path: root/lib/libc/net/getaddrinfo.3

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.\"     From: @(#)gethostbyname.3	8.4 (Berkeley) 5/25/95
.\"     $Id: getaddrinfo.3,v 1.2 1999/07/03 20:26:55 deraadt Exp $
.\"
.Dd May 25, 1995
.Dt GETADDRINFO 3
.Os KAME
.Sh NAME
.Nm getaddrinfo
.Nm freeaddrinfo ,
.Nm gai_strerror
.Nd nodename-to-address translation in protocol-independent manner
.Sh SYNOPSIS
.Fd #include <sys/socket.h>
.Fd #include <netdb.h>
.Ft int
.Fn getaddrinfo "const char *nodename" "const char *servname" \
"const struct addrinfo *hints" "struct addrinfo **res"
.Ft void
.Fn freeaddrinfo "struct addrinfo *ai"
.Ft "char *"
.Fn gai_strerror "int ecode"
.Sh DESCRIPTION
The
.Fn getaddrinfo
function is defined for protocol-independent nodename-to-address translation.
It performs the functionality of
.Xr gethostbyname 3
and
.Xr getservbyname 3 ,
but in a more sophisticated manner.
.Pp
The addrinfo structure is defined as a result of including the
.Li <netdb.h>
header:
.Bd -literal -offset
struct addrinfo {                                                  *
     int     ai_flags;     /* AI_PASSIVE, AI_CANONNAME, AI_NUMERICHOST */
     int     ai_family;    /* PF_xxx */
     int     ai_socktype;  /* SOCK_xxx */
     int     ai_protocol;  /* 0 or IPPROTO_xxx for IPv4 and IPv6 */
     size_t  ai_addrlen;   /* length of ai_addr */
     char   *ai_canonname; /* canonical name for nodename */
     struct sockaddr  *ai_addr; /* binary address */
     struct addrinfo  *ai_next; /* next structure in linked list */
};
.Ed
.Pp
The
.Fa nodename
and
.Fa servname
arguments are pointers to null-terminated strings or
.Dv NULL .
One or both of these two arguments must be a
.Pf non Dv -NULL
pointer.
In the normal client scenario, both the
.Fa nodename
and
.Fa servname
are specified.
In the normal server scenario, only the
.Fa servname
is specified.
A
.Pf non Dv -NULL
.Fa nodename
string can be either a node name or a numeric host address string
.Po
i.e., a dotted-decimal IPv4 address or an IPv6 hex address
.Pc .
A
.Pf non Dv -NULL
.Fa servname
string can be either a service name or a decimal port number.
.Pp
The caller can optionally pass an
.Li addrinfo
structure, pointed to by the third argument,
to provide hints concerning the type of socket that the caller supports.
In this
.Fa hints
structure all members other than
.Fa ai_flags ,
.Fa ai_family ,
.Fa ai_socktype ,
and
.Fa ai_protocol
must be zero or a
.Dv NULL
pointer.
A value of
.Dv PF_UNSPEC
for
.Fa ai_family
means the caller will accept any protocol family.
A value of 0 for
.Fa ai_socktype
means the caller will accept any socket type.
A value of 0 for
.Fa ai_protocol
means the caller will accept any protocol.
For example, if the caller handles only TCP and not UDP, then the
.Fa ai_socktype
member of the hints structure should be set to
.Dv SOCK_STREAM
when
.Fn getaddrinfo
is called.
If the caller handles only IPv4 and not IPv6, then the
.Fa ai_family
member of the
.Fa hints
structure should be set to
.Dv PF_INET
when
.Fn getaddrinfo
is called.
If the third argument to
.Fn getaddrinfo
is a
.Dv NULL
pointer, this is the same as if the caller had filled in an
.Li addrinfo
structure initialized to zero with
.Fa ai_family
set to PF_UNSPEC.
.Pp
Upon successful return a pointer to a linked list of one or more
.Li addrinfo
structures is returned through the final argument.
The caller can process each
.Li addrinfo
structure in this list by following the
.Fa ai_next
pointer, until a
.Dv NULL
pointer is encountered.
In each returned
.Li addrinfo
structure the three members
.Fa ai_family ,
.Fa ai_socktype ,
and
.Fa ai_protocol
are the corresponding arguments for a call to the
.Fn socket
function.
In each
.Li addrinfo
structure the
.Fa ai_addr
member points to a filled-in socket address structure whose length is
specified by the
.Fa ai_addrlen
member.
.Pp
If the
.Dv AI_PASSIVE
bit is set in the
.Fa ai_flags
member of the
.Fa hints
structure, then the caller plans to use the returned socket address
structure in a call to
.Fn bind .
In this case, if the
.Fa nodename
argument is a
.Dv NULL
pointer, then the IP address portion of the socket
address structure will be set to
.Dv INADDR_ANY
for an IPv4 address or
.Dv IN6ADDR_ANY_INIT
for an IPv6 address.
.Pp
If the
.Dv AI_PASSIVE
bit is not set in the
.Fa ai_flags
member of the
.Fa hints
structure, then the returned socket address structure will be ready for a
call to
.Fn connect
.Pq for a connection-oriented protocol
or either
.Fn connect ,
.Fn sendto , or
.Fn sendmsg
.Pq for a connectionless protocol .
In this case, if the
.Fa nodename
argument is a
.Dv NULL
pointer, then the IP address portion of the
socket address structure will be set to the loopback address.
.Pp
If the
.Dv AI_CANONNAME
bit is set in the
.Fa ai_flags
member of the
.Fa hints
structure, then upon successful return the
.Fa ai_canonname
member of the first
.Li addrinfo
structure in the linked list will point to a null-terminated string
containing the canonical name of the specified
.Fa nodename .
.Pp
If the
.Dv AI_NUMERICHOST
bit is set in the
.Fa ai_flags
member of the
.Fa hints
structure, then a
.Pf non Dv -NULL
.Fa nodename
string must be a numeric host address string.
Otherwise an error of
.Dv EAI_NONAME
is returned.
This flag prevents any type of name resolution service (e.g., the DNS)
from being called.
.Pp
All of the information returned by
.Fn getaddrinfo
is dynamically allocated:
the
.Li addrinfo
structures, and the socket address structures and canonical node name
strings pointed to by the addrinfo structures.
To return this information to the system the function
.Fn freeaddrinfo
is called.
The
.Fa addrinfo
structure pointed to by the
.Fa ai argument
is freed, along with any dynamic storage pointed to by the structure.
This operation is repeated until a
.Dv NULL
.Fa ai_next
pointer is encountered.
.Pp
To aid applications in printing error messages based on the
.Dv EAI_xxx
codes returned by
.Fn getaddrinfo ,
.Fn gai_strerror
is defined.
The argument is one of the
.Dv EAI_xxx
values defined earlier and the return value points to a string describing
the error.
If the argument is not one of the
.Dv EAI_xxx
values, the function still returns a pointer to a string whose contents
indicate an unknown error.
.Sh FILES
.Bl -tag -width /etc/resolv.conf -compact
.It Pa /etc/hosts
.It Pa /etc/host.conf
.It Pa /etc/resolv.conf
.El
.Sh DIAGNOSTICS
Error return status from
.Fn getaddrinfo
is zero on success and non-zero on errors.
Non-zero error codes are defined in
.Li <netdb.h> ,
and as follows:
.Pp
.Bl -tag -width EAI_ADDRFAMILY -compact
.It Dv EAI_ADDRFAMILY
address family for nodename not supported
.It Dv EAI_AGAIN
temporary failure in name resolution
.It Dv EAI_BADFLAGS
invalid value for ai_flags
.It Dv EAI_FAIL
non-recoverable failure in name resolution
.It Dv EAI_FAMILY
ai_family not supported
.It Dv EAI_MEMORY
memory allocation failure
.It Dv EAI_NODATA
no address associated with nodename
.It Dv EAI_NONAME
nodename nor servname provided, or not known
.It Dv EAI_SERVICE
servname not supported for ai_socktype
.It Dv EAI_SOCKTYPE
ai_socktype not supported
.It Dv EAI_SYSTEM
system error returned in errno
.El
.Pp
If called with proper argument,
.Fn gai_strerror
returns a pointer to a string describing the given error code.
If the argument is not one of the
.Dv EAI_xxx
values, the function still returns a pointer to a string whose contents
indicate an unknown error.
.Sh SEE ALSO
.Xr getnameinfo 3 ,
.Xr gethostbyname 3 ,
.Xr getservbyname 3 ,
.Xr hosts 5 ,
.Xr services 5 ,
.Xr hostname 7 ,
.Xr named 8
.Pp
R. Gilligan, S.  Thomson, J. Bound, and W. Stevens,
``Basic Socket Interface Extensions for IPv6,'' RFC2553, March 1999.
.Sh STANDARDS
The
.Fn getaddrinfo
function is defined IEEE POSIX 1003.1g draft specification,
and documented in ``Basic Socket Interface Extensions for IPv6''
.Pq RFC2533 .
.Sh BUGS
The text was shamelessly copied from RFC2553.