I've been scratching my head on this one all day. I have a Bluetooth socket that listens for devices. This is done with AsyncTask. The first time I try to connect to it from a remote device, I don't have any problems. Now I'm trying to simulate a disconnect. Either by going out of range, shutting off the remote device's Bluetooth adapter, or just remotely closing the connection. Right now the server socket throws an IOException when the connection is lost. I'm using this as my cue to restart the AsyncTask and start listening again. This appears to work fine, all my logcat messages are showing up on the restart so I know the task is running, but the socket wont accept a connection. Thinking this could be a problem with restarting the AsyncTask, I tried just dumping the connection right after its accepted. After resetting them, I still have the same issue, even if I call system.gc().
Heres some code I'm using now to test:
boolean running = true;
while(running){
btAdapter = BluetoothAdapter.getDefaultAdapter();
btServerSocket = btAdapter.listenUsingRfcommWithServiceRecord(NAME, ID);
btSocket = btServerSocket.accept();
btServerSocket.close();
btSocket.close();
btServerSocket = null;
btSocket = null;
btAdapter = null;
System.gc();
sleep(10);
}
I really dont know what I'm doing wrong. Any help is greatly appreciated.
Thanks.
If you are only seeing this problem on Android 2.3.x, you might be running into a problem I just wrote about on another question. That problem also manifests as accept() working the first time, but then fails on successive tries. See my post here for details.
Related
I am creating a chat application, which runs as a service. I connect to the chat server using a socket, and I declared a timeout using setSoTimeout.
When a connection is idle, (for example when I am at home and connected to WiFi) I never face issues. When I go outside, and my WiFi connection is lost, my phone switches to 3G. The problem is that the socket stays connected without receiving any data. (So the timeout exception isn't called.) < sometimes it connects after 30 mins, but this need to be reduced to at least a few seconds.
I also tried to add a CONNECTIVITY_CHANGE broadcast detector in my AndroidManifest.xml, this also didn't work.
See my socket connection below:
socket = new Socket(proxy);
SocketAddress socketAddress = new InetSocketAddress(HOST,
PORT);
socket.connect(socketAddress);
if (socket.isConnected()) {
socket.setSoTimeout(1020000); //Even when setting to 10000 makes no sense
return true;
} else {
Log.w("WARNING", "Failed to connect to the server");
return false;
}
In the background there are also some loops running which checks the server for chatmessages, these loops triggers a reconnect when no data is received, but this didn't work too. (During reconnect, I set the socket to socket.close() and socket = null before connecting again.)
So are there any ideas, maybe I need to use a different socket? Or some other code to resolve this problem? Thanks.
In such unexpected(as per application's perspective) network disconnection, the socket won't know it was disconnected. If this situation occurs, the only way is to try writing some data to the socket. When the socket is disconnected, writing data would throw IOExcpetion with message like Connection reset.
You'd better implement a heartbeat method to detect the disconnection. A packet sent to server every 5~10 seconds would detect network disconnection speedy enough.
This question already has answers here:
Java socket API: How to tell if a connection has been closed?
(9 answers)
Closed 5 years ago.
When I'm using e.g. PuTTY and my connection gets lost (or when I do a manual ipconfig /release on Windows), it responds directly and notifies my connection was lost.
I want to create a Java program which monitors my Internet connection (to some reliable server), to log the date/times when my internet fails.
I tried use the Socket.isConnected() method but that will just forever return "true". How can I do this in Java?
Well, the best way to tell if your connection is interrupted is to try to read/write from the socket. If the operation fails, then you have lost your connection sometime.
So, all you need to do is to try reading at some interval, and if the read fails try reconnecting.
The important events for you will be when a read fails - you lost connection, and when a new socket is connected - you regained connection.
That way you can keep track of up time and down time.
Even though TCP/IP is "connection oriented" protocol, normally no data is sent over an idle connection. You can have a socket open for a year without a single bit sent over it by the IP stack. In order to notice that a connection is lost, you have to send some data on the application level.(*) You can try this out by unplugging the phone cable from your ADSL modem. All connections in your PC should stay up, unless the applications have some kind of application level keepalive mechanism.
So the only way to notice lost connection is to open TCP connection to some server and read some data from it. Maybe the most simple way could be to connect to some FTP server and fetch a small file - or directory listing - once in a while. I have never seen a generic server which was really meant to be used for this case, and owners of the FTP server may not like clients doing this.
(*) There is also a mechanism called TCP keepalive but in many OS's you have to activate it for all applications, and it is not really practical to use if you want to notice loss of connection quickly
If the client disconnects properly, a read() will return -1, readLine() returns null, readXXX() for any other X throws EOFException. The only reliable way to detect a lost TCP connection is to write to it. Eventually this will throw an IOException 'connection reset', but it takes at least two writes due to buffering.
Why not use the isReachable() method of the java.net.InetAddress class?
How this works is JVM implementation specific but:
A typical implementation will use ICMP ECHO REQUESTs if the privilege can be obtained, otherwise it will try to establish a TCP connection on port 7 (Echo) of the destination host.
If you want to keep a connection open continually so you can see when that fails you could connect to server running the ECHO protocol yourself rather than having isReachable() do it for you and read and write data and wait for it to fail.
You might want to try looking at the socket timeout interval. With a short timeout (I believe the default is 'infinite timeout') then you might be able to trap an exception or something when the host becomes unreachable.
Okay so I finally got it working with
try
{
Socket s = new Socket("stackoverflow.com",80);
DataOutputStream os = new DataOutputStream(s.getOutputStream());
DataInputStream is = new DataInputStream(s.getInputStream());
while (true)
{
os.writeBytes("GET /index.html HTTP/1.0\n\n");
is.available();
Thread.sleep(1000);
}
}
catch (IOException e)
{
System.out.println("connection probably lost");
e.printStackTrace();
}
Not as clean as I hoped but it's not working if I leave out the os.writeBytes().
You could ping a machine every number of seconds, and this would be pretty accurate. Be careful that you don't DOS it.
Another alternative would be run a small server on a remote machine and keep a connection to it.
Its probably simpler to connect to yahoo/google or somewhere like this.
URL yahoo = new URL("http://www.yahoo.com/");
URLConnection yc = yahoo.openConnection();
int dataLen = yc.getContentLength() ;
Neil
The isConnected()method inside Socket.java class is a little misleading. It does not tell you if the socket is currently connected to a remote host (like if it is unclosed). Instead, it tells you whether the socket has ever been connected to a remote host. If the socket was able to connect to the remote host at all, this method returns true, even after that socket has been closed. To tell if a socket is currently open, you need to check that isConnected() returns true and isClosed() returns false.
For example:
boolean connected = socket.isConnected() && !socket.isClosed();
I have been going crazy about the android app I'm developing.
I'm making a socket like this:
Socket socket = new Socket(IPAdress, Port);
And when I freshly installed the app, it works perfectly fine.
But then I close the app (close the server as well, restart the server).
I call
socket.close();
when destroying my app (onDestroy).
When I restart the app, I can't connect again, I need to manually delete the app from the cash, then it works again.
Same thing happens when I enter a wrong IP Adress. I can't just reenter a new Adress and try making a new socket again. I do it like this:
socket.close();
socket = null;
Socket socket = new Socket(IPAdress, Port);
It doesn't let me do it.
I am creating the new socket in a new Thread
onDestroy is not the right place to close the socket. It's called only when the system is low on resources.
I'm not sure exactly what you are doing with the socket, but if you don't need it when the application is no longer visible to the user, you should close it in onPause or onStop.
See the application lifecycle in http://developer.android.com/reference/android/app/Activity.html.
So I figured out the reason on why my app kept crashing when calling.
The socket kept being alive even with the app closed, because it remains in the cache.
So when exiting the app I have a boolean which tells me if I have a valid socket at all, then I'm able to close it. If I wasn't able to open a socket, I don't need to close it.
Then on restart, I simply do this:
socket = null;
then I can create a new socket!
(Sorry for not being able to properly indent and format this text, I tried it with four spaces, but that didn't work :(
I hope you can help. Im fairly new to progamming and Im playing around with java Sockets.
The problem is the code below. for some reason commSocket = new Socket(hostName, portNumber); is returning true even when it has not connected with the server (server not implemented yet!). Any ideas regarding this situation?
For hostName Im passing my local machine IP and for port a manually selected port.
public void networkConnect(String hostName, int portNumber){
try {
networkConnected = false;
netMessage = "Attempting Connection";
NetworkMessage networkMessage = new NetworkMessage(networkConnected, netMessage);
commSocket = new Socket(hostName, portNumber);
// this returns true!!
System.out.println(commSocket.isConnected());
networkConnected = true;
netMessage = "Connected: ";
System.out.println("hellooo");
} catch (UnknownHostException e){
System.out.println(e.getMessage());
} catch (IOException e){
System.out.println(e.getMessage());
}
}
Many thanks.
EDIT: new Socket(.., ..); is blocking isnt it? i thought in that case if that was processed without exceptions then we have a true connection?
EDIT: I played around with anti virus and now it is working!
Had that exact same situation a few days ago on a corporate computer, and searched for it for hours.
Check your antivirus, some antivirus (like E*** N**32) use live TCP scanning that make a connection succeed even if nothing is listening on the target port but will reset it later when you try to read/write from the socket.
Add this to your code:
commSocket.getOutputStream().write(0);
commSocket.getInputStream().read();
If you get a SocketException now, you should really consider to change your antivirus.
Alternatively, set a breakpoint in your application right after creating the socket, and then use netstat -ano (on Windows) to check which process id is associated with the other endpoint of your socket (which should be on your machine if you connect to localhost).
I would suggest you to disable your antivirus, but in some cases even that does not help to unload their broken live TCP scanning driver...
The Socket constructor connects right away and will throw an IOException if it doesn't succeed. So apparently you have connected successfully to a server (this could be one you didn't make yourself).
This question already has answers here:
Java socket API: How to tell if a connection has been closed?
(9 answers)
Closed 5 years ago.
When I'm using e.g. PuTTY and my connection gets lost (or when I do a manual ipconfig /release on Windows), it responds directly and notifies my connection was lost.
I want to create a Java program which monitors my Internet connection (to some reliable server), to log the date/times when my internet fails.
I tried use the Socket.isConnected() method but that will just forever return "true". How can I do this in Java?
Well, the best way to tell if your connection is interrupted is to try to read/write from the socket. If the operation fails, then you have lost your connection sometime.
So, all you need to do is to try reading at some interval, and if the read fails try reconnecting.
The important events for you will be when a read fails - you lost connection, and when a new socket is connected - you regained connection.
That way you can keep track of up time and down time.
Even though TCP/IP is "connection oriented" protocol, normally no data is sent over an idle connection. You can have a socket open for a year without a single bit sent over it by the IP stack. In order to notice that a connection is lost, you have to send some data on the application level.(*) You can try this out by unplugging the phone cable from your ADSL modem. All connections in your PC should stay up, unless the applications have some kind of application level keepalive mechanism.
So the only way to notice lost connection is to open TCP connection to some server and read some data from it. Maybe the most simple way could be to connect to some FTP server and fetch a small file - or directory listing - once in a while. I have never seen a generic server which was really meant to be used for this case, and owners of the FTP server may not like clients doing this.
(*) There is also a mechanism called TCP keepalive but in many OS's you have to activate it for all applications, and it is not really practical to use if you want to notice loss of connection quickly
If the client disconnects properly, a read() will return -1, readLine() returns null, readXXX() for any other X throws EOFException. The only reliable way to detect a lost TCP connection is to write to it. Eventually this will throw an IOException 'connection reset', but it takes at least two writes due to buffering.
Why not use the isReachable() method of the java.net.InetAddress class?
How this works is JVM implementation specific but:
A typical implementation will use ICMP ECHO REQUESTs if the privilege can be obtained, otherwise it will try to establish a TCP connection on port 7 (Echo) of the destination host.
If you want to keep a connection open continually so you can see when that fails you could connect to server running the ECHO protocol yourself rather than having isReachable() do it for you and read and write data and wait for it to fail.
You might want to try looking at the socket timeout interval. With a short timeout (I believe the default is 'infinite timeout') then you might be able to trap an exception or something when the host becomes unreachable.
Okay so I finally got it working with
try
{
Socket s = new Socket("stackoverflow.com",80);
DataOutputStream os = new DataOutputStream(s.getOutputStream());
DataInputStream is = new DataInputStream(s.getInputStream());
while (true)
{
os.writeBytes("GET /index.html HTTP/1.0\n\n");
is.available();
Thread.sleep(1000);
}
}
catch (IOException e)
{
System.out.println("connection probably lost");
e.printStackTrace();
}
Not as clean as I hoped but it's not working if I leave out the os.writeBytes().
You could ping a machine every number of seconds, and this would be pretty accurate. Be careful that you don't DOS it.
Another alternative would be run a small server on a remote machine and keep a connection to it.
Its probably simpler to connect to yahoo/google or somewhere like this.
URL yahoo = new URL("http://www.yahoo.com/");
URLConnection yc = yahoo.openConnection();
int dataLen = yc.getContentLength() ;
Neil
The isConnected()method inside Socket.java class is a little misleading. It does not tell you if the socket is currently connected to a remote host (like if it is unclosed). Instead, it tells you whether the socket has ever been connected to a remote host. If the socket was able to connect to the remote host at all, this method returns true, even after that socket has been closed. To tell if a socket is currently open, you need to check that isConnected() returns true and isClosed() returns false.
For example:
boolean connected = socket.isConnected() && !socket.isClosed();