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Java socket file transfer - Connection reset

I'm trying to make a program that transfer a file using java sockets. This is what I've written so far:
Sender:
private ServerSocket sendSocket;
public Send(int port) throws IOException
{
sendSocket = new ServerSocket(port);
}
public void run()
{
Socket socket = null;
try
{
Scanner scan = new Scanner(System.in);
InputStream inStream = null;
socket = sendSocket.accept();
inStream = socket.getInputStream();
String filePath = scan.nextLine();
OutputStream thisFile = new FileOutputStream(filePath);
byte[] bytes = new byte[16*1024];
int count;
while ((count = inStream.read(bytes)) > 0)
{
thisFile.write(bytes, 0, count);
}
System.out.println("Done!");
}
catch (IOException e)
{
e.printStackTrace();
}
}
}
Receiver:
private static OutputStream thatFile;
public Receive(Socket socket) throws IOException
{
thatFile = socket.getOutputStream();
}
public void run()
{
try
{
System.out.println("Where do you want to save the file?");
Scanner scan = new Scanner(System.in);
String filePath = scan.nextLine();
File saveFile = new File(filePath);
byte[] bytes = new byte[16 * 1024];
InputStream inStream = new FileInputStream(saveFile);
int count;
while ((count = inStream.read(bytes)) > 0)
{
thatFile.write(bytes, 0, count);
}
}
catch (Exception e)
{
}
}
}
But whenever I run the program, after the client gives a destination for the download path, connection reset error happens on the sender side. I'm sure the port is open as I've tested on this port before. What's the problem?
This is what happens when I run the program:
Sender side:
Press 1 to send or 2 to receive.
1
What is the file's path?
C:\Users\orie5\Documents\Cmp\a.txt
java.net.SocketException: Connection reset
at java.base/sun.nio.ch.NioSocketImpl.implRead(NioSocketImpl.java:323)
at java.base/sun.nio.ch.NioSocketImpl.read(NioSocketImpl.java:350)
at java.base/sun.nio.ch.NioSocketImpl$1.read(NioSocketImpl.java:803)
at java.base/java.net.Socket$SocketInputStream.read(Socket.java:966)
at java.base/java.io.InputStream.read(InputStream.java:218)
at def.Send.run(Send.java:47)
Receiver Side:
Press 1 to send or 2 to receive.
2
Please enter the ip of the peer you want to connect to.
Where do you want to save the file?
C:\Users\orie5\Documents\Cmp\b.txt
Thanks in advance!

Java Server-Client Connection reset

I have server and client applications running on my local machine.
Client takes file, changes it and sends to server, then server responds if the file is correct. Client does it multiple times, sending one file at a time.
I send two files from client and on the second file I get Connection reset
Server snippet:
private void initServer() throws IOException {
while (true) {
ServerSocket server = new ServerSocket(55555);
Socket fromclient = server.accept();
InputStream sin = fromclient.getInputStream();
OutputStream sout = fromclient.getOutputStream();
DataInputStream in = new DataInputStream(sin);
DataOutputStream out = new DataOutputStream(sout);
String line = in.readUTF();
if (line.equals("new file")) {
long fileSize = in.readLong();
tempSavedFile = new File("/home/evgeniy/Files/Downloads/temp");
tempSavedFile.createNewFile();
try (FileOutputStream fos = new FileOutputStream(tempSavedFile)) {
int t;
for (int i = 0; i < fileSize; i++) {
t = sin.read();
fos.write(t);
}
}
if (checkPadding(tempSavedFile)) {
out.writeInt(PADDING_OK_RESPONSE);
} else {
out.writeInt(PADDING_ERROR_RESPONSE);
}
out.flush();
}
out.close();
in.close();
sout.close();
sin.close();
fromclient.close();
server.close();
}
}
Client class that calls new thread in for loop
for (byte i = 0; i < 2; i++) {
Callable callable = new FileSender(tempFile);
FutureTask<Integer> ftask = new FutureTask<>(callable);
Thread thread = new Thread(ftask);
thread.start();
int response = 3244;
try {
response = ftask.get();
} catch (InterruptedException | ExecutionException ex) {
Logger.getLogger(FXMLController.class.getName()).log(Level.SEVERE, null, ex);
}
putMessage(String.valueOf(response));
Client Callable thread:
public Integer call() throws Exception {
Socket socket = new Socket(address, serverPort);
InputStream sin = socket.getInputStream();
OutputStream sout = socket.getOutputStream();
DataInputStream in = new DataInputStream(sin);
DataOutputStream out = new DataOutputStream(sout);
out.writeUTF("new file");
out.flush();
out.writeLong(file.length);
out.flush();
sout.write(file);
sout.flush();
System.out.println(socket.isConnected());
int response = in.readInt();
System.out.println("--------RESP="+response);
out.close();
in.close();
sin.close();
sout.close();
socket.close();
return response;
}
As you can see I send two files, and get this console output on client app:
true
--------RESP=200
true
ноя 20, 2018 5:16:36 PM com.evgeniy_mh.paddingoracle.FXMLController SendFileToServer
SEVERE: null
java.util.concurrent.ExecutionException: java.net.SocketException: Connection reset
Also, I don't understand why socket is ok, but
int response = in.readInt();
raising Connection reset exception.

Your code creates a new ServerSocket and later closes the created server socket for every single request that it processes. The code does not use the same ServerSocket instance to serve multiple requests.
The connection reset failure appears to be because of this, as when the second request is creating a socket connection with the server, the existing ServerSocket is closed and recreated on the same port leading to the connection being reset. For a start try taking out the ServerSocket creation outside the while loop.
private void initServer() {
try (ServerSocket server = new ServerSocket(5555)) {
while (true) {
Socket fromclient = server.accept();
... // remaining code
fromclient.close();
}
} catch (IOException ioe) {
// handle failures
}
}
The try-with-resources handles the .close() call on the AutoCloseable server socket.
Also, note that the requests would be processed serially on a single thread in your code. Usually the Socket obtained for a connection from the ServerSocket#accept() (or the streams derived from it) is passed to a separate thread for processing unlike your code that processes the requests serially.

Websocket server to initialise a connection to another websocket server

Is there a way to get a websocket server to connect to another websocket server? I wrote this snippet in Java but it doesn't work. I don't get any errors or exceptions, it just waits forever to connect.
#OnMessage
public void message(Session session, String msg){
String URL = "ws://wildfly2-ciri.rhcloud.com:8000/echo";
try {
System.out.println("**1 Got new message: " + msg);
String forward = "This is WildFly 1: " + msg;
System.out.println("**1 Init new session");
Session newSession = session.getContainer().connectToServer(Client.class, URI.create(URL));
System.out.println("**1 Sending to wildfly2");
newSession.getBasicRemote().sendText(forward);
} catch (Exception e) {
e.printStackTrace();
}
}
Basically, I want this server to initialize a new websocket connection to another server at another address. However, the program stops when it tries to make a new connection. Is there a flaw in my thinking or is this kind of connection impossible?

You may find this useful. This is one of my older socket programs which I used to communicate between client and server. I have attached both of client and code for the program which would send XML files. You will however, need to edit a few things in order to get her workin' for you. Play this with file and get a feel for sockets and apply it to your program. Happy Learnings my friend!
public static void main(String[] args) throws IOException {
Socket socket = null;
String host = "127.0.0.1";
socket = new Socket(host, 4444);
File file = new File("C:\\testXML.xml");
// Get the size of the file
long length = file.length();
if (length > Integer.MAX_VALUE) {
System.out.println("File is too large.");
}
byte[] bytes = new byte[(int) length];
FileInputStream fis = new FileInputStream(file);
BufferedInputStream bis = new BufferedInputStream(fis);
BufferedOutputStream out = new BufferedOutputStream(socket.getOutputStream());
int count;
while ((count = bis.read(bytes)) > 0) {
out.write(bytes, 0, count);
}
out.flush();
out.close();
fis.close();
bis.close();
socket.close();
}
}
public class Server {
/**
* #param args the command line arguments
*/
public static void main(String[] args) throws IOException {
ServerSocket serverSocket = null;
try {
serverSocket = new ServerSocket(4444);
} catch (IOException ex) {
System.out.println("Can't setup server on this port number. ");
}
Socket socket = null;
InputStream is = null;
FileOutputStream fos = null;
BufferedOutputStream bos = null;
int bufferSize = 0;
try {
socket = serverSocket.accept();
} catch (IOException ex) {
System.out.println("Can't accept client connection. ");
}
try {
is = socket.getInputStream();
bufferSize = socket.getReceiveBufferSize();
System.out.println("Buffer size: " + bufferSize);
} catch (IOException ex) {
System.out.println("Can't get socket input stream. ");
}
try {
fos = new FileOutputStream("C:\\xxxXXXXxxx.txt");
bos = new BufferedOutputStream(fos);
} catch (FileNotFoundException ex) {
System.out.println("File not found. ");
}
byte[] bytes = new byte[bufferSize];
int count;
while ((count = is.read(bytes)) > 0) {
bos.write(bytes, 0, count);
}
bos.flush();
bos.close();
is.close();
socket.close();
serverSocket.close();
}
}

Null pointer exception occurs while trying to read repeatedly from an InputStream

The code works fine when I close the client just after sending one instruction. But when I want a client and server connection to persist, so that the client can send multiple instructions to the server one after another, I get a Null pointer exception at the server and the message java.net.SocketException: Socket is closed at the client. This happens after the client sends a file to the server and the server successfully receives it. Need help. The error occurs at the Connection class code line switch(clientMsg). It seems to me that for some reason the BufferedReader in goes null, but I might be mistaken about that. The code is as follows. Thanks.
Server
public class server {
private static ServerSocket serverSocket;
private static Socket socket = null;
public static void print(Object s) {
System.out.println(s);
}
#SuppressWarnings("resource")
public static void main (String args[]) throws IOException {
System.out.print("Specify listening port: ");
Scanner _a = new Scanner(System.in);
int a = _a.nextInt();
try{
serverSocket = new ServerSocket(a);
}
catch(IOException e) {
System.out.println(e);
}
while (true) {
try {
socket = serverSocket.accept();
print("Connected to " + socket);
Thread client = new Thread(new Connection(socket));
client.start();
}
catch (IOException e) {
print(e);
}
}
}
}
Connection
public class Connection implements Runnable {
public static void print(Object s) {
System.out.println(s);
}
private Socket socket;
private BufferedReader in = null;
public Connection(Socket client) {
this.socket = client;
}
#Override
public void run(){
try {
in = new BufferedReader(new InputStreamReader(
socket.getInputStream()));
String clientMsg;
while (true) {
clientMsg = in.readLine();
switch (clientMsg) {
case "1":
receiveFile(); //method code not included
break;
default:
print("Command not recognized");
break;
}
//in.close();
}
}//try run()
catch (IOException e) {
print(e);
}
}
Client
public class client {
private static Socket connectToServer;
private static String fileName;
private static BufferedReader keybrdIn;
private static PrintStream msgToServer;
public static void println(Object e) {
System.out.println(e);
}
public static void print(Object e) {
System.out.print(e);
}
public static void main(String args[]) throws IOException{
try{
print("Enter IP: ");
String ip = new Scanner(System.in).nextLine();
print("Enter port: ");
int port = new Scanner(System.in).nextInt();
connectToServer = new Socket(ip, port);
keybrdIn = new BufferedReader(new InputStreamReader(System.in));
}catch(IOException e) {
println(e);
}
msgToServer = new PrintStream(connectToServer.getOutputStream());
while (true) {
try {
switch(Integer.parseInt(action())) { //action() method code not included
case 1:
msgToServer.println("1");
sendFile();
break;
default:
println("Invalid input");
break;
}
}catch (IOException e) {
println(e);
}
}
}
sendFile()
public static void sendFile() throws IOException {
print("Enter file name: ");
fileName = keybrdIn.readLine();
File file = new File(fileName);
byte[] bytearray = new byte[8192];
FileInputStream fis = new FileInputStream(file);
BufferedInputStream bis = new BufferedInputStream(fis);
DataInputStream dis = new DataInputStream(bis);
OutputStream os = connectToServer.getOutputStream();
DataOutputStream dos = new DataOutputStream(os);
dos.writeUTF(file.getName());
int count;
while ((count = dis.read(bytearray)) > 0){
dos.write(bytearray, 0, count);
}
dis.close();
dos.flush();
dos.close();
}
receiveFile()
public void receiveFile() {
try {
int count;
DataInputStream clientFileStream = new DataInputStream(socket.getInputStream());
String fileName = clientFileStream.readUTF();
OutputStream fileOutput = new FileOutputStream("_" + fileName);
byte[] mybytearray = new byte[8192];
BufferedOutputStream bos = new BufferedOutputStream(fileOutput);
System.out.println("Downloading " + fileName + " ...");
//outToClient().writeBytes("Uploading. Please wait...\n");
while ((count = clientFileStream.read(mybytearray)) > 0){
bos.write(mybytearray, 0, count);
}
fileOutput.close();
bos.close();
clientFileStream.close();
}
catch (IOException e) {
print(e);
}
}

In sendFile(), you close the data output stream which closes your underlying connection's output stream.
According to the documentation of Socket.getOutputStream():
"Closing the returned OutputStream will close the associated socket".

Since you already closed stream, it will also close socket as well as Eyal mentioned. However, at the moment you close the stream, server side will aware of that and return -1 for read() results.
So, even if you didn't specify file length at beginning, this will generally works well.
However, since you already closed stream, you can't reuse it no matter what. To fix this issue, probably you need to change your Client class so that Client should create socket connection, send files, close socket. That's one lifecycle of opened client socket.
Or maybe in while loop of Client class, 1) take ip, port, and filename to send 2) Create new Thread and provide those information so let thread open connection, send file, close connection 3) and in the meantime, client while() can keep take next ip, port, and filename to send from the user. By doing this, you don't need to make client program wait until file transfer to be completed.

Regarding the NPE in the server, readLine() returns null at end of stream. You are ignoring it. You should be testing for it immediately after the call, and if null close the socket and exit the read loop.

Synchronize server with client java sockets

Currently I am working on a server/client application which sends data using java with Runnable and threads. The problem is that the client is sending the data and when the server starts to read it the client has already finished and closed the connection which on the server side only a partially of the data is arrived, can they be setup to be synchronized?
this is the client:
private void ConnectionToServer(final String ipAddress, final int Port) {
final ExecutorService clientProcessingPool = Executors.newFixedThreadPool(10);
Runnable serverTask = new Runnable() {
#Override
public void run() {
try {
socket = new Socket(ipAddress, Port);
bos = new BufferedOutputStream(socket.getOutputStream());
dos = new DataOutputStream(socket.getOutputStream());
File f = new File("C:/Users/lukeLaptop/Downloads/RemoveWAT22.zip");
String data = f.getName()+f.length();
byte[] b = data.getBytes();
sendBytes(b, 0, b.length);
dos.flush();
bos.flush();
bis.close();
dos.close();
//clientProcessingPool.submit(new ServerTask(socket));
} catch (IOException ex) {
Logger.getLogger(ClientClass.class.getName()).log(Level.SEVERE, null, ex); } finally {
}
}
};
Thread serverThread = new Thread(serverTask);
serverThread.start();
public void sendBytes(byte[] myByteArray, int start, int len) throws IOException {
if (len < 0) {
throw new IllegalArgumentException("Negative length not allowed");
}
if (start < 0 || start >= myByteArray.length) {
throw new IndexOutOfBoundsException("Out of bounds: " + start);
}
// Other checks if needed.
// May be better to save the streams in the support class;
// just like the socket variable.
OutputStream out = socket.getOutputStream();
DataOutputStream dos = new DataOutputStream(out);
dos.writeInt(len);
if (len > 0) {
dos.write(myByteArray, start, len);
}
}
server code:
private void acceptConnection() {
try {
final ExecutorService clientProcessingPool = Executors.newFixedThreadPool(10);
Runnable serverTask = new Runnable() {
#Override
public void run() {
try {
ServerSocket server = new ServerSocket(8080);
while (true) {
socket = server.accept();
System.out.println("Got a client !");
bis = new BufferedInputStream(socket.getInputStream());
dis = new DataInputStream(socket.getInputStream());
String data = readBytes().toString();
System.out.println(data);
bos.close();
dis.close();
//clientProcessingPool.submit(new ClientTask(socket));
}
} catch (IOException ex) {
System.out.println(ex.getMessage());
}
}
};
Thread serverThread = new Thread(serverTask);
serverThread.start();
} catch (Exception io) {
io.printStackTrace();
}
}
public byte[] readBytes() throws IOException {
// Again, probably better to store these objects references in the support class
InputStream in = socket.getInputStream();
DataInputStream dis = new DataInputStream(in);
int len = dis.readInt();
byte[] data = new byte[len];
if (len > 0) {
dis.readFully(data);
}
return data;
}

You mixed up many things:
Variables start most of the time with a lowercase letter, e.g. int port, int ipAddress
Classes start with a uppercase letter, e.g. Client, Server
only open one Data*stream on a socket. new DataInputStream(socket.getInputStream()) or new BufferedInputStream(socket.getInputStream()), but not both
If you need both, chain them: new DataInputStream(new BufferedInputStream(socket.getInputStream()));
KISS (Keep it short & simple)
If you use a DataInputStream, then use the given functionality of sending objects and primitives, e.g. sendUTF(), sendInt(), sendShort(), and so on...
Name your vars right: servertask is a client thread? no
Move long anonymous classes to a new class
Don't use port 8080, this port is used for many other application and will cause problems
example code regarding your example an my advices:
Server
public class Server implements Runnable {
private void acceptConnection() {
Thread serverThread = new Thread(this);
serverThread.start();
}
#Override
public void run() {
try {
ServerSocket server = new ServerSocket(8081);
while (true) {
Socket socket = server.accept();
System.out.println("Got a client !");
// either open the datainputstream directly
DataInputStream dis = new DataInputStream(socket.getInputStream());
// or chain them, but do not open two different streams:
// DataInputStream dis = new DataInputStream(new BufferedInputStream(socket.getInputStream()));
// Your DataStream allows you to read/write objects, use it!
String data = dis.readUTF();
System.out.println(data);
dis.close();
// in case you have a bufferedInputStream inside of Datainputstream:
// you do not have to close the bufferedstream
}
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
public static void main(String[] args) {
new Server().acceptConnection();
}
}
description:
main: create a new Server Object, which is a Runnable
acceptConnections: create a Thread
run:
open a Serversocket
wait for a connection
open exactly one stream
read the Data
close the stream and wait for next connection
Client
public class Client {
private static void sendToServer(String ipAddress, int port) throws UnknownHostException, IOException {
Socket socket = new Socket(ipAddress, port);
// same here, only open one stream
DataOutputStream dos = new DataOutputStream(socket.getOutputStream());
File f = new File("C:/Users/lukeLaptop/Downloads/RemoveWAT22.zip");
String data = f.getName()+f.length();
dos.writeUTF(data);
dos.flush();
dos.close();
}
public static void main(String[] args) throws UnknownHostException, IOException {
Client.sendToServer("localhost", 8081);
}
}
description (This one is straight forward):
open socket
open DataStream
send Data
flush and close