TCP/IP program for checksum

//Server

#include<stdio.h>

#include<stdlib.h>

#include<string.h>

#include<sys/types.h>

#include<sys/socket.h>

#include<netinet/in.h>

#include<arpa/inet.h>

char ch2[100];

int makeint(char s){

int d;

d = s — ‘0’;

return d;

}

int checksum(char* s){

//sum

int i,j;

int sum = 0;

int c = 0;

for(i = 0;i<=3;i++){

c = 0;

for(j = strlen(s)-1;j>=0;j = j-4){

c += makeint(s[j-i]);

}

sum+= (c<<i);

}

int num[4] = {0,0,0,0};

//binary and complement

int count = 3;

while(sum != 0){

num[count] = sum%2 ;

sum = sum/2;

count — ;

}

sum = 0;

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

num[i] = (num[i] + 1)%2;

sum += num[i];

}

return sum;

}

char* setsum(char *s){

int len = strlen(s);

int i = 0,j;

char ch1[100];

if(len%4 != 0){

len = len%4;

for(i = 0;i<(4-len);i++)

ch1[i] = ‘0’;

}

for(i = 0;i<100;i++)

ch2[i] = ‘\0’;

ch1[i] = ‘\0’;

strcat(ch1,s);

strcat(ch2,ch1);

printf(“%s”,ch1);

//sum

int sum = 0;

int c = 0;

for(i = 0;i<=3;i++){

c = 0;

for(j = strlen(ch1)-1;j>=0;j = j-4){

c += makeint(ch1[j-i]);

}

sum+= (c<<i);

}

int num[4] = {0,0,0,0};

//binary and complement

int count = 3;

while(sum != 0){

num[count] = sum%2 ;

sum = sum/2;

count — ;

}

printf(“\n”);

char con[4];

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

num[i] = (num[i]+1)%2;

con[i] = num[i] + ‘0’;

//printf(“%c”,con[i]);//ones complement and to char array

}

con[i] = ‘\0’;

strcat(ch2,con);

return ch2;

}

int main(){

int sockfd,newsockfd;

int clilen;

struct sockaddr_in cli_addr, serv_addr;

int i;

char buf[100];

char s[100];

if((sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0){

printf(“Cannot create socket exit\n”);

exit(0);

}

serv_addr.sin_family = AF_INET;

serv_addr.sin_addr.s_addr = INADDR_ANY;

serv_addr.sin_port = htons(6001);

if(bind(sockfd, (struct sockaddr *) &serv_addr,sizeof(serv_addr)) < 0){

printf(“Unable to bind local address”);

exit(0);

}

listen(sockfd, 5);

while(1){

clilen = sizeof(cli_addr);

newsockfd = accept(sockfd, (struct sockaddr *) &cli_addr, &clilen);

if(newsockfd < 0){

printf(“Accept Error \n”);

exit(0);

}

//Message from server

printf(“Server: “);

scanf(“%s”,s);

char *msg;

msg = setsum(s);

for(i = 0;i<100;i++){

buf[i] = ‘\0’;

}

strcpy(buf,msg);

send(newsockfd, buf, 100, 0);

for(i = 0;i<100;i++){

buf[i] = ‘\0’;

}

recv(newsockfd, buf, 100, 0);

int d = checksum(buf);

if(d == 0)

printf(“No error”);

else

{

printf(“Error in the code”);

}

printf(“%s\n”,buf);

close(newsockfd);

}

}

//Client

#include<stdio.h>

#include<stdlib.h>

#include<string.h>

#include<sys/types.h>

#include<sys/socket.h>

#include<netinet/in.h>

#include<arpa/inet.h>

char ch2[100];

int makeint(char s){

int d;

d = s — ‘0’;

return d;

}

int checksum(char* s){

//sum

int i,j;

int sum = 0;

int c = 0;

for(i = 0;i<=3;i++){

c = 0;

for(j = strlen(s)-1;j>=0;j = j-4){

c += makeint(s[j-i]);

}

sum+= (c<<i);

}

int num[4] = {0,0,0,0};

//binary and complement

int count = 3;

while(sum != 0){

num[count] = sum%2 ;

sum = sum/2;

count — ;

}

sum = 0;

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

num[i] = (num[i] + 1)%2;

sum += num[i];

}

return sum;

}

char* setsum(char *s){

int len = strlen(s);

int i = 0,j;

char ch1[100];

if(len%4 != 0){

len = len%4;

for(i = 0;i<(4-len);i++)

ch1[i] = ‘0’;

}

for(i = 0;i<100;i++)

ch2[i] = ‘\0’;

ch1[i] = ‘\0’;

strcat(ch1,s);

strcat(ch2,ch1);

printf(“%s”,ch1);

//sum

int sum = 0;

int c = 0;

for(i = 0;i<=3;i++){

c = 0;

for(j = strlen(ch1)-1;j>=0;j = j-4){

c += makeint(ch1[j-i]);

}

sum+= (c<<i);

}

int num[4] = {0,0,0,0};

//binary and complement

int count = 3;

while(sum != 0){

num[count] = sum%2 ;

sum = sum/2;

count — ;

}

printf(“\n”);

char con[4];

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

num[i] = (num[i]+1)%2;

con[i] = num[i] + ‘0’;

//printf(“%c”,con[i]);//ones complement and to char array

}

con[i] = ‘\0’;

strcat(ch2,con);

return ch2;

}

int main(){

int sockfd;

int clilen;

struct sockaddr_in serv_addr;

int i;

char buf[100];

char s[100];

while(1){

if((sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0){

printf(“Cannot create socket exit\n”);

exit(0);

}

serv_addr.sin_family = AF_INET;

serv_addr.sin_addr.s_addr = inet_addr(“192.168.0.15”);

serv_addr.sin_port = htons(6001);

if((connect(sockfd, (struct sockaddr *) &serv_addr,sizeof(serv_addr))) < 0){

printf(“Unable to connect to server \n”);

exit(0);

}

for(i = 0;i<100;i++){

buf[i] = ‘\0’;

}

recv(sockfd, buf, 100, 0);

int d = checksum(buf);

if(d == 0)

printf(“No error”);

else

{

printf(“Error in the code”);

}

printf(“%s\n”,buf);

for(i = 0;i<100;i++){

buf[i] = ‘\0’;

}

//Message from client

printf(“Client: “);

scanf(“%s”,s);

char *msg;

msg = setsum(s);

strcpy(buf,msg);

send(sockfd, buf, 100, 0);

close(sockfd);

}

}