Question

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 ?

Answer 1

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.