The conversation

The client and server exchange data using a number of functions. They can send data using send(), sendto(), sendmsg(), write(), or writev(). They can receive data using recv(), recvfrom(), recvmsg(), read(), or readv(). The following is an example of the send() and recv() call:

send(s, addr_of_data, len_of_data, 0);
recv(s, addr_of_buffer, len_of_buffer, 0);

The send() and recv() function calls specify the sockets on which to communicate, the address in memory of the buffer that contains, or will contain, the data (addr_of_data, addr_of_buffer), the size of this buffer (len_of_data, len_of_buffer), and a flag that tells how the data is to be sent. Using the flag 0 tells TCP/IP to transfer the data normally. The server uses the socket that is returned from the accept() call.

These functions return the amount of data that was either sent or received. Because stream sockets send and receive information in streams of data, it can take more than one call to send() or recv() to transfer all the data. It is up to the client and server to agree on some mechanism of signaling that all the data has been transferred.

When the conversation is over, both the client and server call the close() function to end the connection. The close() function also deallocates the socket, freeing its space in the table of connections. To end a connection with a specific client, the server closes the socket returned by accept(). If the server closes its original socket, it can no longer accept new connections, but it can still converse with the clients it is connected to. The following is an example of the close() call:

close(s);