getaddrinfo - network address and service translation


SYNOPSIS

       #include <sys/types.h>
       #include <sys/socket.h>
       #include <netdb.h>

       int getaddrinfo(const char *node, const char *service,
                       const struct addrinfo *hints,
                       struct addrinfo **res);

       void freeaddrinfo(struct addrinfo *res);

       const char *gai_strerror(int errcode);


DESCRIPTION

       The  getaddrinfo(3)  function  combines  the functionality
       provided by  the  getipnodebyname(3),  getipnodebyaddr(3),
       getservbyname(3),  and  getservbyport(3)  functions into a
       single interface.  The thread-safe getaddrinfo(3) function
       creates  one or more socket address structures that can be
       used by the bind(2) and connect(2) system calls to  create
       a client or a server socket.

       The  getaddrinfo(3)  function  is  not limited to creating
       IPv4 socket address structures; IPv6 socket address struc­
       tures  can be created if IPv6 support is available.  These
       socket address structures can be used directly by  bind(2)
       or connect(2), to prepare a client or a server socket.

       The  addrinfo structure used by this function contains the
       following members:

       struct addrinfo {
           int     ai_flags;
           int     ai_family;
           int     ai_socktype;
           int     ai_protocol;
           size_t  ai_addrlen;
           struct sockaddr *ai_addr;
           char   *ai_canonname;
           struct addrinfo *ai_next;
       };

       getaddrinfo(3) sets res to point  to  a  dynamically-allo­
       cated  link  list  of  addrinfo  structures, linked by the
       ai_next member.  There are several reasons  why  the  link
       list may have more than one addrinfo structure, including:
       if the network host is multi-homed; or if the same service
       is   available   from   multiple   socket  protocols  (one
       SOCK_STREAM address and another  SOCK_DGRAM  address,  for
       example).

       the same meaning as the corresponding  parameters  in  the
       socket(2)   system   call.   The  getaddrinfo(3)  function
       returns socket addresses in either IPv4  or  IPv6  address
       family,  (ai_family  will  be  set  to  either  PF_INET or
       PF_INET6).

       The hints parameter specifies the preferred  socket  type,
       or  protocol.   A  NULL  hints  specifies that any network
       address or protocol is acceptable.  If this  parameter  is
       not  NULL it points to an addrinfo structure whose ai_fam­
       ily, ai_socktype, and ai_protocol members specify the pre­
       ferred  socket type.  PF_UNSPEC in ai_family specifies any
       protocol family (either IPv4 or IPv6, for example).  0  in
       ai_socktype  or ai_protocol specifies that any socket type
       or protocol is acceptable as well.   The  ai_flags  member
       specifies  additional  options,  defined  below.  Multiple
       flags are specified by  logically  OR-ing  them  together.
       All  the other members in the hints parameter must contain
       either 0, or a null pointer.

       The node or service parameter, but not both, may be  NULL.
       node specifies either a numerical network address (dotted-
       decimal format for IPv4, hexadecimal format for IPv6) or a
       network  hostname,  whose  network addresses are looked up
       and resolved.  If the ai_flags member in the hints parame­
       ter contains the AI_NUMERICHOST flag then the node parame­
       ter must be a numerical network address.   The  AI_NUMERI­
       CHOST flag suppresses any potentially lengthy network host
       address lookups.

       The  getaddrinfo(3)  function  creates  a  link  list   of
       addrinfo  structures, one for each network address subject
       to  any  restrictions  imposed  by  the  hints  parameter.
       ai_canonname  is  set to point to the official name of the
       host, if ai_flags in hints includes the AI_CANONNAME flag.
       ai_family, ai_socktype, and ai_protocol specify the socket
       creation parameters.  A pointer to the socket  address  is
       placed in the ai_addr member, and the length of the socket
       address, in bytes, is placed in the ai_addrlen member.

       If node is NULL, the network address in each socket struc­
       ture  is  initialized  according  to  the AI_PASSIVE flag,
       which is set in the ai_flags member of the  hints  parame­
       ter.  The network address in each socket structure will be
       left unspecified if AI_PASSIVE flag is set.  This is  used
       by server applications, which intend to accept client con­
       nections on any network address.  The network address will
       be set to the loopback interface address if the AI_PASSIVE
       flag is not set.  This is  used  by  client  applications,
       which  intend  to  connect to a server running on the same
       network host.

       service sets the port number in  the  network  address  of

       will be left uninitialized.

       The freeaddrinfo(3) function frees  the  memory  that  was
       allocated for the dynamically allocated link list res.


RETURN VALUE

       getaddrinfo(3)  returns  0  if  it succeeds, or one of the
       following non-zero error codes:

       EAI_FAMILY
              The requested address family is  not  supported  at
              all.

       EAI_SOCKTYPE
              The  requested socket type is not supported at all.

       EAI_BADFLAGS
              ai_flags contains invalid flags.

       EAI_NONAME
              The node or service is not known.   This  error  is
              also returned if both node and service are NULL.

       EAI_SERVICE
              The  requested  service  is  not  available for the
              requested socket type.  It may be available through
              another socket type.

       EAI_ADDRFAMILY
              The  specified  network host does not have any net­
              work addresses in the requested address family.

       EAI_NODATA
              The specified network host  exists,  but  does  not
              have any network addresses defined.

       EAI_MEMORY
              Out of memory.

       EAI_FAIL
              The  name server returned a permanent failure indi­
              cation.

       EAI_AGAIN
              The name server returned a temporary failure  indi­
              cation.  Try again later.

       EAI_SYSTEM
              Other system error, check errno for details.

       The  gai_strerror(3) function translates these error codes
       to a human readable string, suitable for error  reporting.

       getipnodebyname(3), getipnodebyaddr(3)


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