DataOutputStream不发送-1

Question

I'm trying to make a sending option for a chat client and I was able to do it for small files but then I got a problem when I tried to do it with big ones. The way I tried to solve it was: Client side,read from file and send:

while ((buf = bin.read(bytearray, 0, bytearray.length)) != -1) {
     os.write(bytearray,0,bytearray.length);
}
bin.close();

"bin" is my bufferedInputStream from a fileInputStream, "buf" is just an integer, os is my DataOutputStream. Server side, receive and send:

while ((buf = in.read(bytes, 0, bytes.length)) != -1) {
dos.write(bytes,0,bytes.length);
}

"in" is the DataInputStream, "buf" is an integer, "dos" is a DataOutputStream(it does this for all clients) Client side, receive file from server and write to hard drive:

int buf;
while ((buf = in.read(bytes, 0, bytes.length)) != -1) {
     fos.write(bytes,0,bytes.length);
}
fos.close();

Here "in" is a DataInputStream, "fos" is a FileOutputStream. What happens is that when I hit the send button on first client, both the server and the client start receiving the file, but it gets received only when I close the second client(receiver) because that's when the socket closes and probably that's when it actually decides to stop receiving and finish writing the file. Please tell me why it doesn't receive that "-1" when the sending executes once and the dataInputStream should be empty in the server and therefore cause that "-1"?

Answer 1

DataOutputStream never sends -1. The underlying transport signals an EOS to the peer when you close the output stream, and that is returned by the read() API as -1 when encountered. There is no -1 on the wire. If you don't close the output stream, you won't receive the -1.

If you want the reader to stop reading without closing the output stream, you will have to tell it somehow as part of your application protocol: for example, send a length word ahead of the data, and have the reader read exactly that many bytes.