Expands a compressed domain name.
Standard C Library (libc.a)
#include <sys/types.h>
#include <netinet/in.h>
#include <arpa/nameser.h>
#include <resolv.h>
int dn_expand (MessagePtr, EndofMesOrig, CompDomNam, ExpandDomNam, Length)
u_char * MessagePtr, * EndOfMesOrig;
u_char * CompDomNam, * ExpandDomNam;
int Length;
The dn_expand subroutine expands a compressed domain name to a full domain name, converting the expanded names to all uppercase letters. A client process compresses domain names to conserve space. Compression consists of removing the longest possible previously occurring suffixes. The dn_expand subroutine restores a domain name compressed by the dn_comp subroutine to its full size.
The dn_expand subroutine is one of a set of subroutines that form the resolver. The resolver is a set of functions that perform a translation between domain names and network addresses. Global information used by the resolver subroutines resides in the _res data structure. The /usr/include/resolv.h file contains the _res data structure definition.
All applications containing the dn_expand subroutine must be compiled with the _BSD macro set to a specific value. Acceptable values are 43 and 44. In addition, all socket applications must include the BSD libbsd.a library.
| Item | Description |
|---|---|
| MessagePtr | Specifies a pointer to the beginning of a message. |
| EndOfMesOrig | Points to the end of the original message that contains the compressed domain name. |
| CompDomNam | Specifies a pointer to a compressed domain name. |
| ExpandDomNam | Specifies a pointer to a buffer that holds the resulting expanded domain name. |
| Length | Specifies the size of the buffer pointed to by the ExpandDomNam parameter. |
Upon successful completion, the dn_expand subroutine returns the size of the expanded domain name.
If unsuccessful, the dn_expand subroutine returns a value of -1 to the calling program.
| Item | Description |
|---|---|
| /etc/resolv.conf | Defines name server and domain name constants, structures, and values. |