This function looks up an IP address and port number in a
    sockaddr structure specified by sa and returns node name and
    service name text strings in the buffers pointed to by the node
    and service arguments, respectively.
    If the node name is not found, getnameinfo() returns the numeric
    form of the node address, regardless of the value of the flags
    argument. If the service name is not found, getnameinfo() returns
    the numeric form of the service address (port number) regardless
    of the value of the flags argument.
    The application must provide buffers large enough to hold the
    fully-qualified domain name and the service name, including the
    terminating null characters.
    Flags describes the flag bits and, if set, their meanings. The
    flags are defined in the NETDB.H header file.
    Table 4-2 getnameinfo()  Flags
    Flag Value         Description
    NI_DGRAM           Specifies that the service is a datagram
                       service (SOCK_DGRAM). The default assumes
                       a stream service (SOCK_STREAM). This is
                       required for the few ports (512-514) that
                       have different services for UDP and TCP.
    NI_NAMEREQD        Returns an error if the host name cannot be
                       located in the hosts database.
    NI_NOFQDN          Searches the hosts database and returns the
                       node name portion of the fully-qualified
                       domain name for local hosts.
    NI_NUMERICHOST     Returns the numeric form of the host's address
                       instead of its name. Resolution of the host
                       name is not performed.
    NI_NUMERICSERV     Returns the numeric form (port number) of the
                       service address instead of its name. The host
                       name is not resolved.