I'm currently runing a server on Eclipse(local IP 192.168.1.255, listening to port 4567). A client can connect trought sockets and send messages, that will be printed on the terminal by the server.
Part of the server code is the following:
System.out.println("Client connected: " + clientName);
String line;
while (true){
line = in.nextLine();
System.out.println("STRING RECEIVED: " + line + " FROM " + clientName);
}
where in is the input stream of the client socket.
Part of client code, instead, is:
while(true) {
System.out.print("\nEnter your input: ");
line = stdin.next();
socketOut.println(line);
socketOut.flush();
}
So, in example, a possible output on server terminal with two clients connected is the following:
Client connected: Socket[addr=/192.168.1.225,port=54852,localport=4567]
STRING RECEIVED: Hello FROM Socket[addr=/192.168.1.225,port=54852,localport=4567]
STRING RECEIVED: World FROM Socket[addr=/192.168.1.225,port=54852,localport=4567]
Client connected: Socket[addr=/192.168.1.225,port=54945,localport=4567]
STRING RECEIVED: Hello2 FROM Socket[addr=/192.168.1.225,port=54945,localport=4567]
Everything works well, so i'm now trying to access server trough sockets on a simple app developed on Android Studio. The code is:
public class MainActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
new BackgroundTask().execute();
}
private class BackgroundTask extends AsyncTask {
#Override
protected Object doInBackground(Object[] params) {
try {
Socket socket = new Socket("10.0.2.2", 4567);
PrintWriter out = new PrintWriter(socket.getOutputStream());
out.println(new String("Hi from Android!"));
} catch (UnknownHostException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
return null;
}
}
}
But the output is just
Client connected: Socket[addr=/192.168.1.225,port=55001,localport=4567]
and nothing else.
Any advice about the println doesn't send anything? The program works perfectly on Eclipse on both client/server side, so i guess the problem is on Android. Also, i enabled the Android network permissions, so the connection should work.
Thanks in advance to everybody.
EDIT: solved, i just changed Android client code to:
try {
Socket socket = new Socket("10.0.2.2", 4567);
if (socket.isConnected()) {
PrintWriter out = new PrintWriter(new BufferedWriter(
new OutputStreamWriter(socket.getOutputStream())), true);
String line = new String("Hi from Android!");
out.println(line);
}
} catch (UnknownHostException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
You need to either flush the PrintWriter or construct it to auto-flush. It doesn't by default.
Related
I have a client on a PC and a server on a tablet. I know the MAC addresses for both which means I do not do discoveries.
1. On the client if I use
connectString = "btspp://" + MACaddress + ":4;authenticate=false;encrypt=false;master=false";
It connects fine.
If I change the CN number (4) to anything else, it does not work. How is this number determined?
2. Everything works fine if the tablet is a Samsung with Android 5.0.2 When I use a Qunyico tablet with Android 10, it does not work. I get an error: Failed to connect; [10051] A socket operation was attempted to an unreachable network. What is the problem?
Client on PC – code taken from “Bluetooth-java-client-master”
public class IrcBluetoothClient {
private static void openConnection(String MACaddress) throws IOException {
// Tries to open the connection.
String connectString = "btspp://" + MACaddress + ":4;authenticate=false;encrypt=false;master=false";
StreamConnection connection = (StreamConnection) Connector.open(connectString);
if (connection == null) {
System.err.println("Could not open connection to address: " + MACaddress);
System.exit(1);
}
// Initializes the streams.
OutputStream output = connection.openOutputStream();
InputStreamReader isr = new InputStreamReader(System.in);
BufferedReader reader = new BufferedReader(isr);
// Starts the listening service for incoming messages.
ExecutorService service = Executors.newSingleThreadExecutor();
service.submit(new IncomingMessagesLoggingRunnable(connection));
// Main loop of the program which is not complete yet
LocalDevice localDevice = LocalDevice.getLocalDevice();
while (true) {
String toSend = reader.readLine();
byte[] toSendBytes = toSend.getBytes(StandardCharsets.US_ASCII);
output.write(toSendBytes);
System.out.println("[" + localDevice.getFriendlyName() + " - " +
localDevice.getBluetoothAddress() + "]: " + toSend);
System.exit(1);
}
Server on tablet – code taken from https://developer.android.com/guide/topics/connectivity/bluetooth
private static final UUID A_UUID = UUID.fromString("00001101-0000-1000-8000-00805F9B34FB");
public BTacceptConnections( BluetoothAdapter mBluetoothAdapter) {
// Use a temporary object that is later assigned to mmServerSocket
// because mmServerSocket is final.
BluetoothServerSocket tmp = null;
try {
// A_UUID is the app's UUID string, also used by the client code.
tmp = mBluetoothAdapter.listenUsingRfcommWithServiceRecord(NAME, A_UUID);
} catch (IOException e) {
Log.e(TAG, "Socket's listen() method failed", e);
}
mmServerSocket = tmp;
// Closes the connect socket and causes the thread to finish.
public void cancel(){
try {
mmServerSocket.close();
}catch (IOException e){
}
runFlag = 1;
}
//***********************************************************************************************
//
// This thread runs all the time listening for incoming connections.
//
public void run() {
BluetoothSocket socket = null;
// Keep listening until exception occurs or a socket is returned.
while (runFlag == 0) {
try {
socket = mmServerSocket.accept();
} catch (IOException e) {
Log.e(TAG, "Socket's accept() method failed", e);
break;
}
if (socket != null) { // If a connection was accepted
// A connection was accepted. Perform work associated with
// the connection in a separate thread.
// manageMyConnectedSocket(socket);
}else{
try {
mmServerSocket.close();
} catch (IOException e) {
e.printStackTrace();
}
break;
}
}
I know the MAC addresses for both which means I do not do discoveries.
Official Linux Bluetooth protocol stack BlueZ uses D-BUS API to establish bluetooth communication. If you check adapter-api, scanning will create device objects that you need to establish a communication which means discovering is not only done to retrieve MAC addresses only.
Your case might be the same, I would suggest doing discovery first.
I have the following code to receive UDP packets:
public class AsyncReceiveUdp2 extends AsyncTask<String, Void, Boolean> {
#Override
protected Boolean doInBackground(String... f_url) {
int udp=111;
byte[] packet = new byte[2000];
DatagramPacket dp = new DatagramPacket(packet, packet.length);
DatagramSocket ds = null;
try {
ds = new DatagramSocket(udp);
ds.receive(dp);
//...
} catch (SocketException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
if (ds != null) {
ds.close();
}
}
return null;
}
}
I send UDP data to computer from Android device.
Computer immediately sends response as UDP packet.
I save information to my log file on SD.
And I see, that my app stays on the line "ds.receive(dp);" and does not run after it.
I've tested on the Android device against a program on computer.
As I understand it is tricky to receive UDP packets on Emulator.
I could not do it.
Redirect does not work for me as it is described here
Another important issue is to receive all packets, that were sent to the device. Lossless. How to modify the code for that?
Please help! Thanks!
put your receive inside a while(true) loop. When you receive a packet call an if (pkg_received){break;}... or whatever you want to do...
The problem is that you are probably only be receiving one package and you are getting timeout before receiving it.
Code edited and not tested
while(true)
{
byte[] message = new byte[60*1024];
DatagramPacket recv_packet = new DatagramPacket(message, message.length);
try {
socket.receive(recv_packet);
} catch (IOException e) {
e.printStackTrace();
}
Log.d("UDP", "S: Receiving...listening on port " + recv_packet.getPort() );
String rec_str;
rec_str=new String(recv_packet.getData)
Log.d("PACKAGE LENGTH",Integer.toString(recv_packet.getLength()));
}
I have an UDP server wrote in C langage which broadcasts paquets over my LAN every 5seconds, on port 3001.
i'm creating an android application as UDP client, which is listening on port 3001 (in the AsyncTask thread) and it's running until the receive() method, no data seems to be detected on this port.
Here is my code :
private class ConnectionTask extends AsyncTask<Void, Integer, Void> {
#Override
protected void onPreExecute() {
super.onPreExecute();
}
#Override
protected Void doInBackground(Void... arg0) {
String receivedString = "";
byte[] receiveData = new byte[1024];
DatagramSocket clientSocket;
try {
while(true){
clientSocket = new DatagramSocket(5000);
DatagramPacket receivePacket = new DatagramPacket(receiveData,
receiveData.length);
clientSocket.receive(receivePacket);
receivedString = new String(receivePacket.getData());
}
} catch (SocketException e) {
Log.v("SocketExceptionOccured", e.toString());
e.printStackTrace();
//clientSocket.close();
} catch (IOException e) {
Log.v("IOExceptionOccured", e.toString());
e.printStackTrace();
//clientSocket.close();
}
Toast.makeText(getBaseContext(), receivedString, Toast.LENGTH_LONG)
.show();
return null;
}
}
I test my code with my own device for debug, with USB cable.
I've tested my server with a simple UDP client (in C) running on my computer, and the communication is ok.
I don't know why this code doesn't work. Has someone an idea ?
Thanks,
You're never leaving the while loop. You're message is probably received, and after it, the loop causes the datagramsocket to listen again.
Don't create and close the socket every time around the loop. Create it first and close it afterwards. At present there are windows of time during which the socket doesn't exist, so datagrams to it are dropped: also, all queued datagrams are dropped every time you close it.
I had this same problem. You need to add permissions in the android manifest
<uses-permission android:name="android.permission.CHANGE_WIFI_MULTICAST_STATE"/>
<uses-permission android:name="android.permission.CHANGE_WIFI_STATE"/>
Also enable broadcasts in the socket.
clientSocket.setBroadcast(true);
Like everyone else before me mentioned, your code also never leaves the while loop, so it never goes to the the line where the toast is displayed.Remember that you CANNOT show Toast messages from doInBackground as this is accessing the UI Thread, you can only do so from the postExecute and preExecute functions. This will cause your application to crash. To check the data you receive you can either debug it or log it.
Your final doInBackground should be something like this
#Override
protected Void doInBackground(Void... arg0) {
String receivedString = "";
byte[] receiveData = new byte[1024];
DatagramSocket clientSocket;
try {
while(true){
clientSocket = new DatagramSocket(5000);
DatagramPacket receivePacket = new DatagramPacket(receiveData,
receiveData.length);
clientSocket.setBroadcast(true);
clientSocket.receive(receivePacket);
receivedString = new String(receivePacket.getData());
Log.i("Received String= "+receivedString);
}
} catch (SocketException e) {
Log.v("SocketExceptionOccured", e.toString());
e.printStackTrace();
//clientSocket.close();
} catch (IOException e) {
Log.v("IOExceptionOccured", e.toString());
e.printStackTrace();
//clientSocket.close();
} finally{
if(clientSocket!=null){
clientSocket.close();
}
}
return null;
}
Now when you check your logs, you should be able to see the value of the string received.
I've been trying to implement a simple socket communication between two Android emulators but just can't seem to get it.
My server:
public void run() {
if (SERVERIP != null) {
try {
serverStatus.setText("My IP: " + SERVERIP);
serverSocket = new ServerSocket(6798);
serverStatus.setText("ServerSocket Created");
}
catch(Exception e) {
e.printStackTrace();
}
try {
while (true) {
serverStatus.setText("waiting for client");
Socket client = serverSocket.accept();
serverStatus.setText("Connected.");
BufferedReader in = new BufferedReader(new InputStreamReader(client.getInputStream()));
String line = in.readLine();
serverStatus.setText(line);
in.close();
client.close();
}
}
catch(Exception e) {
e.printStackTrace();
}
}
else
serverStatus.setText("Couldn't detect internet connection.");
}
My Client:
try {
InetAddress ina = InetAddress.getByName("10.0.2.2");
socket = new Socket(ina, 6789);
}
catch (Exception e) {
e.printStackTrace();
}
try {
PrintWriter out = new PrintWriter(new BufferedWriter(new OutputStreamWriter(socket.getOutputStream())), true);
out.println("Hey Server!");
dispText.setText("sent");
}
catch (Exception e) {
e.printStackTrace();
}
The Client side goes on to display the message "sent" however the Server does not move beyond "waiting for client" (stuck on the blocking accept()).
I've used telnet on my Windows machine to redirect port 6789 to 6798 on the server emulator's console. I've also tried turning off my firewall and the other suggestions posted on the similar questions asked here. Please help as just can't seem to get it and feel like I'm making a very stupid mistake.
Also, can anyone please tell me how it is possible for the Client to move beyond the Socket creation code line if the Server is still stuck on accept(). Or, does it not matter to the client that the Server isn't responding as long as it is listening on the port??
Android emulators are placed behind a virtual firewall/router by design, and cannot see each other, even when they are on the same network. The "Using Network Redirection", as well as "Interconnecting Emulator Instances" part of Google's doc on the emulator explains how to communicate with an emulator instance.
As for your last question. Use the empty constructor for socket, and then use the connect call with a specified timeout.
This is a continuation of this question because it my orginal question was answered, but it did not solve the bug.
Question:
How do I fix the code hanging on this line inStream.readline()
My Intent:
This is in a thread that will loop through checking if there is an outMessage, if there is, it will send the message.
Next it will check it if there is anything in the in-stream, if there is, it will send it to the handler in my main activity.
Lastly, it will sleep for 1 second, then check again.
This should allow me to read/write multiple times without needing to close and open the socket.
Problem:
It is reading and writing better, but still not working properly
What is happening now:
If outMessage is initialized with a value, upon connection with the server, the socket:
writes and flushes the value (server receives & responds)
updates value of outMessage (to null or to "x" depending on how i have it hard-coded)
reads and shows the response message from the server
re-enters for the next loop
IF i set outMessage to null, it skips over that if statements correctly then hangs; otherwise, if i set outMessage to a string (lets say "x"), it goes through the whole if statement, then hangs.
The code it hangs on is either of the inStream.readline() calls (I currently have one commented out).
Additional info:
- once connected, I can type in the "send" box, submit (updates the outMessage value), then disconnect. Upon re-connecting, it will read the value and do the sequence again until it get stuck on that same line.
Changes since the referenced question:
- Made outMessage and connectionStatus both 'volatile'
- added end-of-line delimiters in neccesary places.
Code:
public void run() {
while (connectionStatus != TCP_SOCKET_STATUS_CONNECTED) {
try {
Thread.sleep(500);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
while (connectionStatus == TCP_SOCKET_STATUS_CONNECTED) {
try {
if (outMessage != null){
OutStream.writeBytes(outMessage + "\n");
OutStream.flush();
sendMessageToAllUI(0, MAINACTIVITY_SET_TEXT_STATE, "appendText" , "OUT TO SERVER: " + outMessage);
outMessage = "x";
}
Thread.sleep(100);
// if (InStream.readLine().length() > 0) {
String modifiedSentence = InStream.readLine();
sendMessageToAllUI(0, MAINACTIVITY_SET_TEXT_STATE, "appendText" , "IN FROM SERVER: " + modifiedSentence);
// }
Thread.sleep(1000);
} catch (IOException e) {
connectionLost();
break;
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
The thread that makes the socket:
public void run() {
setName("AttemptConnectionThread");
connectionStatus = TCP_SOCKET_STATUS_CONNECTING;
try {
SocketAddress sockaddr = new InetSocketAddress(serverIP, port);
tempSocketClient = new Socket(); // Create an unbound socket
// This method will block no more than timeoutMs. If the timeout occurs, SocketTimeoutException is thrown.
tempSocketClient.connect(sockaddr, timeoutMs);
OutStream = new DataOutputStream(tempSocketClient.getOutputStream());
InStream = new BufferedReader(new InputStreamReader(tempSocketClient.getInputStream()));
socketClient = tempSocketClient;
socketClient.setTcpNoDelay(true);
connected();
} catch (UnknownHostException e) {
connectionFailed();
} catch (SocketTimeoutException e) {
connectionFailed();
} catch (IOException e) {
// Close the socket
try {
tempSocketClient.close();
} catch (IOException e2) {
}
connectionFailed();
return;
}
}
Server:
public static void main(String[] args) throws IOException {
String clientSentence;
String capitalizedSentence;
try {
ServerSocket welcomeSocket = new ServerSocket(8888);
SERVERIP = getLocalIpAddress();
System.out.println("Connected and waiting for client input!\n Listening on IP: " + SERVERIP +"\n\n");
Socket connectionSocket = welcomeSocket.accept();
BufferedReader inFromClient = new BufferedReader(new InputStreamReader(connectionSocket.getInputStream()));
DataOutputStream outToClient = new DataOutputStream(connectionSocket.getOutputStream());
while(true)
{
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
clientSentence = inFromClient.readLine();
System.out.println("clientSentance == " + clientSentence);
String ip = connectionSocket.getInetAddress().toString().substring(1);
if(clientSentence != null)
{
System.out.println("In from client ("+ip+")("+ System.currentTimeMillis() +"): "+clientSentence);
capitalizedSentence = clientSentence.toUpperCase() + '\n';
outToClient.writeBytes(capitalizedSentence + '\n');
System.out.println("Out to client ("+ip+"): "+capitalizedSentence);
}
}
} catch (IOException e) {
//if server is already running, it will not open new port but instead re-print the open ports information
SERVERIP = getLocalIpAddress();
System.out.println("Connected and waiting for client input!\n");
System.out.println("Listening on IP: " + SERVERIP +"\n\n");
}
}
Thanks in advance!
Edits:
added the server code after updating
I tried messing around with setting the SoTimout for the socket but took that back out
Your server is specifically designed to receive exactly one line from a client and send exactly one line back. Look at the code:
while (true) {
Socket connectionSocket = welcomeSocket.accept();
BufferedReader inFromClient = new BufferedReader(
new InputStreamReader(connectionSocket.getInputStream()));
DataOutputStream outToClient = new DataOutputStream(
connectionSocket.getOutputStream());
clientSentence = inFromClient.readLine();
String ip = connectionSocket.getInetAddress().toString()
.substring(1);
System.out.println("In from client (" + ip + "): "
+ clientSentence);
if (clientSentence != null) {
capitalizedSentence = clientSentence.toUpperCase() + '\n';
System.out.println("Out to client (" + ip + "): "
+ capitalizedSentence);
outToClient.writeBytes(capitalizedSentence + "\n");
}
Notice that inside the loop it accepts a new connection, reads exactly one line, and then writes exactly one line. It doesn't close the connection. It doesn't sanely end the conversation. It just stops reading.
A client that worked with this server would have to connect, send exactly one line, read exactly one line back, and then the client would have to close the connection. Your client doesn't do that. Why? Because you had no idea that's what you had to do. Why? Because you had no design ... no plan.
So that's your specific issue. But please, let me urge you to take a huge step back and totally change your approach. Before you write a single line of code, please actually design and specify a protocol at the byte level. The protocol should say what data is sent, how messages are delimited, who sends when, who closes the connection, and so on.
Otherwise, it's impossible to debug your code. Looking at the server code above, is it correct? Well, who knows. Because it's unclear what it's supposed to do. When you wrote the client, you assumed the server behaved one way. Was that assumption valid? Is the server broken? Who knows, because there's no specification of what the server is supposed to do.
You need to check if there is data available:
if (InStream.available > 0) {
String modifiedSentence = InStream.readLine();
sendMessageToAllUI(0, MAINACTIVITY_SET_TEXT_STATE, "appendText" , "IN FROM SERVER: " + modifiedSentence);
}
But to be honest, even that is not ideal because you have no gurantee that the eond-of-line will have been received. If the server sends a few bytes but never sends the end-of-line then you will still be blocking forever. Production socket code should never rely on readLine but instead read into a buffer and check that buffer for end-of-line (or whatever criteria your protocol needs).
Didn't read closely enough, I thought InStream was an InputStream instance. InputStream has available. InputStreamReader has ready (which in turn calls InputStream.available. As long as you keep a refernce to either of these then you can see if data is available to be read.