I have a program that creates a socket (server and client program) and sends a message via a TCP port using that socket. My question is, how can I exchange multiple messages? Every time I send a message the port gets closed and I need to use another port to send another message.
For example, I have to send 2 numbers from the client to the server and the server needs to reply back the total sum of the numbers I send. How would I achieve sending undefined number or even 2 numbers over the SAME port?
Here are the codes (pretty much standard stuff):
Server:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/socket.h>
#include <netinet/in.h>
char* Itoa(int value, char* str, int radix)
{
static char dig[] =
"0123456789"
"abcdefghijklmnopqrstuvwxyz";
int n = 0, neg = 0;
unsigned int v;
char* p, *q;
char c;
if (radix == 10 && value < 0) {
value = -value;
neg = 1;
}
v = value;
do {
str[n++] = dig[v%radix];
v /= radix;
} while (v);
if (neg)
str[n++] = '-';
str[n] = '\0';
for (p = str, q = p + (n-1); p < q; ++p, --q)
c = *p, *p = *q, *q = c;
return str;
}
void error (const char *msg)
{
perror (msg);
exit (1);
}
int main (int argc, char *argv[])
{
if (argc < 2)
{
fprintf (stderr, "ERROR, no port provided\n");
exit (1);
}
//nova varijabla za sumiranje primljenih brojeva
int suma=0;
int sockfd, newsockfd, portno,i;
socklen_t clilen;
char buffer[256];
struct sockaddr_in serv_addr, cli_addr;
int n;
for (i=0;i<2;i++)
{
sockfd = socket (AF_INET, SOCK_STREAM, 0);
if (sockfd < 0) error ("ERROR opening socket");
memset ((char *) &serv_addr, 0, sizeof (serv_addr));
portno = atoi (argv[1]);
portno+=i;
serv_addr.sin_family = AF_INET;
serv_addr.sin_addr.s_addr = INADDR_ANY;
serv_addr.sin_port = htons (portno);
if (bind (sockfd, (struct sockaddr *) &serv_addr, sizeof (serv_addr)) < 0) error ("ERROR on binding");
//test za ispis otvorenog porta
printf("Uspjesno otvoren localhost na portu %d\n", portno);
listen (sockfd, 5);
clilen = sizeof (cli_addr);
newsockfd = accept (sockfd, (struct sockaddr *) &cli_addr, &clilen);
if (newsockfd < 0) error ("ERROR on accept");
memset (buffer, 0, 256);
n = read (newsockfd, buffer, 255);
if (n < 0) error ("ERROR reading from socket");
printf ("%d. proslan broj: %s\n", i+1, buffer);
//print
suma=suma+atoi(buffer);
//radi!! printf("suma je %d\n", suma);
//od klijenta: n = write (sockfd, buffer, strlen (buffer));
//char * itoa ( int value, char * str, int base );
Itoa(suma, buffer, 10);
n = write (newsockfd, buffer, strlen(buffer));
if (n < 0) error ("ERROR writing to socket");
close (newsockfd);
close (sockfd);
}
return 0;
}
Client:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
void error (const char *msg)
{
perror (msg);
exit (1);
}
int
main (int argc, char *argv[])
{
if (argc < 3)
{
fprintf (stderr, "usage %s hostname port\n", argv[0]);
exit (1);
}
int sockfd, portno, n,i;
struct sockaddr_in serv_addr;
struct hostent *server;
char buffer[256];
for (i=0;i<2;i++)
{
portno = atoi (argv[2]);
sockfd = socket (AF_INET, SOCK_STREAM, 0);
if (sockfd < 0)
error ("Ne mogu otvoriti socket!");
server = gethostbyname (argv[1]);
if (server == NULL)
{
fprintf (stderr, "Greska, ne postoji!\n");
exit (1);
}
memset ((char *) &serv_addr, 0, sizeof (serv_addr));
serv_addr.sin_family = AF_INET;
bcopy ((char *) server->h_addr,
(char *) &serv_addr.sin_addr.s_addr,
server->h_length);
portno+=i;
serv_addr.sin_port = htons (portno);
if (connect (sockfd, (struct sockaddr *) &serv_addr, sizeof (serv_addr)) < 0)
error ("ERROR connecting");
printf ("%d. broj za slanje: ", i+1);
memset (buffer, 0, 256);
fgets (buffer, 255, stdin);
n = write (sockfd, buffer, strlen (buffer));
if (n < 0)
error ("ERROR writing to socket");
memset (buffer, 0, 256);
n = read (sockfd, buffer, 255);
if (n < 0)
error ("ERROR reading from socket");
if (i==1) printf ("Suma iznosi: %s\n", buffer);
close (sockfd);
}
return 0;
}
So, for example, I run the code and get this for the server side:
j@PC ~/Desktop/Mreze/Lab1/rijeseno $ ./server2 5000
Uspjesno otvoren localhost na portu 5000
1. proslan broj: 45
Uspjesno otvoren localhost na portu 5001
2. proslan broj: 56
j@PC ~/Desktop/Mreze/Lab1/rijeseno $
And on the client side:
j@PC ~/Desktop/Mreze/Lab1/rijeseno $ ./client2 localhost 5000
1. broj za slanje: 45
2. broj za slanje: 56
Suma iznosi: 101
I've tried putting a while loop so it loops the part with sending but without success. Please explain to me where should I even put it so it works. Thank you!