Can't close non-blocking UDP socket in C Fedora16 - c

Question

I built very basic UDP chat using C language and Fedora 16 OS.
When my server connect, he got 5 ports and listen to them.
My problem is: when I'm trying to connect to the server with new client but gives him port that my server don't know, I want him to exit Immediately.
I don't know how to check the "MSG_DONTWAIT" flag.
Here is my code:
Server side:
#define MAX_MESSAGE_SIZE 1024
#define SERVER_CONNECTIONS 5
// Implementation of server that manages a chat.
#include "server.h"
int main(int argc,char* argv[])
{
if(argc != 2) //check if user insert more then one argument to the program
{
printf("Usage server <port>\n‬‬");
fflush(stdout);
exit (-1);
}
/*!
========Server creation flow:========
1) create the socket
2) bind the socket to a port
3) recvfrom (read from socket)
4) sendto (close the socket)
5) close the socket
*/
//!------------------------------------- 1) create the socket-------------------------------------
//!------------------------------- 2) bind the socket to a port-----------------------------------
int fd[SERVER_CONNECTIONS]; //socket descriptor
int port[SERVER_CONNECTIONS]; //socket fd port
int i=0;
for(i=0; i<SERVER_CONNECTIONS; i++)
{
port[i] = atoi(argv[1])+i;
}
create_sockets(fd, port);
char buf[MAX_MESSAGE_SIZE]; //used by read() & write()
int maxfd = find_maxfd(fd);
struct sockaddr_in cli; //used by read() & write()
int cli_len = sizeof(cli); //used by read() & write()
fd_set readfds;
fd_set writefds;
struct timeval timeout;
timeout.tv_sec = 1;
int nbytes=0;
while(1)
{
FD_ZERO(&readfds);
FD_ZERO(&writefds);
for(i=0; i<SERVER_CONNECTIONS; i++)
{
FD_SET(fd[i], &readfds);
FD_SET(fd[i], &writefds);
}
/* Now use FD_SET to initialize other fd’s that have already been returned by accept() */
if (select(maxfd+1, &readfds, 0, 0, 0) < 0)
{
perror("select");
exit(1);
}
for(i=0; i<SERVER_CONNECTIONS; i++)
{
//!------------------------------- recvfrom (read from socket)-----------------------------------
if(FD_ISSET(fd[i], &readfds))
{
fprintf(stderr, "ready to read from %d\n", fd[i]);
memset(&buf, 0, sizeof(buf)); //init buf
if((nbytes = recvfrom(fd[i], buf, sizeof(buf), 0 /* flags */, (struct sockaddr*) &cli, (socklen_t*)&cli_len)) < 0)
{
perror("recvfrom");
exit(1);
}
//!------------------------------- sendto (close the socket)-----------------------------------
FD_ZERO(&writefds);
FD_SET(fd[i], &writefds);
if (select(maxfd+1, 0, &writefds, 0, &timeout) < 0)
{
perror("select");
exit(1);
}
if(FD_ISSET(fd[i], &writefds))
{
fprintf(stderr, "ready to write to %d\n", fd[i]);
string_to_hex(buf);
if ((nbytes = sendto(fd[i], buf, strlen(buf), 0 /* flags */, (struct sockaddr*) &cli, sizeof(cli))) < 0)
{
perror("sendto");
exit(1);
}
}
}
}
}
return 0;
}
void create_sockets(int fd[], int port[])
{
int i=0;
for(i=0; i<SERVER_CONNECTIONS; i++)
{
//!------------------------------------- 1) create the socket-------------------------------------
if((fd[i] = socket(PF_INET, SOCK_DGRAM, 0)) < 0)
{
perror("socket");
exit(1);
}
//!------------------------------- 2) bind the socket to a port-----------------------------------
struct sockaddr_in srv; //used by bind()
srv.sin_family = AF_INET; //use the Internet address family
srv.sin_port = htons(port[i]); //socket ‘fd’ to port
srv.sin_addr.s_addr = htonl(INADDR_ANY); //a client may connect to any of my addresses
if(bind(fd[i], (struct sockaddr*) &srv, sizeof(srv)) < 0)
{
perror("bind");
exit(1);
}
}
}
int find_maxfd(int fd[])
{
int i=0;
int res=fd[0];
for(i=1; i<SERVER_CONNECTIONS; i++)
{
if(fd[i]>res)
{
res = fd[i];
}
}
return res;
}
void string_to_hex(char buf[])
{
int buf_size = strlen(buf);
char result[buf_size*3+1];
memset(&result, 0, sizeof(result));
char temp[4];
int i=0;
for (i=0; i<buf_size-1; i++)
{
memset(&temp, 0, sizeof(temp));
sprintf(temp, "%X:", (int)buf[i]);
strcat(result, temp);
}
memset(&temp, 0, sizeof(temp));
sprintf(temp, "%X", (int)buf[i]);
strcat(result, temp);
strcpy(buf, result);
}
Client side:
#define MAX_MESSAGE_SIZE 1024
// Implementation of client that will use the chat.
#include "client.h"
int main(int argc,char* argv[])
{
if(argc != 3) //check if user insert more then one argument to the program
{
printf("Usage client <host name> <port>\n‬‬");
fflush(stdout);
exit(-1);
}
/*!
========Client creation flow:========
1) create the socket
2) sendto (close the socket)
3) recvfrom (read from socket)
4) close the socket
*/
fprintf(stderr, "please enter something: \n");
//!------------------------------------- 1) create the socket-------------------------------------
int fd; //socket descriptor
if((fd = socket(PF_INET, SOCK_DGRAM, 0)) < 0)
{
perror("socket");
exit(1);
}
struct sockaddr_in srv; //used by sendto()
srv.sin_family = AF_INET;
srand ( time(NULL) ); //new random seed
int rand_num = (rand() % 5) + atoi(argv[2]); //
srv.sin_port = htons(rand_num);
char *srv_name = argv[1];
struct hostent *hp; //ptr to host info for remote
hp = gethostbyname(srv_name);
if( hp == NULL)
{
herror("gethostbyname");
exit(-1);
}
srv.sin_addr.s_addr = ((struct in_addr*)(hp->h_addr))->s_addr; //set IP Address to "srv_name"
char buf[MAX_MESSAGE_SIZE]; //used by read() & write()
int nbytes=0;
while(1)
{
//!------------------------------------- 2) sendto (close the socket)-------------------------------------
memset(&buf, 0, sizeof(buf)); //init buf
fgets(buf, sizeof(buf), stdin); //get input from user
if(strcmp(buf, "quit\n") == 0)
{
break;
}
if(!((strlen(buf) == 1) && (buf[1] == '\n')))
{
buf[strlen(buf)-1] = '\0';
}
//write_to_server(fd, buf, srv);
if ((nbytes = sendto(fd, buf, strlen(buf), MSG_DONTWAIT /* flags */, (struct sockaddr*) &srv, sizeof(srv)) < 0))
{
perror("sendto");
exit(1);
}
//!------------------------------------- 3) recvfrom (read from socket)-------------------------------------
memset(&buf, 0, sizeof(buf)); //init read_buf
//read_from_server(fd, buf);
if((nbytes = recvfrom(fd, buf, sizeof(buf), 0 /* flags */, 0, 0) < 0))
{
perror("recvfrom");
exit(1);
}
if( (errno == EAGAIN) || (errno == EWOULDBLOCK ) )
{
perror("EWOULDBLOCK");
exit(1);
}
printf("%s\n", buf); //print result to client
fflush(stdout);
}
//!------------------------------------- close the socket-------------------------------------
close(fd);
return 0;
}

Answer 1

I got it..
You need to use connect function from client and the "MSG_DONTWAIT" flag.
then when the client connect and you type anything he exit right away..
//!--------------- 2) connect to the server--------------------------
if(connect(fd, (struct sockaddr*) &srv, sizeof(srv)) < 0) //connect to server "srv_name"
{
perror("connect");
exit(-1);
}