What would be some things to keep in mind about programming a file sharing program. (peer 2 peer)

Not bringing down the Internet when more than a few people start using it.

And try to avoid getting sued by RIAA (also "when more than a few people start using it") :)

Make sure everything on it is labeled properly. I hate downloading a game of Kaaza and it being something completely different, I DL'd MOHAA and it turned out to be NFS5 (which I already had)

That label-thing is because of stupid users (can't avoid these) I've noticed downloads on Kazaa in which the contents, its description and title were completely different.

CodeRed: Downloading games? You know that's illegale. If you keep doing that then those designers won't be able to buy their 3th Ferrari (not to mention those trips to Hawaii aren't free either).

RedX

I never said they were fullversion, for all you know I was talking about demos

Right, I'll pretend to believe that. ;-)

RedX

Well you have to think about protocols and mechanisms to maintain file integrity (think MD5, CRC, etc...)Another thing you must look at is lag reduction. This is actually a big topic and there are some resources on that here: http://www.gamedev.net/reference/list.asp?categoryid=30, Although they are for game servers they might give you important insight on handling lag in your p2p program.

Authentication, Scalibility of your server, Protocol design, and many other things are things you should look at before you make your p2p program.

I don't think lag is that big of a problem in a file sharing program. If a node gets too lagged then searches to it will time out and it will be removed from the network anyway. As long as the search goes through...

It really depends on what your file sharing program will be doing, how you'll design it, &c before we can give you too many helpful suggestions. From the start, you should comment your code well, and design it such there there is an open and accessible API for other programmers to extent and embed your file sharing system. That is the key. Start with that assumption, and then ask us more questions as you move on. :)

probably the most important things in a p2p are stability and compatablity. Crossplatform means more users, and stability means more loyal users. Be sure to handle EVERY possible thing that may go wrong with the connections, and be sure to let the user know specific errors when handling exceptions rather than saying 'network problems' for every error. That's all I can think to add.

I known something you shouldn't add: a program that opens a popup windows full of crapp-banners every houre (like Kazaa). There is no excuse for this and such actions will never be forgiven. "Thou shalt not included banner-window opening programs in thy setup program" as written in the Bible.

RedX

Also, don't include any spyware, like Kazaa. Not only are we forced to install Cydoor and Bonzi Buddy (which keep track of your every move), there is also the sneaky B3d program, which is the client for 'alt-net'. Thus, every time you connect to Kazaa, you unwittingly become a node on the decentralised alt-net network, thus stealing bandwidth and CPU cycles!!

Please people, use Kazaa-lite (www.kazaalite.com). It's Kazaa, but with all the spyware hacked out of it. And run Ad-Aware (www.ad-aware.com), to get rid of all that nasty ad/spy ware.

Those who include spyware should be punished by glueing their hands to the back of their head. Then apply something itching.

RedX