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GETRRSETBYNAME(3) Library Functions Manual GETRRSETBYNAME(3)

freerrset, getrrsetbyname — retrieve DNS records

#include <netdb.h>

int
getrrsetbyname(const char *hostname, unsigned int rdclass, unsigned int rdtype, unsigned int flags, struct rrsetinfo **res);

void
freerrset(struct rrsetinfo *rrset);

() gets a set of resource records associated with a hostname, rdclass, and rdtype. hostname is a pointer to a NUL-terminated string. The flags field is currently unused and must be zero.

After a successful call to (), *res is a pointer to an rrsetinfo structure, containing a list of one or more rdatainfo structures containing resource records and potentially another list of rdatainfo structures containing SIG resource records associated with those records. The members rri_rdclass and rri_rdtype are copied from the parameters. rri_ttl and rri_name are properties of the obtained rrset. The resource records contained in rri_rdatas and rri_sigs are in uncompressed DNS wire format. Properties of the rdataset are represented in the rri_flags bitfield. If the RRSET_VALIDATED bit is set, the data has been DNSSEC validated and the signatures verified.

The following structures are used:

struct  rdatainfo {
	unsigned int	rdi_length;	/* length of data */
	unsigned char	*rdi_data;	/* record data */
};

struct  rrsetinfo {
	unsigned int	 rri_flags;	/* RRSET_VALIDATED ... */
	unsigned int	 rri_rdclass;	/* class number */
	unsigned int	 rri_rdtype;	/* RR type number */
	unsigned int	 rri_ttl;	/* time to live */
	unsigned int	 rri_nrdatas;	/* size of rdatas array */
	unsigned int	 rri_nsigs;	/* size of sigs array */
	char		 *rri_name;	/* canonical name */
	struct rdatainfo *rri_rdatas;	/* individual records */
	struct rdatainfo *rri_sigs;	/* individual signatures */
};

All of the information returned by () is dynamically allocated: the rrsetinfo and rdatainfo structures, and the canonical host name strings pointed to by the rrsetinfo structure. Memory allocated for the dynamically allocated structures created by a successful call to getrrsetbyname() is released by (). rrset is a pointer to a struct rrsetinfo created by a call to getrrsetbyname().

getrrsetbyname() returns zero on success, and one of the following error codes if an error occurred:

[ERRSET_NONAME]
The name does not exist.
[ERRSET_NODATA]
The name exists, but does not have data of the desired type.
[ERRSET_NOMEMORY]
Memory could not be allocated.
[ERRSET_INVAL]
A parameter is invalid.
[ERRSET_FAIL]
Other failure.

res_init(3), resolv.conf(5)

getrrsetbyname() first appeared in OpenBSD 3.0. The API first appeared in ISC BIND version 9.

Jakob Schlyter <jakob@openbsd.org>

The RRSET_VALIDATED flag in rri_flags is set if the AD (authenticated data) bit in the DNS answer is set. This flag be trusted unless the transport between the nameserver and the resolver is secure (e.g. IPsec, trusted network, loopback communication).

The data in *rdi_data should be returned in uncompressed wire format. Currently, the data is in compressed format and the caller can't uncompress since it doesn't have the full message.

September 11, 2022 openbsd