Jun 30, 2000
lwres_getipnode 3 BIND9
2004 2005 Internet Systems Consortium, Inc. ("ISC")
2000 2001 2003 Internet Software Consortium.
lwres_getipnodebyname lwres_getipnodebyaddr lwres_freehostent lightweight resolver nodename / address translation API

    #include <lwres/netdb.h>

struct hostent * `lwres_getipnodebyname` const char *name int af int flags int *error_num struct hostent * `lwres_getipnodebyaddr` const void *src size_t len int af int *error_num void `lwres_freehostent` struct hostent *he

## DESCRIPTION

These functions perform thread safe, protocol independent nodename-to-address and address-to-nodename translation as defined in RFC2553.

They use a struct hostent which is defined in `namedb.h`:

    struct  hostent {
            char    *h_name;        /* official name of host */
            char    **h_aliases;    /* alias list */
            int     h_addrtype;     /* host address type */
            int     h_length;       /* length of address */
            char    **h_addr_list;  /* list of addresses from name server */
    };
    #define h_addr  h_addr_list[0]  /* address, for backward compatibility */

The members of this structure are:

`h_name`

  The official (canonical) name of the host.

`h_aliases`

  A NULL-terminated array of alternate names (nicknames) for the host.

`h_addrtype`

  The type of address being returned - usually PF_INET or PF_INET6.

`h_length`

  The length of the address in bytes.

`h_addr_list`

  A NULL terminated array of network addresses for the host. Host addresses are returned in network byte order.

`lwres_getipnodebyname()` looks up addresses of protocol family af for the hostname name. The flags parameter contains ORed flag bits to specify the types of addresses that are searched for, and the types of addresses that are returned. The flag bits are:

`AI_V4MAPPED`

  This is used with an af of AF_INET6, and causes IPv4 addresses to be returned as IPv4-mapped IPv6 addresses.

`AI_ALL`

  This is used with an af of AF_INET6, and causes all known addresses (IPv6 and IPv4) to be returned. If AI_V4MAPPED is also set, the IPv4 addresses are return as mapped IPv6 addresses.

`AI_ADDRCONFIG`

  Only return an IPv6 or IPv4 address if here is an active network interface of that type. This is not currently implemented in the BIND 9 lightweight resolver, and the flag is ignored.

`AI_DEFAULT`

  This default sets the `AI_V4MAPPED` and `AI_ADDRCONFIG` flag bits.

`lwres_getipnodebyaddr()` performs a reverse lookup of address src which is len bytes long. af denotes the protocol family, typically PF_INET or PF_INET6.

`lwres_freehostent()` releases all the memory associated with the struct hostent pointer he. Any memory allocated for the `h_name`, `h_addr_list` and `h_aliases` is freed, as is the memory for the hostent structure itself.

## RETURN VALUES

If an error occurs, `lwres_getipnodebyname()` and `lwres_getipnodebyaddr()` set *error_num to an appropriate error code and the function returns a NULL pointer. The error codes and their meanings are defined in `<lwres/netdb.h>`:

`HOST_NOT_FOUND`

  No such host is known.

`NO_ADDRESS`

  The server recognised the request and the name but no address is available. Another type of request to the name server for the domain might return an answer.

`TRY_AGAIN`

  A temporary and possibly transient error occurred, such as a failure of a server to respond. The request may succeed if retried.

`NO_RECOVERY`

  An unexpected failure occurred, and retrying the request is pointless.

lwres_hstrerror 3 translates these error codes to suitable error messages.

## SEE ALSO

RFC2553 , lwres 3 , lwres_gethostent 3 , lwres_getaddrinfo 3 , lwres_getnameinfo 3 , lwres_hstrerror 3 .