Develop Reference

IOUtils copy and write issues

I'm trying to send strings to a server from a client but it doesn't seem to be reading from the input stream.
Client
Scanner scanner = new Scanner(System.in);
Socket connection = new Socket("localhost", 13)
OutputStream out = connection.getOutputStream();
while(true) {
String message = scanner.nextLine();
IOUtils.write(message, out, "UTF-8");
out.flush();
}
Server
ServerSocket server = new ServerSocket(localhost,13);~
Socket connection = server.accept();
InputStream in = connection.getInputStream();
StringWriter writer = new StringWriter();
while(true) {
try {
IOUtils.copy(in, writer);
System.out.println(writer.toString());
} catch(IOException io) {}
}
It reads if I close the stream from the client's outputstream but I am trying to send multiple messages from the client to the server. Could someone please help

You seem to think that each time you call flush() at client-side, the server will know it and be able to know that this is the end of a message. That's not the case. IOUtils.copy() reads everything from a stream of bytes. While the stream end hasn't been reached, copy() won't return.
You can see streams as two sides of a long tube. If you pour 10 buckets of water in the at the end of the tube, all you'll get at the other side is a continuous flow of water.
If you need multiple separate messages, then you need to design a protocol allowing to separate messages, and read until the end of a message has been reached. It could be based on separators for example. Or you could send the length of the message followed by the message itself, to let the server know how many bytes it must read to get the next message.

File transfer and object serialization in Java

Im working on a Client/server chat application which allows user to send files (images / videos...) through a socket connection.
In order to manage all kind of communication, I use an Object "Packet" which stores all information that I want to send. (Sender, receivers, file ...).
Here is a code sample where I write in the stream :
private void write(Packet packet) throws IOException {
ByteArrayOutputStream bos = new ByteArrayOutputStream();
ObjectOutputStream os = new ObjectOutputStream(bos);
os.writeObject(packet);
this.outStream.write(bos.toByteArray());
}
And outStream is an OutputStream.
Here is my Connection run :
public void run() {
while (isRunning()) {
try {
byte[] buffer = new byte[65536];
// Read from the InputStream
inStream.read(buffer);
ObjectInputStream in = new ObjectInputStream(new ByteArrayInputStream(buffer));
Packet p = (Packet) in.readObject();
} catch (IOException e) {
e.printStackTrace();
this.disconnect();
}
}
}
It works very well for all purpose except files transfer !
I put the file in a byte[] (with filestream) and store the array in my Packet Object.
When the server receive the communication it breaks on the "in.readObject()" and give me a pretty "java io streamcorruptedexception wrong format : 0" exception.
I tried the transfer with a custom byte[] (filled by a string.getBytes()) and it worked very well.
So, what am I doing wrong ?

You're reading from the InputStream to a byte array (with an arbitrary size which could be too small). Then you construct an ObjectInputStream to read from this byte array. Why don't you read your object directly from the InputStream?
ObjectInputStream in = new ObjectInputStream(inStream);
Packet p = (Packet) in.readObject();
No need for a buffer.
Moreover, InputStream.read() doesn't read everything from the InputStream. It reads what is available, and returns the number of bytes read. If you don't loop until it returns -1, you only read a part of what has been sent on the other side.
BTW, you're doing the same mistake on the sending side. Instead of writing your object directly to the output stream, you write it to a byte array, adn then send this byte array. Write your object directly to the stream:
ObjectOutputStream os = new ObjectOutputStream(this.outputStream);
os.writeObject(packet);
No need for a buffer.

how to stream jpeg frame from java client to python server

i am developing an android application wherein i have to send a frame in jpeg format allocated to a BufferedArrayOutputStream (baos variable in code). I convert this baos into a byte array to write into the socket.
On the server side i would like to reconstruct the image in jpeg format. If i write the data received in a variable to a '.jpg' file on the server, on opening the file, it gives an error like "file starting with ffx0 not jpeg format". I think this is because the string variable in python writes the data in the file as a hex string.
The client code is as follows :-
Bitmap memoryImage = Bitmap.createBitmap(rgb, previewSize.width,previewSize.height,Bitmap.Config.ARGB_8888);
ByteArrayOutputStream baos = new ByteArrayOutputStream();
if(memoryImage.compress(CompressFormat.JPEG,100, baos)){
try {
if(count==0){
byte [] Finalbaos = baos.toByteArray();
int tempLen = Finalbaos.length;
Log.v("Client","ImageBytes :"+ tempLen);
String dataMeta = Integer.toString(tempLen);
Log.v("Client","Integer Size :"+ dataMeta.length());
PrintWriter tempOut = new PrintWriter(socket.getOutputStream());
if(tempOut!=null){
tempOut.write(dataMeta);
Log.v("Client","data size sent");
tempOut.flush();
}
DataInputStream in = new DataInputStream(socket.getInputStream());
if(in!=null){
Log.v("Client","read buffer created");
String xyz = in.readLine();
String temp = "recvd";
Log.v("Client",xyz);
if(xyz.equals(temp)){
OutputStream out = socket.getOutputStream();
out.write(Finalbaos,0,tempLen);
out.flush();
Log.d("Client", "Client sent message");
}
}
server code:
import socket,thread
import string
import array
host=""
port=54321
s=socket.socket()
s.setsockopt(socket.SOL_SOCKET,socket.SO_REUSEADDR,1)
s.bind((host,port))
s.listen(5)
conn,address=s.accept()
data=""
mylen=0
dataRecv=0
file1 = open("myfile.jpg","w")
totalLength=""
length=conn.recv(1024)
conn.send("recvd")
mylen=int(length)
while dataRecv<mylen:
newData=""
newData=conn.recv(1)
if not newData:
break
data+=newData
dataRecv+=len(newData)
result= array.array('B',data.decode("hex"))
file1.write(result)
file1.close()
print len(data)
conn.close()
s.close()
can anyone let me know how to reconstruct the frame on server either in python or C++

mylen=len(length) doesn't give you the length you're trying to send. it gives you how many bytes were read in the previsous recv. So you get the wrong lenght there.
on your client side, you use String xyz = in.readLine(); which will block until a newline character is encountered. but you never send a '\n' on the server side, instead you go waiting for a response from the client. so you have a deadlock there.
you use data.decode("hex") on your recieved data. unless you do the equivalend of data.encode("hex") in java on the other side, that won't work. it should give you an error if the string is not a valid hex-representation of a binary string.
result is an array.array, which you write to file. file1.write expects a string as argument, it gives you an error if you pass your result object.
so i can't even see why your code works at all, and why there's anything at all in your file.

Getting end of Inputstream in java

following is my client side code , that retrieves text from server and prints.
Socket socket = new Socket(ip, port);
InputStream in = socket.getInputStream();
OutputStream out = socket.getOutputStream();
String string = "Hello!\n";
byte buffer[] = string.getBytes();
out.write(buffer);
while ((character = in.read()) != -1){
System.out.print((char) character);
}
I am getting the the correct values from the server , but it is happening again and again , how can i find out the length of the value sent.

-1 denotes the end of the stream, and is received when the connection is closed. If you want to keep the connection open and send multiple messages, you need some sort of protocol (kind of like agreement between both ends) that tells where the message ends. The are many ways to do this, but in your example you're writing a line terminator (\n) to the end of the message, so you could check for that at the other end. Another way is to write the amount of bytes you're about to send before the actual message contents.

How can I make sure my server reads what the client has written?

I am writing a byte array from a socket client as:
byte[] arr = { 49, 49, 49, 49, 49};
InetAddress address = InetAddress.getByName(host);
connection = new Socket(address, port);
out = new ObjectOutputStream(connection.getOutputStream());
out.flush();
At receiving end, on the server I have:
byte[] msgType = new byte[5];
in = new BufferedInputStream(connection.getInputStream());
int bytesRead = in.read(msgType, 0, 5);
System.out.println("msg rcvd: " + msgType.toString());
In the output I get weird string:
server: waiting for connection
server: connection received from localhost
server: Connection Successful
bytes read: 5
msg rcvd: ��w
How can make sure I get same bytes as I sent from my client?

I'm not sure exactly what are trying to print out, but I can tell you that msgType.toString() will not print the contents of the byte array.
Here is a link I found to a method which will print out the byte array in a more meaningful fashion.

You're getting the same bytes, it's just a matter of how you interpret them. If you want to see the bytes as a String use this instead:
System.out.println("msg rcvd: " + new String(msgType, "UTF-8"));
Be careful that the bytes you're dealing have the right encoding though (I assumed UTF-8 here). Since you're already ObjectOutputStream though, you could just use its writeUTF() on the server side and ObjectInputStream.readUTF() on the client side.

If you use an ObjectOutputStream on one side, you'll have to use an ObjectInputStream at the other side.
In your case, a simple OutputStream (maybe buffered) and .write() and .read() will do.
But for printing, don't use byte[].toString(), use Arrays.toString() if you want to have a formatted output.
Edit: I just see you are not even writing your array on the sending side. So you are actually only reading the ObjectOutputStream header.
From the comment:
I am handling server side and I am told that I would be send a byte array. How
do I receive and print that byte array ? byte array in this case is bytes of text/strings
This sounds like the server sends something like simply the Strings encoded in some encoding, like ASCII, UTF-8 or ISO-8859-1. If so, on the receiving end you can use something like this:
String encoding = "UTF-8";
BufferedReader in =
new BufferedReader(new InputStreamReader(connection.getInputStream(),
encoding));
String line;
while((line = in.readLine()) != null) {
System.out.println(line);
}
Of course, make sure the encoding is the same encoding as actually used on the sending side.
The corresponding sending code could be something like this:
String encoding = "UTF-8";
Writer w =
new BufferedWriter(new OutputStreamWriter(connection.getOutputStream(),
encoding));
w.write("Hello World!\n");
w.write("And another line.\n");
w.flush();