Develop Reference

Front-end datagram truncation UDP Android

Thanks in advance to any support,
I'm trying to broadcast a UDP message on the local network. After sending a particular string, responders send back metadata about their location, IP address, status etc.
I've gotten communication to occur, but the issue is in the string response itself.
TLDR: My udp receive packet is cutting off front elements of the datagram.
I dont think this is a buffer size issue. My buff is 2048, much larger than the data I'm looking to receive (about 50-200 characters).
I have worked with this setup before and gotten the first part no problem (with iOS). A wireshark (equivalent) console also confirms. Wireshark and Android output have been attached for comparison.
Proper data coming in via packet app
Front-truncated packet in logcat (notice that everything up until "[Red]" has been omitted)
inside onCreate:
try{
socket = new DatagramSocket();
socket.setBroadcast(true);
socket.setSoTimeout(3000);
broadcastPacket = new DatagramPacket(
broadcastString.getBytes(),
broadcastString.length(),
getBroadcastAddress(),
30303);
}catch (IOException e) {
Log.e("MYAPP", "socket error", e);
}
inside an AsyncTask:
try {
while(true) {
byte[] buffer = new byte[2048];
DatagramPacket receivePacket = new DatagramPacket(buffer, buffer.length);
socket.receive(receivePacket);
String receiveString = new String(receivePacket.getData(), 0, receivePacket.getLength() );
Log.d("a", "Received response " + receiveString );
Log.d("a", "From host " + receivePacket.getAddress() );
Log.d("a", "With offset " + receivePacket.getOffset() );
}
}catch (java.io.IOException e) {
Log.d("a", "Receive timed out");
}
note that before using receivePacket.getLength() I'd just get a bunch of ?'s after the partial response

This did end up being an Android Studio bug.
String[] deviceElements = receiveString.split("\r\n");
Log.d("a", deviceElements[0]);
returned the data I was looking for; intially printing the full receiveString returned only a portion of the string.

Android TCP app hanging on inStream.readline()

This is a continuation of this question because it my orginal question was answered, but it did not solve the bug.
Question:
How do I fix the code hanging on this line inStream.readline()
My Intent:
This is in a thread that will loop through checking if there is an outMessage, if there is, it will send the message.
Next it will check it if there is anything in the in-stream, if there is, it will send it to the handler in my main activity.
Lastly, it will sleep for 1 second, then check again.
This should allow me to read/write multiple times without needing to close and open the socket.
Problem:
It is reading and writing better, but still not working properly
What is happening now:
If outMessage is initialized with a value, upon connection with the server, the socket:
writes and flushes the value (server receives & responds)
updates value of outMessage (to null or to "x" depending on how i have it hard-coded)
reads and shows the response message from the server
re-enters for the next loop
IF i set outMessage to null, it skips over that if statements correctly then hangs; otherwise, if i set outMessage to a string (lets say "x"), it goes through the whole if statement, then hangs.
The code it hangs on is either of the inStream.readline() calls (I currently have one commented out).
Additional info:
- once connected, I can type in the "send" box, submit (updates the outMessage value), then disconnect. Upon re-connecting, it will read the value and do the sequence again until it get stuck on that same line.
Changes since the referenced question:
- Made outMessage and connectionStatus both 'volatile'
- added end-of-line delimiters in neccesary places.
Code:
public void run() {
while (connectionStatus != TCP_SOCKET_STATUS_CONNECTED) {
try {
Thread.sleep(500);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
while (connectionStatus == TCP_SOCKET_STATUS_CONNECTED) {
try {
if (outMessage != null){
OutStream.writeBytes(outMessage + "\n");
OutStream.flush();
sendMessageToAllUI(0, MAINACTIVITY_SET_TEXT_STATE, "appendText" , "OUT TO SERVER: " + outMessage);
outMessage = "x";
}
Thread.sleep(100);
// if (InStream.readLine().length() > 0) {
String modifiedSentence = InStream.readLine();
sendMessageToAllUI(0, MAINACTIVITY_SET_TEXT_STATE, "appendText" , "IN FROM SERVER: " + modifiedSentence);
// }
Thread.sleep(1000);
} catch (IOException e) {
connectionLost();
break;
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
The thread that makes the socket:
public void run() {
setName("AttemptConnectionThread");
connectionStatus = TCP_SOCKET_STATUS_CONNECTING;
try {
SocketAddress sockaddr = new InetSocketAddress(serverIP, port);
tempSocketClient = new Socket(); // Create an unbound socket
// This method will block no more than timeoutMs. If the timeout occurs, SocketTimeoutException is thrown.
tempSocketClient.connect(sockaddr, timeoutMs);
OutStream = new DataOutputStream(tempSocketClient.getOutputStream());
InStream = new BufferedReader(new InputStreamReader(tempSocketClient.getInputStream()));
socketClient = tempSocketClient;
socketClient.setTcpNoDelay(true);
connected();
} catch (UnknownHostException e) {
connectionFailed();
} catch (SocketTimeoutException e) {
connectionFailed();
} catch (IOException e) {
// Close the socket
try {
tempSocketClient.close();
} catch (IOException e2) {
}
connectionFailed();
return;
}
}
Server:
public static void main(String[] args) throws IOException {
String clientSentence;
String capitalizedSentence;
try {
ServerSocket welcomeSocket = new ServerSocket(8888);
SERVERIP = getLocalIpAddress();
System.out.println("Connected and waiting for client input!\n Listening on IP: " + SERVERIP +"\n\n");
Socket connectionSocket = welcomeSocket.accept();
BufferedReader inFromClient = new BufferedReader(new InputStreamReader(connectionSocket.getInputStream()));
DataOutputStream outToClient = new DataOutputStream(connectionSocket.getOutputStream());
while(true)
{
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
clientSentence = inFromClient.readLine();
System.out.println("clientSentance == " + clientSentence);
String ip = connectionSocket.getInetAddress().toString().substring(1);
if(clientSentence != null)
{
System.out.println("In from client ("+ip+")("+ System.currentTimeMillis() +"): "+clientSentence);
capitalizedSentence = clientSentence.toUpperCase() + '\n';
outToClient.writeBytes(capitalizedSentence + '\n');
System.out.println("Out to client ("+ip+"): "+capitalizedSentence);
}
}
} catch (IOException e) {
//if server is already running, it will not open new port but instead re-print the open ports information
SERVERIP = getLocalIpAddress();
System.out.println("Connected and waiting for client input!\n");
System.out.println("Listening on IP: " + SERVERIP +"\n\n");
}
}
Thanks in advance!
Edits:
added the server code after updating
I tried messing around with setting the SoTimout for the socket but took that back out

Your server is specifically designed to receive exactly one line from a client and send exactly one line back. Look at the code:
while (true) {
Socket connectionSocket = welcomeSocket.accept();
BufferedReader inFromClient = new BufferedReader(
new InputStreamReader(connectionSocket.getInputStream()));
DataOutputStream outToClient = new DataOutputStream(
connectionSocket.getOutputStream());
clientSentence = inFromClient.readLine();
String ip = connectionSocket.getInetAddress().toString()
.substring(1);
System.out.println("In from client (" + ip + "): "
+ clientSentence);
if (clientSentence != null) {
capitalizedSentence = clientSentence.toUpperCase() + '\n';
System.out.println("Out to client (" + ip + "): "
+ capitalizedSentence);
outToClient.writeBytes(capitalizedSentence + "\n");
}
Notice that inside the loop it accepts a new connection, reads exactly one line, and then writes exactly one line. It doesn't close the connection. It doesn't sanely end the conversation. It just stops reading.
A client that worked with this server would have to connect, send exactly one line, read exactly one line back, and then the client would have to close the connection. Your client doesn't do that. Why? Because you had no idea that's what you had to do. Why? Because you had no design ... no plan.
So that's your specific issue. But please, let me urge you to take a huge step back and totally change your approach. Before you write a single line of code, please actually design and specify a protocol at the byte level. The protocol should say what data is sent, how messages are delimited, who sends when, who closes the connection, and so on.
Otherwise, it's impossible to debug your code. Looking at the server code above, is it correct? Well, who knows. Because it's unclear what it's supposed to do. When you wrote the client, you assumed the server behaved one way. Was that assumption valid? Is the server broken? Who knows, because there's no specification of what the server is supposed to do.

You need to check if there is data available:
if (InStream.available > 0) {
String modifiedSentence = InStream.readLine();
sendMessageToAllUI(0, MAINACTIVITY_SET_TEXT_STATE, "appendText" , "IN FROM SERVER: " + modifiedSentence);
}
But to be honest, even that is not ideal because you have no gurantee that the eond-of-line will have been received. If the server sends a few bytes but never sends the end-of-line then you will still be blocking forever. Production socket code should never rely on readLine but instead read into a buffer and check that buffer for end-of-line (or whatever criteria your protocol needs).
Didn't read closely enough, I thought InStream was an InputStream instance. InputStream has available. InputStreamReader has ready (which in turn calls InputStream.available. As long as you keep a refernce to either of these then you can see if data is available to be read.

Handling all clients in a java Socket Server

I have a server and i am trying to send to all clients a specific input(string). My code is here:
serverSocket = new ServerSocket(SERVERPORT);
while (true)
{
// listen for incoming clients
Socket client = serverSocket.accept();
mClients.add(client);
boolean finished = false;
try
{
for (int i=0; i<mClients.size(); i++)
{
Socket well = mClients.get(i);
DataInputStream in = new DataInputStream(well.getInputStream());
PrintStream out = new PrintStream(well.getOutputStream());
// Print a message:
System.out.println("Client from : " + client.getInetAddress() + " port " + client.getPort());
// now get the input from the socket...
while(!finished)
{
String st = in.readLine();
// Send the same back to client
out.println(st);
// Write it to the screen as well
System.out.println(st);
// If the input was "quit" then exit...
if (st.equals("quit")) { finished = true; System.out.println("Thread exiting..."); }
}
}
As it seems i am doing something wrong. Anyway i am trying to store all the connected sockets to a vector and then send them the string received by one of them. Is this the right approach?

In the first while(true) statement, only listen for incoming connections and then create a separate thread to handle that client connection.
From there, you could add each outPutStream you create, within each thread, into an global ArrayList. Loop through the arrayList(create a method for this with a String Parameter) and write whatever message you want to within said method.
Check out this Oracle Tutorial on Socket Communication for help

Send keystrokes from android device to PC without "stutter"

I'm working on an android app that when a button in the app is pressed, sends a key stroke to a server listing on the PC. Everything is working fine expect for a problem of the output "stuttering" when the button is pressed rapidly. If on the client is press rapidly, the server will "stutter" and sometimes simply become unresponsive. The cod I'm using is extremely simple. To simple?
Server side:
ServerSocket welcomeSocket = new ServerSocket(6789);
while(true)
{
Socket connectionSocket = welcomeSocket.accept();
BufferedReader inFromClient = new BufferedReader(new InputStreamReader(connectionSocket.getInputStream()));
keyin = inFromClient.readLine();
robby.translateAndForward(keyin);
}
}
catch (Exception ex)
....
On the client
public class ImageBoundListener implements OnTouchListener {
private ImageView view;
private static PadClient client;
The On Touch Event handler
#Override
public boolean onTouch(View view, MotionEvent event) {
int action = event.getAction() & MotionEvent.ACTION_MASK;;
if (client==null)
{
client=new PadClient();
}
if (action==MotionEvent.ACTION_DOWN)
{
client.sender("A");
}
Integer actionCode = action & MotionEvent.ACTION_MASK;
Log.d(actionCode.toString()," Event occured on: "+view.getTag());
return true;
}
}
The Actual send implementation
try{
Socket clientSocket = new Socket("192.168.1.104", 6789);
DataOutputStream outToServer = new DataOutputStream(clientSocket.getOutputStream());
System.out.println("Writing bytes to the server..");
outToServer.writeBytes(send);
clientSocket.close();
}
Not sure where to go from here...

There are several issues with your code:
Your code is opening connection every time button is pressed. If it is pressed rapidly - a lot of connections will be opened simultaneously between client and server.
It would be better to make one persistent connection and send all the data through it.
Also you can add some sort of buffering on the client side. I mean that data from several button presses will be combined into one data packet and sent to the server.
When dealing with communication problems between client and server - network I/O logging (what was sent and what was received on either side) is very important.
You server side can look like this:
try {
ServerSocket welcomeSocket = new ServerSocket(6789);
Socket connectionSocket = welcomeSocket.accept();
BufferedReader inFromClient = new BufferedReader(new InputStreamReader(connectionSocket.getInputStream()));
while(true) {
keyin = inFromClient.readLine();
Log.d("SERVER"," received: '" + keyin + "'");
robby.translateAndForward(keyin);
}
}
catch (Exception ex) {}

RFCOMM connection between two Android devices?

I have two Android devices which I want to connect, using Bluetooth, and transfer data over an RFCOMM channel. I only one one device to receive data, while the other device sends it...
Using this code, I am able to connect to the other device and begin listening to an RFCOMM channel:
Method m = device.getClass().getMethod("createRfcommSocket", new Class[] { int.class });
socket = (BluetoothSocket) m.invoke(device, 2);
socket.connect();
class BasicThread implements Runnable{
public void run() {
try {
InputStream stream = socket.getInputStream();
BufferedReader r = new BufferedReader(new InputStreamReader(stream));
while (true){
Log.d("myapp", "now listening...");
latestLine = r.readLine();
Log.d("myapp", latestLine);
}
} catch (IOException e) {
}
}
}
new Thread(new BasicThread()).run();
Using the other device, I have implemented a listening socket like this:
Method m = blue.getClass().getMethod("listenUsingRfcommOn", new Class[] { int.class });
BluetoothServerSocket socket = (BluetoothServerSocket) m.invoke(blue, 2);
BluetoothSocket sock = socket.accept();
Log.d("myapp", "Connected...\n\n\n\n\n\n\n\n");
OutputStream s = sock.getOutputStream();
final PrintWriter out = new PrintWriter(s);
They both connect on RFCOMM channel 2, and both SEE eachother, however, the second device always remains blocked at the BluetoothSocket sock = socket.accept();
Any help?

OK, I am newbie, but I can try to help. So here is my experience, I managed to connect two devices using reflection. My Android phone is receiving data using method listenUsingInsecureRfcommOn, while other devices are masters in communication and send the data over BT SPP. I had a problem with this method since it makes no visible SDP record, so I could not detect it with other devices. Because of that, I made small sniffer using Bluecove and Java SE that tries to connect to every port in given range. Here's the code:
package application.test;
import static java.lang.System.out;
import java.io.InputStream;
import java.io.PrintStream;
import java.text.SimpleDateFormat;
import javax.microedition.io.Connector;
import javax.microedition.io.StreamConnection;
public class RfCommClient {
public static void main(String args[]) {
try {
Thread.sleep(1000);
} catch (InterruptedException e1) {
e1.printStackTrace();
}
String add = "btspp://8C71F894A36D:";
String par = ";authenticate=false;encrypt=false;master=true";
String url = null;
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd;HH-mm-ss-SSS");
for (int i = 1; i < 15; ++i) {
try {
url = add + i + par;
out.format("Time: %s, port = %d\n", sdf.format(System.currentTimeMillis()), i);
StreamConnection conn = (StreamConnection) Connector.open(url);
PrintStream ops = new PrintStream(conn.openOutputStream());
ops.println("Hi there...");
// response
Thread.sleep(1000);
InputStream is = conn.openInputStream();
byte[] resp = new byte[5];
int r = is.read(resp);
out.println("r = " + r + ", response = " + new String(resp, "US-ASCII"));
Thread.sleep(10 * 1000);
conn.close();
} catch (Exception e) {
out.println("Exception occured, time = " + sdf.format(System.currentTimeMillis()) + ", i = " + i);
//e.printStackTrace();
}
}
}
}
What I've learned it that some ports are taken, and that some ports can not be uses (as documentation says, e.g. port 0). For example, port 2 I believe was taken, because when I send some data to it I receive 5 chars back beginning with ERR :).
While, on the other hand, my thread is still waiting?! :)
That leads us to another thing I noticed, ports (or channels) are not always mapped to desired number. For example, to me often happened that I want to send something on port 15, but on Android, thread waiting on port 9 received the data :)
So I suggest, check which port is really allocated!
You can achieve that using the code I posted.
And another thing, here is a link to channelPicker function, which selects channel when ordinary API is used, if I am not mistaken, inside some constants should represent reserved channels.
I just noticed something, my code for registering port is slightly different, here is how I do it:
Method m = cba.getDeclaredMethod("listenUsingInsecureRfcommOn", int.class);
ss = (BluetoothServerSocket) m.invoke(BluetoothAdapter.getDefaultAdapter(), port);
Anyway, I know that this is probably too late, but, maybe someone in future has similar question.