Develop Reference

Java socket getting only NUL characters after writing byte array

I'm trying to send files in chunks from a client to server via byte arrays. I'm using ObjectInputStream. The write works and the filesize matches but when I open the file, I only get a blank textfile(which when opened in a IDE, shows NUL,NUL,NUL...).
Server code:
try(
FileOutputStream fileOut = new FileOutputStream(file);
ObjectOutputStream out = new ObjectOutputStream(socket.getOutputStream());
ObjectInputStream in = new ObjectInputStream(socket.getInputStream());
){
byte[] arr = new byte[chunkSize];
try {
int len = 0;
long bytesRead = 0;
byte[] bytes = new byte[chunkSize];
int chunkNo = 1;
while(true)
{
len = in.read(bytes,0, chunkSize);
System.out.println();
if(len < 0)
break;
fileOut.write(arr, 0, len);
bytesRead += len;
out.writeObject(Server.CHUNK_ACKNOWLEDGE_MSG);
String ackReply = (String) in.readObject();
if(ackReply.equalsIgnoreCase((Server.UPLOAD_ACKNOWLEDGE_RECEIVE_TIMEOUT_MSG))){
if(Server.DEBUG)
System.out.println(fileName + " send timeout.");
deleteFile();
break;
}else if (ackReply.equalsIgnoreCase(Server.UPLOAD_COMPLETE_MSG)){
if(bytesRead != fileSize){
System.out.println(fileName + " File size mismatch");
deleteFile();
break;
}else{
System.out.println( fileName + " File written");
break;
}
}
}
}catch (IOException ioe){
if(Server.DEBUG)
ioe.printStackTrace();
}
Client code:
try(
FileInputStream fileInput = new FileInputStream(file);
ObjectOutputStream out = new ObjectOutputStream(socket.getOutputStream());
ObjectInputStream in = new ObjectInputStream(socket.getInputStream());
){
byte[] arr = new byte[chunkSize];
try {
int len = 0;
int bytesRead = 0;
int chunkCount = 1;
while((len = fileInput.read(arr, 0, chunkSize)) != -1)
{
out.write(arr, 0, len);
out.flush();
bytesRead += len;
}
try {
System.out.println("wait ack");
socket.setSoTimeout(timeout);
String ack = (String) in.readObject();
System.out.println(ack);
if(bytesRead >= fileSize){
out.writeObject(Server.UPLOAD_COMPLETE_MSG);
System.out.println(Server.UPLOAD_COMPLETE_MSG);
break;
}else{
out.writeObject(Server.CHUNK_ACKNOWLEDGE_MSG);
}
}catch (SocketTimeoutException e){
out.writeObject(Server.UPLOAD_ACKNOWLEDGE_RECEIVE_TIMEOUT_MSG);
System.out.println(Server.UPLOAD_ACKNOWLEDGE_RECEIVE_TIMEOUT_MSG);
break;
}finally {
socket.setSoTimeout(0);
}
}
}
}catch (IOException ioe){
ioe.printStackTrace();
}
}catch (FileNotFoundException fnfe){
System.out.println("No such file: " + fileName);
}catch (Exception e){
e.printStackTrace();
}
finally {
try {
socket.close();
}catch (Exception ex){
ex.printStackTrace();
}
}
I tried writing the byte array to another file on the client side and the copy was identical. So the problem must be during sending data over socket.
The Server.X_MSG is just a constant string. I don't know if mixing readobject() and read(bytearray) on the same ObjectInputStream causes any issues though.

Maybe it's because fileOut.write(arr, 0, len); use arr and len = in.read(bytes,0, chunkSize); use bytes? They are not the same array.

creating Socket to connect to windows 10 machine from Raspberry pi 4 Raspbian does not work (Java)

I have a Raspberry pi 4 with Raspbian installed, and I have a computer with Windows 10 installed.I wrote two functions one send a file and the other one receive the file.
when I run this function that sends a file on the raspberry pi 4:
public static void sendFile(String fileName, String ip)
{
BufferedOutputStream outputStream = null;
PrintWriter writer = null;
BufferedReader reader = null;
FileInputStream filein = null;
File file = new File(fileName);
if (!file.exists())
{
System.out.println(fileName + " does not exist");
return;
}
try
{
Socket socket = new Socket(ip, port);
outputStream = new BufferedOutputStream(socket.getOutputStream());
writer = new PrintWriter(socket.getOutputStream());
reader = new BufferedReader(new InputStreamReader(socket.getInputStream()));
filein = new FileInputStream(file);
long fileSize = file.length();
writer.println(fileName); // sending file name
writer.println(fileSize); // sending file size in bytes
writer.flush();
byte[] dataBuffer = new byte[1024];
int numberOfReadBytes = 0; // the number of read bytes for each read() function call
System.out.println("Entering the loop");
for(long i = 0; i < fileSize && numberOfReadBytes > -1;)
{
numberOfReadBytes = filein.read(dataBuffer); // read read() function returns the number of bytes tha has been assigned to the array or -1 if EOF(end of file) is reached
outputStream.write(dataBuffer, 0, numberOfReadBytes); // writing the bytes in dataBuffer from index 0 to index numberOfBytes
i += numberOfReadBytes;
}
outputStream.flush();
System.out.println(fileName + " sent to " + ip);
String status = reader.readLine();
System.out.println("Status: " + status + "\t file save successfully on the other machine.");
}
catch(IOException ioe)
{
System.err.println("Status: 0\n" + ioe.getMessage());
}
finally // closing streams
{
try
{
outputStream.close();
reader.close();
writer.close();
filein.close();
}
catch (IOException ioe)
{
System.err.println("Error closing the connection.");
}
}
}
it stops at this line Socket socket = new Socket(ip, port);
and this is the other function that runs on windows 10
public static void receiveFile()
{
// 1- read the file name
// 2- read the size of the file
// 3- read the file and write it
ServerSocket server = null;
Socket socket = null;
BufferedReader reader = null;
BufferedInputStream inputStream = null;
FileOutputStream fileout = null;
PrintWriter writer = null;
try
{
server = new ServerSocket(9999);
socket = server.accept();
reader = new BufferedReader(new InputStreamReader(socket.getInputStream()));
inputStream = new BufferedInputStream(socket.getInputStream());
writer = new PrintWriter(socket.getOutputStream());
String fileName = reader.readLine(); // reading file name
long fileSize = Long.parseLong(reader.readLine()); // reading file size
System.out.println(fileSize);
// reading file data and write the data
File file = new File(fileName);
fileout = new FileOutputStream(file);
for (long i = 0; i < fileSize; ++i)
{
fileout.write(inputStream.read());
System.out.println(i);
}
fileout.flush();
fileout.close();
writer.println('1');
System.out.println("Status: 1");
System.out.println(fileName+ " is saved successfully");
}
catch (IOException ioe)
{
System.err.println("Status: 0");
System.err.println(ioe.getMessage());
}
finally
{
try
{
reader.close();
inputStream.close();
}
catch(IOException ioe)
{
System.err.println("Error closing connection\n" + ioe.getMessage());
}
}
}
I think windows 10 firewall blocks connection, but I am not sure.

It turns out it was the firewall blocking connection from the raspberry pi

Files downloaded as Binary with Java are corrupted

I have written an downloader which should be used to download text files, as well as images. So I download the files as binaries. Many of the downloads work very well, but some parts of the text files and many image files are corrupted. The errors occur always at the same files and at the same places (as long as I can tell when analysing the text files). I used this code for downloading:
public File downloadFile(HttpURLConnection connection) {
return writeFileDataToFile(getFileData(connection));
}
//downloads the data of the file and returns the content as string
private List<Byte> getFileData(HttpURLConnection connection) {
List<Byte> fileData = new ArrayList<>();
try (InputStream input = connection.getInputStream()) {
byte[] fileChunk = new byte[8*1024];
int bytesRead;
do {
bytesRead = input.read(fileChunk);
if (bytesRead != -1) {
fileData.addAll(Bytes.asList(fileChunk));
fileChunk = new byte[8*1024];
}
} while (bytesRead != -1);
return fileData;
} catch (IOException e) {
System.out.println("Receiving file at " + url.toString() + " failed");
System.exit(1);
return null; //shouldn't be reached
}
}
//writes data to the file
private File writeFileDataToFile(List<Byte> fileData) {
if (!this.file.exists()) {
try {
this.file.getParentFile().mkdirs();
this.file.createNewFile();
} catch (IOException e) {
System.out.println("Error while creating file at " + file.getPath());
System.exit(1);
}
}
try (OutputStream output = new FileOutputStream(file)) {
output.write(Bytes.toArray(fileData));
return file;
} catch (IOException e) {
System.out.println("Error while accessing file at " + file.getPath());
System.exit(1);
return null;
}
}

I could suggest you to not pass through List of Byte, since you create a list of Byte from an array, to get it back to an array of Byte, which is not really efficient.
Moreover you wrongly assume the chunk size (not necesseraly 8192 bytes).
Why don't you just do something as:
private File writeFileDataToFile(HttpURLConnection connection) {
if (!this.file.exists()) {
try {
this.file.getParentFile().mkdirs();
//this.file.createNewFile(); // not needed, will be created at FileOutputStream
} catch (IOException e) {
System.out.println("Error while creating file at " + file.getPath());
//System.exit(1);
// instead do a throw of error or return null
throw new YourException(message);
}
}
OutputStream output = null;
InputStream input = null;
try {
output = new FileOutputStream(file):
input = connection.getInputStream();
byte[] fileChunk = new byte[8*1024];
int bytesRead;
while ((bytesRead = input.read(fileChunk )) != -1) {
output.write(fileChunk , 0, bytesRead);
}
return file;
} catch (IOException e) {
System.out.println("Receiving file at " + url.toString() + " failed");
// System.exit(1); // you should avoid such exit
// instead do a throw of error or return null
throw new YourException(message);
} finally {
if (input != null) {
try {
input.close();
} catch (Execption e2) {} // ignore
}
if (output != null) {
try {
output.close();
} catch (Execption e2) {} // ignore
}
}
}

The failure was adding the whole fileChunk Array to file data, even if it wasn't completely filled by the read operation.
Fix:
//downloads the data of the file and returns the content as string
private List<Byte> getFileData(HttpURLConnection connection) {
List<Byte> fileData = new ArrayList<>();
try (InputStream input = connection.getInputStream()) {
byte[] fileChunk = new byte[8*1024];
int bytesRead;
do {
bytesRead = input.read(fileChunk);
if (bytesRead != -1) {
fileData.addAll(Bytes.asList(Arrays.copyOf(fileChunk, bytesRead)));
}
} while (bytesRead != -1);
return fileData;
} catch (IOException e) {
System.out.println("Receiving file at " + url.toString() + " failed");
System.exit(1);
return null; //shouldn't be reached
}
}
Where the relevant change is changing
if (bytesRead != -1) {
fileData.addAll(Bytes.asList(fileChunk));
fileChunk = new byte[8*1024];
}
into
if (bytesRead != -1) {
fileData.addAll(Bytes.asList(Arrays.copyOf(fileChunk, bytesRead)));
}

Message returned is null

Hi i have a problem with my server, everytime i call "dload" the file gets downloaded but i can't use the other commands i have because they get returned as null. Anyone who can see the problem in the code?
Server :
public class TCPServer {
public static void main(String[] args) {
ServerSocket server = null;
Socket client;
// Default port number we are going to use
int portnumber = 1234;
if (args.length >= 1) {
portnumber = Integer.parseInt(args[0]);
}
// Create Server side socket
try {
server = new ServerSocket(portnumber);
} catch (IOException ie) {
System.out.println("Cannot open socket." + ie);
System.exit(1);
}
System.out.println("ServerSocket is created " + server);
// Wait for the data from the client and reply
boolean isConnected = true;
try {
// Listens for a connection to be made to
// this socket and accepts it. The method blocks until
// a connection is made
System.out.println("Waiting for connect request...");
client = server.accept();
System.out.println("Connect request is accepted...");
String clientHost = client.getInetAddress().getHostAddress();
int clientPort = client.getPort();
System.out.println("Client host = " + clientHost
+ " Client port = " + clientPort);
// Read data from the client
while (isConnected == true) {
InputStream clientIn = client.getInputStream();
BufferedReader br = new BufferedReader(new InputStreamReader(
clientIn));
String msgFromClient = br.readLine();
System.out.println("Message received from client = "
+ msgFromClient);
// Send response to the client
if (msgFromClient != null
&& msgFromClient.equalsIgnoreCase("sum")) {
OutputStream clientOut = client.getOutputStream();
PrintWriter pw = new PrintWriter(clientOut, true);
Double[] list;
list = new Double[5];
String value;
int i;
try {
for (i = 0; i < 5; i++) {
pw.println("Input number in arrayslot: " + i);
value = br.readLine();
double DoubleValue = Double.parseDouble(value);
list[i] = DoubleValue;
}
if (i == 5) {
Double sum = 0.0;
for (int k = 0; k < 5; k++) {
sum = sum + list[k];
}
pw.println("Sum of array is " + sum);
}
} catch (NumberFormatException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
if (msgFromClient != null
&& msgFromClient.equalsIgnoreCase("max")) {
OutputStream clientOut = client.getOutputStream();
PrintWriter pw = new PrintWriter(clientOut, true);
Double[] list;
list = new Double[5];
String value;
int i;
try {
for (i = 0; i < 5; i++) {
pw.println("Input number in arrayslot: " + i);
value = br.readLine();
double DoubleValue = Double.parseDouble(value);
list[i] = DoubleValue;
}
if (i == 5) {
Arrays.sort(list);
pw.println("Max integer in array is " + list[4]);
}
} catch (NumberFormatException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
if (msgFromClient != null
&& msgFromClient.equalsIgnoreCase("time")) {
OutputStream clientOut = client.getOutputStream();
PrintWriter pw = new PrintWriter(clientOut, true);
Calendar calendar = GregorianCalendar.getInstance();
String ansMsg = "Time is:, "
+ calendar.get(Calendar.HOUR_OF_DAY) + ":"
+ calendar.get(Calendar.MINUTE);
pw.println(ansMsg);
}
if (msgFromClient != null
&& msgFromClient.equalsIgnoreCase("date")) {
OutputStream clientOut = client.getOutputStream();
PrintWriter pw = new PrintWriter(clientOut, true);
Calendar calendar = GregorianCalendar.getInstance();
String ansMsg = "Date is: " + calendar.get(Calendar.DATE)
+ "/" + calendar.get(Calendar.MONTH) + "/"
+ calendar.get(Calendar.YEAR);
;
pw.println(ansMsg);
}
if (msgFromClient != null
&& msgFromClient.equalsIgnoreCase("c2f")) {
OutputStream clientOut = client.getOutputStream();
PrintWriter pw = new PrintWriter(clientOut, true);
String celciusValue;
boolean ifRead = false;
try {
pw.println("Input celcius value");
celciusValue = br.readLine();
ifRead = true;
if (ifRead == true) {
double celcius = Double.parseDouble(celciusValue);
celcius = celcius * 9 / 5 + 32;
pw.println(celcius);
}
} catch (NumberFormatException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
if (msgFromClient != null
&& msgFromClient.equalsIgnoreCase("dload")) {
OutputStream outToClient = client.getOutputStream();
if (outToClient != null) {
File myFile = new File("C:\\ftp\\pic.png");
byte[] mybytearray = new byte[(int) myFile.length()];
FileInputStream fis = new FileInputStream(myFile);
BufferedInputStream bis = new BufferedInputStream(fis);
try {
bis.read(mybytearray, 0, mybytearray.length);
outToClient.write(mybytearray, 0,
mybytearray.length);
outToClient.flush();
outToClient.close();
bis.close();
fis.close();
} catch (IOException ex) {
// Do exception handling
}
System.out.println("test");
}
}
if (msgFromClient != null
&& msgFromClient.equalsIgnoreCase("quit")) {
client.close();
break;
}
// if (msgFromClient != null
// && !msgFromClient.equalsIgnoreCase("bye")) {
// OutputStream clientOut = client.getOutputStream();
// PrintWriter pw = new PrintWriter(clientOut, true);
// String ansMsg = "Hello, " + msgFromClient;
// pw.println(ansMsg);
// }
// Close sockets
if (msgFromClient != null
&& msgFromClient.equalsIgnoreCase("bye")) {
server.close();
client.close();
break;
}
msgFromClient = null;
}
} catch (IOException ie) {
}
}
}
Client:
import java.io.*;
import java.net.*;
public class TCPClient {
public static void main(String args[]) {
boolean isConnected = true;
Socket client = null;
int portnumber = 1234; // Default port number we are going to use
if (args.length >= 1) {
portnumber = Integer.parseInt(args[0]);
}
try {
String msg = "";
// Create a client socket
client = new Socket("127.0.0.1", 1234);
System.out.println("Client socket is created " + client);
// Create an output stream of the client socket
OutputStream clientOut = client.getOutputStream();
PrintWriter pw = new PrintWriter(clientOut, true);
// Create an input stream of the client socket
InputStream clientIn = client.getInputStream();
BufferedReader br = new BufferedReader(new InputStreamReader(
clientIn));
// Create BufferedReader for a standard input
BufferedReader stdIn = new BufferedReader(new InputStreamReader(
System.in));
while (isConnected == true) {
System.out
.println("Commands: \n1. TIME\n2. DATE\n3. C2F\n4. MAX\n5. SUM\n6. DLOAD\n7. QUIT");
// Read data from standard input device and write it
// to the output stream of the client socket.
msg = stdIn.readLine().trim();
pw.println(msg);
// Read data from the input stream of the client socket.
if (msg.equalsIgnoreCase("dload")) {
byte[] aByte = new byte[1];
int bytesRead;
ByteArrayOutputStream baos = new ByteArrayOutputStream();
if (clientIn != null) {
try {
FileOutputStream fos = new FileOutputStream("C:\\ftp\\pic.png");
BufferedOutputStream bos = new BufferedOutputStream(fos);
bytesRead = clientIn.read(aByte, 0, aByte.length);
do {
baos.write(aByte, 0, bytesRead);
bytesRead = clientIn.read(aByte);
} while (bytesRead != -1);
bos.write(baos.toByteArray());
bos.flush();
bos.close();
System.out.println("File is successfully downloaded to your selected directory"+ "\n" +"*-----------------*"+ "\n" );
} catch (IOException ex) {
System.out.println("Couldn't dowload the selected file, ERROR CODE "+ex);
}
}
}else{
System.out.println("Message returned from the server = "
+ br.readLine());
}
if (msg.equalsIgnoreCase("bye")) {
pw.close();
br.close();
break;
}
}
} catch (Exception e) {
}
}
}

debugged your code and have two hints:
1)
don't surpress your exceptions. handle them! first step would to print your stacktrace and this question on SO wouldn't ever be opened ;-) debug your code!
2)
outToClient.flush();
outToClient.close(); //is closing the socket implicitly
bis.close();
fis.close();
so in your second call the socket on server-side will already be closed.

first thing:
if (args.length >= 1) {
portnumber = Integer.parseInt(args[0]);
}
This can throw a NumberFormatException, and because args[0] is passed by the user you should handle this.
reading the code also this gave me a problem:
double DoubleValue = Double.parseDouble(value); // LINE 104
Throwing a NumberFormatException when I give c2f as command to the server. You definitively need to handle this exception anywhere in your code and give proper answer to the client, something like:
try{
double DoubleValue = Double.parseDouble(value);
}catch(NumberFormatException e){
// TELL THE CLIENT "ops, the number you inserted is not a valid double numer
}
(in short example, starting from this you have to enlarge the code)
while (isConnected == true) {
I cannot see it! why not use this?
while (isConnected) {
if (msgFromClient != null && msgFromClient.equalsIgnoreCase("sum")){
can be:
if("sum".equalsIgnoreCase(msgFromClient)){
in this case you have no problem with the NullPointerException. (if msgFromClient is null the statement is false).
By the way, date and time command are working fine for me. Check the others.
To fix dload i think you have to delete the line:
outToClient.close();
(EDIT: sorry to maxhax for the same answr, didn't see your answer while writing this)

Java deadlock problem

I am using java sockets for communication. On the client side I have some processing and at this point I send an object to the cient. The code is as follows:
while (true) {
try {
Socket server = new Socket("localhost", 3000);
OutputStream os = server.getOutputStream();
InputStream is = server.getInputStream();
CommMessage commMessage = new CommMessageImpl();
ByteArrayOutputStream bos = new ByteArrayOutputStream();
ObjectOutputStream oos = new ObjectOutputStream(bos);
oos.writeObject(commMessage);
os.write(bos.toByteArray());
os.flush();
byte[] buff = new byte[512];
int bytesRead = 0;
ByteArrayOutputStream receivedObject = new ByteArrayOutputStream();
while ((bytesRead = is.read(buff)) > -1) {
receivedObject.write(buff, 0, bytesRead);
System.out.println(receivedObject);
}
os.close();
Thread.sleep(10000);
} catch (IOException e) {
} catch (InterruptedException e) {
}
}
Next on the server side I have the following code to read the object and write the response (Which is just an echo message)
public void startServer() {
Socket client = null;
try {
server = new ServerSocket(3000);
logger.log(Level.INFO, "Waiting for connections.");
client = server.accept();
logger.log(Level.INFO, "Accepted a connection from: " + client.getInetAddress());
os = new ObjectOutputStream(client.getOutputStream());
is = new ObjectInputStream(client.getInputStream());
// Read contents of the stream and store it into a byte array.
byte[] buff = new byte[512];
int bytesRead = 0;
ByteArrayOutputStream receivedObject = new ByteArrayOutputStream();
while ((bytesRead = is.read(buff)) > -1) {
receivedObject.write(buff, 0, bytesRead);
}
// Check if received stream is CommMessage or not contents.
CommMessage commMessage = getCommMessage(receivedObject);
if (commMessage != null) {
commMessage.setSessionState(this.sessionManager.getState().getState());
ByteArrayOutputStream bos = new ByteArrayOutputStream();
ObjectOutputStream oos = new ObjectOutputStream(bos);
oos.writeObject(commMessage);
os.write(bos.toByteArray());
System.out.println(commMessage.getCommMessageType());
} else {
processData(receivedObject, this.sessionManager);
}
os.flush();
} catch (IOException e) {
} finally {
try {
is.close();
os.close();
client.close();
server.close();
} catch (IOException e) {
}
}
}
The above code works ok if I do not try to read data on the client side (If i exclude the code related to reading). But if I have that code, for some reason, I get some kind of deadlock when accessing input streams. Any ideas what I might have done wrong? Thanks in advance.

Both client and server are attempting to read the whole input stream (i.e. everything up to EOF) but neither is sending an EOF (by calling shutdownOutput() on the socket.)
Why do you need to store the object data temporarily in a ByteArrayOutputStream? This would probably be easier to fix if you read directly from the socket input stream.