We Keep Coding

Oreo: LocalOnlyHotspot is created, but socket exception happens

I am creating some testing app, and I need to connect several devices via Wi-Fi direct. On Android 8 the only way to do it is to create LocalOnlyHotspot. I have done it successfully, devices are connecting. However I need to transfer some strings between devices. For those reason I have made in separate threads
-> on server side
try{
int port = 9802;
ServerSocket serverSocket = new ServerSocket(port);
running = true;
while (running){
Socket socket = serverSocket.accept();
}
} catch (IOException e) { e.printStackTrace(); }
-> on client side
Socket socket = null;
try{
socket = new Socket(address, port);
} catch (IOException e) { e.printStackTrace(); }
I am always getting an exception on client's side
failed to connect to /192.168.43.1 (port 9802) from /:: (port 33044): connect failed: ECONNABORTED (Software caused connection abort)
As I have googled the reason is that the network has no internet connection.
How can I solve this problem? Is any other way to pass strings between 2 devices on Android 8 using Wi-Fi direct?
Thanks in advance.

how to connect esp8266 softAp with android app

I want some brief idea/links for reference to start how to connect esp8266 router/access point with an android app.In esp8266 static ip is 192.168.4.1 wants to control led blink or other feautre with an android app .
how to make establish connection between esp8266 and android app .

On Android side it's just network communication without any features. Take a look at Official Documentation and tutorials like this. Everything depends on esp8266 firmware:
if it implements HTTP web server You can use HttpUrlConnection and GET or POST requests on Android side and corresponding script on esp8266 side;
if it implements ServerSocket You can use Socket connection an implement Socket Client on Android side.
Update:
Socket communication with esp8266 You should do it in separate (not UI) thread. Full example is something like that:
class SocketClientThread implements Runnable {
DataInputStream dis;
DataOutputStream dos;
String strResponseData;
#Override
public void run() {
try {
InetAddress serverAddr = InetAddress.getByName("<address>");
clientSocket = new Socket(serverAddr, <port_number - 80 in your example>);
dos = new DataOutputStream(clientSocket.getOutputStream());
dis = new DataInputStream(clientSocket.getInputStream());
// now you can write data to stream
dos.writeUTF("Hello");
// you can also read data from stream
strResponseData = dis.readUTF();
} catch (UnknownHostException ignore) {
} catch (IOException ignore) {
}
finally{
if (clientSocket != null){
try {
clientSocket.close();
}
catch (IOException ignore) {
}
}
}
}
}
And than You can use SocketClientThread this way:
Thread socketClientThread;
socketClientThread = new Thread(new SocketClientThread());
socketClientThread.start();

Java Socket on Android, connection through 3G internet global ip

I have problems using Sockets on Android. I'm new to this topic so I try to achieve a simple chat, Android phone to another Android phone as a training.
I can use my code to create a ServerSocket and connect to it with another Socket from the same device ( An 'echo' example with only one client on one device works fine) I've done that also using two IP adresses on the same wifi (192.168...) but any tentative to connect a distant client using internet ip address using 3G connection fails with a
java.net.SocketException: recvfrom failed: ETIMEDOUT (Connection timed out)
What I do is, creating the ServerSocket (ServerConnect.java) :
private ServerSocket _mainServer = null;
private void initServer() {
try {
//port I use here is arbitrary: 8081
_mainServer = new ServerSocket(CONNECT_SOCKET_PORT);
} catch (IOException e) {
Log.w("ServerSocket", e.toString());
e.printStackTrace();
}
}
in the same class, in a separate thread I do this to wait for client connections :
while (running) {
GuestConnect ssc = new GuestConnect(_mainServer.accept());
ssc.setListener(this);
ssc.startConnection();
_clientSockets.add(ssc);
performGuestAdded("bra!");
}
it makes the server waiting for multiple client connection, so it can host more than two poeple in the 'chat room'.
The comunication server side is made from the local client callback and dispatch messages to all my guests (I'm still working on this part, its not really done yet but I don't think its relevant to my problem here) :
public void onMessageReceived(TBTGuestConnect sender, String message) {
for(TBTGuestConnect guestConnect : _clientSockets)
if(guestConnect != sender)
guestConnect.sendMessage(message);
}
Clients are store as 'GuestConnect' objects here is how I set them (GuestConnect.java):
public class GuestConnect {
private StringBuilder _currentMessage;
private BufferedReader _is;
private PrintStream _os;
private Socket _clientSocket = null;
private String _hostname;
private boolean _running = false;
public GuestConnect(String hostname) {
_hostname = hostname;
_currentMessage = new StringBuilder();
}
clientSocket initialisation (still GuestConnect.java):
private void initSocket() {
if(_clientSocket==null)
{
// Try to open a server socket on given port
// Here is the fail when I called it from another device
try {
_clientSocket = new Socket(_hostname, ServerConnect.CONNECT_SOCKET_PORT);
} catch (IOException e) {
Log.w("GuestSocket", e.toString());
}
}
// Create a socket object from the ServerSocket to listen and accept
// connections.
// Open input and output streams
try {
_is = new BufferedReader(new InputStreamReader(_clientSocket.getInputStream()));
_os = new PrintStream(_clientSocket.getOutputStream());
} catch (IOException e) {
Log.w("GuestSocket", e.toString());
}
}
again, in the same class there is the comunication part :
initSocket();
_running = true;
performConnectionStarted();
try {
while (_running) {
String received = _is.readLine();
_currentMessage.append(received);
if (received.contains(ServerConnect.CONNECT_SOCKET_MESSAGE_END)) {
String finalMsg = _currentMessage.toString().substring(0, _currentMessage.lastIndexOf(ServerConnect.CONNECT_SOCKET_MESSAGE_END));
performMessageReceived(finalMsg);
_currentMessage.setLength(0);
}
}
} catch (IOException e) {
Log.w("GuestSocket", e.toString());
performError(e);
} finally {
try {
_os.close();
_is.close();
_clientSocket.close();
} catch (IOException e) {
e.printStackTrace();
performError(e);
}
_clientSocket = null;
}
I can then send a message from this method :
public void sendMessage(String toSend) {
if (_running)
_os.println(toSend+ServerConnect.CONNECT_SOCKET_MESSAGE_END);
else
throw new IllegalStateException("Send message : Connection isn't started !");
}
So the question is, what should I do to make this works using global internet ip addresses ?
And more generally, what it the technical difference between same wifi local ip address and internet ip adress ?

i'll start from the end because it's easier - local ip address is private, it's not valid (and not visible) out of your local network, someone out of your local network can't access it directly but you can access hosts with public ip addresses. because they are not universally visible private addresses are not unique, public ip addresses are unique and (normally) visible from any point on the internet. there's more on the subject http://en.wikipedia.org/wiki/Network_address_translation
when it comes to 3g networks take a look here Could I connect to my iphone using 3g ip? and here ServerSocket accept() not accepting connections on Android . so most probably it can't be done

Don't know if this would be of any importance to you but in our country most 3G accounts are blocked by the ISP from incoming connections. You have to apply to unblock the ports. Some ISP's won't unblock them and some will.
Found that out when I wanted to connect my DVR with a 3G modem.

can't connect Socket when not in same IP range. (subnet)

When running a ServerSocket on a machine A with ip 145.74.217.109
And then trying to connect to machine A using machine B with ip 145.74.219.103 I am unable to connect.
But when using machine C with ip 145.74.217.180 it works.
Iam not sure if this is solvable in code or its just network settings. If It is network issues is there another way to go around this problem or would I need to go away from sockets to ...?
Machine A:
public void run() {
try {
sock = new ServerSocket(Constants.PORT);
for (;;) {
Socket newsock = sock.accept();
System.out.println("Accepting new player: ");
new PaintballPlayer(newsock);
}
} catch (Exception e) {
System.out.println("IO error " + e);
}
System.out.println("End!");
try {
sock.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
Machine B, C :
socket = new Socket(ip, Constants.PORT);

if you look at the IP us server has IP 145.74.217.109 IP with 145.74.217.180 are able to connect while 145.74.219.103 is not being able to connect it means subnet 145.74.219.X has no access to 145.74.217.X that is why it is not being able to connect. It is network setting ask you network administrator for that. Make your both machine have same subnet mask

WiFi network programming in android

i want to program a server/client app in android.
i have one server class on my pc and client on my android phone.
all permissions are ok.
Here is client:
try {
mysocket = new Socket("My PC IP Address", 4444);
} catch (UnknownHostException e) {...
} catch (IOException e) {...
}
here is server:
try {
myServerSocket = new ServerSocket(4444);
} catch (IOException e) {...
}
Socket clientSocket = null;
try {
clientSocket = serverSocket.accept();
System.out.println("Connection Established.");
} catch (IOException e) {
}
I uses "Connectify" program on my pc to have an (virtual)access point such that my phone connect to that.
But when I try to connect to server in my android app, it hangs and then throws Timed-out exception.

This code doesn't look bad.
Are you certain Connectify is working well?
You shoud try running both the server and the client you have built on your PC, using two different processes (as an example the server as a standalone and the client in the Android Emulator).
If it works properly from localhost to localhost:4444, the the connection is the cause of the problem, not your code. And otherwise, you will easily find the bug in your code.