TCP (Transmission Control Protocol), referred to as Transmission Control Protocol, is a connection-oriented, reliable, byte-stream-based transport layer communication protocol.
Three steps to create TCP communication:
- create connection
- data transmission
- terminate connection
TCP communication is similar to making a phone call in life, and the relevant connection must be established before the communication starts.
TCP Features:
- Connection-oriented This connection is one-to-one, so TCP is not suitable for broadcast applications
- Reliable Transmission
- TCP uses an acknowledgment mechanism
- timeout retransmission
- error checking
- Flow Control and Congestion Management
TCP advantages:
- reliable and stable
- Suitable for transferring large amounts of data
TCP Disadvantages:
- slow transfer
- High system resource usage
TCP usage scenarios
Higher requirements for network communication quality
- Browser HTTP protocol based on TCP protocol
- file transfer
TCP three-way handshake (connection)
TCP’s 4 waves (disconnect)
TCP network program flow
Case file downloader based on TCP (synchronous download)
TCP strictly distinguishes between client and server.
TCP client
import socket
if __name__ == '__main__':
# create tcp client socket
tcp_client_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
# Establish a connection with the server program
tcp_client_socket.connect(("127.0.0.1", 8989))
# Receive the file name data downloaded by the user
file_name = input("Please enter the file name you want to download:")
# Encode string process into binary data
file_name_data = file_name. encode("utf-8")
# send data
tcp_client_socket.send(file_name_data)
# Specify the path, first create the file to the specified path, and then write data in the open file
with open("/home/python/Desktop/" + file_name, "wb") as file:
# Loop to receive the file binary data sent by the server
while True:
# Receive data sent by the server once
file_data = tcp_client_socket.recv(1024)
if file_data:
# Loop to write data to the file
file. write(file_data)
else:
# The server sends the file to complete
break
# close the socket
tcp_client_socket. close()
TCP server
import socket
import os
if __name__ == '__main__':
tcp_server_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
# Set the socket option, the port number will be released immediately when the program exits, and the port number can be reused
# Tip: The default is tcp disconnection, but it takes 1-2 minutes to actually release the port number
tcp_server_socket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR,True)
# Bind the port number to the program
tcp_server_socket. bind(("", 8989))
# Set up monitoring
tcp_server_socket.listen(128)
# Waiting for the connection request from the client in a loop, it can serve multiple clients, but only after one client downloads the file can the other client download the file
while True:
# Waiting to receive connection requests from clients
service_client_socket, ip_port = tcp_server_socket. accept()
# The code is executed here, indicating that the connection is established successfully
print("Client ip address and port number:", ip_port)
# Receive client request data (actually the file name sent by the client)
recv_data = service_client_socket. recv(1024)
# Decode binary data
file_name = recv_data. decode("utf-8")
print(file_name)
# Check if the requested file exists
# 1. try-except If an exception occurs when opening the file, it means the file does not exist
# 2. os.path.exits to determine whether the file exists
# Determine whether the specified file or folder exists
if os.path.exists(file_name):
# Open the specified file according to the file name requested by the client, and read the data in the file
with open(file_name, "rb") as file:
while True:
# read file data
file_data = file. read(1024)
if file_data:
# send data to client
service_client_socket. send(file_data)
else:
# file read complete
break
else:
service_client_socket.send("No such file".encode("utf-8")
service_client_socket. close()
#tcp_server_socket.close()
TCP note:
- Generally, the tcp server needs to bind the port number, otherwise the client cannot find the server
- The tcp client generally does not bind the port number, just use a randomly generated port number
- When a tcp client is successfully connected to the server, there will be a new socket on the server side, which is used to mark the client and serve the client alone
- The socket after listen is a passive socket, which is only used to receive the connection request of the new client, and the new socket returned by accept marks the new client
- Closing the socket after listening means that the passive socket is closed, which will cause the new client to be unable to connect to the server, but the previously connected client can communicate normally
- Closing the socket returned by accept means that the client has been served, pay attention to the difference from point 5
- When the client’s socket calls close, the server will recv unblock it, and the length returned is 0, so the server can distinguish whether the client has gone offline by the length of the returned data
The difference between TCP and UDP
- TCP is connection-oriented, UDP is not connection-oriented
- TCP needs to connect and the transmission speed is slow, UDP does not need to connect and the transmission speed is fast
- TCP does not support broadcasting, UDP supports broadcasting
- TCP has more requirements on system resources, and UDP has less requirements on system resources.
- TCP provides reliable data transmission, while UDP does not guarantee reliable data transmission and is prone to packet loss
- TCP is suitable for sending large amounts of data, UDP is suitable for sending small amounts of data
- TCP has flow control, UDP has no flow control
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