DHCP NX_DHCP_OPTION_DNS_SVR retrieve value in wrong order (endian)

[MiyukiDark]

Describe the bug
When I use nx_dhcp_user_option_retrieve for NX_DHCP_OPTION_DNS_SVR parameter as in the documentation, the received IP address is in reverse byte order.

Running on ARM Cortex M33 with the Keil compiler
Sources included as a submodule from the current Master branch

To Reproduce
Steps to reproduce the behavior:

Code used (as is in the documentation netx-duo/netx-duo-dhcp-client/chapter3.md ), run after DHCP assigned address

/* Obtain the IP address of the DNS server.  */
	size =    sizeof(dns_ip_string);
	status =  nx_dhcp_user_option_retrieve(&DHCPClient, NX_DHCP_OPTION_DNS_SVR, dns_ip_string, &size);
	
	if (status == NX_SUCCESS)
	{
		DNS_server_address = nx_dhcp_user_option_convert(dns_ip_string);
	}

Expected behavior
DHCP is configured to provide a single DNS server address, in my case 10.6.6.1
dns_ip_string contains values [1, 6, 6, 10]
and DNS_server_address result is 0x0106060A
While expected result is 0x0A060601

Impact
It is not a big deal, but shall be either fixed in the code or in the documentation.

Additional context
It will probably be good to have a function that will be ready to decode multiple IP addresses

[MiyukiDark]

As a workaround, I created a function to decode multiple addresses

/*
 * Parse a DHCP option payload that contains one or more IPv4 addresses.
 *
 * Input:
 *   src      - pointer to option data bytes (NOT including option code/len)
 *              Example for 10.6.6.1 would be { 1, 6, 6, 10 } on your system.
 *              Multiple addresses are concatenated back-to-back (4 bytes each).
 *   src_len  - length in BYTES of src (typically option length)
 *
 * Output:
 *   dst      - array of ULONG to fill with IPv4 addresses as 0x0A060601, etc.
 *              i.e., "correct byte order" meaning bytes are [A,B,C,D] -> 0xAABBCCDD
 *   dst_cap  - number of ULONG slots available in dst
 *
 * Returns:
 *   number of IP addresses written to dst
 */
ULONG dhcp_ipv4_list_to_ulongs(const UCHAR *src, size_t src_len,
                               ULONG *dst, size_t dst_cap)
{
    if (!src || !dst || dst_cap == 0) return 0;

    /* Only full IPv4 addresses (4 bytes) */
    size_t count = src_len / 4;
    if (count > dst_cap) count = dst_cap;

    for (size_t i = 0; i < count; ++i) {
        const UCHAR *p = src + (i * 4);

        dst[i] = ((ULONG)p[3] << 24) |
                 ((ULONG)p[2] << 16) |
                 ((ULONG)p[1] <<  8) |
                 ((ULONG)p[0]);
    }

    return count;
}

Used in the following way:

ULONG DNS_server_addresses[16] = { IP_ADDRESS(8, 8, 8, 8) };
ULONG DNS_server_addresses_count = 1;

UCHAR  dns_ip_string[64];
UINT  size;
ULONG  status;

/* Obtain the IP address of the DNS server.  */
	size =    sizeof(dns_ip_string);
	status =  nx_dhcp_user_option_retrieve(&DHCPClient, NX_DHCP_OPTION_DNS_SVR, dns_ip_string, &size);
	
	if (status == NX_SUCCESS)
	{
		DNS_server_addresses_count = dhcp_ipv4_list_to_ulongs(dns_ip_string, size, DNS_server_addresses, sizeof(DNS_server_addresses) / sizeof(ULONG) );
	}

[fdesbiens]

Hi @MiyukiDark.

Thank you for submitting this issue. I will ask a team member to look at it.

[fdesbiens]

@yuxinzhou5 Would you mind taking a look at this one, please?