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NAME

       Cnetdb - LCG netdb utilities

SYNOPSIS

       #include <Cnetdb.h>

       char  *Cgetnetaddress(int  sock,  const  void  *sa,  size_t  salen,  int *skey, const char
       **numeric_out, const char **name_out, int flags, int cflags);

DESCRIPTION

       Cnetdb provides several netdb like  functions  including  Cgethostbyname,  Cgethostbyaddr,
       Cgetservbyname,  Cgetnameinfo,  Cgetaddrinfo,  Cgai_strerror  which  behave  in a somewhat
       similar way to their system netdb counterparts. In addition  Cnetdb  provides  a  function
       called Cgetnetaddress which is currently the only one documented here.

       Cgetnetaddress  returns a DNS domain name (often called a hostname) given either a network
       socket, in which case the hostname corresponds to the peer address of  the  socket,  or  a
       sockaddr  structure.  The name will be returned as a numeric IP address and/or optionaly a
       DNS domain name.

       Exactly one of either sock or sa must be specified, the other should be set to -1 or  NULL
       respectively.  If both are set the behaviour should be considered undefined and may change
       in the future. If skey is NULL the memory for pointers returned by Cgetnetaddress will  be
       dynamically  allocated  and it is the responsibility of the caller to free them when done.
       If not NULL skey should point to an int which is initially set  to  a  value  of  -1.  The
       memory  used  to store the results returned by Cgetnetaddress will be allocated internally
       and will be reused during subsequent calls to Cgetnetaddress from the same thread and that
       share the same value of skey.

       If  numeric_out  or  name_out  are  not NULL the char pointer which they reference will be
       reset to a pointer to a character array containig the numeric or domain name address to be
       returned  by the function. The output will be NULL if the function is unable to find an IP
       or domain name.  flags accepts the same bitmaped flags that can be set for  getnameinfo().
       cflags accepts bitmaped flags which are unique to Cgetnetaddress.

       If  NI_NUMERICHOST  is  specified  in flags no attempt is made to obtain a domain name. If
       NI_NAMEREQD is specified  nothing  is  returned  unless  a  domain  name  address  can  be
       determined. NI_NUMERICHOST and NI_NAMEREQD are mutually exclusive. Other flags options may
       be set and will have the effect described for getnameinfo().

       cflags may take the bitmaped flags CNA_WANTLOOPBACK, CNA_NOFWDLOOKUP and CNA_FWDLOOKUP.

       By default if the address to be returned is determined to  be  the  loopback  address  any
       domain  name returned will be that of the local machine.  If CNA_WANTLOOPBACK is specified
       any domain name returned will be  that  associated  with  the  loopback  address,  usually
       localhost.localdomain.

       A  forward  lookup  verification  of  the domain name may be optionally specified with the
       CNA_FWDLOOKUP flag.  The forward lookup means that one of the address to  which  a  domain
       name  resolves  must  match  the address passed to Cgetnetaddress. If the match failes the
       domain name will be considered  to  not  be  available.  By  default,  or  if  the  option
       CNA_NOFWDLOOKUP  is  passed  in  cflags,  the  forward  lookup  check  is not performed or
       required. The  behavior  if  both  CNA_FWDLOOKUP  and  CNA_NOFWDLOOKUP  are  specified  is
       undefined.

RETURN VALUE

       Cgetnetaddress()  returns  a pointer to the domain name, if available, or otherwise to the
       numeric IP address, if available.  If neither is available NULL is returned.

SEE ALSO

       gethostbyname(3),  gethostbyaddr(3),  getservbyname(3),  getnameinfo(3),   getaddrinfo(3),
       gai_strerror(3)

AUTHOR

       LCG Grid Deployment Team  and DPM Team <hep-service-dpm@cern.ch>