Develop Reference

Server java app not working on a local connection

hi have at home a rasperry pi running a server java app, connected to de router with the dynamic DNS configured and the in/out communication ports openned.
When i run the android apication client througt 4g everithing is working sucessfull. But when i run the same app connected to the wifi on my local net, where the server are running, the server application looks like death.
Any ideas?
Thanks.
router config

I think the problem is related to your DNS. If you are connected using your wifi, you have to return a local IP-Address. Do you have any chance of configuring your router to return the raspberries local IP-Address for wifi-clients?
Take a look here: link

A simple solution, even if it is not very elegant, is adding the following conditions to your code:
If there is an error connecting to the Dyn DNS, try to connect to the local IP address. (In case you are in the Wifi LAN)
If the local IP address fails, try again your Dyn DNS (in case the user is a real user with real communication problems)
(repeat until the connection is successful)
You can also identify your testing devices (using Settings.Secure.ANDROID_ID, or the IMEI) and use the local IP only for them. Another option is making the URL configurable (with a hidden option for example).

Because of my app can run local, only needs to connect to server for updates. I have block the connection on the server app if the ip from client and server are equals.
At the moment is the best solution to keep the server app running properly.
URL whatismyip = new URL("http://checkip.amazonaws.com");
BufferedReader in = new BufferedReader(new
InputStreamReader(whatismyip.openStream()));
String ip = in.readLine();
try {
SSLServerSocketFactory sslFactory = (SSLServerSocketFactory)SSLServerSocketFactory.getDefault();
SSLServerSocket ss = (SSLServerSocket) sslFactory.createServerSocket(PORT);
int idSession = 0;
while (true) {
SSLSocket socket = (SSLSocket)ss.accept();
if(socket.getInetAddress().getHostAddress().equals(ip)){
if (socket != null && !socket.isClosed()) {
socket.close();
}
}
((ServidorThread) new ServidorThread(socket, idSession)).start();
idSession++;
}
} catch (IOException ex) {
ex.printStackTrace(System.out);
Logger.getLogger(Servidor.class.getName()).log(Level.SEVERE, null, ex);
}
}

How to programmatically connect internet via datacard with AT commands?

I have a datacard ZTE MF190. I want to use AT commands to register in 2G or 3G and access internet via datacard. Found this article about how to make data call:
AT+cgatt=1
AT+CGDCONT=1,”IP”,”epc.tmobile.com” //I used my operator PDP context
AT+CGACT=1,1
But ping from OS terminal shows 100% package loss.
I've tried on Ubuntu 14 and Windows 7.
How can I connect internet with AT commands using datacard on Ubuntu?
UPDATE
I gave bounty to #tripleee's answer because it's more full than first one and answered all my questions. But I'm not satisfied with answers, so I'll answer my own question in a week.
In my answer I'll show how to handle this process with Java. So, please do not move this question to other Stack Exchange websites.

Creating a connection between the card and your provider is not sufficient. You need some mechanism for creating a network interface out of this connection, and set up your network stack to route packets over this interface.
Traditionally, the pppd daemon has been a popular choice for this task. You would create a "chat script" with the commands for establishing a data call (these days, pppd might come packaged with a suitable canned script) and the daemon would handle the entire process of placing the call, authenticating, setting up a network interface over the circuit, and configuring the system to route packets over it, as well as configuring DNS etc to use it for resolver queries, etc.

I tried to sniff USB port but on this case dashboard can not connect because of busy port
It is certainly possible. See this question
Found this article about how to make data call
What that article is about is how to set up the call, not how to make it.
After you made correct setup, connect to internet with this command:
ATD*99***1#
UPDATE1: After a bit of research I believe that article was written only to promote their software and has no practical use. In reality dialing is made with pppd or wvdial
UPDATE2: We discussed ways to solve the problem in a chat room (in Russian). It turned out cnetworkmanager will be the way to go

As far as I know wvdial uses ppp daemon to connect to the internet using modem. wvdial is preinstalled on desktop version of Ubuntu.
wvdial uses a config file located /etc/wvdial.conf. Let's edit this file. Type in your terminal
sudo nano /etc/wvdial.conf
and you will see something like this
[Dialer Defaults]
Init1 = ATZ
Init2 = ATQ0 V1 E1 S0=0 &C1 &D2
Stupid Mode = yes
ISDN = 0
Modem Type = Analog Modem
New PPPD = yes
Phone = *99#
Modem = /dev/ttyUSB2
Username = ''
Password = ''
Baud = 9600
Dial Timeout = 30
Dial Attempts = 3
Explanation of all keys you can find in wvdial.conf(5) - Linux man page. If you need to change your provider dial number, username, password or any other information about connection and device you can change file content and save it.
There are 3 serial ports for ZTE MF190. Normally it's ttyUSB0, ttyUSB1 and ttyUSB2. And in my case ttyUSB2 is for internet connection. It would not work on other ports. So you need to find the right serial port for your modem.
There is an automatic configurator which edits wvdial.conf file, sets serial port baud rate etc. Since it is not always configure correctly I would not recommend to use it:
sudo wvdialconf /etc/wvdial.conf
It would be better if you configure wvdial manually.
Now, when your device connected and wvdial configured to work with device, you can execute this line from terminal:
wvdial
You will see a lot of lines. But if you see those lines - you have succeeded.
local IP address XX.XX.XX.XX
remote IP address XX.XX.XX.XX
primary DNS address XX.XX.XX.XX
secondary DNS address XX.XX.XX.XX
Now, how we can use it in programming? I'll provide some code to work with it on Java. You can use this code to dial.
public int dialer() {
// status for debug. If status == 4 then you connected successfully
int status;
// create process of wvdial
ProcessBuilder builder = new ProcessBuilder("wvdial");
try {
// start wvdial
final Process process = builder.start();
// wvdial listener thread
final Thread ioThread = new Thread() {
#Override
public void run() {
try {
final BufferedReader reader = new BufferedReader(
new InputStreamReader(process.getErrorStream()));
// wvdial output line
String line;
while ((line = reader.readLine()) != null) {
// if "local IP address" line detected set status 1
if (line.contains("local IP address")) {
status = 1;
}
if (line.contains("remote IP address")) {
status = 2;
}
if (line.contains("primary DNS address")) {
status = 3;
}
if (line.contains("secondary DNS address")) {
status = 4;
}
}
reader.close();
} catch (final Exception e) {
}
}
};
// start listener
ioThread.start();
// wait 6 secs and return status. Some kind of timeout
Thread.sleep(6000);
} catch (Exception e) {
}
return status;
}
And here is a disconnector method. All you need is to kill wvdial process and thread will be destroyed:
public boolean disconnect() {
ProcessBuilder builder = new ProcessBuilder("pkill", "wvdial");
try {
builder.start();
return true;
} catch (IOException e) {
return false;
}
}

Socket writing java (android) to python

I want to create a super basic Android App that connects to a python server running on my PC but the python server never gets the connection
my java code:
public class WriteToSocket {
Socket sock;
public void Test() {
try {
this.sock = new Socket("PCName", 9871);
} catch (UnknownHostException e) {
System.out.println("Unknown host: PCName");
System.exit(1);
} catch (IOException e) {
System.out.println("No I/O");
System.exit(1);
}
}
public void Test1(){
try {
this.sock.close();
} catch (IOException e) {
System.out.println("No I/O");
System.exit(1);
}
}
and
public void onClick(View v) {
WriteToSocket a = new WriteToSocket();
a.Test();
}
and my python server is
import socket
sock = socket.socket()
name = "PCName"
port = 9871
sock.bind((name,port))
sock.listen(1)
s,a = sock.accept()
I expected after the button click for the python server to accept the connection (I also tried changing "PCName" to "127.0.0.1")
I've looked around but nothing helped me so far :S

Bind your server socket to one of the IP addresses of your PC which is accessible from your android, and not to 127.0.0.1. Or alternatively bind it to all available interfaces (0.0.0.0).
Then connect from your android to that IP.
E.g. if your PC has IP address 1.2.3.4 then use this IP in both applications.
Use netstat to see if the port is really open on your PC.
Check to see if your android application has the permission to use the internet (specified in the manifest: "USES_INTERNET" or something like that).
Also your python script discards the connection as soon as it is made.

In python change bind address to 0.0.0.0. It will bind for all IPs attached to your machine. Then in android app change to correct IP of your computer.
IP 127.0.0.1 is a loopback and you can't connect to it from outside of the system.

The android phone doesn't know what PCName is, change "PCName" in the python code back to '127.0.0.1', then in the android project put in the local IP address of the server.
This of course assuming that both the phone and the server are on the same local network.

Using InetAddress to get own IP

I have an issue were if I try to InetAddress.getLocalHost() or even InetAddress.getByName(String host) it throws an exception every time even for a known website like nba.com I am a bit confused FYI the target device is an android 4.1.1 GS3 and wifi and mobile network are on. Code below
try{
InetAddress ownIP=InetAddress.getLocalHost();
System.out.println("IP of my Android := "+ownIP.getHostAddress());
}catch (Exception e){
System.out.println("Exception caught ="+e.getMessage());
String t = e.getMessage() + "yes";
}
Below is the System.out
03-12 18:59:52.636: I/System.out(18996): Exception caught =null
Thanks in advance

I use a tricky method to get my own IP. you can see whether it helps you
String getIP() {
try {
Socket socket = new Socket("google.com", 80);
return socket.getLocalAddress().getHostAddress();
} catch (Exception e) {
}
}

I believe I have found out what my issue was basically I guess you are not allowed to perform any network operations in the Main thread for android this was optional before and is now required for Honeycomb (API 11) and up below is the comment as per google specs.
"To prevent blocking the main user interface thread, Google recommends using the AsyncTask class from the android.os package:"
So all I was create a new class NetTask which extends AsyncTask and perform all network applications so now my code is working. IDK if everybody else knew that but I figured I would post this in case any newbs like me were still looking for a solution :) !!!
Thanks

Android bluetooth connection doesn't close after application crash

i'm using SPP profile for connect to my device:
Set<BluetoothDevice> devices = ba.getBondedDevices();
for(BluetoothDevice bd : devices)
{
String name = bd.getName();
if(name.equals("CELLMETER"))
{
try
{
BluetoothSocket bs = bd.createRfcommSocketToServiceRecord(UUID.fromString("00001101-0000-1000-8000-00805F9B34FB"));
bs.connect();
} catch (IOException e)
{
e.printStackTrace(); //To change body of catch statement use File | Settings | File Templates.
}
}
}
All seems okay, i created function where i'm closing input output buffers and close socket.
But when application crashes or i'm stopping application when breakpoints arrives socket doesn't closes, even after i kill process manually and it's not avalible for new connection from new instance of app.
What i'm doing wrong? For each crash/debug operation i have to reboot phone :(
It's manifested only to Android 2.3.5 (Samsung 5830i) and on Android 4.0.4 (Freelander P10). On my Android 4.2.1 (Galaxy Nexus) all okay, after app crash connection closes automatically. (it seems because there is new Bluetooth stack)

I can see 2 options to work that out:
1- Add an UncaughtExceptionHandler in your app, best in Application-derived class:
mUEHandler = new Thread.UncaughtExceptionHandler()
{
#Override
public void uncaughtException(Thread t, Throwable e)
{
// Close any opened sockets here
defaultUEH.uncaughtException(t, e);
}
};
Thread.setDefaultUncaughtExceptionHandler(mUEHandler);
But that only takes care of app crashes. If user kills the app, won't get in there at all.
2- Store some socket identification that allow you to close it when app restarts.
It's not perfect, but that could work-around your issue.

I solved this problem by letting my BluetoothSockets be managed by a Service running in its own process. I open, close, read, and write the sockets by passing Messages to and from the Service. If the app crashes, the Service shuts down cleanly, closing the sockets. (It does not shut down cleanly if it's running in the same process as the app.)