UNET - Broadcast Data from Android changes when PC joins Network

phineliner · November 2, 2015, 6:20pm

Hi all,

I wrote a NetworkBroadcastSender and a NetworkBroadcastReceiver based on this.
I’m currently inspecting the receiving data on different devices.
I’m experiencing a weird behavior which I can not understand.
If I’m running the BroadCastService between Windows only or Android only everything works as expected.
If I’m running it on Android and Windows in the same network, the following happens:

This is the log collected from the Windows Machine (***** Delimiter)

I start the service on two Android devices (!!! and ??? Delimiters).
The messages they sent and receive are displayed in log row 3 and 4.
Those are the correct ones.
Now that the windows machine joined the network (row 5 and 6), the received messages alter to the data displayed in the last two rows of the log image.
As you can see, it seems that the delimiter of the windows machine seems to be appended to the data of the android devices (0*** after the !!! and the ???).
Exactly the same result is delivered in the android log:

This is the log from the android device perspective.

I don’t know why this is happening.
I assume something withing the network is going wrong.
I mean, how should the pc, which is the only one with the ***** delimiters in code, affect the messages generated by the android devices who don’t know about the ***** delimiters?
The android devices even keep sending the altered messages after the windows machine left the network again (until I restart the app on the android devices).

Does anyone have a clue of what is happening here?

Thanks,
phineliner

P.S.: You may wonder why the pc log contains two broadcasts (row 5 and 6) from the windows machine: This is because there are two network cards on the win machine. Only one of these broadcasts will be forwarded to the android devices because of the subnet (this is intended). Thats why you see only one broadcast coming from the win machine in the android log.

phineliner · November 4, 2015, 11:06am

I found out what was wrong (thanks to irwiss and Necromantic from the irc channel #unity3d-unet)!
It was not a platform specific problem.

I was parsing the receiving broadcast data incorrectly.
I did parse the whole msgBuffer, instead of only parsing a certain range (the receivedSize range).
Thus, bufferData from previous messages would be appended to current messages, if the size of previous messages was bigger than the current one.

Refering to the used example mentioned above, you would need to extend the BytesToString method:

static string BytesToString(byte[] bytes)
    {
        char[] chars = new char[bytes.Length/ sizeof(char)];
        System.Buffer.BlockCopy(bytes, 0, chars, 0, bytes.Length);
        return new string(chars);
    }

Extended:

static string BytesToString(byte[] bytes, int sizeToCopy = -1)
    {
        if (sizeToCopy < 0)
            sizeToCopy = bytes.Length;

        char[] chars = new char[sizeToCopy / sizeof(char)];
        System.Buffer.BlockCopy(bytes, 0, chars, 0, sizeToCopy);
        return new string(chars);
    }

In Addition one could ensure to Clear the buffer of exceeding bytes after calling GetBroadcastConnectionMessage(…) like so:

Array.Clear(msgBuffer, receivedSize - 1, msgBuffer.Length - receivedSize);

Hope this helps someone else!

Cheers,
phineliner