Develop Reference

Java socket is stuck on readUTF()

I'm trying to transfer files over a socket in Java, my current approach for the server is:
Create new Thread
Thread sends file name using dos.writeUTF()
Thread sends file size using dos.writeLong()
Thread sends file using dos.write()
Where each Thread represents a client and dos is an instance of DataOutputStream.
Now, on the client I'm doing the same thing but reading instead of writing:
Read file name using dis.readUTF()
Read file size using dis.readLong()
Read file using dis.read()
Where dis is an instance of DataInputStream.
The problem is: when sending one file, everything goes right, but when I try to send 3 files, one after another, it looks like the server is writing everything correctly to the stream as expected but the client (After the first file, which means this starts happening from the second file) is stuck on dis.readUTF() and can't move on.
I've tried fixing this for days but can't get anything to work.
Here's the source code:
SERVER:
Main.java
public class Main {
public static void main(String[] args) {
boolean boolDebug = true;//TODO REMOVE THIS!!
ServerSocket serverSock = null;
List<Socket> clientSocks;
List<ClientThread> clientThreads;
try {
serverSock = new ServerSocket(9090);
} catch(Exception e){
e.printStackTrace();
}
clientSocks = new ArrayList<>();
clientThreads = new ArrayList<>();
ServerSocket finalServerSock = serverSock;
System.out.println();
System.out.println("Listening for incoming connections\n");
new Thread(){
#Override
public void run() {
super.run();
while (true) {
try {
Socket newSock = finalServerSock.accept();
clientSocks.add(newSock); //FIXME Remove sockets when closed
Thread thread = new ClientThread(newSock, usr, psw);
thread.start();
clientThreads.add((ClientThread)thread);
} catch (Exception e) {
e.printStackTrace();
}
}
}
}.start();
}
}
ClientThread.java
public class ClientThread extends Thread {
private Socket socket;
private DataInputStream inStream;
private DataOutputStream outStream;
private String dbUser;
private String dbPassword;
public ClientThread(Socket socket, String DbUser, String DbPass) {
this.socket = socket;
this.dbUser = DbUser;
this.dbPassword = DbPass;
}
#Override
public void run() {
try {
inStream = new DataInputStream(socket.getInputStream());
outStream = new DataOutputStream(socket.getOutputStream());
sendFile("a.txt");
sendFile("b.txt");
sendFile("c.txt");
} catch (Exception e) {
e.printStackTrace();
}
}
void sendFile(String file){
try {
File f = new File(file);
outStream.writeUTF(file);
outStream.writeLong(f.length());
FileInputStream fis = new FileInputStream(f);
byte[] buffer = new byte[4096];
while (fis.read(buffer) > 0) {
outStream.write(buffer);
}
fis.close();
}catch(Exception e){
e.printStackTrace();
}
}
int getSize(byte[] buffer,long remaining){
try {
return Math.toIntExact(Math.min(((long) buffer.length), remaining));
}catch(ArithmeticException e){
return 4096;
}
}
}
CLIENT:
Main.java
class Main {
static int getSize(byte[] buffer, long remaining) {
try {
return Math.toIntExact(Math.min(((long) buffer.length), remaining));
} catch (ArithmeticException e) {
return 4096;
}
}
static void saveFile(Socket clientSock,DataInputStream dis) throws IOException {
String fileName = dis.readUTF();
File f = new File(fileName);
FileOutputStream fos = new FileOutputStream(f);
byte[] buffer = new byte[4096];
long filesize = dis.readLong();
int read = 0;
int totalRead = 0;
long remaining = filesize;
while ((read = dis.read(buffer, 0, getSize(buffer, remaining))) > 0) {
totalRead += read;
remaining -= read;
System.out.println("read " + totalRead + " bytes.");
fos.write(buffer, 0, read);
}
fos.close();
}
public static void main(String[] args) throws Exception {
Socket sock = new Socket("192.168.2.17", 9090);
DataInputStream dis = new DataInputStream(sock.getInputStream());
saveFile(sock,dis);
saveFile(sock,dis);
saveFile(sock,dis);
}
}
Many thanks in advance, looking forward to fix this :(

Fixed by changing
while (fis.read(buffer) > 0) {
outStream.write(buffer);
}
to
int count;
while ((count = fis.read(buffer)) > 0) {
outStream.write(buffer, 0, count);
}
Inside ClientThread.java on the server side

DataInputStream hangs on read

I have a socket client that hangs whenever I try to read the input stream from the socket.
DataInputStream dis = new DataInputStream(socket.getInputStream());
int singleByte;
while((singleByte = dis.read()) != -1) { //<-- hangs here
char c = (char)singleByte;
// append character
message_string += c;
}
Hangs on while((singleByte = dis.read()) != -1) {
I have confirmed that the server is echoing back what I send it in raw ASCII.
What am I not understanding? Why is it hanging when trying to read the server response?
Server side (handles the request):
class HandleInputBuffer implements Runnable {
private String msg = "";
private String response = "8";
public HandleInputBuffer(String str) {
this.msg = str;
}
#Override
public void run() {
String exception_msg = "";
// process incoming message
try {
if(msg!=null){
if(msg.length()>0){
// create and send reply
String response = "8";
// ****************************
// create and send response
// ****************************
try {
response = msg;
output_stream = new DataOutputStream(client_socket.getOutputStream());
output_stream.writeInt(response.getBytes("US-ASCII").length);
output_stream.write(response.getBytes("US-ASCII"));
output_stream.flush();
output_stream.close();
//client_socket.shutdownOutput();
client_socket.close();
} catch (IOException e) {
e.printStackTrace();
try{output_stream.flush();} catch (IOException e1) {}
try {client_socket.close();} catch (IOException e1) {}
try {updateConversationHandler = new Handler();} catch (Exception e1) {}
return;
}
}
}
} catch (Exception e) {
e.printStackTrace();
}
}
}
Client side refactor - This code hangs int length = dis.readInt();
InetAddress serverAddr = InetAddress.getByName(edit_ip_address.getText().toString());
if(socket == null){
socket = new Socket(serverAddr, Integer.parseInt(edit_port.getText().toString()));
}
// send bytes
output_stream = new DataOutputStream(socket.getOutputStream());
output_stream.write(command.getBytes("US-ASCII"));
DataInputStream dis = new DataInputStream(socket.getInputStream());
int length = dis.readInt();
byte[] buffer = new byte[length]; //<-- OutOfMemoryException
dis.readFully(buffer);
for (byte b:buffer){
char c = (char)b;
message_string += c;
}

This loop will block until the peer closes the connection.
Ergo the peer is not closing the connection.
EDIT The correct way to read what you're sending is as follows:
You need to read the integer length word that you're writing. It doesn't magically appear via available():
int length = dis.readInt();
byte[] buffer = new byte[length];
dis.readFully(buffer);
But I would throw the sending and receiving code away and use readUTF()/writeUTF(), assuming the data is character data. If it isn't, you shouldn't be assembling it as a String.
EDIT 2 Proof that this works:
Client.java:
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.net.Socket;
public class Client
{
public static void main(String[] args) throws IOException
{
try (Socket s = new Socket("localhost", 9999))
{
DataOutputStream out = new DataOutputStream(s.getOutputStream());
out.writeInt(1);
out.writeBytes("8");
DataInputStream in = new DataInputStream(s.getInputStream());
int count = in.readInt();
System.out.println("Reading "+count+" bytes");
byte[] buffer = new byte[count];
in.readFully(buffer);
System.out.write(buffer, 0, count);
System.out.println();
}
}
}
Server.java:
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket;
public class Server
{
public static void main(String[] args) throws IOException
{
try (ServerSocket ss = new ServerSocket(9999))
{
try (Socket s = ss.accept())
{
DataInputStream in = new DataInputStream(s.getInputStream());
int count = in.readInt();
System.out.println("Reading "+count+" bytes");
byte[] buffer = new byte[count];
in.readFully(buffer);
System.out.write(buffer, 0, count);
System.out.println();
DataOutputStream out = new DataOutputStream(s.getOutputStream());
out.writeInt(count);
out.write(buffer, 0, count);
}
}
}
}
If yours doesn't, you are reading something else from the socket, or writing something else to it, or not running the code you think you're running.

Java: Send and receive byte array

Well, I want to write a simple java client-server-programme, which exchanges byte arrays over tcp-sockets.
/* Server */
public class Server {
private ServerSocket Server = null;
private Socket Client = null;
public static void main(String[] args) {
Server A = new Server();
A.runServer();
A.listenServer();
}
public void runServer() {
try {
Server = new ServerSocket(1234);
}
catch (Exception e) {
System.out.println("Server fault: "+ e.getMessage());
System.exit(-1);
}
}
public void listenServer() {
try {
while (true) {
System.out.println("Waiting...");
Client = Server.accept();
System.out.println("Got something new");
readMessage(Client);
}
}
catch (Exception e) {
System.out.println("Server fault: "+ e.getMessage());
}
}
public byte [] readMessage (Socket socket) {
try {
ByteArrayOutputStream baos = new ByteArrayOutputStream();
byte[] buf = new byte[1];
int len = -1;
while((len = socket.getInputStream().read(buf))!=-1){
baos.write(buf, 0, len);
}
for (int i=0; i<baos.toByteArray().length; i++) {
System.out.println(baos.toByteArray()[i]);
}
return baos.toByteArray();
}
catch (Exception e) {
System.out.println("Server fault: "+ e.getMessage());
}
return null;
}
public void writeMessage (Socket socket, String Message) {
try {
PrintWriter printWriter = new PrintWriter(new OutputStreamWriter(socket.getOutputStream()));
printWriter.print(Message);
printWriter.flush();
}
catch (Exception e) {
System.out.println("Server fault: "+ e.getMessage());
}
}
}
/* Client */
public class Client {
public static void main(String[] args) {
Client B = new Client();
B.runClient();
}
public void runClient () {
Socket socket = null;
try {
socket = new Socket("127.0.0.1", 1234);
}
catch (Exception e) {
System.out.println("Client fault: "+e.getMessage());
}
byte [] Tmp = new byte[10];
for (int i=0; i<Tmp.length; i++) {
Tmp[i] = 1;
}
writeMessage(socket, Tmp);
for (int i=0; i<10; i++) {
byte [] Message = readMessage(socket);
System.out.println(Message);
}
}
public void writeMessage (Socket socket, byte [] myByteMessage) {
try {
OutputStream out = socket.getOutputStream();
DataOutputStream dos = new DataOutputStream(out);
dos.write(myByteMessage, 0, myByteMessage.length);
PrintWriter printWriter = new PrintWriter(new OutputStreamWriter(socket.getOutputStream()));
printWriter.print(myByteMessage);
printWriter.flush();
}
catch (Exception e) {
System.out.println("Could not send data over TCP");
return;
}
}
public byte [] readMessage (Socket socket) {
try {
ByteArrayOutputStream baos = new ByteArrayOutputStream();
byte[] buf = new byte[1];
int len = -1;
while((len = socket.getInputStream().read(buf))!=-1){
baos.write(buf, 0, len);
}
for (int i=0; i<baos.toByteArray().length; i++) {
System.out.println(baos.toByteArray()[i]);
}
System.out.println("Test");
return baos.toByteArray();
}
catch (Exception e) {
System.out.println("Server fault: "+ e.getMessage());
}
return null;
}
}
The problem is, that the client send something to the server but the server doesn't receive anything, so he hangs at the readMessage function.
On the other hand, the client receive some weird stuff, but not the response from the server.

The server receives bytes, but it never leaves the while loop because read() never returns -1. read() returns -1 when the end of the stream is reached. And that happens only when the client closes the socket output stream. Since the client never closes the output stream, the server keeps waiting for the more bytes to come.
Side note: your code is hard to read because you don't respect the standard Java naming conventions: variables start with a lowercase letter.

client server with multi threading

i write a program client-server with multi threading for send - receive file. The program runs and client send and server receive. the files are created but empty new files are created
Why? please help me
class client :
import java.io.*;
import java.net.Socket;
public class Client extends Thread {
Socket socket = null;
Socket socket1 = null;
public void sendFile() throws IOException {
String host = "127.0.0.1";
String host1 = "127.0.0.2";
socket = new Socket(host, 1024);
socket1 = new Socket(host1, 1025);
File file = new File("/home/reza/Desktop/link help");
File file1 = new File("/home/reza/Desktop/hi");
long length = file.length();
long length1 = file1.length();
final byte[] bytes = new byte[(int) length];
final byte[] bytes1 = new byte[(int) length1];
FileInputStream fis = new FileInputStream(file);
FileInputStream fis1 = new FileInputStream(file1);
#SuppressWarnings("resource")
final BufferedInputStream bis = new BufferedInputStream(fis);
final BufferedOutputStream out = new BufferedOutputStream(socket.getOutputStream());
#SuppressWarnings("resource")
final BufferedInputStream bis1 = new BufferedInputStream(fis1);
final BufferedOutputStream out1 = new BufferedOutputStream(socket1.getOutputStream());
Thread t = new Thread(new Runnable() {
public void run()
{
while(socket.isConnected())
{
Wait2();
try {
System.out.println("ok");
int count;
while ((count = bis.read(bytes)) > 0) {
out.write(bytes, 0, count);
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
});
Thread t1 = new Thread(new Runnable() {
public void run() {
while(socket1.isConnected())
{
Wait2();
try {
System.out.println("ok1");
int count1;
while ((count1 = bis1.read(bytes1)) > 0) {
out1.write(bytes1, 0, count1);
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
});
t1.start();
t.start();
socket.close();
socket1.close();
}
public void Wait2()
{
try {
Thread.sleep(3000);
} catch (InterruptedException x) {
System.out.println("Interrupted!");
}
}
}
class server:
import java.io.*;
import java.net.*;
public class Server {
public Server()
{
Thread t = new Thread(new Client());
t.start();
Thread t1 = new Thread(new Client());
t1.start();
}
//#SuppressWarnings("null")
public void recivefile() throws IOException {
ServerSocket serverSocket = null;
ServerSocket serverSocket1 = null;
try {
serverSocket = new ServerSocket(1024);
} catch (IOException ex) {
System.out.println("Can't setup server on this port number. ");
}
try {
serverSocket1 = new ServerSocket(1025);
} catch (IOException ex) {
System.out.println("Can't setup server on this port number1. ");
}
Socket socket = null;
Socket socket1 = null;
InputStream is = null;
InputStream is1 = null;
FileOutputStream fos = null;
FileOutputStream fos1 = null;
BufferedOutputStream bos = null;
BufferedOutputStream bos1 = null;
int bufferSize = 0;
int bufferSize1 = 0;
try {
socket = serverSocket.accept();
socket1 = serverSocket1.accept();
} catch (IOException ex) {
System.out.println("Can't accept client connection. ");
}
try {
is = socket.getInputStream();
is1 = socket1.getInputStream();
bufferSize = socket.getReceiveBufferSize();
bufferSize1 = socket1.getReceiveBufferSize();
//bufferSize2 = socket2.getReceiveBufferSize();
System.out.println("Buffer size: " + bufferSize);
System.out.println("file recieved");
System.out.println("Buffer size1: " + bufferSize1);
System.out.println("file recieved");
System.out.println("file recieved");
} catch (IOException ex) {
System.out.println("Can't get socket input stream. ");
}
try {
fos = new FileOutputStream("/home/reza/Desktop/reza");
bos = new BufferedOutputStream(fos);
fos1 = new FileOutputStream("/home/reza/Desktop/ali");
bos1 = new BufferedOutputStream(fos1);
} 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);
}
byte[] bytes1 = new byte[bufferSize1];
int count1;
while ((count1 = is1.read(bytes1)) > 0) {
bos1.write(bytes1, 0, count1);
}
bos.flush();
bos.close();
bos1.flush();
bos1.close();
is.close();
is1.close();
socket.close();
serverSocket.close();
socket1.close();
serverSocket1.close();
}
public static void main(String[] args) throws IOException
{
System.out.println("server is run, please send file");
Server s = new Server();
s.recivefile();
}
}
client test class:
import java.io.IOException;
public class clientTest extends Thread {
public static void main(String[] args) throws IOException, InterruptedException
{
Client client = new Client();
client.sendFile();
}
}

I believe this code in the server to be your issue:
while ((count = is.read(bytes)) > 0) {
bos.write(bytes, 0, count);
}
byte[] bytes1 = new byte[bufferSize1];
int count1;
while ((count1 = is1.read(bytes1)) > 0) {
bos1.write(bytes1, 0, count1);
}
bos.flush();
bos.close();
bos1.flush();
bos1.close();
is.close();
is1.close();
socket.close();
serverSocket.close();
socket1.close();
serverSocket1.close();
So the server has connected to the client, then it immediately checks to see if there are any bytes to read, if not it stops reading and closes the connection. If this happens faster than the client can deliver any bytes, boom, no data is received. And it WILL happend faster than the client can send data because the client is connecting THEN starting thread to send the data.
Instead, the server should read on each connection for as long as the client has maintained the connection alive. The server needs to wait for the data to be received.
Notice that in your code, the client is waiting for the server to close the connection. But how is the server supposed to know when all the data is sent? Either the client must close the connection or the client must send an EOF-type marker to the server indicating an end of the data and that it is safe to close the connection.

Threads are facing deadlock in socket program

I am developing one program in which a user can download a number of files. Now first I am sending the list of files to the user. So from the list user selects one file at a time and provides path where to store that file. In turn it also gives the server the path of file where does it exist.
I am following this approach because I want to give stream like experience without file size limitation.
Here is my code..
1) This is server which gets started each time I start my application
public class FileServer extends Thread {
private ServerSocket socket = null;
public FileServer() {
try {
socket = new ServerSocket(Utils.tcp_port);
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
#Override
public void run() {
try {
System.out.println("request received");
new FileThread(socket.accept()).start();
} catch (IOException ex) {
ex.printStackTrace();
}
}
}
2) This thread runs for each client separately and sends the requested file to the user 8kb data at a time.
public class FileThread extends Thread {
private Socket socket;
private String filePath;
public String getFilePath() {
return filePath;
}
public void setFilePath(String filePath) {
this.filePath = filePath;
}
public FileThread(Socket socket) {
this.socket = socket;
System.out.println("server thread" + this.socket.isConnected());
//this.filePath = filePath;
}
#Override
public void run() {
// TODO Auto-generated method stub
try
{
ObjectInputStream ois=new ObjectInputStream(socket.getInputStream());
try {
//************NOTE
filePath=(String) ois.readObject();
} catch (ClassNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
File f = new File(this.filePath);
byte[] buf = new byte[8192];
InputStream is = new FileInputStream(f);
BufferedInputStream bis = new BufferedInputStream(is);
ObjectOutputStream oos = new ObjectOutputStream(
socket.getOutputStream());
int c = 0;
while ((c = bis.read(buf, 0, buf.length)) > 0) {
oos.write(buf, 0, c);
oos.flush();
// buf=new byte[8192];
}
oos.close();
//socket.shutdownOutput();
// client.shutdownOutput();
System.out.println("stop");
// client.shutdownOutput();
ois.close();
// Thread.sleep(500);
is.close();
bis.close();
socket.close();
} catch (IOException ex) {
ex.printStackTrace();
}
}
}
NOTE: here filePath represents the path of the file where it exists on the server. The client who is connecting to the server provides this path. I am managing this through sockets and I am successfully receiving this path.
3) FileReceiverThread is responsible for receiving the data from the server and constructing file from this buffer data.
public class FileReceiveThread extends Thread {
private String fileStorePath;
private String sourceFile;
private Socket socket = null;
public FileReceiveThread(String ip, int port, String fileStorePath,
String sourceFile) {
this.fileStorePath = fileStorePath;
this.sourceFile = sourceFile;
try {
socket = new Socket(ip, port);
System.out.println("receive file thread " + socket.isConnected());
} catch (IOException ex) {
ex.printStackTrace();
}
}
#Override
public void run() {
try {
ObjectOutputStream oos = new ObjectOutputStream(
socket.getOutputStream());
oos.writeObject(sourceFile);
oos.flush();
// oos.close();
File f = new File(fileStorePath);
OutputStream os = new FileOutputStream(f);
BufferedOutputStream bos = new BufferedOutputStream(os);
byte[] buf = new byte[8192];
int c = 0;
//************ NOTE
ObjectInputStream ois = new ObjectInputStream(
socket.getInputStream());
while ((c = ois.read(buf, 0, buf.length)) > 0) {
// ois.read(buf);
bos.write(buf, 0, c);
bos.flush();
// buf = new byte[8192];
}
ois.close();
oos.close();
//
os.close();
bos.close();
socket.close();
//Thread.sleep(500);
} catch (IOException ex) {
ex.printStackTrace();
}
}
}
NOTE : Now the problem that I am facing is at the first time when the file is requested the outcome of the program is same as my expectation. I am able to transmit any size of file at first time. Now when the second file is requested (e.g. I have sent file a,b,c,d to the user and user has received file a successfully and now he is requesting file b) the program faces deadlock at this situation. It is waiting for socket's input stream. I put breakpoint and tried to debug it but it is not going in FileThread's run method second time. I could not find out the mistake here. Basically I am making a LAN Messenger which works on LAN. I am using SWT as UI framework.

A more basic problem.
You are only processing the first socket.
while(true) {
new FileThread(socket.accept()).start();
}

As per the suggestion of Peter Lawrey i removed all the redundant streams code from my source code. Now the changed source code is as follows and the problem remains.
1) No change in FileServer. It is as it is .
2) FileThread
public class FileThread extends Thread {
private Socket socket;
private String filePath;
public String getFilePath() {
return filePath;
}
public void setFilePath(String filePath) {
this.filePath = filePath;
}
public FileThread(Socket socket) {
this.socket = socket;
System.out.println("server thread" + this.socket.isConnected());
// this.filePath = filePath;
}
#Override
public void run() {
// TODO Auto-generated method stub
try
{
OutputStream oos = socket.getOutputStream();
oos.flush();
InputStream ois = socket.getInputStream();
byte[] buf = new byte[8192];
ois.read(buf);
filePath = new String(buf);
System.out.println(filePath);
File f = new File(this.filePath);
InputStream is = new FileInputStream(f);
int c = 0;
while ((c = is.read(buf, 0, buf.length)) > 0) {
oos.write(buf, 0, c);
oos.flush();
}
oos.close();
System.out.println("stop");
ois.close();
is.close();
} catch (IOException ex) {
ex.printStackTrace();
}
}
}
3) FileReceiverThread
public class FileReceiveThread extends Thread {
private String fileStorePath;
private String sourceFile;
private Socket socket = null;
public FileReceiveThread(String ip, int port, String fileStorePath,
String sourceFile) {
this.fileStorePath = fileStorePath;
this.sourceFile = sourceFile;
try {
socket = new Socket(ip, port);
System.out.println("receive file thread " + socket.isConnected());
} catch (IOException ex) {
ex.printStackTrace();
}
}
#Override
public void run() {
try {
OutputStream oos = socket.getOutputStream();
oos.write(sourceFile.getBytes());
oos.flush();
File f = new File(fileStorePath);
OutputStream os = new FileOutputStream(f);
byte[] buf = new byte[8192];
int c = 0;
// ************ NOTE
InputStream ois = socket.getInputStream();
while ((c = ois.read(buf, 0, buf.length)) > 0) {
os.write(buf, 0, c);
os.flush();
}
ois.close();
oos.close();
os.close();
} catch (IOException ex) {
ex.printStackTrace();
}
}
}
is there still something which i am missing ?