This example shows how to create a simple language dictionary based on DNS service within 15 minutes. The translation will be performed using TXT resource records.
On init() module loads dictionary from a text file containing records in word [tab] translation format.
def init(id, cfg):
log_info("pythonmod: dict init")
f = open("examples/dict_data.txt", "r")
...
The suitable file can be found at http://slovnik.zcu.cz
Let’s define the following format od DNS queries: word1[.]word2[.] ... wordN[.]{en,cs}[._dict_.cz.]. Word lookup is done by simple dict lookup from broken DNS request. Query name is divided into a list of labels. This list is accesible as qname_list attribute.
aword = ' '.join(qstate.qinfo.qname_list[0:-4]) #skip last four labels
adict = qstate.qinfo.qname_list[-4] #get 4th label from the end
words = [] #list of words
if (adict == "en") and (aword in en_dict):
words = en_dict[aword]
if (adict == "cs") and (aword in cz_dict):
words = cz_dict[aword] # CS -> EN
In the first step, we get a string in the form: word1[space]word2[space]...word[space]. In the second assignment, fourth label from the end is obtained. This label should contains “cs” or “en”. This label determines the direction of translation.
DNS reply is formed only on valid match and added as TXT answer.
msg = DNSMessage(qstate.qinfo.qname_str, RR_TYPE_TXT, RR_CLASS_IN, PKT_AA)
for w in words:
msg.answer.append("%s 300 IN TXT \"%s\"" % (qstate.qinfo.qname_str, w.replace("\"", "\\\"")))
if not msg.set_return_msg(qstate):
qstate.ext_state[id] = MODULE_ERROR
return True
qstate.return_rcode = RCODE_NOERROR
qstate.ext_state[id] = MODULE_FINISHED
return True
In the first step, a DNSMessage instance is created for a given query (type TXT). The fourth argument specifies the flags (authoritative answer). In the second step, we append TXT records containing the translation (on the right side of RR). Then, the response is finished and qstate.return_msg contains new response. If no error, the module sets module_qstate.return_rcode and module_qstate.ext_state.
Steps:
Run the Unbound server:
root@localhost>unbound -dv -c ./test-dict.conf
In case you use own configuration file, don’t forget to enable Python module:
module-config: "validator python iterator"
and use valid script path:
python-script: "./examples/dict.py"
The translation from english word “a bar fly” to Czech can be done by doing:
>>>dig TXT @127.0.0.1 a.bar.fly.en._dict_.cz
; (1 server found) ;; global options: printcmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 48691 ;; flags: aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0 ;; QUESTION SECTION: ;a.bar.fly.en._dict_.cz. IN TXT ;; ANSWER SECTION: a.bar.fly.en._dict_.cz. 300 IN TXT "barov\253 povale\232" ;; Query time: 5 msec ;; SERVER: 127.0.0.1#53(127.0.0.1) ;; WHEN: Mon Jan 01 17:44:18 2009 ;; MSG SIZE rcvd: 67
>>>dig TXT @127.0.0.1 nic.cs._dict_.cz
; <<>> DiG 9.5.0-P2 <<>> TXT @127.0.0.1 nic.cs._dict_.cz ; (1 server found) ;; global options: printcmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 58710 ;; flags: aa rd ra; QUERY: 1, ANSWER: 6, AUTHORITY: 0, ADDITIONAL: 0 ;; QUESTION SECTION: ;nic.cs._dict_.cz. IN TXT ;; ANSWER SECTION: nic.cs._dict_.cz. 300 IN TXT "aught" nic.cs._dict_.cz. 300 IN TXT "naught" nic.cs._dict_.cz. 300 IN TXT "nihil" nic.cs._dict_.cz. 300 IN TXT "nix" nic.cs._dict_.cz. 300 IN TXT "nothing" nic.cs._dict_.cz. 300 IN TXT "zilch" ;; Query time: 0 msec ;; SERVER: 127.0.0.1#53(127.0.0.1) ;; WHEN: Mon Jan 01 17:45:39 2009 ;; MSG SIZE rcvd: 143
Proof that the unbound still works as resolver.
>>>dig A @127.0.0.1 www.nic.cz
; (1 server found) ;; global options: printcmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 19996 ;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 3, ADDITIONAL: 5 ;; QUESTION SECTION: ;www.nic.cz. IN A ;; ANSWER SECTION: www.nic.cz. 1662 IN A 217.31.205.50 ;; AUTHORITY SECTION: ...
# -*- coding: utf-8 -*-
'''
calc.py: DNS-based czech-english dictionary
Copyright (c) 2009, Zdenek Vasicek (vasicek AT fit.vutbr.cz)
Marek Vavrusa (xvavru00 AT stud.fit.vutbr.cz)
This software is open source.
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:
* Redistributions of source code must retain the above copyright notice,
this list of conditions and the following disclaimer.
* Redistributions in binary form must reproduce the above copyright notice,
this list of conditions and the following disclaimer in the documentation
and/or other materials provided with the distribution.
* Neither the name of the organization nor the names of its
contributors may be used to endorse or promote products derived from this
software without specific prior written permission.
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE
LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
POSSIBILITY OF SUCH DAMAGE.
'''
import os
cz_dict = {}
en_dict = {}
def init(id, cfg):
log_info("pythonmod: dict init")
f = open("examples/dict_data.txt", "r")
try:
for line in f:
if line.startswith('#'):
continue
itm = line.split("\t", 3)
if len(itm) < 2:
continue
en,cs = itm[0:2]
if not (cs in cz_dict):
cz_dict[cs] = [en] # [cs] = en
else:
cz_dict[cs].append(en) # [cs] = en
if not (en in en_dict):
en_dict[en] = [cs] # [en] = cs
else:
en_dict[en].append(cs) # [en] = cs
finally:
f.close()
return True
def deinit(id):
log_info("pythonmod: dict deinit")
return True
def operate(id, event, qstate, qdata):
if (event == MODULE_EVENT_NEW) or (event == MODULE_EVENT_PASS):
if qstate.qinfo.qname_str.endswith("._dict_.cz."):
aword = ' '.join(qstate.qinfo.qname_list[0:-4])
adict = qstate.qinfo.qname_list[-4]
log_info("pythonmod: dictionary look up; word:%s dict:%s" % (aword,adict))
words = []
if (adict == "en") and (aword in en_dict):
words = en_dict[aword] # EN -> CS
if (adict == "cs") and (aword in cz_dict):
words = cz_dict[aword] # CS -> EN
if len(words) and ((qstate.qinfo.qtype == RR_TYPE_TXT) or (qstate.qinfo.qtype == RR_TYPE_ANY)):
msg = DNSMessage(qstate.qinfo.qname_str, RR_TYPE_TXT, RR_CLASS_IN, PKT_RD | PKT_RA | PKT_AA)
for w in words:
msg.answer.append("%s 300 IN TXT \"%s\"" % (qstate.qinfo.qname_str,w.replace("\"","\\\"")))
if not msg.set_return_msg(qstate):
qstate.ext_state[id] = MODULE_ERROR
return True
qstate.return_rcode = RCODE_NOERROR
qstate.ext_state[id] = MODULE_FINISHED
return True
else:
qstate.return_rcode = RCODE_SERVFAIL
qstate.ext_state[id] = MODULE_FINISHED
return True
else: #Pass on the unknown query to the iterator
qstate.ext_state[id] = MODULE_WAIT_MODULE
return True
elif event == MODULE_EVENT_MODDONE: #the iterator has finished
#we don't need modify result
qstate.ext_state[id] = MODULE_FINISHED
return True
log_err("pythonmod: Unknown event")
qstate.ext_state[id] = MODULE_ERROR
return True
def inform_super(id, qstate, superqstate, qdata):
return True