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Diffstat (limited to 'man3/getnameinfo.3')
| -rw-r--r-- | man3/getnameinfo.3 | 344 |
1 files changed, 344 insertions, 0 deletions
diff --git a/man3/getnameinfo.3 b/man3/getnameinfo.3 new file mode 100644 index 0000000..580a265 --- /dev/null +++ b/man3/getnameinfo.3 @@ -0,0 +1,344 @@ +'\" t +.\" %%%LICENSE_START(PUBLIC_DOMAIN) +.\" This page is in the public domain. +.\" %%%LICENSE_END +.\" +.\" Almost all details are from RFC 2553. +.\" +.\" 2004-12-14, mtk, Added EAI_OVERFLOW error +.\" 2004-12-14 Fixed description of error return +.\" +.TH getnameinfo 3 2023-07-20 "Linux man-pages 6.05.01" +.SH NAME +getnameinfo \- address-to-name translation in protocol-independent manner +.SH LIBRARY +Standard C library +.RI ( libc ", " \-lc ) +.SH SYNOPSIS +.nf +.B #include <sys/socket.h> +.B #include <netdb.h> +.PP +.BI "int getnameinfo(const struct sockaddr *restrict " addr \ +", socklen_t " addrlen , +.BI " char " host "[_Nullable restrict ." hostlen ], +.BI " socklen_t " hostlen , +.BI " char " serv "[_Nullable restrict ." servlen ], +.BI " socklen_t " servlen , +.BI " int " flags ); +.fi +.PP +.RS -4 +Feature Test Macro Requirements for glibc (see +.BR feature_test_macros (7)): +.RE +.PP +.BR getnameinfo (): +.nf + Since glibc 2.22: + _POSIX_C_SOURCE >= 200112L + glibc 2.21 and earlier: + _POSIX_C_SOURCE +.fi +.SH DESCRIPTION +The +.BR getnameinfo () +function is the inverse of +.BR getaddrinfo (3): +it converts a socket address to a corresponding host and service, +in a protocol-independent manner. +It combines the functionality of +.BR gethostbyaddr (3) +and +.BR getservbyport (3), +but unlike those functions, +.BR getnameinfo () +is reentrant and allows programs to eliminate +IPv4-versus-IPv6 dependencies. +.PP +The +.I addr +argument is a pointer to a generic socket address structure +(of type +.I sockaddr_in +or +.IR sockaddr_in6 ) +of size +.I addrlen +that holds the input IP address and port number. +The arguments +.I host +and +.I serv +are pointers to caller-allocated buffers (of size +.I hostlen +and +.I servlen +respectively) into which +.BR getnameinfo () +places null-terminated strings containing the host and +service names respectively. +.PP +The caller can specify that no hostname (or no service name) +is required by providing a NULL +.I host +(or +.IR serv ) +argument or a zero +.I hostlen +(or +.IR servlen ) +argument. +However, at least one of hostname or service name +must be requested. +.PP +The +.I flags +argument modifies the behavior of +.BR getnameinfo () +as follows: +.TP +.B NI_NAMEREQD +If set, then an error is returned if the hostname cannot be determined. +.TP +.B NI_DGRAM +If set, then the service is datagram (UDP) based rather than +stream (TCP) based. +This is required for the few ports (512\[en]514) +that have different services for UDP and TCP. +.TP +.B NI_NOFQDN +If set, return only the hostname part of the fully qualified domain name +for local hosts. +.TP +.B NI_NUMERICHOST +If set, then the numeric form of the hostname is returned. +.\" For example, by calling +.\" .BR inet_ntop () +.\" instead of +.\" .BR gethostbyaddr (). +(When not set, this will still happen in case the node's name +cannot be determined.) +.\" POSIX.1-2001 TC1 has NI_NUMERICSCOPE, but glibc doesn't have it. +.TP +.B NI_NUMERICSERV +If set, then the numeric form of the service address is returned. +(When not set, this will still happen in case the service's name +cannot be determined.) +.SS Extensions to getnameinfo() for Internationalized Domain Names +Starting with glibc 2.3.4, +.BR getnameinfo () +has been extended to selectively allow +hostnames to be transparently converted to and from the +Internationalized Domain Name (IDN) format (see RFC 3490, +.IR "Internationalizing Domain Names in Applications (IDNA)" ). +Three new flags are defined: +.TP +.B NI_IDN +If this flag is used, then the name found in the lookup process is +converted from IDN format to the locale's encoding if necessary. +ASCII-only names are not affected by the conversion, which +makes this flag usable in existing programs and environments. +.TP +.BR NI_IDN_ALLOW_UNASSIGNED ", " NI_IDN_USE_STD3_ASCII_RULES +Setting these flags will enable the +IDNA_ALLOW_UNASSIGNED (allow unassigned Unicode code points) and +IDNA_USE_STD3_ASCII_RULES (check output to make sure it is a STD3 +conforming hostname) +flags respectively to be used in the IDNA handling. +.SH RETURN VALUE +.\" FIXME glibc defines the following additional errors, some which +.\" can probably be returned by getnameinfo(); they need to +.\" be documented. +.\" +.\" #ifdef __USE_GNU +.\" #define EAI_INPROGRESS -100 /* Processing request in progress. */ +.\" #define EAI_CANCELED -101 /* Request canceled. */ +.\" #define EAI_NOTCANCELED -102 /* Request not canceled. */ +.\" #define EAI_ALLDONE -103 /* All requests done. */ +.\" #define EAI_INTR -104 /* Interrupted by a signal. */ +.\" #define EAI_IDN_ENCODE -105 /* IDN encoding failed. */ +.\" #endif +On success, 0 is returned, and node and service names, if requested, +are filled with null-terminated strings, possibly truncated to fit +the specified buffer lengths. +On error, one of the following nonzero error codes is returned: +.TP +.B EAI_AGAIN +The name could not be resolved at this time. +Try again later. +.TP +.B EAI_BADFLAGS +The +.I flags +argument has an invalid value. +.TP +.B EAI_FAIL +A nonrecoverable error occurred. +.TP +.B EAI_FAMILY +The address family was not recognized, +or the address length was invalid for the specified family. +.TP +.B EAI_MEMORY +Out of memory. +.TP +.B EAI_NONAME +The name does not resolve for the supplied arguments. +.B NI_NAMEREQD +is set and the host's name cannot be located, +or neither hostname nor service name were requested. +.TP +.B EAI_OVERFLOW +The buffer pointed to by +.I host +or +.I serv +was too small. +.TP +.B EAI_SYSTEM +A system error occurred. +The error code can be found in +.IR errno . +.PP +The +.BR gai_strerror (3) +function translates these error codes to a human readable string, +suitable for error reporting. +.SH FILES +.I /etc/hosts +.br +.I /etc/nsswitch.conf +.br +.I /etc/resolv.conf +.SH ATTRIBUTES +For an explanation of the terms used in this section, see +.BR attributes (7). +.TS +allbox; +lbx lb lb +l l l. +Interface Attribute Value +T{ +.na +.nh +.BR getnameinfo () +T} Thread safety MT-Safe env locale +.TE +.sp 1 +.SH STANDARDS +POSIX.1-2008. +RFC\ 2553. +.SH HISTORY +glibc 2.1. +POSIX.1-2001. +.PP +Before glibc 2.2, the +.I hostlen +and +.I servlen +arguments were typed as +.IR size_t . +.SH NOTES +In order to assist the programmer in choosing reasonable sizes +for the supplied buffers, +.I <netdb.h> +defines the constants +.PP +.in +4n +.EX +#define NI_MAXHOST 1025 +#define NI_MAXSERV 32 +.EE +.in +.PP +Since glibc 2.8, +these definitions are exposed only if suitable +feature test macros are defined, namely: +.BR _GNU_SOURCE , +.B _DEFAULT_SOURCE +(since glibc 2.19), +or (in glibc versions up to and including 2.19) +.B _BSD_SOURCE +or +.BR _SVID_SOURCE . +.PP +The former is the constant +.B MAXDNAME +in recent versions of BIND's +.I <arpa/nameser.h> +header file. +The latter is a guess based on the services listed +in the current Assigned Numbers RFC. +.SH EXAMPLES +The following code tries to get the numeric hostname and service name, +for a given socket address. +Note that there is no hardcoded reference to +a particular address family. +.PP +.in +4n +.EX +struct sockaddr *addr; /* input */ +socklen_t addrlen; /* input */ +char hbuf[NI_MAXHOST], sbuf[NI_MAXSERV]; +\& +if (getnameinfo(addr, addrlen, hbuf, sizeof(hbuf), sbuf, + sizeof(sbuf), NI_NUMERICHOST | NI_NUMERICSERV) == 0) + printf("host=%s, serv=%s\en", hbuf, sbuf); +.EE +.in +.PP +The following version checks if the socket address has a +reverse address mapping. +.PP +.in +4n +.EX +struct sockaddr *addr; /* input */ +socklen_t addrlen; /* input */ +char hbuf[NI_MAXHOST]; +\& +if (getnameinfo(addr, addrlen, hbuf, sizeof(hbuf), + NULL, 0, NI_NAMEREQD)) + printf("could not resolve hostname"); +else + printf("host=%s\en", hbuf); +.EE +.in +.PP +An example program using +.BR getnameinfo () +can be found in +.BR getaddrinfo (3). +.SH SEE ALSO +.BR accept (2), +.BR getpeername (2), +.BR getsockname (2), +.BR recvfrom (2), +.BR socket (2), +.BR getaddrinfo (3), +.BR gethostbyaddr (3), +.BR getservbyname (3), +.BR getservbyport (3), +.BR inet_ntop (3), +.BR hosts (5), +.BR services (5), +.BR hostname (7), +.BR named (8) +.PP +R.\& Gilligan, S.\& Thomson, J.\& Bound and W.\& Stevens, +.IR "Basic Socket Interface Extensions for IPv6" , +RFC\ 2553, March 1999. +.PP +Tatsuya Jinmei and Atsushi Onoe, +.IR "An Extension of Format for IPv6 Scoped Addresses" , +internet draft, work in progress +.UR ftp://ftp.ietf.org\:/internet\-drafts\:/draft\-ietf\-ipngwg\-scopedaddr\-format\-02.txt +.UE . +.PP +Craig Metz, +.IR "Protocol Independence Using the Sockets API" , +Proceedings of the freenix track: +2000 USENIX annual technical conference, June 2000 +.ad l +.UR http://www.usenix.org\:/publications\:/library\:/proceedings\:/usenix2000\:/freenix\:/metzprotocol.html +.UE . |