Develop Reference

Sending bluetooth data between Android and Hololens

I have created an application to Android and Microsoft Hololens, where it is possible to send some GPS-data with bluetooth from an Android-phone to a Hololens (with Bluetooth LE Advertiser) and that works allright. But when I am trying to send other data from Hololens to Android, I have a problem that Android-phone can't discover Hololens, although these devices are paired. Is it even possible to send data from Hololens with bluetooth, or is there only something wrong in my code? Does Bluetooth LE Advertising support two-way data transfering?

I am guessing you have a BluetoothConnected thread in your android app with an InputStream (mine is mmInStream). Try using this as your 'run' function in the thread:
public void run() {
System.out.println("BT THREAD RUNNING");
mmBuffer = new byte[1024];
int numBytes; // bytes returned from read()
InputStreamReader mmInStreamReader = new InputStreamReader(mmInStream);
BufferedReader mmReader = new BufferedReader(mmInStreamReader);
// Keep listening to the InputStream until an exception occurs.
while (true) {
try {
// Read from the InputStream.
Thread.sleep(100);
String s = mmReader.readLine();
Thread.sleep(100);
//Static class that handles the response
BluetoothCommunications.responseHandler(s);
} catch (IOException e) {
System.out.println("Input stream was disconnected" + e);
main.disconnected();
break;
} catch (Exception e) {
System.out.println(e.getMessage());
}
}
}

Android TCP Socket InputStrem Intermittent Read or too Slow

I need to implement a TCP comunication between an IoT device(custom) and an Android App.
For the Wifi device we have a Server Socket, while in Android i have an AsyncTask as a Client Socket. Both the device and the smarthone are connected to the same network.
Here is the Android Client Socket code for the initialization/socket-read and socket-write:
Variables:
static public Socket nsocket; //Network Socket
static public DataInputStream nis; //Network Input Stream
static private OutputStream nos; //Network Output Stream
AsyncTask method doInBackgroud:
#Override
protected Boolean doInBackground(Void... params) { //This runs on a different thread
boolean result = false;
try {
//Init/Create Socket
SocketInit(IP, PORT);
// Socket Manager
SocketUpdate();
} catch (IOException e) {
e.printStackTrace();
Log.i("AsyncTask", "doInBackground: IOException");
clearCmdInStack();
MainActivity.SocketDisconnectAndNetworkTaskRestart();
result = true;
} catch (Exception e) {
e.printStackTrace();
Log.i("AsyncTask", "doInBackground: Exception");
result = true;
} finally {
try {
SocketDisconnect();
} catch (IOException e) {
e.printStackTrace();
} catch (Exception e) {
e.printStackTrace();
}
Log.i("AsyncTask", "doInBackground: Finished");
}
return result;
}
Socket Initializzation:
public void SocketInit(String ip, int port) throws IOException {
InetAddress addr = InetAddress.getByName(ip);
SocketAddress sockaddr = new InetSocketAddress(addr, port);
nsocket = new Socket();
nsocket.setReuseAddress(false);
nsocket.setTcpNoDelay(true);
nsocket.setKeepAlive(true);
nsocket.setSoTimeout(0);
nsocket.connect(sockaddr, 0);
StartInputStream();
StartOutputStream();
}
Read from Socket:
private void SocketUpdate() throws IOException, ClassNotFoundException {
int read = 0;
// If connected Start read
if (socketSingleton.isSocketConnected()) {
// Print "Connected!" to UI
setPublishType(Publish.CONNECTED);
publishProgress();
if(mConnectingProgressDialog != null)
mConnectingProgressDialog.dismiss(); //End Connecting Progress Dialog Bar
//Set Communications Up
setCommunicationsUp(true);
Log.i("AsyncTask", "doInBackground: Socket created, streams assigned");
Log.i("AsyncTask", "doInBackground: Waiting for inital data...");
byte[] buffer = new byte[3];
do{
nis.readFully(buffer, 0, 3);
setPublishType(Publish.READ);
publishProgress(buffer);
}while(!isCancelled());
SocketDisconnect();
}
}
Streams init:
public void StartInputStream() throws IOException{
nis = new DataInputStream(nsocket.getInputStream());
}
public void StartOutputStream() throws IOException{
nos = nsocket.getOutputStream();
}
Read and Write methods:
public int Read(byte[] b, int off, int len) throws IOException{
return nis.read(b, off, len); //This is blocking
}
public void Write(byte b[]) throws IOException {
nos.write(b);
nos.flush();
}
public boolean sendDataToNetwork(final String cmd)
{
if (isSocketConnected())
{
Log.i("AsyncTask", "SendDataToNetwork: Writing message to socket");
new Thread(new Runnable()
{
public void run()
{
try
{
Write(cmd.getBytes());
}
catch (Exception e)
{
e.printStackTrace();
Log.i("AsyncTask", "SendDataToNetwork: Message send failed. Caught an exception");
}
}
}).start();
return true;
}
Log.i("AsyncTask", "SendDataToNetwork: Cannot send message. Socket is closed");
return false;
}
The application is very simple, the android app sends a command(via sendDataToNetwork method) to the IoT device and the latter sends back an "ACK" Command string.
The problem
The problem is that while the IoT device always receives the command, the smartphone rarely gets the ACK back. Sometimes i get something like "ACKACKACKACK". By debugging the IoT device i'm sure that it successfully sends back the ACK, so the problem lies in the InputStream read() method which doesn't retrieve the string right away.
Is there a way to empty the InputStream buffer right away, so that i get an "ACK" string back from the IoT device every time i send a command?
Update
I've updated the socket config so that there are no more buffer limitations and i've replaced read() method with readFully. It greatly improved, but still make some mistakes. For istance one out of 2-3 times no ack is received and i get 2 ack the next turn. Is this perhaps the computational limit of the IoT device? Or is there still margin for a better approach?

the problem lies in the InputStream read() method which doesn't empty the buffer right away.
I don't know what 'empty the buffer' means here, but InputStream.read() is specified to return as soon as even one byte has been transferred.
Is there a way to empty the InputStream buffer right away, so that i get an "ACK" string back from the IoT device every time i send a command?
The actual problem is that you could be reading more than one ACK at a time. And there are others.
If you're trying to read exactly three bytes, you should be using DataInputStream.readFully() with a byte array of three bytes.
This will also get rid of the need for the following array copy.
You should not mess with the socket buffer sizes except to increase them. 20 and 700 are both ridiculously small values, and will not be the actual values used, as the platform can adjust the value supplied. Your claim that this improved things isn't credible.
You should not spin-loop while available() is zero. This is literally a waste of time. Your comment says you are blocked in the following read call. You aren't, although you should be. You are spinning here. Remove this.

Android bluetooth socket cannot disconnect

I'm working on a BluetoothChat sample based app, one device send another device parameters and the second send the data. I think that problem is in Connected thread run() method which i must edit because the original version receive data in not correct order . If I close program running on one device the second device is still connected to disconnected device.
public void run() {
int bytes;
int availableBytes=0;
while (true) {
try {
availableBytes=mmInStream.available();
byte[] buffer = new byte[availableBytes];
// Read from the InputStream
bytes = mmInStream.read(buffer);
if (bytes>0){
mHandler.obtainMessage(Constants.MESSAGE_READ, bytes, -1, buffer)
.sendToTarget();
}
// Send the obtained bytes to the UI Activity
} catch (IOException e) {
connectionLost();
// Start the service over to restart listening mode
BluetoothClientService.this.start();
break;
}
}
}

Android Bluetooth inputstream unable to read continuously

I have the following android code where I am connecting to a device which is sending me continuous stream of data using Bluetooth. In the following code, after getting some data, I am unable to read any more data even though Bluetooth connection is still established and data is being sent by device.
I start getting the following error
Info: error in stream reader:bt socket closed, read return: -1
private void readStreamDataInSeparateThread()
{
new Thread(new Runnable() {
#Override
public void run() {
while(inputStream != null && isConnected())
{
try
{
byte[] buffer = new byte[1024];
int readCount = inputStream.read(buffer);
System.out.println("Info: ReadCount:"+readCount);
if(readCount > 0)
byteBuffer.add(buffer,0,readCount);
else
{
if(time_out_counter >= TIME_OUT)
{
closeConnection();
break;
}
time_out_counter++;
System.err.println("Info: error end of stream reached for stram reader");
}
Thread.sleep(50);
}catch(IOException e){
System.err.println("Info: error in stream reader:"+e.getMessage());
// closeConnection();
}
catch(InterruptedException e){}
}
System.out.println("Info: stream stoped reading ");
}
}).start();
}
But strange thing is if I keep my device'c (Samsung tab 3 neo) wifi on and connected, then i receive no error.
Also, if i increase the time delay to more than 6 secs then, i don't receive this error for very long time.
Please let me know, if anyone can rootcause the issue or give me some pointers

How to detect EOF on android bluetooth file transfer?

I have implemented a bluetooth connection using the now-classic Google Bluetooth Chat code. However, I have a question which I just cannot seem to wrap my brain around.
The reading of the input stream goes something like this:
public void run() {
byte[] buffer = new byte[1024]; // buffer store for the stream
int bytes; // bytes returned from read()
// Keep listening to the InputStream until an exception occurs
while (true) {
try {
// Read from the InputStream
bytes = mmInStream.read(buffer);
// Send the obtained bytes to the UI Activity
mHandler.obtainMessage(MESSAGE_READ, bytes, -1, buffer)
.sendToTarget();
} catch (IOException e) {
break;
}
}
}
Now, that's fine if I was just printing out the characters I was receiving as in the original example. However, suppose I wanted to transfer an image file. I don't know the size of the file, so I cannot count the bytes received or anything like that. In my tests, I don't seem to be ever receiving a "-1" from the input stream, which appears to be the "norm" for reading from input streams. So how can I know that I have reached the end of the file that was being sent?
Thank you for your help and your time.

It seems Android bluetooth input streams never return -1.
I guess setup a simple protocol by sending file size in the first place and EOF signals at last will help.

No it does not. Android sends -1 only when the Socket is closed as far as I know. So a workaround could be to do a reconnect, but I was trying that for hours and did not get it working, since I do not understand this "special" Code here (copied from a Stackoverflow Thread) for setting up the socket:
BluetoothSocket tmp = null;
Log.d(TAG, "New Connection initialized");
Method m;
try {
m = device.getClass().getMethod("createRfcommSocket",
new Class[] { int.class });
tmp = (BluetoothSocket) m.invoke(device, 1);
} catch (Exception e) {
e.printStackTrace();
}
mmSocket = tmp;
This Socket only works, when my App is started for the first filetransfer. If I want to "Reconnect" with a completely new instantiated Object (and a new Socket created with that Code), the program freezes on the blocking method mmSocket.connect(). It seems like the Method never comes to an ending. This is driving me nuts...

Try
while ((bytes = mmInStream.read(buffer) != -1)
and see if that helps.

Try this:
public void run() {
byte[] buffer;
ArrayList<Integer> arr_byte = new ArrayList<Integer>();
while (true) {
try {
int data = mmInStream.read();
if(mmInStream.available()>0) {
arr_byte.add(data);
} else {
arr_byte.add(data);
buffer = new byte[arr_byte.size()];
for(int i = 0 ; i < arr_byte.size() ; i++) {
buffer[i] = arr_byte.get(i).byteValue();
}
Log.e("INPUT",new String(buffer));
mHandler.obtainMessage(MESSAGE_READ, bytes, -1, buffer)
.sendToTarget();
arr_byte = new ArrayList<Integer>();
}
} catch (IOException e) {
break;
}
}
}