Interface between Python and Matlab using tcpserver

I am currently trying to run an instance of matlab as a tcp server using the tcpserver function from the Instrument Control Toolbox. I want a python script that acts as the TCP client to connect to the matlab server, send it commands and get the results back via TCP. Here is a simple example of this connection, as I am trying to implement it:

server = tcpserver('127.0.0.1', 1234)
while true
    if server.NumBytesAvailable>0
       try
           data = read(server, 11, "string")
           write(server, "Hello back!")
       catch ME
           clear server
           rethrow(ME)
       end
    end
end

The code for the Python client is the following:

import socket

with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as sock:
    sock.connect(('127.0.0.1', 1234))
    print("Connection to server established!")
    sock.sendall(b'Hello World')
    data = sock.recv(1024)

print('Received', repr(data))

When I run the server and client, although Matlab receives the message from the Python client, I get the following error when it tries to send the answer:

data = 

    "Hello World"

Error using testserver (line 6)
Failed to write from the server. A TCP/IP client must be connected to the server.

Does anyone know why this happens and if there is a way to work around it?

Answer 1

[Kunal Kandhari]

Changing matlab code to following will work:

server = tcpserver('127.0.0.1', 1234,"ConnectionChangedFcn",@connectionFcn)

function connectionFcn(src, ~)
    if src.Connected
       data = read(src, 11, "string")
       write(src, "Hello back!")
    end
end

It will not close the connection also infinite clients can connect to this server.

[文韬 王]

Hello! I have encountered the same problem described above. I have tried your code and it worked well.

But unfortunately I have some special demands since I want to send abundant real-time data through a long-term iteration and embed the whole thing in the appdesigner environment, that is to say, I cannot stand the limited functionality that those data could only be sent when the connection state changes. For more detail, please see https://www.mathworks.com/matlabcentral/answers/1818280-error-occurred-when-communicating-between-matlab-server-and-python-client-via-tcp-ip

As for my tricky situation, Do you have any other suggestions? Please lend me a hand.