aquatic

Blazingly fast, multi-threaded BitTorrent tracker written in Rust.

Consists of three sub-implementations for different protocols:

• aquatic_udp: BitTorrent over UDP. Implementation achieves double the throughput of opentracker (see benchmarks below)
• aquatic_http: BitTorrent over HTTP/TLS (slightly experimental)
• aquatic_ws: WebTorrent (experimental)

Copyright and license

Copyright (c) 2020-2021 Joakim Frostegård

Distributed under Apache 2.0 license (details in LICENSE file.)

Technical overview of tracker design

One or more socket workers open sockets, read and parse requests from peers and send them through channels to request workers. They in turn go through the requests, update internal state as appropriate and generate responses, which are sent back to the socket workers, which serialize them and send them to peers. This design means little waiting for locks on internal state occurs, while network work can be efficiently distributed over multiple threads, making use of SO_REUSEPORT setting.

Installation prerequisites

• Install Rust with rustup (stable is recommended)
• Install cmake with your package manager (e.g., apt-get install cmake)
• On GNU/Linux, also install the OpenSSL components necessary for dynamic linking (e.g., apt-get install libssl-dev)
• Clone the git repository and refer to the next section.

Compile and run

To compile the master executable for all protocols, run:

./scripts/build-aquatic.sh

To start the tracker for a protocol with default settings, run:

./target/release/aquatic udp
./target/release/aquatic http
./target/release/aquatic ws

To print default settings to standard output, pass the "-p" flag to the binary:

./target/release/aquatic udp -p
./target/release/aquatic http -p
./target/release/aquatic ws -p

Note that the configuration files differ between protocols.

To adjust the settings, save the output of the relevant previous command to a file and make your changes. Then run aquatic with a "-c" argument pointing to the file, e.g.:

./target/release/aquatic udp -c "/path/to/aquatic-udp-config.toml"
./target/release/aquatic http -c "/path/to/aquatic-http-config.toml"
./target/release/aquatic ws -c "/path/to/aquatic-ws-config.toml"

The configuration file values you will most likely want to adjust are socket_workers (number of threads reading from and writing to sockets) and address under the network section (listening address). This goes for all three protocols.

Some documentation of the various options might be available under src/lib/config.rs in crates aquatic_udp, aquatic_http, aquatic_ws.

Details on implementations

aquatic_udp: UDP BitTorrent tracker

Aims to implements the UDP BitTorrent protocol, except that it:

• Doesn't care about IP addresses sent in announce requests. The packet source IP is always used.
• Doesn't track of the number of torrent downloads (0 is always sent).

Supports IPv4 and IPv6 (BitTorrent UDP protocol doesn't support IPv6 very well, however.)

Benchmarks

Performance was compared to opentracker using aquatic_udp_load_test.

Server responses per second, best result in bold:

workers	aquatic	opentracker
1	n/a	177k
2	168k	98k
3	187k	118k
4	216k	127k
6	309k	109k
8	408k	96k

See documents/aquatic-load-test-2020-04-19.pdf for details on benchmark, and end of README for more information about load testing.

aquatic_http: HTTP BitTorrent tracker

Aims for compatibility with the HTTP BitTorrent protocol, as described here, including TLS and scrape request support. There are some exceptions:

• Doesn't track of the number of torrent downloads (0 is always sent).
• Doesn't allow full scrapes, i.e. of all registered info hashes

aquatic_http has not been tested as much as aquatic_udp but likely works fine.

TLS

To run over TLS, a pkcs12 file (.pkx) is needed. It can be generated from Let's Encrypt certificates as follows, assuming you are in the directory where they are stored:

openssl pkcs12 -export -out identity.pfx -inkey privkey.pem -in cert.pem -certfile fullchain.pem

Enter a password when prompted. Then move identity.pfx somewhere suitable, and enter the path into the tracker configuration field tls_pkcs12_path. Set the password in the field tls_pkcs12_password and set use_tls to true.

aquatic_ws: WebTorrent tracker

Aims for compatibility with WebTorrent clients, including wss protocol support (WebSockets over TLS), with some exceptions:

• Doesn't track of the number of torrent downloads (0 is always sent).
• Doesn't allow full scrapes, i.e. of all registered info hashes

For information about running over TLS, please refer to the TLS subsection of the aquatic_http section above.

aquatic_ws is experimental software. Connections are established successfully when using aquatic_ws_load_test, but so far, I haven't been able to implement CI for testing if aquatic_ws works as the tracker for a full file transfer session between two real-world clients. One reason for this is the general lack of high-quality WebTorrent clients.

Load testing

There are load test binaries for all protocols. They use a CLI structure similar to aquatic and support generation and loading of configuration files.

To run, first start the tracker that you want to test. Then run the corresponding load test binary:

./scripts/run-load-test-udp.sh
./scripts/run-load-test-http.sh
./scripts/run-load-test-ws.sh

To fairly compare HTTP performance to opentracker, set keepalive to false in aquatic_http settings.

Trivia

The tracker is called aquatic because it thrives under a torrent of bits ;-)