.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved 
.TH "FREEADDRINFO" 3P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\" freeaddrinfo 
.SH PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
.SH NAME
freeaddrinfo, getaddrinfo \- get address information
.SH SYNOPSIS
.LP
\fB#include <sys/socket.h>
.br
#include <netdb.h>
.br
.sp
void freeaddrinfo(struct addrinfo *\fP\fIai\fP\fB);
.br
int getaddrinfo(const char *restrict\fP \fInodename\fP\fB,
.br
\ \ \ \ \ \  const char *restrict\fP \fIservname\fP\fB,
.br
\ \ \ \ \ \  const struct addrinfo *restrict\fP \fIhints\fP\fB,
.br
\ \ \ \ \ \  struct addrinfo **restrict\fP \fIres\fP\fB);
.br
\fP
.SH DESCRIPTION
.LP
The \fIfreeaddrinfo\fP() function shall free one or more \fBaddrinfo\fP
structures returned by \fIgetaddrinfo\fP(), along
with any additional storage associated with those structures. If the
\fIai_next\fP field of the structure is not null, the entire
list of structures shall be freed. The \fIfreeaddrinfo\fP() function
shall support the freeing of arbitrary sublists of an
\fBaddrinfo\fP list originally returned by \fIgetaddrinfo\fP().
.LP
The \fIgetaddrinfo\fP() function shall translate the name of a service
location (for example, a host name) and/or a service
name and shall return a set of socket addresses and associated information
to be used in creating a socket with which to address
the specified service. 
.TP 7
\fBNote:\fP
In many cases it is implemented by the Domain Name System, as documented
in RFC\ 1034, RFC\ 1035, and
RFC\ 1886.
.sp
.LP
The \fIfreeaddrinfo\fP() and \fIgetaddrinfo\fP() functions shall be
thread-safe.
.LP
The \fInodename\fP and \fIservname\fP arguments are either null pointers
or pointers to null-terminated strings. One or both
of these two arguments shall be supplied by the application as a non-null
pointer.
.LP
The format of a valid name depends on the address family or families.
If a specific family is not given and the name could be
interpreted as valid within multiple supported families, the implementation
shall attempt to resolve the name in all supported
families and, in absence of errors, one or more results shall be returned.
.LP
If the \fInodename\fP argument is not null, it can be a descriptive
name or can be an address string. If the specified address
family is AF_INET,  AF_INET6,  or AF_UNSPEC, valid
descriptive names include host names. If the specified address family
is AF_INET or AF_UNSPEC, address strings using Internet
standard dot notation as specified in \fIinet_addr\fP() are valid.
.LP
If the specified address family is AF_INET6 or AF_UNSPEC, standard
IPv6 text forms described in \fIinet_ntop\fP() are valid. 
.LP
If \fInodename\fP is not null, the requested service location is named
by \fInodename\fP; otherwise, the requested service
location is local to the caller.
.LP
If \fIservname\fP is null, the call shall return network-level addresses
for the specified \fInodename.\fP If \fIservname\fP
is not null, it is a null-terminated character string identifying
the requested service. This can be either a descriptive name or a
numeric representation suitable for use with the address family or
families. If the specified address family is AF_INET,  
\ AF_INET6,  or AF_UNSPEC, the service can be specified as a
string specifying a decimal port number.
.LP
If the \fIhints\fP argument is not null, it refers to a structure
containing input values that may direct the operation by
providing options and by limiting the returned information to a specific
socket type, address family, and/or protocol. In this
\fIhints\fP structure every member other than \fIai_flags\fP, \fIai_family\fP,
\fIai_socktype\fP, and \fIai_protocol\fP shall
be set to zero or a null pointer. A value of AF_UNSPEC for \fIai_family\fP
means that the caller shall accept any address family.
A value of zero for \fIai_socktype\fP means that the caller shall
accept any socket type. A value of zero for \fIai_protocol\fP
means that the caller shall accept any protocol. If \fIhints\fP is
a null pointer, the behavior shall be as if it referred to a
structure containing the value zero for the \fIai_flags\fP, \fIai_socktype\fP,
and \fIai_protocol\fP fields, and AF_UNSPEC for
the \fIai_family\fP field.
.LP
The \fIai_flags\fP field to which the \fIhints\fP parameter points
shall be set to zero or be the bitwise-inclusive OR of one
or more of the values AI_PASSIVE, AI_CANONNAME, AI_NUMERICHOST, AI_NUMERICSERV,
AI_V4MAPPED, AI_ALL, and AI_ADDRCONFIG.
.LP
If the AI_PASSIVE flag is specified, the returned address information
shall be suitable for use in binding a socket for
accepting incoming connections for the specified service. In this
case, if the \fInodename\fP argument is null, then the IP
address portion of the socket address structure shall be set to INADDR_ANY
for an IPv4 address or IN6ADDR_ANY_INIT for an IPv6
address. If the AI_PASSIVE flag is not specified, the returned address
information shall be suitable for a call to \fIconnect\fP() (for a
connection-mode protocol) or for a call to \fIconnect\fP(), \fIsendto\fP(),
or \fIsendmsg\fP() (for a connectionless protocol). In this case,
if the \fInodename\fP argument is
null, then the IP address portion of the socket address structure
shall be set to the loopback address. The AI_PASSIVE flag shall
be ignored if the \fInodename\fP argument is not null.
.LP
If the AI_CANONNAME flag is specified and the \fInodename\fP argument
is not null, the function shall attempt to determine the
canonical name corresponding to \fInodename\fP (for example, if \fInodename\fP
is an alias or shorthand notation for a complete
name). 
.TP 7
\fBNote:\fP
Since different implementations use different conceptual models, the
terms ``canonical name'' and ``alias'' cannot be precisely
defined for the general case. However, Domain Name System implementations
are expected to interpret them as they are used in
RFC\ 1034. 
.LP
A numeric host address string is not a ``name'', and thus does not
have a ``canonical name'' form; no address to host name
translation is performed. See below for handling of the case where
a canonical name cannot be obtained.
.sp
.LP
If the AI_NUMERICHOST flag is specified, then a non-null \fInodename\fP
string supplied shall be a numeric host address string.
Otherwise, an [EAI_NONAME] error is returned. This flag shall prevent
any type of name resolution service (for example, the DNS)
from being invoked.
.LP
If the AI_NUMERICSERV flag is specified, then a non-null \fIservname\fP
string supplied shall be a numeric port string.
Otherwise, an [EAI_NONAME] error shall be returned. This flag shall
prevent any type of name resolution service (for example, NIS+)
from being invoked.
.LP
If the AI_V4MAPPED flag is specified along with an \fIai_family\fP
of AF_INET6, then \fIgetaddrinfo\fP() shall return IPv4-mapped
IPv6 addresses on finding no matching IPv6 addresses ( \fIai_addrlen\fP
shall be 16). The AI_V4MAPPED flag shall be ignored unless
\fIai_family\fP equals AF_INET6. If the AI_ALL flag is used with the
AI_V4MAPPED flag, then \fIgetaddrinfo\fP() shall return all
matching IPv6 and IPv4 addresses. The AI_ALL flag without the AI_V4MAPPED
flag is ignored. 
.LP
If the AI_ADDRCONFIG flag is specified, IPv4 addresses shall be returned
only if an IPv4 address is configured on the local
system,  and IPv6 addresses shall be returned only if an IPv6 address
is configured on the local system. 
.LP
The \fIai_socktype\fP field to which argument \fIhints\fP points specifies
the socket type for the service, as defined in \fIsocket\fP(). If
a specific socket type is not given (for example, a value of zero)
and the service name
could be interpreted as valid with multiple supported socket types,
the implementation shall attempt to resolve the service name
for all supported socket types and, in the absence of errors, all
possible results shall be returned. A non-zero socket type value
shall limit the returned information to values with the specified
socket type.
.LP
If the \fIai_family\fP field to which \fIhints\fP points has the value
AF_UNSPEC, addresses shall be returned for use with any
address family that can be used with the specified \fInodename\fP
and/or \fIservname\fP. Otherwise, addresses shall be returned
for use only with the specified address family. If \fIai_family\fP
is not AF_UNSPEC and \fIai_protocol\fP is not zero, then
addresses are returned for use only with the specified address family
and protocol; the value of \fIai_protocol\fP shall be
interpreted as in a call to the \fIsocket\fP() function with the corresponding
values of
\fIai_family\fP and \fIai_protocol\fP.
.SH RETURN VALUE
.LP
A zero return value for \fIgetaddrinfo\fP() indicates successful completion;
a non-zero return value indicates failure. The
possible values for the failures are listed in the ERRORS section.
.LP
Upon successful return of \fIgetaddrinfo\fP(), the location to which
\fIres\fP points shall refer to a linked list of
\fBaddrinfo\fP structures, each of which shall specify a socket address
and information for use in creating a socket with which to
use that socket address. The list shall include at least one \fBaddrinfo\fP
structure. The \fIai_next\fP field of each structure
contains a pointer to the next structure on the list, or a null pointer
if it is the last structure on the list. Each structure on
the list shall include values for use with a call to the \fIsocket\fP()
function, and a
socket address for use with the \fIconnect\fP() function or, if the
AI_PASSIVE flag was
specified, for use with the \fIbind\fP() function. The fields \fIai_family\fP,
\fIai_socktype\fP, and \fIai_protocol\fP shall be usable as the arguments
to the \fIsocket\fP() function to create a socket suitable for use
with the returned address. The fields
\fIai_addr\fP and \fIai_addrlen\fP are usable as the arguments to
the \fIconnect\fP() or
\fIbind\fP() functions with such a socket, according to the AI_PASSIVE
flag.
.LP
If \fInodename\fP is not null, and if requested by the AI_CANONNAME
flag, the \fIai_canonname\fP field of the first returned
\fBaddrinfo\fP structure shall point to a null-terminated string containing
the canonical name corresponding to the input
\fInodename\fP; if the canonical name is not available, then \fIai_canonname\fP
shall refer to the \fInodename\fP argument or a
string with the same contents. The contents of the \fIai_flags\fP
field of the returned structures are undefined.
.LP
All fields in socket address structures returned by \fIgetaddrinfo\fP()
that are not filled in through an explicit argument
(for example, \fIsin6_flowinfo\fP) shall be set to zero. 
.TP 7
\fBNote:\fP
This makes it easier to compare socket address structures.
.sp
.SH ERRORS
.LP
The \fIgetaddrinfo\fP() function shall fail and return the corresponding
value if:
.TP 7
.B EAI_AGAIN
The name could not be resolved at this time. Future attempts may succeed.
.TP 7
.B EAI_BADFLAGS
.sp
The \fIflags\fP parameter had an invalid value.
.TP 7
.B EAI_FAIL
A non-recoverable error occurred when attempting to resolve the name.
.TP 7
.B EAI_FAMILY
The address family was not recognized.
.TP 7
.B EAI_MEMORY
There was a memory allocation failure when trying to allocate storage
for the return value.
.TP 7
.B EAI_NONAME
The name does not resolve for the supplied parameters. 
.LP
Neither \fInodename\fP nor \fIservname\fP were supplied. At least
one of these shall be supplied.
.TP 7
.B EAI_SERVICE
The service passed was not recognized for the specified socket type.
.TP 7
.B EAI_SOCKTYPE
.sp
The intended socket type was not recognized.
.TP 7
.B EAI_SYSTEM
A system error occurred; the error code can be found in \fIerrno\fP.
.TP 7
.B EAI_OVERFLOW
.sp
An argument buffer overflowed.
.sp
.LP
\fIThe following sections are informative.\fP
.SH EXAMPLES
.LP
None.
.SH APPLICATION USAGE
.LP
If the caller handles only TCP and not UDP, for example, then the
\fIai_protocol\fP member of the \fIhints\fP structure should
be set to IPPROTO_TCP when \fIgetaddrinfo\fP() is called.
.LP
If the caller handles only IPv4 and not IPv6, then the \fIai_family\fP
member of the \fIhints\fP structure should be set to
AF_INET when \fIgetaddrinfo\fP() is called.
.LP
The term ``canonical name'' is misleading; it is taken from the Domain
Name System (RFC\ 2181). It should be noted that the
canonical name is a result of alias processing, and not necessarily
a unique attribute of a host, address, or set of addresses. See
RFC\ 2181 for more discussion of this in the Domain Name System context.
.SH RATIONALE
.LP
None.
.SH FUTURE DIRECTIONS
.LP
None.
.SH SEE ALSO
.LP
\fIconnect\fP(), \fIgai_strerror\fP(), \fIgethostbyaddr\fP(), \fIgetnameinfo\fP(),
\fIgetservbyname\fP(), \fIsocket\fP(), the Base Definitions volume
of
IEEE\ Std\ 1003.1-2001, \fI<netdb.h>\fP, \fI<sys/socket.h>\fP
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .