socket programming issue

hey guys! im struggling for the past couple of days with a socket problem.
im trying to master the basics in order to proceed and integrate this mechanism in my program which is supposed to run on a server.

basically the problem is weird and there's couple of parts to it that i quite cant understand, mainly in the client program.
in my client code i run an infinite while loop with 1 send() and 1 recv() - straightforward and simple; server is supposed to recv() and send() back to the client a string.
but here's what bothers me:
first of all when running client - the server receives only the first message; after that the strings wont be sent..
second - the while loop that is supposed to be infinite - terminates after 3 iterations..

Code:

int main (int argc, char **argv)
{
        int sock;
        struct sockaddr_in cudaserver;
        char buffer[BUFFSIZE];
        unsigned int cudalen;
        int received = 0;
        msg temp_msg;
        
        if ((sock = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP)) < 0)
        {
                Die("Failed to create socket");
        }
                 
        memset(&cudaserver, 0, sizeof(cudaserver));     
        cudaserver.sin_family = AF_INET;                  
        cudaserver.sin_addr.s_addr = inet_addr(argv[1]);            
        cudaserver.sin_port = htons(atoi(argv[2]));      
              
        while (connect(sock,(struct sockaddr *) &cudaserver,sizeof(cudaserver)) < 0)
        {
                        Die("Failed to connect with server");
        }

        while (1)
        {
                printf("input the word to send to server\n");
                scanf("%s",&buffer);
                             
                        cudalen = strlen(buffer);
                        if (send(sock, buffer, cudalen, 0) != cudalen)
                        {
                                Die("Mismatch in number of sent bytes");
                        }

                        while (received > 0)
                        {
                                int bytes = 0;
                                if ((bytes = recv(sock, buffer, BUFFSIZE-1, 0)) < 1)
                                {
                                        Die("Failed to receive bytes from server");
                                }
                                received += bytes;
                                buffer[bytes] = '\0';
                                fprintf(stdout, buffer);
                        }
        }
        close (sock);
        exit(0);
}

any help related to this issue would be appreciated

P.S. btw, gdb says that "Program received signal SIGPIPE, Broken pipe." (if that helps anyhow)

Code:

                        if (send(sock, buffer, cudalen, 0) != cudalen)
                        {
                                Die("Mismatch in number of sent bytes");
                        }
 
                        while (received > 0)
                        {
                                int bytes = 0;
                                if ((bytes = recv(sock, buffer, BUFFSIZE-1, 0)) < 1)
                                {
                                        Die("Failed to receive bytes from server");
                                }

So which of those two are you getting?


Quzah.

Originally Posted by quzah

Code:

                        if (send(sock, buffer, cudalen, 0) != cudalen)
                        {
                                Die("Mismatch in number of sent bytes");
                        }
 
                        while (received > 0)
                        {
                                int bytes = 0;
                                if ((bytes = recv(sock, buffer, BUFFSIZE-1, 0)) < 1)
                                {
                                        Die("Failed to receive bytes from server");
                                }

So which of those two are you getting?


Quzah.

hey Quzah,

that's the problem - my client wont throw any errors out - it compiles, runs and terminates without any. and that's why im a bit lost..

> scanf("%s",&buffer);
bar.c:47: warning: format ‘%s’ expects type ‘char *’, but argument 2 has type ‘char (*)[300]’
Drop the & when scanning into a char array.

> fprintf(stdout, buffer);
bar.c:64: warning: format not a string literal and no format arguments

The second one is a killer - all the sender has to do is send a % character, and the receiver is screwed.

thanks for your prompt reply Salem,

but after tweaking the code - the problem remains.
oh, and the receiver (server) seems to work correctly.

Code:

while (received > 0)

What's the value of received the first time?

You should step through this in a debugger. Actually, it looks like you are?

yeah im using gdb for debugging.
the value of received is 0 when initialized (line 7)
after "received" is supposed to get incremented by the amount of bytes it actually received (return of recv())

Originally Posted by santarus

yeah im using gdb for debugging.
the value of received is 0 when initialized (line 7)
after "received" is supposed to get incremented by the amount of bytes it actually received (return of recv())

if it's 0 on entry, the current loop never executes.
Flip your while loop over to a do - while() construct, at least then you're guaranteed it will execute at least once.

ahhh! finally it did reach the loop;
it sent the string to the server, but failed to receive with error "Failed to receive bytes from server: Success"
so i assume that it simply doesn't receive anything?!
running in gdb in a sec!

im really confused why the client fails to receive, when my server is trying to send on the same socket with a live established connection.
any ideas?

Good catch on the recv():

Originally Posted by santarus

Code:

int main (int argc, char **argv)
{
        ...
        int received = 0;
                        ...
                        while (received > 0)
                        {

Quzah.

What's your current code look like? Note. if you read the man page on recv, particularly the Return Value section, you're treating receiving 0 bytes as an error, which it is not:

These calls return the number of bytes received, or -1 if an error occurred. The return value will be 0 when the peer has performed an orderly shutdown.

Emphasis mine.

In the future, note that there is a Networking/Device Communication forum here where a question like this is more appropriate.