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 45% higher throughput than 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.)

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.

Access control by info hash is supported for all protocols. Relevant part of configuration:

[access_list]
mode = 'off' # Change to 'black' (blacklist) or 'white' (whitelist)
path = '' # Path to text file with newline-delimited hex-encoded info hashes

Some more documentation of configuration file values 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

Server responses per second, best result in bold:

workers	aquatic	opentracker
1	n/a	232k
2	309k	293k
3	597k	397k
4	603k	481k
6	757k	587k
8	850k	431k
10	826k	165k
16	785k	139k

Please refer to documents/aquatic-udp-load-test-2021-08-19.pdf for more details.

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.

Benchmarks

The following benchmark is not very realistic, as it simulates a small number of clients, each sending a large number of requests. Nonetheless, I think that it gives a useful indication of relative performance.

Server responses per second, best result in bold:

workers	aquatic	wt-tracker	bittorrent-tracker
1	n/a	117k	45k
2	225k	n/a	n/a
4	627k	n/a	n/a
6	831k*	n/a	n/a
8	1209k*	n/a	n/a
10	1455k*	n/a	n/a
12	1650k*	n/a	n/a
14	1804k*	n/a	n/a
16	1789k*	n/a	n/a

* Using a VPS with 32 vCPUs. The other measurements were made using a 16 vCPU VPS.

Please refer to documents/aquatic-ws-load-test-2021-08-18.pdf for more details.

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.

Architectural overview

One or more socket workers open sockets, read and parse requests from peers and send them through channels to request workers. The request workers go through the requests, update shared internal tracker state as appropriate and generate responses that are sent back to the socket workers. The responses are then serialized and sent back to the 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.

Trivia

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