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java-udp-motd-server's Introduction

udp-motd-server

An experimental MOTD server over UDP with a UDP version of TCP handshake mechanism.

Try it on your machine

  1. Clone the repository
  2. Run javac *.java
  3. Open a new terminal session (or TMUX) and run java MOTDServer
  4. Run java MOTDClient to see the communication

Expected result

$ java MOTDServer
MOTDServer: Ready to connect.
Handshake: Waiting
Handshake: Complete
MOTDServer: Starting to send MOTD.
MOTDServer: Ready to connect.
Handshake: Waiting

$ java MOTDClient
Client: MOTD -> Good day. It has been 86400000s since the server started.

Protocol

The MOTD server and a MOTD Client communicate with this packet format.

A protocol for the MOTD server.
This protocol establishes a connection over UDP and
sends packets of data in 16 byte blocks.

---------------------------
| t | s | data            |
---------------------------

t = 1 byte. type of the transmission
  public static byte FLAG_TYPE_SYN = 0b01;
  public static byte FLAG_TYPE_ACK = 0b10;
  public static byte FLAG_TYPE_SYNACK = (byte) (FLAG_TYPE_SYN | FLAG_TYPE_ACK) = 0b11;
  public static byte FLAG_TYPE_REQUEST = 0b100;
  public static byte FLAG_TYPE_DATA = 0b1000;
  public static byte FLAG_TYPE_FIN = 0b10000;
s = 1 byte. sequence number. Can be 1 or 0
data = 16 bytes.

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