I am working on an android application which would measure distance between two mobile device. I have been able to get rssi of nearby wifi enabled devices which I then use to roughly calculate the distance which usually does not have great accuracy. To improve the accuracy I also want to measure round trip time.
So my question is how can you send a packet from one android device to another via bluetooth or wifi signal if possible and then receive a response? Also do the devices have to be paired in each case or is knowing a mac address enough?
A quick googling will lead you to the android dev tutorial. There you should find the answer for your questions. However to sum it up: To find other devices via bluetooth you can use the bluetooth adapter. There you can try to discover new bluetooth devices or query a list of devices, which have been connected to the android device before.
Sending a packet works with OutputStream.write() reading with InputStream.read()
You will find at the dev site an example for this, but in short it could look like this (modified version of the example provided in the tutorial):
InputStream is = null;
OutputStream os = null;
public ConnectedThread(BluetoothSocket socket) {
try{
is= socket.getInputStream();
os = socket.getOutputStream();
} catch (IOException e) { System.out.println(e); }
}
public void run() {
byte[] buffer = new byte[1024]; // buffer store for the stream
int bytes=0; // bytes returned from read()
// Keep listening to the InputStream until an exception occurs or the stream ends
while (bytes != -1) {
try {
// Read from the InputStream, the read bytes will be stored in the array
bytes = is.read(buffer); //reads 1024 bytes into the buffer
} catch (IOException e) {
System.out.println(e);
break;
}
}
}
/* Call this from the main activity to send data to the remote device */
public void write(byte[] bytes) {
try {
os.write(bytes);
} catch (IOException e) { System.out.println(e); }
}
Related
I am currently trying to get a little network communication going between a qt server and a java client.
In my example, the client wants to send an image to the Server. My problem is now, that the server never sees the data, so bytesAvailable() returns 0.
I already tried QDataStream, QTextStream and readAll(), still no data.
Server:
QTcpServer* tcpServer;
QTcpSocket* client;
tcpServer = new QTcpServer();
if(!tcpServer->listen(QHostAddress::Any, 7005)){
tcpServer->close();
return;
}
...
tcpServer->waitforNewConnection();
client = tcpServer->nextPendingConnection();
client->waitForConencted();
while(client->state()==connected){
// Syntax here might be iffy, did it from my phone
if(client->bytesAvailable()>0){
//do stuff here, but the program doesnt get here, since bytesAvailable returns 0;
}
}
CLient:
public SendPackage() {
try {
socket = new Socket(ServerIP, Port);
socket.setSoTimeout(60000);
output = new BufferedOutputStream(socket.getOutputStream());
outwriter = new OutputStreamWriter(output);
} catch (ConnectException e) {
System.out.println("Server error, no connection established.");
} catch (Exception e) {
e.printStackTrace();
}
}
public void Send(BufferedImage img) {
try {
ByteArrayOutputStream baos = new ByteArrayOutputStream();
ImageIO.write(img, GUI.imageType, baos);
baos.flush();
byte[] imgbyte = baos.toByteArray();
System.out.println(imgbyte.length);
System.out.println("sending");
outwriter.write(imgbyte.length);
outwriter.flush();
// here i'd send the image, if i had a connection ...
output.flush();
} catch (Exception e) {
e.printStackTrace();
}
}
The connection and everything builds up fine, the code even tells me when the socket was disconnected when trying to send, so I guess connection isn't a problem.
I just started using Qt, so if you guys have any idea to why this wouldn't work, I'd be pleased to try it.
client->waitForConencted();
// At this point the client is connected, but it is likely that no data were received yet
client->waitForReadyRead(-1); // <- Add this
// Now there should be at least 1 byte available, unless waitForConencted or waitForReadyRead failed (you should check that)
if(client->bytesAvailable() > 0) {
// ...
}
Note that you can not expect all the data to arrive at once. The TCP stream can get fragmented in any way and the data will be received in randomly sized pieces. You must repeat waiting and reading until you receive everything. This also means that you must somehow know when you did receive everything. So you need to know how much data is coming, or somehow recognize the end of it. You can for example disconnect right after the data transfer, or send the data length first. Depends on your application.
Also have a look at QIDevice::readyRead signal which would allow you to handle reading asynchronously.
My code can't receive UDP messages from outside my home net. The communication is between Android and Java computer application, with IP inside my LAN (for example 192.168.0.3) the code works, if I put my Java computer application inside my online server (and obviously I changed every IP with external IPs) this doesn't work; Android can send but it can't receive.
Android code :
#Override
protected Integer doInBackground(Void... params) {
DatagramSocket socket = null;
byte[] buf = new byte[1024];
DatagramPacket packet = new DatagramPacket(buf, buf.length);
try {
socket = new DatagramSocket(25565);
} catch (Exception e) {
Log.i("Ex ", "");
}
while (true) {
try {
socket.receive(packet);
String message = new String(packet.getData(), 0,packet.getLength());
Log.i("message", "" + message);
} catch (IOException e) {
Log.i("IO Ex", "");
}
catch (Exception e){
}
}
}
Java computer application code :
http://pastebin.com/2hVGeP6R
192.168.0.X is an internal NAT address. Any network can use it, but it can't be reached from anywhere outside. You either need to configure your router to pass it through to your PC and hit the router's external IP, or you need a real network address.
Read carefully this example. I suppose you that you are trying to read and write in the same socket while it is open. In case it not working paste some more code in order to help you
I'm struggling here...
I'm trying to determine if data was successfully sent to the server through a TCP socket using the OutputStream object. For testing on emulator socket communications is loss after 30 sec. For write data OutputStream.write(); its doesn't throw an exception , and local server continuously running its not crashing, only tcp socket connection is loss after some time. All the methods in the socket class return as though the socket is active and working. Is there anything I'm doing wrong here? Is there any socket implementation or stream implementation I can use to get an exception or error when the stream/ socket doesn't actually send the data in the buffer? Also setting setSoTimeout() on the socket doesn't seem to do anything.
Please guide me...
Here is my code:
private void sendRec() {
int lstream;
int port = 1012;
byte[] byterecv = new byte[1040];
while (true) {
System.out.println("POOL-2");
synchronized (recSendThread) {
try {
recSendThread.wait(20);
} catch (InterruptedException e) {
}
}
if (stopcall == true) {
// break;
}
try {
// Provides a client-side TCP socket
Socket clientRec = new Socket();
// serverSocket = new ServerSocket(port);
// serverSocket.setSoTimeout(5000);
// Connects this socket to the given remote host address and
// port
clientRec.connect(new InetSocketAddress("192.168.1.36", port));
System.out.println("Just connected to "
+ clientRec.getRemoteSocketAddress());
System.out.println("SENTS Rec BEFORE");
// output streams that write data to the network
OutputStream outToServerRec = clientRec.getOutputStream();
DataOutputStream outStreamRec = new DataOutputStream(
outToServerRec);
outStreamRec.write(bData);
System.out.println("SENTS Rec AFTER");
// input streams that read data from network
InputStream inFromServerRec = clientRec.getInputStream();
// clientRec.setSoTimeout(5000);
DataInputStream inStreamRec = new DataInputStream(
inFromServerRec);
while ((lstream = inStreamRec.read(byterecv)) != -1) {
System.out.println("startrec bytearray -- "
+ byterecv.length);
bos1.write(byterecv, 0, lstream);
}
inStreamRec.close();// for closing dataouputstream
clientRec.close();// for closing socket connection
} catch (IOException e) {
e.printStackTrace();
}
}
}
Here is my receiver and player code..
/**
* start receiving the voice data from server
* */
protected void startplay() {
System.arraycopy(frndid, 0, playByteData, 0, 4);
System.arraycopy(userid, 0, playByteData, 4, 4);
ByteBuffer.wrap(sessionid).order(ByteOrder.LITTLE_ENDIAN).asIntBuffer().
put(call_sessionid);
System.arraycopy(sessionid, 0, playByteData, 8, 4);
int lstream;
int port = 1014;
while (true) {
System.out.println("POOL-3");
try {
if (stopcall == true) {
System.out.println("BREAKEDDDD1111");
//break;
}
// Host name
// port++;
InetAddress addressPlay = InetAddress.getByName("192.168.1.36");
// Creates a new streaming socket connected to the target host
Socket clientPlay = new Socket(addressPlay, port);
System.out.println("Just connected to play : " +
clientPlay.getRemoteSocketAddress());
System.out.println("SENTS Play BEFORE");
// output streams that write data
OutputStream outToServer = clientPlay.getOutputStream();
DataOutputStream outStreamPlay = new DataOutputStream(outToServer);
outStreamPlay.write(playByteData);
System.out.println("SENTS Play after");
// input streams that read data
InputStream inFromServerPlay = clientPlay.getInputStream();
DataInputStream inStreamPlay = new DataInputStream(inFromServerPlay);
//clientPlay.setSoTimeout(5000);
while ((lstream = inStreamPlay.read(byteArray)) != -1) {
System.out.println("startplay() bytearray -- " +
byteArray.length);
bos.write(byteArray, 0, lstream);
}
inStreamPlay.close();
clientPlay.close();// for closing play socket connection
responseBuffer = bos.toByteArray();
System.out.println("BAOSSIZE " + bos.size());
bos.reset();
bos.flush();
bos.close();
playing = true;
System.out.println("res length -- " + responseBuffer.length);
rcvbb=ByteBuffer.wrap(responseBuffer).order(ByteOrder.LITTLE_ENDIAN).
asShortBuffer().get(playShortData);
playVoiceReceived();// plays received data
} catch (ParseException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
}
/**
* start playing received the voice data from server
* */
public void playVoiceReceived() {
System.out.println("POOL-4");
try {
if (at != null) {
if (at.getPlayState() != AudioTrack.PLAYSTATE_PLAYING) {
at.play();// starts playing
} else {
System.out.println("Play BEFORE WRITE");
// Writes the audio data to the audio hardware for playback.
at.write(playShortData, 0, BufferElements2Play);
System.out.println("Play AFTER WRITE");
at.flush();
}
}
} catch (Exception e) {
e.printStackTrace();
}
}
The socket has sent the data ... to the local socket send buffer. What happens after that is up to the local TCP stack, the network, the remote TCP stack, and the remote application. If you want to know whether the remote application got the data, it will have to send you a reply.
Operator write does not check whether data was delivered because otherwise it would have to wait for too long time. If network connection is actually down, TCP layer of operating system, will try to send data anyway, but will detect problems somewhat later, i.e. 1 minute later, because it will not receive acknowledgement messages from the opposite side. It will then try to resend data several times, see that problem persists and only then will report exception condition on the socket. To know that socket is in exception condition, you need to perform some operator on socket, i.e. another write attempt. Try doing write in a loop like this:
while (true)
{
outStreamRec.write (data);
Thread.sleep (1000L);
}
It should throw an error about 2 minutes after network will be down.
Note, that in opposite to write operation, operation connect is synchronous, so it actually waits for response from the opposite side, and if there is not respose, it will throw an exception.
I'm facing a very weird problem with receiving data using UDP in Android.
I'm writing an application to control a wifi module from an android device. I'm able to successfully send data to this remote wifi device. But I'm not able to receive 'complete' data packet from this wifi device.
My code in android is:
public static void receivePacket(int receiverPort, Context context) {
DatagramSocket socket = null;
String text = "";
try {
byte[] message = new byte[1500];
DatagramPacket packet = new DatagramPacket(message, message.length);
socket = new DatagramSocket(receiverPort);
//socket.setSoTimeout(5000);
for (int i = 0; i < 12; i++) {
socket.receive(packet);
text += new String(message, 0, packet.getLength()) + "\n";
}
socket.close();
Log.d("Received Message", text);
} catch (Exception e) {
Log.e("UDP", "S: Error", e);
} finally {
if(null != socket){
socket.close();
}
}
}
So if I'm expecting the data "$BEG1;$PID2;$PIP192.168.15.245;$PPN80;$DAT987654321;$END1;" I'm only getting "$BEG1;$PID2;$PIP192.168.15.245;$PPN80;$DAT98"
I tried to use UDP WinChat application to see if it's able to get the message from the wifi module and I'm able to get the entire data.
Also if i try sending a really long message to the android device using UDP Win Chat Application I'm able to get the entire data!
I'm totally confused! Please Help.
I was able to isolate the problem. (Still havent found the fix though :(...)
From the above code I'm making use of the same packet.getLength() for every iteration assuming that it will change each time according to the data it has received. But sadly that's not the expected behavior. The getLength() makes use of the previous value and truncates the newly arrived messages.
[Please note: This is a random behavior and doesn't happen all the time]
Now the question is, how do I change or refresh this attribute everytime I receive a new message within the loop?
You need to reset the DatagramPacket length before every receive. Otherwise it keeps shrinking to the smallest packet received so far.
I am using bluetooth chat in order to connect and recieve data from a bluetooth device.
I use the following code for reading data:
public void run() {
byte[] buffer = new byte[1024];
int bytes;
Log.v("MR", "start listening....");
// Keep listening to the InputStream while connected
while (true) {
try {
// Read from the InputStream
Log.d("MR", "buffer in try");
bytes = mmInStream.read(buffer);
Log.d("MR", "input stream :"+(new String(buffer)));
// Send the obtained bytes to the UI Activity
mHandler.obtainMessage(Conn.MESSAGE_READ, bytes, -1, buffer).sendToTarget();
Log.d("MR", "buffer after");
} catch (Exception e) {
Log.e("MR", "Error :"+e.getMessage());
//
connectionLost();
// break;
}
Log.d("MR", "buffer after while");
}
}
The device is sending data all the time without stopping.
With the above code I get the message of:
Log.d("MR", "buffer in try");
then it goes to the next line:
bytes=mmInStream.read(buffer);
and never returns from that call. I guess this is because it starts reading data from the device and doesn't stop until it disconnects. How can I read a certain amount of bytes at a time?
EDIT
Unless it stay to the bytes = mmInStream.read(buffer); code due to that it don;t get any data back on from the device?
I use DataInputStreams instead as you can do a readFully() method which waits to read a certain number of bytes before returning. I setup the BT connection like this:
BluetoothDevice btDevice = bta.getRemoteDevice(macAddress);
BluetoothSocket btSocket = InsecureBluetooth.createRfcommSocketToServiceRecord(
btDevice, UUID.fromString("00001101-0000-1000-8000-00805F9B34FB"), false);
btSocket.connect();
InputStream input = btSocket.getInputStream();
DataInputStream dinput = new DataInputStream(input);
then later on when I want to read I use readFully:
dinput.readFully(byteArray, 0, byteArray.length);