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tvl-depot/lisp/dns/message.lisp
Vincent Ambo 3f9546197e feat(lisp/dns): Export struct fields
2020-01-26 20:34:03 +00:00

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(in-package :dns)
;; 3.2.2. TYPE values
;; TYPE fields are used in resource records. Note that these types are a
;; subset of QTYPEs.
;; TYPE value and meaning
;; A 1 a host address
;; NS 2 an authoritative name server
;; MD 3 a mail destination (Obsolete - use MX)
;; MF 4 a mail forwarder (Obsolete - use MX)
;; CNAME 5 the canonical name for an alias
;; SOA 6 marks the start of a zone of authority
;; MB 7 a mailbox domain name (EXPERIMENTAL)
;; MG 8 a mail group member (EXPERIMENTAL)
;; MR 9 a mail rename domain name (EXPERIMENTAL)
;; NULL 10 a null RR (EXPERIMENTAL)
;; WKS 11 a well known service description
;; PTR 12 a domain name pointer
;; HINFO 13 host information
;; MINFO 14 mailbox or mail list information
;; MX 15 mail exchange
;; TXT 16 text strings
;; 3.2.3. QTYPE values
;; QTYPE fields appear in the question part of a query. QTYPES are a
;; superset of TYPEs, hence all TYPEs are valid QTYPEs. In addition, the
;; following QTYPEs are defined:
;; AXFR 252 A request for a transfer of an entire zone
;; MAILB 253 A request for mailbox-related records (MB, MG or MR)
;; MAILA 254 A request for mail agent RRs (Obsolete - see MX)
;; * 255 A request for all records
;; 3.2.4. CLASS values
;; CLASS fields appear in resource records. The following CLASS mnemonics
;; and values are defined:
;; IN 1 the Internet
;; CS 2 the CSNET class (Obsolete - used only for examples in
;; some obsolete RFCs)
;; CH 3 the CHAOS class
;; HS 4 Hesiod [Dyer 87]
;; 3.2.5. QCLASS values
;; QCLASS fields appear in the question section of a query. QCLASS values
;; are a superset of CLASS values; every CLASS is a valid QCLASS. In
;; addition to CLASS values, the following QCLASSes are defined:
;; * 255 any class
;; 3.3. Standard RRs
;; The following RR definitions are expected to occur, at least
;; potentially, in all classes. In particular, NS, SOA, CNAME, and PTR
;; will be used in all classes, and have the same format in all classes.
;; Because their RDATA format is known, all domain names in the RDATA
;; section of these RRs may be compressed.
;; <domain-name> is a domain name represented as a series of labels, and
;; terminated by a label with zero length. <character-string> is a single
;; length octet followed by that number of characters. <character-string>
;; is treated as binary information, and can be up to 256 characters in
;; length (including the length octet).
;; 3.3.1. CNAME RDATA format
;; +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
;; / CNAME /
;; / /
;; +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
;; where:
;; CNAME A <domain-name> which specifies the canonical or primary
;; name for the owner. The owner name is an alias.
;; CNAME RRs cause no additional section processing, but name servers may
;; choose to restart the query at the canonical name in certain cases. See
;; the description of name server logic in [RFC-1034] for details.
;; 3.3.11. NS RDATA format
;; +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
;; / NSDNAME /
;; / /
;; +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
;; where:
;; NSDNAME A <domain-name> which specifies a host which should be
;; authoritative for the specified class and domain.
;; NS records cause both the usual additional section processing to locate
;; a type A record, and, when used in a referral, a special search of the
;; zone in which they reside for glue information.
;; The NS RR states that the named host should be expected to have a zone
;; starting at owner name of the specified class. Note that the class may
;; not indicate the protocol family which should be used to communicate
;; with the host, although it is typically a strong hint. For example,
;; hosts which are name servers for either Internet (IN) or Hesiod (HS)
;; class information are normally queried using IN class protocols.
;; 3.3.12. PTR RDATA format
;; +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
;; / PTRDNAME /
;; +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
;; where:
;; PTRDNAME A <domain-name> which points to some location in the
;; domain name space.
;; PTR records cause no additional section processing. These RRs are used
;; in special domains to point to some other location in the domain space.
;; These records are simple data, and don't imply any special processing
;; similar to that performed by CNAME, which identifies aliases. See the
;; description of the IN-ADDR.ARPA domain for an example.
;; 3.3.13. SOA RDATA format
;; +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
;; / MNAME /
;; / /
;; +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
;; / RNAME /
;; +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
;; | SERIAL |
;; | |
;; +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
;; | REFRESH |
;; | |
;; +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
;; | RETRY |
;; | |
;; +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
;; | EXPIRE |
;; | |
;; +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
;; | MINIMUM |
;; | |
;; +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
;; where:
;; MNAME The <domain-name> of the name server that was the
;; original or primary source of data for this zone.
;; RNAME A <domain-name> which specifies the mailbox of the
;; person responsible for this zone.
;; SERIAL The unsigned 32 bit version number of the original copy
;; of the zone. Zone transfers preserve this value. This
;; value wraps and should be compared using sequence space
;; arithmetic.
;; REFRESH A 32 bit time interval before the zone should be
;; refreshed.
;; RETRY A 32 bit time interval that should elapse before a
;; failed refresh should be retried.
;; EXPIRE A 32 bit time value that specifies the upper limit on
;; the time interval that can elapse before the zone is no
;; longer authoritative.
;; MINIMUM The unsigned 32 bit minimum TTL field that should be
;; exported with any RR from this zone.
;; SOA records cause no additional section processing.
;; All times are in units of seconds.
;; Most of these fields are pertinent only for name server maintenance
;; operations. However, MINIMUM is used in all query operations that
;; retrieve RRs from a zone. Whenever a RR is sent in a response to a
;; query, the TTL field is set to the maximum of the TTL field from the RR
;; and the MINIMUM field in the appropriate SOA. Thus MINIMUM is a lower
;; bound on the TTL field for all RRs in a zone. Note that this use of
;; MINIMUM should occur when the RRs are copied into the response and not
;; when the zone is loaded from a master file or via a zone transfer. The
;; reason for this provison is to allow future dynamic update facilities to
;; change the SOA RR with known semantics.
;; 3.3.14. TXT RDATA format
;; +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
;; / TXT-DATA /
;; +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
;; where:
;; TXT-DATA One or more <character-string>s.
;; TXT RRs are used to hold descriptive text. The semantics of the text
;; depends on the domain where it is found.
;; 3.4. Internet specific RRs
;; 3.4.1. A RDATA format
;; +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
;; | ADDRESS |
;; +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
;; where:
;; ADDRESS A 32 bit Internet address.
;; Hosts that have multiple Internet addresses will have multiple A
;; records.
;; A records cause no additional section processing. The RDATA section of
;; an A line in a master file is an Internet address expressed as four
;; decimal numbers separated by dots without any imbedded spaces (e.g.,
;; "10.2.0.52" or "192.0.5.6").
;; 3.4.2. WKS RDATA format
;; +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
;; | ADDRESS |
;; +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
;; | PROTOCOL | |
;; +--+--+--+--+--+--+--+--+ |
;; | |
;; / <BIT MAP> /
;; / /
;; +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
;; where:
;; ADDRESS An 32 bit Internet address
;; PROTOCOL An 8 bit IP protocol number
;; <BIT MAP> A variable length bit map. The bit map must be a
;; multiple of 8 bits long.
;; The WKS record is used to describe the well known services supported by
;; a particular protocol on a particular internet address. The PROTOCOL
;; field specifies an IP protocol number, and the bit map has one bit per
;; port of the specified protocol. The first bit corresponds to port 0,
;; the second to port 1, etc. If the bit map does not include a bit for a
;; protocol of interest, that bit is assumed zero. The appropriate values
;; and mnemonics for ports and protocols are specified in [RFC-1010].
;; For example, if PROTOCOL=TCP (6), the 26th bit corresponds to TCP port
;; 25 (SMTP). If this bit is set, a SMTP server should be listening on TCP
;; port 25; if zero, SMTP service is not supported on the specified
;; address.
;; The purpose of WKS RRs is to provide availability information for
;; servers for TCP and UDP. If a server supports both TCP and UDP, or has
;; multiple Internet addresses, then multiple WKS RRs are used.
;; WKS RRs cause no additional section processing.
;; In master files, both ports and protocols are expressed using mnemonics
;; or decimal numbers.
;; 3.5. IN-ADDR.ARPA domain
;; The Internet uses a special domain to support gateway location and
;; Internet address to host mapping. Other classes may employ a similar
;; strategy in other domains. The intent of this domain is to provide a
;; guaranteed method to perform host address to host name mapping, and to
;; facilitate queries to locate all gateways on a particular network in the
;; Internet.
;; Note that both of these services are similar to functions that could be
;; performed by inverse queries; the difference is that this part of the
;; domain name space is structured according to address, and hence can
;; guarantee that the appropriate data can be located without an exhaustive
;; search of the domain space.
;; The domain begins at IN-ADDR.ARPA and has a substructure which follows
;; the Internet addressing structure.
;; Domain names in the IN-ADDR.ARPA domain are defined to have up to four
;; labels in addition to the IN-ADDR.ARPA suffix. Each label represents
;; one octet of an Internet address, and is expressed as a character string
;; for a decimal value in the range 0-255 (with leading zeros omitted
;; except in the case of a zero octet which is represented by a single
;; zero).
;; Host addresses are represented by domain names that have all four labels
;; specified. Thus data for Internet address 10.2.0.52 is located at
;; domain name 52.0.2.10.IN-ADDR.ARPA. The reversal, though awkward to
;; read, allows zones to be delegated which are exactly one network of
;; address space. For example, 10.IN-ADDR.ARPA can be a zone containing
;; data for the ARPANET, while 26.IN-ADDR.ARPA can be a separate zone for
;; MILNET. Address nodes are used to hold pointers to primary host names
;; in the normal domain space.
;; Network numbers correspond to some non-terminal nodes at various depths
;; in the IN-ADDR.ARPA domain, since Internet network numbers are either 1,
;; 2, or 3 octets. Network nodes are used to hold pointers to the primary
;; host names of gateways attached to that network. Since a gateway is, by
;; definition, on more than one network, it will typically have two or more
;; network nodes which point at it. Gateways will also have host level
;; pointers at their fully qualified addresses.
;; Both the gateway pointers at network nodes and the normal host pointers
;; at full address nodes use the PTR RR to point back to the primary domain
;; names of the corresponding hosts.
;; For example, the IN-ADDR.ARPA domain will contain information about the
;; ISI gateway between net 10 and 26, an MIT gateway from net 10 to MIT's
;; net 18, and hosts A.ISI.EDU and MULTICS.MIT.EDU. Assuming that ISI
;; gateway has addresses 10.2.0.22 and 26.0.0.103, and a name MILNET-
;; GW.ISI.EDU, and the MIT gateway has addresses 10.0.0.77 and 18.10.0.4
;; and a name GW.LCS.MIT.EDU, the domain database would contain:
;; 10.IN-ADDR.ARPA. PTR MILNET-GW.ISI.EDU.
;; 10.IN-ADDR.ARPA. PTR GW.LCS.MIT.EDU.
;; 18.IN-ADDR.ARPA. PTR GW.LCS.MIT.EDU.
;; 26.IN-ADDR.ARPA. PTR MILNET-GW.ISI.EDU.
;; 22.0.2.10.IN-ADDR.ARPA. PTR MILNET-GW.ISI.EDU.
;; 103.0.0.26.IN-ADDR.ARPA. PTR MILNET-GW.ISI.EDU.
;; 77.0.0.10.IN-ADDR.ARPA. PTR GW.LCS.MIT.EDU.
;; 4.0.10.18.IN-ADDR.ARPA. PTR GW.LCS.MIT.EDU.
;; 103.0.3.26.IN-ADDR.ARPA. PTR A.ISI.EDU.
;; 6.0.0.10.IN-ADDR.ARPA. PTR MULTICS.MIT.EDU.
;; Thus a program which wanted to locate gateways on net 10 would originate
;; a query of the form QTYPE=PTR, QCLASS=IN, QNAME=10.IN-ADDR.ARPA. It
;; would receive two RRs in response:
;; 10.IN-ADDR.ARPA. PTR MILNET-GW.ISI.EDU.
;; 10.IN-ADDR.ARPA. PTR GW.LCS.MIT.EDU.
;; The program could then originate QTYPE=A, QCLASS=IN queries for MILNET-
;; GW.ISI.EDU. and GW.LCS.MIT.EDU. to discover the Internet addresses of
;; these gateways.
;; A resolver which wanted to find the host name corresponding to Internet
;; host address 10.0.0.6 would pursue a query of the form QTYPE=PTR,
;; QCLASS=IN, QNAME=6.0.0.10.IN-ADDR.ARPA, and would receive:
;; 6.0.0.10.IN-ADDR.ARPA. PTR MULTICS.MIT.EDU.
;; Several cautions apply to the use of these services:
;; - Since the IN-ADDR.ARPA special domain and the normal domain
;; for a particular host or gateway will be in different zones,
;; the possibility exists that that the data may be inconsistent.
;; - Gateways will often have two names in separate domains, only
;; one of which can be primary.
;; - Systems that use the domain database to initialize their
;; routing tables must start with enough gateway information to
;; guarantee that they can access the appropriate name server.
;; - The gateway data only reflects the existence of a gateway in a
;; manner equivalent to the current HOSTS.TXT file. It doesn't
;; replace the dynamic availability information from GGP or EGP.
;; 3.6. Defining new types, classes, and special namespaces
;; The previously defined types and classes are the ones in use as of the
;; date of this memo. New definitions should be expected. This section
;; makes some recommendations to designers considering additions to the
;; existing facilities. The mailing list NAMEDROPPERS@SRI-NIC.ARPA is the
;; forum where general discussion of design issues takes place.
;; In general, a new type is appropriate when new information is to be
;; added to the database about an existing object, or we need new data
;; formats for some totally new object. Designers should attempt to define
;; types and their RDATA formats that are generally applicable to all
;; classes, and which avoid duplication of information. New classes are
;; appropriate when the DNS is to be used for a new protocol, etc which
;; requires new class-specific data formats, or when a copy of the existing
;; name space is desired, but a separate management domain is necessary.
;; New types and classes need mnemonics for master files; the format of the
;; master files requires that the mnemonics for type and class be disjoint.
;; TYPE and CLASS values must be a proper subset of QTYPEs and QCLASSes
;; respectively.
;; The present system uses multiple RRs to represent multiple values of a
;; type rather than storing multiple values in the RDATA section of a
;; single RR. This is less efficient for most applications, but does keep
;; RRs shorter. The multiple RRs assumption is incorporated in some
;; experimental work on dynamic update methods.
;; The present system attempts to minimize the duplication of data in the
;; database in order to insure consistency. Thus, in order to find the
;; address of the host for a mail exchange, you map the mail domain name to
;; a host name, then the host name to addresses, rather than a direct
;; mapping to host address. This approach is preferred because it avoids
;; the opportunity for inconsistency.
;; In defining a new type of data, multiple RR types should not be used to
;; create an ordering between entries or express different formats for
;; equivalent bindings, instead this information should be carried in the
;; body of the RR and a single type used. This policy avoids problems with
;; caching multiple types and defining QTYPEs to match multiple types.
;; For example, the original form of mail exchange binding used two RR
;; types one to represent a "closer" exchange (MD) and one to represent a
;; "less close" exchange (MF). The difficulty is that the presence of one
;; RR type in a cache doesn't convey any information about the other
;; because the query which acquired the cached information might have used
;; a QTYPE of MF, MD, or MAILA (which matched both). The redesigned
;; service used a single type (MX) with a "preference" value in the RDATA
;; section which can order different RRs. However, if any MX RRs are found
;; in the cache, then all should be there.
;; 4. MESSAGES
;; 4.1. Format
;; All communications inside of the domain protocol are carried in a single
;; format called a message. The top level format of message is divided
;; into 5 sections (some of which are empty in certain cases) shown below:
;; The names of the sections after the header are derived from their use in
;; standard queries. The question section contains fields that describe a
;; question to a name server. These fields are a query type (QTYPE), a
;; query class (QCLASS), and a query domain name (QNAME). The last three
;; sections have the same format: a possibly empty list of concatenated
;; resource records (RRs). The answer section contains RRs that answer the
;; question; the authority section contains RRs that point toward an
;; authoritative name server; the additional records section contains RRs
;; which relate to the query, but are not strictly answers for the
;; question.
;; The header section is always present. The header includes fields that
;; specify which of the remaining sections are present, and also specify
;; whether the message is a query or a response, a standard query or some
;; other opcode, etc.
;; 4.1.1. Header section format
(defbinary dns-header (:byte-order :big-endian)
;; A 16 bit identifier assigned by the program that
;; generates any kind of query. This identifier is copied
;; the corresponding reply and can be used by the requester
;; to match up replies to outstanding queries.
(id 0 :type 16)
;; A one bit field that specifies whether this message is a
;; query (0), or a response (1).
(qr 0 :type 1)
;; A four bit field that specifies kind of query in this
;; message. This value is set by the originator of a query
;; and copied into the response. The values are:
;;
;; 0 a standard query (QUERY)
;; 1 an inverse query (IQUERY)
;; 2 a server status request (STATUS)
;; 3-15 reserved for future use
(opcode 0 :type 4) ; TODO(tazjin): use define-enum
;; Authoritative Answer - this bit is valid in responses,
;; and specifies that the responding name server is an
;; authority for the domain name in question section.
(aa nil :type 1)
;; TrunCation - specifies that this message was truncated
;; due to length greater than that permitted on the
;; transmission channel.
(tc nil :type 1)
;; Recursion Desired - this bit may be set in a query and
;; is copied into the response. If RD is set, it directs
;; the name server to pursue the query recursively.
;; Recursive query support is optional.
(rd nil :type 1)
;; Recursion Available - this be is set or cleared in a
;; response, and denotes whether recursive query support is
;; available in the name server.
(ra nil :type 1)
;; Reserved for future use. Must be zero in all queries and
;; responses.
(z 0 :type 3)
;; Response code - this 4 bit field is set as part of
;; responses. The values have the following
;; interpretation:
;; 0 No error condition
;; 1 Format error - The name server was
;; unable to interpret the query.
;; 2 Server failure - The name server was
;; unable to process this query due to a
;; problem with the name server.
;; 3 Name Error - Meaningful only for
;; responses from an authoritative name
;; server, this code signifies that the
;; domain name referenced in the query does
;; not exist.
;; 4 Not Implemented - The name server does
;; not support the requested kind of query.
;; 5 Refused - The name server refuses to
;; perform the specified operation for
;; policy reasons. For example, a name
;; server may not wish to provide the
;; information to the particular requester,
;; or a name server may not wish to perform
;; a particular operation (e.g., zone
;; transfer) for particular data.
;; 6-15 Reserved for future use.
(rcode 0 :type 4)
;; an unsigned 16 bit integer specifying the number of
;; entries in the question section.
(qdcount 0 :type 16)
;; an unsigned 16 bit integer specifying the number of
;; resource records in the answer section.
(ancount 0 :type 16)
;; an unsigned 16 bit integer specifying the number of name
;; server resource records in the authority records
;; section.
(nscount 0 :type 16)
;; an unsigned 16 bit integer specifying the number of
;; resource records in the additional records section.
(arcount 0 :type 16))
;; Representation of DNS QNAMEs.
;;
;; A QNAME can be either made up entirely of labels, which is
;; basically a list of strings, or be terminated with a pointer to an
;; offset within the original message.
(deftype qname-field ()
'(or
;; pointer
(unsigned-byte 14)
;; label
string))
(defstruct qname
(start-at 0 :type (unsigned-byte 14))
(names #() :type (vector qname-field)))
;; Domain names in questions and resource records are represented as a
;; sequence of labels, where each label consists of a length octet
;; followed by that number of octets.
;;
;; The domain name terminates with the zero length octet for the null
;; label of the root. Note that this field may be an odd number of
;; octets; no padding is used.
(declaim (ftype (function (stream) (values qname integer)) read-qname))
(defun read-qname (stream)
"Reads a DNS QNAME from STREAM."
(let ((start-at (file-position stream)))
(iter (for byte next (read-byte stream))
;; Each fragment is collected into this byte vector pre-allocated
;; with the correct size.
(for fragment = (make-array byte :element-type '(unsigned-byte 8)
:fill-pointer 0))
;; If the bit sequence (1 1) is encountered at the beginning of
;; the fragment, a qname pointer is being read.
(let ((byte-copy byte))
(when (equal #b11 (lisp-binary/integer:pop-bits 2 8 byte-copy))
(let ((next (read-byte stream)))
(lisp-binary/integer:push-bits byte-copy 8 next)
(collect next into fragments result-type vector)
(sum 2 into size)
(finish))))
;; Total size is needed, count for each iteration byte, plus its
;; own value.
(sum (+ 1 byte) into size)
(until (equal byte 0))
;; On each iteration, this will interpret the current byte as an
;; unsigned integer and read from STREAM an equivalent amount of
;; times to assemble the current fragment.
;;
;; Advancing the stream like this also ensures that the next
;; iteration occurs on a new fragment or the final terminating
;; byte.
;;
;; TODO(tazjin): Use lisp-binary:read-counted-string.
(dotimes (_ byte (collect (babel:octets-to-string fragment)
into fragments result-type vector))
(vector-push (read-byte stream) fragment))
(finally (return (values (make-qname :start-at start-at
:names fragments)
size))))))
(declaim (ftype (function (stream qname)) write-qname))
(defun write-qname (stream qname)
"Write a DNS qname to STREAM."
;; Write each fragment starting with its (byte-) length, followed by
;; the bytes.
(iter (for fragment in-vector (qname-names qname))
(for bytes = (babel:string-to-octets fragment))
(write-byte (length bytes) stream)
(iter (for byte in-vector bytes)
(write-byte byte stream)))
;; Always finish off the serialisation with a null-byte!
(write-byte 0 stream))
;; 4.1.2. Question section format
(defbinary dns-question (:byte-order :big-endian :export t)
;; a domain name represented
(qname "" :type (custom :lisp-type qname
:reader #'read-qname
:writer #'write-qname))
;; a two octet code which specifies the type of the query.
;; The values for this field include all codes valid for a
;; TYPE field, together with some more general codes which
;; can match more than one type of RR.
(qtype 0 :type 16) ;; TODO(tazjin): define type after the RR binary
;; a two octet code that specifies the class of the query. For
;; example, the QCLASS field is IN for the Internet.
(qclass 0 :type 16)) ; TODO(tazjin): enum?
;; 4.1.3. Resource record format
(define-enum dns-type 2
(:byte-order :big-endian)
;; http://www.iana.org/assignments/dns-parameters/dns-parameters.xhtml
(A 1)
(NS 2)
(CNAME 5)
(SOA 6)
(PTR 12)
(MX 15)
(TXT 16)
(SRV 33)
(AAAA 28)
(ANY 255)) ;; (typically wants SOA, MX, NS and MX)
(defbinary dns-rr (:byte-order :big-endian :export t)
(name nil :type (custom :lisp-type qname
:reader #'read-qname
:writer #'write-qname))
;; two octets containing one of the RR type codes. This
;; field specifies the meaning of the data in the RDATA
;; field.
(type 0 :type dns-type)
;; two octets which specify the class of the data in the
;; RDATA field.
(class 0 :type 16) ; TODO(tazjin): enum
;; a 32 bit unsigned integer that specifies the time
;; interval (in seconds) that the resource record may be
;; cached before it should be discarded. Zero values are
;; interpreted to mean that the RR can only be used for the
;; transaction in progress, and should not be cached.
(ttl 0 :type 32)
;; an unsigned 16 bit integer that specifies the length in
;; octets of the RDATA field.
(rdlength 0 :type 16)
;; 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.
;; For example, the if the TYPE is A and the CLASS is IN,
;; the RDATA field is a 4 octet ARPA Internet address.
(rdata #() :type (eval (case type
;; TODO(tazjin): Deal with multiple strings in single RRDATA
((TXT) '(counted-string 1))
((A) '(simple-array (unsigned-byte 8) (4)))
(otherwise `(simple-array (unsigned-byte 8) (,rdlength)))))))
(defbinary dns-message (:byte-order :big-endian :export t)
(header nil :type dns-header)
;; the question for the name server
(question #() :type (simple-array dns-question ((dns-header-qdcount header))))
;; ;; RRs answering the question
;; (answer #() :type (simple-array (unsigned-byte 8) (16)))
(answer #() :type (simple-array dns-rr ((dns-header-ancount header))))
;; ;; ;; RRs pointing toward an authority
(authority #() :type (simple-array dns-rr ((dns-header-nscount header))))
;; ;; RRs holding additional information
(additional #() :type (simple-array dns-rr ((dns-header-arcount header)))))
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