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.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved 

.TH "FREEADDRINFO" P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"

.\" freeaddrinfo 

.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 .