 - thanks to @jkl-caliber) Fix display of non-printable characters in TXT records (Issue #32 - thanks to @sbv-csis) Add --strip-aaaa option to dnslib.proxy * 0.9.21 2022-09-19 Minor clean-up / add wheels to distro * 0.9.22 2022-09027 Issue #43 (0.9.21 Raises TypeError instead of DNSError when failing to parse HTTPS records) Note that we just fix the exception - there still seems to be a problem with parsing HTTPS records (Thanks to @robinlandstrom) * 0.9.23 2022-10-28 Issue #43: HTTPS reads after RD end (thanks to @robinlandstrom for pull request) Issue #45: Dnslib fails to handle unknown RR types in NSEC RD type bitmap Bimap now supports a function to map unknown types which we use to dynamically map from rtype <-> TYPExxxx for unknown record types RR zone representation updated to match RFC3597 Pull Request #47: Add support for DS, SSHFP, and TLSA records (thanks to @rmbolger) License: -------- BSD Author: ------- * PaulC Master Repository/Issues: ------------------------- * https://github.com/paulc/dnslib (Note: https://bitbucket.org/paulc/dnslib has been deprecated and will not be updated)
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