Fish for ducks v1.0
(multicast version)

This is the result of the third part of my assignment in the course 2G1118 Network Programming in Java at KTH. The task was to develop a multicast File Sharing program (FiSh) to be run over internet and by using Sun Java platform for coding. There may be restrictions on multicast traffic in routers, and therfor the program may only work on LAN under some circumstances.
   The server has been removed and all clients holds it owns list of files they want share. To send search request, the clients connects to the same multicast group and use UDP to send the messages. The users can use multiple keywords to search for files. On matches, the results are returned in UDP packets directly to the requester from the other clients after a random delay to not flood the network so packets with results get lost. The results is then presented to the user who then can choose which files he/she wants to download. The download is then established directly with the users client holding the desired file. On disconnection the client sends a leave message to the multicast group and stops listening for requests.

Hardware Information
The client has been developed and tested on Intel-platforms under Windows XP and Red Hat Linux 7.2 (kernel 2.4.9-31). Java's platform independence should make the program run on many many more platforms that hasn't been tested yet.

Java Software Information
The whole program has been developed by using the editor GNU Emacs 21.1.1 with extended java support by JDEE. The official release of Java 2 platform, Standard Edition v1.4.0 with its tools has been used for development. But the programs are tested and proven compatible with v1.3.1.

Implementation
The client
There aren't many changes in the GUI of the client compared to the centralized server version, and the functionality is also very similar. In this version the centralized server has been removed and a multicast group is used for sending searchrequests with the UDP protocol. A separate thread has been added to listen for requests on the specified group, and perform the search of the locally shared files. The results, if any, are then sent back to the client asking using connectionless communication with the UDP protocol. To not flood the network with results on requests, there is a random delay between 0 and 8 seconds before transmission of results begin. The client will stop reciveiving results when it got 100 results or 10 seconds has passed. During the search no other search is allowed to be issued by the client. The threads handling downloads, and uploads had not been modified from the centralized server version.

Security
When sharing subdirectories there must be a way to tell exactly which file the user want to download, especially if there is several files with the same name. Any absolute or relative way to address the file could be a risc if there are bugs in the code or JVM. To avoid that I have choosen to implement a local vector at the client holding information of all shared files. When sending the list of shared files to the server, only the filename (no path included), the filesize and the index in the vector are sent to the server. Index and filename are then used when another client wants to download a file. The index is used to pick out a record from the local vector, and the filenames are compared. If there is a match, information from the local vector is used to choose file and start the download to the requesting client. Therefor only files in the vector can be downloaded, and the local client is the only one that can access the vector.

Download

Getting started
To start the precompiled version of the Client use:

Source Code
Client:

Documentation

Contact information
Any comments, suggestions and repports of bugs are welcome.
Send a mail to me at: e98_bbe@e.kth.se

(c) 2002 Björn Bertilsson e98_bbe@e.kth.se