Potentially incorrect Host Name during DHCP

[Dmitro25]

Hi.
There are following lines of code inside module dhcp.c in functions send_DHCP_DISCOVER() and send_DHCP_REQUEST() :

	// host name
	pDHCPMSG->OPT[k++] = hostName;
	pDHCPMSG->OPT[k++] = 0;          // fill zero length of hostname
	for(i = 0 ; HOST_NAME[i] != 0; i++)
   	pDHCPMSG->OPT[k++] = HOST_NAME[i];
	pDHCPMSG->OPT[k++] = DHCP_CHADDR[3];
	pDHCPMSG->OPT[k++] = DHCP_CHADDR[4];
	pDHCPMSG->OPT[k++] = DHCP_CHADDR[5];
	pDHCPMSG->OPT[k - (i+3+1)] = i+3; // length of hostname

This code adds the last three bytes of the MAC address to the constant DCHP_HOST_NAME, which in sum forms the full DHCP host name. The problem may occur if MAC address contains bytes smaller than 0x20. Some routers (for example, Zyxel Keenetic Omni II) in this case cease to display the page with DHCP clients list at all.
I propose to replace the above code with the following:

	// host name
	pDHCPMSG->OPT[k++] = hostName;
	pDHCPMSG->OPT[k++] = 0;          // fill zero length of hostname
	for(i = 0 ; HOST_NAME[i] != 0; i++)
   	pDHCPMSG->OPT[k++] = HOST_NAME[i];
	pDHCPMSG->OPT[k++] = NibbleToHex(DHCP_CHADDR[3] >> 4); 
	pDHCPMSG->OPT[k++] = NibbleToHex(DHCP_CHADDR[3]);
	pDHCPMSG->OPT[k++] = NibbleToHex(DHCP_CHADDR[4] >> 4); 
	pDHCPMSG->OPT[k++] = NibbleToHex(DHCP_CHADDR[4]);
	pDHCPMSG->OPT[k++] = NibbleToHex(DHCP_CHADDR[5] >> 4); 
	pDHCPMSG->OPT[k++] = NibbleToHex(DHCP_CHADDR[5]);
	pDHCPMSG->OPT[k - (i+6+1)] = i+6; // length of hostname

and to add function NibbleToHex():

char NibbleToHex(uint8_t nibble)
{
  nibble &= 0x0F;
  if (nibble <= 9)
    return nibble + '0';
  else 
    return nibble + ('A'-0x0A);
}

[Ricky-Kwon]

thank you. this will be updated after confirmation.