Learn Python network programming from scratch: Explore TCP protocol and example demonstrations!

Python is a high-level programming language with an extensive library for network programming.

These libraries allow Python developers to communicate using TCP and other network protocols.

In this article, we'll explore the TCP protocol and use a simple example to demonstrate how to write networking code in Python.

TCP Protocol Introduction

TCP (Transmission Control Protocol) is the basic transmission protocol for the Internet and many other networks.

The TCP protocol ensures that data is transmitted reliably over the network. It includes a mechanism to detect lost packets and request retransmission, and can also handle the problems of out-of-order arrival and packet loss.

Therefore, TCP is a more reliable protocol compared to other protocols such as UDP, ICMP, and IP.

The TCP protocol is a connection-based protocol, so a connection must be established before data can be transmitted.

Connecting involves creating and maintaining a virtual pipe (called a socket or endpoint) through which data can be transferred.

After the connection is established, data can be transferred between the two computers through the pipe.

After the transfer is complete, the connection can be closed to free up used resources and terminate the network connection.

TCP/IP Model

The TCP protocol is based on the TCP/IP suite protocol stack.

In this protocol stack, each layer handles specific tasks and relies on the layers below to complete them.

The main layers of the TCP/IP model are:

• Application layer: This layer is the interface between applications and network protocols, including application protocols such as FTP, HTTP, and Telnet.
• Transport layer: This layer is the core of all data transmission, and the protocols include TCP and UDP.
• Network layer: This layer uses IP protocol for packet routing.
• Link layer: This layer includes the physical layer and the data link layer. The task between these two layers is to establish and maintain data link connections on the physical network connection.

Establishing a TCP connection

To establish a TCP connection in Python, you need to use the socket library.

The socket library provides various socket functions and constants that make communication between Python and the network easier.

To establish a TCP connection, the following steps are required:

• Creating a Socket
• Binding Sockets
• Listening Socket
• Accept connection requests from clients

Next, we will perform these steps in Python and create a simple server that listens for connection requests from clients.

 import socket # 创建一个TCP/IP 套接字server_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM) # 绑定套接字到特定的地址和端口server_address = ('localhost', 8888) print('Starting up on {} port {}'.format(*server_address)) server_socket.bind(server_address) # 开始监听连接server_socket.listen(1) # 等待连接请求print('Waiting for a connection...') connection, client_address = server_socket.accept() print('Connection from', client_address) # 处理请求while True: data = connection.recv(1024) print('Received {!r}'.format(data)) if data: connection.sendall(data) else: break # 关闭连接connection.close()

Let's explain line by line how this program works:

• First, we import the socket library and create a TCP/IP socket. The socket.AF_INET parameter specifies that the socket will use the IPv4 cipher, and the socket.SOCK_STREAM parameter specifies that this is a stream socket.
• We then use the bind() function to bind the socket to a specific IP address and port. Here, we bind to port 8888 on localhost.
• Next, we listen for connections. In this example, we set the socket to wait for at most 1 connection request.
• Finally, we use the accept() function to accept the connection request from the client. This function will wait until a client connects. Once the connection is accepted, the accept() function will return a new socket and the client's address information.
• From here, we can handle the client's request. In this example, we simply read any data sent by the client and then send them back to the client. When the client sends empty data, the loop will terminate and close the connection code.

Make a TCP connection

To connect to the Python server, we need to use another socket to represent the client endpoint.

The client socket needs to use the same protocol as the server socket.

The initialization IP address and port must be the same as the binding address and port used by the server.

The steps for client connection are as follows:

• Creating a Socket
• Execute the connection

Next, we will follow these steps in Python and create a simple client to connect to the server we created earlier.

 import socket # 创建一个TCP/IP 套接字client_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM) # 连接到服务器server_address = ('localhost', 8888) print('Connecting to {} port {}'.format(*server_address)) client_socket.connect(server_address) # 发送数据message = b'This is a test message' client_socket.sendall(message) # 接收数据data = client_socket.recv(1024) print('Received', repr(data)) # 关闭连接client_socket.close()

Let's explain line by line how this program works:

• First, we imported the socket library and created a TCP/IP socket using the same protocol as the server.
• We then connect to the server using the connect() function. The connect() function requires the IP address and port to be specified.
• Once we are connected to the server we can send data. In this example we simply send a test message.
• Finally, we wait to receive data back from the server. Once the data is received, we can output it and close the client socket.

in conclusion

This article briefly introduces the TCP protocol and its use in Python programs.

Using the socket library, you can create sockets, bind sockets, listen on sockets, accept client connections, and send and receive data to other computers.

With these steps, we can connect the program to the TCP protocol and start network communication.

Of course, this article only introduces the basic principles and applications of the TCP protocol. There is still a lot of in-depth and complex knowledge that needs to be learned and mastered.