CODEWITHSUNDEEP
androidsockets
user1530101
user1530101

Reputation: 77

Reconnecting to an Android Socket in order to wait for Server

So I have TCP server in Windows that is programmed in C++ and a client in JAVA, Android 4.0.4.

In Android, I connect like this:

public boolean sendConnectRequest()
{
    while (isSocketConnected == false)
    {
        try {
            if(comSocket == null)
            comSocket = new Socket("192.168.0.1",1531);
            isSocketConnected = comSocket.isConnected();
            if (isSocketConnected) {
                out = comSocket.getOutputStream();
                in = comSocket.getInputStream(); 
            }
            else
                comSocket.close();
        } 
        catch (IOException ex)
        {
            Log.e("TCP Error", ex.getLocalizedMessage());
        }
    }
return true;
}

I typically have no problems with this code on the first connection to the server.

When i disconnect from the server, I call this:

public void closeConnection() {
    if (comSocket != null)
    {
        try {
            comSocket.close();
            isSocketConnected = false;
            if (out != null)
                out.close();
            if (in != null)
                out.close();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
}

So here is the problem... I hit the home button on the smartphone, which places the program in pause. I start the program again and it calls the resume function in activity, which in turn starts the process toward reconnection. The connection is attempted and i get no errors. However, my Windows server records no connection. In Windows, I know that I am still blocked at:

SOCKET connectionSocket = accept(tcpNetworkData->socket, (struct sockaddr*)&from, &fromlen);

I believe this is normal. When I am in debug mode on the Android side, I notice that it returns immediately from the line: comSocket = new Socket("192.168.0.1",1531); This should indicate to me that a connection is made.

If you follow me so far... I should also say that if I shut the server down, the client resets by closing the connection and opening a new one. This time the comSocket = new Socket("192.168.0.1",1531) does not block as it should and the execution keeps going. This is obviously wrong. I think it is a resource release problem but why? With Winsock you can solve this problem with this line of code:

int so_reuseaddr = TRUE;
setsockopt(networkData->socket, SOL_SOCKET, SO_REUSEADDR, (const char*)&so_reuseaddr,sizeof(so_reuseaddr));

Can you do something similar with Android or do you have to? Thank you for your help!

Upvotes: 1

Views: 6452

Answers (2)

crazylpfan
crazylpfan

Reputation: 1088

Something to keep in mind is that the isConnected() method isn't very reliable for detecting when the remote side has closed the connection, (here is an example).

You have to figure this out by reading or writing on the associated Input/Output Streams.

Try using PrintWriter.checkError(), which will return true as soon as the client can no longer connect to the server.

Upvotes: 1

fedepaol
fedepaol

Reputation: 6862

According to the javadoc the connection is established once you call the constructor. 

  Socket(InetAddress address, int port)
      Creates a stream socket and connects it to the specified port number at the specified IP address.

When you press the home button, your app goes in background but it does not get killed immediately, so your comSocket might be not null when you get back to your application. In that case you are not calling the constructor again, thus you are not reconnecting to the server. What you should do is

if(comSocket == null){
        comSocket = new Socket("192.168.0.1",1531);
}else{
     comSocket.connect(new InetSocketAddress("192.168.0.1",1531));
}

(and please please place the curly brackets :-) )

Upvotes: 3

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