Multiplexing stdin and socket in client C

Question

I wrote a simple TCP Server to serve many clients (it works brilliant with telnet). But, I wanted to write also my own simple TCP client with multiplexing socket and stdin input. Connection with server I wrote as usual, the connection code is ok.

I have a problem with multiplexing socket and stdin input. My code which makes the biggest problem:

    void multiplexClient(FILE *fp, int sockfd, char inbuffer[], char outbuffer[])
    {
        int maxfd;
        fd_set rset;

        FD_ZERO(&rset);
        for(;;)
        {
            FD_SET(fileno(fp), &rset);
            FD_SET(sockfd, &rset);
            maxfd = std::max(fileno(fp), sockfd) + 1;

            int res = select(maxfd, &rset, NULL, NULL, NULL);

            if(res < 0)
            {
                printf("'select error\n");
            }

            if(FD_ISSET(sockfd, &rset))
            {
                if(read(sockfd, inbuffer, sizeof(inbuffer)) == 0)
                   printf("read error\n");
                printf("Received: %s\n", inbuffer);
                fflush(stdout);
                 memset(inbuffer, 0, sizeof(inbuffer));
            }

            else if(FD_ISSET(fileno(fp), &rset))
            {
                fprintf(stdout, "\n> ");
                if(fgets(outbuffer, sizeof(outbuffer), fp) == NULL)
                    return;
                write(sockfd, outbuffer, strlen(outbuffer));
                printf("Send: %s\n", outbuffer);
                fflush(stdout);
                 memset(outbuffer, 0, sizeof(outbuffer));
            }
        }
    }

// int main
// sockfd = socket...
// connect

while(1)
{
 multiplexClient(stdin, socket_fd, inbuffer, outbuffer);
}

// ...
    return 0;
}

My first client:

$ ./client localhost 9034
hello, other client!

> Send: hel
Received: hel
Received: lo! ��~�~���~�
Received: :)

Received: wha

My second client:

$ ./client localhost 9034
hello! :)

> Send: hel
whats is wrong with this chat?!

> Send: lo!

> Send:  :)

> Send: 


> Send: wha

How to fix this?

Answer 1

Your problem lies here (slightly paraphrased):

read(sockfd, inbuffer, sizeof(inbuffer));
printf("Received: %s\n", inbuffer);

The read call returns the number of bytes written (which you ignore) and the buffer is not a C string (ie, it's not null terminated).

What you should have is something along the following lines:

quant = read (sockfd, inbuffer, sizeof(inbuffer));
printf ("Received: %*.*s\n", quant, quant, inbuffer);

Answer 2

You're missing a FD_ZERO() before re-adding the file selectors to the set.

Also, this is C++ since it uses std::max().