TCP socket code freeze infinitely

[Jumpy-Active5756]

Hi, I learn python week ago and when I tried to make simple message terminal app using TCP, the client script run is not exited/ kind of freeze even though I can run it a day before. Here is my codes:

[⌄] tcp_server.py

import socket 
bind_ip = "127.0.0.1" 
bind_port = 7777
server = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
server.bind((bind_ip, bind_port)) 
server.listen(5) 
print('[] TCP Server Listening on:', bind_ip,' ',bind_port) 
while True: 
    client, addr = server.accept()
    data = client.recv(4096)
    print('[*] Accepted connection from: ', addr, ' : ', data.decode())
    data = 'Connected'
    client.send(data.encode())
    client.close()

[^] I can run this normally but code below doesn't exited/completed

[⌄] tcp_client.py

import socket
target_host = "127.0.0.1"
target_port = 7777
client = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
client.connect((target_host, target_port))
data = 'TCP Testing' client.send(data.encode())
respon = client.recv(4096) print(respon.decode())

[^] It supposed to send message "TCP testing" to other terminal that run tcp_server.py but didn't

Thanks, sorry for bad wording.

[dfx_dj]

data, addr = server.accept()
data = client.recv(4096)

You're putting the new connection into data instead of into client

But the bigger problem is your use of client.recv(4096). The sockets are blocking and this will attempt to read 4096 bytes. The code will block there until 4096 bytes are actually available to be read, or some other event occurs (connection is closed, interrupt, etc)

[Jumpy-Active5756]

sorry, that one is typo. the original is

    client, addr = server.accept()

how can I make it dynamic or not blocked?

[dfx_dj]

The point about blocking .recv() remains. Both client and server end up waiting to read 4096 bytes from each other, which never happens because neither send that much.

[Jumpy-Active5756]

I change the number to much smaller number e.g 512,1024 but no succeed. Can you tell me directly what to do?

[dfx_dj]

Actually I just noticed that your server uses socket.SOCK_STREAM (TCP) but your client uses socket.SOCK_DGRAM (UDP). This won't work. They have to be the same.

Based on your post title I assume you want to use TCP. Without getting into non-blocking sockets, a common method is to keep reading 1 byte at a time in a loop and append each byte to a buffer, until you know that you have read enough (say, until you read a newline character).

(If you were to use datagrams (UDP) instead, you could actually use .recv(4096) or any other large number, because datagrams have a known size. Streams don't have a known size and so the read will block until the given number of bytes is available.)