HOST
First, my host is dreamhost. I have root access. The system is a linux system.
SERVER
**UPDATE: It looks like the server uses modsecurity (modsecurity.org). I'll look into it more now, but if anyone has any tips or knows how to work with it, that's where I'm stuck now. **
Second, I wrote a java server that binds to port #### and the listens for connections. I can run this local & connect, but I'm trying to put it up on my server and connect from anywhere. That is the idea behind a server.
private int port;
private ServerSocketChannel ssc;
private Selector selector;
public Server(int port) {
this.port = port;
}
public void run() {
try {
ssc = ServerSocketChannel.open();
selector = Selector.open();
ssc.socket().bind((new InetSocketAddress(port)));
new Thread(new ReadLoop(selector)).start();
new Thread(new AcceptingLoop(ssc, selector)).start();
System.out.println("Bound to port " + port + " and awake:");
} catch (IOException e) {
System.out.println("Server could not start.");
e.printStackTrace();
}
}
I launched this on the server. The program says it successfully bound to the port.
CLIENT
The client is flash, AS3. Here's the code i use to attempt the connect:
var mySocket:XMLSocket = new XMLSocket();
mySocket.connect("http://mydomain.net", ####);
I'm well aware of the sandbox policies. This is something else. I receive this error:
IOERROR [IOErrorEvent type="ioError" bubbles=false cancelable=false eventPhase=2 text="Error #2031: Socket Error. URL: http:--mydomain.net"] (replace -- with //, stackoverflow was reading it as a link)
This error apparently means that Flash never found a server. I would have gotten a security error if it had been the sandbox.
Anyway, how do I tell if ports are open correctly, if they are blocked, etc?
I'm also wondering if this has something to do with it:
http://wiki.dreamhost.com/Mod_security
I unfortunately don't understand a lot of this stuff, but I'm trying to learn.
Try and run your server program on a port that is unlikely to be blocked (e.g. 80, 443). Of course, make sure that nothing else is using the port that you choose.
Related
I am creating a simple learning project (chat using sockets) in Java and today I faced a problem. Maybe the point is an obvious one for somebody, but I am confused with it
The purpose
To get to know (at least one of the following):
A list of the currently opened free/taken ports on a PC
Whether the port I want to use is locked
What I tried
I've created a simple raw-project and run two ServerSocket on one port. In this case I have caught a java.net.BindException with notification that "...Address already in use: JVM_Bind...". But in this way I am able to check the port avaliability only if my JVM has captured it. In case if other program listens to the port, I do not know anything about it. I am adding a code below.
public class Main {
public static void main(String[] args) throws IOException {
MyThread myThread = new MyThread();
ServerSocket serverSocket = new ServerSocket(5940);
myThread.start();
serverSocket.accept();
}
}
public class MyThread extends Thread {
#Override
public void run() {
try {
ServerSocket serverSocket = new ServerSocket(5940);// exception is thrown here
serverSocket.accept();
} catch (IOException e) {
System.err.println("SECOND SERVER");
e.printStackTrace();
interrupt();
}
}
}
PS Any advice is warmly welcomed
I've created a simple raw-project and run two ServerSocket on one
port. In this case I have caught a java.net.BindException with
notification that "...Address already in use: JVM_Bind...". But in
this way I am able to check the port avaliability only if my JVM has
captured it. In case if other program listens to the port, I do not
know anything about it.
I think you're misinterpreting your result. I have every reason to believe that if the port you request is already bound by any process then your attempt to bind it will fail with a BindException. That takes care of
Whether the port I want to use is locked
. As for
A list of the currently opened free/taken ports on a PC
, there are system utilities that can get you that information, but it is useless to you. Whichever end initiates the connection (i.e. the client) needs to know in advance what port to try to connect to. It cannot get that from the server, because that presents a chicken & egg problem.
The usual approach is that the server listens to a specific port chosen by its developer or its admin, and that port number is provided to clients out of band -- often simply by it being a standard, well-known port number. That's how most of the basic network protocols work; for example, HTTP servers run on port 80 by default. If the wanted port happens to be unavailable when the server attempts to bind to it then that indicates a misconfiguration of the machine, and the server simply fails to start.
The client, on the other hand, does not need to choose a port number at all. The system will choose one for it automatically when it attempts to connect to the server.
I'm trying to build a project where I must pilot an IoT device from smartphone via Wifi.
This device has the SPWF01 Wifi Module integrated, and is configured as an access point (that has no Internet access) with security type WEP. On this access point configuration we also have a TCP Socket Server that intercepts smartphone communications.
On the smartphone side, we have the part which scans and connects to our device's access point(which works, although i get the esclamation point on the wifi icon since it has no Internet access). After we've connected, we start the Client Socket which connects to the server on our IoT device(the ip address of the server socket is actually the gateway of the access point). And here is where the trouble starts, because the client socket won't start. Here is the code:
public void SocketInit(String ip, int port) throws IOException {
InetAddress addr = InetAddress.getByName(ip);
SocketAddress sockaddr = new InetSocketAddress(addr, port);
nsocket = new Socket();
nsocket.setReuseAddress(true);
nsocket.setTcpNoDelay(false);
nsocket.setReceiveBufferSize(700); //Must be less than 730byte witch is the module buffer
nsocket.setSendBufferSize(700);
nsocket.connect(sockaddr, 5000); //5 second connection timeout
}
And here is the exception i get:
java.net.SocketException: socket failed: ENONET (Machine is not on the network)
And I get that error even before reaching nsocket.connect(), precisely on setReuseAddress.
Since the exception I get is ENONET, I thought that it must be because the access point has no internet access so I used the solution proposed here for testing purpose:
adb shell settings put global captive_portal_detection_enabled 0
This is a solution that can't be done programmatically without having root access, but I wanted to test if that was the problem. But although the exclamation mark on the wifi icon had disappeared, the client socket still gave me the same exception error.
Does anybody have a solution for this behaviour? Thank you in advance!
Sometimes the client socket manages to open, with a success rate of 1 out of 20 times. But when it does, i usually get another exception after a couple of messages sent:
java.net.SocketException: recvfrom failed: ECONNRESET (Connection reset by peer)
Here is the code I used to connect to the access point from the smartphone:
WifiConfiguration wc=new WifiConfiguration();
wc.SSID= host;
wc.status = WifiConfiguration.Status.ENABLED;
wc.priority = 40;
wc.allowedKeyManagement.set(WifiConfiguration.KeyMgmt.NONE);
wc.allowedProtocols.set(WifiConfiguration.Protocol.RSN);
wc.allowedProtocols.set(WifiConfiguration.Protocol.WPA);
wc.allowedAuthAlgorithms.set(WifiConfiguration.AuthAlgorithm.OPEN);
wc.allowedAuthAlgorithms.set(WifiConfiguration.AuthAlgorithm.SHARED);
wc.allowedGroupCiphers.clear();
wc.allowedPairwiseCiphers.set(WifiConfiguration.PairwiseCipher.CCMP);
wc.allowedPairwiseCiphers.set(WifiConfiguration.PairwiseCipher.TKIP);
wc.allowedGroupCiphers.set(WifiConfiguration.GroupCipher.WEP40);
wc.allowedGroupCiphers.set(WifiConfiguration.GroupCipher.WEP104);
wc.wepKeys[0] = password;
wc.wepTxKeyIndex = 0;
int netId = mainWifi.addNetwork(wc);
try {
//mainWifi.setWifiEnabled(true);
mainWifi.disconnect();
mainWifi.enableNetwork(netId, true);
mainWifi.reconnect();
startConnectionCheck = true;
System.out.println("enabled network");
} catch (Exception e) {
e.printStackTrace();
System.out.println(e.getMessage());
}
The access point's security type is WEP. That is because the Wifi module can't implement WPA.
Tests done on Marshmallow.
I am not 100% certain if this issue is the same.
I had to do a project a whileback and used Java sockets.
When doing intial testing, I used the local loopback and used ports on the same computer and multiple threads. Eventually it worked well enough to test between two computers. I found it didn't work between two computers. After turning off all my firewalls and protections etc on the network and getting desperate enough to use direct connection ethernet cables, I figured out the issue.
Sockets cares which gateway you use. The solution was for me to use the gateway rather than the loopback... It is obvious looking back now...
Anyway, it is likely that your mobile gateway, wifi gateway, and local loopback are all different.
Here is an ugly code blurbe that I hope gives direction with very little inspiration...
Socket socket = null;
try {
socket = new Socket(ip, port, InetAddress.getLoopbackAddress(), localServerPort);
}
catch (Exception e) {
}
if (socket == null) {
try {
socket = new Socket(ip, port, InetAddress.getLocalHost(), localServerPort);
}
catch (Exception e) {
}
}
if(socket == null) {
throw new Exception("Neither the loop back nor the host could find this sucker.");
}
I'm trying to write an android app that interacts with a server. I'm trying now to write the server side with sockets. I created an instance of ec2 and ran it. I connected to it with putty and ran a simple "hello world" java program. Now I'm trying to run a server which use a socket, but I get this as the server socket: ServerSocket[addr=0.0.0.0/0.0.0.0,localport=5667].
This is my code, very basic so far:
public class EchoServer {
public static void main(String[] args) throws IOException {
int portNumber = 5667;
System.out.println("server socket main");
try (ServerSocket serverSocket = new ServerSocket(portNumber);
) {
System.out.println(serverSocket.toString());
} catch (IOException e) {
System.out
.println("Exception caught when trying to listen on port "
+ portNumber + " or listening for a connection");
System.out.println(e.getMessage());
}
}
}
What should I do to run the server so I could connect to it via my andriod device?
Thanks!
You are on the right track. 0.0.0.0 simply means:
A way to specify "any IPv4-interface at all". It is used in this way when configuring servers (i.e. when binding listening sockets).
Next, your server will need to listen for incoming connections by using SocketServer.accept().
And then of course you'll want to receive and send data on the socket. This tutorial should help.
Finally, if you plan on serving multiple clients simultaneously with your server, you will want to consider concurrency and scalability, and perhaps consider using a framework like Netty.
I created a simple echo server in Java. When I try it locally, it works as it should. However, when I try to connect it from a different computer using the IP address and the port number the server is running on, it never connects. Is there anything else that should be done to connect to a server from a different computer?
import java.net.Socket;
import java.net.ServerSocket;
public class EchoServer {
public static void main(String[] args) throws Exception {
// create socket
int port = 4444;
ServerSocket serverSocket = new ServerSocket(port);
System.err.println("Started server on port " + port);
// repeatedly wait for connections, and process
while (true) {
// a "blocking" call which waits until a connection is requested
Socket clientSocket = serverSocket.accept();
System.err.println("Accepted connection from client");
// open up IO streams
In in = new In (clientSocket);
Out out = new Out(clientSocket);
// waits for data and reads it in until connection dies
// readLine() blocks until the server receives a new line from client
String s;
while ((s = in.readLine()) != null) {
out.println(s);
}
// close IO streams, then socket
System.err.println("Closing connection with client");
out.close();
in.close();
clientSocket.close();
}
}
}
Please check the following things.
Is the server computer behind a network proxy ?
Does it have an independent public IP Address by which it is accessible from
anywhere ? Or, does it have an internal IP, by which it can be accessed in your LAN ?
Make sure FireWalls has an exception for port 4444. Or you may turn it of in both client and server.
If it does not help, post the exception you are getting (by editing the question). Or the server program is just freezing without any error ?
If this is on your LAN refer to the machine running your EchoServer by name (the actual machine name, I believe they show you to do it this way on the Sun Tutorial that posted this echo server excercise correct?). If that works it would help a lot in troubleshooting the issue.
Because I didn't want to implement a communication protocol for my client-server based application, I implemented a RMI client and a RMI server on both sides for the information exchange between the two components.
If I try to use my application by starting the two components on the same machine, everything is working fine. But if I split the components to two different computers (Kubuntu 9.04 within as a virtual machine within an Windows 7 RC environment with disabled firewall and a native Ubuntu 9.04 environment), it seems like the RMI client is not able to execute the methods which are defined on the server side. (Every functions call leads to a RMI exception.)
Currently I only set the system property "java.rmi.server.hostname" on both sides to the network interface which should be used for the data exchange and registered the default port for the communication with rmi daemon (?) rmid.
Does somebody has an idea what might be going wrong? Do I have to set some other parameters like "java.rmi.server.codebase" (http://java.sun.com/j2se/1.4.2/docs/guide/rmi/javarmiproperties.html) to be able to use the RMI functionality within my application?
Edit: Okay, here is some additional information for you:
In the initialization phase my client tries to establish a connection to the RMI server of server component, which was initialized using the following two methods:
private void initialize()
{
// set ip address of rmi server
System.setProperty("java.rmi.server.hostname", ipAddress);
// try to register rmi server
try
{
LocateRegistry.createRegistry(Registry.REGISTRY_PORT);
}
catch (Exception e)
{
// ignore
}
}
public void start()
{
System.out.print("starting master control RMI server ...");
try
{
Naming.rebind("MasterControl", this);
}
catch (Exception e)
{
System.out.println("error: could not initialize master control RMI server");
System.exit(1);
}
// set running flag
isRunning = true;
System.out.println(" done");
}
"ipAddress" is here the ip address of the network interface of the server component.
The method which is used by the client component to establish the connection looks like this:
public void connect()
{
// build connection url
String url = "rmi://" + masterControlIpAddress + "/MasterControl";
System.out.println(url);
System.out.print("connecting to master control ...");
// try to connect to master control server
while (connection == null)
{
try
{
connection = (MasterControlInterface) Naming.lookup(url);
id = connection.register(localIpAddress);
}
catch (Exception e)
{
// ignore
}
if (connection == null)
{
try
{
Thread.sleep(100);
}
catch (InterruptedException e)
{
e.printStackTrace();
}
}
}
System.out.println(" done");
}
As you can see my client calls a function to register the connection at the server:
#Override
public int register(String ipAddress) throws RemoteException
{
// add connection to registrationHandler
masterControl.registrationHandler.addConnection(ipAddress);
// log
int connectionCount = masterControl.registrationHandler.getConnectionCount();
System.out.println("slave control (" + ipAddress + ") instance has been registered at the master control server under the following id: " + connectionCount);
return connectionCount;
}
If I run my program using a real network connection, the text "slave control ..." is not displayed on the server side. Therefore I'm not sure, if the function is really called by the client component.
After the client component is intialized it tries to notify the server component by calling the following method using it's RMI connection to the server:
public void sendInitializationDone()
{
try
{
connection.initializationDone();
}
catch (RemoteException e)
{
System.out.println("error: could not send 'initializationDone' message to master control");
System.out.println(e);
System.exit(1);
}
}
to set a flag on the server side.
The error occures inside this function on the client side:
java.rmi.ConnectException: Connection refused to host 127.0.1.1; nested exception is: java.net.ConnectException: Connection refused.
I have no idea why the host is here 127.0.1.1 ...
#nos
Of course, I disabled the windows firewall and the protection mechanismn of Kaspersky Internet Security. I don't think that there is a running firewall in my Kubuntu. In generell it is possible to establish a connection, because I already used scp to copy my program to the other machine.
Edit2:
Mhhh, after setting the entry in /etc/hosts which refers to the machine to the ip address of the machine it seems to work, but don't really understand why it does ...
BR,
Markus
You need to add an entry to the hosts file of the machines containing an entry of the form
machinename privateip
e.g.
virtualmachine 192.168.1.16
This will prevent RMI from sending the localhost host name as a 'call me back' address.
To test this approach, run the following code before and after performing the change.
System.out.println(java.net.InetAddress.getLocalHost());
It should output a local address before the changes and a non-local address after the changes.
Using different versions of the JDK on each server could cause this problem.
Use the
java -version
command to make sure that you are using the same version of the jre.