TCP/IP Communications in Matlab

Sends/receives TCP packets using Matlab's Java interface. Now handles matrices and cell arrays, etc.

Description

Transmission Control Protocol (TCP/IP) communications are used to send data from one computer to another over a network or from one application to another within a single computer.

The jtcp.m program uses Matlab's ability to call Java code to enable it to send and/or receive TCP packets. One Matlab session can communicate with another Matlab session (on the same machine or over the network) or it can communicate with a completely different program (again, on the same machine or over the network).

This latest version of jtcp.m uses Java's serialization functionality to write and read strings, matrices, cell arrays and primitives (that is, just about any Matlab variable type other than structures).

Serialization will cause errors if jtcp.m is talking to a program or piece of hardware that does not itself implement serialization. In this case, set the 'serialize' argument to false when requesting or accepting a connection. This will limit read and write operations to variables of type "int8", which most socket applications will be able to handle.

• Required Products: MATLAB
• MATLAB release: MATLAB 7.8 (R2009a)

[Jayson Brouchoud]

Kevin,

This tool has been extremely useful for me. There is one problem I haven't gotten around yet. I'm regularily checking to see if other PCs have "logged on" so I'm doing a jtcp('accept') command triggered off a timer. The problem is that if the PC is not logging on, then I get a timeout as expected, but it hangs the port. I added a try/catch, but this kicks the jtcp routine back before it closes the port so I have the same problem. I'm sure it's my lack of how to use the tool properly, but if you have any suggestions, I would appreciate them.

Thanks,
Jayson

[Kevin Bartlett]

Hi Jayson,

No, it wasn't your fault; I failed to close the server socket in the event of a timeout. I've posted an updated version that I hope fixes the problem, but it hasn't appeared online yet. Look for an "Updates" section to appear in the next day or so below this "Comments and Ratings" section and then download the new version.

Glad you're finding it useful! And thanks for your help!

Kevin.

[Derek Eggiman]

Very nice example. However I've noticed your read function could be improved or perhaps cleaned up a little. Instead of the while loop for timeout you could do the following.

import java.net.Socket
import java.net.InetSocketAddress
            
%Set SocketAddress
sAddress = InetSocketAddress(Host,Port);
            
%Establish unconnected socket.
socket = Socket();

%connect
try
socket.connect(sAddress,timeout);
end

[Wei Ren]

Can the output be anything else besides char? like hexidecimal for example?

[Edwin Carter]

Great little example.
The only problem I've found is that binary numbers >127 get mapped to zero on read. I found that replacing
mssg(i) = jTcpObj.dataInputStream.readByte;
with
mssg(i) = read( jTcpObj.dataInputStream );
(in jtcp_read(), line 396)
solves this issue, but I don't know if this is the right thing to do...

[Kevin Bartlett]

Edwin, changing line 396 to
   "mssg(i) = read( jTcpObj.dataInputStream );"
might well be the right thing to do, but I can't say for sure that this won't cause more problems.

When I wrote jtcp.m, I limited it to handling strings because I don't really understand the internal workings of Sockets very well. Making it handle binary, hex, etc., seemed overly ambitious. I figured that for most applications the user could convert data to strings on one end and back to the original format (e.g., binary or hex) on the other.

I originally had a line testing to see if the user had entered a value of mssg that was not a string, but for some reason I commented it out. I have re-enabled this line, so now a non-string message will raise an error. Anybody who really wants to use jtcp.m to transmit binary or hex will have to re-comment out this test.

If there are any Sockets experts out there who want to take on the challenge of enhancing jtcp.m to handle other data types, I would encourage them to copy my code, build an improved version and post it to the File Exchange themselves, since this sort of thing is well outside my area of expertise.

Wei Ren, I hope this answers your question as well.

[Wei Ren]

Hey thanks for the reply.
I'll try to see what matlab can do with changing the formats correctly how I need it. This is going to take some trial and error.

I wish it was more well documented.

[Kevin Bartlett]

Hexadecimal should be easy, since (as I understand it) Matlab stores hexadecimal numbers as strings anyway. If you have a decimal number to send, you can convert it to a string with sprintf or num2str. You can also switch back and forth from hex to decimal with hex2dec and dec2hex.

[Wei Ren]

The thing is that I need my server to communicate to an application that will need it in HEX. so :(

[Wei Ren]

so according to wireshark
mssg = sscanf(' 02 04 05 B4 01 01 04 02','%x');
using either
jTcpObj.dataOutputStream.writeBytes(char(mssg));
or
jTcpObj.dataOutputStream.write(mssg);
show as 02 04 05 B4 01 01 04 02 sent correctly. which is what I want.

also have you tried
 data_reader = DataReader(d_input_stream);
message = data_reader.readBuffer(bytes_available);
Rodney had that new in his 2nd update of his syntax.
I tried adding that to your script but couldnt get it to work right.

[Wei Ren]

I forgot to note that even though it's sent correctly through wireshark, im still unable to read it correctly yet on matlab.
any ideas on how 0xB4 becomes -74?

[Kevin Bartlett]

@Wei Ren: I saw Rodney's new DataReader class. I might try to incorporate it into jtcp to make it more efficient, but I haven't gotten around to it yet.

Regarding sending/receiving hex data: sorry, no clue. I'll keep playing with jtcp to see if it can be expanded to data types other than strings. If you figure anything out in the meantime, please let me know.

[Wei Ren]

so using mssg(i) = read( jTcpObj.dataInputStream ) actually solved the problem of why 0xB4 was becoming -74. (Thanks Edwin)

So this is what i do sending hex data
mssg = sscanf(' 02 04 05 B4 01 01 04 02','%x');
jTcpObj.dataOutputStream.write(mssg);
jTcpObj.dataOutputStream.flush;

jTcpObj.dataOutputStream.writeBytes(mssg) works as well and both would work without using the flush class too.

on the receiving end
convert the mssg to hex using dec2hex(mssg)

[Matthias Geier]

Hi Kevin and others.

I had a similar problem when I wanted to send strings which contained binary zeros (\0) as separators.
This didn't work with writeBytes() because the binary zero was interpreted as end-of-string.
Also, when I analyzed the IP traffic with wireshark, I saw that sometimes (strangely not always) an IP packet was sent for every single character of my message-string, which seemed quite inefficient to me.

So I changed line 351 from

jTcpObj.dataOutputStream.writeBytes(char(mssg));

to

jTcpObj.dataOutputStream.write(uint8(mssg), 0, length(mssg));

... where the second argument is an offset (which I chose to be 0).

This worked perfectly for me, I think it could also work for others, but of course I'm not sure about any side-effects or pitfalls ...

BTW, I didn't didn't care about receiving data, because I used another application for that.

Thanks for the this great m-file, it was very useful!

[Kevin Bartlett]

@Matthias and Rei Wen: I think we may be running into some platform-dependent stuff (I'm running Linux). I never had the problem in which 0xB4 becomes -74, and binary zeroes were coming through fine. I've rewritten jtcp.m to send messages in int8 format, rather than as strings. I'm hoping this will result in less variability in its behaviour. I also took Matthias' suggestion of using write() instead of writeBytes(). I'd appreciate you letting me know how this works for you.

In addition, I have incorporated Rodney Thomson's DataReader java class into the program (its use is optional). Again, let me know how this works for you.

[Wei Ren]

Kevin: I just wanted to make sure that you didn't misunderstood what i said last. 0xB4 is 180 in decimal. I was getting -74 until I corrected what Edwin pointed out.

[Kevin Bartlett]

@Wei Ren: Thanks for the feedback. I don't think I misunderstood you. You were finding that when you sent 0xB4 (decimal 180), you were receiving -74; you found that Edwin's fix of using
   mssg(i) = read( jTcpObj.dataInputStream );
instead of
   mssg(i) = jTcpObj.dataInputStream.readByte;
solved this problem.

However my point is that I never experienced this same problem using readByte(), which is why I think there may be some platform-dependent issues here.

I think that switching from transmitting chars to transmitting int8 values, as I've done in the newest version, ought to avoid some of these issues.

Let me know how it works for you and if any of the same problems crop up again.

[Matthias Geier]

@Kevin: Thanks for your response and for the adaptation of your code!
Just for the records: I was also running Matlab on Linux and I did have problems sending binary zeros.
I didn't try it on other operating systems.
I didn't try other strange characters either, just binary zeros and plain ASCII letters and punctuation.

[Tanyer Alan]

 

[Timothy]

I'm looking at MATLAB (+ Add ons as requried) as part of my dissertaion to model SCADA vulnerabilities, when they use TCP/IP (UDP) etc. This has popped up in my searching. Anybody any ideas if this file is suitable?

[Elham Dolatabadi]

Hello Kevin,

I tried to run the code and start a request from client to server but I got this error;
"??? Java exception occurred:
java.lang.IllegalArgumentException: timeout < 0

at java.net.PlainSocketImpl.setOption(Unknown Source)

at java.net.ServerSocket.setSoTimeout(Unknown Source)

Error in ==> jtcp>jtcp_accept_connection at 345
serverSocket.setSoTimeout(timeout);

Error in ==> jtcp at 256
    jTcpObj = jtcp_accept_connection(port,timeout);"

What does that mean?

[Kotya Karapetyan]

Hello,

I am trying to use this tool to control a GPIB device over Ethernet using a Prologix' GPIB-Ethernet controller. Somehow I fail so far.

E.g., this controller can accept the command '++addr' and return the address of the device it is controlling. With a terminal program (I am using PuTTY), I type in '++addr' and get '5' in return. I am trying the code:

JTCPOBJ = jtcp('REQUEST', '131.220.157.23', 1234)
jtcp('WRITE',JTCPOBJ,int8('++addr'))
mssg = jtcp('READ', JTCPOBJ)

in the hope to see the response, but get a 1-by-0 matrix in response. Can you see what I am doing wrong? The IP address and the port are exactly the same as with the terminal.

[Kotya Karapetyan]

I've found the problem: I was submitting int8('++addr'), but I should have submitted [int8('++addr') 13 10] to imitate CR.

[Alan]

Thanks. Very nice.

[Ian]

I'd love to be able to use this to send / receive class objects too. The way PNET does this is serialize an object to file (save it), then send the bytes, saved to file on the remote end and loaded back in. This is not efficient, but until TMW allows us to serialize objects properly, this works well enough.

[Patrick Damiani]

Kevin,

I just downloaded your code, but I haven't had a chance to run it yet. I noticed in the description, you specifically say that it does not work on structures. Do you have plans to update this to send and receive structures?

[Kevin Bartlett]

Hi Patrick. No, no plans to accommodate structures. You can easily pass any particular structure type by writing encode/decode functions to loop over the fields, passing each one to jtcp.m and re-assembling the structure on the other side. To make jtcp.m send and receive arbitrary structures, however, would require recursive programming to handle multiply-nested structures of all possible data types, and I didn't want to go that route.

[Jesse Hopkins]

Patrick and Ian, take a look at CompressLib on the file exchange. Using this you can serialize almost any matlab structure to an array of bytes, and deserialize it back to a matlab structure on the other side. You can do classes as well, although that takes some work in the class definition itself.

[Patrick Damiani]

Kevin, I was planning as much, but then I was going to ask if you knew if it was possible to... do exactly what Jesse has suggested. Thank you Jesse. I will check out CompressLib and see if the combination works for what I need.

[Patrick Damiani]

Hey Jesse, I looked up and down the file exchange for something called CompressLib. I tried searches for: convert, compress, structures, binary, tcp, bytes, variables, and the like. Is CompressLib still on the exchange?

[Jesse Hopkins]

Here's a link to CompressLib: http://www.mathworks.com/matlabcentral/fileexchange/25656-compression-routines

[Nor Muzakkir]

i cant connect at all. i've tried adding Rules in the firewall (even tried when turning off the firewall) but still i keep failing to make connection.

i really dont understand much on networking procedures, but if anyone could help point out the steps to make this works (especially establishing connection) it would be very helpful.

Thanks so much.

[Kevin Bartlett]

Hi Nor, are you connecting two Matlab sessions together or trying to connect Matlab with some other software? Are you on Windows? Mac? Linux? What error message do you get when you fail to make a connection?

Probably the easiest way to play with jtcp.m is to get two Matlab sessions running on one computer (assuming your licence permits it). Assign one session the role of "client" and the other the role of "server and follow the example code in jtcp.m's help, with "client" lines being executed in the client session and the "server" lines being executed in the server session. EXECUTE THE LINES IN THE ORDER SHOWN IN THE HELP EXAMPLES. You can substitute a higher value than 2000 milliseconds for the timeout, if that makes things easier. I have used port 21566 in the examples; this port will have to be open in your firewall, or the firewall turned off.
Kevin.

[Mr Smart]

 

[Musharaf Ali]

Excellent ,I works great and easy to use ,Bless you

[Dean Kleissas]

 

[Alexander Kosenkov]

 

[Ueli Rutishauser]