Question

我为两台PC创建了插槽，一台是Raspberry Pi，另一台是我的笔记本电脑。我只连接了两个，然后发送字符串来测试连接。如果我从RPi发送字符“ q”，则我的PC应该跳出循环并关闭连接，但不会。 print("Listening")部分仍在运行。为什么？参见下面的代码。

import socket
import time

# IP address of this PC.
TCP_IP = '192.168.137.1'

# Port.
TCP_PORT = 5005

# Size of buffer.
BUFFER_SIZE = 1024

# Create a socket, connect and listen to it.
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.bind((TCP_IP, TCP_PORT))
s.listen(1)

conn, addr = s.accept()
print('Connection address:', addr)

while 1:
    print("Listening")
    data = conn.recv(BUFFER_SIZE)
    data = data.decode()

    if data=='q':
        break

    if  data: 
        print ("Received data:", data)
        # Echo back. 
        conn.send(data.encode())

    time.sleep(1)

print("It breaks.") 
conn.close()
s.close()

Answer 1

TCP is a stream oriented protocol. So data transmitted is a stream not a sequence of messages. So when you expect data to be q it actually is some_data_sent_before_q_and_finally_q.

The simplest way to repair the code is to use if data.endswith('q') instead of if data=='q'. May work and may not depending on how you actually use the connection. For example, this approach may fail with some_data_sent_before_q pretty long pause more_data_and_q and with some_data_sent_before_q_and_finally_q_plus_something_else_why_not.

Little bit more advanced way to solve the problem is to divide the stream into messages with separators - message_1<separator>message_2<separator>q<separator>. This method will allow you to treat every message separately.

Python套接字循环不中断

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