C, Sockets: Connection Refused error - c

Question

I've a data acquisition module from which I would like to collect data from the Ethernet port. I'm getting there in steps, currently I would like to just connect to server from a client. I've used Beej's guide to get the basic C code. But I just keep getting this connect error connect: Connection refused.
This is what I do:
The network IP mentioned here is STATIC IP which I have configured.
The port number is set to 50000 on Server side and from the client side I connect to this IP on the port 50000.
I build and run the server side application and then try to connect to it by running a client side application.
One doubt about server side, server side application returns before I start the client side application, so should I keep it running (while(1);) so that I can connect to it from the client side?
What's going wrong am I forgetting something here? Help!
I'm pasting the very slightly modified (IP and port numbers are different) Beej's C code for Server side and Client side here:
Server.c
/*
** server.c
*/
#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
#include <arpa/inet.h>
#include <netinet/in.h>
int main(int argc, char *argv[])
{
// code for a server waiting for connections
// namely a stream socket on port 3490, on this host's IP
// either IPv4 or IPv6.
int sockfd;
struct addrinfo hints, *servinfo, *p;
int rv;
memset(&hints, 0, sizeof hints);
hints.ai_family = AF_UNSPEC; // use AF_INET6 to force IPv6
hints.ai_socktype = SOCK_STREAM;
hints.ai_flags = AI_PASSIVE; // use my IP address
if ((rv = getaddrinfo(NULL, "50000", &hints, &servinfo)) != 0)
{
fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(rv));
exit(1);
}
// loop through all the results and bind to the first we can
for(p = servinfo; p != NULL; p = p->ai_next)
{
if ((sockfd = socket(p->ai_family, p->ai_socktype,
p->ai_protocol)) == -1)
{
perror("socket");
continue;
}
if (bind(sockfd, p->ai_addr, p->ai_addrlen) == -1)
{
close(sockfd);
perror("bind");
continue;
}
break; // if we get here, we must have connected successfully
}
if (p == NULL)
{
// looped off the end of the list with no successful bind
fprintf(stderr, "failed to bind socket\n");
exit(2);
}
freeaddrinfo(servinfo); // all done with this structure
}
Client.c
/*
** client.c
*/
#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
#include <arpa/inet.h>
#include <netinet/in.h>
int main(int argc, char *argv[])
{
// code for a client connecting to a server
// namely a stream socket to www.example.com on port 80 (http)
// either IPv4 or IPv6
int sockfd;
struct addrinfo hints, *servinfo, *p;
int rv;
memset(&hints, 0, sizeof hints);
hints.ai_family = AF_UNSPEC; // use AF_INET6 to force IPv6
hints.ai_socktype = SOCK_STREAM;
if ((rv = getaddrinfo("192.168.2.4", "50000", &hints, &servinfo)) != 0)
{
fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(rv));
exit(1);
}
// loop through all the results and connect to the first we can
for(p = servinfo; p != NULL; p = p->ai_next)
{
if ((sockfd = socket(p->ai_family, p->ai_socktype,
p->ai_protocol)) == -1)
{
perror("socket");
continue;
}
if (connect(sockfd, p->ai_addr, p->ai_addrlen) == -1)
{
close(sockfd);
perror("connect");
continue;
}
break; // if we get here, we must have connected successfully
}
if (p == NULL)
{
// looped off the end of the list with no connection
fprintf(stderr, "failed to connect\n");
exit(2);
}
freeaddrinfo(servinfo); // all done with this structure
}

Answer 1

Your server code is missing listen() and accept() code to "wait" for a connection by calling listen() and then performing an accept() to accept new connections. Doesn't the example you are using show how to do that? Typically you will also fork a new thread for each new connection.
See http://www.linuxhowtos.org/C_C++/socket.htm for more information.
Here's a link to a more complete implementation: http://www.thegeekstuff.com/2011/12/c-socket-programming/

Answer 2

Yes, you need to keep the server program running. In your server program you have created the socket using socket() and bound to an address bind(), now you need to start listening for incoming connections. This is done with the listen() call. Once the socket is listening for incoming connections you have to use the accept() call to actually accept a connection and get the socket for communication with that particular client.
As a quick example, after the freeaddrinfo you could add the following code:
listen(sockfd, 8); /* allow up to 8 pending connections, i.e. created but not accepted */
while (1) {
int clientfd;
struct sockaddr_in client_addr;
socklen_t client_addr_len = sizeof(struct sockaddr_in);
clientfd = accept(sockfd, &client_addr, &client_addr_len);
/* communicate with client by send()/recv() or write()/read() on clientfd */
close(clientfd);
}
This code has the deficiency that only one client at a time is handled. There are a few ways to handle multiple simultaneous clients: multiple processes using fork(), multiple threads, or polling. Each of these approaches are, in my opinion, outside the scope of this question.

Answer 3

Please look at your Server.c file: it does not call listen() at all!
If the targeted server does not listen on the specified port, then it would return RST packet upon receiving SYN packet from the client, so connect() would return with "Connection refused".
Normal flow of functions at server side is socket -> bind -> listen -> accept :
getaddrinfo();
socket();
bind();
listen();
/* accept() goes here */
Please refer to https://beej.us/guide/bgnet/html/multi/syscalls.html#listen

Answer 4

I was getting the error "connection refused" due to not having the entry of remote host in /etc/hosts file. Entry should be present both side. In Client machines /etc/hosts, there should be a entry of server machine and vice versa in below pattern.
<ip address> <hostname with domain> <alias hostname>
This solved the error which i was in getaddrinfo() function.