## Name

lwres_getipnodebyname, lwres_getipnodebyaddr, lwres_freehostent — lightweight resolver nodename / address translation API

## Synopsis

    #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).