pgn-reader

A fast non-allocating and streaming reader for chess games in PGN notation, as a Rust library.

Introduction

Reader parses games and calls methods of a user provided Visitor. Implementing custom visitors allows for maximum flexibility:

• The reader itself does not allocate (besides a single fixed-size buffer). The visitor can decide if and how to represent games in memory.
• The reader does not validate move legality. This allows implementing support for custom chess variants, or delaying move validation.
• The visitor can signal to the reader that it does not care about a game or variation.

Example

A visitor that counts the number of syntactically valid moves in the mainline of each game.

use std::io;
use pgn_reader::{Visitor, Skip, BufferedReader, SanPlus};

struct MoveCounter {
    moves: usize,
}

impl MoveCounter {
    fn new() -> MoveCounter {
        MoveCounter { moves: 0 }
    }
}

impl Visitor for MoveCounter {
    type Result = usize;

    fn begin_game(&mut self) {
        self.moves = 0;
    }

    fn san(&mut self, _san_plus: SanPlus) {
        self.moves += 1;
    }

    fn begin_variation(&mut self) -> Skip {
        Skip(true) // stay in the mainline
    }

    fn end_game(&mut self) -> Self::Result {
        self.moves
    }
}

fn main() -> io::Result<()> {
    let pgn = b"1. e4 e5 2. Nf3 (2. f4)
                { game paused due to bad weather }
                2... Nf6 *";

    let mut reader = BufferedReader::new_cursor(&pgn[..]);

    let mut counter = MoveCounter::new();
    let moves = reader.read_game(&mut counter)?;

    assert_eq!(moves, Some(4));
    Ok(())
}

Documentation

Read the documentation

State of the library

The API could be cleaner and performance may have regressed slightly compared to the mmap based approach from old versions (#12). This needs some attention. Until I get around to it, I am doing only minimal maintenance, following shakmaty as required.

Nonetheless, it is probably still one of the fastest PGN parsers around.

Benchmarks (v0.12.0)

Run with lichess_db_standard_rated_2018-10.pgn (24,784,600 games, 52,750 MB uncompressed) on an SSD (Samsung 850), Intel i7-6850K CPU @ 3.60 GHz:

Benchmark	Time	Throughput
examples/stats.rs	111.9s	471.4 MB/s
examples/validate.rs	237.1s	222.5 MB/s
examples/parallel_validate.rs	148.6s	355.0 MB/s
scoutfish make	269.2s	196.0 MB/s
grep -F "[Event " -c	39.2s	1345.7 MB/s

examples/stats.rs with compressed files:

Compression	File size	Time	Throughput
none	52,750 MB	111.9s	471.4 MB/s
bz2	6,226 MB	1263.1s	4.9 MB/s
xz	6,989 MB	495.9s	14.1 MB/s
gz	10,627 MB	335.7s	31.7 MB/s
lz4	16,428 MB	180.0s	91.3 MB/s

License

pgn-reader is licensed under the GPL-3.0 (or any later version at your option). See the COPYING file for the full license text.