Bug with InputStream.read after BufferedReader.readLine in a Thread ?

Question

I just found something strange when reading bytes on a socket after reading lines.
I'll show you an example :
In this example, when a connexion is established, I launch a thread where a single line of String then 3 bytes are read from the socket. I use BufferedReader.readLine for the String line then just InputStream.read to read the 3 bytes.
The results are quite random. Sometimes it works, sometimes not (most times it doesn't)... it seems to always work under linux (but haven't tested it as many times than on windows). Most of the time the program is stuck on the "socket.getInputStream().read(bytes);" line with 0 bytes available. I tried to do the same thing outside of a thread, I thought it worked better beaucause I was able to run it without any problem but it doesn't work anymore when I test it again.
I can't say if I'm doing something wrong or if it's a java bug (I've got JDK 1.6.0_03-b05).
Can you please have a look a this little example and maybe test it and let me know if it works or not. I tried to code my own readLine function and it seems to work with it but I'd like to know if it's a bug or what. Thank you.
Server side :
import java.io.*;
import java.net.*;
public class testServer extends Thread {
     private Socket socket;
     public testServer(Socket testSocket)
          socket = testSocket;
     public void readData() throws Exception
          BufferedReader br = new BufferedReader(new InputStreamReader(socket.getInputStream()));
          String str;
          str = br.readLine();
          System.out.println(str);
          System.out.println("Bytes available : " + socket.getInputStream().available());
                //Try to read the bytes
                byte[] bytes = new byte[3];
                //STOPS THERE UNDER WINDOWS, BUT WORKS WITH LINUX
          socket.getInputStream().read(bytes);
                //Simple "ack" to say to the client that he can close the connexion
          socket.getOutputStream().write(0);
          socket.getOutputStream().flush();
                //Print the bytes values
          for(byte value : bytes)
               System.out.println(value);
     public void run()
          try {
               readData();
          } catch (Exception e) {
               e.printStackTrace();
     public static void main(String[] args) {
          try {
               ServerSocket welcomeSocket = new ServerSocket(3333);
               while(true)
                    new testServer(welcomeSocket.accept()).start();
          } catch (Exception e) {
               e.printStackTrace();
}client side :
import java.io.*;
import java.net.*;
public class testClient {
     public static void main(String[] args) {
          try {
                        //Some test values
               byte[] testValues = new byte[]{1,2,3};
               Socket socket = new Socket(InetAddress.getLocalHost(), 3333);
                        //Send the line through the socket
               BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream()));
               bw.write("HELLO WORLD\r\n");
               bw.flush();
                        //then the bytes
               socket.getOutputStream().write(testValues);
               socket.getOutputStream().flush();
                        //Just waits for the server's ack to close the connexion
               socket.getInputStream().read();
               socket.close();
          } catch (Exception e) {
               e.printStackTrace();
}

Answer 1

It's your bug.
When you create a BufferedReader and ask it to read a line, the first thing it does is to read a whole buffer full of data (hence the name of the class) from its underlying input stream. That's probably about 4000 characters or something like that. It stores that internally and then starts doling it out in response to calls to readLine() and so on.
Then when you go back to reading from the underlying input stream, those 4000 or so characters are already gone from it. You have no access to the data the BufferedReader is hanging on to this way. All you can do is to start reading at the point after that whole buffer, which is not what you want.