#include <stdio.h>

#include <string.h>

#include <stdlib.h>

typedef unsigned short u16;

typedef unsigned long u32;

struct UDP

{

char SIA[20] = "172.30.1.17";

char DIA[20] = "210.107.197.252";

int SPN = 2443;

int DPN = 80;

char PL[100] = "MMcN Lab.";

}UDP;

u16 SIA[5] = { 0 };

u16 DIA[5] = { 0 };

// tokking IP address

void tokking(char SIP[], char DIP[])

{

char* SIPtok = strtok(SIP, ".");

for (int i = 0; SIPtok != NULL; i++)

{

int l = strlen(SIPtok);

int t = 1;

for (int j = l - 1; j >= 0; j--)

{

SIA[i] += (SIPtok[j] - '0') * t;

t *= 10;

}

SIPtok = strtok(NULL, ".");

}

char* DIPtok = strtok(DIP, ".");

for (int i = 0; DIPtok != NULL; i++)

{

int l = strlen(DIPtok);

int t = 1;

for (int j = l - 1; j >= 0; j--)

{

DIA[i] += (DIPtok[j] - '0') * t;

t *= 10;

}

DIPtok = strtok(NULL, ".");

}

}

u16 udp_sum_calc(u16 len_udp, u16 src_addr[], u16 dest_addr[], int padding, u16 buff[])

{

u16 prot_udp = 17;

u16 padd = 0;

u16 word16;

u32 sum;

// Find out if the length of data is even or odd number. If odd,

// add a padding byte = 0 at the end of packet

if (padding) {

padd = 1;

buff[len_udp] = 0;

}

//initialize sum to zero

sum = 0;

// make 16 bit words out of every two adjacent 8 bit words and

// calculate the sum of all 16 vit words

for (int i = 0; i < len_udp + padd; i = i + 2) {

word16 = ((buff[i] << 8) & 0xFF00) + (buff[i + 1] & 0xFF);

sum = sum + (unsigned long)word16;

}

// add the UDP pseudo header which contains the IP source and destinationn addresses

for (int i = 0; i<4; i = i + 2) {

word16 = ((src_addr[i] << 8) & 0xFF00) + (src_addr[i + 1] & 0xFF);

sum = sum + word16;

}

for (int i = 0; i<4; i = i + 2) {

word16 = ((dest_addr[i] << 8) & 0xFF00) + (dest_addr[i + 1] & 0xFF);

sum = sum + word16;

}

// the protocol number and the length of the UDP packet

sum = sum + prot_udp + len_udp;

// keep only the last 16 bits of the 32 bit calculated sum and add the carries

while (sum >> 16)

sum = (sum & 0xFFFF) + (sum >> 16);

// Take the one's complement of sum

sum = ~sum;

return ((u16)sum);

}

int main()

{

// input SIA

printf("source IP address : %s\n", UDP.SIA);

// scanf("%s", UDP.SIA);

// input DIA

printf("destination IP address : %s\n", UDP.DIA);

// scanf("%s", UDP.DIA);

// input SPN

printf("source port number : %d\n", UDP.SPN);

// scanf("%d", &UDP.SPN);

// input DPN

printf("destination port number : %d\n", UDP.DPN);

// scanf("%d", &UDP.DPN);

char nullbuff;

// scanf("%c", &nullbuff);

// input PL

printf("udp payload : %s\n", UDP.PL);

// fgets(UDP.PL, 100, stdin);

tokking(UDP.SIA, UDP.DIA);

/*

for (int i = 0; i < 4; i++)

printf("%d ", SIA[i]);

printf("\n");

for (int i = 0; i < 4; i++)

printf("%d ", DIA[i]);

printf("\n");

*/

u16 buff[200];

buff[0] = (UDP.SPN >> 8) & 0xFF;

buff[1] = (UDP.SPN) & 0x00FF;

buff[2] = (UDP.DPN >> 8) & 0xFF;

buff[3] = (UDP.DPN) & 0x00FF;

/*

for (int i = 0; i < 4; i++)

printf("%hd ", buff[i]);

printf("\n");

*/

buff[6] = 0;

buff[7] = 0;

for (int i = 0; i < strlen(UDP.PL); i++)

{

buff[8 + i] = UDP.PL[i];

}

u16 len_udp = 8 + strlen(UDP.PL);

buff[4] = (len_udp >> 8) & 0xFF;

buff[5] = (len_udp) & 0x00FF;

/*

for (int i = 0; i < len_udp; i++)

{

printf("%hd ", buff[i]);

if ((i % 2))

printf("\n");

}

*/

u16 checksum = udp_sum_calc(len_udp, SIA, DIA, len_udp & 0x01, buff);

buff[6] = (checksum >> 8) & 0xFF;

buff[7] = (checksum) & 0x00FF;

u16 result = udp_sum_calc(len_udp, SIA, DIA, 0, buff);

printf("checksum : %hd\nresult : %hd\n", checksum, result);

}