Question

For an application in C, i need to response more than one clients.

I setup the connection with a code like,

    bind(...);
    listen(...);
    while(1){
        accept(...);//accept a client
        recv(...);//receive something
        send(...);//send something to client
        bzero(buf);//clear buffer
    }  

This works great when i have only one client. Other clients also can connect to the server but although they command something, server does not response back to clients who connected after the first client. How can i solve this problem?

Answer 1

Write a server using asynchronous, nonblocking connections.

Instead of a single set of data about a client, you need to create a struct. Each instance of the struct holds the data for each client.

The code looks vaguely like:

socket(...)
fcntl(...) to mark O_NONBLOCK
bind(...)
listen(...)
create poll entry for server socket.
while(1) {
    poll(...)
    if( fds[server_slot].revents & POLLIN ) {
        accept(...)
        fcntl(...) mark O_NONBLOCK
        create poll and data array entries.
    }
    if( fds[i].revents & POLLIN ) {
        recv(...) into data[i]
        if connection i closed then clean up.
    }
    if( fds[i].revents & POLLOUT ) {
        send(...) pending info for data[i]
    }
 }

If any of your calls return the error EAGAIN instead of success then don’t panic. You just try again later. Be prepared for EAGAIN even if poll claims the socket is ready: it’s good practice and more robust.