I have a device here that I can send a status request command to, and then I read it using
bytes = mmInStream.read(statusBuffer);
I'm having trouble when it changes it's status though. Sometimes I will get back the current status, other times the program will hang on that line and not do anything else. It doesn't crash, move onto the next line or anything. I can only move on by turning off the device and severing the connection.
We have a blackberry torch here that does not have this error at all so it must be my code.
Can anyone give me some troubleshooting tips? Below is the while loop that reads the devices current status.
while (true) {
getStatus();
try {
bytes = 0;
while(bytes < 1){
bytes = mmInStream.read(statusBuffer);
if (bytes != 0){
response = new String(statusBuffer);
//Handle response code
}
}
}
} catch (Exception e) {
Log.e(TAG, "disconnected FROM WHILE TRUE LOOP", e);
connectionLost();
break;
}
}
If there is no byte available, -1 is returned by read, you miss your comparison and you go on looping.
If your line ends with a \n char it would be far easier to read it through an BufferedReader for instance. Anyhow, your loop is not very well designed.
do
{
//read bytes
//store the result in byteRead
//if( byteRead != -1 )
//build a string
}//do
while( byteRead != -1 )
Regards,
Stéphane
Related
I am developing Client-Server application in C++ using Qt framework, but the clients can be android phones and computers(Qt client app)
Now i'm having troubles to handle Reception of data on the server side; the server is not receiving data properly.
First, I got things working nicely between the server(Qt app) and the client(Qt app) using these methods for sending and receiving:
The size of the message is kept at the beginning of the packet to help check whether the whole message is received or not.
This is the method to send message to the clients
void Server::send(const QString &message)
{
QByteArray paquet;
QDataStream out(&paquet, QIODevice::WriteOnly);
out << (quint16) 0; // just put 0 at the head of the paquet to reserve place to put the size of the message
out << message; // adding the message
out.device()->seek(0); // coming back to the head of the paquet
out << (quint16) (paquet.size() - sizeof(quint16)); // replace the 0 value by the real size
clientSocket->write(paquet); //sending...
}
This slot is called every time a single paquet is received.
void Server::dataReceived()
{
forever
{
// 1 : a packet has arrived from any client
// getting the socket of that client (recherche du QTcpSocket du client)
QTcpSocket *socket = qobject_cast<QTcpSocket *>(sender());
if (socket == 0)
return;
QDataStream in(socket);
if (dataSize == 0) // if we don't know the size of data we are suppose to receive...
{
if (socket->bytesAvailable() < (int)sizeof(quint16)) // we haven't yet receive the size of the data completly then return...
return;
in >> dataSize; // now we know the amount of data we should get
}
if (socket->bytesAvailable() < dataSize)
return;
// Here we are sure we got the whole data then we can startreadind
QString message;
in >> message;
//Processing....
dataSize = 0; // re-initialize for the coming data
}
}
This is working well when the server is talking with the Qt app Client, because the same methods are used there, and the size of quint16 will remain the same hover it doesn't work with android client, then i tried another way in which i wanted to ignore the size of the message sent, but format the message in a way such that i can know where it starts and where it ends, then with some controls i can get it however i'm stuck here, cause the data read doesn't contain anything when printed, but his size has a value(which even vary according to the amount of text the client send)!
void Server::dataReceived() // a packet is received!
{
QTcpSocket *socket = qobject_cast<QTcpSocket *>(sender());
if (socket == 0)
return;
QByteArray data= socket->readAll(); //reading all data available
QString message(data)
qDebug() << data; // this prints nothing!
qDebug() << data.size();// But this prints a non null number, wich means we got something, and that number varies according to the amount of text sent!
qDebug() << message; // this also prints notghing!
}
PS: it's not working even for the Qt app Client.
Can you help me find out what's wrong, i'm a bit confused how the tcp protocol is handling the data, and if you could and also advise me a good way for doing this.
here is the android class I made for the purpose
class QTcpSocket implements Runnable {
private String ip="";
private int port;
private Socket socket;
private PrintWriter printWriter;
private DataOutputStream dataOutputStream;
private DataInputStream dataInputStream;
public QTcpSocket(String ip, int port) {
this.ip = ip;
this.port = port;
}
public void setIp(String ip) {
this.ip = ip;
}
public String getIp() {
return this.ip;
}
public void setPort(int port) {
this.port = port;
}
public void run() {
try {
socket = new Socket(this.ip, this.port);
dataOutputStream = new DataOutputStream( socket.getOutputStream() );
dataInputStream = new DataInputStream(socket.getInputStream());
String response = dataInputStream.readUTF();
dataOutputStream.writeUTF("Hello server!");
} catch (IOException e) {
e.printStackTrace();
}
}
public void sendMessage(String message) {
try {
dataOutputStream.writeUTF(message);
}catch (IOException e) {
e.printStackTrace();
}
}
public void disconnect() {
try {
printWriter.flush();
printWriter.close();
socket.close();
} catch (IOException e) {
e.printStackTrace();
}
}
public boolean isClosed() {
return socket.isClosed();
}
}
Replace in 'data' all bytes with value 0 by value 20 and print again. I think you see nothing printed because the first byte is 0. You could also replace with 'X'. Did you already replace writeUTF() by write() ?
20 is the space character. But then you also see nothing printed so better use a X char. Strings get printed until a \0 char (which indicates the end of a string) is met. Because nothing was printed i supposed one right at the beginning. So writeUTF causes that leading 0. I could only explain that if all chars had doubled. What was the first char you sent?
But now: send size-of-message first so it equals your qt client.
I am working on an Android application that receives a real time data by Bluetooth and plots it on the screen.
The data is a gyro sensor position information. I am sending it from a custom Freescale Kinetis K10 microcontroller board (designed and tested by myself). For the Bluetooth communication I am using HC-05 Bluetooth module.
The format of the data is as follows:
byte_1: position identification byte, always equals to -128
byte_2: position of axis 1
byte_3: position of axis 2
byte_4: position of axis 3
I am sending these 4 bytes continuously one after another, in that particular order. I am sending this packet of 4 bytes every 5 ms and sending the packet takes about 4.7 ms (9600 baud rate).
The data output from the microcontroller is perfect in terms of accuracy and timing (checked with a logic analyzer).
The problem is that when it is being received from the phone, some of the bytes seem to get lost. Here is the part of the code, where I am reading the InputStream:
private class ConnectedThread extends Thread {
private final BluetoothSocket mmSocket;
private final InputStream mmInStream;
private final OutputStream mmOutStream;
public ConnectedThread(BluetoothSocket socket) {
mmSocket = socket;
InputStream tmpIn = null;
OutputStream tmpOut = null;
try {
tmpIn = socket.getInputStream();
tmpOut = socket.getOutputStream();
} catch (IOException e) {
Log.e("Printer Service", "temp sockets not created", e);
}
mmInStream = tmpIn;
mmOutStream = tmpOut;
}
#Override
public void run() {
Log.i("BluetoothService", "BEGIN mConnectedThread");
byte[] buffer = new byte[4];
int bytes;
while (true) {
try {
bytes = mmInStream.read(buffer);
int position = 0;
if(buffer[0] == -128) {
if(bytes >= 2) {
sendArray.errorTilt = buffer[1];
}
if(bytes >= 3) {
sendArray.errorRoll = buffer[2];
}
if(bytes == 4) {
sendArray.errorPan = buffer[3];
}
}
else if(buffer[1] == -128) {
position = 1;
if(bytes >= 3) {
sendArray.errorTilt = buffer[2];
}
if(bytes == 4) {
sendArray.errorRoll = buffer[3];
}
if(bytes >= 2) {
sendArray.errorPan = buffer[0];
}
}
else if(buffer[2] == -128 && bytes >= 3) {
position = 2;
sendArray.errorRoll = buffer[0];
sendArray.errorPan = buffer[1];
if(bytes == 4) {
sendArray.errorTilt = buffer[3];
}
}
else if(buffer[3] == -128 && bytes == 4) {
position = 3;
sendArray.errorTilt = buffer[0];
sendArray.errorRoll = buffer[1];
sendArray.errorPan = buffer[2];
}
if(position <= bytes && bytes > 1) {
sendArray.errorUpdate = true;
}
} catch (Exception e) {
e.printStackTrace();
connectionLost();
BluetoothService.this.stop();
break;
}
}
}
public void write(int oneByte) {
try {
mmOutStream.write(oneByte);
} catch (IOException e) {
Log.e("BluetoothService", "Exception during write", e);
}
}
public void cancel() {
try {
mmSocket.close();
} catch (IOException e) {
Log.e("BluetoothService", "close() of connect socket failed", e);
}
}
}
sendArray is a singleton that keeps many different variables.
errorTilt, errorRoll and errorPan are the current values of the axis, which are being updated from the receiving buffer.
"position" keeps the position of the position identification byte. It is used for a check if any variables have been updated.
Many times just one byte is received in the input buffer and since I don't know which axis is that supposed to be, since I don't have information about it's relative position to the position byte, this particular byte is useless and gets lost.
I've tested the accuracy of receiving by the following method. I made the MCU output a triangular wave on one of the axis, instead of the axis data. On the phone the lines of the triangular wave are not straight as they are supposed to be, but randomly curved and containing artifacts.
To plot the data I am using GraphView and I am updating the graph on equal intervals from a separate thread.
I've tried using longer receiving buffer (with a modified receiving algorithm), but this doesn't help as only a few bytes are being received at a time.
I've tried implementing InputStream.available() but it was always giving 127 bytes available, which didn't seem to be true.
I've read many threads about similar problems and I spent the last 5 days working on it, but I couldn't find a good solution.
To summarize, I need to achieve accurate, real time (or close to real time) receiving of all the bytes.
Thread with a similar problem:
How to do good real-time data streaming using Java Android SDK
Thank you.
UPDATE:
I've tried sending the information just for one of the axis, so it is simple and clear, without the need of position bytes. I was sending it again every 5 ms, but this time it was more time between the consecutive bytes, since it's just one byte in the packet.
I used InputStream.read() this time, which doesn't require a buffer. However, the incoming data was corrupted again, because random bytes couldn't be received.
I've seen different project using this method successfully, I don't know why it's not working with me. I thought it might be a problem with the HC-05 Bluetooth module I'm using, but I tried a different one - HC-06, and the situation is the same. I haven't tried a different phone, but my phone (Samsung Galaxy S3, Android 4.1.2) seems to be working OK.
UPDATE2: I've tried again testing the original code with InputStream.available() before reading from the stream.
When the condition is available()>0, there are no major changes, maybe it works slightly worse.
When the condition is available()>1, it never reads. I guess that is because of the unreliable available() method, as it says in the documentation.
you have incorrect processing of data, if you want to get data from microcontroller board. You have to use bytesAvaliable because android bluetooth Socket is pretty slow over microcontroller boards with bluetooth. But "bytesAvaliable way" has nuance - As socket is slow receiver, bytesAvaliable can catch more then 1 packet from board in one time so you gotta devide readed data by yourself, Check my code out below! My code is getting 38 bytes packets from inertial sensor so you gotta only change count of bytes! 0xAA is the first byte of every next packet so if you find 0xAA byte and have 38 bytes you get packet and nullify iterator. But anyway I'm sure that you still can sometimes lose data because it's not high frequency data transfering way
public void run() {
byte[] bytes = new byte[38];
int iterator = 0;
while (true) {
try {
int bytesAvailable = mmInStream.available();
if (bytesAvailable > 0) {
byte[] curBuf = new byte[bytesAvailable];
mmInStream.read(curBuf);
for (byte b : curBuf) {
if (b == (byte) 0xAA && iterator == 38) {
mHandler.obtainMessage(MainActivity.DATA_READ, bytes.length, -1, bytes).sendToTarget();
iterator = 0;
bytes[iterator] = b;
} else {
bytes[iterator] = b;
}
iterator++;
}
}
} catch (IOException ex) {
Log.e(TAG, "disconnected", ex);
connectionLost();
break;
}
}
}
I'm developing an Android real-time-data app that sends data (floats and ints) to a server on the local subnet via a TCP socket. The problem I'm facing is that after sending some data simultaneously the socket doesn't send anymore data at all. I debugged the app and it shows that data is being sent but doesn't show up on the server. After this happens if I close the connection the server doesn't even get the notification that the connection has been terminated which it should according to my design model. Meanwhile I get an exception on the app saying it can not write to a broken pipe. This tells me that the problem is with the app because I also did test using a desktop app and I can send huge amounts of data to the server and it gets delivered.
And please keep in mind that the data size I'm talking about here is 252 bytes per packet.
Here's my class I'm using. (This runs in an AsyncTask object )
public class Network
{
private Socket handle;
public static enum TASK
{
TASK_CONNECT, TASK_SEND, TASK_CLOSE
}
public Network()
{
}
public String lastError = "";
public boolean Connect(String host, int port)
{
try
{
lastError = "Connecting to server.";
handle = new Socket(host, port);
handle.setTcpNoDelay(true); //
handle.setSendBufferSize(SIZE_OF_PACKET); ///==> These don't seem to help at all
handle.setKeepAlive(true); ///
return true;
}catch(IOException e)
{
lastError += e.getMessage() != null ? " "+ e.getMessage() : "";
return false;
}
}
private void err(String e){
System.err.println(e);
}
private boolean SendPacket(byte buffer[])
{
OutputStream oStream = null;
err("sending: " + buffer.length + " bytes");
try
{
lastError = "Obtaining output stream.";
oStream = handle.getOutputStream();
lastError = "Error sending data.";
oStream.write(buffer);
oStream.flush();
return true;
}catch(Exception e)
{
lastError += e.getMessage() != null ? " "+ e.getMessage() : "";
}
return false;
}
public void Close()
{
try{ handle.close(); handle = null; }catch(Exception e){} // swallow exception
}
}
I send my data in a loop depending on how many numbers I have. I tried a Google search but didn't find anything relevant. Has anyone experienced this before? It's making me mad now.
EDIT: Wireshark shows incoming "red" packets that don't reach the desktop app (server)
Look at this picture.
You can see the first few have Len > 0 the red ones have 0.
I think it's time Google interfaced the USB so we can use it. At least that'd would have been my first option.
Should you not be calling oStream.close() after you flush the stream, given that you never use it again?
Also, you say that this is being run in an AsyncTask object. Is it possible that multiple threads could be attempting to send packets at the same time? If so, you might need some form of synchronisation around the SendPacket method.
Ok. I solved the issue by using UDP instead. Thank you all.
But I still didn't find the source of the problem.
Problem
How to send UTF-8 data between the server and the client, if I can use on client only
inputStream.read()
?
Docs
Reads a single byte from this stream and returns it as an integer in
the range from 0 to 255. Returns -1 if the end of the stream has been
reached.
Without reader.readLine() and any another. (With reader I cant see end of stream)
Help please!
(full code:)
int c;
String str = new String();
while ((c = inputStream.read( )) != -1)
{
char ch = (char)c;
if(ch == '\n')
{
Log.v("", str);
final String data = str;
runOnUiThread(new Runnable()
{
#Override
public void run()
{
String put[] = data.split("#");
try
{
//cmd parsing
}
catch(Exception e)
{
//stop connection
}
}
});
str = "";
}else{
str += Character.toString(ch);
}
}
//Communication error
Help please
You might want to take a look at this previous post. There's a couple of good options on there. The read() method can be overloaded with different parameters, so you can read one byte, or n bytes. Check out the full documentation here. Basically, you'll have to read in the raw bytes, then convert them to ASCII characters. Also, I'm curious as to why you can't use BufferedReader or an equivalent class?
So this is the weirdest thing ever to happen to me during programing. Yes I'm no pro at programing, but I'm learning as I go. I've got an app talking to a server, a socket in the main thread, reading is done in a separate class and thread and writing in a separate class with asynctask.
The problem is LocationManager. I could talk to server and write/read commands just fine, I implemented the LocationManager and its listener.
I then proceeded to implement a method to update my textview with the new coordinates on locatinChanged. So far so good. Thing is when I use the Emulator control in eclipse and send coordinates the app crashed with a stringOutOfBoundsException (I've programed for 3 years now never seen this). I looked at the code stepped through it and so on. Read the stacktrace, logcat, console and everywhere I could think of but it got me nowhere. Until I finally went to the readerthread which looks like this:
public class ReaderThread extends Thread {
public void run() {
new Thread(new Runnable(){
public void run(){
try {
//Establish a bufferedreader to read from the socket/server.
in = new BufferedReader(new InputStreamReader(socket.getInputStream()), 8 * 1024);
}
catch(Exception e) { e.printStackTrace(); }
//As long as connect is true.
while (connected) {
String line;
try {
//Try to read a line from the reader.
line = in.readLine();
System.out.println(in.readLine());
if (in == null) {
//No one has sent a message yet.
System.out.println("No data recieved");
}
else {
int i = 0;
//As long as someone is sending messages.
while((line = in.readLine()) != null ){
//Make a new Message.
Message msg;
msg = new Message();
//Set the object to the input line.
msg.obj = line;
//Set an id so it can be identified in the main class and used in a switch.
msg.what = i;
System.out.println("i is: "+i);
//Send the message to the handler.
Main.this.h.sendMessage(msg);
}
}
}
catch (Exception e) {
System.out.println(e.getMessage());
}
}
}
}).start();
}
The variable i is in an if statement depending on what the server sent but I cut that out as it has nothing to do with this problem.
The problem is the freaking catch. When the catch is IOException, the app crashes. Out of dumb luck I changed this to Exception and printed e.message to catch the error and see what caused it. Thing is this change fixed it. How can switching IOException to just plain Exception fix a problem like this?
Its like with IOException the program says: "hey your not gonna catch the error but there is no error" but with Exception it says "Well now you could catch it so I'll proceed".
My app is working but I just can't grasp this, why and how does this happen?
You're essentially telling the application to catch the base Exception class. This means that any type of error will be caught, since all exception classes descend from that base type. Since StringOutOfBoundsException does not descend from IOException it was not being caught before and the error was not being caught. Instead of catching all exceptions, you might try the following:
try {
// Your code here...
} catch (IOException e) {
Log.e(TAG, "Caught an IOException!", e);
} catch (StringOutOfBoundsException e) {
Log.e(TAG, "Caught a string out of bounds Exception!", e);
}
I'm unable to determine what is actually throwing the StringOutOfBoundsException to begin with. It may be in the if statement that you cut out of your example.
while (connected) {
String line;
try {
//Try to read a line from the reader.
line = in.readLine();
System.out.println(in.readLine());
if (in == null) {
//No one has sent a message yet.
System.out.println("No data recieved");
}
The test for in == null is in a funny location. You should receive a NullPointerException if that test were to ever return true by nature of calling methods on it a few lines earlier. Obviously something is a little funny with this code.
You fail to save the return value from in.readLine() the second time you call it. I hope it did not contain anything useful. (Though, since you print the line, you obviously wanted to know what data it contained.)
Whatever that line was (from the first call to in.readLine()), it gets thrown away; there's nothing else in the loop that uses it before it is over-written on this line:
while((line = in.readLine()) != null ){
At this point, the two lines that you read are gone forever.
I'm not entirely sure what should be done to fix this; if it were me, I'd be sorely tempted to start over with a sheet of paper and sketch out what the method should be doing without looking at the existing code, then compare the sketch against the code to see which cases each one has overlooked.