Develop Reference

Problems writing to network device using sockets

I have a wireless device communicating over port 22 connected to my network. Once the device starts up, it immediately starts sending log data. Once this device is sent a command, it stops logging and responds accordingly. This all works, I have tested it using a telnet client.
My problem is that I can't seem to send it a command properly in my app. I am reading the log data as planned, but when I send it a command, in this case the command "r", it continues outputting log data instead what it should be showing me for that particular command. This has to mean that I am not properly sending the command. This is my code for the task that sends it the command and logs the output in the android logcat:
public class ReceiveVarTask extends AsyncTask<Void, Void, Void>{
String dstAddress;
int Port;
ReceiveVarTask(String addr, int port) {
dstAddress = addr;
Port = port;
}
protected Void doInBackground(Void... vars){
Socket socket = null;
String command = "r";
try {
Log.i(TAG, "Connecting to port 22");
socket = new Socket(dstAddress, Port);
Log.i(TAG, "Connected to port 22");
PrintWriter writer = new PrintWriter(new BufferedWriter(
new OutputStreamWriter(socket.getOutputStream())), true);
InputStream inputStream = socket.getInputStream();
BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream));
writer.println(command);
String line = reader.readLine();
Log.i(TAG, line);
while(line!=null && !isCancelled()){
line = reader.readLine();
Log.i(TAG, line);
}
} catch (UnknownHostException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}finally {
if (socket != null) {
try {
socket.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
return null;
}
protected void onPostExecute(Void arg) {
taskRunning = false;
}
}
What am I doing wrong? Why is it not registering the command?
UPDATE:
I have used several telnet clients for testing, and the server is reading the 'r' command as expected on some. It works using a windows telnet client, and it works using the vSSH app by Velestar. Interestingly enough, when testing this with the android telnet client by ClockworkMod, the server is not registering the command either.
Could it be something to do with encoding?
Do I need any additional permissions to work with sockets? I have android.permission.INTERNET declared in the manifest.
UPDATE 2:
The developer of of the hardware just told me that the hardware is expecting the command to be ASCII encoded and CR terminated. So I will try changing PrintWrite initialization to:
PrintWriter writer = new PrintWriter(new BufferedWriter( new OutputStreamWriter(socket.getOutputStream(), "ASCII")), true);
and the print command to:
writer.print(command+"\r");

Changing the the encoding type to "US-ASCII" and adding a carriage return instead of a new line did the trick. I'm able to read and write data as expected.

From my understanding of your problem description, you have a telnet server, and when a telnet client connects to that server, the server start sending the client log data. The client may send an "r" to the server to stop the log stream.
I suggest you first confirm using another telnet client that sending an "r" does stop the server from generating more log data.
You could use Wireshark to check if the "r" command is indeed sent.

Sending message from Android client to Java server

I am developing an Android application, and I need to send a message from the application to the Java Server.
Java Server works like this:
thread = new Thread(){
public void run(){
System.out.println("Server is running...");
try {
ServerSocket socket = new ServerSocket(7000);
while(true){
Socket s = socket.accept();
DataInputStream dis = new DataInputStream(s.getInputStream());
System.out.println("Received from client: " + dis.readUTF());
dis.close();
s.close();
}
} catch (IOException e) {
e.printStackTrace();
}
}
};
thread.start();
In my application I send the message in this way:
mt = new Thread() {
public void run() {
try {
Socket socket = new Socket("192.168.1.100", 7000);
DataOutputStream dos = new DataOutputStream(socket.getOutputStream());
dos.writeUTF(song_field.getText().toString());
dos.flush();
dos.close();
socket.close();
} catch (IOException e) {
e.printStackTrace();
}
}
};
mt.start();
Toast.makeText(context, "Your Message is sent. Thank you!", Toast.LENGTH_SHORT).show();
I can send the message with emulator and my phone successfully, since they are connected to the same wifi connection, but if the device is not connected to the same network, message is not sent to the server. I want everybody to be able to send message to my computer server regardless of their internet connection.
How can I fix this problem?

In general you'll need to use something like Web Sockets to achieve what you're trying to do where, as would typically be the case, client/server are on different networks. There are a few different Web Socket implementations e.g. https://medium.com/square-corner-blog/web-sockets-now-shipping-in-okhttp-3-5-463a9eec82d1#.w9hrc1icw
EDIT
I initially misread question and thought you were trying to asynchronously send message from server to client (which would require something like Web Sockets). If you are just making requests from client to server then a typical solution would be to expose REST API from your server (and using something like Retrofit to make requests from client).

Android WiFi Direct Data Communication Example

Can anyone suggest a good example for get an idea about creating TCP server and client with android WiFi direct to transfer data. (Actually transfering of strings not files)
Actually I did one, but I cannot get the IP of server from client side.

If server and client are connected to the same wifi network, then please try use the 192.168.1.40 IP in the client to send data to server.
For example in client:
Socket socket = new Socket("192.168.1.40", port);
Hope it helps.

package com.example.androidclient;
MyClientTask(String addr, int port){
dstAddress = addr;
dstPort = port;
}
try {
socket = new Socket(dstAddress, dstPort);
ByteArrayOutputStream byteArrayOutputStream =
new ByteArrayOutputStream(1024);
byte[] buffer = new byte[1024];
int bytesRead;
InputStream inputStream = socket.getInputStream();
catch (UnknownHostException e) {
// TODO Auto-generated catch block
e.printStackTrace();
response = "UnknownHostException: " + e.toString();
}

Check if RESTful server is available on Android

I'm developping an Android REST-API oriented application.
I need to create a method to check whether the server is available or not.
The problem is if you use the URL.openStream() method, there's no way to determine whether a request was successful or not.
Is there a way to do it without the need to operate of performing a full HttpURLConnection and read the return code?

You can use TCP Sockets
SocketAddress socketAddress = new InetSocketAddress(address, port);
try {
int timeout = 2000;
socket.connect(socketAddress, timeout);
}
catch (IOException e) {
return false;
}
finally {
if (socket.isConnected()) {
try {
socket.close();
}
catch (IOException e) {
e.printStackTrace();
}
}
}

Android Bluetooth file sending

I am trying to send a file over bluetooth in an android device. I have done discovery, connection and have made a bluetooth socket. Problem is when i am writing the byte array in the output stream of the bluetooth socket, the recieving side does not receive anything although it accept that something is being sent.
Here's what Iam doing (bad is the bluetooth adaptor)
Please advise.
try
{
BluetoothDevice dev = bad.getRemoteDevice(a);
bad.cancelDiscovery();
dev.createRfcommSocketToServiceRecord(new UUID(1111, 2222));
Method m = dev.getClass().getMethod("createRfcommSocket", new Class[] {int.class});
bs = (BluetoothSocket) m.invoke(dev, Integer.valueOf(1));
bs.connect();
tmpOut = bs.getOutputStream();
}catch(Exception e)
{
}
File f = new File(filename);
byte b[] = new byte[(int) f.length()];
try
{
FileInputStream fileInputStream = new FileInputStream(f);
fileInputStream.read(b);
}catch(IOException e)
{
Log.d(TAG, "Error converting file");
Log.d(TAG, e.getMessage());
}
try {
tmpOut.write(b);
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}

I am using the below code snipped to connect to the serial service in a remote Bluetooth device and it is working fine for me. Just make sure that the other device (can be mobile or PC) has a server socket for serial communication over Bluetooth (see the server side code below)
Client Side:
UUID serialUUID = UUID.fromString("00001101-0000-1000-8000-00805F9B34FB");
BluetoothDevice btDevice = btAdapter.getRemoteDevice(BTAddress); // Get the BTAddress after scan
BluetoothSocket btSocket = btDevice.createRfcommSocketToServiceRecord(SERIAL_UUID);
btSocket.connect();
InputStream iStream = btSocket.getInputStream();
OutputStream oStream = btSocket.getOutputStream();
Server Side:
UUID serialUUID = new UUID("1101", true);
String serviceURL = "btspp://localhost:" + serialUUID
+ ";name=Android BT Server;authorize=false;authenticate=false";
StreamConnectionNotifier connectionNotifier = (StreamConnectionNotifier) Connector
.open(serviceURL);
// Blocking method will wait for client to connect
StreamConnection connection = connectionNotifier.acceptAndOpen();
RemoteDevice remoteDevice = RemoteDevice.getRemoteDevice(connection);
InputStream btInput = connection.openInputStream();
OutputStream btOutput = connection.openOutputStream();

Why not use the standard api call instead of calling through reflection, eg:
BluetoothSocket socket = destination
.createRfcommSocketToServiceRecord(new UUID(...)) ;
Also your catch block is empty. Are you sure the socket was connected without any exception? Connect will throw IOException if the connection failed for some reason. See this link

It might be because dev and bs go out of scope before tmpout is used because they are declared within your try/catch block.