Creating a connection-oriented socket

The following figure illustrates the client/server relationship of the sockets API for a connection-oriented protocol.

Socket flow of events: Connection-oriented server

The following sequence of the socket calls provides a description of the figure. It also describes the relationship between the server and client application in a connection-oriented design. Each set of flows contains links to usage notes on specific APIs.

1. The socket() API returns a socket descriptor, which represents an endpoint. The statement also identifies that the Internet Protocol version 6 address family (AF_INET6) with the TCP transport (SOCK_STREAM) is used for this socket.
2. The setsockopt() API allows the local address to be reused when the server is restarted before the required wait time expires.
3. After the socket descriptor is created, the bind() API gets a unique name for the socket. In this example, the user sets the s6_addr to zero, which allows connections to be established from any IPv4 or IPv6 client that specifies port 3005.
4. The listen() API allows the server to accept incoming client connections. In this example, the backlog is set to 10. This means that the system queues 10 incoming connection requests before the system starts rejecting the incoming requests.
5. The server uses the accept() API to accept an incoming connection request. The accept() call blocks indefinitely, waiting for the incoming connection to arrive.
6. The select() API allows the process to wait for an event to occur and to wake up the process when the event occurs. In this example, the system notifies the process only when data is available to be read. A 30-second timeout is used on this select() call.
7. The recv() API receives data from the client application. In this example, the client sends 250 bytes of data. Thus, the SO_RCVLOWAT socket option can be used, which specifies that recv() does not wake up until all 250 bytes of data have arrived.
8. The send() API echoes the data back to the client.
9. The close() API closes any open socket descriptors.

Socket flow of events: Connection-oriented client

The following sequence of APIs calls describes the relationship between the server and client application in a connection-oriented design.

1. The socket() API returns a socket descriptor, which represents an endpoint. The statement also identifies that the Internet Protocol version 6 address family (AF_INET6) with the TCP transport (SOCK_STREAM) is used for this socket.
2. In the client example program, if the server string that was passed into the inet_pton() API was not a valid IPv6 address string, then it is assumed to be the host name of the server. In that case, use the getaddrinfo() API to retrieve the IP address of the server.
3. After the socket descriptor is received, the connect() API is used to establish a connection to the server.
4. The send() API sends 250 bytes of data to the server.
5. The recv() API waits for the server to echo the 250 bytes of data back. In this example, the server responds with the same 250 bytes that was just sent. In the client example, the 250 bytes of the data might arrive in separate packets, so the recv() API can be used over and over until all 250 bytes have arrived.
6. The close() API closes any open socket descriptors.