Develop Reference

Can't write an input to stdin in a Java program via command line, although I can do it on eclipse

I wrote a Server-Client model program in java, and it works great on eclipse. However, when I try to run the client via command line (in Windows 10), I can't write anything to stdin (while I can do it on Eclipse). Why is that?
Here is the client code (not the best one, I know):
import java.io.*;
import java.net.*;
public class MyEchoClient {
public static void main(String[] args) throws IOException{
Socket clientSocket = null; // the connection socket
PrintWriter out = null;
BufferedReader in = null;
String host = args[0], msg, tmp;
int port = Integer.decode(args[1]).intValue(), len;
System.out.println("Connecting to " + host + ":" + port);
try { // Trying to connect to a socket and initialize an output stream
clientSocket = new Socket(host, port); // host and port
out = new PrintWriter(new OutputStreamWriter(clientSocket.getOutputStream(), "UTF-8"), true);
} catch (UnknownHostException e) {
System.out.println("Unknown host: " + host);
System.exit(1);
} catch (IOException e) {
System.out.println("Couldn't get output to " + host + " connection");
System.exit(1);
}
try { // Initialize an input stream
in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream(),"UTF-8"));
} catch (IOException e) {
System.out.println("Couldn't get input to " + host + " connection");
System.exit(1);
}
System.out.println("Connected to server!");
BufferedReader userIn = new BufferedReader(new InputStreamReader(System.in));
try{
while(true){
while(!userIn.ready()){
if (in.ready()){ // if server has something to write, when client does'nt have something to write
tmp=in.readLine();
len=tmp.length();
System.out.print(tmp);
if ((len>0 && tmp.charAt(tmp.length()-1)=='>') || tmp.contains("UNIDENTIFIED"))
System.out.println();
}
}
System.out.println();
msg = userIn.readLine();
if (msg==null) { break; }
out.println(msg);
tmp=in.readLine();
if (tmp.contains("~")) { break; }
System.out.println(tmp);
}
}
catch(IOException e){ System.out.println("Error with server connection."); }
System.out.println("Exiting...");
out.close();
in.close();
userIn.close();
clientSocket.close();
}
}
Edit: this is the input I get when I try to run MyEchoClient with the command (after connecting to a server on port 4000) java client.MyEchoClient 127.0.0.1 4000 :
Connecting to 127.0.0.1:4000
Connected to server!
(MyEchoClient is at folder named client).
And as I said, I can't write anything to stdin...

Reliable UDP in java

I am working on my assignment to make UDP reliable using java. How can i add Timeout and re-transmission to handle data-grams that are discarded and add Sequence numbers so the client can verify that a reply is for the appropriate request ??
this is client code
import java.net.*;
import java.io.*;
public class EchoClient {
// UDP port to which service is bound
public static final int SERVICE_PORT = 7;
// Max size of packet
public static final int BUFSIZE = 256;
public static void main(String args[]){
if (args.length != 1)
{
System.err.println ("Syntax - java EchoClient hostname");
return;
}
String hostname = args[0];
// Get an InetAddress for the specified hostname
InetAddress addr = null;
try
{
// Resolve the hostname to an InetAddr
addr = InetAddress.getByName(hostname);
}
catch (UnknownHostException uhe)
{
System.err.println ("Unable to resolve host");
return;
}
try
{
// Bind to any free port
DatagramSocket socket = new DatagramSocket();
// Set a timeout value of two seconds
socket.setSoTimeout (2 * 1000);
for (int i = 1 ; i <= 10; i++)
{
// Copy some data to our packet
String message = "Packet number " + i ;
char[] cArray = message.toCharArray();
byte[] sendbuf = new byte[cArray.length];
for (int offset = 0; offset < cArray.length ; offset++)
{
sendbuf[offset] = (byte) cArray[offset];
}
// Create a packet to send to the UDP server
DatagramPacket sendPacket = new DatagramPacket(sendbuf, cArray.length, addr, SERVICE_PORT);
System.out.println ("Sending packet to " + hostname);
// Send the packet
socket.send (sendPacket);
System.out.print ("Waiting for packet.... ");
// Create a small packet for receiving UDP packets
byte[] recbuf = new byte[BUFSIZE];
DatagramPacket receivePacket = new DatagramPacket(recbuf, BUFSIZE);
// Declare a timeout flag
boolean timeout = false;
// Catch any InterruptedIOException that is thrown
// while waiting to receive a UDP packet
try
{
socket.receive (receivePacket);
}
catch (InterruptedIOException ioe)
{
timeout = true;
}
if (!timeout)
{
System.out.println ("packet received!");
System.out.println ("Details : " + receivePacket.getAddress() );
// Obtain a byte input stream to read the UDP packet
ByteArrayInputStream bin = new ByteArrayInputStream (
receivePacket.getData(), 0, receivePacket.getLength() );
// Connect a reader for easier access
BufferedReader reader = new BufferedReader (
new InputStreamReader ( bin ) );
// Loop indefinitely
for (;;)
{
String line = reader.readLine();
// Check for end of data
if (line == null)
break;
else
System.out.println (line);
}
}
else
{
System.out.println ("packet lost!");
}
// Sleep for a second, to allow user to see packet
try
{
Thread.sleep(1000);
}catch (InterruptedException ie) {}
}
}
catch (IOException ioe)
{
System.err.println ("Socket error " + ioe);
}
}
}

What you can do is adding import TCP headers like sequence number, windows into the UDP message body to make it more like TCP. Here is the a solution that might help you.

java socket programming chat

I'm Playing with a simple Client and Server application using socket, and i attempt to print a message in the console and get a response from the server but nothing shows up, i'm fairly new to sockets so i assume i have a logical error. It's a simple app that i want the client to prompt a user a user for a command (in my case an input string where the server will perform an action based on the 'thcharacter), send it to the server and just display the server response.I'm pretty sure my client isn't correct, can someone points out why i can't write anything from the client console.
package socketProgramming;
import java.io.*;
import java.net.*;
public class MyClient {
#SuppressWarnings("resource")
public static void main(String[] args) {
// TODO Auto-generated method stub
Socket socket= new Socket();
BufferedReader in = null;
String msg;
int port = 2222;
try {
System.out.println("CLient wants to connect on port: "+port);
socket = new Socket(InetAddress.getLocalHost().getHostAddress(), port);
System.out.println("The client is connected");
} catch (UnknownHostException e) {
System.exit(1);
} catch (IOException e) {
System.out.println("connect failed");
System.exit(1);
}
try{
BufferedReader input = new BufferedReader(new InputStreamReader(socket.getInputStream()));
PrintStream output = new PrintStream(socket.getOutputStream());
String text = null;
output.print(text);
while ((text = input.readLine()) != null){
System.out.println("Client "+text);
}
socket.close();
System.out.println("Client Exiting");
}
catch(IOException e) {
System.out.println(e);
}}
}
package socketProgramming;
import java.io.*;
import java.net.*;
public class MyServer {
public static void main(String[] args) throws IOException {
// TODO Auto-generated method stub
String msg = "";
ServerSocket sSocket = null;
Socket clientSocket;
int port = 2222;//Integer.parseInt(args[0]);
try{
sSocket = new ServerSocket(port);
} catch(IOException e){
System.out.println(e);
}
while(true){
try {// listen for a connection from client and accept it.
System.out.println("Server is listenning on host: "
+InetAddress.getLocalHost().getHostAddress() +""
+ " and on port: "
+ port);
clientSocket = sSocket.accept();
System.out.println("Connection accepted");
BufferedReader input = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
// PrintWriter out =
// new PrintWriter(clientSocket.getOutputStream(), true);
PrintStream output = new PrintStream(clientSocket.getOutputStream());
msg = input.readLine();
if(msg != null){
if(msg.charAt(12)=='4'){
System.out.println("reading message "+msg+" ");
output.print("Bye");
sSocket.close();
System.out.println("Server exits");
}else{
if(msg.charAt(12)=='0'){
System.out.println("reading message "+msg+" ");
output.print("OK");
}else if (msg.charAt(12)=='1'){
System.out.println("reading message "+msg+" ");
//Should return IP address
output.print(clientSocket.getInetAddress());
}else if (msg.charAt(12)=='2'){
System.out.println("reading message "+msg+" ");
for(int i = 1; i<=10; ++i){
output.print(i);
output.print(" ");
}
}else if (msg.charAt(12)=='3'){
System.out.println("reading message "+msg+" ");
output.print("GOT IT");
}else{
System.out.println("*******************");
}
}
}
sSocket.close();
System.out.println("Server exits");
}
catch(IOException e) {
System.out.println("accept failed");
System.exit(1);
}
System.out.println("Hello world");
}
}
}

I took some liberties with your code and changed it a bit. It is by no means a perfect version of what you've supplied; however, it should get you pointed in the right direction. These were the problems that were solved:
MyClient was never prompting for user input.
MyServer was sending strings without newlines. MyClient was expecting strings with newlines.
In MyServer, the main socket was being closed at the bottom of the loop. I believe you intended to close the client socket so that the server would loop around and process another client.
In MyServer, you're checking the 13th character of the user's input (because you were indexing the 12th byte (zero based) of the string. I put in brute-force protection against checking the 13th byte of strings that are too short.
Again, I simply corrected certain problems in your code. I may have altered it beyond what your true goals actually are. These examples are intended to get you going on your way...
MyClient.java:
import java.io.*;
import java.net.*;
public class MyClient {
#SuppressWarnings("resource")
public static void main(String[] args) {
// TODO Auto-generated method stub
Socket socket = new Socket();
int port = 2222;
try {
System.out.println("CLient wants to connect on port: " + port);
socket = new Socket(InetAddress.getLocalHost().getHostAddress(), port);
System.out.println("The client is connected");
} catch (UnknownHostException e) {
System.exit(1);
} catch (IOException e) {
System.out.println("connect failed");
System.exit(1);
}
try {
BufferedReader input = new BufferedReader(new InputStreamReader(socket.getInputStream()));
PrintStream output = new PrintStream(socket.getOutputStream());
// Get a line of input from the user.
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
String inputFromUser = br.readLine();
// Send that line of input to MyServer.
output.println(inputFromUser);
// Print out the response from MyServer.
System.out.println("SERVER RESPONSE: " + input.readLine());
socket.close();
System.out.println("Client Exiting");
} catch (IOException e) {
System.out.println(e);
}
}
}
MyServer.java:
import java.io.*;
import java.net.*;
public class MyServer {
public static void main(String[] args) throws IOException {
// TODO Auto-generated method stub
String msg = "";
ServerSocket sSocket = null;
Socket clientSocket;
int port = 2222;// Integer.parseInt(args[0]);
try {
sSocket = new ServerSocket(port);
} catch (IOException e) {
System.out.println(e);
}
while (true) {
try {// listen for a connection from client and accept it.
System.out.println("Server is listenning on host: " + InetAddress.getLocalHost().getHostAddress() + "" + " and on port: "
+ port);
clientSocket = sSocket.accept();
System.out.println("Connection accepted");
BufferedReader input = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
// PrintWriter out =
// new PrintWriter(clientSocket.getOutputStream(), true);
PrintStream output = new PrintStream(clientSocket.getOutputStream());
msg = input.readLine();
if (msg != null) {
if (msg.length() > 12 && msg.charAt(12) == '4') {
System.out.println("reading message " + msg + " ");
output.println("Bye");
System.out.println("Server exits");
} else {
if (msg.length() > 12 && msg.charAt(12) == '0') {
System.out.println("reading message " + msg + " ");
output.println("OK");
} else if (msg.length() > 12 && msg.charAt(12) == '1') {
System.out.println("reading message " + msg + " ");
// Should return IP address
output.println(clientSocket.getInetAddress());
} else if (msg.length() > 12 && msg.charAt(12) == '2') {
System.out.println("reading message " + msg + " ");
for (int i = 1; i <= 10; ++i) {
output.println(i + " ");
}
} else if (msg.length() > 12 && msg.charAt(12) == '3') {
System.out.println("reading message " + msg + " ");
output.println("GOT IT");
} else {
System.out.println("*******************");
// Invalid question from client, I guess.
output.println("HUH?");
}
}
// Make sure output is flushed to client. It will be, but
// just in case...
output.flush();
}
// We're done with this client. Close his socket.
clientSocket.shutdownOutput();
clientSocket.close();
System.out.println("Closed client socket");
}
catch (IOException e) {
System.out.println("accept failed");
e.printStackTrace();
System.exit(1);
}
System.out.println("Hello world");
}
}
}

The problem is that nobody is actually sending any lines. This is what your client does:
output.print(text); //sends null
while ((text = input.readLine()) != null){ //waits to receive a line
This last part is where your client stops because it waits for input that the server never sends. So here is where the server stops:
msg = input.readLine(); //waits to recieve a line
It never reads in null because you didn't send a line (e.g. ending with '\n'). You can easily fix this problem by replacing your output.print() calls with output.println() calls, so that your readers know the line has end and can be read in now.

Why is my data missing from my file after transfering it over a socket?

I have the same code written for both server and client when attempting to upload a file to the server or download it from the server.
Downloading from the server works just fine and no data is missing in my file, but for some reason when uploading the file, not all is transmitted.
For instance, the file size on my client is smaller then when it is on the server. Then when it is opened up on the server, not all of it is there (since not all of it was received)
Server:
Algorithm:
Get message from client
Client tells server it wants to send a file (push)
Server reads where to put the file, and then receives the file from the client
public static void GetClientMessage() {
while (true) {
try {
try {
try {
serverSocket = new ServerSocket(PORT_NUMBER);
} catch (IOException ex) {
System.out.println("GetClientMessage():serverSocket:IOException:ex " + ex);
SendBackException(ex.toString()); // Inform client
}
try {
System.out.println("Waiting for client");
socket = serverSocket.accept();
} catch (IOException ex) {
System.out.println("GetClientMessage():socket = serverSocket.accept():IOException:ex " + ex);
SendBackException(ex.toString()); // Inform client
}
bufOut = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream()));
brffReadIn = new BufferedReader(new InputStreamReader(socket.getInputStream(), "UTF-8"));
// 1 - Read Line (it is the flag)
flag = brffReadIn.readLine();
// 2 - Handle Flag
HandleClientMessage(flag);
// Make decisions based upon that message
} catch (IOException ex) {
System.out.println("GetClientMessage():IOException:ex: " + ex);
SendBackException(ex.toString()); // Inform client
}
socket.close();
serverSocket.close();
} // Close while loop
catch (IOException ex) {
System.out.println("GetClientMessage:serverSocket.close():IOException:ex " + ex);
}
}
}
public static void HandleClientMessage(String message) {
System.out.println("HandleClientMessage:message: '" + message + "'");
switch (message) {
case "push":
GetClientFile();
break;
case "open_cla":
OpenCla();
break;
case "kill_cla":
KillCla();
break;
case "get":
SendFile();
break;
default:
break;
}
}
// Gets path to where to place file on local
public static String GetPath() {
String filePath = " ";
try {
bufOut = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream()));
brffReadIn = new BufferedReader(new InputStreamReader(socket.getInputStream(), "UTF-8"));
filePath = brffReadIn.readLine();
System.out.println("Path to place file on local: " + filePath);
} catch (IOException ex) {
System.out.println(("GetPath():IOException:ex: " + ex));
}
return filePath;
}
public static void GetClientFile() {
// Get the location where to place the file on local
fileOnLocal = GetPath();
int count;
try {
File file = new File(fileOnLocal);
// Get the size of the file
long length = file.length();
byte[] bytes = new byte[16* 1024];
InputStream in = socket.getInputStream();
OutputStream out = new FileOutputStream(fileOnLocal);
while ((count = in.read(bytes)) > 0) {
System.out.println("strByteArray: " + strByteArray);
out.write(bytes, 0, count);
}
out.flush();
System.out.println("File Size in bytes: " + file.length());
if (file.length() < 5) {
System.out.println("FileClient:Error:File:" + fileOnLocal + " not found on server");
out.close();
in.close();
socket.close();
file.delete();
System.out.println("File:" + file.getAbsolutePath() + " deleted");
} else {
out.close();
in.close();
socket.close();
}
} catch (IOException ex) {
System.out.println(":FileClient:GetServerFile():IOException:ex:" + ex);
}
}
Client Code:
Client tells the server it wants to "push" a file, then it passes the location where to put it on the server, then transmits the file
public void SendFlagToServer(String flag){
try {
bufOut = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream()));
brffReadIn = new BufferedReader(new InputStreamReader(socket.getInputStream(), "UTF-8"));
bufOut.write(flag);
bufOut.newLine();
bufOut.flush();
System.out.println(host + ":SendFlagToServer: " + flag);
} catch (IOException ex) {
Logger.Log((host + ":FileClient:SendFileToGetToServer():IOException:ex: " + ex));
}
}
After performing this the bytes are received on the client, but not all of them. Is there something I have coded wrong? Should my byte[] array be a different size? This will be used on Win7 & Win8, and possibly Mac in the future.
Edit: I figured it out. I was trying to send a message followed by a string of bytes too quickly.
This fixed my problem:
SendFlagToServer(fileLocaitonOnServer);
Thread.sleep(1000);
....

You are closing sockets after first client conneciton
socket.close();
serverSocket.close();
Solution:
Once you accept a client socket, create a new Thread with the socket connection and handle all IO operations in that thread
Do not close serverSocket. Once you close serverSocket, no more client socket connections will be accepted.
Can you provide the exception you are getting?

Java Socket not sending message to the server

I have the following client socket for sending a string to the server. The server is not getting message. What could be the prob;em?
public void startClient() throws IOException {
Socket socket = null;
PrintWriter out = null;
BufferedReader in = null;
InetAddress host = null;
BufferedReader stdIn = null;
try {
host = InetAddress.getByName("172.16.2.97");
socket = new Socket(host, 52000);
out = new PrintWriter(socket.getOutputStream(), true);
in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
stdIn = new BufferedReader(new InputStreamReader(System.in));
String fromServer;
String fromUser = null;
//ClientHelper.unpackISO();
fromUser = ClientHelper.createISO();
if (fromUser != null) {
//System.out.println("Client - " + fromUser);
out.write(fromUser);
System.out.println("Sent message");
}
while ((fromServer = in.readLine()) != null) {
System.out.println("Server - " + fromServer);
if (fromUser != null) {
//System.out.println("Client - " + fromUser);
out.println(fromUser);
}
}
} catch (ISOException ex) {
Logger.getLogger(ClientDemo.class.getName()).log(Level.SEVERE, null, ex);
} catch (UnknownHostException e) {
System.err.println("Cannot find the host: " + host.getHostName());
System.exit(1);
} catch (IOException e) {
System.err.println("Couldn't read/write from the connection: " + e.getMessage());
System.exit(1);
} finally { //Make sure we always clean up
out.close();
in.close();
stdIn.close();
socket.close();
}
}
The method ClientHelper.createISO() return a string which is supposed to be sent to the server. Unfortunately the server is not getting any string. Could the problem be proxy settings. If so how can solve it. Or is it another problem with my code?
What is the problem with my code?

You must flush() the stream after writing to it. Sockets buffer until you get a full packet otherwise

Check the 5th line below, you need to flush your output stream. Otherwise server will not get any packet and you will stuck on your first in.readLine() because its blocking.
fromUser = ClientHelper.createISO();
if (fromUser != null) {
//System.out.println("Client - " + fromUser);
out.write(fromUser);
out.flush(); // FLUSH IT HERE, packet wont be sent until you flush your stream
System.out.println("Sent message");
}
Also add flush after your out.write(fromUser) inside the loop.