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socket connect to invalid ip don't raise error (python)

I'm Trying to send and receive data using TCP communication.
I tried to communicate using the IP of a specific embedded device, but i check that the 'connect' was going well even when the device was turned off.
When the device is turned off, I want to output an error message, but I can't check it because the connect is performed normally.
So, I checked with wireshark and I found something strange.
My code
import socket
HOST = '105.0.0.121' # random IP
PORT = 9999
client_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
client_socket.settimeout(2)
client_socket.connect((HOST, PORT))
client_socket.send('some data'.encode())
data = client_socket.recv(1024)
print('Received', repr(data.decode()))
client_socket.close()
I use random IP 105.0.0.121
I expect at client_socket.connect((HOST, PORT)) raise an error, but at line 'data = client_socket.recv(1024)' raise the error that print "socket.timeout: timed out".
wireshark image
When I checked with Wireshark, it seems to have sent an "ACK" from 105.0.121.
Because of receiving ACK, it seems that the "connect" has passed normally, but I don't know why this phenomenon occurs.
Give me a help plz
Thank you

Ruby client and Python server not receiving the full message while exchanging

I am trying to establish a client-server communication. The client is written in Ruby whereas the server is written in Python.
client.rb
require 'socket'
hostname = 'localhost'
port = 7778
s = TCPSocket.open(hostname, port)
s.write("2020-06-25T11:11:00+00:00 5 127.0.0.1 printer: event")
while line = s.gets
puts line.chop
end
s.close()
The ruby client sends a log to the Python server and tries to receive it back.
server.py
import socket
#Create a TCP/IP socket
sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
#bind the socket to the port - tuple
server_address = ('localhost', 7778)
print('starting up on %s port %s' %server_address)
sock.bind(server_address)
#Listen for incoming connections
sock.listen(1)
while True:
print('waiting for a connection')
connection, client_address = sock.accept()
while True:
data = connection.recv(1024)
print('received "%s"' % data)
if data:
print('sending data back to the client')
connection.send(data)
else:
print('no more data from', client_address)
break
connection.close()
The log is sent to the python server and when the python server sends it back. When the ruby client receives it, it doesn't receive the full log.
example:
2020-06-25T11:11:00+00:00 5 127.0.0.1 printer: eve
I think this comes from the fact that TCP is a streaming protocol and we never know if we can get the full message each time.
Could you propose me a solution for both the client and the server so I can be sure they always receive the full message between each other? I would really appreciate it if anyone would help.

So the issue is that you're assuming the data received has a new line character - however the data you're sending is not terminated by a new line.
s.write("2020-06-25T11:11:00+00:00 5 127.0.0.1 printer: event") will not write the string with a new line character - you should use puts IO#puts
s.gets will return the data because the socket is closed by the python server after it has sent the data. So even getssays it will read the next line from the socket, in reality its just reading what remained in the buffer after the socket was closed.
line.chop will remove the last character, and you're using it here to strip a newline character (assuming that it has one from gets). However since there is no newline character it will remove the last character instead.
So the fix would be to replace in the ruby client s.write with s.puts.

A request to send or receive data was disallowed because the socket is not connected in Python

I'm trying to make a console chat app in python using socket library.
Whenever I send a message to the server, the server code crashes with the following message:
OSError: [WinError 10057] A request to send or receive data was disallowed because the socket is not connected and (when sending on a datagram socket using a sendto call) no address was supplied
Server code
import socket
HOST = socket.gethostbyname(socket.gethostname()) # get the ip address of PC
PORT = 5050
ADDRESS = (HOST, PORT)
socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
socket.bind(ADDRESS)
while True:
socket.listen()
conn, addr = socket.accept()
print(f"Connected by {addr}")
while True:
data = conn.recv(64)
print(data.decode('utf-8'))
socket.send(data)
Client code
import socket
HOST = socket.gethostbyname(socket.gethostname()) # get the ip address of PC
PORT = 5050
ADDRESS = (HOST, PORT)
socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
socket.connect(ADDRESS)
while True:
msg = input("Enter your message")
socket.send(msg.encode('utf-8'))
data = socket.recv(64)
print(data.decode('utf-8'))
What I am trying to achieve is whenever I send a message to the server, the client script should print the sent message. How can I fix that?

You're attempting to send data to your own server socket. You instead want to send to the client that you accepted.
socket.send(data)
Should be:
conn.send(data)
If you think about it, if you had multiple clients, how would you send data to a specific client? By using the socket that accept gave you.
As a side note, you probably don't want to import the module as socket, and also call your variable socket. It's fine here, but if you were to make a more complicated project, you may accidentally refer to the object when you meant to refer to the module. I'd rename the socket object to sock or server_socket to avoid shadowing.

How to send UDP message from UDP server without sending to itself?

I'd like to make a UDP server that sends a message to a UDP client soon after the server gets the message from the client. I'm using Python and Google Protobuffer as a message protocol.
Currently, the message receiving part seems working, but regarding the message sending part, it has an issue: the response message from the server doesn't arrive the client and even worse, the server shows that message (maybe it sends to itself? Right now, the console shows both the message from client and the message that should be sent to client). This issue didn't happen when I tried the similar code on C++ or C#.
The followings are some excerpt from my code:
def connect(self):
remote = ('x.x.x.x',xxxx) #ip and port
self.sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
self.sock.settimeout(2.5)
self.sock.bind(remote)
self.sock.settimeout(None)
def start(self):
while not self.exit_thread:
# Get the message from client
data, address = self.sock.recvfrom(8192)
if data is not None:
# De-serialize inbound message from client
msg_client = xxx_pb2.msgClient()
msg_client.ParseFromString(data)
# Display message from client
self.display_inbound_message(msg_client)
# Create a new message from server
msg_serer = xxx_pb2.msgServer()
self.create_outbound_message(msg_serer)
# Send the Udp message to the client, return the number of bytes sent
bytes_sent = self.sock.sendto(msg_server.SerializeToString(), self.remote)
if (bytes_sent < 0):
print("Error send message")
I don't have enough experience for UDP programming on Python. Please let me know if you notice anything.

The issue with this code is that the server replies to itself, rather than the remote client. In here:
data, address = self.sock.recvfrom(8192)
# ...
bytes_sent = self.sock.sendto(msg_server.SerializeToString(), self.remote)
It should be:
bytes_sent = self.sock.sendto(msg_server.SerializeToString(), address)
It makes good sense to rename remote to server_address because it is this server's address.

Communicating with multiple clients using one TCP socket python

I am using TCP sockets to communicate between my server and clients. The server code and socket code are as below:
server:
from socket import *
HOST = 'xx.xx.xx.xx'
PORT = 1999
serversocket = socket(AF_INET,SOCK_STREAM)
serversocket.bind((HOST,PORT))
print 'bind success'
serversocket.listen(5)
print 'listening'
while True:
(clientsocket, address) = serversocket.accept()
print ("Got client request from",address)
#clientsocket.send('True')
data = clientsocket.recv(1024)
print data
clientsocket.send('True')
clientsocket.close()
client:
import socket
import sys
# Create a TCP/IP socket
sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
# Connect the socket to the port on the server given by the caller
server_address = ('xx.xx.xx.xx', 1999)
print >>sys.stderr, 'connecting to %s port %s' % server_address
sock.connect(server_address)
try:
message = 'This is the message. It will be repeated.'
print >>sys.stderr, 'sending'
for x in range (0,1):
name=raw_input ('what is ur name')
print type(name)
sock.send(name)
print sock.recv(1024)
finally:
sock.close()
I am able to communicate with the server from client and able to send and receive data. But the problem I am facing is that I am not able to send and receive data continuously from the server. I have to restart my client code on my laptop to send and receive data again from the server. The way the above client code is working is that when I give a keyboard input, then the socket sends data to server and server responds back. But in the client code, in the for loop if I do two iterations, for the second iteration the data I enter from keyboard is not reaching server. I need to restart my client code to send data again. How do I fix this ?
Also, when once client is connected to the server, the other cannot connect to the server. Any ideas on how to do this ?

You need to design and implement a protocol that specifies what each side is supposed to do and then implement that protocol. You're expecting it to work by magic.
For example:
data = clientsocket.recv(1024)
I suspect you are expecting this to receive a "message". But TCP has no notion of messages. If you need to send and receive messages, you need to define precisely what a "message" is for your protocol and write code to send and receive them.
It may be helpful to look at the specifications for other protocols that use TCP such as HTTP, FTP, or IRC. It really is worth the time to write out a specification of your protocol before you write any code. It will save a lot of pain.