DataOutputStream.writeBytes adds zero-bytes

Question

I have a small TCP server program and a corresponding client, and they communicate via ServerSocket and Socket classes and DataInputStream/DataOutputStream. And I have a problem with sending Strings to the server.

connection = new Socket("localhost", 2233);

outStream = new DataOutputStream(connection.getOutputStream());

outStream.writeBytes(fileName);

fileName is, at this point in time, a hard-coded String with the value "listener.jardesc". The server reads the string with the following code:

inStream = new DataInputStream(connection.getInputStream());

String fileName = inStream.readLine();

The string is received properly, but three zero-value bytes have been added to the end. Why is that and how can I stop it from happening? (I could, of course, trim the received string or somehow else stop this problem from mattering, but I'd rather prevent the problem completely)

Answer 1

I'm just going to throw this out there. You're using the readLine() method which has been deprecated in Java 5, 6 & 7. The API docs state quite clearly that this method "does not properly convert bytes to characters". I would read it as bytes or use a Buffered Reader.

http://docs.oracle.com/javase/1.5.0/docs/api/java/io/DataInputStream.html#readLine%28%29

Answer 2

writeBytes() does not add extra bytes.

The code you've written is invalid, as you aren't writing a newline. Therefore it doesn't work, and blocks forever in readLine().

In trying to debug this you appear to have read the bytes some other way, probably with read(); and to have ignored the return value returned by read, and to have concluded that read() filled the buffer you provided, when it didn't, leaving three bytes in their initial state, which is zero.