TCP Connection Fread data Size Warning Error

I have a TCP server in my Matlab code, my client sends some data (max 4 bytes) on some triggers from another application to Matlab. I am receiving those numbers but I am also receiving this warning message many times:

Warning: The specified amount of data was not returned within the Timeout period. 'tcpip' unable to read all requested data. For more information on possible reasons, see TCPIP Read Warnings.

clc;

t = tcpip('0.0.0.0', 55000,'InputBufferSize', 1024,'NetworkRole','Server', 'TimeOut', 0.5);
fopen(t);

while(1)    
    data = fread(t, 4, 'char');    
    dataChar = char(data);
    dataDouble = str2double(dataChar);  

      if (~isnan(dataDouble))
          if (dataDouble == 0)
              fclose(t); % closing the tcp connecting
              error('0 value is received!') % to jump out of Matlab run mode
          else
              disp("Last Receieved double was: " + dataDouble)
          end       
      end       
  end

I also tried get(obj1,'BytesAvailable'), but it gives me error. Does anyone know how to bypass this warning?

Answer 1

[Mohsenne Chaverdie]

https://stackoverflow.com/questions/53141534/matlab-tcp-connection-fread-data-size-warning-error

Answer 2

[Walter Roberson]

You did not configure for termination mode 'datagram' so when you fread 4 then tcpip is going to read as many packets as it needs in order to get the 4 bytes. It is encountering a timeout in doing so, which is generating the warning.

If you use fread with a size you should be sure that the other end is going to send that size. If the sender is sending variable size then the easiest way to handle it is to have the sender emit a termination character, configure the tcpip connection for matching character, and use fgetl()

It is possible to configure for termination mode datagram and send a variable length packet with no terminator, but for that it is recommended to configure bytes available fcn callback and fread(obj1, obj1.BytesAvailable)