dn_comp(3) Library Functions Manual dn_comp(3)
NAME
dn_comp - Compresses a domain name
LIBRARY
Standard C Library (libc.a, libc.so)
SYNOPSIS
#include <sys/types.h> #include <netinet/in.h> #include <arpa/nameser.h> #include <resolv.h>
int dn_comp (
const char *expanded_name,
u_char *compressed_name,
int length,
u_char **name_ptrs,
u_char **end_ptr );
PARAMETERS
Points to a domain name. Points to an array containing the compressed domain name. Specifies the size of the array pointed to by the com-
pressed_name parameter. Specifies a list of pointers to previously compressed names in the current message. Points to the end of the
array pointed to by the compressed_name parameter.
DESCRIPTION
The dn_comp() (domain name compression) function compresses the domain name pointed to by the expanded_name parameter and stores it in the
area pointed to by the compressed_name parameter.
The dn_comp() function inserts labels into the message as the name is compressed. The dn_comp() function also maintains a list of pointers
to the message labels.
If the value of the name_ptrs parameter is null, the dn_comp() function does not compress any names, but instead translates a domain name
from ASCII to internal format without removing suffixes (compressing). Otherwise, the name_ptrs parameter is the address of pointers to
previously compressed suffixes. The list ends with NULL.
If the end_ptr parameter is null, the dn_comp() function does not update the list of label pointers.
The dn_comp() function is one of a set of subroutines that form the resolver, a set of functions that resolves domain names. Global infor-
mation that is used by the resolver functions is kept in the _res data structure. The /include/resolv.h file contains the _res data
structure definition.
RETURN VALUES
Upon successful completion, the dn_comp() function returns the size of the compressed domain name. Otherwise, a value of -1 is returned
and the h_errno external variable is set with an error code, if any. Error code values and reasons are defined in <netdb.h>.
FILES
Defines name server and domain name structures, constants, and values.
RELATED INFORMATION
Functions: dn_expand(3), dn_find(3), dn_skipname(3), putshort(3), putlong(3), res_init(3), res_mkquery(3), res_query(3), res_search(3),
res_send(3), _getshort(3), _getlong(3).
Commands: named(8). delim off
dn_comp(3)
