Comtrol eCos - Manual (Page 523)

Chapter 38. TCP/IP Library Reference
getnameinfo
GETNAMEINFO(3) System Library Functions Manual GETNAMEINFO(3)
NAME
getnameinfo - address-to-nodename translation in protocol-independent
manner
SYNOPSIS
#include < sys/types.h>
#include < sys/socket.h>
#include < netdb.h>
int
getnameinfo(const struct sockaddr *sa, socklen_t salen, char *host,
size_t hostlen, char *serv, size_t servlen, int flags);
DESCRIPTION
The getnameinfo() function is defined for protocol-independent address-
to-nodename translation. Its functionality is a reverse conversion of
getaddrinfo(3), and implements similar functionality with
gethostbyaddr(3) and getservbyport(3) in more sophisticated manner.
This function looks up an IP address and port number provided by the
caller in the DNS and system-specific database, and returns text strings
for both in buffers provided by the caller. The function indicates suc-
cessful completion by a zero return value; a non-zero return value indi-
cates failure.
The first argument, sa, points to either a sockaddr_in structure (for
IPv4) or a sockaddr_in6 structure (for IPv6) that holds the IP address
and port number. The salen argument gives the length of the sockaddr_in
or sockaddr_in6 structure.
The function returns the nodename associated with the IP address in the
buffer pointed to by the host argument. The caller provides the size of
this buffer via the hostlen argument. The service name associated with
the port number is returned in the buffer pointed to by serv, and the
servlen argument gives the length of this buffer. The caller specifies
not to return either string by providing a zero value for the hostlen or
servlen arguments. Otherwise, the caller must provide buffers large
enough to hold the nodename and the service name, including the terminat-
ing null characters.
Unfortunately most systems do not provide constants that specify the max-
imum size of either a fully-qualified domain name or a service name.
Therefore to aid the application in allocating buffers for these two
returned strings the following constants are defined in < netdb.h>:
#define NI_MAXHOST MAXHOSTNAMELEN
#define NI_MAXSERV 32
The first value is actually defined as the constant MAXDNAME in recent
versions of BIND’s < arpa/nameser.h> header (older versions of BIND define
this constant to be 256) and the second is a guess based on the services
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