I did a script to exchange data between a client and a server with socket on specific port.
In order, I am expecting:
Server is listening
Client opens a socket
Server akwnoledges by sending a int -> never received !
I just noticed that my client receives the int, when I quit the server brutally
Here is my (simple) code.
Client:
Socket socket = new Socket(SERVER_ADDR, PORT);
DataOutputStream dOut = new DataOutputStream(socket.getOutputStream());
DataInputStream dIn = new DataInputStream(socket.getInputStream());
Log.v("[DEBUG]", "waiting aknowledgement");
status = dIn.readInt(); //<-- BLOCKS HERE
Log.v("[DEBUG]", "ack"); //<-- RECEIVED WHEN SERVER IS EXITED
Server:
try {
DataInputStream stdIn = new DataInputStream(client.getInputStream());
DataOutputStream stdOut = new DataOutputStream(client.getOutputStream());
while (incoming) {
stdOut.writeInt(1);
stdOut.flush();
System.out.println("Waiting...");
var_from_client = stdIn.readInt(); //<-- BLOCKS HERE (BECAUSE CLIENT IS BLOCKED)
// ...
}
} catch (Exception e) {}
How to explain this error?
'Socket not flushing data' has exactly nothing to do with it. This is a deadlock, caused by a bug in your application.
Your server sends an int.
Your client receives the int.
Your server blocks trying to read another int.
Your client doesn't send an int.
The server can never send another int because it is blocked waiting for the non-existent reply int.
Your client blocks while trying to receive another int because the server is blocked from sending it.
Solution: send the int from the client.
Notes:
Flushing the output stream of a socket does nothing, and neither does flushing a DataOutputStream wrapped directly around it.
NEVER ignore exceptions.
Related
I have built a client-server application in Android(Compiling with java-6) to send and receive udp packets.
My client code is as follow:
DatagramSocket socket =new DatagramSocket();
socket.setBroadcast(true);
DatagramPacket packet = new DatagramPacket(dgram, dgramLength, host, port);
socket.send( packet );
socket.close();
My server code is as follows:
DatagramSocket socket =new DatagramSocket(this.port);
byte[] data=new byte[512];
DatagramPacket packet = new DatagramPacket(data, data.length) ;
// Wait for a response from the server
try
{
socket.receive(packet) ;
}
catch (Exception e)
{}
The issue that I am facing is that when I am working on a wired network then all the sent packets are being received by master properly but when I am running the same code over wifi then sometimes sent packets are being received and sometimes not. I want to know that whether it is the general behavior of a wifi network or not.
Any kind of help is appreciated.
I'm trying to send some commands to Android (client) from VB.NET (server) using sockets. I can connect the client to the server, but I don't know how to receive the commands sent by the server.
Here's a part of my Android code:
public void connect(View v){ //called on button click
SERVER_IP = ip.getText().toString(); //it gets the server's ip from an editText
SERVER_PORT = Integer.parseInt(port.getText().toString()); //and the port too
Toast.makeText(this, "Trying to connect to\n" + SERVER_IP + ":" + SERVER_PORT + "...", Toast.LENGTH_SHORT).show();
new Thread(new Runnable() {
public void run() {
InetAddress serverAddr;
try {
serverAddr = InetAddress.getByName(SERVER_IP);
socket = new Socket(serverAddr, SERVER_PORT); //It establishes the connection with the server
if(socket != null && socket.isConnected()){ //not sure if it is correct
BufferedReader input = new BufferedReader(new InputStreamReader(socket.getInputStream()));
//Here comes the problem, I don't know what to add...
}
} catch (Exception e) {
}
}
}).start();
}
And here's a part of my VB.NET send code:
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
send(TextBox1.text)
End Sub
Private Sub Send(ByVal command)
Dim temp() As Byte = UTF8.GetBytes(command) 'Is UTF8 right to use for that?
stream.Write(temp, 0, temp.Length)
stream.Flush()
End Sub
Question1: is it right to us UTF8 instead of for example ASCII encoding?
Question2: what would I change in the Android code if it wanted to use a timer that sends a command every second?
Thanks.
To read input from a BufferedReader you need to do something similiar to this:
BufferedReader input = new BufferedReader(new InputStreamReader(socket.getInputStream()));
String line;
while((line = input.readLine()) != null){
// do something with the input here
}
A nice tutorial on sockets is available from oracle in the docs: http://docs.oracle.com/javase/tutorial/networking/sockets/readingWriting.html
The default charset on Android is UTF-8 http://developer.android.com/reference/java/nio/charset/Charset.html, so no worries there but you can always send a byte stream from the server onto the client and decode it however you want.
To receive a byte stream you need to do this:
BufferedInputStream input = new BufferedInputStream(socket.getInputStream());
byte[] buffer = new byte[byteCount];
while(input.read(buffer, 0, byteCount) != -1 ){
// do something with the bytes
// for example decode it to string
String decoded = new String(buffer, Charset.forName("UTF-8"));
// keep in mind this string might not be a complete command it's just a decoded byteCount number of bytes
}
As you see it's much easier if you send strings instead of bytes.
If you want to receive input from the server periodically, one of the solutions would be to create a loop which opens a socket, receives input, process it, closes the socket, and then repeats, our you could just keep the loop running endlessly until some command like "STOP" is received.
I have a http server code (I tried both TJWS or NanoHTTPD), the client from the same application would connect to server running on port 8080 or whatever.
I am starting server object in a separate AsyncTask so it should be okay.
While NanoHTTPD completely failed to start other ways I can see from TJWS logs, it says something like;
server listening on 0.0.0.0/0.0.0.0 port:0 localport:8080
This means server started successfully, first question is 0.0.0.0 bind address acceptable? I mean it should be 127.0.0.1 instead? sorry if that is a noob question.
When I connect to my emulator using adb shell and run netstat, I can see the following lines
Proto Recv-Q Send-Q Local Address Foreign Address State
tcp 0 0 127.0.0.1:5037 0.0.0.0:* LISTEN
tcp 0 0 0.0.0.0:5555 0.0.0.0:* LISTEN
tcp 0 0 10.0.2.15:5555 10.0.2.2:52132 ESTABLISHED
tcp6 0 0 :::8080 :::* LISTEN
By googling I learned that 0 :::8080 means server is listening on ipv6 and ipv4 both and that is okay.
But from my client code when i tried to access it continues to wait for eternity.
my httpClient Code
try {
URL url = new URL("http://0.0.0.0:"+8080+"/media");
URLConnection conn = url.openConnection();
InputStream is = conn.getInputStream();
BufferedReader br = new BufferedReader(new InputStreamReader(is));
String line;
while((line = br.readLine()) != null){
Log.d("server", line);
}
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
For the server, the address 0.0.0.0 is like a wildcard and means, it is listening on all IP addresses the device has.
For the client, you need to use a real IP address like 127.0.0.1
After debugging a little I found that problem is not where client opens a connection but issue was at where server was starting it never returned onPostExecute() method, but after wrapping my server start code inside a Runnable
new Thread(new Runnable() {
#Override
public void run() {
Log.d("server", "server starting on port: " + port);
srv.serve();
}
}).start();
it Works!!
Server is a infinite loop so does it have to be started from inside thread? I thought AsyncTask can handle that?
Its also worth mentioning that client side connection must also be wrapped inside AsyncTask
I've got Android device acting as a client, the PC is a Bluetooth Server, using Bluecove library
Code snippet from the client:
btSocket = serverBt.createRfcommSocketToServiceRecord(myUuid);
btAdapter.cancelDiscovery();
btSocket.connect();
InputStream in = btSocket.getInputStream();
OutputStream out = btSocket.getOutputStream();
OutputStreamWriter osw = new OutputStreamWriter(out);
InputStreamReader isr = new InputStreamReader(in);
osw.write(55);
osw.flush();
out.flush();
//osw.close();
logTheEvent("Stuff got written, now waiting for the response.");
int dummy = isr.read();
logTheEvent("Servers response: "+ new Integer(dummy).toString());
And the server:
StreamConnectionNotifier streamConnNotifier = (StreamConnectionNotifier)Connector.open( connectionString, Connector.READ_WRITE );
StreamConnection incomingConnection=streamConnNotifier.acceptAndOpen();
InputStream in = incomingConnection.openInputStream();
OutputStream out = incomingConnection.openOutputStream();
OutputStreamWriter osw = new OutputStreamWriter(out);
InputStreamReader isr = new InputStreamReader(in);
int fromClient = isr.read();
System.out.println("Got from client " + new Integer(fromClient).toString());
osw.write(999);
When the osw.close(); at the client is uncommented, the message gets transferred to the server, however, client is then unable to receive the response, IOException with message "socket already closed" is thrown.
However, when osw.close(); is commented, both client and server freeze:
A. Client hangs on reading server's response of course
B. Server hangs on streamConnNotifier.acceptAndOpen();
What should be done to enable two-way communication?
Is my code, or PC Bluetoototh stack, or bluecove to blame?
Bluetooth uses buffered output. That means there is a small memory location that contains all of the data you write to the stream. When this memory location gets full, it writes the buffer data to the socket in a packet. When you prematurely close the socket, that buffer gets wiped, and the data is gone.
In order to force the stream to write, try calling flush()
Something else you could do is set the buffer size to be very small, so data always gets written. The performance won't be very good if you do this, though.
Unfortunately, I don't have all of the code I wrote, but there's a base project here
I'm receiving an image through a socket in an android aplication, I did debugging and when I'm going to save the image in Drawable d, the program waits for something happens.
I think it has to have relation with clientSocket.getInputStream(); or with the socket.
I have a multithreading server in C++ and when I stop the server, the android aplication continues and I can see the image I sent before. But, I think it's not a server problem, because the socket in the server send the data and shows the message printf("Bytes enviados %d\n", bytesEnviados); which is at the end of the server code.
Here you have the code:
public Drawable mandaMensajeVideo(String mensaje, String ip, int puerto ) throws IOException{
Socket clientSocket = new Socket(ip, puerto);
DataOutputStream outToServer = new DataOutputStream(clientSocket.getOutputStream());
outToServer.writeBytes(mensaje);
outToServer.flush();
InputStream inputStream = clientSocket.getInputStream();
Drawable d = Drawable.createFromStream(inputStream, null);
clientSocket.close();
outToServer.close();
return d;
}
Thanks!
Sounds like the end of the inputStream is never reached, as you never properly close the communication.