Setting a timeout for socket operations

Question

When I create a socket:

Socket socket = new Socket(ipAddress, port);

It throws an exception, which is OK, because the IP address is not available. (The test variables where String ipAddress = "192.168.0.3" and int port = 300.)

The problem is: how do I set it to timeout for that socket?

When I create the socket, how do I reduce the time before I get a UnknownHostException and get the socket to timeout?

Answer 1

Use the Socket() constructor, and connect(SocketAddress endpoint, int timeout) method instead.

In your case it would look something like:

Socket socket = new Socket();
socket.connect(new InetSocketAddress(ipAddress, port), 1000);

---

Quoting from the documentation

connect

public void connect(SocketAddress endpoint, int timeout) throws IOException

Connects this socket to the server with a specified timeout value. A timeout of zero is interpreted as an infinite timeout. The connection will then block until established or an error occurs.

Parameters:

endpoint - the SocketAddress
timeout - the timeout value to be used in milliseconds.

Throws:

IOException - if an error occurs during the connection
SocketTimeoutException - if timeout expires before connecting
IllegalBlockingModeException - if this socket has an associated channel, and the channel is in non-blocking mode
IllegalArgumentException - if endpoint is null or is a SocketAddress subclass not supported by this socket

Since: 1.4

Answer 2

You don't set a timeout for the socket, you set a timeout for the operations you perform on that socket.

For example socket.connect(otherAddress, timeout)

Or socket.setSoTimeout(timeout) for setting a timeout on read() operations.

See: http://docs.oracle.com/javase/7/docs/api/java/net/Socket.html

Answer 3

You could use the following solution:

SocketAddress sockaddr = new InetSocketAddress(ip, port);
// Create your socket
Socket socket = new Socket();
// Connect with 10 s timeout
socket.connect(sockaddr, 10000);

Hope it helps!

Answer 4

You can't control the timeout due to UnknownHostException. These are DNS timings. You can only control the connect timeout given a valid host. None of the preceding answers addresses this point correctly.

But I find it hard to believe that you are really getting an UnknownHostException when you specify an IP address rather than a hostname.

EDIT To control Java's DNS timeouts see this answer.

Answer 5

Use the default constructor for Socket and then use the connect() method.

Answer 6

One solution is to execute the DNS resolution on a different thread which is given only a certain amount of time to complete.

Here's a simple utility that can help you do this:

public class TimeSliceExecutor {

  public static class TimeSliceExecutorException extends RuntimeException {
    public TimeSliceExecutorException(String message, Throwable cause) {
      super(message, cause);
    }
  }

  public static void execute(Runnable runnable, long timeoutInMillis) {
    ExecutorService executor = Executors.newSingleThreadExecutor();
    try {
      Future<?> future = executor.submit(runnable);
      getFuture(future, timeoutInMillis);
    }
    finally {
      if (executor != null) {
        executor.shutdown();
      }
    }
  }

  public static <T> T execute(Callable<T> callable, long timeoutInMillis) {
    ExecutorService executor = Executors.newSingleThreadExecutor();
    try {
      Future<T> future = executor.submit(callable);
      return getFuture(future, timeoutInMillis);
    }
    finally {
      if (executor != null) {
        executor.shutdown();
      }
    }
  }

  public static <T> T getFuture(Future<T> future, long timeoutInMillis) {
    try {
      return future.get(timeoutInMillis, TimeUnit.MILLISECONDS);
    }
    catch (InterruptedException ex) {
      Thread.currentThread().interrupt();
      throw new TimeSliceExecutorException("Interrupton exception", ex);
    }
    catch (ExecutionException ex) {
      throw new TimeSliceExecutorException("Execution exception", ex);
    }
    catch (TimeoutException ex) {
      throw new TimeSliceExecutorException(String.format("%dms timeout reached", timeoutInMillis), ex);
    }
  }
}

Then build the socket along these lines:

private Socket buildSocket() throws IOException {
  final Socket socket = new Socket();
  socket.setSoTimeout(socketTimeout);
  socket.connect(new InetSocketAddress(resolveHost(host, dnsTimeout), port), connectionTimeout);
  return socket;
}

private static InetAddress resolveHost(String host, long dnsTimeout) throws IOException {
  try {
    return TimeSliceExecutor.execute(() -> InetAddress.getByName(host), dnsTimeout);
  }
  catch (TimeSliceExecutor.TimeSliceExecutorException ex) {
    throw new UnknownHostException(host);
  }
}

Ref: https://stackoverflow.com/a/70610305/225217