man resparse () - parse and manipulate DNS resolver responses


res_parse, res_copy, res_print, res_free - parse and manipulate DNS resolver responses


#include rr.h

res_response * res_parse(msg) char *msg;

res_response * res_copy(resp) res_response *resp;

res_print(resp) res_response *resp;

res_free(resp) res_response *resp;


These routines are used for parsing the response from a call to the DNS resolver routines into a C structure suitable for programmer use, and to manipulate such structures.

Res_parse takes the result of a call to res_query or res_search. This is then parsed into an appropriate structure, and domain names unpacked into standard null-terminated C strings. It then returns a pointer to this structure.

Res_copy takes a pointer to a res_response structure, makes a copy of it and returns a pointer to the copy.

Res_print prints out the specified res_response structure, using a similar style to nslookup.

Res_free takes a pointer to a res_response structure, frees all memory allocated to it and clears the counts of the number of records of each type present.


The structures used are as follows:

res_response { HEADERtheader; The header as defined in <arpa/nameser.h>. s_questiont**question; Pointer to an array of question records. s_rrt**answer; Pointer to an array of answer resource records. s_rrt**authority; Pointer to an array of nameserver resource records. s_rrt**additional; Pointer to an array of additional resource records (the addresses of the authoritative nameservers). }

s_question { chart*qname; The name that the query was sent for. u_shorttqtype

u_shorttqclass The type and class of query, as defined in <arpa/nameser.h>. }

s_rr { chart*name; The name of the resource record. u_shortttype

u_shorttclass The type and class of the record, as defined in <arpa/nameser.h>. u_longtttl How long (in seconds) this record may be cached. u_longtdlen; The length of the type-specific data.

This need not be the same as the size of the unpacked data - particularly for domain names. union u_rdatatrdata; The type-specific data (see rr.h for details). }


Res_parse and res_copy will return a pointer to the new structure, or a NULL pointer in case of errors.

Res_print and res_free do not return anything.


Res_parse now returns a pointer to a dynamically assigned area, (previous releases used a static area which which would be overwritten by subsequent calls).

The pointer returned by res_parse should be freed using res_free (contrary to the instructions with earlier releases of this library).

If res_print is called with a pointer that has been freed, it will (probably) print out an "empty" header.

This is a Bad Thing to do anyway!




resolver(3), gethostbyname(3)



Dave Shield <>