Quick ?s
Cheat Sheets
Man Pages
The Lynx
Software
GETADDRINFO(3)		   Linux Programmers Manual	       GETADDRINFO(3)



NAME
       getaddrinfo,  freeaddrinfo,  gai_strerror - network address and service
       translation

SYNOPSIS
       #include 
       #include 
       #include 

       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
       Given node and service, which identify an Internet host and a  service,
       getaddrinfo()  returns  one  or more addrinfo structures, each of which
       contains an Internet address that can be specified in a call to bind(2)
       or  connect(2).	 The getaddrinfo() function combines the functionality
       provided by the getservbyname(3) and getservbyport(3) functions into  a
       single  interface,  but	unlike	the latter functions, getaddrinfo() is
       reentrant and allows programs to eliminate  IPv4-versus-IPv6  dependen
       cies.

       The  addrinfo  structure  used  by getaddrinfo() contains the following
       fields:

	   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;
	   };

       The hints argument points to an addrinfo structure that specifies  cri
       teria  for selecting the socket address structures returned in the list
       pointed to by res.  If hints is not  NULL  it  points  to  an  addrinfo
       structure  whose ai_family, ai_socktype, and ai_protocol specify crite
       ria that limit the set of socket addresses returned  by	getaddrinfo(),
       as follows:

       ai_family   This  field	specifies  the	desired address family for the
		   returned addresses.	Valid values for  this	field  include
		   AF_INET  and  AF_INET6.  The value AF_UNSPEC indicates that
		   getaddrinfo()  should  return  socket  addresses  for   any
		   address  family (either IPv4 or IPv6, for example) that can
		   be used with node and service.

       ai_socktype This field specifies the preferred socket type, for example
		   SOCK_STREAM	or  SOCK_DGRAM.   Specifying  0  in this field
		   indicates that socket addresses of any type can be returned
		   by getaddrinfo().

       ai_protocol This  field	specifies the protocol for the returned socket
		   addresses.  Specifying  0  in  this	field  indicates  that
		   socket  addresses  with  any  protocol  can	be returned by
		   getaddrinfo().

       ai_flags    This field specifies additional options,  described	below.
		   Multiple  flags  are  specified  by	logically  OR-ing them
		   together.

       All the other fields in the structure pointed to by hints must  contain
       either  0  or a null pointer, as appropriate.  Specifying hints as NULL
       is equivalent to setting ai_socktype and ai_protocol to 0; ai_family to
       AF_UNSPEC; and ai_flags to (AI_V4MAPPED | AI_ADDRCONFIG).

       node  specifies	either a numerical network address (for IPv4, numbers-
       and-dots notation as supported by inet_aton(3); for  IPv6,  hexadecimal
       string  format  as  supported  by inet_pton(3)), or a network hostname,
       whose network addresses are looked up and resolved.  If	hints.ai_flags
       contains  the AI_NUMERICHOST flag then node must be a numerical network
       address.  The AI_NUMERICHOST flag suppresses  any  potentially  lengthy
       network host address lookups.

       If  the	AI_PASSIVE  flag  is  specified in hints.ai_flags, and node is
       NULL,  then  the  returned  socket  addresses  will  be	suitable   for
       bind(2)ing  a  socket  that  will  accept(2) connections.  The returned
       socket address will contain the "wildcard address" (INADDR_ANY for IPv4
       addresses, IN6ADDR_ANY_INIT for IPv6 address).  The wildcard address is
       used by applications (typically servers) that intend to accept  connec
       tions  on  any  of the hostss network addresses.  If node is not NULL,
       then the AI_PASSIVE flag is ignored.

       If the AI_PASSIVE flag is not set in hints.ai_flags, then the  returned
       socket  addresses  will be suitable for use with connect(2), sendto(2),
       or sendmsg(2).  If node is NULL, then the network address will  be  set
       to  the loopback interface address (INADDR_LOOPBACK for IPv4 addresses,
       IN6ADDR_LOOPBACK_INIT for IPv6 address); this is used  by  applications
       that intend to communicate with peers running on the same host.

       service	sets  the  port  in  each returned address structure.  If this
       argument is a service name (see services(5)), it is translated  to  the
       corresponding  port  number.   This argument can also be specified as a
       decimal number, which is simply converted to  binary.   If  service  is
       NULL,  then  the  port  number of the returned socket addresses will be
       left uninitialized.  If AI_NUMERICSERV is specified  in	hints.ai_flags
       and service is not NULL, then service must point to a string containing
       a numeric port number.  This flag is used to inhibit the invocation  of
       a  name	resolution  service  in  cases	where  it  is  known not to be
       required.

       Either node or service, but not both, may be NULL.

       The getaddrinfo() function allocates and initializes a linked  list  of
       addrinfo structures, one for each network address that matches node and
       service, subject to any restrictions imposed by hints,  and  returns  a
       pointer	to the start of the list in res.  The items in the linked list
       are linked by the ai_next field.  There are  several  reasons  why  the
       linked  list  may have more than one addrinfo structure, including: the
       network host is multi-homed; or the same service is available from mul
       tiple  socket protocols (one SOCK_STREAM address and another SOCK_DGRAM
       address, for example).

       If hints.ai_flags includes the AI_CANONNAME flag, then the ai_canonname
       field  of  the first of the addrinfo structures in the returned list is
       set to point to the official name of the host.

       The remaining fields of each returned addrinfo structure  are  initial
       ized as follows:

       * The  ai_family, ai_socktype, and ai_protocol fields return the socket
	 creation parameters (i.e., these fields have the same meaning as  the
	 corresponding	arguments of socket(2)).  For example, ai_family might
	 return AF_INET or AF_INET6; ai_socktype might	return	SOCK_DGRAM  or
	 SOCK_STREAM; and ai_protocol returns the protocol for the socket.

       * A  pointer  to the socket address is placed in the ai_addr field, and
	 the length of	the  socket  address,  in  bytes,  is  placed  in  the
	 ai_addrlen field.

       If  hints.ai_flags includes the AI_ADDRCONFIG flag, then IPv4 addresses
       are returned in the list pointed to by result only if the local	system
       has  at	least one IPv4 address configured, and IPv6 addresses are only
       returned if the local system has at least one IPv6 address  configured.

       If  hint.ai_flags  specifies  the AI_V4MAPPED flag, and hints.ai_family
       was specified as AF_INET6, and no  matching  IPv6  addresses  could  be
       found, then return IPv4-mapped IPv6 addresses in the list pointed to by
       result.	If both AI_V4MAPPED and AI_ALL are specified in  hints.ai_fam
       ily,  then  return both IPv6 and IPv4-mapped IPv6 addresses in the list
       pointed to by result.  AI_ALL is ignored if  AI_V4MAPPED  is  not  also
       specified.

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

   Extensions to getaddrinfo() for Internationalized Domain Names
       Starting with glibc 2.3.4, getaddrinfo() has been  extended  to	selec
       tively  allow  the  incoming and outgoing hostnames to be transparently
       converted to and from the Internationalized Domain  Name  (IDN)	format
       (see RFC 3490, Internationalizing Domain Names in Applications (IDNA)).
       Four new flags are defined:

       AI_IDN If this flag is specified, then the node name given in  node  is
	      converted  to  IDN  format if necessary.	The source encoding is
	      that of the current locale.

	      If the input name contains non-ASCII characters,	then  the  IDN
	      encoding	is  used.   Those parts of the node name (delimited by
	      dots) that contain non-ASCII characters are encoded using  ASCII
	      Compatible  Encoding (ACE) before being passed to the name reso
	      lution functions.

       AI_CANONIDN
	      After a successful name lookup, and if the AI_CANONNAME flag was
	      specified,  getaddrinfo()  will return the canonical name of the
	      node corresponding to the addrinfo structure value passed  back.
	      The  return  value is an exact copy of the value returned by the
	      name resolution function.

	      If the name is encoded using ACE, then it will contain the  xn--
	      prefix for one or more components of the name.  To convert these
	      components into a readable form  the  AI_CANONIDN  flag  can  be
	      passed  in  addition  to	AI_CANONNAME.  The resulting string is
	      encoded using the current locales encoding.

       AI_IDN_ALLOW_UNASSIGNED, AI_IDN_USE_STD3_ASCII_RULES
	      Setting these flags will enable the IDNA_ALLOW_UNASSIGNED (allow
	      unassigned  Unicode  code  points) and IDNA_USE_STD3_ASCII_RULES
	      (check output to make sure it is	a  STD3  conforming  hostname)
	      flags respectively to be used in the IDNA handling.

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

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

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

       EAI_BADFLAGS
	      ai_flags contains invalid flags.

       EAI_FAIL
	      The name server returned a permanent failure indication.

       EAI_FAMILY
	      The requested address family is not supported.

       EAI_MEMORY
	      Out of memory.

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

       EAI_NONAME
	      The  node  or service is not known; or both node and service are
	      NULL; or AI_NUMERICSERV was specified in hints.ai_flags and ser
	      vice was not a numeric port-number string.

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

       EAI_SOCKTYPE
	      The requested socket type is not supported.

       EAI_SYSTEM
	      Other system error, check errno for details.

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

CONFORMING TO
       POSIX.1-2001.  The getaddrinfo() function is documented in RFC 2553.

NOTES
       getaddrinfo() supports the address%scope-id notation for specifying the
       IPv6 scope-ID.

       AI_ADDRCONFIG, AI_ALL, and AI_V4MAPPED are available since glibc 2.3.3.
       AI_NUMERICSERV is available since glibc 2.3.4.

EXAMPLE
       The  following  programs demonstrate the use of getaddrinfo(), gai_str
       error(), freeaddrinfo(), and getnameinfo(3).  The programs are an  echo
       server and client for UDP datagrams.

       This is the server:

	 #include 
	 #include 
	 #include 
	 #include 
	 #include 
	 #include 
	 #include 

	 #define BUF_SIZE 500

	 int
	 main(int argc, char *argv[])
	 {
	     struct addrinfo hints;
	     struct addrinfo *result, *rp;
	     int sfd, s;
	     struct sockaddr_storage peer_addr;
	     socklen_t peer_addr_len;
	     ssize_t nread;
	     char buf[BUF_SIZE];

	     if (argc != 2) {
		 fprintf(stderr, "Usage: %s port\n", argv[0]);
		 exit(EXIT_FAILURE);
	     }

	     memset(&hints, 0, sizeof(struct addrinfo));
	     hints.ai_family = AF_UNSPEC;    /* Allow IPv4 or IPv6 */
	     hints.ai_socktype = SOCK_DGRAM; /* Datagram socket */
	     hints.ai_flags = AI_PASSIVE;    /* For wildcard IP address */
	     hints.ai_protocol = 0;	     /* Any protocol */
	     hints.ai_canonname = NULL;
	     hints.ai_addr = NULL;
	     hints.ai_next = NULL;

	     s = getaddrinfo(NULL, argv[1], &hints, &result);
	     if (s != 0) {
		 fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(s));
		 exit(EXIT_FAILURE);
	     }

	     /* getaddrinfo() returns a list of address structures.
		Try each address until we successfully bind(2).
		If socket(2) (or bind(2)) fails, we (close the socket
		and) try the next address. */

	     for (rp = result; rp != NULL; rp = rp->ai_next) {
		 sfd = socket(rp->ai_family, rp->ai_socktype,
			 rp->ai_protocol);
		 if (sfd == -1)
		     continue;

		 if (bind(sfd, rp->ai_addr, rp->ai_addrlen) == 0)
		     break;		     /* Success */

		 close(sfd);
	     }

	     if (rp == NULL) {		     /* No address succeeded */
		 fprintf(stderr, "Could not bind\n");
		 exit(EXIT_FAILURE);
	     }

	     freeaddrinfo(result);	     /* No longer needed */

	     /* Read datagrams and echo them back to sender */

	     for (;;) {
		 peer_addr_len = sizeof(struct sockaddr_storage);
		 nread = recvfrom(sfd, buf, BUF_SIZE, 0,
			 (struct sockaddr *) &peer_addr, &peer_addr_len);
		 if (nread == -1)
		     continue;		     /* Ignore failed request */

		 char host[NI_MAXHOST], service[NI_MAXSERV];

		 s = getnameinfo((struct sockaddr *) &peer_addr,
				 peer_addr_len, host, NI_MAXHOST,
				 service, NI_MAXSERV, NI_NUMERICSERV);
		if (s == 0)
		     printf("Received %ld bytes from %s:%s\n",
			     (long) nread, host, service);
		 else
		     fprintf(stderr, "getnameinfo: %s\n", gai_strerror(s));

		 if (sendto(sfd, buf, nread, 0,
			     (struct sockaddr *) &peer_addr,
			     peer_addr_len) != nread)
		     fprintf(stderr, "Error sending response\n");
	     }
	 }

       This is the client:

	 #include 
	 #include 
	 #include 
	 #include 
	 #include 
	 #include 
	 #include 

	 #define BUF_SIZE 500

	 int
	 main(int argc, char *argv[])
	 {
	     struct addrinfo hints;
	     struct addrinfo *result, *rp;
	     int sfd, s, j;
	     size_t len;
	     ssize_t nread;
	     char buf[BUF_SIZE];

	     if (argc < 3) {
		 fprintf(stderr, "Usage: %s host port msg...\n", argv[0]);
		 exit(EXIT_FAILURE);
	     }

	     /* Obtain address(es) matching host/port */

	     memset(&hints, 0, sizeof(struct addrinfo));
	     hints.ai_family = AF_UNSPEC;    /* Allow IPv4 or IPv6 */
	     hints.ai_socktype = SOCK_DGRAM; /* Datagram socket */
	     hints.ai_flags = 0;
	     hints.ai_protocol = 0;	     /* Any protocol */

	     s = getaddrinfo(argv[1], argv[2], &hints, &result);
	     if (s != 0) {
		 fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(s));
		 exit(EXIT_FAILURE);
	     }

	     /* getaddrinfo() returns a list of address structures.
		Try each address until we successfully connect(2).
		If socket(2) (or connect(2)) fails, we (close the socket
		and) try the next address. */

	     for (rp = result; rp != NULL; rp = rp->ai_next) {
		 sfd = socket(rp->ai_family, rp->ai_socktype,
			      rp->ai_protocol);
		 if (sfd == -1)
		     continue;

		 if (connect(sfd, rp->ai_addr, rp->ai_addrlen) != -1)
		     break;		     /* Success */

		 close(sfd);
	     }

	     if (rp == NULL) {		     /* No address succeeded */
		 fprintf(stderr, "Could not connect\n");
		 exit(EXIT_FAILURE);
	     }

	     freeaddrinfo(result);	     /* No longer needed */

	     /* Send remaining command-line arguments as separate
		datagrams, and read responses from server */

	     for (j = 3; j < argc; j++) {
		 len = strlen(argv[j]) + 1;
			 /* +1 for terminating null byte */

		 if (len + 1 > BUF_SIZE) {
		     fprintf(stderr,
			     "Ignoring long message in argument %d\n", j);
		     continue;
		 }

		 if (write(sfd, argv[j], len) != len) {
		     fprintf(stderr, "partial/failed write\n");
		     exit(EXIT_FAILURE);
		 }

		 nread = read(sfd, buf, BUF_SIZE);
		 if (nread == -1) {
		     perror("read");
		     exit(EXIT_FAILURE);
		 }

		 printf("Received %ld bytes: %s\n", (long) nread, buf);
	     }

	     exit(EXIT_SUCCESS);
	 }

SEE ALSO
       gethostbyname(3), getnameinfo(3), inet(3), hostname(7), ip(7)

COLOPHON
       This  page  is  part of release 3.05 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found at http://www.kernel.org/doc/man-pages/.



GNU				  2008-06-18			GETADDRINFO(3)




Yals.net is © 1999-2009 Crescendo Communications
Sharing tech info on the web for more than a decade!
This page was generated Thu Apr 30 17:05:26 2009