I am working on a Java-C# socket communication and I would like to send the coordinates of a C# object to java periodically. The problem is that the java client Stream only reads the coordinates (20 mile long buffer) when I close the connection. I would like the connection to remain open and the coordinates to update without having to open and close this connection all the time.
P.S. This was working but I somehow deleted the previous C# script I was using now I cannot figure it out.
The Java LocationRequester, will connect to the server and then periodically call getline() and pass it to coordinates. The connect part works and getline() only completes if I close the connection, otherwise it hangs. When I close the connection I get a super long row of coordinates.
public Socket clientSocket;
BufferedReader inputBuff;
String hostName;
int hostPort;
public LocationListener(String host, int port) {
hostName = host;
hostPort = port;
}
public void connect()
{
try {
clientSocket = new Socket(hostName, hostPort);
System.out.println("Connected to"+clientSocket.toString());
InputStream input = clientSocket.getInputStream();
InputStreamReader reader = new InputStreamReader(input);
inputBuff = new BufferedReader(reader);
String str;
}
catch(IOException e)
{
e.printStackTrace();
}
}
public String getLine() {
String rstring = "";
try {
rstring = inputBuff.readLine();
System.out.println(rstring);
}
catch(IOException e) {
e.printStackTrace();
}
return rstring;
}
C# code seems to be where the problem is.
private void Start()
{
IPAddress address = IPAddress.Any;
server = new TcpListener(address, 9999);
server.Start();
client = server.AcceptTcpClient();
StartCoroutine(SendCords());
}
private IEnumerator SendCords()
{
while (true)
{
yield return new WaitForSeconds(0.5f);
NetworkStream stream = client.GetStream();
byte[] msg = System.Text.Encoding.ASCII.GetBytes(transform.position.ToString());
stream.Write(msg, 0, msg.Length);
stream.Flush();
// client.Close();
Debug.Log("Sending "+transform.position);
}
}
The java code is reading a line. That means it will block until it gets a line feed character '\n'. And I guess your C# code is not adding a line feed. In my opinion, if you add a line feed character in the end, to your C# message payload, the java code should get the information and come out of the wait. Give a try.
#ferosekhanj has already said very well. I add that the function ofBufferedReader.readLine() will stop reading at'\n' and also at EOF. This is why when your C# program close the Socket, and your java program will receive a super long row of coordinates.
Related
I am trying to send data to one of my servers and receive an ACK back from it. However, the processing gets hung up when waiting for a response from the server. I know for a fact that there is a connection because I can see the data reaching the server. I also know that the server is outputting data correctly because my C# client is receiving data back from the server. I will note that this client is running on a centOS virtual machine. The server is a remote windows machine. I wouldn't imagine that there would be an issue due to the virtual environment because I am able to use an SNMP java client (SNMP4j package) to make calls to a remote server. I believe my server is outputting raw binary too, but I would expect to see some kind of output either way.
// A Java program for a Client
import java.net.*;
import java.io.*;
public class Client
{
// initialize socket and input output streams
private Socket socket = null;
private DataInputStream input = null;
private DataOutputStream out = null;
private DataInputStream serveroutput= null;
// constructor to put ip address and port
public Client(String address, int port)
{
// establish a connection
try
{
socket = new Socket(address, port);
System.out.println("Connected");
// takes input from terminal
input = new DataInputStream(System.in);
// sends output to the socket
out = new DataOutputStream(socket.getOutputStream());
serveroutput = new DataInputStream(socket.getInputStream());
}
catch(UnknownHostException u)
{
System.out.println(u);
}
catch(IOException i)
{
System.out.println(i);
}
// string to read message from input
String line = "";
// keep reading until "Over" is input
while (!line.equals("Over"))
{
try
{
line = input.readLine();
out.writeUTF(line);
System.out.println(serveroutput.readLine())
}
catch(IOException i)
{
System.out.println(i);
}
}
// close the connection
try
{
input.close();
out.close();
socket.close();
}
catch(IOException i)
{
System.out.println(i);
}
}
Could be great if you would share the otherside codes. (sorry cannot comment yet)
Try use something else over writeUTF(), simply maybe a PrintStream, as mentioned by #marquis-of-lorne (read|write)UTF may be confusing by the peer.
Also this might be a good practice to flush() out the output from both side when there is nothing else to send to make sure data is sent completely.
You may also try BufferedReader over InputDataStream as you are trying to read lines. readLine() from InputDataStream is deprecated.
I am currently working on a Java console application. It is run through the command prompt, connects to a server application coded in python and communicates with that server over TCP. My application sends "ISND" string to server which it accepts and in return server sends three images. The format in which Images are sent in is
Where "<"">" are not actually included. "ISND" is encoded into bytes using ascii. Size is the size of the image converted into bytes from int and it is always composed of 3 bytes regardless of the size of the image. For each individual image, a message in this format is sent.
I have been using BufferedReader to read server responses but at this point, I am at a loss on how to actually handle this message. I searched for ways to separate the incoming message into components since I know the length of the first two parts which are always fixed yet I couldn't find a way to actually accomplish that goal.
It has come to the point it feels like I am smashing my head into a wall. As such, I need advice from anyone that is more familiar with Java and Socket programming on how to handle this issue.
My current code
public class ImageLabeler {
/**
* #param args
*/
public static void main(String[] args) {
String IP = args[0];
System.out.println(IP + "\n");
String port = args[1];
System.out.println(port + "\n");
Socket clientSocket;
DataOutputStream outToServer = null;
BufferedReader inFromServer = null;
String serverResponse;
try {
clientSocket = new Socket(IP, Integer.parseInt(port));
outToServer = new DataOutputStream(clientSocket.getOutputStream());
inFromServer = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
System.out.println("Connection success\n");
} catch (IOException ex) {
System.out.println("Connection failed\n");
System.exit(0);
}
PrintWriter writer = new PrintWriter(outToServer, true);
try {
//outToServer.writeBytes("USER bilkentstu\\n");
//outToServer.flush();
//System.out.println("check\n");
writer.println("USER bilkentstu");
serverResponse = inFromServer.readLine();
System.out.println(serverResponse + "\n");
writer.println("PASS cs421f2019");
//outToServer.writeBytes("PASS cs421f2019\\r\\n");
//outToServer.flush();
serverResponse = inFromServer.readLine();
System.out.println(serverResponse + "\n");
writer.println("IGET");
//This is where I need to handle the incoming Image messages.
writer.println("EXIT");
} catch (IOException ex) {
Logger.getLogger(ImageLabeler.class.getName()).log(Level.SEVERE, null, ex);
}
System.exit(0);
}
}
Don't use buffered reader. You need to write the code reading a string from the InputStream of the socket one byte at a time.
I am trying to create a client-server system: my server is a raspberry pi which is running a python webserver on it, and my client is on a different pc and is written is Java. The idea is that the server collects data and when it gets a request from a client, it sends the data to the client.
My client should request the data, wait for 10 seconds and request again etc.
Currently this system is working, but after a day or so, the client starts getting a lot (but not continuously) socket timeouts. I think that this may be the case because for each request I create a new socket for communication and I think that after a day the sockets run out or something like that. This is the code the client executes every 10 seconds:
public static String getData() throws Exception {
TreeSet<Integer> primes = MathUtils.primesSieve(10000);
try {
String data = "";
Socket socket = new Socket(SERVER_ADDRESS, SERVER_PORT);
socket.setReuseAddress(true);
PrintWriter out = new PrintWriter(socket.getOutputStream(), true);
BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
int msg = ColUtils.drawRandomlyWithReplacement(primes, 1, ArrayList::new).get(0);
out.write(msg+"");
out.flush();
String input;
while ((input = in.readLine()) != null) {
data += input;
if (!data.endsWith("#" + prod(msg))) {
throw new Exception("WRONG ECHO");
}
}
socket.close();
return data;
} catch (Exception e) {
e.printStackTrace();
}
return null;
}
I tried fixing it by having a socket which is a member of the encapsulating class, but after a singe request the inputstream stopped working. Is there any way where I can keep using a single socket for ALL communications with the server? Or is this the recommended way of doing this sort of communication?
Try first closing the socket and input, output streams. As in your code there is no quarantee that you are releasing the acquired objects.
PrintWriter out = null;
BufferedReader in = null;
Socket socket = null;
try {
...//your statements
} catch (Exception ex) {
//catch or whatever
} finally {
if (out != null) out.close();
if (in != null) in.close();
if (socket != null) socket.close();
}
try to make the Socket object static If possible that would created only once and read the data every 10 sec
Otherwise u can instantiate it before calling the getData method and then read it.
Doing so will make only 1 copy of Socket.
And I don't think u are running out of ports.
The reason might be quit simple that your Program is not receiving the data before the time out. and it is a normal case in a bad network
Socket generally waits indefinitely until it receives data if the timeout is not set Programmatically
I'm trying to learn sockets using Java and I sucessfully sent data to a ServerSocket running in my own machine. When I try to read from this socket using readline (so I can just echo my own sent message) my program hangs and won't return.
Here's the code:
public static void main(String[] args) throws UnknownHostException, IOException {
TCPClient cli = new TCPClient("127.0.0.1", "15000");
try {
cli.ostream.writeUTF("Teste");
String echo = cli.istream.readLine(); //it hangs in this line
System.out.println(echo);
}
TCPClient is a class I defined so I can test my program on a simpler interface before using swing on my homwework. here's the code:
public class TCPClient {
public DataOutputStream ostream = null;
public BufferedReader istream = null;
public TCPClient(String host, String port) throws UnknownHostException {
InetAddress ip = InetAddress.getByName(host);
try {
Socket socket = new Socket(host, Integer.parseInt(port));
ostream = new DataOutputStream(socket.getOutputStream());
istream = new BufferedReader(new InputStreamReader(socket.getInputStream()));
} catch (IOException ex) {
Logger.getLogger(TCPClient.class.getName()).log(Level.SEVERE, null, ex);
}
}
My server is pretty simple. After the connection is estabilished, it enters in this loop and stays here until I close the client (because of the infinite loop). Afterwards, some exception handling returns it to the point before the connection started.
while(true){
String msg = istream.readLine();
System.out.println("Arrived on server: " + msg); //just works on debug
ostream.writeUTF("ACK: " + msg);
ostream.flush();
}
I don't see what am I missing.
PS: the wierd stuff is that if I debug the server, I can see the message arriving there (I can print it, for example), but this isn't possible if I just run this code. Does this have some concurrency relation I'm overlooking?
thx
The problem is that readLine tries reading a line. It will not return the line until it's sure that the end of line has been reached. This means that it expects either a newline character, or the end of the communication. Since the server doesn't send any newline char and doesn't close the stream, the client waits indefinitely.
cli.ostream.writeUTF("Teste");
Shouldn't this be containing a new line? Otherwise read method will be waiting for new line I think.
Also as suggested you can try flushing the ostream after writing to it.
writeUTF() doesn't write a line. See the Javadoc. writeUTF() is for use with readUTF(). And Readers are for use with Writers. So change the DataOutputStream to a BufferedWriter and call write() and then newline().
Okay this is a revised question from earlier today, I have included code to help explain the problem. I am sending two messages from the client to the server. The server then picks the messages up and processes them. The server finally attempts to send a message back to the client(please note in the server code "testmessage"), it is here I am having problems. Either I am not recieving the message at the client side or sending it incorrectly from the server side.
public class ClientConnection {
String address, language, message;
int portNumber;
Socket clientSocket = null;
public ClientConnection(String lan, String mes, String add, int pn) throws IOException{
address = add;
portNumber = pn;
language = lan;
message = mes;
}
public String createAndSend() throws IOException{
// Create and connect the socket
Socket clientSocket = null;
clientSocket = new Socket(address, portNumber);
PrintWriter pw = new PrintWriter(clientSocket.getOutputStream(),true);
BufferedReader br = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
// Send first message - Message is being correctly received
pw.write(language+"\n");
pw.flush();
// Send off the data
// Send the second message - Message is being correctly received
pw.write(message);
pw.flush();
pw.close();
// Send off the data
// NOTE: Either I am not receiving the message correctly or I am not sending it from the server properly.
String translatedMessage = br.readLine();
br.close();
//Log.d("application_name",translatedMessage); Trying to check the contents begin returned from the server.
return translatedMessage;
}
Server Code:
public class ServerConnection {
public static void main(String[] args) throws Exception {
// Delete - Using while loop to keep connection open permanently.
boolean status = false;
while( !status){
ServerSocket serverSocket = null;
try {
serverSocket = new ServerSocket(4444);
} catch (IOException e) {
System.err.println("Could not listen on port: 4444.");
System.exit(1);
}
Socket clientSocket = null;
try {
clientSocket = serverSocket.accept();
} catch (IOException e) {
System.err.println("Accept failed.");
System.exit(1);
}
// Delete - Working as of here, connection is established and program runs awaiting connection on 4444
BufferedReader br = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
String language = br.readLine();
String message = br.readLine();
// Test - Works
System.out.println(language);
// Test - Works
System.out.println(message);
// Delete - Working as of here, both messages are passed and applied. Messages are received as sent from client.
TranslateMessage tm = new TranslateMessage();
String translatedMessage = tm.translateMessage(language, message);
// NOTE: This seems to be where I am going wrong, either I am not sending the message correctly or I am not receiving it correctly..
// PrintWriter writer = new PrintWriter(new BufferedOutputStream(clientSocket.getOutputStream()));
PrintWriter pw = new PrintWriter(clientSocket.getOutputStream(),true);
// Send translation back
System.out.println(translatedMessage);
// pw.write(translatedMessage+"\n");
pw.write("Return test"); // Test message!
pw.flush();
// Send off the data
pw.close();
br.close();
clientSocket.close();
serverSocket.close();
}
}
}
The code is a bit of a mess and I can see a few duplicates, I have commented where I feel the problems occour.
Thanks for any help!
You are using BufferedReader.readLine() to read the response from the server, but in the test case you are sending a string that is not terminated with a \n or \r\n, so it will not get the line as far as I can tell from the docs...
public String readLine()
throws IOException
Read a line of text. A line is considered to be terminated by any one of a line feed ('\n'), a carriage return ('\r'), or a carriage return followed immediately by a linefeed.
Returns:
A String containing the contents of the line, not including any line-termination characters, or null if the end of the stream has been reached
An additional suggestion...
When writing request response protocols like this I would not rely on line endings to terminate the requests or responses. Typically I would use either a fully formatted JSON string, or my preference is for a binary protocol where all requests and response are prepended with a binary count (usually 4 bytes bigendian/network byte order). Then the client and server reads the 4 bytes then reads the number of bytes that follow. This handles the packet fragmentation that typically happens over network connections, also it helps avoid DOS attacks by malicious users sending long strings that never terminate.
In Java you can use ByteBuffer.order() to handle bigendian numbers.