How can I send and recv from the same socket?

Question

I am going through Beej's guide and I wanted to elaborate on one of the examples, a stream client/server example. In the example the server sends messages, and the client receives.

I would like to make a program that sends AND receives messages. In this case, it would no longer be a server/client architecture, since both the former server and client would perform the same duties. They would be very similar.

In the example the server does the following :

 getaddrinfo(NULL, PORT, &hints, &p);
 sockfd = socket(p->ai_family, p->ai_socktype, p->ai_protocol));
 bind(sockfd, p->ai_addr, p->ai_addrlen);
 listen(sockfd, BACKLOG);
 new_fd = accept(sockfd, (struct sockaddr *)&their_addr, &sin_size);
 send(new_fd, "Hello, world!", 13, 0);

What do I need to add in order to receive messages as well from the same socket? Is it possible?

I tried many things that didn't work, such as trying to connect() using the original socketfd and using the destinations information. In the end I used two sockets and bind them to the same port with the help of setsockopt(), but I would like to know if there is a better or more efficient method.

Answer 1

You can send and recv from any connected socket.

The direction of the data flow does not have anything to do with the client/server relationship.

It is very common for clients and servers to both send and receive. The pattern they use to send and expect answers is called a protocol (in the sense of an application defined protocol).