We Keep Coding

How to debug remote JVM exposed by ngrok tunnel

I have a java process on one of my machines listening on port 4502. I have created a tunnel using ngrok so that I can access the application on my development machine. The issue I'm facing is attaching a debugger to the remote JVM.
Here is the debug java configuration I'm using:
-agentlib:jdwp=transport=dt_socket,address=*:5005,server=y,suspend=n
Here is the ngrok configuration for the tunnel to the application:
ngrok http 4502
Here is the ngrok configuration for the tunnel to the JVM (I have also tried http protocol with no luck):
ngrok tcp 5005
ngrok outputs the following for the tcp tunnel:
Forwarding tcp://2.tcp.eu.ngrok.io:10928 -> 127.0.0.1:5005
Using IntelliJ, I configure the remote debugging like this:
Debugger mode: Attach to remote JVM
Host: tcp://2.tcp.eu.ngrok.io
Port: 10928
I get the following error when starting the debugger:
Error running 'Debug Author Desktop': Unable to open debugger port (tcp://2.tcp.eu.ngrok.io:10928): java.io.IOException "handshake failed - connection prematurally closed"
On the machine running the java process, I have made sure that the 5005 port is open before starting the process. On the machine using IntelliJ, I have made sure that the 10928 port is open. What must I do so that I can attach the debugger to the process running on my second machine? Any help would be appreciated.

I've found the solution. The issue was in the Remote Debugger configuration. When specifying the host, you must not include the protocol. Once I changed tcp://2.tcp.eu.ngrok.io to 2.tcp.eu.ngrok.io, it worked!

How to bind DatagramSocket to particular port in Openshift

I am running siple java jar service on openshift which tried to connect with DatagramSocket and Getting this Exception:
java.net.BindException: Permission denied
at java.net.PlainDatagramSocketImpl.bind0(Native Method)
at java.net.AbstractPlainDatagramSocketImpl.bind(AbstractPlainDatagramSocketImpl.java:96)
at java.net.DatagramSocket.bind(DatagramSocket.java:397)
at java.net.DatagramSocket.<init>(DatagramSocket.java:251)
at java.net.DatagramSocket.<init>(DatagramSocket.java:304)
at java.net.DatagramSocket.<init>(DatagramSocket.java:276)
at com.gasmps.service.TerminationListener.run(EmailService.java:542)
at java.lang.Thread.run(Thread.java:745)
I know this is port permission problems but i tried with port like 8000,8443,15005,16005 but getting same how could i resolve this? How i can know all open port that can i use in my application.
Edit: My jboss server is already running in the same application and I don't want to create separate application for these jar service bcos I have to run this jar from my application from remote location.

Iv looked into this before after having the same issue and discovered the answer on stack-overflow before:
In Openshift, you may only bind to the port that the server allocates
for you. Typically that is the value of the environment variable
$OPENSHIFT_JBOSS_PORT (it varies between cartridges) and the value
differs between gears. Binding to any other port will be reported as
an SELinux policy violation and denied.
link
The port is usually 8080
you can bind your app to 8080 (not to 8000 or 8443), all traffic >received on 8000 and 8443 will be routed by the proxy to your app >listening on 8080.
This worked for me, but let me know how it goes and if it still doesn't work i'll try and help.

java.net.BindException: Address already in use while re using same connection

I am getting BindException exception while reusing same Address.Following is my code.
in openConnection method :
69. Selector selector = SelectorProvider.provider().openSelector();
70. SocketChannel socketChannel = SocketChannel.open();
71. socketChannel.bind(new InetSocketAddress(port));// Edited
72. socketChannel.socket().setReuseAddress(true);
73. socketChannel.configureBlocking(false);
74. socketChannel.connect(remoteAddress);
Exception:
java.net.BindException: Address already in use
at sun.nio.ch.Net.bind0(Native Method)
at sun.nio.ch.Net.bind(Net.java:414)
at sun.nio.ch.Net.bind(Net.java:406)
at sun.nio.ch.SocketChannelImpl.bind(SocketChannelImpl.java:580)
at sun.nio.ch.SocketAdaptor.bind(SocketAdaptor.java:135)
at com.example.client.request.Client.openConnection(Client.java:72)
Edit
I solved InvalidArgument exception and I have edited the post above but now while reconnecting on same port I get the above exception.Is some thing I am doing wrong?

If you want to reuse an address you have to call setReuseAddress(true) before binding the socket.

Signals that an error occurred while attempting to bind a socket to a local address and port. Typically, the port is in use, or the requested local address could not be assigned.
When you start a web server or application server, which typically listen on a port e.g. Tomcat or Jetty listens on 8080 and 8084 for HTTP and HTTPS traffic, they bind a socket to a local address and port. If you give them hostname e.g. localhost or devhost, then they used /etc/host in both Windows and Linux to resolve domain name into IP address, if this mapping is incorrect than you will get java.net.BindException: Cannot assign requested address: JVM_Bind. This host to IP address mapping file can be found at C:\Windows\System32\Drivers\etc\hosts, where C:\Windows is where you have installed windows operating system. If you look at this file, you will see it contains IP address and hostname as shown below :
127.0.0.1 localhost
192.168.52.1 localhost
Just, correct the mapping, or add 127.0.0.1 against localhost to resolve this issue

Connection problem with sockets in java

i tried this code:
http://programming-guides.com/java/tcp-client-server-chat
(full example)
and it's working but when i switch the "host" int the client side to an external IP (insted of localhost) it give me this error:
"Cannot get IO for connection to.."
i treid to switch the port but it didnt work..

Is the server running on that remote machine? Is the port open in the firewall?

Try to netcat to the remote host. If you get an connection the example maybe wrong. If not, you cannot connect to that host: host not exists, not listen on that port, port is filtered, etc, etc.

UnknkownHostException

Please help;
Am trying to deploy a web application.
The build is returning successful,and am not getting any errors on the sever.log
however am getting a http 503 error:the requested service() is not currently available
and also my
Java DB Database Process has this message
Warning: UnknkownHostException: intracare: intracare.
Could not listen on port 1527 on host localhost.
am using glassfish v3 prelude

Possibly you already have another application (perhaps another JavaDB instance?) listening on port 1527 - that could explain the "could not listen" message. Use netstat to check.

I think that UnknownHostException is related that intracare can't be resolved to an IP.
I would:
Ping that host.
Check C:\WINDOWS\system32\drivers\etc\hosts or /etc/hosts files.
Regards.

Check the DNS settings on the host. Your short names do not resolve correctly.

Mayby string you are typing as a host name is wrong? Maybe it is firewall problem?