man-pages/man3/getaddrinfo.3

.\" Copyright 2000 Sam Varshavchik <mrsam@courier-mta.com>
.\"
.\" Permission is granted to make and distribute verbatim copies of this
.\" manual provided the copyright notice and this permission notice are
.\" preserved on all copies.
.\"
.\" Permission is granted to copy and distribute modified versions of this
.\" manual under the conditions for verbatim copying, provided that the
.\" entire resulting derived work is distributed under the terms of a
.\" permission notice identical to this one.
.\" 
.\" Since the Linux kernel and libraries are constantly changing, this
.\" manual page may be incorrect or out-of-date.  The author(s) assume no
.\" responsibility for errors or omissions, or for damages resulting from
.\" the use of the information contained herein.  The author(s) may not
.\" have taken the same level of care in the production of this manual,
.\" which is licensed free of charge, as they might when working
.\" professionally.
.\" 
.\" Formatted or processed versions of this manual, if unaccompanied by
.\" the source, must acknowledge the copyright and authors of this work.
.\"
.\" References: RFC 2553
.TH getaddrinfo 3 2000-12-18 "Linux Man Page" "Linux Programmer's Manual"
.SH NAME
getaddrinfo, freeaddrinfo, gai_strerror \- network address and service translation
.SH SYNOPSIS
.nf
.B #include <sys/types.h>
.B #include <sys/socket.h>
.B #include <netdb.h>
.sp
.BI "int getaddrinfo(const char *" "node" ", const char *" "service" ,
.BI "                const struct addrinfo *" "hints" ,
.BI "                struct addrinfo **" "res" );
.sp
.BI "void freeaddrinfo(struct addrinfo *" "res" );
.sp
.BI "const char *gai_strerror(int " "errcode" );
.fi
.SH DESCRIPTION
The
.BR getaddrinfo (3)
function combines the functionality provided by the
.BR getipnodebyname (3),
.BR getipnodebyaddr (3),
.BR getservbyname (3),
and
.BR getservbyport (3)
functions into a single interface.
The thread-safe
.BR getaddrinfo (3)
function creates one or more socket address structures that can be used by the
.BR bind (2)
and
.BR connect (2)
system calls to create a client or a server socket.
.PP
The
.BR getaddrinfo (3)
function is not limited to creating IPv4 socket address structures;
IPv6 socket address structures can be created if IPv6 support is available.
These socket address structures can be used directly by
.BR bind (2)
or
.BR connect (2),
to prepare a client or a server socket.
.PP
The
.B addrinfo
structure used by this function contains the following members:
.sp
.nf
.B struct addrinfo {
.BI "    int     " "ai_flags" ";"
.BI "    int     " "ai_family" ";"
.BI "    int     " "ai_socktype" ";"
.BI "    int     " "ai_protocol" ";"
.BI "    size_t  " "ai_addrlen" ";"
.BI "    struct sockaddr *" "ai_addr" ";"
.BI "    char   *" "ai_canonname" ";"
.BI "    struct addrinfo *" "ai_next" ";"
.B };
.fi
.PP
.BR getaddrinfo (3)
sets
.I res
to point to a dynamically-allocated link list of
.B addrinfo
structures, linked by the
.I ai_next
member.
There are several reasons why
the link list may have more than one
.B addrinfo
structure, including: if the network host is
multi-homed; or if the same service
is available from multiple socket protocols (one
.B SOCK_STREAM
address and another 
.B SOCK_DGRAM
address, for example).
.PP
The members
.IR ai_family ,
.IR ai_socktype ,
and
.I ai_protocol
have the same meaning as the corresponding parameters in the
.BR socket (2)
system call.
The
.BR getaddrinfo (3)
function returns socket addresses in either IPv4 or IPv6
address family,
.RI "(" "ai_family"
will be set to either
.B PF_INET
or
.BR PF_INET6 ).
.PP
The
.I hints
parameter specifies
the preferred socket type, or protocol.
A NULL
.I hints
specifies that any network address or protocol is acceptable.
If this parameter is not
.B NULL
it points to an
.B addrinfo
structure
whose
.IR ai_family ,
.IR ai_socktype ,
and
.I ai_protocol
members specify the preferred socket type.
.B PF_UNSPEC
in
.I ai_family
specifies any protocol family (either IPv4 or IPv6, for example).
0 in
.I ai_socktype
or
.I ai_protocol
specifies that any socket type or protocol is acceptable as well.
The
.I ai_flags
member
specifies additional options, defined below.
Multiple flags are specified by logically OR-ing them together.
All the other members in the
.I hints
parameter must contain either 0, or a null pointer.
.PP
The
.I node
or
.I service
parameter, but not both, may be NULL.
.I 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
.I ai_flags
member in the
.I hints
parameter contains the
.B AI_NUMERICHOST
flag then the
.I node
parameter must be a numerical network address.
The
.B AI_NUMERICHOST
flag suppresses any potentially lengthy network host address lookups.
.PP
The
.BR getaddrinfo (3)
function creates a link list of
.B addrinfo
structures, one for each network address subject to any restrictions
imposed by the
.I hints
parameter.
.I ai_canonname
is set to point to the official name of the host, if
.I ai_flags
in
.I hints
includes the
.B AI_CANONNAME
flag.
.IR ai_family ,
.IR ai_socktype ,
and
.I ai_protocol
specify the socket creation parameters.
A pointer to the socket address is placed in the
.I ai_addr
member, and the length of the socket address, in bytes,
is placed in the
.I ai_addrlen
member.
.PP
If
.I node
is NULL,
the
network address in each socket structure is initialized according to the
.B AI_PASSIVE
flag, which is set in the
.I ai_flags
member of the
.I hints
parameter.
The network address in each socket structure will be left unspecified
if
.B AI_PASSIVE
flag is set.
This is used by server applications, which intend to accept
client connections on any network address.
The network address will be set to the loopback interface address
if the
.B 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.
.PP
.I service
sets the port number in the network address of each socket structure.
If
.I service
is NULL the port number will be left uninitialized.
.PP
The
.BR freeaddrinfo (3)
function frees the memory that was allocated
for the dynamically allocated link list
.IR res .
.SH "RETURN VALUE"
.BR getaddrinfo (3)
returns 0 if it succeeds, or one of the following non-zero error codes:
.TP
.B EAI_FAMILY
The requested address family is not supported at all.
.TP
.B EAI_SOCKTYPE
The requested socket type is not supported at all.
.TP
.B EAI_BADFLAGS
.I ai_flags
contains invalid flags.
.TP
.B EAI_NONAME
The
.I node
or
.I service
is not known.
This error is also returned if both
.I node
and
.I service
are NULL.
.TP
.B EAI_SERVICE
The requested service is not available for the requested socket type.
It may be available through another socket type.
.TP
.B EAI_ADDRFAMILY
The specified network host does not have any network addresses in the
requested address family.
.TP
.B EAI_NODATA
The specified network host exists, but does not have any
network addresses defined.
.TP
.B EAI_MEMORY
Out of memory.
.TP
.B EAI_FAIL
The name server returned a permanent failure indication.
.TP
.B EAI_AGAIN
The name server returned a temporary failure indication.
Try again later.
.TP
.B EAI_SYSTEM
Other system error, check
.I errno
for details.
.PP
The
.BR gai_strerror (3)
function translates these error codes to a human readable string,
suitable for error reporting.
.SH "CONFORMING TO"
POSIX 1003.1-2003.
The
.B getaddrinfo()
function is documented in RFC 2553.
.SH "SEE ALSO"
.BR getipnodebyaddr (3),
.BR getipnodebyname (3)