char *Cgetnetaddress(int sock, const void *sa, size_t salen, int *skey, const char **numeric_out, const char **name_out, int flags, int cflags);
Cnetdb provides several netdb like functions including Cgethostbyname, Cgethostbyaddr, Cgetservbyname, Cgetnameinfo, Cgetaddrinfo, Cgai_strerror which behave in a somewhat similar way to their system netdb counterparts. In addition Cnetdb provides a function called Cgetnetaddress which is currently the only one documented here.
Cgetnetaddress returns a DNS domain name (often called a hostname) given either a network socket, in which case the hostname corresponds to the peer address of the socket, or a sockaddr structure. The name will be returned as a numeric IP address and/or optionaly a DNS domain name.
Exactly one of either sock or sa must be specified, the other should be set to -1 or NULL respectively. If both are set the behaviour should be considered undefined and may change in the future. If skey is NULL the memory for pointers returned by Cgetnetaddress will be dynamically allocated and it is the responsibility of the caller to free them when done. If not NULL skey should point to an int which is initially set to a value of -1. The memory used to store the results returned by Cgetnetaddress will be allocated internally and will be reused during subsequent calls to Cgetnetaddress from the same thread and that share the same value of skey.
If numeric_out or name_out are not NULL the char pointer which they reference will be reset to a pointer to a character array containig the numeric or domain name address to be returned by the function. The output will be NULL if the function is unable to find an IP or domain name. flags accepts the same bitmaped flags that can be set for getnameinfo(). cflags accepts bitmaped flags which are unique to Cgetnetaddress.
If NI_NUMERICHOST is specified in flags no attempt is made to obtain a domain name. If NI_NAMEREQD is specified nothing is returned unless a domain name address can be determined. NI_NUMERICHOST and NI_NAMEREQD are mutually exclusive. Other flags options may be set and will have the effect described for getnameinfo().
cflags may take the bitmaped flags CNA_WANTLOOPBACK, CNA_NOFWDLOOKUP and CNA_FWDLOOKUP.
By default if the address to be returned is determined to be the loopback address any domain name returned will be that of the local machine. If CNA_WANTLOOPBACK is specified any domain name returned will be that associated with the loopback address, usually localhost.localdomain.
A forward lookup verification of the domain name may be optionally specified with the CNA_FWDLOOKUP flag. The forward lookup means that one of the address to which a domain name resolves must match the address passed to Cgetnetaddress. If the match failes the domain name will be considered to not be available. By default, or if the option CNA_NOFWDLOOKUP is passed in cflags, the forward lookup check is not performed or required. The behavior if both CNA_FWDLOOKUP and CNA_NOFWDLOOKUP are specified is undefined.