lwres_getaddrinfo, lwres_freeaddrinfo − socket address
structure to host and service name

#include <lwres/netdb.h>
, const char *int lwres_getaddrinfo(const char *hostname
);void lwres_freeaddrinfo(struct addrinfo *ai

     If the operating system does not provide a struct
addrinfo, the following structure is used:

     struct  addrinfo {
        int             ai_flags;       /* AI_PASSIVE, AI_CANONNAME */
        int             ai_family;      /* PF_xxx */
        int             ai_socktype;    /* SOCK_xxx */
        int             ai_protocol;    /* 0 or IPPROTO_xxx for IPv4 and IPv6 */
        size_t          ai_addrlen;     /* length of ai_addr */
        char            *ai_canonname;  /* canonical name for hostname */
        struct sockaddr *ai_addr;       /* binary address */
        struct addrinfo *ai_next;       /* next structure in linked list */

     lwres_getaddrinfo() is used to get a list of IP
addresses and port numbers for host hostname and service
servname. The function is the lightweight resolver's
implementation of getaddrinfo() as defined in RFC2133.
hostname and servname are pointers to null−terminated
strings or NULL.  hostname is either a host name or a
numeric host address string: a dotted decimal IPv4 address
or an IPv6 address.  servname is either a decimal port
number or a service name as listed in /etc/services.

     hints is an optional pointer to a struct addrinfo. This
structure can be used to provide hints concerning the type
of socket that the caller supports or wishes to use. The
caller can supply the following structure elements in

     The protocol family that should be used. When ai_family
     is set to PF_UNSPEC, it means the caller will accept
     any protocol family supported by the operating system.

     denotes the type of socket — SOCK_STREAM, SOCK_DGRAM or
     SOCK_RAW — that is wanted. When ai_socktype is zero the
     caller will accept any socket type.

     indicates which transport protocol is wanted:


     IPPROTO_UDP or IPPROTO_TCP. If ai_protocol is zero the
     caller will accept any protocol.

     Flag bits. If the AI_CANONNAME bit is set, a successful
     call to lwres_getaddrinfo() will return a
     null−terminated string containing the canonical name of
     the specified hostname in ai_canonname of the first
     addrinfo structure returned. Setting the AI_PASSIVE bit
     indicates that the returned socket address structure is
     intended for used in a call to bind(2). In this case,
     if the hostname argument is a NULL pointer, then the IP
     address portion of the socket address structure will be
     set to INADDR_ANY for an IPv4 address or
     IN6ADDR_ANY_INIT for an IPv6 address.

     When ai_flags does not set the AI_PASSIVE bit, the
     returned socket address structure will be ready for use
     in a call to connect(2) for a connection−oriented
     protocol or connect(2), sendto(2), or sendmsg(2) if a
     connectionless protocol was chosen. The IP address
     portion of the socket address structure will be set to
     the loopback address if hostname is a NULL pointer and
     AI_PASSIVE is not set in ai_flags.

     If ai_flags is set to AI_NUMERICHOST it indicates that
     hostname should be treated as a numeric string defining
     an IPv4 or IPv6 address and no name resolution should
     be attempted.

     All other elements of the struct addrinfo passed via
hints must be zero.

     A hints of NULL is treated as if the caller provided a
struct addrinfo initialized to zero with ai_familyset to

     After a successful call to lwres_getaddrinfo(), *res is
a pointer to a linked list of one or more addrinfo
structures. Each struct addrinfo in this list cn be
processed by following the ai_next pointer, until a NULL
pointer is encountered. The three members ai_family,
ai_socktype, and ai_protocol in each returned addrinfo
structure contain the corresponding arguments for a call to
socket(2). For each addrinfo structure in the list, the
ai_addr member points to a filled−in socket address
structure of length ai_addrlen.

     All of the information returned by lwres_getaddrinfo()
is dynamically allocated: the addrinfo structures, and the
socket address structures and canonical host name strings
pointed to by the addrinfostructures. Memory allocated for
the dynamically allocated structures created by a successful
call to lwres_getaddrinfo() is released by


lwres_freeaddrinfo().  ai is a pointer to a struct addrinfo
created by a call to lwres_getaddrinfo().

     lwres_getaddrinfo() returns zero on success or one of
the error codes listed in gai_strerror(3) if an error
occurs. If both hostname and servname are
NULLlwres_getaddrinfo() returns EAI_NONAME.

     lwres(3), lwres_getaddrinfo(3), lwres_freeaddrinfo(3),
lwres_gai_strerror(3), RFC2133(), getservbyname(3), bind(2),
connect(2), sendto(2), sendmsg(2), socket(2).

     Internet Systems Consortium, Inc.

Copyright © 2000, 2001, 2003‐2005, 2007, 2014‐2016 Internet
Systems Consortium, Inc. ("ISC")