BitTorrent Framework

Background BT is a very popular peer to peer protocol with many implementations: – Torrent_clientshttp://en.wikipedia.org/wiki/Comparison_of_Bit Torrent_clients The first one was created in Python by Bram Cohen.

Workshop goal Exploit BitTorrent protocol to give less for more. Real world motivation –Places with low upload (Africa, China) –Bad character

How do I test my idea Create my own (or modified) BitTorrent client. Run together: –“The World”: N “standard” BitTorrent Clients. Specific upload rate Various download stages –My Client See how much time my client ran, and what was its upload / download ratio.

Execution example run-all.sh Tracker BT

How does it work? Run tracker Run the “world” Run your client (if given)

How does it work? Both tracker and the “world” run on the same computer we have –pc-hanoch-w1 –pc-hanoch-w2 –Please reserve time in: Or from course www - "Scheduling computers for tests."

The main script - run_all.sh Location: –/users/courses/hanochworkshop/bittorrent Run_all.sh: –Parameters: Start / stop My client – optional

run_all.sh operation Start: –Create download directory –Run the “world” Each world client starts with different “saved” amount. –Run “my client” – if given –All uploads rates are restricted. Stop –Kill all python threads

To run client separately: BitTornado-My-Client/btdownloadheadless.py –--saveas /vol/scratch/bt-download/picture.tst.bmp –--max_upload_rate 70 –--security 0 –./picture.pc-hanoch-w[1,2].bmp.torrent Not necessarily on the same machine as the world.

What implementation we use The clients are a modified version based on an up to date version of Bram Python Client. Modifications: –“World” clients do not print as it would only make a mess reincarnate after the finish to make a real world feel. –“My Client” template – kills all clients when finished –All clients – print total time

Python Very common script language Intuitive and readable References: –python.org : – – The book "Think like a Computer Scientist in Python" has a very good reputation:

My Client We supply a default “My Client” which is like the “standard” one. If you want you may replace it with any other implementation, with certain reservations: –Remember we compare to our client. –It does not count to download a faster client than our client and simply say it is faster. –Client should either limit it’s upload rate, or be able to work with trickle.

Getting started Run the environment –ssh pc-hanoch-w[1,2] –cd /users/courses/hanochworkshop/bittorrent –run_all.sh start [BitTornado-My-Client/btdownloadheadless.py] –Note tracker prints a message for each GET. You can connect to the tracker with a browser at: – Do ls -l /vol/scratch/bt-download/ to see downloaded files

What is it doing? Run bttrack. Copy From FreshFiles a set of “downloaded” files to download directory. Run X seeds Run a python client per “downloaded” file. Run my client if given

For debug: run client separately./run_all.sh start to start the world BitTornado-My-Client/btdownloadheadless.py –--saveas /vol/scratch/bt-download/picture.tst.bmp –--max_upload_rate 70 –--security 0 –./picture.pc-hanoch-w[1,2].bmp.torrent Start debug. Use your favorite debug environment. IDLE is standard source level debugger.

Directory Structure BitTornado-My-Client – –high level application BitTornado-My-Client/BitTornado – –services BitTornado-My-Client/BitTornado/BT1 – –Actual work

Client Operation btdownloadheadless.py – First to run. –Performs initializations. get_response – parse the.torrent Infohash – the ID of the.torrent startEngine – Start connection with peers startRerequester - Start connection with tracker –Run rawserver.listen_forever from RawServer.py. –listen_forever is: Polling port executing func() from a task queue.

Receiving messages From listen_forever loop it goes to: –BT1/Connecter.py/got_message CHOKE UNCHOKE INTERESTED NOT_INTERESTED BITFIELD REQUEST CANCEL PIECE HAVE

Influencing decisions Can be done in in one of the callbacks which spring from Connecter.py / got_message: Downloader.py –HAVE->got_have->send_interested maybe check connection before sending?

BT tracker Send GET request in Rerequester.py / announce Receive GET data in thread in Rerequester.py / _rerequest

Influencing decisions In Encrypter.py / start_connection or _start_connection_from_queue For instance try different max_connections. _rerequest_single – check timout for scheduling.

Policy Choker.py/_round_robin – decide who to choke / optimistically un choke / send_have to. Downloader.py / _request_more. PiecePicker.py / next - rarest piece, etc. got_unchoke->_request_more->next…