path: root/usr/src/man/man3socket/getipnodebyname.3socket

'\" te
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.TH GETIPNODEBYNAME 3SOCKET "Sep 10, 2013"
.SH NAME
getipnodebyname, getipnodebyaddr, freehostent \- get IP node entry
.SH SYNOPSIS
.LP
.nf
\fBcc\fR [ \fIflag\fR... ] \fIfile\fR... \fB-lsocket\fR \fB -lnsl \fR [ \fIlibrary\fR... ]
#include <sys/socket.h>
#include <netdb.h>

\fBstruct hostent *\fR\fBgetipnodebyname\fR(\fBconst char *\fR\fIname\fR, \fBint\fR \fIaf\fR,
     \fBint\fR \fIflags\fR, \fBint *\fR\fIerror_num\fR);
.fi

.LP
.nf
\fBstruct hostent *\fR\fBgetipnodebyaddr\fR(\fBconst void *\fR\fIsrc\fR, \fBsize_t\fR \fIlen\fR,
     \fBint\fR \fIaf\fR, \fBint *\fR\fIerror_num\fR);
.fi

.LP
.nf
\fBvoid\fR \fBfreehostent\fR(\fBstruct hostent *\fR\fIptr\fR);
.fi

.SH PARAMETERS
.ne 2
.na
\fB\fIaf\fR\fR
.ad
.RS 13n
Address family
.RE

.sp
.ne 2
.na
\fB\fIflags\fR\fR
.ad
.RS 13n
Various flags
.RE

.sp
.ne 2
.na
\fB\fIname\fR\fR
.ad
.RS 13n
Name of host
.RE

.sp
.ne 2
.na
\fB\fIerror_num\fR\fR
.ad
.RS 13n
Error storage
.RE

.sp
.ne 2
.na
\fB\fIsrc\fR\fR
.ad
.RS 13n
Address for lookup
.RE

.sp
.ne 2
.na
\fB\fIlen\fR\fR
.ad
.RS 13n
Length of address
.RE

.sp
.ne 2
.na
\fB\fIptr\fR\fR
.ad
.RS 13n
Pointer to \fBhostent\fR structure
.RE

.SH DESCRIPTION
.LP
The \fBgetipnodebyname()\fR function searches the \fBipnodes\fR database from
the beginning. The function finds the first \fBh_name\fR member that matches
the hostname specified by \fIname\fR. The function takes an \fIaf\fR argument
that specifies the address family. The address family can be \fBAF_INET\fR for
IPv4 addresses or \fBAF_INET6\fR for IPv6 addresses. The \fIflags\fR argument
determines what results are returned based on the value of \fIflags\fR. If the
\fIflags\fR argument is set to \fB0\fR (zero), the default operation of the
function is specified as follows:
.RS +4
.TP
.ie t \(bu
.el o
If the \fIaf\fR argument is \fBAF_INET\fR, a query is made for an IPv4 address.
If successful, IPv4 addresses are returned and the \fBh_length\fR member of the
\fBhostent\fR structure is 4. Otherwise, the function returns a \fINULL\fR
pointer.
.RE
.RS +4
.TP
.ie t \(bu
.el o
If the \fIaf\fR argument is \fBAF_INET6\fR, a query is made for an IPv6
address. If successful, IPv6 addresses are returned and the \fBh_length\fR
member of the \fBhostent\fR structure is 16. Otherwise, the function returns a
\fINULL\fR pointer.
.RE
.sp
.LP
The \fIflags\fR argument changes the default actions of the function. Set the
\fIflags\fR argument with a logical \fBOR\fR operation on any of combination of
the following values:
.RS +4
.TP
.ie t \(bu
.el o
\fBAI_V4MAPPED\fR
.RE
.RS +4
.TP
.ie t \(bu
.el o
\fBAI_ALL\fR
.RE
.RS +4
.TP
.ie t \(bu
.el o
\fBAI_ADDRCONFIG\fR
.RE
.sp
.LP
The special flags value, \fBAI_DEFAULT\fR, should handle most applications.
Porting simple applications to use IPv6 replaces the call
.sp
.in +2
.nf
hptr = gethostbyname(name);
.fi
.in -2

.sp
.LP
with
.sp
.in +2
.nf
hptr = getipnodebyname(name, AF_INET6, AI_DEFAULT, &error_num);
.fi
.in -2

.sp
.LP
The \fIflags\fR value \fB0\fR (zero) implies a strict interpretation of the
\fIaf\fR argument:
.RS +4
.TP
.ie t \(bu
.el o
If \fIflags\fR is \fB0\fR and \fIaf\fR is \fBAF_INET\fR, the caller wants only
IPv4 addresses. A query is made for \fBA\fR records. If successful, IPv4
addresses are returned and the \fBh_length\fR member of the \fBhostent\fR
structure is 4. Otherwise, the function returns a \fINULL\fR pointer.
.RE
.RS +4
.TP
.ie t \(bu
.el o
If \fIflags\fR is \fB0\fR and \fIaf\fR is \fBAF_INET6\fR, the caller wants only
IPv6 addresses. A query is made for \fBAAAA\fR records. If successful, IPv6
addresses are returned and the \fBh_length\fR member of the \fBhostent\fR
structure is 16. Otherwise, the function returns a \fINULL\fR pointer.
.RE
.sp
.LP
Logically \fBOR\fR other constants into the \fIflags\fR argument to modify the
behavior of the \fBgetipnodebyname()\fR function.
.RS +4
.TP
.ie t \(bu
.el o
If the \fBAI_V4MAPPED\fR flag is specified with \fIaf\fR set to \fBAF_INET6\fR,
the caller can accept IPv4-mapped IPv6 addresses. If no \fBAAAA\fR records are
found, a query is made for \fBA\fR records. Any \fBA\fR records found are
returned as IPv4-mapped IPv6 addresses and the \fBh_length\fR is 16. The
\fBAI_V4MAPPED\fR flag is ignored unless \fIaf\fR equals \fBAF_INET6\fR.
.RE
.RS +4
.TP
.ie t \(bu
.el o
The \fBAI_ALL\fR flag is used in conjunction with the \fBAI_V4MAPPED\fR flag,
exclusively with the IPv6 address family. When \fBAI_ALL\fR is logically
\fBOR\fRed with \fBAI_V4MAPPED\fR flag, the caller wants all addresses: IPv6
and IPv4-mapped IPv6 addresses. A query is first made for \fBAAAA\fR records
and, if successful, IPv6 addresses are returned. Another query is then made for
\fBA\fR records. Any \fBA\fR records found are returned as IPv4-mapped IPv6
addresses and the \fBh_length\fR is 16. Only when both queries fail does the
function return a \fINULL\fR pointer. The \fBAI_ALL\fR flag is ignored unless
\fIaf\fR is set to \fBAF_INET6\fR.
.RE
.RS +4
.TP
.ie t \(bu
.el o
The \fBAI_ADDRCONFIG\fR flag specifies that a query for \fBAAAA\fR records
should occur only when the node is configured with at least one IPv6 source
address. A query for \fBA\fR records should occur only when the node is
configured with at least one IPv4 source address. For example, if a node is
configured with no IPv6 source addresses, \fIaf\fR equals \fBAF_INET6\fR, and
the node name queried has both \fBAAAA\fR and \fBA\fR records, then:
.RS +4
.TP
.ie t \(bu
.el o
A \fINULL\fR pointer is returned when only the \fBAI_ADDRCONFIG\fR value is
specified.
.RE
.RS +4
.TP
.ie t \(bu
.el o
The \fBA\fR records are returned as IPv4-mapped IPv6 addresses when the
\fBAI_ADDRCONFIG\fR and \fBAI_V4MAPPED\fR values are specified.
.RE
.RE
.sp
.LP
The special flags value, \fBAI_DEFAULT\fR, is defined as
.sp
.in +2
.nf
#define  AI_DEFAULT  (AI_V4MAPPED | AI_ADDRCONFIG)
.fi
.in -2

.sp
.LP
The \fBgetipnodebyname()\fR function allows the \fIname\fR argument to be a
node name or a literal address string: a dotted-decimal IPv4 address or an IPv6
hex address. Applications do not have to call \fBinet_pton\fR(3C) to
handle literal address strings.
.sp
.LP
Four scenarios arise based on the type of literal address string and the value
of the \fIaf\fR argument. The two simple cases occur when \fIname\fR is a
dotted-decimal IPv4 address and \fIaf\fR equals \fBAF_INET\fR and when
\fIname\fR is an IPv6 hex address and \fIaf\fR equals \fBAF_INET6\fR. The
members of the returned \fBhostent\fR structure are:
.sp
.ne 2
.na
\fB\fBh_name\fR\fR
.ad
.RS 15n
Pointer to a copy of the name argument
.RE

.sp
.ne 2
.na
\fB\fBh_aliases\fR\fR
.ad
.RS 15n
\fINULL\fR pointer.
.RE

.sp
.ne 2
.na
\fB\fBh_addrtype\fR\fR
.ad
.RS 15n
Copy of the \fIaf\fR argument.
.RE

.sp
.ne 2
.na
\fB\fBh_length\fR\fR
.ad
.RS 15n
4 for \fBAF_INET\fR or 16 for \fBAF_INET6\fR.
.RE

.sp
.ne 2
.na
\fB\fBh_addr_list\fR\fR
.ad
.RS 15n
Array of pointers to 4-byte or 16-byte binary addresses. The array is
terminated by a \fINULL\fR pointer.
.RE

.SH RETURN VALUES
.LP
Upon successful completion, \fBgetipnodebyname()\fR and \fBgetipnodebyaddr()\fR
return a \fBhostent\fR structure. Otherwise they return \fINULL\fR.
.sp
.LP
The \fBhostent\fR structure does not change from the existing definition when
used with \fBgethostbyname\fR(3NSL). For example, host entries are represented
by the \fBstruct hostent\fR structure defined in <\fBnetdb.h\fR>:
.sp
.in +2
.nf
struct  hostent {
        char    *h_name;        /* canonical name of host */
        char    **h_aliases;    /* alias list */
        int     h_addrtype;     /* host address type */
        int     h_length;       /* length of address */
        char    **h_addr_list;  /* list of addresses */
};
.fi
.in -2

.sp
.LP
An error occurs when \fIname\fR is an IPv6 hex address and \fIaf\fR equals
\fBAF_INET\fR. The return value of the function is a \fINULL\fR pointer and
\fBerror_num\fR equals \fBHOST_NOT_FOUND\fR.
.sp
.LP
The \fBgetipnodebyaddr()\fR function has the same arguments as the existing
\fBgethostbyaddr\fR(3NSL) function, but adds an error number. As with
\fBgetipnodebyname()\fR, \fBgetipnodebyaddr()\fR is thread-safe. The
\fBerror_num\fR value is returned to the caller with the appropriate error code
to support thread-safe error code returns. The following error conditions can
be returned for \fBerror_num\fR:
.sp
.ne 2
.na
\fB\fBHOST_NOT_FOUND\fR\fR
.ad
.RS 18n
Host is unknown.
.RE

.sp
.ne 2
.na
\fB\fBNO_DATA\fR\fR
.ad
.RS 18n
No address is available for the \fIname\fR specified in the server request.
This error is not a soft error. Another type of \fIname\fR server request might
be successful.
.RE

.sp
.ne 2
.na
\fB\fBNO_RECOVERY\fR\fR
.ad
.RS 18n
An unexpected server failure occurred, which is a non-recoverable error.
.RE

.sp
.ne 2
.na
\fB\fBTRY_AGAIN\fR\fR
.ad
.RS 18n
This error is a soft error that indicates that the local server did not receive
a response from an authoritative server. A retry at some later time might be
successful.
.RE

.sp
.LP
One possible source of confusion is the handling of IPv4-mapped IPv6 addresses
and IPv4-compatible IPv6 addresses, but the following logic should apply:
.RS +4
.TP
1.
If \fIaf\fR is \fBAF_INET6\fR, and if \fIlen\fR equals 16, and if the IPv6
address is an IPv4-mapped IPv6 address or an IPv4-compatible IPv6 address, then
skip over the first 12 bytes of the IPv6 address, set \fIaf\fR to
\fBAF_INET\fR, and set \fIlen\fR to 4.
.RE
.RS +4
.TP
2.
If \fIaf\fR is \fBAF_INET\fR, lookup the \fIname\fR for the given IPv4
address.
.RE
.RS +4
.TP
3.
If \fIaf\fR is \fBAF_INET6\fR, lookup the \fIname\fR for the given IPv6
address.
.RE
.RS +4
.TP
4.
If the function is returning success, then the single address that is
returned in the \fBhostent\fR structure is a copy of the first argument to the
function with the same address family that was passed as an argument to this
function.
.RE
.sp
.LP
All four steps listed are performed in order.
.sp
.LP
This structure, and the information pointed to by this structure, are
dynamically allocated by \fBgetipnodebyname()\fR and \fBgetipnodebyaddr()\fR.
The \fBfreehostent()\fR function frees this memory.
.SH EXAMPLES
.LP
\fBExample 1 \fRGetting the Canonical Name, Aliases, and Internet IP Addresses
for a Given Hostname
.sp
.LP
The following is a sample program that retrieves the canonical name, aliases,
and all Internet IP addresses, both version 6 and version 4, for a given
hostname.

.sp
.in +2
.nf
     #include <stdio.h>
     #include <string.h>
     #include <sys/types.h>
     #include <sys/socket.h>
     #include <netinet/in.h>
     #include <arpa/inet.h>
     #include <netdb.h>

     main(int argc, const char **argv)
     {
     char abuf[INET6_ADDRSTRLEN];
     int error_num;
     struct hostent *hp;
     char **p;

         if (argc != 2) {
             (void) printf("usage: %s hostname\en", argv[0]);
             exit (1);
         }

     /* argv[1] can be a pointer to a hostname or literal IP address */
     hp = getipnodebyname(argv[1], AF_INET6, AI_ALL | AI_ADDRCONFIG |
        AI_V4MAPPED, &error_num);
     if (hp == NULL) {
        if (error_num == TRY_AGAIN) {
            printf("%s: unknown host or invalid literal address "
                "(try again later)\en", argv[1]);
        } else {
            printf("%s: unknown host or invalid literal address\en",
                argv[1]);
        }
        exit (1);
     }
     for (p = hp->h_addr_list; *p != 0; p++) {
        struct in6_addr in6;
        char **q;

        bcopy(*p, (caddr_t)&in6, hp->h_length);
        (void) printf("%s\et%s", inet_ntop(AF_INET6, (void *)&in6,
            abuf, sizeof(abuf)), hp->h_name);
        for (q = hp->h_aliases; *q != 0; q++)
        (void) printf(" %s", *q);
        (void) putchar('\en');
     }
     freehostent(hp);
     exit (0);
     }
.fi
.in -2

.SH ATTRIBUTES
.LP
See \fBattributes\fR(5) for descriptions of the following attributes:
.sp

.sp
.TS
box;
c | c
l | l .
ATTRIBUTE TYPE	ATTRIBUTE VALUE
_
Interface Stability	Committed
_
MT-Level	Safe
.TE

.SH SEE ALSO
.LP
\fBgetaddrinfo\fR(3SOCKET), \fBgethostbyname\fR(3NSL), \fBhtonl\fR(3C),
\fBinet\fR(3SOCKET), \fBnetdb.h\fR(3HEAD), \fBhosts\fR(4),
\fBnsswitch.conf\fR(4), \fBattributes\fR(5)
.SH NOTES
.LP
No enumeration functions are provided for IPv6. Existing enumeration functions
such as \fBsethostent\fR(3NSL) do not work in combination with the
\fBgetipnodebyname()\fR and \fBgetipnodebyaddr()\fR functions.
.sp
.LP
All the functions that return a \fBstruct hostent\fR must always return the
canonical in the \fBh_name\fR field. This name, by definition, is the
well-known and official hostname shared between all aliases and all addresses.
The underlying source that satisfies the request determines the mapping of the
input name or address into the set of names and addresses in \fBhostent\fR.
Different sources might make such as determination in different ways. If more
than one alias and more than one address in \fBhostent\fR exist, no pairing is
implied between the alias and address.
.sp
.LP
The current implementations of these functions return or accept only addresses
for the Internet address family (type \fBAF_INET\fR) or the Internet address
family Version 6 (type \fBAF_INET6\fR).
.sp
.LP
IPv4-mapped addresses are not recommended. The \fBgetaddrinfo\fR(3SOCKET)
function is preferred over \fBgetipnodebyaddr()\fR because it allows
applications to lookup IPv4 and IPv6 addresses without relying on IPv4-mapped
addresses.
.sp
.LP
The form for an address of type \fBAF_INET\fR is a \fBstruct in_addr\fR defined
in <\fBnetinet/in.h\fR>. The form for an address of type \fBAF_INET6\fR is a
\fBstruct in6_addr\fR, also defined in <\fBnetinet/in.h\fR>. The functions
described in \fBinet_ntop\fR(3C) and \fBinet_pton\fR(3C) that are
illustrated in the EXAMPLES section are helpful in constructing and
manipulating addresses in either of these forms.