mirror of https://github.com/mkerrisk/man-pages
263 lines
6.8 KiB
Groff
263 lines
6.8 KiB
Groff
.\" This page is in the public domain.
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.\" Almost all details are from RFC 2553.
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.\"
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.\" 2004-12-14, mtk, Added EAI_OVERFLOW error
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.\" 2004-12-14 Fixed description of error return
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.\"
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.TH GETNAMEINFO 3 2007-06-08 "GNU" "Linux Programmer's Manual"
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.SH NAME
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getnameinfo \- address-to-name translation in protocol-independent manner
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.SH SYNOPSIS
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.nf
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.B #include <sys/socket.h>
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.B #include <netdb.h>
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.sp
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.BI "int getnameinfo(const struct sockaddr *" "sa" ", socklen_t " "salen" ,
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.BI " char *" "host" ", size_t " "hostlen" ,
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.BI " char *" "serv" ", size_t " "servlen" ", int " "flags" );
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.fi
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.SH DESCRIPTION
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The
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.BR getnameinfo ()
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function is defined for protocol-independent address-to-nodename translation.
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It combines the functionality of
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.BR gethostbyaddr (3)
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and
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.BR getservbyport (3)
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and is the inverse of
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.BR getaddrinfo (3).
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The
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.I sa
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argument is a pointer to a generic socket address structure
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(of type
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.I sockaddr_in
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or
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.IR sockaddr_in6 )
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of size
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.I salen
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that holds the input IP address and port number.
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The arguments
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.I host
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and
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.I serv
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are pointers to buffers (of size
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.I hostlen
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and
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.I servlen
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respectively) to hold the return values.
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The caller can specify that no hostname (or no service name)
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is required by providing a NULL
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.I host
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(or
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.IR serv )
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argument or a zero
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.I hostlen
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(or
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.IR servlen )
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parameter.
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However, at least one of hostname or service name
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must be requested.
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The
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.I flags
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argument modifies the behavior of
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.BR getnameinfo ()
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as follows:
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.TP
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.B NI_NOFQDN
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If set, return only the hostname part of the FQDN for local hosts.
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.TP
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.B NI_NUMERICHOST
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If set, then the numeric form of the hostname is returned.
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.\" For example, by calling
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.\" .BR inet_ntop ()
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.\" instead of
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.\" .BR gethostbyaddr ().
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(When not set, this will still happen in case the node's name
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cannot be looked up.)
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.TP
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.B NI_NAMEREQD
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If set, then a error is returned if the hostname cannot be looked up.
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.TP
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.B NI_NUMERICSERV
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If set, then the service address is returned in numeric form,
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for example by its port number.
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.TP
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.B NI_DGRAM
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If set, then the service is datagram (UDP) based rather than
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stream (TCP) based.
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This is required for the few ports (512-514)
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that have different services for UDP and TCP.
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.SS "Extensions to getaddrinfo() for Internationalized Domain Names"
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.PP
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Starting with glibc 2.3.4,
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.BR getnameinfo ()
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has been extended to selectively allow
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host names to be transparently converted to and from the
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Internationalized Domain Name (IDN) format (see RFC 3490,
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.IR "Internationalizing Domain Names in Applications (IDNA)" ).
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Three new flags are defined:
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.TP
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.B NI_IDN
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If this flag is used, then the name found in the lookup process is
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converted from IDN format to the locale's encoding if necessary.
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ASCII-only names are not affected by the conversion, which
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makes this flag usable in existing programs and environments.
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.TP
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.BR NI_IDN_ALLOW_UNASSIGNED ", " NI_IDN_USE_STD3_ASCII_RULES
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Setting these flags will enable the
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IDNA_ALLOW_UNASSIGNED (allow unassigned Unicode code points) and
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IDNA_USE_STD3_ASCII_RULES (check output to make sure it is a STD3
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conforming host name)
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flags respectively to be used in the IDNA handling.
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.SH "RETURN VALUE"
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.\" FIXME glibc defines the following additional errors, some which
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.\" can probably be returned by getnameinfo(); they need to
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.\" be documented.
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.\" #ifdef __USE_GNU
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.\" #define EAI_INPROGRESS -100 /* Processing request in progress. */
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.\" #define EAI_CANCELED -101 /* Request canceled. */
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.\" #define EAI_NOTCANCELED -102 /* Request not canceled. */
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.\" #define EAI_ALLDONE -103 /* All requests done. */
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.\" #define EAI_INTR -104 /* Interrupted by a signal. */
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.\" #define EAI_IDN_ENCODE -105 /* IDN encoding failed. */
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.\" #endif
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On success 0 is returned, and node and service names, if requested,
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are filled with null-terminated strings, possibly truncated to fit
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the specified buffer lengths.
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On error one of the following nonzero error codes is returned:
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.TP
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.B EAI_AGAIN
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The name could not be resolved at this time.
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Try again later.
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.TP
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.B EAI_BADFLAGS
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The
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.I flags
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parameter has an invalid value.
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.TP
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.B EAI_FAIL
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A non-recoverable error occurred.
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.TP
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.B EAI_FAMILY
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The address family was not recognized,
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or the address length was invalid for the specified family.
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.TP
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.B EAI_MEMORY
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Out of memory.
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.TP
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.B EAI_NONAME
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The name does not resolve for the supplied parameters.
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.B NI_NAMEREQD
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is set and the host's name cannot be located,
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or neither hostname nor service name were requested.
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.TP
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.B EAI_OVERFLOW
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The buffer pointed to by
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.I host
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or
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.I serv
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was too small.
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.TP
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.B EAI_SYSTEM
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A system error occurred.
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The error code can be found in
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.IR errno .
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.PP
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The
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.BR gai_strerror (3)
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function translates these error codes to a human readable string,
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suitable for error reporting.
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.SH FILES
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/etc/hosts
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.br
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/etc/nsswitch.conf
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.br
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/etc/resolv.conf
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.SH "CONFORMING TO"
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RFC\ 2553, POSIX.1-2001.
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.SH NOTES
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In order to assist the programmer in choosing reasonable sizes
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for the supplied buffers,
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.I <netdb.h>
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defines the constants
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.in +4n
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.nf
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#define NI_MAXHOST 1025
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#define NI_MAXSERV 32
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.fi
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.in
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.PP
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The former is the constant
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.B MAXDNAME
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in recent versions of BIND's
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.I <arpa/nameser.h>
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header file.
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The latter is a guess based on the services listed
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in the current Assigned Numbers RFC.
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.SH EXAMPLE
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The following code tries to get the numeric hostname and service name,
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for a given socket address.
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Note that there is no hardcoded reference to
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a particular address family.
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.in +4n
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.nf
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struct sockaddr *sa; /* input */
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char hbuf[NI_MAXHOST], sbuf[NI_MAXSERV];
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if (getnameinfo(sa, sa\->sa_len, hbuf, sizeof(hbuf), sbuf,
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sizeof(sbuf), NI_NUMERICHOST | NI_NUMERICSERV) == 0)
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printf("host=%s, serv=%s\en", hbuf, sbuf);
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.fi
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.in
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The following version checks if the socket address has a
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reverse address mapping.
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.in +4n
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.nf
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struct sockaddr *sa; /* input */
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char hbuf[NI_MAXHOST];
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if (getnameinfo(sa, sa\->sa_len, hbuf, sizeof(hbuf),
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NULL, 0, NI_NAMEREQD))
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printf("could not resolve hostname");
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else
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printf("host=%s\en", hbuf);
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.fi
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.in
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.PP
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An example program using
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.BR getnameinfo ()
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can be found in
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.BR getaddrinfo (3).
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.SH "SEE ALSO"
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.BR socket (2),
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.BR getaddrinfo (3),
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.BR gethostbyaddr (3),
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.BR getservbyname (3),
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.BR getservbyport (3),
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.BR inet_ntop (3),
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.BR hosts (5),
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.BR services (5),
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.BR hostname (7),
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.BR named (8)
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.LP
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R. Gilligan, S. Thomson, J. Bound and W. Stevens,
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.IR "Basic Socket Interface Extensions for IPv6" ,
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RFC\ 2553, March 1999.
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.LP
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Tatsuya Jinmei and Atsushi Onoe,
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.IR "An Extension of Format for IPv6 Scoped Addresses" ,
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internet draft, work in progress.
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ftp://ftp.ietf.org/internet\-drafts/draft\-ietf\-ipngwg\-scopedaddr\-format\-02.txt
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.LP
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Craig Metz,
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.IR "Protocol Independence Using the Sockets API" ,
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Proceedings of the freenix track:
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2000 USENIX annual technical conference, June 2000.
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http://www.usenix.org/publications/library/proceedings/usenix2000/freenix/metzprotocol.html
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