Question

I’m running a server and a client. i’m testing my program on my computer.

this is the funcion in the server that sends data to the client:

int sendToClient(int fd, string msg) {

    cout << "sending to client " << fd << " " << msg <<endl;
    int len = msg.size()+1;
    cout << "10\n";
    /* send msg size */
    if (send(fd,&len,sizeof(int),0)==-1) {
        cout << "error sendToClient\n";
        return -1;
    }
    cout << "11\n";
    /* send msg */
    int nbytes = send(fd,msg.c_str(),len,0); //CRASHES HERE
    cout << "15\n";
    return nbytes;
}

when the client exits it sends to the server “BYE” and the server is replying it with the above function. I connect the client to the server (its done on one computer, 2 terminals) and when the client exits the server crashes – it never prints the 15.
any idea why ? any idea how to test why?

thank you.

EDIT: this is how i close the client:

void closeClient(int notifyServer = 0) {

/** notify server before closing */
if (notifyServer) {
    int len = SERVER_PROTOCOL[bye].size()+1;
    char* buf = new char[len];
    strcpy(buf,SERVER_PROTOCOL[bye].c_str());   //c_str - NEED TO FREE????
    sendToServer(buf,len);
    delete[] buf;
}
close(_sockfd);
}

btw, if i skipp this code, meaning just leave the close(_sockfd) without notifying the server everything is ok – the server doesn’t crash.

EDIT 2: this is the end of strace.out:

5211  recv(5, "BYE\0", 4, 0)            = 4
5211  write(1, "received from client 5 \n", 24) = 24
5211  write(1, "command: BYE msg: \n", 19) = 19
5211  write(1, "BYEBYE\n", 7)           = 7
5211  write(1, "response = ALALA!!!\n", 20) = 20
5211  write(1, "sending to client 5 ALALA!!!\n", 29) = 29
5211  write(1, "10\n", 3)               = 3
5211  send(5, "\t\0\0\0", 4, 0)         = 4
5211  write(1, "11\n", 3)               = 3
5211  send(5, "ALALA!!!\0", 9, 0)       = -1 EPIPE (Broken pipe)
5211  --- SIGPIPE (Broken pipe) @ 0 (0) ---
5211  +++ killed by SIGPIPE +++

broken pipe can kill my program?? why not just return -1 by send()??

Answer 1

Probably the clients exits before the server has completed the sending, thus breaking the socket between them. Thus making send to crash.

link

This socket was connected but the
connection is now broken. In this
case, send generates a SIGPIPE signal
first; if that signal is ignored or
blocked, or if its handler returns,
then send fails with EPIPE.