BitTorrent on iOS
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This document discusses using BitTorrent on iOS. It provides an overview of BitTorrent, including its history, usage statistics, and technical details. It then discusses challenges with using BitTorrent on iOS and potential solutions, including using the libtorrent C++ library. It covers how to build and configure libtorrent for iOS, and how to interface it with Swift. It also describes how to implement an event loop to fetch torrent updates and progress. Some caveats mentioned are the need for fine-tuning to avoid heavy battery usage and lack of background session support on iOS.
BitTorrent on iOS
- 1. BitTorrent on iOS Michael Caylus / Simone Civetta 12/01/2017
- 3. Quiz
- 4. ‘How many of you need to sync large quantity of files periodically?’
- 5. BitTorrent
- 8. Designed: April 2001 First released: July 2001 Bram Cohen A Peer-To-Peer Protocol #1 usage: Sharing Large Media Files
- 9. 170M active users* 40% of all Internet traffic** 10 popular clients uTorrent, Xunlei, Transmission, Vuze, qBittorent, Deluge, BitComet and Tixatit * Wikipedia CompaniesPiracy ** BitTorrent Inc.
- 10. Facilitates transfer of large/multiple files Works on unreliable network connections Downloads can be resumed any time ✔ ✔ ✔
- 11. In Detail
- 12. Basics Files are shared among the users Files to be shared are split in multiple chunks Peers contribute
- 13. Torrent (metadata) Pieces / Segment Swarm Peers / Leechers Seeds Trackers Stakeholders
- 14. Metainfo file (bencoded dictionary) Torrent File ANNOUNCE Announce URL of the tracker PIECE LENGTH INFO Dictionary describing the files’ chunks PIECES (20-byte SHA1 Hash Values) LENGTH NAME PIECE LENGTH PIECES (20-byte SHA1 Hash Values) NAME FILES LENGTH PATH
- 15. Always-available seed Firewall-friendly stream Easy-to-manage service Our Challenges ! ! !
- 16. Torrent (metadata) Pieces / Segment Swarm Peers / Leechers Seeds Trackers WebSeed
- 17. 2 WebSeed Similar to HTTP direct download Guarantees availability of resources Independent of swarm sanity Extension on bitTorrent protocol Introduced in 2006
- 18. Quiz
- 19. ‘How many of you have already developed a BitTorrent client?’
- 20. libtorrent
- 21. BitTorrent OSS Implementation Developed by Arvid Norberg, since 2003 Written in C++, Cross Platform Memory/CPU efficient, feature-packed ✔ ✔ ✔ ✔ libtorrent
- 22. Pros Easily configurable Supports trackerless mode, with DHT Supports Web Seeds (i.e. a seed can be a HTTP host), and SSL Torrents Supports Local Service Discovery Pros and Cons Cons No CocoaPods/Carthage distribution Depends on other libraries Not based on URLConnection Does not support iOS background sessions
- 23. Alternatives
- 25. Alternatives: Pros MultiPeer Connectivity Couchbase It’s a real DB Sync based on NSURLSession Supports MPC Realm It’s a real DB Sync based on NSURLSession Native Supports Bluetooth
- 26. Alternatives: Cons MultiPeer Connectivity Couchbase Depends on a proprietary stack Doesn’t work with chunks Realm Depends on a proprietary stack No real P2P 8 devices per session Manual handling of chunks
- 27. How to Build
- 28. OpenSSL Boost C++ TLS/SSL and crypto C library Requirements
- 29. How to Build https://github.com/xebia-france/libtorrent-ios-resources Option A: Pre-configured Xcode Project - https://github.com/chublix/libtorrent-ios - Adapt for OpenSSL Option B: Qt Creator - Build OpenSSL and Boost separately - Build libtorrent, for all the platforms (e.g. iphoneos and iphonesimulator) - lipo (i.e., merge the slices) of the different platforms Option C: Bash Script - cf. xebia-france/libtorrent-ios-resources/build-script
- 30. Sources Popcorn Time iOS https://github.com/danylokostyshyn/popcorntime-ios Popcorn Time TV: https://github.com/PopcornTimeTV/PopcornTimeTV Popcorn Torrent: https://github.com/PopcornTimeTV/PopcornTorrent (GCD WebServer / Torrent client for iOS)
- 31. Configuration
- 32. Configuration session_settings settings = ses.settings(); settings.ssl_listen = 4443; settings.active_loaded_limit = 1; settings.max_peerlist_size = 10; settings.min_announce_interval = 30; settings.urlseed_wait_retry = 10; ses.set_settings(settings); // http://libtorrent.org/reference-Settings.html
- 33. settings.local_service_announce_interval = 30; settings.active_lsd_limit = 1; // ... ses.start_lsd(); // ... ses.stop_lsd(); Configuration (Local Service Discovery)
- 35. How Incremental Download Works No modification in the content: No Download Modification in the content referenced changed: Download Starts The SHA1 of each chunk is compared to the version on disk:
- 36. Implementation
- 37. C++ / Swift Bridging 03 04 01 02 Add wrapper class’s header file into bridging header Implement a wrapper class in .mm file (Obj C++ ) Use wrapper class in Swift03
- 38. C++ / Swift Bridging 02 Implement a wrapper class Wrapper Class (Header) #import <Foundation/Foundation.h> @interface LibTorrentWrapper : NSObject { - (void)initSession:(NSInteger)fromPort toPort:(NSInteger)toPort; - (void)addNewTorrentFromFile:(NSString *)filePath; }
- 39. C++ / Swift Bridging 02 Implement a wrapper class Wrapper Class (Implementation) @interface LibtorrentWrapper() @property libtorrent::session *session; @end @implementation LibtorrentWrapper - (void)initSession:(NSInteger)fromPort toPort:(NSInteger)toPort { self.session = new libtorrent::session(); session_settings settings = self.session->settings(); // Apply Settings here... self.session->set_settings(settings); libtorrent::error_code ec; self.session->listen_on(std::make_pair(fromPort, toPort), ec) }
- 40. C++ / Swift Bridging 02 Implement a wrapper class Wrapper Class (Implementation) //... - (void)addNewTorrentWithData:(NSData *)data { libtorrent::add_torrent_params params; params.save_path = // Some dir... libtorrent::error_code ec; params.ti = new libtorrent::torrent_info((const char*)data.bytes, data.length, ec); self.session->add_torrent(params, ec); } @end
- 41. C++ / Swift Bridging 02 Implement a wrapper class Invoke Wrapper Class in Swift func startTorrentSession() { var torrentWrapper = LibtorrentWrapper() torrentWrapper.initSession(6881, toPort: 6889) torrentWrapper.addNewTorrentWithData(/* Some Data */) }
- 42. Event loop 03 04 01 02 Pop alert events each time callback is invoked Set-up a timer that triggers a callback periodically Feed torrent progress info03
- 43. Fetch alerts - (void)fetchAlerts { std::deque<alert *> deque; _session->pop_alerts(&deque); for (std::deque<alert *>::iterator it=deque.begin(); it != deque.end(); ++it) { std::unique_ptr<alert> alert(*it); switch (alert->type()) { case metadata_received_alert::alert_type: //** case piece_finished_alert::alert_type: //** You can feed progress info here case torrent_finished_alert::alert_type: //** default: break; } } deque.clear(); }
- 44. Fetch torrent progress info - (dl_info)getCurrentTorrentInfo:(piece_finished_alert *)alert { dl_info result; torrent_handle t = alert->handle; try { t->get_torrent_info(); } catch (libtorrent_exception &e) { return result; } torrent_status ts = t->status(torrent_handle::query_pieces); result.seeders = ts.num_seeds; result.peers = ts.num_peers; result.downloadRateBs = ts.download_rate; result.uploadRateBs = ts.upload_rate; torrent_info ti = t->get_torrent_info(); result.downloaded = ts.total_done; result.progress = ts.progress_ppm; result.completed_time = ts.completed_time; return result }
- 45. Caveats
- 46. Caveats 1 Needs fine tuning, i.e. for avoiding heavy battery consumption No background sessions Almost no iOS help resource available System proxy support to be manually implemented (via CFNetworkCopySystemProxySettings) 2 3 4