Thanks a lot for sharing, Ian.

The error occurs because the InetAddress class has not been loaded. Add this line after InstallJava[]:

LoadJavaClass["java.net.InetAddress"]

Hi,

When applying the above code, I get the following message after using the writeSocket:

writeSocket[udpSocket, "127.0.0.1", 5000, ToCharacterCode["hello from mathematica"]]

JavaNew::argx: Incorrect number or type of arguments to constructor for class java.net.DatagramPacket. The arguments, shown here in a list, were {{104,101,108,108,111,32,102,114,111,109,32,109,97,116,104,101,109,97,116,105,99,97},22,InetAddress`getByName[127.0.0.1],5000}.

Java::argx1: Method named send defined in class java.net.DatagramSocket was called with an incorrect number or type of arguments. The argument was $Failed.

$Failed

any idea why?

Ah. Copy/pasting the writeSocket function to the reply section here seems to have taken out some necessary formatting. When I added back in the underscores for the function arguments and matched those arguments to the variables in the function body, all is good.

Hi,

Unfortunately SocketConnect doesn't yet support UDP sockets like you are describing. However, you can use J/Link to create a DatagramSocket Java object to accomplish the same thing. I have some example code below.

Needs["JLink`"];
InstallJava[];
udpSocket = JavaNew["java.net.DatagramSocket", 5000];

This creates a socket object that you can send and receive with using the methods receive and send. Both of these methods take a DatagramPacket object as their arguments, which can be created with JavaNew as below in the Module.

readSocket[sock_, size_] := 
    JavaBlock@
       Block[
         {datagramPacket = JavaNew["java.net.DatagramPacket", Table[0, size], size]},
         sock@receive[datagramPacket];
         datagramPacket@getData[]
       ]

To write a byte array to the socket, you can use the following function, which will use the provided socket to send data over UDP :

writeSocket[sock_, dest_String, port_Integer, data_ /; AllTrue[data, IntegerQ[#] && # >= 0 && # <= 255 &]] := 
    JavaBlock@
        sock@send[
            JavaNew["java.net.DatagramPacket", data, Length[data], InetAddress`getByName[dest],port]
        ]

Here's an example of sending data to a socket and receiving it:

writeSocket[udpSocket, "127.0.0.1", 5000, ToCharacterCode["hello from mathematica"]]

Then read in the raw byte data:

readSocket[udpSocket, 40]

{104, 101, 108, 108, 111, 32, 102, 114, 111, 109, 32, 109, 97, 116, 104, 101, 109, 97, 116, 105, 99, 97, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}

This can be turned back into the original string with FromCharacterCode:

DeleteCases[%, 0] // FromCharacterCode    

"hello from mathematica"

I hope this helps, and I'd be delighted to hear more about your robot.

Thanks, Ian

Hi Christopher,

What exactly is the error message you're seeing? It's possible that there were changes in 11.0.1 that broke the code I posted above.

Thanks,

Ian