TCP/IP Socket Communications in MATLAB

A simple example TCP/IP server and client

Description

Provides an example Server / Client written in MATLAB that utilises the ability to call Java inline to perform message communication using TCP/IP.

Importantly it does not require any pre-compiled DLLs or force you to compile some MEX c-files. Nor does it require any additional toolboxes Its all contained within the .m files.

To use the example:

- Start 2 instances of MATLAB
- in the first execute the following:
  message = char(mod(1:1000, 255)+1);
  server(message, 3000, 10)
- in the second execute the following:
  data = client('localhost', 3000)

For more details see:
http://iheartmatlab.blogspot.com/2008/08/tcpip-socket-communications-in-matlab.html

• Acknowledgements: This submission has inspired the following:; A simple UDP communications application
• MATLAB release: MATLAB 7.0.4 (R14SP2)

[Felipe Posada]

Very useful, thank you.

[Jorge Ramírez]

Thanks, it is very easy to use and very useful.

[Maurizio]

It's very useful to build a simple network with MatLab, but in the example you read abyte in a loop. I've tried to read the buffer with the method read (byte [ ] b, int off, int len) of the class DataInputStream, but I don't find anything into the buffer b; the result of this method (the of bytes read) is correct! How can I pass the input buffer to the method?

[Rodney Thomson]

Hi Maurizio,

Unfortunately the read(byte []) method will not work directly from within MATLAB. My thoughts as to why:

When you execute:
  data = zeros(1, 100, 'char');
  data_input_stream.read(data, 0, 100);
It supplies a COPY of the data array which would be populated. Unfortunately you don't have access to this. This requires pass-by-reference semantics which I don't think MATLAB currently support.

To get around this issue personally I've created helper Java classes to read blocks of data and RETURN the Byte array. This requires creating Java classes and compiling them.

Email me if you want some examples.

Rod
  

[Ricardo Correia]

Hello! I have one question.. Can i send wav files through this? Or this is only to send messages?
Thanks for your help

[Eric]

Thanks s lot for Rodney effort.
But in my current project, I need to use socket to communicate with a phycial layer model. So I need to write and read from the model via socket. The example only gives one way direction communication, i.e. client read data from the server. So i hope to know: how does the client send data to server by socket ?
I copy some commands from the server:

            output_stream = output_socket.getOutputStream;
            d_output_stream = DataOutputStream(output_stream);

            % output the data over the DataOutputStream
            % Convert to stream of bytes
            fprintf(1, 'Writing %d bytes\n', length(message))
            d_output_stream.writeBytes(char(message));
            d_output_stream.flush;

And apply these in sending data to server, but i found this doesn't work, i.e. the client can't send data to server. Could you please give me some help? Thanks very much.

[Eric]

I have solved my problem. Just write here to share with everyone. I also read a lot java documentations about socket. Finally i think this program is most simple and suitable for our use. We can change it to a bidirectional program according to our requests. This is example is very important. Thanks!

[Jens]

Hey Eric, my client have to send data to the server. Could you give me some help and tell me the way you solved the problem?

[Bebbe]

Hello Eric .. I read your problem and I need to communicate with clients and servers in bidirectional mode ... how did you solve your problem? I am not a java expert so I am a bit in trouble ...
sorry for my bad English ..
thanks a lot ..

[Sharath]

if i am getting data continuosly say for every 1milli sec from server to client how do we handle this

[Rodney Thomson]

Sharath,

To receive data continuously, you will need to call read() many times after you have successfully connected to the server.

For high update scenarios, you may want to use the Java class approach (http://iheartmatlab.blogspot.com.au/2009/09/tcpip-socket-communications-in-matlab.html) to read the data in chunks as I doubt you would be able to keep up with 1000Hz data otherwise.