View Full Version : connection refused in my client server program

October 23rd, 2010, 03:32 PM
I wrote a simple client server socket program in C.
The program did worked I compiled

cc server.c -o server.o
cc client.c -o client.o
and executed

./client.oThings were running successfully.
After this I disconnected and again tried to run the client program this time I got error

ooprs: client1: Connection refused
here is the code server.c

#include <sys/types.h>
#include <sys/socket.h>
#include <stdio.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
main ()
int server_sockfd, client_sockfd;
int server_len, client_len;
struct sockaddr_in server_address;
struct sockaddr_in client_address;
server_sockfd = socket (AF_INET, SOCK_STREAM, 0);
server_address.sin_family = AF_INET;
server_address.sin_addr.s_addr = inet_addr ("");
server_address.sin_port = 9734;
server_len = sizeof (server_address);
bind (server_sockfd, (struct sockaddr *) &server_address, server_len);
listen (server_sockfd, 5);
while (1)
char ch;
printf ("server waiting\n");
client_len = sizeof (client_address);
client_sockfd =
accept (server_sockfd, (struct sockaddr *) &client_address,
read (client_sockfd, &ch, 1);
write (client_sockfd, &ch, 1);
close (client_sockfd);

and client.c

#include <sys/types.h>
#include <sys/socket.h>
#include <stdio.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <stdlib.h>
main ()
int sockfd;
int len;
int result;
struct sockaddr_in address;
char ch = 'A';
sockfd = socket (AF_INET, SOCK_STREAM, 0);
address.sin_family = AF_INET;
address.sin_addr.s_addr = inet_addr ("");
address.sin_port = 9734;
len = sizeof (address);
result = connect (sockfd, (struct sockaddr *) &address, len);
if (result == -1)
perror ("ooprs: client1");
exit (1);
write (sockfd, &ch, 1);
read (sockfd, &ch, 1);
printf ("char from server = %c\n", ch);
close (sockfd);
exit (0);

October 23rd, 2010, 03:47 PM
You set up the port incorrectly, in both the server and the client.

You need to pass the port number to htons(). For example:

server_address.sin_port = htons(9734);

P.S. Also, fix the declaration of the parameter(s) to accept(). Use -Wall when you compile your source code.... and please, refer to the man-pages before using an unfamiliar function from the C library.

October 23rd, 2010, 05:41 PM
I am running this program on local machine and as I mentioned it was executing also so why do I need to use htons here.
When I run this program
./server.o and ./client.o every thing is going fine for some time.
I get following response

char from server = B

When I do a Ctrl+C on server program
and then again try to run

./server.o and ./client.o
then I get ooprs: client1: Connection refused

October 23rd, 2010, 05:53 PM
1. There's no need to bounce the server every time you want to run the client.

2. When you do bounce the server, more than likely the bind() is failing because you are attempting to use a port that technically is still in "use".

3. To mitigate item 2 above, a) check the returned result value from bind(), and b) consider setting up the socket option to "re-use" the port. For example:

int yes = 1;
setsockoption(server_sockfd, SOL_SOCKET, SO_REUSEADDR, (void*) &yes, (socklen_t) sizeof(yes));

As for the use of the htons(), you do it because that is what the documentation says to do. If you want a more detailed or better explanation, use Google.

October 23rd, 2010, 06:05 PM
You are right bind is returning -1 if interrupt and restart server.o I checked.
htons,atons I know have read in beejs network programming guide.
The book I have will deal about setsockopt in coming sections. I am reading and understanding how to write client server programs.
Thanks for your help I was initially thinking my program is not able to maintain proper que of incoming connections.
Is there any command by which I can find out if a port is busy.