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LWRES_GETHOSTENT(3)                  BIND9                 LWRES_GETHOSTENT(3)



NAME
       lwres_gethostbyname, lwres_gethostbyname2, lwres_gethostbyaddr, lwres_gethostent, lwres_sethostent,
       lwres_endhostent, lwres_gethostbyname_r, lwres_gethostbyaddr_r, lwres_gethostent_r, lwres_sethostent_r,
       lwres_endhostent_r - lightweight resolver get network host entry

SYNOPSIS
       #include <lwres/netdb.h>

       struct hostent * lwres_gethostbyname(const char *name);

       struct hostent * lwres_gethostbyname2(const char *name, int af);

       struct hostent * lwres_gethostbyaddr(const char *addr, int len, int type);

       struct hostent * lwres_gethostent(void);

       void lwres_sethostent(int stayopen);

       void lwres_endhostent(void);

       struct hostent * lwres_gethostbyname_r(const char *name, struct hostent *resbuf, char *buf, int buflen,
                                              int *error);

       struct hostent * lwres_gethostbyaddr_r(const char *addr, int len, int type, struct hostent *resbuf, char *buf,
                                              int buflen, int *error);

       struct hostent * lwres_gethostent_r(struct hostent *resbuf, char *buf, int buflen, int *error);

       void lwres_sethostent_r(int stayopen);

       void lwres_endhostent_r(void);

DESCRIPTION
       These functions provide hostname-to-address and address-to-hostname lookups by means of the lightweight
       resolver. They are similar to the standard gethostent(3) functions provided by most operating systems. They use
       a struct hostent which is usually 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 -- 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.

       For backward compatibility with very old software, h_addr is the first address in h_addr_list.

       lwres_gethostent(), lwres_sethostent(), lwres_endhostent(), lwres_gethostent_r(), lwres_sethostent_r() and
       lwres_endhostent_r() provide iteration over the known host entries on systems that provide such functionality
       through facilities like /etc/hosts or NIS. The lightweight resolver does not currently implement these
       functions; it only provides them as stub functions that always return failure.

       lwres_gethostbyname() and lwres_gethostbyname2() look up the hostname name.  lwres_gethostbyname() always looks
       for an IPv4 address while lwres_gethostbyname2() looks for an address of protocol family af: either PF_INET or
       PF_INET6 -- IPv4 or IPV6 addresses respectively. Successful calls of the functions return a struct hostentfor
       the name that was looked up.  NULL is returned if the lookups by lwres_gethostbyname() or
       lwres_gethostbyname2() fail.

       Reverse lookups of addresses are performed by lwres_gethostbyaddr().  addr is an address of length len bytes
       and protocol family type -- PF_INET or PF_INET6.  lwres_gethostbyname_r() is a thread-safe function for forward
       lookups. If an error occurs, an error code is returned in *error.  resbuf is a pointer to a struct hostent
       which is initialised by a successful call to lwres_gethostbyname_r().  buf is a buffer of length len bytes
       which is used to store the h_name, h_aliases, and h_addr_list elements of the struct hostent returned in
       resbuf. Successful calls to lwres_gethostbyname_r() return resbuf, which is a pointer to the struct hostent it
       created.

       lwres_gethostbyaddr_r() is a thread-safe function that performs a reverse lookup of address addr which is len
       bytes long and is of protocol family type -- PF_INET or PF_INET6. If an error occurs, the error code is returned
       in *error. The other function parameters are identical to those in lwres_gethostbyname_r().  resbuf is a
       pointer to a struct hostent which is initialised by a successful call to lwres_gethostbyaddr_r().  buf is a
       buffer of length len bytes which is used to store the h_name, h_aliases, and h_addr_list elements of the struct
       hostent returned in resbuf. Successful calls to lwres_gethostbyaddr_r() return resbuf, which is a pointer to
       the struct hostent() it created.

RETURN VALUES
       The functions lwres_gethostbyname(), lwres_gethostbyname2(), lwres_gethostbyaddr(), and lwres_gethostent()
       return NULL to indicate an error. In this case the global variable lwres_h_errno will contain one of the
       following error codes defined in <lwres/netdb.h>:

       HOST_NOT_FOUND
           The host or address was not found.

       TRY_AGAIN
           A recoverable error occurred, e.g., a timeout. Retrying the lookup may succeed.

       NO_RECOVERY
           A non-recoverable error occurred.

       NO_DATA
           The name exists, but has no address information associated with it (or vice versa in the case of a reverse
           lookup). The code NO_ADDRESS is accepted as a synonym for NO_DATA for backwards compatibility.

       lwres_hstrerror(3) translates these error codes to suitable error messages.

       lwres_gethostent() and lwres_gethostent_r() always return NULL.

       Successful calls to lwres_gethostbyname_r() and lwres_gethostbyaddr_r() return resbuf, a pointer to the struct
       hostent that was initialised by these functions. They return NULL if the lookups fail or if buf was too small
       to hold the list of addresses and names referenced by the h_name, h_aliases, and h_addr_list elements of the
       struct hostent. If buf was too small, both lwres_gethostbyname_r() and lwres_gethostbyaddr_r() set the global
       variable errno to ERANGE.

SEE ALSO
       gethostent(3), lwres_getipnode(3), lwres_hstrerror(3)

BUGS
       lwres_gethostbyname(), lwres_gethostbyname2(), lwres_gethostbyaddr() and lwres_endhostent() are not thread
       safe; they return pointers to static data and provide error codes through a global variable. Thread-safe
       versions for name and address lookup are provided by lwres_gethostbyname_r(), and lwres_gethostbyaddr_r()
       respectively.

       The resolver daemon does not currently support any non-DNS name services such as /etc/hosts or NIS,
       consequently the above functions don't, either.

COPYRIGHT
       Copyright (C) 2004, 2005, 2007 Internet Systems Consortium, Inc. ("ISC")
       Copyright (C) 2001 Internet Software Consortium.



BIND9                            Jun 30, 2000              LWRES_GETHOSTENT(3)