Reading a C# byte array in Java

Question

I'm transferring a file from a C# client to a Java server using TCP Sockets. On the C# client I convert the file to a byte array for transmission and send it using a NetworkStream.

On the Java server I use the following code to convert the received byte array back into a file;

public void run()  {

       try {

            byte[] byteArrayJAR = new byte[filesize];
            InputStream input = socket.getInputStream();

            FileOutputStream fos = new FileOutputStream(
                    "Controller " + controllerNumber + ".jar");

            BufferedOutputStream output = new BufferedOutputStream(fos);

            int bytesRead = input.read(byteArrayJAR, 0, byteArrayJAR.length);
            int currentByte = bytesRead;

            System.out.println("BytesRead = " + bytesRead);

            do {

                bytesRead = input.read(
                        byteArrayJAR,
                        currentByte,
                        (byteArrayJAR.length - currentByte));

                if (bytesRead >= 0) {

                    currentByte += bytesRead;

                }
            }

            while (bytesRead > -1);

            output.write(byteArrayJAR, 0, currentByte);
            output.flush();
            output.close();
            socket.close();

        }

        catch (IOException e) {

            e.printStackTrace();

        }
}

The code above works if the received byte array comes from a client programmed with Java but for C# clients the code hangs in the do-while loop at the bytesRead = input.read(...) method.

Does anybody know why the code is hanging at this point for a C# client but not a Java client? According to the output from the println message data is definately being received by the InputStream and is read once at the bytesRead variable initialization, but not during the do-while loop.

Any solutions or suggestions for overcoming this problem would be welcome.

Regards,

Midavi.

If filesize is not smaller or equal to the data effectively sent, read() will block. You should never try to guess the size of the data you are going to receive, you must keep reading until the stream is empty. — Viruzzo
– Viruzzo, Commented Jan 18, 2012 at 16:55

Charles Lambert · Accepted Answer · 2012-01-18 19:21:54Z

1

You need to send your bytes as sbyte from c# instead of byte.

In addition you should change your do/while loop to a regular while loop. If you have already read everything from the stream in your first call to input.read then you will block on the second call because read will wait for input.

edited Jan 18, 2012 at 19:21

answered Jan 18, 2012 at 17:28

Charles Lambert

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3 Comments

user7116 Over a year ago

That shouldn't cause it to hang, but may be a problem at some point.

Charles Lambert Over a year ago

until you fix that problem, you aren't going to be able to reliably solve any other problems due to the binary data being wrong.

user7116 Over a year ago

A signed byte is the same width as an unsigned byte, therefore, the difference in representation is not going to effect reading from the socket. The OP's current problem lies elsewhere.

endofsource · Accepted Answer · 2012-01-18 17:14:10Z

0

Based on: http://docs.oracle.com/javase/1.4.2/docs/api/java/io/InputStream.html

 int bytesRead = input.read(byteArrayJAR, 0, byteArrayJAR.length);

Reads all available bytes that means your byte-data is alread in byteArrayJAR or am I completly wrong here?

EDIT:

Just checked some of my projects...I send data from Android <=> C# Server Application.

I use String data = input.readLine();(java) and _sw.WriteLine("Testdata");(C#)

edited Jan 18, 2012 at 17:14

answered Jan 18, 2012 at 16:56

endofsource

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1 Comment

midavi Over a year ago

That is what I believe too. As far as I'm aware if the file being sent is rather large more bytes may become available after bytesRead is initialized. The do-while loop is there to make sure the entire byte array is read before being reconstructed into a file. Or do I have this wrong?

user7116 · Accepted Answer · 2012-01-18 19:42:20Z

Since you cannot know the amount of data being sent in advance in the general case, it would be better to receive the data in chunks and ignore the offset into your bigger array. Your code as-is doesn't handle the case very well if the data is larger than your array, nor if it is smaller than the array.

A much simpler case would be to remove the currentByte offset:

InputStream input = socket.getInputStream();
BufferedOutputStream output = new BufferedOutputStream(
    new FileOutputStream("test.exe"));

byte[] bytes = new byte[2048];
int bytesRead;
do {
    bytesRead = input.read(bytes, 0, bytes.length);
    System.out.println("size: " + bytes.length + " read(): " + bytesRead);

    if (bytesRead > 0) {
        output.write(bytes, 0, bytesRead);
    }
} while (bytesRead > -1);

output.close();
socket.close();
input.close();

And I used the following C# code on the client side:

if (!args.Any())
{
    Console.Error.WriteLine("Usage: send.exe <executable>");
    Environment.Exit(-1);
}

using (var client = new TcpClient("localhost", 10101))
using (var file = File.Open(args.First(), FileMode.Open, FileAccess.Read))
{
    file.CopyTo(client.GetStream());
}

Client side results:

C:\temp>csc send.cs
Microsoft (R) Visual C# 2010 Compiler version 4.0.30319.1
Copyright (C) Microsoft Corporation. All rights reserved.


C:\temp>send send.exe

C:\temp>

Server side results:

C:\temp>javac.exe Server.java

C:\temp>java Server
size: 2048 read(): 2048
size: 2048 read(): 2048
size: 2048 read(): 512
size: 2048 read(): -1

C:\temp>test.exe
Usage: send.exe <executable>

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