Howto combine TCP and UDP in a single Server? - c

Question

I am totally new to socket programming and I want to program a combined TCP/UDP-Server socket in C but I don't know how to combine those two.
So at the moment, I do know how TCP- and UDP-Server/-Clients work and I have already coded the Clients for TCP and UDP. I also know that I have to use the select()-function somehow, but I don't know how to do it.
I have to read two numbers, which are sent to the TCP-/UDP-Server with either TCP- or UDP-Clients and then do some calculations with these numbers and then print the result on the server.
Does anyone know a tutorial for that or an example code or can help me with that?
Or at least a good explanation of the select() function.

Answer 1

Basically, use an event loop. It works like this:
Is there anything I need to do now? If so, do it.
Compute how long until I next need to do something.
Call select specifying all sockets I'm willing to read from in the read set and all sockets I'm trying to write to in the write set.
If we discovered any sockets that are ready for reading, read from them.
If we discovered any sockets that are ready from writing, try to write to them. If we wrote everything we need to write, remove them from the write set.
Go to step 1.
Generally, to write to a socket, you follow this logic:
Am I already trying to write to this socket? If so, just add this to the queue and we're done.
Try to write the data to the socket. If we sent it all, we're done.
Save the leftover in the queue and add this socket to our write set.
Three things to keep in mind:
You must set all sockets non-blocking.
Make sure to copy your file descriptor sets before you pass them to select because select modifies them.
For TCP connections, you will probably need your own write queue.

Answer 2

The idea is to mix inside your server a TCP part and a UDP part.
Then you multiplex the inputs. You could use the old select(2) multiplexing call, but it has limitations (google for C10K problem). Using the poll(2)
multiplexing call is preferable.
You may want to use some event loop libraries, like libev (which uses select or poll or some fancier mechanisms like epoll). BTW, graphical toolkits (e.g. GTK or Qt) also provide their own even loop machinery.
Read some good Linux programming book like the Advanced Linux Programming
book (available online) which has good chapters about multiplexing syscalls and event loops. These are too complex to be explained well in a few minutes in such an answer. Books explain them better.

Answer 3

1) Simple write a tcp/udp server code, and when receive the message, just print it out.
2) substitute print code to process_message() function.
Then you have successfully combine TCP and UDP server to the same procedure.
Be careful with your handling procedure, it's should be cope with parellel execution.

Answer 4

You may try this stream_route_handler, it is c/c++ application, you can add tcp/udp handler in your single c/c++ application. This has been using by transportation heavy traffic route, and logging service purpose.
Example of using
void read_data(srh_request_t *req);
void read_data(srh_request_t *req) {
char *a = "CAUSE ERROR FREE INVALID";
if (strncmp( (char*)req->in_buff->start, "ERROR", 5) == 0) {
free(a);
}
// printf("%d, %.*s\n", i++, (int) (req->in_buff->end - req->in_buff->start), req->in_buff->start);
srh_write_output_buffer_l(req, req->in_buff->start, (req->in_buff->end - req->in_buff->start));
// printf("%d, %.*s\n", i++, (int) (req->out_buff->end - req->out_buff->start), req->out_buff->start);
}
int main(void) {
srh_instance_t * instance = srh_create_routing_instance(24, NULL, NULL);
srh_add_udp_fd(instance, 12345, read_data, 1024);
srh_add_tcp_fd(instance, 3232, read_data, 64);
srh_start(instance);
return 0;
}
If you are using C++ program, you may like this sample code.
stream route with spdlog