1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
|
Resolving the MX records
==============================
This basic example shows how to create a resolver which asks for MX records which contain the information about mail servers.
::
#!/usr/bin/python
#
# MX is a small program that prints out the mx records for a particular domain
#
import ldns
resolver = ldns.ldns_resolver.new_frm_file("/etc/resolv.conf")
dname = ldns.ldns_dname("nic.cz")
pkt = resolver.query(dname, ldns.LDNS_RR_TYPE_MX, ldns.LDNS_RR_CLASS_IN, ldns.LDNS_RD)
if (pkt):
mx = pkt.rr_list_by_type(ldns.LDNS_RR_TYPE_MX, ldns.LDNS_SECTION_ANSWER)
if (mx):
mx.sort()
print mx
Resolving step by step
------------------------
First of all we import :mod:`ldns` extension module which make LDNS functions and classes accessible::
import ldns
If importing fails, it means that Python cannot find the module or ldns library.
Then we create the resolver by :meth:`ldns.ldns_resolver.new_frm_file` constructor ::
resolver = ldns.ldns_resolver.new_frm_file("/etc/resolv.conf")
and domain name variable dname::
dname = ldns.ldns_dname("nic.cz")
To create a resolver you may also use::
resolver = ldns.ldns_resolver.new_frm_file(None)
which behaves in the same manner as the command above.
In the third step we tell the resolver to query for our domain, type MX, of class IN::
pkt = resolver.query(dname, ldns.LDNS_RR_TYPE_MX, ldns.LDNS_RR_CLASS_IN, ldns.LDNS_RD)
The function should return a packet if everything goes well and this packet will contain resource records we asked for.
Note that there exists a simpler way. Instead of using a dname variable, we can use a string which will be automatically converted.
::
pkt = resolver.query("fit.vutbr.cz", ldns.LDNS_RR_TYPE_MX, ldns.LDNS_RR_CLASS_IN, ldns.LDNS_RD)
Now, we test whether the resolver returns a packet and then get all RRs of type MX from the answer packet and store them in list mx::
if (pkt):
mx = pkt.rr_list_by_type(ldns.LDNS_RR_TYPE_MX, ldns.LDNS_SECTION_ANSWER)
If this list is not empty, we sort and print the content to stdout::
if (mx):
mx.sort()
print mx
|
