File content as of revision 0:a56239ae90c2:

#include "DHCPOptions.h"

int DHCPOptions::getOptions(char* tftp_server, const char* mac_address, const uint32_t timeout)
{
    char mac_bin[DHCP_CHADDR_SIZE + 1] = {0}; // Initialize the hardware address array to zeros.
    int bind_result;
    DHCPPacket pkt, rec_pkt;
    
    // Generate binary version of the MAC string.
    macStrToBin(mac_bin, mac_address);
    
    SocketAddress dhcp_addr(DHCP_BROADCAST_ADDRESS, DHCP_SERVER_PORT);
    m_sock.open(m_eth);
    m_sock.set_timeout(timeout);
    bind_result = m_sock.bind(DHCP_CLIENT_PORT);
    
    if (bind_result < 0)
    {
        printf("DHCP Port Binding Failed: %d\n", bind_result);
        return -1; // DHCP port bind failed.
    }
    
    // Construct a DHCP DISCOVER packet
    pkt.op = DHCP_OP_REQUEST;
    pkt.htype = DHCP_HTYPE;
    pkt.hlen = DHCP_HLEN;
    pkt.hops = DHCP_HOPS;
    pkt.xid = htonl(rand());
    pkt.secs = htons(DHCP_SECS);
    pkt.flags = htons(DHCP_FLAGS);
    pkt.ciaddr = htonl(DHCP_CIADDR);
    pkt.yiaddr = htonl(DHCP_YIADDR);
    pkt.siaddr = htonl(DHCP_SIADDR);
    pkt.giaddr = htonl(DHCP_GIADDR);
    // MAC address with padding - 16 bytes total
    memcpy(pkt.chaddr, mac_bin, DHCP_CHADDR_SIZE);
    memset(pkt.sname, 0, DHCP_SNAME_SIZE);
    memset(pkt.file, 0, DHCP_FILE_SIZE);
    // Options List
    pkt.magic = htonl(DHCP_MAGIC_COOKIE);
    pkt.op_mtype = 53;
    pkt.mtype_len = 1;
    pkt.mtype = 1;
    char discover_options[] = {DHCP_PREQLIST, 1, DHCP_OPTION_TFTPSERVER, DHCP_OPTION_STOP};
    memcpy(pkt.options, discover_options, sizeof(discover_options));
    
    // Send read request
    int bytes_sent = m_sock.sendto(dhcp_addr, (char*)&pkt, sizeof(DHCPPacket));
    if (bytes_sent < 0)
    {
        printf("DHCP Discover Failed: %d\n", bytes_sent);
        return -2; // DHCP Discover send failed.
    }
    else
    {
        //printf("Sent: %d\n", bytes_sent);
    }
    
    // Get data packet from the DHCP server
    int bytes_received = m_sock.recvfrom(&dhcp_addr, (char*)&rec_pkt, sizeof(DHCPPacket));
    if (bytes_received < 0)
    {
        printf("DHCP Offer Failed: %d\n", bytes_received);
        return -3; // UDP packet recevie failed.
    }
    else
    {
        //printf("Received: %d\n", bytes_received);
    }
    
    if (decodeOptions(tftp_server, rec_pkt) < 0)
    {
        printf("Failed to find the TFTP server option.\n");
        return -4; // Failed to find the TFTP server name option from the DHCP offer response packet.
    }
    
    m_sock.close();
    return 0;
}

int DHCPOptions::decodeOptions(char* tftp_server, DHCPPacket& pkt)
{
    char* dhcp_options = pkt.options;
    int optionIndex = 0;
    int optionLength = 0;
    
    while (optionIndex < DHCP_OPTIONS_SIZE && dhcp_options[optionIndex] != DHCP_OPTION_STOP)
    {
        // Get the length of the current DHCP option field.
        optionLength = dhcp_options[optionIndex + 1];
        
        // Check for the TFTP server option code.
        if (dhcp_options[optionIndex] == DHCP_OPTION_TFTPSERVER)
        {
            // Copy the TFTP server string to the output string.
            memcpy(tftp_server, dhcp_options + optionIndex + 2, optionLength);
            return 0;
        }
        
        // Move to the next option.
        optionIndex += 2 + optionLength;
    }
    
    return -1; // Failed to find the DHCP option.
}

int DHCPOptions::macStrToBin(char* macBin, const char* macStr)
{
    if (strlen(macStr) != MAC_STRING_LENGTH)
    {
        return -1; // Invalid MAC string
    }
    else
    {
        for (int byteIndex = 0; byteIndex < 6; byteIndex++)
        {
            macBin[byteIndex] = (charToNum(macStr[byteIndex * 3]) * 16) + charToNum(macStr[(byteIndex * 3) + 1]);
        }
    }
    
    return 0;
}

unsigned char DHCPOptions::charToNum(const char input)
{
    if(input >= '0' && input <= '9')
    {
        return input - '0';
    }
    if(input >= 'A' && input <= 'F')
    {
        return input - 'A' + 10;
    }
    if(input >= 'a' && input <= 'f')
    {
        return input - 'a' + 10;
    }

    return 0;
}