Determine where client is from

[TAYBENGH%NUSDISCS.BITNET at cunyvm.cuny.edu]

Dear Marvin,

        In Unix wizard u write:
>I have a client and server program. I would like the server program to log
>where the client is calling from (hostname). So if I were to call the server
>, the server would print: from: oliver.vcu.edu
>I'm pretty sure this isn't a wizard-type question, but we don't subscribe
>to usenet news here, there is no other applicable listserv group for me to
>ask/join, and there aren't any wizs around here.

        If u are using BSD socket interface, the u can use recvfrom() to get
the caller's identity. Below are the portion of code doing it.
        I hope this helps...

-Beng Hang Tay (email address: taybengh at nusdiscs.bitnet)
 Department of Information Systems and Computer Science
 National University of Singapore

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        int     size, socklen, socket_id;
        struct  sockaddr_in     from_sock;      /* caller's sockaddr_in */
        struct  hostent         *from;

        /* recvfrom() will return caller's identity in from_sock */
        socklen = sizeof(from_sock);
        size = recvfrom(socket_id, buf, buflen, option,
                        (struct sockaddr *)&from_sock, &socklen);
        if (size < 0)
           errmsg("bs_recvfr(): sendto()")

        /* display caller identity */
        printf("\nfrom sock: \n");
        printf("family = %d \n", from_sock.sin_family);
        printf("sin_addr.s_addr = %x \n", ntohl(from_sock.sin_addr.s_addr));
        printf("net number = %x \n", inet_netof(from_sock.sin_addr));
        printf("local address part = %x \n", inet_lnaof(from_sock.sin_addr));
        printf("port # = %u\n", ntohs(from_sock.sin_port));

        /* get the caller's host name */
        from = gethostbyaddr((char*)&from_sock.sin_addr,
                             sizeof(from_sock.sin_addr), type);

        /* display caller host name */
        printf("\nfrom host: \n");
        printf("name %s \n", from->h_name);
        printf("address type %d \n", from->h_addrtype);
        printf("address length %d \n", from->h_length);
        printf("Internet address %s, %x \n", from->h_addr,
                ntohl(from->h_addr));

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