Linux TCP connection refused - c

Question

I am doing a TCP connection program and I want to set the address and connection step as a function. The program can be compiled but when I running it the screen displays: ERROR CONNECTION: Connection refused. Could you please help me? Here is the server code:
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <string.h>
void error(char *msg)
{
perror(msg);
exit (1);
}
struct sockaddr_in createSockAddr(int portnum)
{
struct sockaddr_in addr;
addr.sin_family = AF_INET;
addr.sin_addr.s_addr = INADDR_ANY;
addr.sin_port = htons(portnum);
return addr;
}
int createServerSocket(struct sockaddr_in serv_addr)
{
int newsockfd;
int sockfd;
int clilen;
sockfd = socket(AF_INET, SOCK_STREAM, 0);//create socket
if (sockfd < 0)
error("ERROR opening socket");
//bind socket
if (bind(sockfd, (struct sockaddr *) &serv_addr,sizeof(serv_addr)) < 0)
error("ERROR on binding");
listen(sockfd,5);//listen
clilen = sizeof(serv_addr);
newsockfd = accept(sockfd, (struct sockaddr *) &serv_addr, &clilen);//accept
if (newsockfd < 0)
error("ERROR on accept");
return newsockfd;
}
int main(int argc, char *argv[])
{
int sockfd, newsockfd, portnum, clilen;
char buffer[256];
struct sockaddr_in serv_addr, cli_addr;
int n;
if (argc < 2) {
fprintf(stderr,"ERROR, no port provided\n");
exit (2);
}
portnum = atoi(argv[1]);
serv_addr = createSockAddr(portnum);
newsockfd = createServerSocket(serv_addr);
bzero(buffer,256);
n = read(newsockfd,buffer,255);
if (n < 0) error("ERROR reading from socket");
printf("Here is the message: %s\n",buffer);
n = write(newsockfd,"I got your message",18);
if (n < 0) error("ERROR writing to socket");
return 0;
}
Here is the client code:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
void error(char *msg)
{
perror(msg);
exit(1);
}
struct sockaddr_in createSockAddr(int portnum)
{
struct sockaddr_in addr;
addr.sin_family = AF_INET;
addr.sin_addr.s_addr = inet_addr("127.0.0.1");
addr.sin_port = htons(portnum);
return addr;
}
int createClientSocket(struct sockaddr_in sockAddr)
{
int sockfd;
sockfd = socket(AF_INET, SOCK_STREAM, 0);
if (sockfd < 0)
error("ERROR opening socket");//create socket
if (connect(sockfd,(struct sockaddr *)&sockAddr,sizeof(sockAddr)) < 0)
error("ERROR connecting");
return sockfd;
}
int main(int argc, char *argv[])
{
int sockfd, portnum, n;
struct sockaddr_in serv_addr;
struct hostent *server;
char buffer[256];
if (argc < 3) {
fprintf(stderr,"usage %s hostname port\n", argv[0]);
exit(2);
}
portnum = atoi(argv[2]);
serv_addr = createSockAddr(portnum);
sockfd = createClientSocket(serv_addr);
printf("Please enter the message: ");
bzero(buffer,256);
fgets(buffer,255,stdin);
n = write(sockfd,buffer,strlen(buffer));
if (n < 0)
error("ERROR writing to socket");
bzero(buffer,256);
n = read(sockfd,buffer,255);
if (n < 0)
error("ERROR reading from socket");
printf("%s\n",buffer);
return 0;
}

Answer 1

The only questionable thing I see is that you aren't zeroing the sockaddr_in structs before you assign the fields. Otherwise, it looks fine. It's a little atypical to pass structures around (as opposed to pointers to those structures) in C but I don't see any reason why it wouldn't work. (By "zeroing", I mean memset(&addr, 0, sizeof(addr))).)

Answer 2

The code compiles (with some minor warnings), but works for me (client ignores the first parameter and expects port at the second).
Please, try again, and you can also run the server and client under the supervision of strace which is a great tool to see kernel syscalls that an application performs.