Develop Reference

No data on socket input stream even though there is data

I have a problem with my Java socket and connection. It seems like my input stream does not read any data even though there is data on the stream. Here is an example on how we read data:
InputStream is = socket.getInputStream();
StringBuffer buf = new StringBuffer();
final int SO_TIME = 2500;
socket.setSoTimeout(SO_TIME);
long readTime = 0;
boolean remoteSocketClosed = false;
//Read data while the Remote-Socket is opened and the timeout is OK
while (!remoteSocketClosed && readTime < 30000)
{
try
{
int c = is.read();
if (c != -1)
{
buf.append((char)c);
}
else //c==-1
{
remoteSocketClosed = true;
}
}
catch (SocketTimeoutException socketTimeout)
{
readTime += SO_TIME;
}
}
if (readTime >= 30000)
{
throw new IOException("No answer from server after request (" + readTime +"ms )");
}
else
{
if (buf.length() > 0)
{
return buf;
}
else
{
return null;
}
}
finally
{
try
{
if (socket!=null)
socket.close();
}
catch (Exception e)
{
l.error("Socket not closed", e);
}
try{Thread.sleep(250);}catch(Exception e){}
}
Now this looks fine to me. However when there is data on the stream, it will not get picked up. I can use telnet and see that data is coming in on that connection, yet Java just throws the IOException (timeout).
The server is running on the same machine (localhost), and we can send data to the server, yet the answer is lost somehow (only in Java not in telnet). Is this some weird setting I don't know about? We are using Windows 10 and Java 8, firewalls are all disabled. I have never experienced something like this so any help is appreciated.

Sometimes you just don't see the forest for the trees and have to sleep over it...
The problem is my condition
if (c != -1)
{
buf.append((char)c);
}
else //c==-1
{
remoteSocketClosed = true;
}
But the server never closes the connection... So I never exit my loop and im stuck for 30 seconds running into socket timeouts. After the 30 seconds of waiting my answer is in the StringBuffer but of course my readTime is 30000 so I throw the exception rather providing an answer... I will have to think of an EndOfPackage Byte or something to avoid this.
Thanks for any help tho

Java socket time out does not work

I've a class which is responsible for listening two other machines which have exactly the same classes, so it's a network of three computers having the same code. The connection is there and I can see them passing data to each other. Everything until there works OK.
Things get tricky when I take out one of the machines and observe how the other two behave. Expectedly, when one of the machines stops working for some reason, other two should continue. And if two of them stop, the remaining should go on.
I tried to implement this mechanism below. However, when I take out one of the machines, the program keeps waiting, so it does not switch to "two-way comparison mode".
public void listen() {
try {
logger.info("Creating listener sockets");
while (isRunning) {
final byte[] buf = new byte[bufferSize];
final DatagramPacket packetOne = new DatagramPacket(buf, buf.length);
final DatagramPacket packetTwo = new DatagramPacket(buf, buf.length);
MediatorMessageMsg mediatorMessageOne = null;
MediatorMessageMsg mediatorMessageTwo = null;
try {
socketReceiverOne.receive(packetOne);
ByteArrayInputStream firstInput = new ByteArrayInputStream(buf);
mediatorMessageOne = MediatorMessageMsg.parseDelimitedFrom(firstInput);
socketReceiverTwo.receive(packetTwo);
ByteArrayInputStream secondInput = new ByteArrayInputStream(buf);
mediatorMessageTwo = MediatorMessageMsg.parseDelimitedFrom(secondInput);
logger.trace("Received packets");
} catch (final SocketTimeoutException e) {
logger.trace(e.getMessage());
continue;
} catch (final SocketException e) {
logger.warn(e);
logger.warn("Ignore the error and go on.");
continue;
} catch (final IOException e) {
logger.error("Incoming communication stopped!");
logger.error(e);
stop();
}
// if two mediators sent the data, it's OK
if (packetOne.getLength() > 0 && packetTwo.getLength() > 0) {
handlePackets(mediatorMessageOne, mediatorMessageTwo);
logger.info("Number of active mediators: 2. Comparison style: 1v1v1");
}
// if only one sent the data, compare it with our own
else if (packetOne.getLength() > 0 || packetTwo.getLength() > 0) {
// whicehever sent the data, compare its data with our own
logger.info("Number of active mediators: 1. Comparison style: 1v1");
if (packetOne.getLength() > 0) {
handlePackets(mediatorMessageOne);
} else {
handlePackets(mediatorMessageTwo);
}
}
// if no data is sent, then pass our own directly
else {
logger.info("Number of active mediators: 0. Comparison style: No Comparison");
// our datamodel to retrieve data on our own
DataModel modelOwn = DataModel.getInstance();
MediatorMessageMsg newMessage = MediatorMessageMsg.newBuilder().setHeading(modelOwn.getHeading()).setSpeed(modelOwn.getSpeed()).setSender(getId()).build();
// publish(topicName, newMessage);
}
Thread.sleep(1);
}
socketReceiverOne.close();
socketReceiverTwo.close();
logger.info("stopped");
} catch (final IllegalArgumentException e) {
logger.error("Illegal argument received: " + e);
} catch (final Exception e) {
logger.error("Unexpected error occured: " + e);
} finally {
if (socketReceiverOne instanceof DatagramSocket && socketReceiverTwo instanceof DatagramSocket) {
if (!socketReceiverOne.isClosed() || !socketReceiverTwo.isClosed()) {
socketReceiverOne.close();
socketReceiverTwo.close();
}
}
}
}
To save your time, let me share my opinion on the matter. I suspect the problem to be in this part:
socketReceiverOne.receive(packetOne);
ByteArrayInputStream firstInput = new ByteArrayInputStream(buf);
mediatorMessageOne = MediatorMessageMsg.parseDelimitedFrom(firstInput);
socketReceiverTwo.receive(packetTwo);
ByteArrayInputStream secondInput = new ByteArrayInputStream(buf);
mediatorMessageTwo = MediatorMessageMsg.parseDelimitedFrom(secondInput);
To me it seems like the program expects a package and when it cannot receive it, it keeps waiting. Although I have time out exception condition, I cannot get this done.
private int socketTimeout = 1000 * 2;// 2sec
socketReceiverOne.setSoTimeout(socketTimeout);
socketReceiverTwo.setSoTimeout(socketTimeout);
Any thoughts?

Okay I found where I was mistaken. I needed more ports (for in and out). Once I incorporated those ports, the problem did not occur again.

cannot get server socket to close

I'm making a simple chat server and just made it so each connection runs on a new thread.
The old version started a single thread for the server, it did a while loop, which would stop when a stop message was sent then close the socket.
The new version loops forever and create a new thread for each new connection. Now I cannot close the socket connection.
If you press a key and the main thread stops, the socket stays open. Thus when I run the program again I need to change the socket number.
code of server
while(true)
{
///////////////////////////////////////////////////
// get a new connection
///////////////////////////////////////////////////
System.out.println("Aceepting connections on port 1030 \r");
try{
// Get New Connection
// wait for ever on accepting new connections
server.setSoTimeout(0);
connection=server.accept();
cConnection thread = new cConnection("thread3", connection);
} catch(IOException ec)
{
System.out.println(ec.getMessage());
}
}
code that starts server
Now each message comes in on a new thread, so I cannot tell it to stop and close the socket.

You need to provide a flag that must be globally accesible, so when some client wants to stop the server then change the variable ans stops the bucle. By example:
class YourServer {
private static boolean execute = true;
public static synchronized void stop() {
execute = false;
}
public void yourMethod() {
while(execute) {
// implement your server here
}
}
}
When a client send the command STOP you must be do
YourServer.stop();

If you want a stop command to stop the server you can call System.exit() to force the program to store or just closing server is likely to be all you need.

Looking into your problem, I understood one thing, that since you are putting
while (true), so your control always gets stuck at connection=server.accept(); listening for a new connection. So in order to stop the sockets you need to first find a way to stop looping in that while loop. Either you can set a Variable, like (int clientsConnected) to check the number of Clients, when that comes to zero stop that while loop. So you can stop your sockets.
Below is my sample code for clients which is doing the same thing for closing the Sockets.
Hopefully this solves your problem.
class GetNamesFromServer implements Runnable
{
private Socket sForName, sForId;
private BufferedReader in, inForName, inForId;
private PrintWriter outForName, outForId;
private static String clientNames;
public GetNamesFromServer(Socket s1, Socket s2)
{
sForName = s1;
sForId = s2;
}
public void run()
{
try
{
outForName = new PrintWriter(sForName.getOutputStream(), true);
outForName.println(Client.clientName);
System.out.println("Send Name : " + Client.clientName);
outForName.flush();
}
catch(IOException e)
{
System.err.println("Error sending Name to the Server.");
}
try
{
inForId = new BufferedReader(new InputStreamReader(sForId.getInputStream()));
Client.clientId = (inForId.readLine()).trim();
System.out.println("Client ID is : " + Client.clientId);
}
catch(IOException e)
{
System.err.println("Error Receiving ID from Server.");
}
try
{
inForName = new BufferedReader(new InputStreamReader(sForName.getInputStream()));
while (true)
{
clientNames = inForName.readLine();
if (clientNames != null && clientNames != "")
{
clientNames = clientNames.substring(1, clientNames.length() - 1);
System.out.println("Names Received : " + clientNames);
String[] names = clientNames.split(", ");
Client.nameClients.clear();
for (String element: names)
Client.nameClients.add(element);
Client.nPane.setText("");
int size = Client.nameClients.size();
System.out.println("Size of list : " + size);
for (int i = 0; i < size; i++)
{
String name = Client.nameClients.get(i);
String colour = Character.toString(name.charAt(0));
name = name.substring(1, name.length()) + "\n";
appendToNamePane(name, ReceiveMessages.getColour(Integer.parseInt(colour)), "Lucida Console");
}
System.out.println("Clients Online : " + Client.nameClients);
}
int index = Client.nameClients.indexOf(Client.clientId + Client.clientName);
**if (index == -1)
{
sForName.close();
break;
}**
}
}
catch(IOException e)
{
System.err.println("Error Receiving Names of Clients from Server");
}
}
NEW EDITION :
You can add a cap to maximum number of clients that can connect, once that reaches your while loop will not go to connection = server.accept(); and hence when they are done chatting (after some time) i.e. totalClients = 0, you can stop your sockets as well, to stop the program.
if (totalClients == 0)
{
socket.close();
serverSocket.close();
}
Regards

sockets long reading data

This is my code:
private String receiveData(String sjson) {
Log.i(TAG,"send request: " + sjson);
String jstr="";
try {
OutputStream out = s.getOutputStream();
out.write(sjson.getBytes());
out.flush();
//out.close();
Log.v(TAG,"sended data");
BufferedReader input = new BufferedReader(new InputStreamReader(s.getInputStream()));
char[] cbuf = new char[1];
input.read(cbuf);
String size = new String(cbuf);
while (input.read(cbuf) != 0) {
if((new String(cbuf)).equals("{") == true)
break;
size = size + new String(cbuf);
}
char[] jbuf = new char[Integer.valueOf(size)];
input.read(jbuf);
jstr = "{" + new String(jbuf);
}catch (Exception e) {
Log.e(TAG,e.toString());
}
Log.d(TAG,"responce: " + jstr);
return jstr;
}
public void connectSocket() {
Log.v(TAG,"connecting Socket: "+URL+":"+PORT);
try {
s = new Socket(URL, PORT);
Log.v(TAG,"connect Socket!");
ERROR_CODE = 0;
}catch (Exception e) {
Log.e(TAG,e.toString());
ERROR_CODE = ERROR_SOCKET_CONNECT_SUCCESSFULL;
}
Log.e(TAG,getErrorMsg(ERROR_CODE));
}
public void closeSocket() {
Log.v(TAG,"closeSocket");
try {
s.close();
}catch (Exception e) {
Log.e(TAG,e.toString());
}
}
At server the answer is less than a second. At the client it passes 1 minute before reading data.
Apps stoped at input.read(cbuf); waiting for answer.
Logs:
05-23 06:35:17.540: VERBOSE/Utilits(358): Auth: 77.221.129.100:10598
05-23 06:35:17.660: INFO/Utilits(358): send request: 0119{"data":{"password":"12345","imei":"000000000000001"},"method":"login"}
05-23 06:36:17.909: DEBUG/Utilits(358): responce: {"response":{"success":true,"user":{"id":"6","properties":{"auto":"model":"audi","color":"ffff","number":"td123r"}},"is_driver":"1"}}}
Why does it take so long to read an answer?

What on earth do you expect that method to do? There are bugs in it, and it does things that it should do.
You should specify encoding/charset when you create the InputStreamReader
Why do you read character by character from start to "{"
Why do you create a string for each character that you read before you hit "{"
Why do you append strings in a loop? Use a StringBuilder if you must append.
input.read returns an integer that says how many bytes/character that you have received
It's never guaranteed that it will fill the buffer. So you might not get all data.
Why aren't you closing resources?
.. and now to why it might be slow. Is the server flushing the data? If not, make sure that the server is flushing the data.

java.nio.channels.ClosedChannelException

How can i solve this problem. I got following error:
java.nio.channels.ClosedChannelException
This is coding:
public void run() {
try {
SocketChannel socketChannel = (SocketChannel) key.channel();
ByteBuffer buffer = ByteBuffer.allocate(512);
int i1 = socketChannel.read(buffer);
if (buffer.limit() == 0 || i1 == -1) {
Socket s = null;
try {
s = socketChannel.socket();
s.close();
key.cancel();
} catch (IOException ie) {
if (UnitDataServer.isLog) {
log.error("Error closing socket " + s + ": " + ie);
}
}
} else {
buffer.flip();
if (UnitDataServer.isLog) {
log.info(" Recvd Message from Unit : " + buffer.array());
}
byte byteArray[] = buffer.array();
log.info("Byte Array length :" + byteArray.length);
hexString = new StringBuffer();
for (int i = 0; i < i1 /* byteArray.length */; i++) {
String hex = Integer.toHexString(0xFF & byteArray[i]);
if (hex.length() == 1) {
// could use a for loop, but we're only dealing with a
// single byte
hexString.append('0');
}
hexString.append(hex);
}
hexString.trimToSize();
log.info("Hex String :" + hexString);
Communicator.dataReceive(new DataReceive(
socketChannel, hexString.toString(), dst));
}
} catch (Exception e) {
if (UnitDataServer.isLog) {
// log.error(e);
}
try {
socketChannel.socket().close();
key.cancel();
} catch (IOException ex) {
if (UnitDataServer.isLog) {
log.error(ex);
}
}
}
}

You have closed the channel and are still trying to use it.
There are several issues with your code.
First, your test for EOS is faulty. Remove the limit() == 0 test. That doesn't indicate EOS, it just indicates a zero length read, which can happen in non-blocking mode at any time. It doesn't mean the peer has closed his end of the connection, and it doesn't mean you should close your end.
Second, closing a channel closes the socket as well. You should close the channel only, not the socket.
Third, closing a channel cancels the key. You don't need to follow every close with a cancel.
You may also have failed to check whether a ready key is valid in the select loop before using it, e.g. for reading.
I continue to be amazed, and amused, and bemused, by the claim elsewhere in this thread that 'source code is untrue' under some circumstances.

You need to fix/secure code that is throwing this exception. ClosedChannelException is ...
... thrown when an
attempt is made to invoke or complete
an I/O operation upon channel that is
closed, or at least closed to that
operation. That this exception is
thrown does not necessarily imply that
the channel is completely closed. A
socket channel whose write half has
been shut down, for example, may still
be open for reading
(as described in Java 6 API)
But really, you would need to provide us code snipped and stack trace in order to get more detailed help.