Overview

Each of these generic routines calls type specific routines that provide the type specific details.

From time to time new types are defined and it is necessary to add these types into the existing structure. This document is written to provide instruction on how to do this.

Adding new RDATA types

Each rdata module must perform the following operations:

Convert from text format to internal format

Convert from internal format to text format

Convert from wire format to internal format

Convert from internal format to wire format

Convert from a structure to internal format

Convert from internal format to a structure

Compare two rdata in internal format

There is an additional set of support functions and macros only available to to rdata code.

RDATA Hierarchy

	rdata/
		generic/
			typename_typenumber.h
		classname_classnumber/
			typename_typenumber.h

Initial rdata hierarchy:

	rdata/
		generic/
			ns_2.h
			md_3.h
			mf_4.h
			cname_5.h
			soa_6.h
			mb_7.h
			mg_8.h
			mr_9.h
			null_10.h
			ptr_12.h
			hinfo_13.h
			minfo_14.h
			mx_15.h
			txt_16.h
			rp_17.h
			afsdb_18.h
			x25_19.h
			isdn_20.h
			rt_21.h
			sig_24.h
			key_25.h
			gpos_27.h
			loc_29.h
			nxt_30.h
			cert_37.h
			dname_39.h
			unspec_103.h
			tkey_249.h
		in_1/
			a_1.h
			wks_11.h
			nsap_22.h
			nsap-ptr_23.h
			px_26.h
			aaaa_28.h
			srv_33.h
			naptr_35.h
			kx_36.h
			a6_38.h
		any_255/
			tsig_250.h


CLASSNAME and TYPENAME
Class and type names must be from the following alphabet and less that 11
characters in length or otherwise they will be ignored.
Permissible alphabet: a to z, 0 to 9 and dash (-).
Dash is mapped to underscore (_) for the C function names below.

Internal Format
The internal format chosen is DNS wire format without any compression being
applied to domain names in the rdata.

Convert from text format to internal format
The functions to convert from text format has the following call formats and
is declared as follows for class generic functions.
static dns_result_t
fromtext_typename(dns_rdataclass_t class, dns_rdatatype_t type,
		  isc_lex_t *lexer, dns_name_t *origin,
		  isc_boolean_t downcase, isc_buffer_t *target);

Class specific functions contain the class name in addition to the
type name.
static dns_result_t
fromtext_classname_typename(dns_rdataclass_t class, dns_rdatatype_t type,
		           isc_lex_t *lexer, dns_name_t *origin,
			   isc_boolean_t downcase, isc_buffer_t *target);



class

This argument should be ignored when used with a class generic RR type
otherwise REQUIRE(class == #) should be present at the start
of the function.
type

This should be tested with a REQUIRE(type == #) statement at
the begining of the function.
lexer

This is used to read the input text stream.
origin

This is a absolute name used to qualify unqualified / partially qualified
domainnames in the text stream.
It is passed to the name parsing routines.
downcase

This is passed to the name parsing routines to determine whether to downcase
the names it generates or leave them in the case they are pesented in.
target

This is a BINARY buffer used to write the internal format of the rdata record being read in to.


fromtext_typename() reads tokens from lexer,
up to but not including the end of line (EOL) token or end of file (EOF) token.
If the EOL / EOF token is read it should be returned to the input stream.
gettoken()
should be used to read the next token from the input stream and
will return EOL / EOF tokens
automatically unless
they are specifcally requested.
isc_lex_ungettoken() should
be used to return EOL / EOF (or any other token) to the input stream if
the EOL / EOF token is read.
Unused tokens will cause dns_rdata_fromtext() to return
DNS_R_EXTRATOKEN if fromtext_typename() was successful.

fromtext_typename() reads external input and as such is a high security area and must be paranoid about its input.
Convert from internal format to text format
static dns_result_t
totext_typename(dns_rdata_t *rdata, dns_name_t *origin,
		isc_buffer_t *target);

static dns_result_t
totext_classname_typename(dns_rdata_t *rdata, dns_name_t *origin,
			  isc_buffer_t *target);


rdata

This is the rdata record to be converted from internal format to text.
rdata->type and rdata->class for class specific
RR types should be checked at the start of the function with
REQUIRE(rdata->type == #) statements.
origin

If this in non NULL then any domainnames with this suffix
should be written out unqualified.
name_prefix() can be used to
check if origin is NULL and provide the correct
arguments to the name conversion routines.
target

This is a TEXT buffer used to hold the output.

Convert from wire format to internal format
static dns_result_t
fromwire_typename(dns_rdataclass_t class, dns_rdatatype_t type,
                  isc_buffer_t *source, dns_decompress_t *dctx,
	          isc_boolean_t downcase, isc_buffer_t *target);

static dns_result_t
fromwire_classname_typename(dns_rdataclass_t class, dns_rdatatype_t type,
			    isc_buffer_t *source, dns_decompress_t *dctx,
			    isc_boolean_t downcase, isc_buffer_t *target);


fromwire_classname_typename() is required to set the valid
decompression methods if there is a domain name in the rdata.
if (dns_decompress_edns(dctx) >= # || !dns_decompress_strict(dctx))
	dns_decompress_setmethods(dctx, DNS_COMPRESS_ALL);
else
	dns_decompress_setmethods(dctx, DNS_COMPRESS_GLOBAL14);



class

This argument should be ignored when used with a class generic RR type
otherwise REQUIRE(class == #) should be present at the start
of the function.
type

This should be tested with a REQUIRE(type == #) statement at
the begining of the function.
source

This is a BINARY buffer with the active region
containing a RR record in wire format.
dctx

This is the decompression context and is passed to
dns_name_fromwire(),
along with downcase, to enable a compressed domain name
to be extracted from the source.
downcase

This is passed to dns_name_fromwire() to say whether the
extracted domainname should be downcased during the extraction.
target

This is a BINARY buffer where the decompressed and checked
RR record is written.

fromwire_typename() is a security sensitive routine
as it reads external data and should take extreme care to ensure that
the input data matches its description.

If the active buffer is not empty at completion and
fromwire_typename() was otherwise successful
dns_rdata_fromwire() will return DNS_R_EXTRADATA.
Convert from internal format to wire format
static dns_result_t
towire_typename(dns_rdata_t *rdata, dns_compress_t *cctx,
                isc_buffer_t *target);

static dns_result_t
towire_classname_typename(dns_rdata_t *rdata, dns_compress_t *cctx,
                          isc_buffer_t *target);


towire_classname_typename() is required to set the
allowed name compression methods based on EDNS version if there is a
domain name in the rdata.
if (dns_compress_getedns(cctx) >= #)
	dns_compress_setmethods(cctx, DNS_COMPRESS_ALL);
else
	dns_compress_setmethods(cctx, DNS_COMPRESS_GLOBAL14);


rdata

This is the rdata record to be converted from internal format to text.
rdata->type and rdata->class for class specific
RR types should be checked at the start of the function with
REQUIRE(rdata->type == #) statements.
cctx

This is the compression context, it should be passed to dns_name_towire() when putting domainnames on the wire.
target

This is a BINARY buffer used to write the rdata to.

Simple RR types without domainnames can use the following code to
transfer the contents of the rdata to the target buffer.
	return (mem_tobuffer(target, rdata->data, rdata->length));

Convert from a structure to internal format
static dns_result_t
fromstruct_typename(dns_rdataclass_t class, dns_rdatatype_t type,
		    void *source, isc_buffer_t *target);

static dns_result_t
fromstruct_classname_typename(dns_rdataclass_t class, dns_rdatatype_t type,
		    	      void *source, isc_buffer_t *target);


class

This argument should be ignored when used with a class generic RR type
otherwise REQUIRE(class == #) should be present at the start
of the function.
type

This should be tested with a REQUIRE(type == #) statement at
the beginning of the function.
source

This points to a type specific structure.
target

This is a BINARY buffer used to write the internal format of the rdata record being read in to.

Convert from internal format to a structure
static dns_result_t
tostruct_typename(dns_rdata_t *rdata, void *target);

static dns_result_t
tostruct_classname_typename(dns_rdata_t *rdata, void *target);


rdata

This is the rdata record to be converted from internal format to a structure.
rdata->type and rdata->class for class specific
RR types should be checked at the start of the function with
REQUIRE(rdata->type == #) statements.
target

Pointer to a type specific structure.

Compare two rdata in internal format
static int
compare_typename(dns_rdata_t *rdata1, dns_rdata_t *rdata2);

static int
compare_classname_typename(dns_rdata_t *rdata1, dns_rdata_t *rdata2);

Compares rdata1 and rdata2 as required for DNSSEC
ordering.  The routine should
ensure that the type and class of the two rdata
match with REQUIRE(rdata1->type == rdata2->type); and
REQUIRE(rdata1->class == rdata2->class); statements. The
rdata->type should also be verified and if the RR type is
class specific the rdata->class.

compare_classname_typename() returns -1, 0, 1.
Support Functions
The following static support functions are available to use.

static unsigned int

name_length(dns_name_t *name);


Returns the length of name.

static dns_result_t

txt_totext(isc_region_t *source, isc_buffer_t *target);


Extracts the octet length tagged text string at the start of
source and writes it as a quoted string to target.
source is adjusted so that it points to first octet after the
text string.

Returns DNS_R_NOSPACE or DNS_R_SUCCESS.

static dns_result_t

txt_fromtext(isc_textregion_t *source, isc_buffer_t *target);


Take the text region source and convert it to a length tagged
text string writing it to target.

Returns DNS_R_NOSPACE, DNS_R_TEXTTOLONG
or DNS_R_SUCCESS.

static dns_result_t

txt_fromwire(isc_buffer_t *source, isc_buffer_t *target);


Read a octet length tagged text string from source and
write it to target.
Ensures that octet length tagged text string was wholly within the active
area of source.
Adjusts the active area of source so that it refers to the first
octet after the octet length tagged text string.

Returns DNS_R_UNEXPECTEDEND, DNS_R_NOSPACE or
DNS_R_SUCCESS.

static isc_boolean_t

name_prefix(dns_name_t *name, dns_name_t *origin, dns_name_t *target);



If origin is NULL or the root label set target to
refer to name and return ISC_FALSE.
Otherwise see if name is a sub domain of origin
and are not equal.
If so make target refer to the prefix of name and
return ISC_TRUE.
Otherwise make target refer to name and return
ISC_FALSE.

Typical use:

static dns_result_t
totext_typename(dns_rdata_t *rdata, dns_name_t *origin,
		isc_buffer_t * target)
{
	isc_region_t region;
	dns_name_t name, prefix;
	isc_boolean_t sub;

	dns_name_init(&name, NULL);
	dns_name_init(&prefix, NULL);
	dns_rdata_toregion(rdata, &region);
	dns_name_fromregion(&name, &region);
	sub = name_prefix(&name, origin, &prefix);
	return (dns_name_totext(&prefix, sub, target));
}

static dns_result_t

str_totext(char *source, isc_buffer_t *target);



This adds the NULL terminated string source
up to but not including NULL to target.

Returns DNS_R_NOSPACE and DNS_R_SUCCESS.

static isc_boolean_t

buffer_empty(isc_buffer_t *source);


Returns ISC_TRUE if the active region of source is
empty otherwise ISC_FALSE.

static void

buffer_fromregion(isc_buffer_t *buffer, isc_region_t *region,
unsigned int type);


Make buffer refer to the memory in region and
make it active.

static dns_result_t

uint32_tobuffer(isc_uint32_t value, isc_buffer_t *target);


Write the 32 bit value in network order to target.

Returns DNS_R_NOSPACE and DNS_R_SUCCESS.

static dns_result_t

uint16_tobuffer(isc_uint32_t value, isc_buffer_t *target);


Write them 16 bit value in network order to target.

Returns ISC_R_RANGE, DNS_R_NOSPACE and DNS_R_SUCCESS.

static isc_uint32_t

uint32_fromregion(isc_region_t *region);


Returns the 32 bit at the start of region in host order.

Requires (region->length >= 4).

static isc_uint16_t

uint16_fromregion(isc_region_t *region);


Returns the 16 bit at the start of region in host order.

Requires (region->length >= 2).

static dns_result_t

gettoken(isc_lex_t *lexer, isc_token_t *token, isc_tokentype_t expect, isc_boolean_t eol);


Gets the next token from the input stream lexer. Ensure that the
returned token matches expect (isc_tokentype_qstring can also
return isc_tokentype_string), or isc_tokentype_eol and isc_tokentype_eof if
eol is ISC_TRUE.

Returns DNS_R_UNEXPECTED, DNS_R_UNEXPECTEDEND,
DNS_R_UNEXPECTEDTOKEN and DNS_R_SUCCESS.


static dns_result_t

mem_tobuffer(isc_buffer_t *target, void *base, unsigned int length);


Add the memory referred to by base to target.

Returns DNS_R_NOSPACE and DNS_R_SUCCESS.

static int

compare_region(isc_region_t *r1, isc_region_t *r2)


Compares two regions returning -1, 0, 1 based on their DNSSEC ordering.

static int

hexvalue(char value);


Returns the hexadecimal value of value or -1 if not
a hexadecimal character.

static int

decvalue(char value);


Returns the decimal value of value or -1 if not
a decimal character.

static dns_result_t

base64_totext(isc_region_t *source, isc_buffer_t *target);


Convert the region referred to by source to base64 encoded text
and put it into target.

Returns DNS_R_NOSPACE or DNS_R_SUCCESS.

static dns_result_t

base64_tobuffer(isc_lex_t *lexer, isc_buffer_t *target,
int length);


Read a series of tokens from lexer that containing base64 data
until one of end of line, length (length >= 0)
bytes have been read or base64 pad characters are seen.
If length < 0 it is ignored otherwise it is an error if there
are not length octets of data or when processing a token
length octets would have been exceeded.

Returns DNS_R_BADBASE64, DNS_R_UNEXPECTED,
DNS_R_UNEXPECTEDEND, DNS_R_UNEXPECTEDTOKEN
and DNS_R_SUCCESS.

static dns_result_t

time_totext(unsigned long value, isc_buffer_t *target);


Convert the date represented by value into YYYYMMDDHHMMSS format
taking into account the active epochs. This code is Y2K and Y2038 compliant.

Returns DNS_R_NOSPACE and DNS_R_SUCCESS.
static dns_result_t

time_tobuffer(char *source, isc_buffer_t *target);


Take the date in source and convert it seconds since January 1,
1970 (ignoring leap seconds) and place the least significant 32 bits into
target.

Returns ISC_R_RANGE, DNS_R_SYNTAX,
DNS_R_NOSPACE and DNS_R_SUCCESS.

Support Macros

The following macro is available:

RETERR(x)



Evaluate x and call return (<value of x>); if the result is not DNS_R_SUCCESS.