tcpserver not getting any data if client writes 4096 bytes or more

I am playing around with tcpserver and tcpclient. I came across an issue when writing >=4096 bytes to the server. This is my server:

server = tcpserver('0.0.0.0', 10000);

And this is my client:

client = tcpclient('X.X.X.X', 10000);
n = 4096;
write(client, uint8(ones(1, n)))

If n<4096 life is easy and everything goes fine. However, if n>=4096, I get server.NumBytesAvailable = 0. Also, if I retry the last line in my client, I get the following error:

Error using asyncio.MessageHandler/onError (line 31)
An existing connection was forcibly closed by the remote host

I suspect it has something to do with buffers. I know there is a buffer size in udp(), but I cannot find any similar property in tcpserver.

Thanks in advance.

Answer 1

[Zinea]

Hi Alberto Reig,

I can see that you are unable to send more than 4096 bytes from client to server using “write” function in MATLAB R2021a using tcp. I have given below a working code for your use. Client is successfully able to send >= 4096 bytes to Server.

Below is the code for client:

% Create a TCP client to connect to the server
client = tcpclient(serverAddress, serverPort);

% Define the amount of data to send
n = 4096;
dataToSend = uint8(ones(1, n));

% Write the data to the server
write(client, dataToSend);

Below is the code for server :

% Wait for a connection  
while true
    if server.NumBytesAvailable >= 4096  
        data = read(server, server.NumBytesAvailable, 'uint8');  
        
        % Process your data here  
        disp(data);
        
        break;
    end
end

Note – Once a data is read, it is removed from the buffer. So after one read, “NumBytesAvailable” will give 0.