Go back N protocol implememtation - sockets

Question

I am implementing Go back N protocol in C.I keep a char buffer and append the header informationa and data and send it to the server from the client process.
When I keep window size less than 10, the sequence number takes the value 1-9and occupies only one byte in the buffer. When the window size is >= 10 , sequence number may 1 or 2 bytes in the character array. So I am appending length of sequence number also as a header information. That time I am getting some random data written in the output file at the server. Whereas for window size less than 10 I coded without adding sequence no. length info. Everything works fine that time.
The codes are quiet exhaustive. Yet,
Can anybody suggest any corrections to be made in the code?
client code for window size 10:-
#include<stdio.h>
#include<sys/types.h>
#include<netinet/in.h>
#include<netdb.h>
#include<string.h>
#include<stdlib.h>
#include<unistd.h>
#include<errno.h>
#include<arpa/inet.h>
#include<sys/socket.h>
#include<time.h>
#include<sys/time.h>
unsigned short int checksum_2(void *buffer,unsigned int len,unsigned short int seed)
{
unsigned char *buf1 = (unsigned char*)buffer;
int i;
for(i=0;i<len;i++)
{
seed+=(unsigned int)(*buf1++);
}
//fold 32-bit sum to 16 bit
while(seed>>16)
seed = (seed & 0xFFFF)+ (seed>>16);
return seed;
}
unsigned short int checksum(unsigned char * buff,unsigned int count)
{
register unsigned int sum = 0;
//main summing loop
while(count >1)
{
sum += *((unsigned short int*) buff);
(buff)++;
count = count -2;
}
//add left over byte if any
if(count>0)
{
sum += *((unsigned char *)buff);
}
//fold 32-bit sum to 16 bit
while(sum>>16)
sum = (sum & 0xFFFF)+ (sum>>16);
return (~sum);
}
char* rand_corrupt(unsigned char* buff)
{
int n = strlen(buff);
char* str_temp = (char*)calloc(1,n); //allocate memory for a string
int i;
int num;
num = rand() %100;
if(num>95)
{
for(i=0;i<strlen(buff);i++)
{
buff[i] = buff[i]+1;
}
}
strcpy(str_temp,buff);
return str_temp;
}
char *itoa(long i,char *s,int dummy_radix)
{
sprintf(s,"%ld",i);
return s;
}
void rand_wait()
{
int num;
int i;
num = rand() %100;
if(num<5)
{
for(i=0;i<10;i++)
{
sleep(1);
}
}
return;
}
int
main (int argc, char **argv)
{
int sock,length,n;
struct sockaddr_in server,from;
struct hostent *hp;
long int packets =0;
clock_t t; //to measure CPU time
struct timeval start,end; //to measure actual execution time
struct timeval timer; //for the timer implementation
double time_diff;//to measure the timer for the execution time of code
unsigned short int check;
void* buff;
printf("initializing 2 d array\n");
char buf[1024][1024]={0};
printf("initialisation failed\n");
int nread[1024] = {0,};
char new_buff[65535]={0, };
char ack_buf[65535]={0, };
char* temp;
char checksum_info[1024]={0, } ;
char bytes_info[1024] = {0, } ;
unsigned short int bytes_len;
char bytes_len_str[1024]={0, };
char seqnum[10] = {0,};
int seq_no;
char current;
char data_1[75535]={0, };
unsigned short int check_length;
char check_len_str[1024]={0, };
char ack_check_len[1024]={0, };
unsigned short int ack_checksum_len;
char ack_check[65535]={0, };
unsigned short int ack_checksum;
char temp_buf[65535]={0, };
char temp_buffer[655]={0,};
unsigned short int actual_checksum;
unsigned short int length1;
char content[65535]={0, };
int i,j;
char end_flag =0; //to mark the end of file or error occured while reading file
int total_len[1024]={0,};
char data[1024][6553]= {0,};
char *tmp = NULL;
int msec,trigger;
clock_t difference,initial;
char ack_seqlen_char[8]= {0,};
int ack_seqlen;
int ack_seq;
char ack_seq_char[10] ={0,};
int seqnum_len;
char seqlen_char[10] = {0,};
t = clock();
gettimeofday(&start,NULL);
buff = calloc(1,1024);//allocating memory for message buffer
if(buff == NULL)
{
printf("memory allocation failedi\n");
return 1;
}
temp = calloc(1,65535); //allocating memory for new message
if(temp == NULL)
{
printf("memory allocation failed\n");
return 1;
}
// checking if hostname and the port address is provided //
if(argc!=3)
{
printf("insufficient arguments\n");
exit(1);
}
//create a socket//
sock = socket(AF_INET,SOCK_DGRAM,0);
if(sock<0)
{
printf("error in opening socket\n");
return 1;
}
//to get the hostname of the system or the machine//
hp= gethostbyname(argv[1]);
if(hp==0)
{
printf("Unknown host\n");
return 1;
}
//build the server's IP address //
bzero((char *)&server,sizeof(server));
bcopy((char*)hp->h_addr,(char *)&server.sin_addr,hp->h_length);
server.sin_family = AF_INET;
server.sin_port = htons(atoi(argv[2]));
length = sizeof(server);
/*open the file that we wish to transfer*/
FILE *fp = fopen("alice.txt","rb");
if(fp==NULL)
{
printf("file open error");
return 1;
}
fseek(fp,0,SEEK_END); //if exists read the size of the file
size_t file_size = ftell(fp);
fseek(fp,0,SEEK_SET);
printf("size of the file is %d\n", file_size);
/*find the number of packets*/
if(file_size == 0)
{
packets = 0;
}
else
{
packets = (file_size/1024)+1 ;
}
/*send the number of packets to the server*/
itoa(packets,(char*)buff,10);
printf("packets =%s\n",(char*)buff);
n= sendto(sock,buff,1024,0,(struct sockaddr *)&server,sizeof(struct sockaddr));
if(n<0)
{
printf("error in sending message to the server");
return 1;
}
int loop =1;
/*Read data from file and send it*/
int packetNum = 0;
int N = 10;
int base = 1;
int nextseqnum =1;
int sequence;
int seqnum_next = 1;
while(1)
{
while(nextseqnum<base+N) //send N consecutive packets
{
memset(buf[nextseqnum], 0, 65535); //clear the contents of buf before fread
memset(seqnum,0,10);
memset(seqlen_char,0,10);
memset(checksum_info,0,1024);
memset(check_len_str,0,1024);
memset(bytes_info,0,1024);
memset(bytes_len_str,0,1024);
memset(data[nextseqnum],0,6553);
/*First read file in chunks of 1024 bytes */
nread[nextseqnum] = fread(buf[nextseqnum],1,1024,fp);
printf("Bytes read %d\n",nread[nextseqnum]);
/*if read was success ,send data*/
if(nread[nextseqnum]>0)
{
printf ("I am HERE\n");
check = checksum(buf[nextseqnum],nread[nextseqnum]); //calculate the checksum
printf("checksum is %d\n",check);
itoa(check,checksum_info,10); //convert checksum into string
check_length = strlen(checksum_info); //calculate the length of the checksum
itoa(check_length,check_len_str,10); //convert the checksum lenght to string form
itoa(nread[nextseqnum],bytes_info,10); //the data length in string format
bytes_len = strlen(bytes_info);
itoa(bytes_len,bytes_len_str,10);
itoa(seqnum_next,seqnum,10); //combine seq no,checksum and the data content into one packet
printf("sequence number is %s\n",seqnum);
seqnum_len = strlen(seqnum); //getting the length of the sequence
itoa(seqnum_len,seqlen_char,10); //converting it into string format
strncat(data[nextseqnum],seqlen_char,strlen(seqlen_char));
strncat(data[nextseqnum],seqnum,strlen(seqnum));
strncat(data[nextseqnum],check_len_str,(strlen(check_len_str)));
strncat(data[nextseqnum],checksum_info,(strlen(checksum_info))); //adding checksum
strncat(data[nextseqnum],bytes_len_str,strlen(bytes_len_str)); //adding data length
strncat(data[nextseqnum],bytes_info,strlen(bytes_info)); //adding the data length info
j= seqnum_len+3+bytes_len+check_length;
for(i=0;i<nread[nextseqnum];i++)
{
data[nextseqnum][j] = buf[nextseqnum][i];
j++;
}
total_len[nextseqnum] = nread[nextseqnum]+3+bytes_len+check_length;//finding the total length
data[nextseqnum][total_len[nextseqnum]] = '\0';
n= sendto(sock,data[nextseqnum],total_len[nextseqnum],0,(struct sockaddr *)&server,sizeof(struct sockaddr));///send the data packet after adding the header info
if(n<0)
{
printf("error in sending message to the server");
fclose(fp);
return 1;
}
if(nextseqnum == base)
{
msec = 0;
trigger = 50; /*50 ms*/
initial = clock(); /*start the timer*/
}
nextseqnum++;
seqnum_next = nextseqnum%N;
if(seqnum_next == 0)
{
seqnum_next = N;
}
sleep(1);
}
/*There is something tricky going on with the read..
* Either there was error ,or we reached end of file.
*/
else
{
if(feof(fp))
printf("End of file\n");
if(ferror(fp))
printf("Error reading\n");
end_flag = 1; //set the flag that it has reached EOF or encountered error
break;
}
}
while(1) //wait for the acknowledgement for the sent packets till timeout , here timer value is set to 50 ms
{
difference = clock()-initial;
msec = difference*1000/CLOCKS_PER_SEC;
if(msec<trigger) //if it is not timeout then receive the ack packets
{
memset(ack_buf, 0, 65535); //clear the contents of ack_buf
memset(ack_check_len,0,1024);
memset(ack_check,0,65535);
memset(content,0,65535);
memset(temp_buf,0,65535);
//printf ("Receiving packet\n");
n = recvfrom(sock,ack_buf,1024,MSG_DONTWAIT,&server, &length); //receive the ack from the server
if(n>0)
{
j=0;
for(i=0;i<1;i++)
{
temp_buffer[j] = ack_buf[i];
j++;
}
temp_buffer[j] = '\0';
strcpy(ack_seqlen_char,temp_buffer);//get the length of the ack sequence //number
ack_seqlen = atoi(ack_seqlen_char); //converting it to int
j=0;
for(i=1;i<1+ack_seqlen;i++)
{
ack_seq_char[j]= ack_buf[i];
j++; //next bytes till i=ack_seqlen will be sequence number
}
seq_no = atoi(ack_seq_char);
printf("Ack received for the sequence number %d\n",seq_no);
j =0;
for(i=1+ack_seqlen;i<2+ack_seqlen;i++) //next byte will have the length of checksum
{
temp_buf[j] = ack_buf[i]; //extracting the checksum length
j++;
}
temp_buf[j] = '\0'; //ending the string with a null character
strcpy(ack_check_len,temp_buf); //length of checksum will be in string format
ack_checksum_len = atoi(ack_check_len); //convert it into int
j = 0;
for(i=2+ack_seqlen;i<(2+ack_seqlen+ack_checksum_len);i++) //extract the checksum
{
ack_check[j] = ack_buf[i];
j++;
}
ack_check[j] ='\0';
ack_checksum = atoi(ack_check); //the checksum will be in string format,convert it into the integer format
j=0; //extract the content i.e the actual ack message
while(i<n)
{
content[j] = ack_buf[i];
i++;
j++;
}
content[j] ='\0';
length1 = strlen(content);
actual_checksum = checksum(content,length1);//calculate the actual checksum
printf("checksum of the ack received is %d\t and the checksum of the ack sent is %d\n",actual_checksum,ack_checksum);
if(actual_checksum == ack_checksum) //if the ack is not corrupt then update the base
{
printf("successfully recived packet %d\n",seq_no);
base =seq_no+1;
if(base == nextseqnum) //go to sending next series of packets
{
printf ("base is %d\n", base);
break;
}
else
{
initial = clock(); //start timer for next in-flight packet
}
}
else //if it is a corrupt ack
{
printf("Ack corrupted,wait till timeout\n");
}
} else {
if (end_flag == 1) {
printf ("Reached END\n");
break;
}
}
}
else //if the timer is out, resend the packet from the packet with seqno
// base till nextseqnum-1,start timer
{
initial = clock();
sequence = base;
while(sequence <= nextseqnum-1)
{
n= sendto(sock,data[sequence],total_len[sequence],0,(struct sockaddr *)&server,sizeof(struct sockaddr));///send the data packet after adding the header info
if(n<0)
{
printf("error in sending message to the server");
fclose(fp);
return 1;
}
sleep(0.5);
}
}
}
if(end_flag == 1) //if there had been an error in reading file of EOF had reached break out of
// the outermost while loop
{
printf ("I am at the END\n");
break;
}
}
printf ("Sending finish packet\n");
strcpy(buff,"Finish");
n= sendto(sock,buff,1024,0,(struct sockaddr *)&server,sizeof(struct sockaddr));
if(n<0)
{
printf("error in sending message to the server");
return 1;
}
fclose(fp); //close the file to complete the transmission
t = clock()-t;
gettimeofday(&end,NULL);
double time_taken = ((double)t)/CLOCKS_PER_SEC; //in secconds
printf(" The CPU time for transmission %f seconds \n",time_taken);
double delta = ((end.tv_sec - start.tv_sec)*1000000u+ end.tv_usec - start.tv_usec)/1.e6;
printf("The actual execution time took %f seconds\n", delta);
close(sock); //close api tries to complete the transmission if there is data waiting to be transmitted
return 0;
}