UDP Packet received okay in Java but corrupted in Python

Question

I am trying to record audio from an Android tablet and send it to a python server. At the start of the byte packet, I include some relevant information about the state of the Android app (A byte array called "actives" -- but considering it's receiving fine by a Java server, this should not be relevant). The android code is as follows:

                   int read = recorder.read(buffer, 0, buffer.length);

                    for (int a = 0; a < actives.length; a++) {
                        outBuffer[a+1] = (byte)actives[a];
                        logger = logger + Byte.toString(actives[a]) + ",";
                    }
                    int furthest=0;
                    for(int a =0; a < buffer.length; a++){
                        outBuffer[actives.length+1+a]=buffer[a];
                        if(buffer[a]!=0)furthest=a;
                    }
                    packet = new DatagramPacket(outBuffer, read,
                            serverAddress, PORT);
                    Log.d("writing", logger+Byte.toString(outBuffer[7])+".length"+Integer.toString(1+furthest+actives.length+1));
                    Log.d("streamer","Packet length "+outBuffer.length);
                    try {
                        socket.send(packet);
                    }catch (IOException e){
                        Log.e("streamer", "Exception: " + e);
                    }
                    Log.d("streamer","packetSent");

I receive a clean signal on the other end using a Java server. Image of received java output: !(https://i.sstatic.net/OCFmP.png) This is my Java server:

DatagramSocket serverSocket = new DatagramSocket(3001);
int byteSize=970;
byte[] receiveData = new byte[byteSize];
DatagramPacket receivePacket = new DatagramPacket(receiveData,
        receiveData.length);
while(true){        // recieve data until timeout
                        try {
                            serverSocket.receive(receivePacket);
                            String rcvd = "rcvd from " + receivePacket.getAddress();
                           System.out.println("receiver"+"Received a packet!" +rcvd);

                            break;
                        }
                        catch (Exception e) {
                            // timeout exception.
                            System.out.println("Timeout reached without packet!!! " + e);
            timeoutReached=true;
                            break;

                        }
                 }
if(timeoutReached)continue;
    currTime = System.currentTimeMillis();

    data = receivePacket.getData();

Here is my Python server's output: !(https://i.sstatic.net/VXjLX.png) And here is the code:

import socket
ip="192.ip.address"
port=3001;
sock=socket.socket(socket.AF_INET,socket.SOCK_DGRAM);
sock.bind(('',port));
while(True):
    data,addr=sock.recvfrom(970);
    print("address",addr);
    print("received a data!");
    print(data);

In the last line of the python script, I have tried to change "print(data)" to "print(data.decode())", in which case I get this error:

UnicodeDecodeError: 'ascii' codec can't decode byte 0xff in position 0: ordinal not in range(128)

I am not running these servers at the same time My guess is that it has to do something with Java using unsigned ints and python not doing that. Is there a way in Python that I can convert this data, because data.decode() is not working? Alternatively I should be able to convert the data in Java somehow? None of the answers on stackoverflow that I have tried have worked.

Answer 1

This was pretty brutal to attack head-on. I tried specifying the encoding in Java (before sending) like another SO post suggested, but that didn't help. So I side-stepped the problem by converting my Android byte array into a comma-separated string, then converting the string back into UTF-8 bytes.

sendString="";
for(int a =0; a < buffer.length; a++){
           sendString=sendString+Byte.toString(buffer[a])+",";
}
byte[] outBuffer = sendString.getBytes("UTF-8");

Make sure you reset your string to null ("") each time you go through the while loop, or your ish will get very slow af.

Then in Python,right after receiving:

data=data.decode("utf8");

Although I am stringifying 980 characters, it does not appear to add much to the processing time... although I do wish that I could send the raw bytes, as speed is very important to me here. I'll leave the question open in case someone can come up with a better solution.