69 lines
2.1 KiB
ReStructuredText
69 lines
2.1 KiB
ReStructuredText
Resolving the MX records
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==============================
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This basic example shows how to create a resolver which asks for MX records which contain the information about mail servers.
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::
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#!/usr/bin/python
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#
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# MX is a small program that prints out the mx records for a particular domain
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#
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import ldns
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resolver = ldns.ldns_resolver.new_frm_file("/etc/resolv.conf")
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dname = ldns.ldns_dname("nic.cz")
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pkt = resolver.query(dname, ldns.LDNS_RR_TYPE_MX, ldns.LDNS_RR_CLASS_IN, ldns.LDNS_RD)
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if (pkt):
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mx = pkt.rr_list_by_type(ldns.LDNS_RR_TYPE_MX, ldns.LDNS_SECTION_ANSWER)
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if (mx):
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mx.sort()
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print mx
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Resolving step by step
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------------------------
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First of all we import :mod:`ldns` extension module which make LDNS functions and classes accessible::
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import ldns
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If importing fails, it means that Python cannot find the module or ldns library.
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Then we create the resolver by :meth:`ldns.ldns_resolver.new_frm_file` constructor ::
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resolver = ldns.ldns_resolver.new_frm_file("/etc/resolv.conf")
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and domain name variable dname::
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dname = ldns.ldns_dname("nic.cz")
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To create a resolver you may also use::
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resolver = ldns.ldns_resolver.new_frm_file(None)
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which behaves in the same manner as the command above.
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In the third step we tell the resolver to query for our domain, type MX, of class IN::
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pkt = resolver.query(dname, ldns.LDNS_RR_TYPE_MX, ldns.LDNS_RR_CLASS_IN, ldns.LDNS_RD)
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The function should return a packet if everything goes well and this packet will contain resource records we asked for.
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Note that there exists a simplier way. Instead of using a dname variable, we can use a string which will be automatically converted.
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::
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pkt = resolver.query("fit.vutbr.cz", ldns.LDNS_RR_TYPE_MX, ldns.LDNS_RR_CLASS_IN, ldns.LDNS_RD)
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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::
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if (pkt):
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mx = pkt.rr_list_by_type(ldns.LDNS_RR_TYPE_MX, ldns.LDNS_SECTION_ANSWER)
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If this list is not empty, we sort and print the content to stdout::
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if (mx):
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mx.sort()
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print mx
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