Junk output or random character in Data::Dumper output for Net::DNS::Resolver object - perl

Question

I am getting familiarized with the Net::DNS library in Perl and an object is created using
my $res = Net::DNS::Resolver->new();
However, simply trying to query a domain name shows a lot f junk values, though the output itself is correct. Here is the code snippet
#!/usr/bin/perl
use Net::DNS;
use Net::IP;
use Data::Dumper;
my $rr;
$domain = 'google.com';
my $res = Net::DNS::Resolver->new();
my $ns_req = $res->query($domain, "NS");
print "\n\n###\n".Dumper($ns_req)."\n###\n\n";
Here are 2 outputs for various domains tested against this object:
What are these junk values being displayed? Is there a way to clean up the output a bit in order to read the output properly?

Answer 1

You are dumping the internals of the object which include the buffer which holds the original response bytes.
You should use the API defined in the module documentation to access the information.
#!/usr/bin/env perl
use strict;
use warnings;
use Net::DNS;
my $resolver = Net::DNS::Resolver->new;
my $result = $resolver->query('google.com', "NS");
$result->print;
Output:
;; Answer received from x.x.x.x (100 bytes)
;; HEADER SECTION
;; id = 39595
;; qr = 1 aa = 0 tc = 0 rd = 1 opcode = QUERY
;; ra = 1 z = 0 ad = 0 cd = 0 rcode = NOERROR
;; qdcount = 1 ancount = 4 nscount = 0 arcount = 0
;; do = 0
;; QUESTION SECTION (1 record)
;; google.com. IN NS
;; ANSWER SECTION (4 records)
google.com. 21599 IN NS ns4.google.com.
google.com. 21599 IN NS ns2.google.com.
google.com. 21599 IN NS ns1.google.com.
google.com. 21599 IN NS ns3.google.com.
;; AUTHORITY SECTION (0 records)
;; ADDITIONAL SECTION (0 records)
The query method returns a Net::DNS::Packet which provides other methods to obtain specific parts of the response.
For example:
#!/usr/bin/env perl
use strict;
use warnings;
use Net::DNS;
my $resolver = Net::DNS::Resolver->new;
my $result = $resolver->query('google.com', "NS");
for my $answer ($result->answer) {
print $answer->nsdname, "\n";
}
Output:
ns2.google.com
ns1.google.com
ns3.google.com
ns4.google.com
If you are interested in the contents of the binary buffer, Net::DNS::Packet has a data method which returns the contents of that buffer. As RFC 1035 points out:
3.2. RR definitions
3.2.1. Format
All RRs have the same top level format shown below:
1 1 1 1 1 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| |
/ /
/ NAME /
| |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| TYPE |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| CLASS |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| TTL |
| |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| RDLENGTH |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--|
/ RDATA /
/ /
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
where:
NAME an owner name, i.e., the name of the node to which this
resource record pertains.
TYPE two octets containing one of the RR TYPE codes.
CLASS two octets containing one of the RR CLASS codes.
TTL a 32 bit signed integer that specifies the time interval
that the resource record may be cached before the source
of the information should again be consulted. Zero
values are interpreted to mean that the RR can only be
used for the transaction in progress, and should not be
cached. For example, SOA records are always distributed
with a zero TTL to prohibit caching. Zero values can
also be used for extremely volatile data.
RDLENGTH an unsigned 16 bit integer that specifies the length in
octets of the RDATA field.
RDATA a variable length string of octets that describes the
resource. The format of this information varies
according to the TYPE and CLASS of the resource record.
You can examine the contents of $result->data by doing a hexdump:
#!/usr/bin/env perl
use strict;
use warnings;
use Net::DNS;
my $resolver = Net::DNS::Resolver->new;
my $result = $resolver->query('google.com', "NS");
print $result->data;
C:\...\t> perl tt.pl | xxd
00000000: 3256 8180 0001 0004 0000 0000 0667 6f6f 2V...........goo
00000010: 676c 6503 636f 6d00 0002 0001 c00c 0002 gle.com.........
00000020: 0001 0000 545f 0006 036e 7333 c00c c00c ....T_...ns3....
00000030: 0002 0001 0000 545f 0006 036e 7334 c00c ......T_...ns4..
00000040: c00c 0002 0001 0000 545f 0006 036e 7332 ........T_...ns2
00000050: c00c c00c 0002 0001 0000 545f 0006 036e ..........T_...n
00000060: 7331 c00c s1..