dnsjit.core.object.dns(3)

💖 dnsjit.core.object.dns — the manual page bestie 💖

okay so you're reading the dnsjit.core.object.dns page from the Library Functions Manual, and honestly? it's giving container-of-a-DNS-message energy and I am obsessed. let's get into it 🦋

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✨ NAME ✨

dnsjit.core.object.dns — the container of a DNS message. that's it, that's the whole vibe 💅

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🌸 SYNOPSIS 🌸

parse a DNS header and check if it's a query or a 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

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👑 DESCRIPTION 👑

so this is the object that describes a DNS message. the main character, fr fr. 🎀

💜 Attributes

• includes_dnslen — if this is non-zero, that means the DNS length is included in the payload (like, for example, when the transport is TCP) and it affects how the payload gets parsed. lowkey important.
• have_dnslen — set when the dnslen was actually included in the payload and could be read.
• have_id — set if there's a DNS ID.
• have_qr — set if there's a QR flag.
• have_opcode — set if there's an OPCODE.
• have_aa — set if there's an AA flag.
• have_tc — set if there's a TC flag.
• have_rd — set if there's a RD flag.
• have_ra — set if there's a RA flag.
• have_z — set if there's a Z flag.
• have_ad — set if there's an AD flag.
• have_cd — set if there's a CD flag.
• have_rcode — set if there's a RCODE.
• have_qdcount — set if there's a QDCOUNT.
• have_ancount — set if there's an ANCOUNT.
• have_nscount — set if there's a NSCOUNT.
• have_arcount — set if there's an ARCOUNT.
• dnslen — the DNS length that was 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

these tables exist for DNS parameters, and they were taken from https://www.iana.org/assignments/dns-parameters/dns-parameters.xhtml on the 2016-12-09. periodt, that's the source date, no cap.

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

the *_STR tables are the ones you use to turn numbers into their textual glow-up ✨ see also class_tostring(), type_tostring(), opcode_tostring(), rcode_tostring(), afsdb_tostring(), dhcid_tostring() and edns0_tostring().

🫶 Functions

• Dns.new(obj) — create a fresh new DNS object, optionally sitting on top of another object.
• Dns:type() — returns the textual type of the object.
• Dns:prev() — returns the previous object.
• Dns:cast() — casts the object to the underlining object module and hands it back to you.
• Dns:uncast() — casts the object to the generic object module and returns it.
• Dns:copy() — makes a copy of the object and returns it.
• Dns:free() — frees the object. only use this on copies or stuff that was otherwise allocated, bestie, I'm serious.
• Dns:reset() — resets the object, getting it all ready for reuse.
• Dns:log() — returns the Log object so you can control the logging of this module.
• Dns:parse_header() — starts parsing the underlaying object: first the header gets parsed, then you optionally keep calling parse_q() for however many questions there are (check qdcount). after that you keep calling parse_rr() for the number of answers, authorities and additionals resource records (check ancount, nscount and arcount). returns 0 on success, or a negative integer on error — which can be malformed or truncated DNS (-2), or needing more space for labels (-3).
• Dns:parse_q(q, labels, num_labels) — parses the next resource record as a question. returns 0 on success, or a negative integer on error — malformed or truncated DNS (-2), or needing more space for labels (-3).
• Dns:parse_rr(rr, labels, num_labels) — parses the next resource record. returns 0 on success, or a negative integer on error — malformed or truncated DNS (-2), or needing more space for labels (-3).
• Dns:parse(num_labels) — starts parsing the underlaying object using parse_header(), parse_q() and parse_rr(). the optional num_labels lets you set a specific number of labels used for each question and resource record (default is 16). returns a result code, an array of questions, an array of question labels, an array of resource records, and an array of resource records labels. the result code is 0 on success, or a negative integer on error — malformed or truncated DNS (-2), or needing more space for labels (-3).
• Dns:print(num_labels) — starts parsing the underlaying object using parse_header(), parse_q() and parse_rr(), and prints its content. the optional num_labels lets you set a specific number of labels used for each question and resource record (default is 16).
• Dns.class_tostring(class) — returns the textual name for a class. unknown classes come back as "CLASS<NUM>", exactly as described in RFC 3597.
• Dns.type_tostring(type) — returns the textual name for a type. unknown types come back as "TYPE<NUM>", as described in RFC 3597.
• Dns.opcode_tostring(opcode) — returns the textual name for an opcode.
• Dns.rcode_tostring(rcode) — returns the textual name for a rcode.
• Dns.afsdb_tostring(afsdb) — returns the textual name for an afsdb subtype.
• Dns.dhcid_tostring(dhcid) — returns the textual name for a dhcid type.
• Dns.edns0_tostring(edns0) — returns the textual name for an EDNS0 OPT record.

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🔥 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)

go read your siblings, they're iconic too 💖

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💫 AUTHORS and CONTRIBUTORS 💫

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

maintained by DNS-OARC 🫶

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

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😭 BUGS 😭

for issues and feature requests please use:

https://codeberg.org/DNS-OARC/dnsjit/issues

for questions and help please use:

admin@dns-oarc.net

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okay bestie that's the whole page, you ate it, no crumbs left 🍓 this was dnsjit 1.5.1, page dnsjit.core.object.dns(3), and yes it's the version from the Library Functions Manual — now go parse something and slay 💅✨🦋