dnsjit.core.object.dns(3)

NAME
dnsjit.core.object.dns - Container of a DNS message

SYNOPSIS

  Parse DNS header and check if query or response
  local dns = require("dnsjit.core.object.dns").new(payload)
  if dns:parse_header() == 0 then
    if dns.qr == 0 then
      print(dns.id, dns.opcode_tostring(dns.opcode))
    else
      print(dns.id, dns.rcode_tostring(dns.rcode))
    end
  end

  Print a DNS payload
  local dns = require("dnsjit.core.object.dns").new(payload)
  dns:print()

  Parse a DNS payload
  local dns = require("dnsjit.core.object.dns").new(payload)
  local qs, q_labels, rrs, rr_labels = dns:parse()
  if qs and q_labels then
    ...
    if rrs and rr_labels then
      ...
    end
  end

DESCRIPTION
The object that describes a DNS message.

  Attributes

includes_dnslen
    If non-zero then this indicates that the DNS length is included in the payload (for example if the transport is TCP) and will affect parsing of it.

have_dnslen
    Set if the dnslen was included in the payload and could be read.

have_id
    Set if there is a DNS ID.

have_qr
    Set if there is a QR flag.

have_opcode
    Set if there is an OPCODE.

have_aa
    Set if there is a AA flag.

have_tc
    Set if there is a TC flag.

have_rd
    Set if there is a RD flag.

have_ra
    Set if there is a RA flag.

have_z
    Set if there is a Z flag.

have_ad
    Set if there is a AD flag.

have_cd
    Set if there is a CD flag.

have_rcode
    Set if there is a RCODE.

have_qdcount
    Set if there is an QDCOUNT.

have_ancount
    Set if there is an ANCOUNT.

have_nscount
    Set if there is a NSCOUNT.

have_arcount
    Set if there is an ARCOUNT.

dnslen
    The DNS length found in the payload.

id  The DNS ID.

qr  The QR flag.

opcode
    The OPCODE.

aa  The AA flag.

tc  The TC flag.

rd  The RD flag.

ra  The RA flag.

z   The Z flag.

ad  The AD flag.

cd  The CD flag.

rcode
    The RCODE.

qdcount
    The QDCOUNT.

ancount
    The ANCOUNT.

nscount
    The NSCOUNT.

arcount
    The ARCOUNT.

  Constants
The following tables exists for DNS parameters, taken from https://www.iana.org/assignments/dns-parameters/dns-parameters.xhtml on the 2016-12-09.

CLASS, CLASS_STR, TYPE, TYPE_STR, OPCODE, OPCODE_STR, RCODE, RCODE_STR, AFSDB, AFSDB_STR, DHCID, DHCID_STR, ENDS0, ENDS0_STR

The *_STR tables can be used to get a textual representation of the numbers, see also class_tostring(), type_tostring(), opcode_tostring(), rcode_tostring(), afsdb_tostring(), dhcid_tostring() and edns0_tostring().

  Functions

Dns.new(obj)
    Create a new DNS object, optionally on-top of another object.

Dns:type()
    Return the textual type of the object.

Dns:prev()
    Return the previous object.

Dns:cast()
    Cast the object to the underlining object module and return it.

Dns:uncast()
    Cast the object to the generic object module and return it.

Dns:copy()
    Make a copy of the object and return it.

Dns:free()
    Free the object, should only be used on copies or otherwise allocated.

Dns:reset()
    Reset the object readying it for reuse.

Dns:log()
    Return the Log object to control logging of this module.

Dns:parse_header()
    Begin parsing the underlaying object, first the header is parsed then optionally continue calling parse_q() for the number of questions (see qdcount). After that continue calling parse_rr() for the number of answers, authorities and additionals resource records (see ancount, nscount and arcount). Returns 0 on success or negative integer on error which can be for malformed or truncated DNS (-2) or if more space for labels is needed (-3).

Dns:parse_q(q, labels, num_labels)
    Parse the next resource record as a question. Returns 0 on success or negative integer on error which can be for malformed or truncated DNS (-2) or if more space for labels is needed (-3).

Dns:parse_rr(rr, labels, num_labels)
    Parse the next resource record. Returns 0 on success or negative integer on error which can be for malformed or truncated DNS (-2) or if more space for labels is needed (-3).

Dns:parse(num_labels)
    Begin parsing the underlaying object using parse_header(), parse_q() and parse_rr(). The optional num_labels can be used to set a specific number of labels used for each question and resource record (default 16). Returns result code, an array of questions, an array of question labels, an array of resource records and an array of resource records labels. Result code is 0 on success or negative integer on error which can be for malformed or truncated DNS (-2) or if more space for labels is needed (-3).

Dns:print(num_labels)
    Begin parsing the underlaying object using parse_header(), parse_q() and parse_rr(), and print it's content. The optional num_labels can be used to set a specific number of labels used for each question and resource record (default 16).

Dns.class_tostring(class)
    Return the textual name for a class.

Dns.type_tostring(type)
    Return the textual name for a type.

Dns.opcode_tostring(opcode)
    Return the textual name for an opcode.

Dns.rcode_tostring(rcode)
    Return the textual name for a rcode.

Dns.afsdb_tostring(afsdb)
    Return the textual name for an afsdb subtype.

Dns.dhcid_tostring(dhcid)
    Return the textual name for a dhcid type.

Dns.edns0_tostring(edns0)
    Return the textual name for an EDNS0 OPT record.

SEE ALSO
dnsjit.core.object(3), dnsjit.core.object.payload(3), dnsjit.core.object.dns.label(3), dnsjit.core.object.dns.q(3), dnsjit.core.object.dns.rr(3)

AUTHORS and CONTRIBUTORS
Jerry Lundström (DNS-OARC), Tomáš Křížek (CZ.NIC), Petr Špaček (ISC)

Maintained by DNS-OARC

    https://www.dns-oarc.net/

BUGS
For issues and feature requests please use:

    https://github.com/DNS-OARC/dnsjit/issues

For question and help please use:

    admin@dns-oarc.net