Computers communicate with each other using a variety of protocols, the most common of which are the Transmission Control Protocol (TCP) and the User Datagram Protocol (UDP).
TCP is a connection-oriented protocol, which means that two computers must establish a connection before they can communicate. Once a connection is established, data can be transferred in both directions. TCP is a reliable protocol, which means that data is delivered in the order in which it was sent and that lost or damaged data is retransmitted.
UDP is a connectionless protocol, which means that two computers can communicate without first establishing a connection. Data is not guaranteed to be delivered in the order in which it was sent, and lost or damaged data is not retransmitted.
A socket is an endpoint for communication between two computers. A socket can be associated with a specific port number, which is used to identify the socket.
Socket programming is a way of writing software that can take advantage of the features of the TCP and UDP protocols. Socket programming can be used to create a variety of applications, including web servers, file transfer applications, and chat applications.
In order to create a socket, you must first create a socket address structure. This structure contains the information that is needed to identify a socket, including the address family, the port number, and the IP address.
Once you have created the socket address structure, you can call the socket() function to create the socket. The socket() function takes the address family, the socket type, and the protocol as arguments.
Once you have created a socket, you can connect to a remote socket by calling the connect() function. The connect() function takes the socket and the socket address structure as arguments.
In order to receive data from a remote socket, you must first bind the socket to a local port. This is done by calling the bind() function. The bind() function takes the socket and the socket address structure as arguments.
Once you have bound the socket to a local port, you can listen for incoming connections by calling the listen() function. The listen() function takes the socket and the backlog as arguments. The backlog is the maximum number of pending connections that can be queued up at any given time.
Once you have called the listen() function, you can accept incoming connections by calling the accept() function. The accept() function takes the socket and the address of the client that is connecting as arguments.
Once you have established a connection, you can send and receive data using the send() and recv() functions. The send() function takes the socket, a pointer to the data to be sent, the length of the data, and the flags as arguments. The recv() function takes the socket, a pointer to the buffer to store the data, the length of the buffer, and the flags as arguments.
Once you are finished sending and receiving data, you can close the connection by calling the close() function. The close() function takes the socket as an argument.