Frequently Asked Questions

Homework 5 Protocol corrections/questions

• September 25, 2001 - Download new Frame.java version. Old version generated timeout even though start_timer not called. Affected Protocol 1.
• September 27, 2001 - Download new sender3.java version. Old version started timer on send frame:
 

s.start_timer(r.seq); event = r.wait_for_event();

but should be started on receive frame
 

r.start_timer(r.seq); event = r.wait_for_event();

 Result that timeout event always occurred on send  frame s though frame_arrival event occurred on receive frame r.
• September 28, 2001 - Download new Frame.java version. Old version did not force the loss of frames. Affected Protocol 1.
• September 28, 2001 - Thanks to Ed Harlan who is able and willing to answer Java questions about the assignment over the weekend. Click here to send Ed email.

• October 23, 2001

Input - InputStream in = sc.getInputStream(); int c = in.read(); reads an integer (which could be cast to a character, etc.) from the connection on socket sc.

Often simplest to use buffered input. BufferedReader class for input supports input of a complete string or individual characters and has the following useful characteristics:

• It can read any InputStream so can read either the keyboard or a socket.

 public String readLine() throws IOException

     Read a line of text. A line is considered to be terminated by any one of a line feed ('\n'), a carriage return ('\r'), or a
     carriage return followed immediately by a linefeed.

     Returns:
          A String containing the contents of the line, not including any line-termination characters, or null if the end of
          the stream has been reached

• in.readLine() returns the string preceeding the carriage return on the in object. Note that the input stream must contain a carriage retrun before readLine() returns.
• Returns null when nothing on the input stream such as when the input stream socket has been closed. The following server-side connection reads the socket input stream until either:
• the socket is closed - in.readLine( ) == null
• or a blank line - from.equals("");

Socket s = connection.accept();                 // Wait for connection BufferedReader in = new BufferedReader(         // Socket input                          new InputStreamReader( s.getInputStream() ) );   while( (from=in.readLine()) != null && !from.equals("")) {    System.out.println( from ); }