printf("Can't open net driver '%s'\n", netcfg);
        else
        {                                           /* Save ether address */
            memcpy(np->mac, ether_addr(dtype), MACLEN);
            np->dtype = dtype;                      /* ..and driver type */
            b = (BYTE)(np->ip >> 24);
            if (read_cfgstr(fname, "mask", temps, 30))
                np->mask = atoip(temps);            /* Get netmask */
            else
                np->mask = b<128 ? 0xff000000L: b<192 ? 0xffff0000L:0xffffff00L;
            if (read_cfgstr(fname, "gate", temps, 30))
                np->gate = atoip(temps);            /* Get gateway IP addr */
            else
                np->gate = 0;
        }
    }
    return(dtype);
}

/* Return ptr to local node 'n' (n=0 for first), return 0 if doesn't exist
** Used by IP functions to get my netmask & gateway addresses */
NODE *locnode_n(int n)
{
    return(n==0 ? &locnode : 0);
}

/* Check for incoming packets, send response if required
** Return state-change value if ARP response or datagram received */
int do_receive(GENFRAME *gfp)
{
    NODE node;
    ARPKT *arp;
    IPKT *ip;
    ICMPKT *icmp;
    int rxlen, txlen, len, ret=0;

    if ((rxlen=get_frame(gfp)) > 0)                 /* Any incoming frames? */
    {
        ip = getframe_datap(gfp);
        if (is_arp(gfp, rxlen))
        {                                           /* ARP response? */
            arp = getframe_datap(gfp);
            if (arp->op==ARPREQ && arp->dip==locnode.ip)
            {                                       /* ARP request? */
                node.ip = arp->sip;                 /* Make ARP response */
                memcpy(node.mac, arp->smac, MACLEN);
                txlen = make_arp(gfp, &locnode, &node, ARPRESP);
                put_frame(gfp, txlen);              /* Send packet */
            }
            if (arp->op==ARPRESP && arp->dip==locnode.ip)
            {                                       /* ARP response? */
                memcpy(remnode.mac, arp->smac, MACLEN);
                ret = ARP_RX;
            }
        }
        else if ((rxlen=is_ip(gfp, rxlen))!=0 &&    /* IP datagram? */
                 ip->i.dip==locnode.ip || ip->i.dip==BCASTIP)
        {
            getip_srce(gfp, &node);
            if ((len=is_icmp(ip, rxlen))!=0)        /* ICMP? */
            {
                icmp = (ICMPKT *)ip;
                if (icmp->c.type == ICREQ)          /* Echo request? */
                {
                    len = (WORD)maxi(len, 0);       /* Make response */
                    txlen = make_icmp(gfp, &locnode, &node, ICREP,
                                      icmp->c.code, (WORD)len);
                    put_frame(gfp, txlen);          /* Send packet */
                }
                else if (icmp->c.type == ICUNREACH)
                    printf("ICMP: destination unreachable\n");
            }
            else if ((len=is_udp(ip, rxlen))!=0)    /* UDP? */
            {
                ret = udp_receive(gfp, maxi(len, 0));
            }
        }
    }
    return(ret);
}

/* Receive a UDP datagram: return non-0 if client state-change */
int udp_receive(GENFRAME *gfp, int len)
{
    UDPKT *udp;
    int ret=0;
    NODE loc, rem;
    char temps[30];
    time_t t;

    udp = getframe_datap(gfp);
    getudp_srce(gfp, &rem);                         /* Get srce & dest nodes */
    getudp_locdest(gfp, &loc);
    if (loc.port == locnode.port)                   /* Client response */
    {
        disp_data(udp->data, len);                  /* Display data.. */
        ret = CLIENT_DONE;                          /* ..and exit */
    }
    else if (loc.port == ECHOPORT)                  /* Echo req: resend data */
        udp_transmit(gfp, &loc, &rem, udp->data, len);
    else if (loc.port == DAYPORT)                   /* Daytime req: get date */
    {
        time(&t);                                   /* Get standard string */
        strcpy(temps, ctime(&t));
        strcpy(&temps[24], "\r\n");                 /* Patch newline chars */
        udp_transmit(gfp, &loc, &rem, (BYTE *)temps, 26);
    }
    else                                            /* Unreachable: send ICMP */
    {
        swap_udp(udp);
        put_frame(gfp, icmp_unreach(gfp, &loc, &rem, UNREACH_PORT));
    }
    return(ret);
}

/* Send a UDP datagram, given destination node, data and length */
void udp_transmit(GENFRAME *gfp, NODE *sp, NODE *dp, void *dat, int len)
{
    UDPKT *udp;

    udp = getframe_datap(gfp);
    memmove(udp->data, dat, len);
    put_frame(gfp, make_udp(gfp, sp, dp, (WORD)maxi(len, 0)));
}

/* Send a UDP datagram, given destination node, data and length */
void udp_transmit_file(GENFRAME *gfp, NODE *sp, NODE *dp, FILE *in)
{
    UDPKT *udp;
    WORD len;

    udp = getframe_datap(gfp);
    len = fread(udp->data, 1, sizeof(udp->data), in);
    put_frame(gfp, make_udp(gfp, sp, dp, len));
}

/* Poll the network interface to keep it alive */
void do_poll(GENFRAME *gfp)
{
    poll_net(gfp->g.dtype);
}

/* Convert string (numeric or alphabetic) into a port number, 0 if error */
WORD str2service(char *str)
{
    WORD port=0;

    if (isdigit(*str))
        port = atoi(str);
    else if (!stricmp(str, "echo"))
        port = ECHOPORT;
    else if (!stricmp(str, "daytime"))
        port = DAYPORT;
    else if (!stricmp(str, "time"))
        port = TIMEPORT;
    else if (!stricmp(str, "snmp"))
        port = SNMPORT;
    return(port);
}

/* Display the incoming UDP data */
void disp_data(BYTE *data, int len)
{
    BYTE b;
    int i, n, oset=0;

    if (!binmode)
    {
        while (len--)
        {
            b = *data++;
            if ((b>=' '&&b<='~') || b=='\n')
                putchar(b);
            else
                putchar(' ');
        }
    }
    else while (len > 0)
    {
        n = mini(len, 24);
        printf("%04X: ", oset);
        for (i=0; i<n; i++)
            printf("%02X ", data[i]);
        printf("\n      ");
        for (i=0; i<n; i++, data++)
        {
            putchar(' ');
            putchar(*data>=' ' && *data<='~' ? *data : 0);
            putchar(' ');
        }
        len -= n;
        oset += n;
        putchar('\n');
    }
}

/* Display usage help */
void disp_usage(void)
{
    printf("Usage:    DATAGRAM [options] [IP_addr [portnum [data]]]\n");
    printf("                    Default port number is %u\n", DEFPORT);
    printf("Options:  -b        Binary data (hexadecimal data display)\n");
    printf("          -i name   Input data filename\n");
    printf("          -c name   Config filename (default %s)\n", cfgfile);
    printf("          -u        UDP datagram display\n");
    printf("          -v        Verbose (frame) display\n\n");
    printf("Example:  DATAGRAM -c test.cfg 10.1.1.1 echo \"test string\"\n");
}

/* Ctrl-break handler: set flag and return */
void break_handler(int sig)
{
    breakflag = sig;
}

/* EOF */