java nio socketChannel.write() missing bytes

Question

System.out.println(" @ bBuffer = " + bBuffer.capacity());

headerBuffer.rewind();
socketChannel.write(headerBuffer);

int writen = socketChannel.write(bBuffer);
System.out.println(" @ writen = " + writen);

bBuffer is an object of type ByteBuffer and it came from FileChannel.map() (it's an image file). When I receive this image file on client, it wasn't a complete image--about half of image was missing. So I checked how much bytes was written by printing some statistics to the console. The output was:

 @ bBuffer = 319932
 @ writen = 131071

What happened to the rest of the bytes? It seems that (319923 - 131071) bytes are missing.

Sometimes written is equals to bBuffer.capacity() and it's seems irrespective to file size or buffer capacity.

Answer 1

Your code makes an invalid assumption. read() and write() aren't obliged to transfer more than one byte per call. You have to loop. But you're doing this wrong anyway. It should be:

while (headerBuffer.position() > 0)
{
    headerBuffer.flip();
    socketChannel.write(headerBuffer);
    headerBuffer.compact();
}

or

headerBuffer.flip();
while (headerBuffer.hasRemaining())
{
    socketChannel.write(headerBuffer);
}
headerBuffer.compact();

If the SocketChannel is in non-blocking mode, it gets considerably more complex, but you haven't mentioned that in your question.

You also need to check your receiving code for the same assumption.