UDP Listener Hex

Add-ons Bindings
1

Hi,

Has anyone implemented a UDP Listener that can consume Hex, or put in a layer to translate Hex to an ascii string that can then be processed in the rules ?

Thanks

Paul

2

What do you mean by “Hex”? Do you mean a representation of binary data using ASCII digits representing base 16 (0-F) or do you want to translate raw binary data?

3

Hi,

Sorry, its a 12 byte format that needs to be broken down and parsed.

9.1 General UDP Packet format

The UDP Packet Format is formed as follows:

Field

    • Len (byte) - The overall size of the UDP packet.
    • udpType (byte) - The packet type one of the characters ’A’, ’G’, ’R’.
    • Source 0-1 (2bytes) - These are two characters to identify the Udp source see later table.
    • srcChannel (byte) - The channel/event index.
    • tgtChannel (byte) - The target channel when sending remote commands, if the target channel type is analogue then the top bit is set, i.e. values are 128+channel.
    • action (byte) - The action being triggered (low 4 bits), includes Dwell number (high 4 bits).
    • fromNodeNr (byte) - Source webrick number 1-253.
    • toNodeNr (byte) - Target webrick number for remote commands. .
    • setPointNr (byte) - Where relevant for packet type
    • curValH (byte) - High byte of any value being sent
    • curValL (byte) - Low byte of any value being sent
4

Hi Paul

While I don’t have a ready made solution for you, I’ve been working with UDP sockets/packets for a binding I’m working on.

If you read in the bytes from the socket into an array, then pass that byte array into the constructor for a new string then you should have the ascii representation of the data (not Hex characters).

If I haven’t got the full picture then let me know.

5

Hi Daniel,

Thanks for the reply. Are you using the TCP/UDP binding or are you writing a new binding from scratch ? How do you intercept the UDP packet into a new constructor to translate into the string?

Paul

6

No I didn’t use the TCP/UDP binding, I wrote the network code pretty much from scratch (+ some google searching) using DatagramSockets.

snip

    byte[] buffer = new byte[256];
          DatagramPacket p = new DatagramPacket(buffer, buffer.length);
            try {
                socket.receive(p);
                if (!p.getAddress().equals(InetAddress.getLocalHost())) {
                    byte[] data = Arrays.copyOf(p.getData(), p.getLength());
                    String message = Utils.toHexString(data); // this gives you the Hex string such as 686400067161
                    String ascii = new String(data); // this gives you ascii such as hd\00\06qa

snip

Here’s the toHexString() method if you need it:

public static String toHexString(byte[] array) {
    return DatatypeConverter.printHexBinary(array).toUpperCase();
}

Now that you’ve mentioned the TCP/UDP binding, is there any reusable core functionality for this kind of stuff instead of having to roll your own code each for each binding?

7

I’ve not started yet, but had been reading this (am planning to use openhab2)

https://www.eclipse.org/smarthome/documentation/development/bindings/how-to.html

but…

could also adapt this, as it seems compatible with 2

8

Had a look but the network code seems pretty integrated into the binding itself, not sure how easy/difficult it would be to separate the two.

If you go down the route of trying to adapt I’d be interested to see how you get on.

9

thanks - will have to see if I can get some time to play around, may just clone and try to update around here, but won’t be for a while

Cheers

Paul

10

The line you highlighted is essentially the same as my String ascii = new String(data) line. You receive the byte buffer somehow and pass it to a String constructor.