problem with sending messages in socket programs

shifter · 08-04-2008, 08:31 AM

I have a big problem with sockets.
My two programs are:

- server.c (TCP server)
- client..c (TCP client)

I type in first shell:

#./server 3000 (./server <port number>)

and after I type:

#./client CC1 3000 (./client <hostname> <port number>)

I send a message from client to server, but server don't receive above message.

vladmihaisima · 08-04-2008, 09:43 AM

Without some code, nobody will be able to help you.

shifter · 08-04-2008, 09:49 AM

I am doing some test.
The client.c program send byte, but the error is in server.c. The server don't receive byte. recv return -1, the error is:

Error code = 88: Socket operation on non-socket

shifter · 08-04-2008, 10:32 AM

My code is the following:

#include <stdio.h>
#include <errno.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>

int main(int argc, char*argv[])
{

int connectFd, listenFd, portn, clientlen, nbyte, i;
char buffer[256];
struct sockaddr_in addrserv, addrclient;
int cltlen;

if (argc < 2) printf("Devi inserire il numero di porta");
listenFd = socket(AF_INET, SOCK_STREAM, 0);
printf("listenFd = %d ", listenFd);
if (listenFd < 0)
perror("Errore nella apertura del socket");
bzero(&addrserv, sizeof(addrserv));
portn = atoi(argv[1]);
addrserv.sin_family = AF_INET;
addrserv.sin_addr.s_addr = htonl(INADDR_ANY);
addrserv.sin_port = htons(portn);
if (bind(listenFd, (struct sockaddr*)&addrserv, sizeof(addrserv)) < 0)
perror("Errore nella operazione di bind del socket");
if (listen(listenFd, 5) < 0)
perror("Errore nella operazione di listen del socket");
cltlen = sizeof(addrclient);

if (connectFd = accept(listenFd, (struct sockaddr*)&addrclient, (socklen_t*)&cltlen) <= 0) {
printf("ConnectFd = %d ", connectFd);
perror("Errore nella operazione di accept ");
}
printf("ConnectFd = %d ", connectFd);
bzero(buffer, 256);
if (nbyte = recv(connectFd, buffer, 255, 0) < 0) {
printf("Codice errore: %d", errno);
perror("Errore nella ricezione");
}
printf("Byte ricevuti: %d", nbyte);

shutdown(connectFd, SHUT_RDWR);
close(connectFd);
return 0;

}

In my opinion the problem is in accept function. Accept() return 0 as socket descriptor, but I think that is not valid!

vladmihaisima · 08-04-2008, 12:58 PM

From man page of accept:

Quote:

On success, accept() returns a non-negative integer that is a descriptor for the accepted socket. On error, -1 is returned, and errno is set appropriately.

0 seems a good value. You should change the test to:

Code:

if (connectFd = accept(listenFd, (struct sockaddr*)&addrclient, (socklen_t*)&cltlen) < 0) {

And please, when you put code, use the code tag. (it is in the editor...)

paulsm4 · 08-04-2008, 09:46 PM

Another problem is that you need to handle errors a bit better. In this example, I simply terminate the program with a "perror()" and a "return 1" if anything goes wrong.

Also note the "code tags" vladmihaisima mentioned:

Code:

#include <stdio.h>
#include <errno.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>

int main(int argc, char*argv[])
{

  int connectFd, listenFd, portn, clientlen, nbyte, total_bytes, i;
  char buffer[256];
  struct sockaddr_in addrserv, addrclient;
  int cltlen;

  if (argc < 2) 
  {
    printf("Devi inserire il numero di porta");
    return 1;
  }

  listenFd = socket(AF_INET, SOCK_STREAM, 0);
  if (listenFd < 0)
  {
    perror("Errore nella apertura del socket");
    return 1;
  }
  printf("listenFd = %d ", listenFd);

  bzero(&addrserv, sizeof(addrserv));
  portn = atoi(argv[1]);
  addrserv.sin_family = AF_INET;
  addrserv.sin_addr.s_addr = htonl(INADDR_ANY);
  addrserv.sin_port = htons(portn);
  if (bind(listenFd, (struct sockaddr*)&addrserv, sizeof(addrserv)) < 0)
  {
    perror("Errore nella operazione di bind del socket");
    return 1;
  }

  if (listen(listenFd, 5) < 0)
  {
    perror("Errore nella operazione di listen del socket");
    return 1;
  }

  cltlen = sizeof(addrclient);
  if (connectFd = accept(listenFd, (struct sockaddr*)&addrclient, (socklen_t*)&cltlen) < 0) 
  {
    perror("Errore nella operazione di accept ");
    return 1;
  }
  printf("ConnectFd = %d ", connectFd);

  bzero(buffer, 256);
  if (nbyte = recv(connectFd, buffer, 255, 0) < 0)
  {
     printf("Codice errore: %d", errno);
     perror("Errore nella ricezione");
  }
  printf("Byte ricevuti: %d", nbyte);

  shutdown(connectFd, SHUT_RDWR);
  close(connectFd);
  close(listenFd);
  printf ("Ciao!\n");
  return 0;
}

Also - are you sure the client actually *sends* a byte?

Please be sure to put the same kind of error checking into your client as we did above, in your server.

Also: consider a tool like Wireshark (formerly "Ethereal") to study the bytes being sent and received over the specified port:

http://www.wireshark.org/

'Hope that helps .. PSM

shifter · 08-05-2008, 06:13 AM

The program don't work.
About ethereal or wireshark use, I am trying my client and server on local host.

My client is the following:

#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/types.h>
#include <sys/socket.h>

int main(int argc, char* argv[]) {

int sockfd, nbyte;
struct sockaddr_in srv_addr;
char buffer[256];

if (argc != 3) {
printf("Command syntax \n");
printf(" server <IP ADDRESS> <PORT NUMBER> \n");
}
else {
if (sockfd = socket(AF_INET, SOCK_STREAM, 0) < 0) {
printf("Error code: %d\n", errno);
perror("Error in socket()");
}
srv_addr.sin_family = AF_INET;
srv_addr.sin_port = htons(argv[2]);
srv_addr.sin_addr.s_addr = inet_addr(argv[1]);

if (connect(sockfd, (struct sockaddr*)&srv_addr, sizeof(srv_addr)) < 0) {
printf("Error code: %d\n", errno);
perror("Error in connect()");
}
printf("Inserrt message to send");
bzero(buffer, 256);
fgets(buffer, 255, stdin);

if (nbyte = send(sockfd, buffer, strlen(buffer), 0) < 0) {
printf("Error code: %d\n", errno);
perror("Error in send()");
}
printf("Sent bytes: %d ", nbyte);
if (nbyte < 0)
perror("Errore nella scrittura su socket");
bzero(buffer, 255);

}
shutdown(sockfd, SHUT_RDWR);
close(sockfd);
return 0;

}

My server program is the following:

#include <stdio.h>
#include <errno.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/types.h>
#include <sys/socket.h>

int main(int argc, char* argv[]) {

int sockfd, new_fd;
struct sockaddr_in srv_addr, clt_addr;
int clt_size, nbyte;
char buffer[256];

if (argc != 2) {
printf("Command syntax \n");
printf(" server <PORT NUMBER> \n");
}
else {
if (sockfd = socket(AF_INET, SOCK_STREAM, 0) < 0)
perror("Error in socket()");
clt_addr.sin_family = AF_INET;
clt_addr.sin_port = htons(argv[1]);
clt_addr.sin_addr.s_addr = htonl(INADDR_ANY);
memset(srv_addr.sin_zero, '\0', sizeof(srv_addr.sin_zero));

if (bind(sockfd, (struct sockaddr*)&clt_addr, sizeof(srv_addr)) < 0) {
printf("Error code: %d\n", errno);
perror("Error in bind()");
}
if (listen(sockfd, 5) < 0) {
printf("Error code: %d\n", errno);
perror("Error in listen()");
}
clt_size = sizeof(clt_addr);
if (new_fd = accept(sockfd, (struct sockaddr*)&clt_addr, &clt_size) < 0) {
printf("Error code: %d\n", errno);
perror("Error in accept()");
}
bzero(buffer, 256);
if (nbyte = recv(new_fd, buffer, 255, 0) < 0) {
printf("Error code: %d\n", errno);
perror("Error in recv()");
}
printf("Received bytes: %d", nbyte);

shutdown(new_fd, SHUT_RDWR);
close(new_fd);
return 0;

}

}

The test is:

#./server 5500
Error code: 88
Error in bind(): Socket operation on non-socket
Error code: 88
Error in listen(): Socket operation on non-socket
Error code: 88
Error in accept(): Socket operation on non-socket
Error code: 88
Error in recv(): Socket operation on non-socket
#

...

#./client CC1 6000
Error code: 88
Error in connect(): Socket operation on non-socket
Inserrt message to send

I am desperated...

theNbomr · 08-05-2008, 09:12 AM

Without having read your client code (I might have, if you'd taken the advice of at least two others, and posted it in [CODE] tags), I always advocate for using a known good client or server for the peer node when developing networking applications. As a client, telnet is usually a good choice. As a server, I favor netcat (nc). Doing this allows you to focus your efforts on only one end of the system, getting it working without having to consider which side of the system is causing a failure. Sometimes, a very simple client or server implementation in a scripting language such as Perl can be an asset, due to the easy parsing or disassembly of received data, and fast turnaround of modifications.
--- rod.

ntubski · 08-05-2008, 10:48 AM

I think the problem is in tests like:

Code:

if (sockfd = socket(AF_INET, SOCK_STREAM, 0) < 0) {

= has a lower precedence than <, so if the socket call succeeds, sockfd gets the result of the comparison which is 1 (true). You should write it like this:

Code:

if ((sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0) {

or even

Code:

sockfd = socket(AF_INET, SOCK_STREAM, 0);
if (sockfd < 0) {

If you compile with -Wall gcc will tell about this ("suggest parentheses around assignment used as truth value").

Also

Code:

srv_addr.sin_port = htons(argv[2]);

should be

Code:

srv_addr.sin_port = htons(atoi(argv[2]));

(same fix needed in client, of course)

skoona · 08-05-2008, 04:11 PM

shifter,

the following code sections contain you original source with some markup from me. Most of the markup is in the server.c file. The code compiles, and works as designed. Although you know you should make several improvements in error checking and flow control. Let me know what more you need. Again, here is a link with more detailed examples and discussion. http://www.beej.us/guide/bgnet/outpu...l#simpleserver

Code:

/* client.c 
 *  gcc -Wall -o client client.c
 *  usage: ./client 127.0.0.1 6000
*/
#include <stdio.h>
#include <stdlib.h>             /* for atoi()     */
#include <unistd.h>             /* for close()    */
#include <string.h>             /* for strerror(), bzero() */
#include <errno.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/types.h>
#include <sys/socket.h>

int main(int argc, char* argv[]) 
{

  int sockfd, nbyte;
  struct sockaddr_in srv_addr;
  char buffer[256];

  if (argc != 3) {
    printf("Command syntax \n");
    printf(" server <IP ADDRESS> <PORT NUMBER> \n");
  }
  else {
    if ((sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0) {
      perror("Error in socket()");
    }
    srv_addr.sin_family = AF_INET;
    srv_addr.sin_port = htons(atoi(argv[2]));
    srv_addr.sin_addr.s_addr = inet_addr(argv[1]);

    if (connect(sockfd, (struct sockaddr*)&srv_addr, sizeof(srv_addr)) < 0) {
      perror("Error in connect()");
      return 1;
    }
    printf("Inserrt message to send");
    bzero(buffer, 256);
    fgets(buffer, 255, stdin);

    if ((nbyte = send(sockfd, buffer, strlen(buffer), 0)) < 0) {
        perror("Error in send()");
    }
    printf("Sent bytes: %d ", nbyte);
    if (nbyte < 0)
      perror("Errore nella scrittura su socket");
    
    bzero(buffer, 255);
    shutdown(sockfd, SHUT_RDWR);
    close(sockfd);
    return 0;
  }

  return 1;
}

Code:

/* server.c 
 *  gcc -Wall -o server server.c
 *  usage: ./server 6000 
*/

#include <stdio.h>
#include <stdlib.h>             /* for atoi()     */
#include <unistd.h>             /* for close()    */
#include <string.h>             /* for strerror() */
#include <errno.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/types.h>
#include <sys/socket.h>

int main(int argc, char* argv[]) 
{

  int sockfd, new_fd;
  struct sockaddr_in srv_addr, clt_addr;
  int clt_size, nbyte;
  char buffer[256];

  if (argc != 2) {
    printf("Command syntax \n");
    printf(" server <PORT NUMBER> \n");
  }
  else {
    if ( (sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0) {
      printf("Error in socket() %d, %s", errno, strerror(errno));   /* added some extra info */
      return 1;                                                      /* no need to continue */
    }
    
    clt_addr.sin_family = AF_INET;
/*    clt_addr.sin_port = htons(argv[1]);          needs to be an int, argv[1] is a string now] */
    clt_addr.sin_port = htons(atoi(argv[1]));  
/*    clt_addr.sin_addr.s_addr = htonl(INADDR_ANY);        INADDR_ANY is already in the right format */ 
    clt_addr.sin_addr.s_addr = INADDR_ANY;
    memset(srv_addr.sin_zero, '\0', sizeof(srv_addr.sin_zero));

    if (bind(sockfd, (struct sockaddr*)&clt_addr, sizeof(srv_addr)) < 0) {
        printf("Error in bind(): %d, %s", errno, strerror(errno));
        close (sockfd);
        return 1;
    }
    if (listen(sockfd, 5) < 0) {
        printf("Error in listen(): %d, %s", errno, strerror(errno));
        close (sockfd);
        return 1;
    }
    clt_size = sizeof(clt_addr);
    if ( (new_fd = accept(sockfd, (struct sockaddr*)&clt_addr, (socklen_t *)&clt_size)) < 0) {        /* cast to (socklen_t *)&clt_size   */
      printf("Error in accept(): %d, %s", errno, strerror(errno));
      close (sockfd);
      return 1;
    }
    bzero(buffer, 256);
    if ( (nbyte = recv(new_fd, buffer, 255, 0)) < 0) {                          /* more () to clean up compile warning */
      printf("Error in recv(): %d, %s", errno, strerror(errno));
      close (new_fd);    
      close (sockfd);      
      return 1;
    }
    printf("Received bytes: %d", nbyte);

    shutdown(new_fd, SHUT_RDWR);
    close(new_fd);
    return 0;
  }

  return 1;
}

shifter · 08-06-2008, 06:58 AM

I solved above problem. I posted an other question for my current question

Thanks everyone answered.