C, Sockets: Connection Refused error

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:

1. The network IP mentioned here is STATIC IP which I have configured.

2. The port number is set to 50000 on Server side and from the client side I connect to this IP on the port 50000.

3. 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/